CDNA Coding for Carcinoembryonic Antigen

1. Field of the Invention

The present invention concerns a nucleic acid sequence which codes for a carcinoembryonic antigen peptide sequence.

2. Background Information

Carcinoembryonic antigen ("CEA") was first described by Gold and Freedman, J. Exp. Med., 121, 439-462, (1965). CEA is characterized as a glycoprotein of approximately 200,000 molecular weight with 50-60% by weight of carbohydrate. CEA is present during normal human fetal development, but only in very low concentration in the normal adult intestinal tract. It is produced and secreted by a number of different tumors.

CEA is a clinically useful tumor marker for the management of colorectal caner patients. CEA can be measured using sensitive immunoassay methods. When presurgical serum levels of CEA are elevated, a postsurgical drop in serum CEA to the normal range typically indicates successful resection of the tumor. Postsurgical CEA levels that do not return to normal often indicate incomplete resection of the tumor or the presence of additional tumor sites in the patient. After returning to normal levels, subsequent rapid rises in serum CEA levels usually indicate the presence of metastages. Slower postsurgical rises from the normal level are most often interpreted to indicate the presence of new primary tumors not previously detected. Post surgical management of colon cancer patients is thus facilitated by the measurement of CEA.

CEA is a member of an antigen family. Because of this, the immunoassay of CEA by presently available methods is complicated by the fact that CEA is but one of several potentially reactive antigens. There have been at least sixteen CEA-like antigens described in the literature. Since some of these appear to be the same antigen described by different investigators, the actual number of different antigens is somewhat less than this number. Nonetheless, there is a complex array of cross-reactive antigens which can potentially interfere with an immunoassay of the CEA released by tumors. It is known that serum levels of CEA-like antigens are elevated in many non-cancerous conditions such an inflammatory liver diseases and also in smokers. It is important that immunoassays used for the monitoring of cancer patient status not be interfered with by these other CEA-like antigens. Conversely, it is important to be able to distinguish the antigens by immunoassay because of the possibility that different tumor types may preferentially express different forms of CEA. If so, then the ability to reliably measure the different forms of CEA might provide the means to diagnose or more successfully treat different forms of cancer.

U.S. Pat. No. 3,663,684, entitled "Carcinoembryonic Antigen and Diagnostic Method Using Radioactive Iodine", concerns purification and radioiodination of CEA for use in a RIA.

U.S. Pat. No. 3,697,638 describes that CEA is a mixture of antigens (Components A and B in this case). U.S. Pat. No. 3,697,638 mentions methods for separating and radioiodinating each component and their use in specific RIA's.

U.S. Pat. No. 3,852,415, entitled "Compositions for Use in Radioimmunoassay, as Substitute for Blood Plasma Extract in Determination of Carcinoembryonic Antigen" relates to the use of a buffer containing EDTA and bovine serum albumin as a substitute for plasma as a diluent for CEA RIA's.

U.S. Pat. No. 3,867,363, entitled "Carcinoembryonic Antigens", is directed to the isolation of CEA components A and B, their labelling and use in a RIA.

U.S. Pat. No. 3,927,193, entitled "Localization of Tumors by Radiolabelled Antibodies", concerns the use of radiolabelled anti-CEA antibodies in whole body tumor imaging.

U.S. Pat. No. 3,956,258, entitled "Carcinoembryonic Antigens", relates to the isolation of CEA components A and B.

U.S. Pat. No. 4,086,217, entitled "Carcinoembryonic Antigens", is directed to the isolation of CEA components A and B.

U.S. Pat. No. 4,140,753, entitled "Diagnostic Method and Reagent", concerns the purification of a CEA isomer called CEA-S1 and its us in a RIA.

U.S. Pat. No. 4,145,336, entitled "Carcinoembryonic Antigen Isomer", relates to the antigen CEA-S1.

U.S. Pat. No. 4,180,499, entitled "Carcinoembryonic Antigens", describes a process for producing CEA component B.

U.S. Pat. No. 4,228,236, entitled "Process of Producing Carcinoembryonic Antigen", is directed to the use of the established cell lines LS-174T and LS-180 or clones or derivatives thereof for the production of CEA.

U.S. Pat. No. 4,272,504, entitled "Antibody Adsorbed Support Method for Carcinoembryonic Antigen Assay", concerns two concepts for the radioimmunoassay of CEA. First, U.S. Pat. No. 4,272,504 relates to a sample pretreatment in the form of heating to 65.degree. to 85.degree. C. at pH 5 to precipitate and eliminate extraneous protein. Second, it describes the use of a solid phase antibody (either on beads or tubes) as a means to capture analyte and radiolabelled CEA tracer.

U.S. Pat. No. 4,299,815, entitled "Carcinoembryonic Antigen Determination", concerns diluting a CEA sample with water and pretreating by heating to a temperature below which precipitation of protein will occur. The pretreated sample is then immunoassayed using RIA, EIA, FIA or chemiluminescent immunoassay.

U.S. Pat. No. 4,349,528, entitled "Monoclonal Hybridoma Antibody Specific for High Molecular Weight Carcinoembryonic Antigen", is directed to a monoclonal antibody reacting with 180 kD CEA, but not with other molecular weight forms.

U.S. Pat. No. 4,467,031, entitled "Enzyme-Immunoassay for Carcinoembryonic Antigen", relates to a sandwich enzyme immunoassay for CEA in which the first of two anti-CEA monoclonal antibodies is attached to a solid phase and the second monoclonal is conjugated with peroxidase.

U.S. Pat. No. 4,489,167, entitled "Methods and Compositions for Cancer Detection", described that CEA shares an antigenic determinant with alpha-acid glycoprotein (AG), which is a normal component of human serum. The method described therein concerns a solid-phase sandwich enzyme immunoassay using as one antibody an antibody recognizing AG and another antibody recognizing CEA, but not AG.

U.S. Pat. No. 4,578,349, entitled "Immunoassay for Carcinoembryonic Antigen (CEA)", is directed to the use of high salt containing buffers as diluents in CEA immunoassays.

EP 113072-A, entitled "Assaying Blood Sample for Carcinoembryonic Antigen--After Removal of Interfering Materials by Incubation with Silica Gel", relates to the removal from a serum of a plasma sample of interfering substances by pretreatment with silica gel. The precleared sample is then subjected to an immunoassay.

EP 102008-A, entitled "Cancer Diagnostics Carcinoembryonic Antigen--Produced from Perchloric Acid Extracts Without Electrophoresis", relates to a procedure for the preparation of CEA from perchloric acid extracts, without the use of an electrophoresis step.

EP 92223-A, entitled "Determination of Carcinoembryonic Antigen in Cytosol or Tissue--for Therapy Control and Early Recognition of Regression", concerns an immunoassay of CEA, not in serum or plasma, but in the cytosol fraction of the tumor tissue itself.

EP 83103759.6, entitled "Cytosol-CEA-Measurement as Predictive Test in Carcinoma, Particularly Mammacarcinoma", is similar to EP 92223-A.

EP 83303759, entitled "Monoclonal Antibodies Specific to Carcinoembryonic Antigen", relates to the production of "CEA specific" monoclonal antibodies and their use in immunoassays.

WO 84/02983, entitled "Specific CEA-Family Antigens, Antibodies Specific Thereto and Their Methods of Use", is directed to the use of monoclonal antibodies to CEA-meconium (MA)-, and NCA-specific epitopes in immunoassays designed to selectively measure each of these individual components in a sample.

All of the heretofore CEA assays utilize either monoclonal or polyclonal antibodies which are generated by immunizing animals with the intact antigen of choice. None of them address the idea of making sequence specific antibodies for the detection of a unique primary sequence of the various antigens. They do not cover the use of any primary amino acid sequence for the production of antibodies to synthetic peptides or fragments of the natural product. They do not include the concept of using primary amino acid sequences to distinguish the CEA family members. None of them covers the use of DNA or RNA clones for isolating the genes with which to determine the primary sequence.

Nucleotide--A monomeric unit of DNA or RNA containing a sugar moiety (pentose), a phosphate, and a nitrogenous heterocyclic base. The base is linked to the sugar moiety via the glycosidic carbon (1' carbon of the pentose) and that combination of base and sugar is called a nucleoside. The base characterizes the nucleotide. The four DNA bases are adenine ("A"), guanine ("G"), cytosine ("C"), and thymine ("T"). The four RNA bases are A, G, C and uracil ("U").

DNA Sequence--A linear array of nucleotides connected one to the other by phosphodiester bonds between the 3' and 5' carbons of adjacent pentoses.

Functional equivalents--It is well known in the art that in a DNA sequence some nucleotides can be replaced without having an influence on the sequence of the expression product. With respect to the peptide this term means that one or more amino acids which have no function in a particular use can be deleted or replaced by another one.

Codon--A DNA sequence of three nucleotides (a triplet) which encodes through mRNA an amino acid, a translation start signal or a translation termination signal. For example, the nucleotide triplets TTA, TTG, CTT, CTC, CTA and CTG encode the amino acid leucine ("Leu"), TAG, TAA and TGA are translation stop signal and ATG is a translation start signal.

Reading Frames--The grouping of codons during translation of mRNA into amino acid sequences. During translation, the proper reading frame must be maintained. For example, the sequence GCTGGTTGTAAG may be translated in three reading frames or phases, each of which affords a different amino acid sequence

Polypeptide--A linear array of amino acids connected one to the other by peptide bonds between the alpha-amino and carboxy groups of adjacent amino acids.

Genome--The entire DNA of a cell or a virus. It includes inter alia the structural genes coding for the polypeptides of the cell or virus, as well as its operator, promoter and ribosome binding and interaction sequences, including sequences such as the Shine-Dalgarno sequences.

Structural Gene--A DNA sequence which encodes through its template or messenger RNA ("mRNA") a sequence of amino acids characteristic of a specific polypeptide.

Transcription--The process of producing mRNA from a structural gene.

Translation--The process of producing a polypeptide from mRNA.

Expression--The process undergone by a structural gene to produce a polypeptide. It is a combination of transcription and translation.

Plasmid--A non-chromosomal double-stranded DNA sequence comprising an intact "replicon" such that the plasmid is replicated in a host cell. When the plasmid is placed within a unicellular organism, the characteristics of that organism may be changed or transformed as a result of the DNA of the plasmid. For example, a plasmid carrying the gene for tetracycline resistance (Tet.sup.R) transforms a cell previously sensitive to tetracycline into one which is resistant to it. A cell transformed by a plasmid is called a "transformant".

Phage or Bacteriophage--Bacterial virus, many of which consist of DNA sequence encapsilated in a protein envelope or coat ("capsid protein").

Cloning Vehicle--A plasmid, phage DNA or other DNA sequence which is capable of replicating in a host cells, which is characterized by one or a small number of endonuclease recognition sites at which such DNA sequences may be cut in a determinable fashion without attendant loss of an essential biological function of the DNA, e.g., replication, production of coat proteins or loss of promoter or binding sites, and which contains a marker suitable for use in the identification of transformed cells, e.g., tetracycline resistance or ampicillin resistance. A cloning vehicle is often called a vector.

Cloning--The process of obtaining a population of organisms or DNA sequences derived from one such organism or sequence by asexual reproduction.

Recombinant DNA Molecule or Hybrid DNA--A molecule consisting of segments of DNA from different genomes which have been joined end-to-end outside of living cells and have the capacity to infect some host cell and be maintained therein.

Expression Control Sequence--A sequence of nucleotides that controls and regulates expression of structural genes when operatively linked to those genes. They include the lac system, the trp system, major operator and promoter of phage .lambda., the control region of fd coat protein and other sequences known to control the expression of genes or prokaryotic or eukaryotic cells of their viruses.

Transformation/Transfection--DNA or RNA is introduced into cells to allow gene expression. "Infected" referred to herein concerns the introduction of RNA or DNA by a viral vector into the host. "Injected" referred to herein concerns the microinjection (use of a small syringe) of DNA into a cell.

CEA-(a), CEA-(b), CEA-(c), CEA-(d) mentioned hereinbelow are members of the CEA family which are described in the examples below.

The present invention concerns new nucleic acid sequences, e.g., DNA or RNA sequences, comprising a base sequence which codes for a CEA peptide sequence or nucleic acids having a base sequence (DNA or RNA) that is hybridizable therewith. Such nucleic acid can be a genomic DNA comprising a complete CEA gene or a portion thereof, including intron sequences, as well as exon sequences, or can be a DNA constructed to be complementary to messenger RNA coding for the CEA protein, i.e., cDNA. A nucleic acid sequence of the present invention comprises the DNA sequence set forth below or a fragment thereof, as well as sequences hybridizable therewith:

The nucleic acid of the present invention which codes for the complete CEA protein and comprises the above sequence will have a total of no more than about 5000, more usually no more than about 3600, bases. Fragments of cDNA of the above sequences will have at least 10, and in some cases at least about 50, bases.

The above DNA sequence of 859 bases codes for an immunoreactive fragment of CEA which can be expressed, such as in lambda gt11. The sequence has an internal repeat sequence approximately 300 bases long and codes for a theoretical protein 285 amino acids long. This cDNA encodes for sequences found in other human genes and it is believed that this entire family of genes may code for the CEA family of proteins.

The present invention also concerns a DNA sequence having 2839 bp comprising the base sequence set forth below or a fragment thereof, as well as sequences hybridizable therewith; ##STR1##

Further sequences are shown in the examples hereinbelow which code for proteins which are also members of the CEA family.

The present invention is also directed to a replicable recombinant cloning vehicle ("vector") having an insert comprising a nucleic acid, e.g., DNA, which comprises a base sequence which codes for a CEA peptide or a base sequence hybridizable therewith.

This invention also relates to a cell that is transformed/transfected, infected or injected with the above described replicable recombinant cloning vehicle or nucleic acid hybridizable with the aforementioned cDNA. Thus the invention also concerns the transfection of cells using free nucleic acid, without the use of a cloning vehicle.

Still further, the present invention concerns a polypeptide expressed by the above described transfected, infected or injected cell, which polypeptide exhibits immunological cross-reactivity with a CEA, as well as labelled forms of the polypeptide. The invention also relates to polypeptides having an amino acid sequence, i.e., synthetic peptides, of the expression product of a cell that is transfected, injected, infected with the above described replicable recombinant cloning vehicles, as well as labelled forms thereof. Stated otherwise, the present invention concerns a synthetic peptide having an amino acid sequence corresponding to the entire amino acid sequence or a portion thereof having no less than five amino acids of the aforesaid expression product.

The invention further relates to an antibody preparation specific for the above described polypeptide.

Another aspect of the invention concerns an immunoassay method for detecting CEA or a functional equivalent thereof in a test sample comprising

(a) contacting the sample with the above described antibody preparation, and

(b) determining binding thereof to CEA in the sample.

The invention also is directed to a nucleic acid hybridization method for detecting a CEA or a related nucleic acid (DNA or RNA) sample in a test sample comprising

(a) contacting the test sample with a nucleic acid probe comprising a nucleic acid, which comprises a base sequence which codes for a CEA peptide sequence or a base sequence that is hybridizable therewith, and

(b) determining the formation of the resultant hybridized probe.

The present invention also concerns a method for detecting the presence of carcinoembryonic antigen or a functional equivalent thereof in an animal or human patient in vivo comprising

a) introducing into said patient a labeled (e.g., a radio-opaque material that can be detected by X-rays, radiolabeled or labeled with paramagnetic materials that can be detected by NMR) antibody preparation according to the present invention and

b) detecting the presence of such antibody preparation in the patient by detecting the label.

In another aspect, the present invention relates to the use of an antibody preparation according to the present invention for therapeutic purposes, namely, attaching to an antibody preparation radionuclides or toxins to form a complex and introducing an effective amount of such complex into an animal or human patient, e.g., by injection or orally. The labeled complex would attach to CEA in a patient and the radionuclide or toxin would serve to destroy the CEA expressing cell.

FIG. 1 is an amino acid and nucleic acid sequence (859 bases) of a cDNA sequence according to the present invention.

FIG. 2 is a graph depicting an enzyme immunoassay of CEA fusion protein according to the present invention with an without antigen ("Ag").

FIG. 3 is an immunoblot of a CEA fusion protein according to the present invention.

FIG. 4 is an autoradiograph of blots for the detection of a poly A+ RNA according to the present invention.

FIG. 5 is an amino acid and nucleic acid sequence (2839 bases) of a cDNA sequence according to the present invention. In FIG. 5, the first amino acid for residue sequence purposes is Lys in the second row third amino acid from the right. Thereafter, the remaining amino acids are numbered consecutively.

Some CEA epitopes are unique. These are the epitopes which have been useful for distinguishing the various CEA-like antigens immunologically. Peptide epitopes are defined by the linear amine acid sequence of the antigen and/or features resulting from protein folding. The information required for protein folding is encoded in the primary amino acid sequence. Therefore, antigenic differences ultimately result from differences in the primary structure of the different CEA molecules. The differences residing in the CEA protein in the CEA species can thus be determined by determining the primary amino acid sequences. This can be most readily accomplished by cloning and sequencing each of the genes for CEA. To determine which gene products will be most useful for cancer diagnosis, unique probes can be selected for each gene and expression of each gene can be determined in different tumor types by nucleic acid hybridization techniques. The present invention provides a tool with which to identify potential genes coding for different members of the CEA family and to determine the theoretical primary amino acid sequences for them. Using the method of automated peptide synthesis, peptides can then be synthesized corresponding to unique sequences in these antigens. With these peptides, antibodies to these sequences can be produced which, in the intact CEA molecule, might not be recognized by the animal being immunized. Having accomplished this, advantage can then be taken of the differences in these antigens to generate specific immunoassays for the measurement of each antigen.

A wide variety of host/cloning vehicle combinations may be employed in cloning the double-stranded nucleic acid prepared in accordance with this invention. For example, useful cloning vehicles may consist of segments of chromosomal, non-chromosomal and synthetic DNA sequences, such as various known derivatives of SV40 and known bacterial plasmids, e.g., plasmids from E. coli including col E1, pCR1, pBR322, pMB89 and their derivatives, wider host range plasmids, e.g., RP4, and phase DNAs, e.g., the numerous derivatives of phage, e.g., NM989, and other DNA phages, e.g., M13 and Filamenteous single-stranded DNA phages and vectors derived from combinations of plasmids and phage DNAs such as plasmids which have been modified to employ phase DNA or other expression control sequences or yeast plasmids such as the 2.mu. plasmid or derivatives thereof. Useful hosts may include bacterial hosts such as strains of E. coli, such as E. coli HB 101, E. coli X1776, E. coli X2282, E. coli MRC1 and strains of Pseudomonas, Bacillus subtilis, Bacillus stearothermophilus and other E. coli, bacilli, yeasts and other fungi, animal or plant hosts such as animal (including human) or plant cells in culture or other hosts. Of course, not all host/vector combinations may be equally efficient. The particular selection of host/cloning vehicle combination may be made by those of skill in the art after due consideration of the principles set forth without departing from the scope of this invention.

Furthermore, within each specific cloning vehicle, various sites may be selected for insertion of the nucleic acid according to the present invention. These sites are usually designated by the restriction endonuclease which cuts them. For example, in pBR322 the Pstl site is located in the gene for beta-lactamase, between the nucleotide triplets that code for amino acids 181 and 182 of that protein. One of the two HindII endonuclease recognition sites is between the triplets coding for amino acids 101 and 102 and one of the several Taq sites at the triplet coding for amino acid 45 of beta-lactamase in pBR322. In similar fashion, the EcoRI site and the PVUII site in this plasmid lie outside of any coding region, the EcoR1 site being located between the genes coding for resistance to tetracycline and ampicillin, respectively. These sites are well recognized by those of skill in the art. It is, of course, to be understood that a cloning vehicle useful in this invention need not have a restriction endonuclease site for insertion of the chosen DNA fragment. Instead, the vehicle could be cut and joined to the fragment by alternative means.

The vector or cloning vehicle and in particular the site chosen therein for attachment of a selected nucleic acid fragment to form a recombinant nucleic acid molecule is determined by a variety of factors, e.g., the number of sites susceptible to a particular restriction enzyme, the size of the protein to be expressed, the susceptibility of the desired protein to proteolytic degradation by host cell enzymes, the contamination of the protein to be expressed by host cell proteins difficult to remove during purification, the expression characteristics, such as the location of start and stop codons relative to the vector sequences, and other factors recognized by those of skill in the art. The choice of a vector and an insertion site for a particular gene is determined by a balance of these factors, not all sections being equally effective for a given case.

Methods of inserting nucleic acid sequences into cloning vehicles to form recombinant nucleic acid molecules include, for example dA-dT tailing, direct ligation, synthetic linkers, exonuclease and polymerase-linked repair reactions followed by ligation, or extension of the nucleic acid strand with an appropriate polymerase and an appropriate single-stranded template followed by ligation.

It should also be understood that the nucleotide sequences or nucleic acid fragments inserted at the selected site of the cloning vehicle may include nucleotides which are not part of the actual structural gene for the desired polypeptide or mature protein or may include only a fragment of the complete structural gene for the desired protein or mature protein.

The cloning vehicle or vector containing the foreign gene is employed to transform an appropriate host so as to permit that host to replicate the foreign gene and to express the protein coded by the foreign gene or portion thereof. The selection of an appropriate host is also controlled by a number of factors recognized by the art. These include, for example, the compatibility with the chosen vector, the toxicity of proteins encoded by the hybrid plasmid, the ease of recovery of the desired protein, the expression characteristics, biosafety and costs. A balance of these factors must be struck with the understanding that not all hosts may be equally effective for expression of a particular recombinant DNA molecule.

The level of production of a protein is governed by two major factors: the number of copies of its gene within the cell and the efficiency with which those gene copies are transcribed and translated. Efficiency of transcription and translation (which together comprise expression) is in turn dependent upon nucleotide sequences, normally situated ahead of the desired coding sequence. These nucleotide sequences or expression control sequences define inter alia, the location at which RNA polymerase interacts to initiate transcription (the promoter sequence) and at which ribosomes bind and interact with the mRNA (the product of transcription) to initiate translation. Not all such expression control sequences function with equal efficiency. It is thus of advantage to separate the specific coding sequences for the desired protein from their adjacent nucleotide sequences and fuse them instead to other known expression control sequences so as to favor higher levels of expression. This having been achieved, the newly engineered nucleic acid, e.g., DNA, fragment may be inserted into a multicopy plasmid or a bacteriophage derivative in order to increase the number of gene copies within the cell and thereby further improve the yield of expressed protein.

Several expression control sequences may be employed as described above. These include the operator, promoter and ribosome binding and interaction sequences (including sequences such as the Shine-Dalgarno sequences) of the lactose operon of E. coli ("the lac system"), the corresponding sequences of the tryptophan synthetase system of E. coli ("the trp system"), the major operator and promoter regions of phage .lambda.(O.sub.L P.sub.L and O.sub.R P'.sub.R), the control region of Filamenteous single-stranded DNA phages, or other sequences which control the expression of genes of prokaryotic or eukaryotic cells and their viruses. Therefore, to improve the production of a particular polypeptide in an appropriate host, the gene coding for that polypeptide may be selected and removed from a recombinant nucleic acid molecule containing it and reinserted into a recombinant nucleic acid molecule closer or in a more appropriate relationship to its former expression control sequence or under the control of one of the above described expression control sequences. Such methods are known in the art.

As used herein "relationship" may encompass many factors, e.g., the distance separating the expression enhancing and promoting regions of the recombinant nucleic acid molecule and the inserted nucleic acid sequence, the transcription and translation characteristics of the inserted nucleic acid sequence or other sequences in the vector itself, the particular nucleotide sequence of the inserted nucleic acid sequence and other sequences of the vector and the particular characteristics of the expression enhancing and promoting regions of the vector.

Further increases in the cellular yield of the desired products depend upon an increase in the number of genes that can be utilized in the cell. This is achieved, for illustration purposes, by insertion of recombinant nucleic acid molecules engineered into the temperate bacteriophage .lambda.(NM989), most simply by digestion of the plasmid with a restriction enzyme, to give a linear molecule which is then mixed with a restricted phage .lambda. cloning vehicle (e.g., of the type described by N. E. Murray et al, "Lambdoid Phages That Simplify the Recovery of In Vitro Recombinants", Molec. Gen. Genet., 150, pp. 53-61 (1977) and N. E. Murray et al, "Molecular Cloning of the DNA Ligase Gene From Bacteriophage T4", J. Mol. Biol., 132, pp. 493-505 (1979)) and the recombinant DNA molecule recircularized by incubation with DNA ligase. The desired recombinant phage is then selected as before and used to lysogenize a host strain of E. coli.

Particularly useful .lambda. cloning vehicles contain a temperature-sensitive mutation in the repression gene c1 and suppressible mutations in gene S, the product of which is necessary for lysis of the host cell, and gene E, the product of which is major capsid protein of the virus. With this system, the lysogenic cells are grown at 32.degree. C. and then heated to 45.degree. C. to induce excision of the prophage. Prolonged growth at 37.degree. C. leads to high levels of production of the protein, which is retained within the cells, since these are not lysed by phage gene products in the normal way, and since the phage gene insert is not encapsulated it remains available for further transcription. Artificial lysis of the cells then releases the desired product in high yield.

In addition, it should be understood that the yield of polypeptides prepared in accordance with this invention may also be improved by substituting different codons for some or all of the codons of the present DNA sequences, these substituted codons coding for amino acids identical to those coded for by the codons replaced.

Finally, the activity of the polypeptides produced by the recombinant nucleic acid molecules of this invention may be improved by fragmenting, modifying or derivatizing the nucleic acid sequences or polypeptides of this invention by well-known means, without departing from the scope of this invention.

The polypeptides of the present invention include the following:

(1) the polypeptide expressed by the above described cells,

(2) polypeptides prepared by synthetic means,

(3) fragments of polypeptides (1) or (2) above, such fragments produced by synthesis of amino acids or by digestion or cleavage.

Regarding the synthetic peptides according to the invention, chemical synthesis of peptides is described in the following publications: S. B. H. Kent, Biomedical Polymers, eds. Goldberg, E. P. and Nakajima, A. (Academic Press, New York), 213-242, (1980); A. R. Mitchell, S. B. H. Kent, M, Engelhard and R. B. Merrifield, J. Org. Chem., 43, 2845-2852, (1978); J. P. Tam, T.-W. Wong, M. Riemen, F.-S. Tjoeng and R. B. Merrifield, Tet. Letters, 4033-4036, (1979); S. Mojsov, A. R. Mitchell and R. B. Merrifield, J. Org. Chem., 45, 555-560, (1980); J. P. Tam, R. D. DiMarchi and R. B. Merrifield, Tet. Letters, 2851-2854, (1981); and S. B. H. Kent, M. Riemen, M. Le Doux and R. B. Merrifield, Proceedings of the IV International Symposium on Methods of Protein Sequence Analysis, (Brookhaven Press, Brookhaven, N.Y.), in press, 1981.

In the Merrifield solid phase procedure, the appropriate sequence of L-amino acids is built up from the carboxyl terminal amino acid to the amino terminal amino acid. Starting with the appropriate carboxyl terminal amino acid attached to a polystyrene (or other appropriate) resin via chemical linkage to a chloromethyl group, benzhydrylamine group, or other reactive group of the resin, amino acids are added one by one using the following procedure. The peptide-resin is:

(a) washed with methylene chloride;

(b) neutralized by making for 10 minutes at room temperature with 5% (v/v) diisopropylethylamine (or other hindered base) in methylene chloride;

(c) washed with methylene chloride;

(d) an amount of amino acid equal to six times the molar amount of the growing peptide chain is activated by combining it with one-half as many moles of a carbodiimide (e.g., dicyclohexylcarbodiimide, or diisopropylcarbodiimide) for ten minutes at 0.degree. C., to form the symmetric anhydride of the amino acid. The amino acid used should be provided originally as the N-alpha-tert.-butyloxycarbonyl derivative, with side chains protected with benzyl esters (e.g., aspartic or glutamic acids), benzyl ethers (e.g., serine, threonine, cysteine or tyrosine), benzyloxycarbonyl groups (e.g., lysine) or other protecting groups commonly used in peptide synthesis;

(e) the activated amino acid is reacted with the peptide-resin for two hours at room temperature, resulting in addition of the new amino acid to the end of the growing peptide chain;

(f) the peptide-resin is washed with methylene chloride;

(g) the N-alpha-(tert.-butyloxycarbonyl) group is removed from the most recently added amino acid by reacting with 30 to 65%, preferably 50% (v/v) trifluoroacetic acid in methylene chloride for 10 to 30 minutes at room temperature;

(h) the peptide-resin is washed with methylene chloride;

(i) steps (a) through (h) are repeated until the required peptide sequence has been constructed.

The peptide is ten removed from the resin and simultaneously the side-chain protecting groups are removed, by reaction with anhydrous hydrofluoric acid containing 10% v/v or anisole or other suitable (aromatic) scavenger. Subsequently, the peptide can be purified by gel filtration, ion exchange, high pressure liquid chromatography, or other suitable means.

In some cases, chemical synthesis can be carried out without the solid phase resin, in which case the synthetic reactions are performed entirely in solution. The reactions are similar and well known in the art, and the final product is essentially identical.

Digestion of the polypeptide can be accomplished by using proteolytic enzymes, especially those enzymes whose substrate specificity results in cleavage of the polypeptide at sites immediately adjacent to the desired sequence of amino acids.

Cleavage of the polypeptide can be accomplished by chemical means. Particular bonds between amino acids can be cleaved by reaction with specific reagents. Examples include the following: bonds involving methionine are cleaved by cyanogen bromide; asparaginyl-glycine bonds are cleaved by hydroxylamine.

The following is a non-limiting list of sequences believed to be important for the purpose of making synthetic peptides and antibodies to them. Each antigen is categorized into three levels: 1)large regions containing potentially useful sites within; 2) sub regions of 1 and; 3) individual sites considered to be the prime targets for use as synthetic peptide antigens.

The present invention has the following advantages:

(1) The nucleic acid coding for CEA according to the invention can be used as a probe to isolate the complete gene of which it is a part.

(2) It can be used as probe to isolate other members of the CEA gene family.

(3) It can be used as an oligonucleotide probe to determine the expression of this gene in various tumor types.

(4) The nucleotide sequence can be used to predict the primary amino acid sequence of the protein for production of synthetic peptides and can be used to distinguish members of the CEA family.

(5) The synthetic peptides derived from the above sequences can be used to produce sequence-specific antibodies.

(6) Immunoassays for each member of the CEA family can be produced with these sequence-specific antibodies and synthetic peptides.

(7) These immunoassays can be used as diagnostics for different types of cancer if it is determined that different members of the CEA family are clinically useful markers for different types of cancer.

Polypeptides according to the present invention are labelled by conventional means using radioactive moieties, e.g., I.sup.125, enzymes, dyes and fluorescent compounds, just to name a few.

Several possible configurations for immunoassays according to the present invention can be used. The readout systems capable of being employed in these assays are numerous and non-limiting examples of such systems include fluorescent and colorimetric enzyme systems, radioisotopic labelling and detection and chemiluminescent systems. Two examples of immunoassay methods are as follows:

(1) An enzyme linked immunoassay (ELISA) using an antibody preparation according to the present invention (including Fab or F(ab)' fragments derived therefrom) to a solid phase (such as a microtiter plate or latex beads) is attached a purified anti-CEA antibody of a specificity other than that which is conjugated to the enzyme. This solid phase antibody is contacted with the sample containing CEA. After washing, the solid phase antibody-CEA complex is contacted with the conjugated anti-peptide antibody (or conjugated fragment). After washing away unbound conjugate, color or fluorescence is developed by adding a chromogenic or fluorogenic substrate for the enzyme. The amount of color or fluorescence developed is proportional to the amount of CEA in the sample.

(2) A competitive fluorometric immunoassay using fluorescently labelled peptide or synthetic peptides of the sequence specified by cLV7. In this example, the purified peptide expressed by cells or synthetic peptides thereof are fluorescently labelled. To a solid phase is attached a purified anti-CEA antibody. This solid phase is then contacted with sample containing CEA to which has been added fluorescent peptide probe. After binding, excess probe is washed away the amount of bound probe is quantitated. The amount of bound fluorescent probe will be inversely proportional to the amount of CEA in the sample.

In the nucleic acid hydridization method according to the present invention, the nucleic acid probe is conjugated with a label, for example, an enzyme, a fluorophore, a radioisotope, a chemiluminescent compound, etc. In the most general case, the probe would be contacted with the same and the presence of any hybridizable nucleic acid sequence would be detected by developing in the presence of a chromogenic enzyme substrate, detection of the fluorophore by epifluorescence, by autoradiography of the radioisotopically labelled probe or by chemiluminescence. The detection of hybridizable RNA sequences can be accomplished by (1) a dot blot methodology or (2) an in situ hybridization methodology. Methods for these last two techniques are described by D. Gillespie and J. Bresser, "mRNA Immobilization in NaI; Quick Blots", Biotechniques, 184-192, November/December 1983 and J. Lawrence and R. Singer, "Intracellular Localization of Messenger RNAs for Cytosketal Proteins", Cell, 45, 407-415, May 9, 1986, respectively. The readout systems can be the same as described above, e.g., enzyme labelling, radiolabelling, etc.

As stated above, the invention also relates to the use in medicine of the aforementioned complex of the invention.

The present invention provides a pharmaceutical composition containing as an active ingredient the complex of the invention in admixture with a solid, liquid or liquefied gaseous diluent.

The invention further provides a pharmaceutical composition containing as an active ingredient a complex of the invention in the form of a sterile and/or physiologically isotonic aqueous solution.

The invention also provides a medicament in dosage unit form comprising the complex of the invention.

The invention also provides a medicament in the form of tablets (including lozenges and granules), dragees, capsules, caplets, pills, ampoules or suppositories comprising the complex of the invention.

"Medicament" as used herein means physically discrete coherent portions suitable for medical administration. "Medicament in dosage unit form" as used herein means physically discrete coherent units suitable for medical administration, each containing a daily dose or a multiple or a sum-multiple of a daily dose of the compound of the invention in association with a carrier and/or enclosed within an envelope.

The pharmaceutical compositions according to the invention may, for example, take the form of suspensions, solutions and emulsions of the active ingredient in aqueous or non-aqueous diluents, syrups, granulates or powders.

The diluents to be used in pharmaceutical compositions (e.g., granulates) adapted to be formed into tablets, dragees, capsules, caplets and pills include the following: (a) fillers and extenders, (b) binding agents, (c) moisturizing agents, (d) disintegrating agents, (e) agents for retarding dissolution, (f) resorption accelerators, (g) surface active agents, (h) adsorptive carriers, (i) lubricants.

The tablets, dragees, capsules, caplets and pills formed from the pharmaceutical compositions of the invention can have the customary coatings, envelopes and protective matrices, which may contain opacifiers. They can be so constituted that they release the active ingredient only or preferably in a particular part of the intestinal tract, possibly over a period of time.

The active ingredient can also be made up in microencapsulated form together, with one or several of the above-mentioned diluents.

For parenteral administration, solutions and emulsions should be sterile and, if appropriate, blood-isotonic.

In addition to the complex of the invention, the pharmaceutical compositions and medicaments according to the invention can also contain other pharmaceutically active compounds.

The discrete coherent portions constituting the medicament according to the invention will generally be adapted by virtue of their shape or packaging for medical administration and may be, for example, any of the following: tablets (including lozenges and granulates), pills, dragees, capsules, caplets, suppositories and ampoules. Some of these forms may be made up for delayed release of the active ingredient. Some, such as capsules, may include a protective envelope which renders the portions of the medicament physically discrete and coherent.

The product of the above-mentioned pharmaceutical compositions and medicaments is carried out by any method known in the art, for example, by mixing the active ingredient(s) with the diluent(s) to form a pharmaceutical composition (e.g., a granulate) and then forming the composition into the medicament (e.g., tablets).

It is envisaged that the active complex will be administered perorally, parenterally (for example, intramuscularly, intraperitoneally, subcutaneously or intravenously), rectally or locally.

Tumor messenger RNA was prepared by the proteinase K-phenol extraction method of J. Favolaro, E. Treisman and R. Kamen, Methods in Enzymology, 65, 718, Academic Press, Inc., (1980), followed by oligo dT cellulose chromatography to yield poly A+ RNA (3'-polyadenylated eucaryotic RNA containing most mRNA sequences that can be translated into polypeptides). To obtain approximately 1.2 mg of poly A+ RNA, approximately 5.times.10.sup.9 LoVo cells (ATCC CCL 229) were harvested from 100.times.850 cm.sup.3 roller bottles after late logarithmic growth. Cells were lysed by homogenization in an ice-cold solution of 140 mM NaCl, 1.5 mM MgCl.sub.2, 10 mM Tris-HCl, pH 8, 0.5% NP40, 4 mM dithiothreitol and 20 units of placental ribonucelase inhibitor/ml. Sodium deoxycholate was then added to 0.2%. Cytoplasm and nuclei were separated by centrifugation of the homogenate at 12,000.times.g for 20 minutes. The cytoplasmic fraction was mixed with an equal volume of 0.2M Tris-HCl, pH 7.8, 25 mM EDTA, 0.3M NaCl, 2% sodium dodecyl sulfate and 400 .mu.g/ml of proteinase K, incubated for 1 hour at 37.degree. C., then extracted once with an equal volume of phenol/chloroform (1:1/v:v) solution. Nucleic acids were obtained by ethanol precipitation of the separated aqueous phase. Total RNA was enriched for poly A+ RNA by passage in 0.5M NaCl, 10 mM Tris-HCl, pH 7.8, 0.1% sarcosyl through an oligo dT(12-18) cellulose column. After washing, bound RNA was eluted in the same solution without sodium chloride.

Five micrograms of poly A+ LoVo RNA were primed for reverse transcription with oligo dT(12-18). Fifty microliter reactions were performed for 90 minutes at 42.degree. C. with 75 units AMV reverse transcriptase (Life Sciences, Inc., St. Petersburg, Fla., U.S.A.). RNA was removed by alkaline hydrolysis, and single-stranded cDNA was made double-stranded and blunt-ended by incubation with the large fragment (Klenow) of DNA polymerase I and T.sub.4 DNA polymerase, respectively.

Synthetic EcoRI DNA linkers (5' pGGAATTCC 3') were attached to the ends of cDNA prepared as described in Example 2 by blunt-end ligation with excess T.sub.4 DNA ligase (20 Weiss units). Excess linkers were removed by gel permeation chromatography through "SEPHADEX" G-50 (medium), EcoRI sticky ends were generated by cleavage with EcoRI restriction enzyme and franctionation by agarose exclusion chromatography on A15m (BioRad, Laboratories, Richmond, Calif., U.S.A.). DNA fragments greater than 500 bp were selected after sizing on agarose gels and were precipitated with 95% ethanol. DNA was resuspended in a small volume of 10 mM Tris-HCl, pH 7.8, 1 mM EDTA and added to an equimolar amount of 5' phosphatased and EcoRI terminated arms of lambda gt11 (Promega Biotech, Madison, Wis., U.S.A.). This phage has the advantageous property that foreign DNAs inserted at the EcoRI site of lambda gt11 are translated as part of the beta-galactosidase fusion protein that can be screened for immunoreactivity with antibodies to CEA. DNAs were ligated for 24 hours at a concentration of 100 to 200 .mu.g/ml in the presence of T.sub.4 DNA ligase. Three microliters of ligated DNA were added to an in vitro lambda packaging mix (Stratagene, San Diego, Calif., U.S.A.) and packaged particles were assayed by infecting E. coli host Y1088 (ATCC 37195). Of four million phage, 1.2 million were determined by beta-galactosidase complementation to have cDNA inserts in them.

Fifty thousand phage were plated on E. coli Y1090 (ATCC 37197) for screening on each of twenty 150 mm dishes containing LB-broth with 10 mM MgSO.sub.4 and 100 .mu.g/ml of ampicillin. In some cases, phage stocks were prepared by amplification and titering prior to screening. Phage were grown lytically for 4 hours at 42.degree. C., then nitrocellulose circles impregnated with 10 mM IPTG (isopropyl thiogalactoside) were placed on the surface of the dishes and incubated an additional 2 hours at 37.degree. C. During this period, fusion protein synthesis was induced and proteins which were absorbed to the nitrocellulose matrix were screened in a modified ELISA format. In applicants' library some LoVo fusion proteins may express a portion of a CEA or CEA-related epitope that can be recognized by appropriate antibodies. Applicants took advantage of commercially-available antisera directed against native CEA (180 kd) and of in-house prepared antisera against reduced and alkylated CEA to detect antigens on the filters. These rabbit polyclonal antisera were diluted in PBS/T (phosphate buffered saline (50 mM Na phosphate, pH 7.3, (50 mM NaCl) containing 0.05% "TWEEN-20" and 0.01% thimerosal) and incubated for two hours to allow recognition of proteins adhering to nitrocellulose circles. Excess antibody was removed and rabbit IgG molecules bound to fusion proteins were detected by mouse anti-rabbit IgG antibody conjugated with alkaline phosphatase. Color detection was in the presence of 5-bromo-4-chloro-3-indolyl phosphate and nitroblue tetrazolium. Darkly staining plaque images were marked and keyed with the master phage plate for retrieval of potential positive areas. The phage continuing to express anti-CEA reactive peptides after repeated dilution and screening by immunoblotting and amplification of the assay were used to prepare DNA.

Phage DNA was prepared according to T. Maniatis, E. F. Fritsch and J. Sambrook, Molecular Cloning, A laboratory Manual, Cold Spring Harbor, (1982). DNA segments were isolated from low melting agarose gels and inserted for subcloning in Bluescribe plasmid vectors (Stratagene, San Diego, Calif., U.S.A.). DNA sequencing was performed by the dideoxy termination method of F. Sanger, S. Nicklen and A. R. Coolson, Proc. Natl. Acad. Sci. (U.S.A.), 74, 5463-5467, (1977).

Lambda cLV7 were induced in E. coli Y 1089 for 20 minutes with isopropyl thiogalactoside and grown for 1 hour at 37.degree. C. Cells were centrifuged for 5 minutes in a Beckman Microfuge at room temperature. The cells were resuspended in 1% of the original volume in 50 mM Tris HCl, pH 7.5, containing 10 .mu.g/ml of leupeptin and pepstatin, 10 mM EDTA, 1 mM phenylmethyl sulfonylfluoride and 0.01% thimerosal. The cells were frozen at -80.degree. C., thawed and sonicated in a for 6 minutes at 0.degree. C. The sonicated suspension was centrifuged and the supernatant fluid was assayed for CEA immunoreactivity by enzyme linked immunoassay. A Linbro 96 well microtiter plate was coated with 400 ng of mouse monoclonal anti-beta galactosidase antibody overnite at 4.degree. C. The unbound antibody was washed away and the plate was blocked with PBS/T (phosphate buffered saline (50 mM Na phosphate, pH 7.3, 150 mM NaCl) containing 0.05% "TWEEN-20" and 0.01% thimerosal) for 3 hours at room temperature. The supernatant from the sonicated cells was diluted as in PBS/T and 100 .mu.l of the diluted antigen was added to the antibody-coated wells. After incubation for 2 hours at room temperature, unbound antigen was washed away and diluted rabbit anti-CEA antibody was added in 100 .mu.l of PBS/T. The plate was then incubated for 2 hours at room temperature. After washing, each well received 100 .mu.l of horseradish peroxidase-conjugated IgG from goat anti-rabbit IgG in PBS/T. After incubation for 2 hours at room temperature, the wells were washed and peroxidase substrate (3,3,5,5'-tetramethylbenzidine and hydrogen peroxide) was added for 5 minutes. The color development reaction was stopped by addition of 50 .mu.l of 8M sulfuric acid. An absorbance of 450 nm was determined for each well. The open squares in FIG. 2 represent wells receiving fusion protein antigen as described above. The + data points represent control wells treated as above, but receiving 100 .mu.l of PBS/T instead of diluted fusion protein antigen.

E. coli Y1089 lysate containing fusion protein was run on SDS-PAGE according to the method of U. K. Laemmli, Nature (London), 227, 680-685 (1970). After electrophoresis on 10% acrylamide SDS-PAGE gels, proteins were electrophoretically transferred to nitrocellulose. After transfer, the filter was blocked in PBS/T. The immunoblot was developed by sequential incubation with rabbit anti-CEA and horseradish peroxidase-conjugated IgG from goat anti-rabbit IgG in PBS/T. After washing, the transfer was incubated with 4-chloro-1-naphthol to visualize the bands. Lane 1 in FIG. 3 is a control, namely, E. coli lysate without any phage. Lane 2 in FIG. 3 is a lysate containing lambda cLV7 fusion protein. The numbers on the left of FIG. 3 indicate the mobilities and molecular weights (in kilodaltons) of protein standards. The numbers on the right of FIG. 3 indicate the calculated molecular weight and mobility of lambda LV7 fusion protein (upper marker) and of E. coli beta-galactosidase subunit (lower marker).

Cytoplasmic poly A+ RNA was prepared from LoVo tumor cells and from the lymphoblastoid line GM1989 (control cell line). Five micrograms of each RNA was denatured and electrophoresed in a 1% agarose-2.2M formaldehyde gel and then transferred to nitrocellulose paper. Transfer blots were then challenged with .sup.32 P-radiolabelled cLV7 DNA in 2XSSPE, 5X Denhardt's, 50 .mu.g/ml denatured salmon sperm DNA at 68.degree. C. for 18 hours. Blots were washed in 0.2X SSPE, 0.25% SDS at 688.degree. C. for 2 hours, then autoradiographed overnight on "KODAK" X-AR film with two intensifying screens. RNA size markers (BRL, Inc. Gaithersburg, Md., U.S.A.) were co-electrophoresed in adjacent wells of the agarose gel and visualized by staining with 0.04% methylene blue.

Of nearly one million independently derived LoVo cDNA molecules inserted into the lambda gt11 expression system and screened as polypeptides for anti-CEA immunoreactivity, two positive clones were isolated. Inserts were subcloned into the EcoRI site of Bluescribe (+) plasmid closing vector and one of these, designated, pcLV7, was analyzed further. Deposited with the American Type Culture Collection ("ATCC") on Jul. 30, 1986 was a plasmid in Escherichia coli containing pcLV7, ATCC No. 67169. By DNA sequence analysis, the insert size of this clone is 859 bp and its sequence is shown in FIG. 1. The upper line represents the nucleotide sequence of the open reading frame of pcLV7. Below it is the peptide sequence for which it codes. The general term used to designate the cDNA clone herein is cLV7 or LV7. When appended to this term, the prefixes lambda- or p- refer, respectively, to this clone as inserted into lambda phage or in plasmid.

The same procedure of Example 1 for LV7 cDNA was followed for 1LV7 cDNA.

Fifty micrograms of poly A+ RNA were primed for reverse transcription with oligo dt.sub.(12-18) and random deoxyhexamers. The 350 microliter reaction was incubated for 2.5 hours at 42.degree. C. with 900 units of AMV reverse transcriptase (Life Sciences Inc., St. Petersburg, Fla., U.S.A.). The RNA component of the cDNA/RNA hybrids was then replaced with the cDNA complementary strand by treatment with RNase H, E. coli DNA polymerase I and E. coli DNA ligase at 12.degree. C. and 22.degree. C. for 1.5 hours each. Molecular ends were polished by treatment with T.sub.4 DNA polymerase.

In order to protect EcoRI sites internal to the newly-synthesized cDNA from subsequent digestions steps, total cDNA was subjected to treatment with EcoRI methylase in the presence of 80 .mu.M S-adenosyl methionine for 1 hour at 37.degree. C. The DNA was then size-fractionated by electrophoresis through a 1% low melting point agarose gel. cDNA segments in the size range of 2 to 5 kb were excised, extracted from the gel slice and incubated in the presence of a 100-fold molar excess of synthetic EcoRI linkers (5' pdGGAATTCC 3') with T.sub.4 DNA ligase. Excess linkers were removed by gel permeation chromatography through Sephadex G-50 (medium) and EcoRI sticky ends were generated by cleavage with EcoRI restriction enzyme. EcoRI terminated cDNA segments were incubated with EcoRI cleaved and phosphatase arms of bacteriophage vector lambda gt11 in the presence of T.sub.4 DNA ligase at 5.degree. C. overnight. Aliquots of the ligation mixture were then mixed with in vitro packaging extracts (Stratagene, San Diego, Calif., U.S.A.) and phage particles were titrated on E. coli Y1090 cells.

Fifty thousand phage (pfu) from the in vitro packaged library were plated on each of four 150 mm LB plates containing 1.4% agar, 10 mM MgSO.sub.4 and 100 .mu.g/ml ampicillin. Phage were permitted to lyse host cells until plaque sizes were 0.2 to 0.5 mm in diameter. Plates were then cooled and nitrocellulose filter replicas were prepared by the method of W. D. Benton and R. W. Davis, "Screening Lambda GT Recombinant Clones by Hybridization to Single Plaques In Situ", Science, 196, 180-182, (1977). Filters were prehybridized and hybridized in 2X SSPE, 5X Denhardt's, 0.1% SDS, 100 .mu.g/ml of denatured salmon sperm DNA and for the hybridization step, 2 ng/ml of .sup.32 P-labelled cLV7 insert DNA. Non-specific DNA hybridization was removed by washing filters in 0.5X SSPE, 0.25% SDS. Positive plaques were detected by autoradiography, picked and screened for two additional rounds of positive hybridization with radiolabeled probe.

Inserts from the positive plaques from Example 12 were introduced into a bacterial plasmid vector, and exonuclease III-generated double stranded segments were sequenced by the dideoxy chain termination method. DNA sequences were computer-analyzed using Pustell DNA sequence analysis programs (IBI International, New Haven, Conn., U.S.A.).

Of nearly two hundred thousand independently derived LoVo cDNA molecules inserted into lambda gt11 vector and screened for reactivity with a radiolabeled LV7 probe, forty positive phage were selected. The largest of these (approximately 3 Kb) was sequenced and its nucleic acid and protein sequence is given in FIG. 5.

Deposited with the ATCC on Feb. 6, 1987 was a plasmid in Escherichia coli containing Pc1LV7, ATCC No. 67312.

By DNA sequence analysis, the insert size of this clone is 2839 bp and its sequence is shown in FIG. 5. The upper line represents the nucleotide sequence of the open reading frame of pc1LV7. Below it is the peptide sequence for which it codes. The general term used to designate the cDNA clone herein is c1LV7 or 1LV7. When appended to this term, the prefixes lambda- or p- refer, respectively, to this clone as inserted into lambda phage or in plasmid.

A recombinant library containing 2.times.10.sup.5 independent inserts of fetal liver cDNA in bacteriophage vector lambda gt11 (Clontech, Palo Alto, Calif., U.S.A.) was screened with radiolabeled LV7 cDNA according to W. D. Benton and R. W. Davis, Science, 196, 180-182, (1977). A single positive clone was selected and the EcoRI insert was subcloned into plasmid vector Bluescript KS+ (Stratagene, San Diego, Calif., U.S.A.). The deletion clones were prepared in both directions and sequenced by the dideoxy chain termination method of F. Sanger, S. Nicklen and A. R. Coulson, Proc. Natl. Acad, Sci., U.S.A., 74, 5463-5647, (1977). This clone, named FL5, was incomplete as judged by the lack of a translation termination signal. A single copy probe derived from the 3' end of FL5 was used to rescreen the commercial fetal liver library described above. Five positive clones were obtained, inserts were cloned into Bluescript KS+ vector, and the longest, named FL4, was sequenced. These two cDNA plasmids, FL5 and FL4 overlap and together contain the entire open reading frame of the polypeptide, designated herein as FL-CEA. The translated sequence of FL-CEA is as follows: (a cDNA clone from a cell transfectant and consisting of the full length FL-CEA sequence was deposited with the ATCC on May 25, 1988, and given the identification number 67710) ##STR2##

For residue sequence purposes, the first amino acid is Gln which is under nucleic acid 190. Thereafter the amino acids are numbered consecutively.

Tumor messenger RNA was prepared by the proteinase K-phenol extraction method of Favolaro, Treisman and Kamen, Methods in Enzymology, 65, 718, (1980), followed by oligo dT-cellulose chromatography to yield poly A+ RNA. To obtain approximately 100 micrograms of pA+ RNA, 1 gram (wet weight) of BT-20 cells (ATCC HTB 19) were resuspended and lysed in 20 ml ice-cold RNA lysis buffer (140 mM NaCl, 1.5 mM MgCl.sub.2, 10 mM Tris-HCl, pH 7.8, 0.5% NP-40 4 mM 2-mercatoethanol and 20 units of placental ribonuclease inhibitor per ml). Sodium desoxycholate was added to 0.2%. Cytoplasm and nuclei were separated by centrifugation of the homogenate at 12,000.times.g for 20 minutes. The cytoplasmic fraction was mixed with an equal volume of PK buffer (0.2M Tris-HCl, pH 7.8, 25 mM EDTA, 0.3M NaCl, 2% sodium dodecyl sulfate and 400 .mu.g f proteinase K per ml), incubated for 2 hours at 37.degree. C., then extracted once with an equal volume of phenol/chloroform (1:1/v:v) solution. Nucleic acids were obtained by ethanol precipitation of the separated aqueous phase. Total RNA was enriched for poly A+ RNA by passage in 0.5M NaCl, 10 mM Tris-HCl, pH 7.8, 0.1% sarcosyl through an oligo dT (12-18) cellulose column. After washing, bound RNA was eluted in the same solution without sodium chloride.

Ten micrograms of poly A+ BT-20 RNA were primed for reverse transcription with oligo dT (12-18) and pdN.sub.6 primers. One hundred microliter reaction was performed for 4 hours at 42.degree. C. with 200 units of AMV reverse transcriptase (Life Sciences, Inc., St. Petersburg, Fla., U.S.A.). The RNA component of the cDNA/mRNA hybrids was replaced with the second complementary strand by treatment with RNase H, E. coli DNA polymerase I and E. coli DNA ligase at 12.degree. C. and 22.degree. C. for 1.5 hours each. Molecular ends were polished by treatment with T.sub.4 DNA polymerase. cDNA was phenol/chloroform extracted, ethanol precipitated and purified over a "SEPHADEX G-50" spun column prepared in 10 mM Tris-HCl, pH 7.8, 1 mM EDTA (TE).

were attached to the ends of cDNA by blunt end ligation with excess T.sub.4 DNA ligase. Excess linkers were removed by chromatography through "SEPHADEX G-50" (medium) in TE, and by fractionation on 0.8% low melting agarose gel. Based on Northern blot analysis of poly A+ RNA of the BT-20 cell line, the size of the CEA-related mRNA was estimated at 3.0 kb. Therefore, cDNA fragments between 2 and 4 kb were recovered from gel slices and fragments were ethanol precipitated. After resuspension of cDNA in TE, EcoRI-cleaved lambda gt10 arms were added to cDNA at an estimated molar ratio of 1:1. Ligation proceeded at 7.degree. C. for 2 days in the presence of T.sub.4 DNA ligase. Aliquots of the ligation reaction were added to commercially-obtained packaging mix (Stratagene, San Diego, Calif., U.S.A.) for preparation of lambda particles. Five million phage particles were obtained after in vitro packaging and infection of E. coli host NM514.

Five hundred thousand packaged lambda particles were plated on lawns of E. coli NM514 and replicate patterns were lifted onto nitrocellulose sheets as described by W. D. Benton and R. W. Davis, Science, 196, 180-182, (1977). Positive phage were selected by hybridization with .sup.32 P-labeled LV7 cDNA insert probe that contained a domain repeated among various CEA family members. By this selection method, twenty positive phage were obtained after multiple rounds of screening. Phage from individual plaques were amplified and titered, and these were used to prepare small quantities of recombinant phage DNA.

Phage DNA was prepared according to T. Maniatis, E. F. Fritsch and J. Sambrook, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor, (1982). DNA segments were isolated from low melting agarose gels and inserted for subcloning into Bluescript plasmid vectors (Stratagene, San Diego, Calif., U.S.A.) DNA sequencing was performed by the dideoxy termination method of F. Sanger, S. Nicklen and A. R. Couslon, Proc. Natl. Acad, Sci., U.S.A., 74, 5463-5467, (1977). One of the above-mentioned twenty positive clones (labeled as BT20) that contained the expected full length sequence for NCA was deposited with the ATCC on May 25, 1988, and given the identification number 67711, and its translated sequence is as follows: ##STR3##

For residue sequence purposes, the first amino acid is Lys in row four, 11 amino acids from the left. Thereafter the amino acids are numbered consecutively.

It will be appreciated that the instant specification and claims are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention.