We have cloned the genomic DNA fragments encoding the heavy and light chain variable regions of monoclonal antibody 17-1A, and we have inserted them into mammalian expression vectors containing genomic DNA segments encoding human y3 and K constant regions. The transfer of these expression vectors containing mouse-human chimeric immunoglobulin genes into Sp2/0 mouse myeloma cells resulted in the production of functional IgG that retained the specific binding to the surface antigen 17-lA expressed on colorectal carcinoma cells.Monoclonal antibodies (mAbs) are highly specific wellcharacterized reagents. They have found wide applications in vitro for immunochemical characterization and quantitation of antigens. Increasingly they are being used in vivo for both diagnosis and therapy (1). Their in vivo application is limited because in most cases human mAbs of the desired specificity are difficult to prepare (2). Most available mAbs are derived from mouse hybridomas, and their inherent immunogenicity in patients precludes their long-term administration (1). In an attempt to circumvent this problem, chimeric antibodies in which the antigen-specific variable (V) regions of the mouse antibodies are joined to the constant (C) regions of human antibodies have been produced (3, 4). These molecules, which are largely human in composition, should be much less immunogenic and hence should be more suitable for application in vivo.The mouse mAb 17-1A was raised against SW1083 colorectal carcinoma cells and appears to recognize a cancerassociated surface antigen expressed on these cells (5). Here we describe the construction of immunoglobulin genes in which the DNA segments encoding the V regions from the heavy (H) and light (L) chains of this mouse hybridoma were joined to the DNA segments encoding human -y3 and K C regions. Transfection of expression vectors containing these chimeric immunoglobulin genes into mouse myeloma cells resulted in the production of functional chimeric IgG with the same binding specificity as the original hybridoma antibody.MATERIALS AND METHODS cDNA Library Construction. Cytoplasmic RNA was extracted from 17-1A cells (the hybridoma cells that produce mAb 17-1A), and poly(A)+ RNA was prepared by oligo(dT)-cellulose chromatography. Double-stranded cDNA was synthesized with poly(A)+ RNA as a template, using avian myeloblastosis virus reverse transcriptase and Escherichia coli DNA polymerase I. Double-stranded cDNA was treated with S1 nuclease, elongated with deoxycytidine residues, and annealed with oligo(dG)-tailed pUC8 previously cut with Pst I (6). The recombinant plasmids were used to transform E. coli DH1, and colonies were screened according to the general method described by Maniatis et al. (7).Genomic Library Construction. A genomic DNA library for 17-1A cells was constructed in X phage vector EMBL3A. High molecular weight DNA was partially digested with restriction endonuclease Sau3A and size-fractionated on a 10-40% sucrose density gradient. DNA fragments 18-23 kilobases (kb) long were ...

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RAK antigens p120, p42, and p25 exhibit molecular and immunological similarity to the proteins encoded by human immunodeficiency virus type 1 (HIV-1) and are expressed by 95% of breast and gynecological cancer cases in women and prostate cancer cases in men. The binding of an epitope-specific anti-HIV-1 gp120 monoclonal antibody (MAb) (amino acids 308 to 322) to cancer RAK antigens has been found to be inhibited by a peptide derived from variable loop V3 of HIV-1. Breast cancer DNAs of 40 patients were PCR amplified with HIV-1 gp41-derived primers, and all of the samples were found to be positive. The DNA fragments amplified in seven blindly selected breast cancer samples were sequenced. The breast cancer DNA sequences showed at least 90% homology to the HIV-1 gene for gp41. Antisense oligonucleotides complementary to the HIV-1-like sequences inhibited reverse transcriptase activity and inhibited the growth of breast cancer cells in vitro. Viral particles detected in breast cancer cell lines were strongly immunogold labeled with the anti-HIV-1 gp120 MAb. The results obtained strongly suggest that the long-postulated breast cancer virus may, in fact, be related to HIV-1.