Hybridoma cells which secrete colorectal carcinoma-specific antibodies have been produced and used to study the antigenic structure of these tumor cells. Nineteen antibodies have been studied in detail, and 15 of these are colorectal carcinoma specific. Only two antibodies reactive with carcinoembryonic antigen (CEA) have been discovered and five other antibodies that react with distinct epitopes on the cell surface have been defined. Several antigens with distinct molecular characteristics have been shown to exist by use of hybridoma antibodies. Six hybridoma antibodies have been shown to mediate antibody-dependent cell-mediated cytotoxicity (ADCC).

The antigen of a monoclonal antibody that is specific for cells of human carcinoma of the colon is a monosialoganglioside as determined by the direct binding of antibody to thin-layer chromatograms of total lipid extracts of tissues. Binding of antibody to chromatograms is detected by autoradiography after the application of iodine-125-labeled F(ab')2 of rabbit immunoglobulin G antibodies to mouse immunoglobulins.

We have constructed cell-specific cytotoxic agens by covalently coupling the A chain from diphtheria toxin or ricin toxin to monoclonal antibody directed against a colorectal carcinoma tumor-associated antigen. Antibody 1083-17-1A was modified by attachment of 3-(2-pyridyldithio)propionyl or cystaminyl groups and then treated with reduced A chain to give disulfide-linked conjugates that retained the original binding specificity of the antibody moiety. the conjugates showed cytotoxic activity for colorectal carcinoma cells in culture, but were not toxic in the same concentration range for a variety of cell lines that lacked the antigen. Under defined conditions virtually 100% of antigen-bearing cultured cells were killed, whereas cells that lacked the antigen were not affected. Conjugates containing toxin A chains coupled to monoclonal antibodies may be useful in studying functions of various cell surface components and, possibly, as tumor-specific therapeutic agents.

Most translocations that occur in Burkitt's lymphoma involve movement of part of chromosome 8, containing the c-myc gene, from its normal position to the immunoglobulin heavy-chain locus on chromosome 14. The genes are often joined at their 5' ends in opposite transcriptional directions. However, a significant minority of Burkitt translocations involve the light-chain loci on chromosome 2 (kappa) or 22 (lambda). We have characterized one of these from a European-derived cell line (IARC-BL37) that carries an 8;22 translocation. Here the translocation has joined the 5' portion of the lambda light-chain locus to the 3' portion of the c-myc gene at a position about 7 kilobases from the normal c-myc promoters. The translocation is reciprocal and relatively conservative, involving the loss of only 21 base pairs from the site of recombination. This translocation allows us to orient the lambda genes with respect to the centromere of chromosome 22 and to predict the orientation of other translocations involving these chromosomal segments. The 3' translocation is accompanied by an increased level of c-myc transcripts, especially that derived from a normally under-used c-myc promoter.

An antibody molecule is constructed from four polypeptides, two identical L chains, (x or X), and two identical H chains (t~, 6, 3', ~, or a). In its germline state, Ig K L chain DNA exists in three discrete groups of noncontiguous segments: V, J, and C. H chain-related DNA is slightly more complex, and includes a fourth group of discrete D segments. To form a functional L chain gene, one V region undergoes a site-specific recombination event and becomes contiguous with one J segment, H chain gene formation is a slightly more complicated variation on this theme, which includes the rearrangement of a D segment to a J segment before V-D recombination (for review see 1).Antibody diversity can be accounted for by combinations obtained from this V-J (or V-D-J)joining and the association within a cell of such recombined L and H chain genes. Toward the expansion of antibody diversity, higher organisms have evolved hundreds of V regions capable of recolnbining with several separate J segments. In tbe case of the human x or H chain gene systems, gene duplication has increased the number of J regions to about six, located just 5' of the single K or # C region (2, 3). Because these J regions encode different amino acid sequences, and each of these J regions is capable of recombining with any appropriate V region, the number of different polypeptide chains that can be made is increased manyfold.The human X gene system also has increased the number of available J regions by gene duplication. However, in the X locus, the unit of duplication includes