IMMUNOLOGICAL EVIDENCE FOR COEXPRESSION OF CLUSTER-5 AND CLUSTER-5A SMALL-CELL LUNG-CANCER ANTIGEN ON A SINGLE-MOLECULE

We have investigated immunologically the molecular association of the cell-surface sialoglycoprotein antigens cluster-5 (CL-5) and cluster-5 A (CL-5A), known to be co-expressed in human small-cell lung cancer (S CLC). CL-5 antigen is exclusively defined by IgM antibodies as represe nted by MAb LAM8, whereas CL-5A antigen is exclusively defined by IgG antibodies as represented by MAbs SWA20 and SEN31. Because of the unav ailability of purified antigens, the question of the molecular relatio nship between these antigens was addressed by immunological studies. W e generated an anti-anti-idiotypic MAb of the IgG isotype using a CL-5 -antigen-mimicking anti-idiotype defined by rat MAb Ly8-229 as an immu nogen to circumvent the avidity problems observed with the IgM MAb LAM 8 in binding-competition experiments. In addition, we developed a hete rologous double antibody sandwich assay able to identify circulating C L-5/5a antigens in pre-treatment sera of patients with SCLC. The resul ts of both types of immunological studies demonstrated the expression of CL-5 and CL-5A antigens on a single molecule, both in cellular assa ys and in assays detecting antigens shed into the serum of patients wi th SCLC. (C) 1994 Wiley-Liss, Inc.