GM2, fucosyl GM1, globo H and polysialic acid are suitable targets for a tetravalent vaccine against SCLC

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Glycolipids GM2, GD2, GD3, fucosyl GM1, sialyl Lewis a (sLe^a) and globo H, and polysialic acid on embryonal NCAM, are cell-surface antigens widely expressed on small cell lung cancer (SCLC) biopsy specimens. To identify the minimum optimal combination of target antigens and to confirm that antibodies against this combination are able to mediate complement activation, we tested ten SCLC cell lines (DMS-79, H69, H82, H187, H196, H211, H345, H524, N417 AND SHP77) with fluorescence activated cell sorter (FACS) and complement dependent cytotoxicity (CDC) assays using complement activating mAbs against the seven antigens. We have previously described our preliminary results (AACR 44: 945, 2003) and expand on them here. We find that 1) none of these mAbs demonstrated strong FACS reactivity with more than 6 of the 10 cell lines, 2) no mAb had strong CDC reactivity with more than 4 of the cell lines, 3) when the mAbs were pooled, 9 cell lines were strongly positive by FACS and 9 cell lines were strongly positive by CDC, and 4) mAbs against GM2, FucGM1, Globo H and polysialic acid was the minimum optimal combination for inducing FACS reactivity. The addition of mAbs against sLe^a, GD2 and GD3 had no additional impact by FACS and only minimal additional impact in CDC assays. H345, the only cell line that had less than 30% CDC with any mAb pool was strongly positive by FACS. To understand the lack of correlation between FACS and CDC in the case of H345, the 10 cell lines were screened for expression of complement resistance factors CD55 and CD59. Three cell lines were strongly positive for CD55 and 8 were strongly positive for CD59. Overall, no correlation was seen between expression of either of these factors on the 10 cell lines and sensitivity to CDC (using human complement). In the case of cell line H345, however, complement resistance was demonstrated to be mediated by CD59. In the presence of mAb MEM-43 against CD59, the 4 mAb pool induced strong (94%) CDC. Complement activation represents an enzyme cascade resulting in opsonization and inflammation with C3b binding and membrane attack complex formation and CDC with C5b-9 binding. CD59 inhibits membrane attack complex formation but not activation of earlier complement components. Consequently, all 10 cell lines are good targets for complement activation by the four antibody pool and for elimination by effector mechanisms including complement mediated inflammation and opsonization. These findings support our plan to develop a tetravalent vaccine against SCLC targeting GM2, fucosyl GM1, globo H and polysialic acid. Supported by grants from the NIH (PO1CA33049), and the Lawrence and Selma Ruben Foundations.