Glycolipids GM2, GD2, GD3,
fucosyl GM1,
sialyl Lewis a (sLe(a)) and
globo H, and
polysialic acid on embryonal
NCAM, are
cell-surface antigens expressed on
small cell lung cancer (SCLC) biopsy specimens. They are all candidates for inclusion in a polyvalent, antibody-inducing
vaccine or for adoptive
therapy with
monoclonal antibodies (mAbs) against SCLC. To identify the minimum optimal combination of target
antigens on SCLC and to confirm that
antibodies against this combination might be able to mediate complement activation and lysis in the majority of cases, we tested ten SCLC cell lines with fluorescence activated cell sorter (FACS) and
complement dependent cytotoxicity (CDC) assays using mAbs against these seven target
antigens individually or pooled in different combinations. 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, nine cell lines were strongly positive by FACS and nine 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 the four mAb pool was strongly positive by FACS. To understand the lack of correlation between FACS and CDC in the case of H345, the ten cell lines were screened for expression of
complement resistance factors CD55 and CD59. Three cell lines were strongly positive for CD55 and eight were strongly positive for CD59. Overall, no correlation was seen between expression of either of these factors on the ten cell lines and sensitivity to CDC. In the case of H345 however,
complement resistance of H345 is demonstrated to be mediated primarily by CD59, and in the presence of mAb against CD59, the four mAb MEM-43 pool induced strong (94%) CDC. CD59 inhibits
membrane attack complex formation but not activation of earlier
complement components. Consequently, all ten 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.