CD40-CD40L INTERACTIONS PROVIDE 3RD-PARTY COSTIMULATION FOR T-CELL RESPONSE AGAINST B7-1-TRANSFECTED HUMAN BREAST-TUMOR CELLS

In this study we provide evidence that a human breast carcinoma cell l ine, MDA-MB-231 (MDA), can be made immunogenic following B7 transfecti on and that full T cell activation is obtained through cooperation of T-B lymphocytes via CD40-CD40L interactions, Tumor cells transfected w ith either B7 gene (MDAB7), neomycin-resistant gene only (MDAneo), or untransfected (MDA) were used in an allogeneic mixed lymphocyte tumor culture (MLTC) to investigate their ability to stimulate T cell prolif eration and generate cytotoxic T lymphocytes (CTL), MDAB7 induced mode rate T cell proliferation while MDAneo or MDA did not. Substantial T c ell proliferation and de novo generation of cytolytic T cells was obta ined only in response to MDAB7 when B cells were present during the ML TC, CD8(+)-purified T + B cells proliferated to a greater extent than whole T cell populations + B or CD4(+) + B in response to MDAB7. Addit ion of alpha-B7-1 or alpha-CD40 in the MLTC inhibited T cell prolifera tion by 65 and 40%, respectively, whereas T cell proliferation and gen eration of CTL was completely abrogated when MLTC was performed in the presence of both antibodies. These data suggest that the engagement o f CD40L on T cells with CD40 on B cells provides a costimulatory signa l which, in synergism with TCR-dependent MDAB7-T cell recognition (sig nal 1) and B7/CD28 interactions (signal 2), leads to full T cell activ ation.