An autologous T cell clone overcomes intra-melanoma heterogeneity for susceptibility to cell-mediated lysis by using multiple lytic mechanisms: in vitro and in vivo analysis.

An HLA-A2-specific cytotoxic T lymphocyte (CTL) clone (CTL49), capable of killing the HLA-A2-negative autologous melanoma (Me665/2) in a T cell receptor and MHC-independent fashion, lysed six of 16 Me665/2 tumour clones in short-term (4 and 18 hour) 51Cr-release assays. In long-term (96 hour) lytic assays, CTL49 could lyse all the 16 tumour clones. The lysis observed in the 96 hour assay could be enhanced by stimulating CTL49 with anti-CD3 monoclonal antibodies (MAb) and interleukin-2 (IL-2). Supernatants of anti-CD3- or antigen-stimulated CTL49, known to contain tumour necrosis factor (TNF) alpha and interferon (IFN)gamma, were also able to lyse all but one (665/2/51) of the tumour clones in 96 hour assays. Absence of lysis of tumour clone 2/51 by supernatants correlated with resistance of the same tumour clone to lysis by recombinant IFN-gamma plus TNF-alpha. Antibodies to TNF-alpha and, to a lesser extent, to IFN-gamma, reduced significantly the 96 hour lysis of Me2/9 and Me2/10, two of the tumour clones killed in long term but not in short term assays. Winn assays in nude mice revealed that CTL49, stimulated with anti-CD3-MAb plus IL-2, could abolish tumour cell growth when injected together with clones 2/9 or 2/10. These results indicate that intra-tumour heterogeneity for susceptibility to lysis can be overcome even by a single CTL clone providing that appropriate signals (i.e. anti-CD3-MAb and IL-2) are supplied to an effector able to mediate tumour cell lysis by multiple mechanisms.