Effector mechanisms of syngeneic anti-tumour responses in mice. II. Cytotoxic T lymphocytes mediate neutralization and rejection of radiation-induced leukaemia RL male 1 in the nude mouse system.

We demonstrated the efficacy of a long-term cultured cytotoxic T-lymphocyte line, CTLL-D4, on tumour growth inhibition using athymic nude mice as recipients. CTLL-D4, specific for a unique surface determinant on a radiation-induced leukaemia RL male 1 of BALB/c origin, was obtained from the limiting dilution culture of MLTC cells performed between spleen cells of a CB6F1-nu/+ mouse immunized in vivo and RL male 1 stimulator cells, and cultured for several months in the absence of added TCGF as described in our preceding paper (Kuribayashi, 1985). The specific inhibition of tumour growth by CTLL-D4 was demonstrated both in Winn-type neutralization assay and in systemic transfer experiments. A subcutaneous inoculation of the mixture of CTLL-D4 and RL male 1 cells resulted in the complete inhibition of tumour growth, even at the effector to tumour cell ratio of 1:1, whereas non-cytolytic D4f, which was self-Ia antigen(s)-reactive, composed entirely of Lyt-1+23- T cells and derived originally from CTLL-D4 but completely lost its cytotoxic activity during culture with the irradiated syngeneic feeder cells alone, had no inhibitory effect at all. In the adoptive transfer studies, the subcutaneously established tumours were rejected by the single i.v. transfer of 2 X 10(7) CTLL-D4 cells into CB6F1-nu/nu mice. However, D4f was ineffective again in this systemic transfer system. When the effect of CTLL-D4 cells on tumour rejection in vivo was compared to that of non-cultured spleen cells hyperimmunized with RL male 1 cells, the former exhibited more rapid rejection in nude mice after i.v. transfer than the latter did, suggesting that CTLL-D4 cells also attack the tumour cells much more effectively as effectors in vivo. Thus, it is conceivable that CTLs are mainly involved in tumour rejection in this adoptive transfer system using RL male 1 tumour cells and athymic nude mice.