Mechanisms of in vivo generation of cytotoxic activity against syngeneic tumours. I. Local differentiation of mature cytotoxic T lymphocytes in the rejection of tumours.

Mature cytotoxic T lymphocytes (CTL) were detected in the peritoneal cavity of syngeneic mice immunized intraperitoneally (i.p.) with mitomycin C (MC)-treated EL-4 or X5563 cells, but were not found in their spleens or lymph nodes. Mature CTL appeared among PE cells after transfer of spleen cells from those immune mice, along with MC-treated tumour cells, to the peritoneal cavity of syngeneic mice. These results lead us to the hypothesis that immature CTL primed in the spleen and lymph nodes may migrate to the site of tumour inoculation and differentiate into mature CTL after antigenic or non-specific stimulation at that site. Inability of primed CTL to differentiate to mature CTL in the spleen might be explained by the effect of splenic suppressor cells, since mature CTL became detectable in the spleen of immune mice by treatment with cyclophosphamide.