CD4 super(+) T cells recovered from a mixed immune lymphocyte-tumor cell culture induce thymidine incorporation by naive rat lymphocytes in response to tumor cells

Spleen cells from tumor-immune rats incorporate thymidine when co-cultured for 4 days with syngeneic cancer cells. Non-adherent cells, recovered from a 7-day mixed culture with cancer cells, had lost their capacity for incorporating thymidine when exposed again to the same tumor cells; however, in these conditions, the non-adherent cells induce thymidine incorporation by fresh naive spleen cells. This response is restricted to tumor lines which originate from the same tumor as the cells used for immunization and is due to memory and/or activated CD45RC super(-) CD4 super(+) T cells. Our results indicate that tumor-specific T cells maintain their capacity to respond to tumor antigens, even after an extended culture time with tumor cells. In another study, in the same conditions, spleen cells from normal or tumor-bearing rats did not evoke significant responses. (DBO)