Role of donor immunocompetent cells in allograft rejection

Allotransplantable lines of the BALB/c (H-2d) Leydig cell tumor C4092 were established in DBA/1 (H-2q) mice after maintenance in organ culture. These modified tumors had reduced immunogenicity but were recognized and rejected by previously sensitized DBA/1 mice. The addition of 3.4 X 10(3)-1 X 10(5) peritoneal exudate cells (PEC) from untreated BALB/c mice to cell suspensions of the modified tumor did not restore Immunogenicity when the cell mixture was Inoculated sc Into DBA/1 recipients. However, when equivalent numbers of PEC or spleen cells were inoculated iv into animals receiving the tumor cell suspension sc, the acceptance of the tumors was significantly reduced or prevented. This indicated that the BALB/c lymphoid cells inoculated iv stimulated the immune system of the host, which in turn recognized the tumor cell inoculum. The lack of effect of the BALB/c lymphoid cells when admixed with the tumor did not support the assumption that the loss of passenger lymphoid cells was responsible for the allotransplantability of grafts after organ culture explantation. Additional evidence was presented that supports our view that the reduced immunogenicity was associated with a phenotypic modification of the tumor cells per se.