In vivo studies of spleen lymphoid cells implicated in antitumor immunity in hamsters.

Hamsters were immunized with repeated and progressive doses of strongly antigenic SV40-transformed cells (ZDCl25) and these animals rejected a tumor graft. According to the in vivo Winn test, spleen cells from such immunized animals could be used to transfer the antitumor immunity and protect naive recipients. To characterize the immune effector cells, different techniques of fractionation were used. In all cases the best protection was obtained by whole cell populations, even after reconstitution. The "T-depleted' fraction was more active than the T cell fraction. As shown by the treatment with specific antisera, part of the active population bore surface IgG. The protective activity could be the result of cooperation between different cell populations, one of which, unknown at present, could be the promotor of the transferred immunity and of the tumor neutralization effect.