Cell-mediated immunity to mouse tumors: some recent findings.

Lymphocyte mediated immune reactions play a major role in the immunological defense against antigenic tumor cells. Serum factors (antigens, antigen-antibody complexes) can thwart these reactions, perhaps by interfering with a lymphocyte "activation" process. Blocking factors can be eluted from lymphoid cells harvested from tumor-bearing animals. One way of increasing cell-mediated reactivity to tumor antigens appears to be to sensitize (or "activate") lymphocytes against tumor antigens in vitro. Another way may be to inoculate animals with sera containing lymphocyte-dependent and unblocking antibodies. Preliminary evidence is presented that inoculation of such sera from rabbits immunized with mouse embryonie cells and extensively absorbed may delay the appearance of primary, methyleholanthrene-induced sarcomas in BALB/c mice; the mechanisms responsible for this delay remain unknown.