Innate Cell-mediated Immunity

In trying to imagine a biological role for killer lymphocytes, aside from the obviously irrelevant one of graft rejection, many early researchers focused on a possible role in tumor surveillance and control. Tumors were usually found to be infiltrated with leukocytes, including lymphocytes, and the collective wisdom, supported in a few but admittedly not many cases by hard data, was that the degree of infiltration correlated inversely with progression of the tumor. This is a point of view still held (Eerola et al., 2000). When cell-mediated cytotoxicity in vitro was demonstrated in the 1960s, it seemed reasonable to ask whether animals mounted this type of immune response to their own tumors as well as to tissue grafts. Indeed, lymphocytes from tumor-bearing patients and experimental animals often displayed significant cell-mediated cytotoxicity toward their tumor cells in vitro. A great deal of effort was expended to show that cell-mediated tumor cytotoxicity, like cytotoxicity against allografts, was specific – in this case toward putative tumor antigens, rather than toward the MHC antigens controlling transplant rejection (Hellström et al., 1968; Bubenik et al., 1971; Baldwin et al., 1973; Hellström and Hellström, 1974).