Modulation of antitumor immune responses.

Based on experimentation in animal model systems it is reasonable to expect immunomodulation by anticancer drugs and biological response modifiers to be instrumental in at least some of the antitumor effects of such agents. Even in the defined animal models, however, the immunomodulating effects of any given agent are in most cases correlated only with the therapeutic response to that agent, whereas causal relationships still evade unequivocal demonstration. The difficulties in this respect are magnified in humans, in whom the very nature and regulation of antitumor immunity, taken in a broad sense, are not yet well defined; thus at this time the basis on which to interpret the therapeutic or toxicological causative relevance of an immunomodulating effect is insufficient. Despite these limitations and uncertainties, or perhaps responding to the challenge they provide, experimentation evaluating the potential of immunomodulation is being carried out in a number of diversified areas. Salient findings from selected investigations of the actions of 1) drugs, 2) cytokines, and 3) combinations of agents or effectors are discussed as examples of the realization of the potential of this overall approach as well as to outline the requirements for future development of biological response modifiers.