Tumor induced immunosuppression

As increasing numbers of investigators have focused their interests upon immunosuppression associated with tumors, the mechanistic complexity of this suppression has become apparent. Both the host and the tumor contribute immunosuppressive factors, but the significance of each contribution remains unclear. The absence of data from experiments performed in vivo makes any conclusions about the effects of these factors upon the response of the host to the tumor tentative at best. Further purification and characterization of these factors, although difficult, should enable their activity in vivo to be assessed in future studies. The effect of these factors upon active specific and nonspecific immunotherapy also must be assessed. Several methods of therapy are currently available that may eliminate these sources of immunosuppression and possibly enhance the response of the host to the tumor. The administration of cyclophosphamide or low doses of radiation therapy is effective in eliminating some populations of suppressor cells. Levels of circulating antigen-antibody complexes, acute phase reactants and suppressor factors derived from tumors may be eliminated by plasmapheresis. Monoclonal antibodies specifically directed against these suppressive substances, possibly combined with the other techniques, might also be effective in eliminating immunosuppressive factors. Clearly, much more investigation is needed in this rapidly expanding field.