CANCER THERAPY AND THE IMMUNE SYSTEM
Although manipulation of the host immune response in animal tumor models has at times yielded impressive therapeutic results, attempts to extend these results to human cancers generally have been disappointing.
Several proteins that stimulate subsets of lympho-cytes involved in various aspects of the immune re-sponse are now produced by recombinant DNA tech-niques. The pharmacology of these “lymphokines” as potential anticancer agents is being investigated. Interleukin (IL) 2, originally described as a T-cell growth factor, induces the production of cytotoxic lym-phocytes (lymphokine-activated killer cells, or LAK cells). IL-2 produces remissions in 10 to 20% of patients with melanoma or renal cell carcinoma when infused at high doses either alone or with lymphocytes that were previously harvested from the patient and incubated with IL-2 in vitro.
The ability of certain anticancer agents to suppress both humoral and cellular immunity has been exploited in the field of organ transplantation and in diseases thought to be caused by an abnormal or heightened im-mune response. In particular, the alkylating agents cy-clophosphamide and chlorambucil have been used in this context, as have several of the antimetabolites, in-cluding methotrexate, mercaptopurine, azathioprine, and thioguanine. Daily treatment with these agents rather than high-dose intermittent therapy is the pre-ferred schedule for immune suppression.