In vivo resistance of secondary antitumor immune response to cyclophosphamide: effects on T cell subsets.
We have analyzed the effects of high doses of cyclophosphamide (Cy) on primary and secondary antitumor immune response against immunogenic (tum-) variants of Lewis lung carcinoma (3LL) treated in vitro with UV light. Normal mice and mice previously immunized with tum- clones wer inoculated i.p. with Cy (200 mg/kg body weight) and 24 h later challenged intrafootpad with tum- or parental 3LL cells. Cy treatment suppressed the primary immune response of normal animals and allowed the growth of tum- cells. In contrast, Cy-treated immune mice rejected the tumor challenge. The in vivo treatment with Cy decreased the total number of lymphoid cells in the spleens, as well as the proportion of B lymphocytes; however, it increased the percentage of both Lyt2+ and L3T4+ lymphocytes. Thus, the immunosuppressive effects of Cy on the primary antitumor response could not be attributed to elimination of major T lymphocyte subpopulations. Although the treatment of immune mice with Cy did not significantly impair their antitumor resistance, nor the proportion of Lyt2+ and L3T4+ lymphocytes in their spleens, the in vitro generation of cytotoxic T lymphocytes (CTL) was markedly reduced. After Cy treatment, the proliferative ability of spleen cells in response to interleukin-2 (IL-2) was substantially impaired. Using monoclonal antibodies to the IL-2 receptor, we found that Cy-treated T lymphocytes failed to fully express the IL-2 receptor following in vitro stimulation with irradiated tumor cells. In line with these findings, the in vitro generation of CTL was not restored by addition of recombinant IL-2 to the cultures. In vivo experiments using purified functional subsets of immune T cells showed that Lyt1+, but not Lyt2+ lymphocytes were able to transfer antitumor immunity in normal irradiated recipients. Therefore, since Ly1+ T lymphocytes were responsible for the antitumor resistance in vivo, the Cy-induced impairment of CTL generation did not affect the ability of immune mice to reject a secondary tumor challenge.
D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology; D003520:Cyclophosphamide / Q000494:pharmacology*; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D005260:Female; D006801:Humans; D007116:Immunization, Passive; D007376:Interleukin-2 / Q000494:pharmacology; D008175:Lung Neoplasms / Q000276:immunology*; D008213:Lymphocyte Activation / Q000187:drug effects; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D008810:Mice, Inbred C57BL; D011994:Recombinant Proteins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000145:classification / Q000187:drug effects / Q000276:immunology*
D007376:Interleukin-2; D011994:Recombinant Proteins; D003520:Cyclophosphamide