title: Tumor-induced immunosuppression: a barrier to immunotherapy of large tumors by cytokine-secreting tumor vaccine.
abstract: An active immunotherapy strategy with cytokine-assisted tumor vaccine, although often effective for small tumor burdens, is much less so for large tumor burdens. This study examines how large tumors might suppress the T cell functions and escape from the immune responses elicited by a granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccine. According to our results, the T cells isolated from the tumor-bearing mice treated late with the vaccine failed to confer protective activity on naive mice against a wild-type tumor challenge, unlike those isolated from the early-treated group. Nevertheless, the antitumor activity of the inactive T cells could be restored on in vitro stimulation. Expression of transforming growth factor beta (TGF-beta) and interleukin 10 (IL-10), the potent immunosuppressive factors, was detected in the parental tumor cell line RLmale 1 (a murine T leukemia cell line), as well as in the tumor region, the levels of which correlated with tumor progression. An in vitro assay of T cell functions revealed that the TGF-beta in the conditioned medium of RLmale 1 cells mainly affected the activation, whereas the IL-1male affected the activation to a lesser extent, but significantly affected the cytolytic activity, of tumor-specific T cells. The immunosuppressive activity of IL-10 was also signified by the findings that administration of the conditioned medium of RLmale 1 cultured in a serum-free medium, in which the TGF-beta activity was then lost while the IL-10 activity still remained, or of recombinant IL-10 to the early-treated group of mice abrogated the known efficacy of tumor vaccine on the small tumors. These data suggested that the efficacy of cytokine-secreting tumor vaccine was blocked by the immunosuppressive factors secreted from the large tumors. The results have important implications for the clinical design of immunotherapeutic strategies for advanced cancer patients.
authors.affiliation: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei.
authors.forename: C L
authors.initials: CL
authors.lastname: Hsieh
authors.forename: D S
authors.initials: DS
authors.lastname: Chen
authors.forename: L H
authors.initials: LH
authors.lastname: Hwang
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D019496:Cancer Vaccines / Q000276:immunology* / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism*; D007165:Immunosuppression Therapy; D007167:Immunotherapy / Q000379:methods; D016753:Interleukin-10 / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology; D007942:Leukemia, Experimental / Q000276:immunology / Q000628:therapy; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009374:Neoplasms, Experimental / Q000276:immunology* / Q000473:pathology / Q000628:therapy; D011994:Recombinant Proteins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D019496:Cancer Vaccines; D017077:Culture Media, Conditioned; D016207:Cytokines; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D016753:Interleukin-10