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Original Article |
Correspondence to: James P. Allison, HHMI/Cancer Research Lab, 401 LSA UC Berkeley, Berkeley, CA 94720. Tel:510-643-6012 Fax:510-643-5692 E-mail:jallison{at}uclink4.berkeley.edu.
We have previously shown that small B16 melanomas can be successfully treated using a combination of anticytotoxic T lymphocyte antigen (CTLA)-4 monoclonal antibody with a granulocyte/macrophage colony-stimulating factor (GM-CSF) producing irradiated tumor cell vaccine. Regression of tumors results in long-lasting immunity and is frequently accompanied by autoimmune depigmentation. Here we examine the cellular and molecular mechanisms of this combined treatment. Histological examination of depigmented lesions revealed infiltration of polymorphonuclear cells and deposition of antibody. The combination therapy also induced tumor rejection and skin depigmentation in B celldeficient and in CD4+ T celldepleted mice. Both effects of the treatment absolutely required CD8+ T cells. Analysis of the response in successfully treated mice revealed elevated levels of CD8+ T cells specific for a nonameric peptide consisting of residues 180188 of the melanocyte differentiation antigen tyrosinase-related protein (TRP)2. There was no evidence of reactivity to the melanocyte antigens gp100, tyrosinase, Mart1/MelanA, or TRP1. FasFasL interactions and perforin played a role in mounting the effector response, whereas the tumor necrosis factor pathway was not required. The cellular requirements for tumor rejection in this therapeutic setting were strikingly different from those in a prophylactic setting. In particular, if mice received a prophylactic vaccine consisting of antiCTLA-4 and B16GM-CSF before tumor challenge, full protection was obtained even in the absence of CD8+ T cells. Our data demonstrate that therapeutic autoreactive CD8+ T cell responses can effectively be generated in tumor-bearing mice and stresses the value of studying tumor immunity in a therapeutic rather than a prophylactic setting.
Key Words: immunotherapy, prophylaxis, T lymphocyte, TRP-2, depigmentation
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