CXC chemokine receptor 3 expression by activated CD8+ T cells is associated with survival in melanoma patients with stage III disease.

Despite the presence of tumor Ag-specific CD8(+) T cells in the peripheral blood, metastatic melanoma often evades immune-mediated destruction. Even after therapeutic efforts to expand Ag-specific T-cell populations, the correlation between magnitude of response and clinical efficacy has been weak. Because the migratory phenotype of tumor Ag-specific effector T cells may determine their ability for tumor control, we hypothesized that the expression of CC or CXC chemokine receptor (CCR) molecules on activated CD8(+) T cells may define phenotypes associated with more effective control of melanoma progression and prolonged survival. In a retrospective evaluation of patient isolates, CCR expression was determined for activated CD8(+) T cells derived from the peripheral blood or tumor-involved lymph nodes of 52 patients with stage III or IV metastatic melanoma. In patients with stage III disease, expression of CXCR3 by CD8(+)CD45RO(+) cells was significantly associated with enhanced survival. This was a stage-specific effect, because it was not observed in patients with stage IV disease. In addition, CCR4 and CXCR3 were highly coexpressed and associated with enhanced survival in stage III patients; however, CXCR3 seems to be the dominant receptor associated with clinical outcome. These findings support the hypothesis that the host immune system affects cancer progression and control, and that measures of CCR status of circulating lymphocytes may have prognostic value.

Competition among peptides in melanoma vaccines for binding to MHC molecules.

The effectiveness of peptide-based cancer vaccines depends on the ability of peptides to bind to MHC molecules on the surface of antigen-presenting cells, where they reconstitute epitopes for cytotoxic T lymphocytes (CTLs). Multivalent vaccines have advantages over single-peptide vaccines; however, peptides may compete for binding to the same MHC molecules. In particular, it is possible that peptides with high affinity for MHC molecules prevent the binding of lower-affinity peptides. However, only small numbers of peptide/MHC complexes per cell are required for CTL recognition. Thus, the authors hypothesized that competition of peptides for MHC binding would not significantly reduce CTL recognition of individual peptides within a multiple-peptide mixture, and this hypothesis was tested by a series of experiments performed in vitro. In multiple experiments, two peptides with different affinities for HLA-A*0201 molecules were mixed at various concentrations and pulsed onto HLA-A2 cells, which were then evaluated for susceptibility to lysis by HLA-A*0201-restricted CTLs. CTL recognition of the melanoma peptides gp100(154-162) (KTWGQYWQV), gp100(280-288) (YLEPGPVTA), and tyrosinase(369-377D) (YMDGTMSQV) was maintained even when target cells were co-pulsed with equimolar concentrations of peptides with comparable or higher affinity for HLA-A2. In some cases, CTL recognition was maintained even when the higher-affinity peptide was present at concentrations several orders of magnitude higher than the target peptide. In addition, CTLs generated by in vitro stimulation with a peptide mixture developed reactivity to three different peptides, at a level comparable to that obtained by stimulation with each individual peptide separately. These data suggest that CTLs can respond to multiple peptides presented on the same antigen-presenting cells and justify further investigation, in clinical trials, of multiple-peptide cancer vaccines.