Promiscuous survivin peptide induces robust CD4+ T-cell responses in the majority of vaccinated cancer patients.

CD4(+) T cells have been shown to be crucial for the induction and maintenance of cytotoxic T cell responses and to be also capable of mediating direct tumor rejection. Therefore, the anticancer therapeutic efficacy of peptide-based vaccines may be improved by addition of HLA class II epitopes to stimulate T helper cells. Survivin is an apoptosis inhibiting protein frequently overexpressed in tumors. Here we describe the first immunological evaluation of a survivin-derived CD4(+) T cell epitope in a multipeptide immunotherapy trial for prostate carcinoma patients. The survivin peptide is promiscuously presented by several human HLA-DRB1 molecules and, most importantly, is naturally processed by dendritic cells. In vaccinated patients, it was able to induce frequent, robust and multifunctional CD4(+) T cell responses, as monitored by IFN-γ ELISPOT and intracellular cytokine staining. Thus, this HLA-DR restricted epitope is broadly immunogenic and should be valuable for stimulating T helper cells in patients suffering from a wide range of tumors.

Human melanoma cytolysis by combined inhibition of mammalian target of rapamycin and vascular endothelial growth factor/vascular endothelial growth factor receptor-2.

Vascular endothelial growth factor (VEGF) plays a vital role in tumor angiogenesis. VEGF is produced by human melanomas, and the VEGF receptor 2 (VEGFR-2) is expressed by most advanced stage melanomas, suggesting the possibility of an autocrine loop. Here, we show that bevacizumab, an anti-VEGF antibody, inhibits proliferation of VEGFR-2(+) melanoma cell lines by an average of 41%; however, it failed to inhibit proliferation of VEGFR-2(neg) melanoma cell lines. The growth inhibitory effect of bevacizumab was eliminated by VEGFR-2 knockdown with small interfering RNA, showing that VEGF autocrine growth in melanoma is mediated through VEGFR-2. However, bevacizumab inhibition of autocrine signals did not completely inhibit cell proliferation nor cause cell death. Cell survival is mediated partially through mammalian target of rapamycin (mTOR), which is inhibited by rapamycin. Combination of bevacizumab with rapamycin caused loss of half of the VEGFR-2(+) melanoma cells, but no reduction in the number of VEGFR-2(neg) melanoma cells. The results show (a) an autocrine growth loop active in VEGFR-2(+) melanoma, (b) a nonangiogenic mechanism for inhibition of melanoma by blocking autocrine VEGFR-2 activation, and (c) a possible therapeutic role for combination of inhibitors of mTOR plus VEGF in selected melanomas.