gp100209–2M Peptide Immunization of Human Lymphocyte Antigen-A2+ Stage I-III Melanoma Patients Induces Significant Increase in Antigen-Specific Effector and Long-Term Memory CD8+ T Cells

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Abstract
Thirty-five HLA-A2+ patients with completely resected stage I-III melanoma were vaccinated multiple times over 6 months with a modified melanoma peptide, gp100209–2M, emulsified in Montanide adjuvant. Direct ex vivo gp100209–2M tetramer analysis of pre- and postvaccine peripheral blood mononuclear cells (PBMCs) demonstrated significant increases in the frequency of tetramer+ CD8+ T cells after immunization for 33 of 35 evaluable patients (median, 0.36%; range, 0.05–8.9%). Ex vivo IFN-γ cytokine flow cytometry analysis of postvaccine PBMCs after brief gp100209–2M in vitro activation showed that for all of the patients studied tetramer+ CD8+ T cells produced IFN-γ; however, some patients had significant numbers of tetramer+ IFN-γ− CD8+T cells suggesting functional anergy. Additionally, 8 day gp100209–2M in vitro stimulation (IVS) of pre- and postvaccine PBMCs resulted in significant expansion of tetramer+ CD8+ T cells from postvaccine cells for 34 patients, and these IVS tetramer+ CD8+ T cells were functionally responsive by IFN-γ cytokine flow cytometry analysis after restimulation with either native or modified gp100 peptide. However, correlated functional and phenotype analysis of IVS-expanded postvaccine CD8+ T cells demonstrated the proliferation of functionally anergic gp100209–2M- tetramer+ CD8+ T cells in several patients and also indicated interpatient variability of gp100209–2M stimulated T-cell proliferation. Flow cytometry analysis of cryopreserved postvaccine PBMCs from representative patients showed that the majority of tetramer+ CD8+ T cells (78.1 ± 4.2%) had either an “effector” (CD45 RA+/CCR7−) or an “effector-memory” phenotype (CD45RA−/CCR7−). Notably, analysis of PBMCs collected 12–24 months after vaccine therapy demonstrated the durable presence of gp100209–2M-specific memory CD8+ T cells with high proliferation potential. Overall, this report demonstrates that after vaccination with a MHC class I-restricted melanoma peptide, resected nonmetastatic melanoma patients can mount a significant antigen-specific CD8+ T-cell immune response with a functionally intact memory component. The data further support the combined use of tetramer binding and functional assays in correlated ex vivo and IVS settings as a standard for immunomonitoring of cancer vaccine patients.