Third Keystone Symposium on Cellular Immunology and the Immunotherapy of Cancer Antigen Processing and Presentation Autologous Human Dendriphages Pulsed with Synthetic or Natural Tumor Peptides Elicit Tumor-Specific CTLs In Vitro

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The recent identification of tumor-associated antigens and tumor-associated antigen-derived peptide epitopes recognized by cytolytic T lymphocytes (CTLs) in the context of major hislocompatibility complex (MHC) class I molecules has prompted the development of peptide-based vaccines for the treatment of human cancers, particularly melanoma. The design of such clinical protocols requires an understanding of the inherent immunogenicity of the peptide(s) and a choice of a facilitating adjuvant promoting cellular immunity against these peptidcs. We have evaluated the abilities of a series of defined synthetic peptide epitopes derived from MART-1/Melan-A, gp100, tyrosinase, and MAGE-3 or unfractionatcd peptides natu-rally presented by melanoma MHC molecules to elicit HLA-A2-restricted and melanoma-reactive CTLs from the peripheral blood of normal donors or patients with metastatic melanoma. Autologous peripheral blood dendritic cells (DCs), which were easily generated from all donors when cultured in the presence of recombinant human interleukin-4 and recombinant human granulocyte-macrophage colony-stimulating factor were pulsed with melanoma peptides and used to “prime” and/or “boost” CTL cultures in vitro. Our results suggest that antimelanoma CTLs may be reproducibly generated in short-term in vitro cultures in this manner using either a subset of the defined synthetic peptides (MART-1/Melan-A27–35, MART-1/Melan-A32–40, gp100280–288, tyrosinase368–376 and MAGE-3271–279) or unfractionated peptides (containing both idiotypic and shared melanoma epitopes) derived from freshly isolated autologous melanoma lesions. These in vitro data support the use of autologous DCs prepulsed with such peptides as an appropriate antigen adjuvant delivery system in melanoma peptide-based vaccines.

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