Altered CD8(+) T-cell responses when immunizing with multiepitope peptide vaccines

Efforts to develop effective cancer vaccines often use combinations of immunogenic peptides to increase the applicability and effectiveness of the immunizations. The immunologic consequences of combining more than 1 self/tumor antigen in a single vaccine emulsion remain unclear, however. We performed 2 sequential clinical trials in patients at high risk for melanoma recurrence. Patients were given the highly immunogenic gp100:209-217(210M) peptide and the less immunogenic tyrosinase:368-376(370D) peptide once every 3 weeks for 4 weeks. This vaccination course was 12 weeks long, and patients were vaccinated for up to 4 courses (16 total vaccinations). In the first trial in 31 patients, the peptides were emulsified separately in incomplete Freund adjuvant and injected at 2 different sites. In the second trial in 33 patients, the peptides were emulsified together and injected at the same site. Cryopreserved lymphocytes were obtained by apheresis after each course and were evaluated for antipeptide activity using tetramer, enzyme-linked immunospot, and in vitro sensitization boost assays. When the peptides were injected at separate sites, robust specific reactivity to the native gp100:209-217 peptide was measured by each of the assays, whereas immunization with the tyrosinase:368-376(370D) peptide was far less effective. When the peptides were emulsified and injected together at the same site, immunization to the gp100:209-217(210M) epitope dropped precipitously, whereas reactivity to the tyrosinase:368-376(370D) peptide was enhanced. These cautionary data indicate that mixing peptides in the same emulsion can alter reactivity compared with peptides injected separately by mechanisms that may include the induction of localized nonspecific inflammation or competitive binding of peptides to major histocompatibility complex molecules.