A Decaepitope Polypeptide Primes for Multiple CD8+ IFN-γ and Th Lymphocyte Responses: Evaluation of Multiepitope Polypeptides as a Mode for Vaccine Delivery

Proteins are generally regarded as ineffective immunogensfor CTL responses. We synthesized a 100-mer decaepitope polypeptide and tested its capacity to induce multiple CD8+ IFN-γ and Th lymphocyte (HTL) responses in HLA transgenic mice. Following a single immunization in the absence of adjuvant, significant IFN-γ in vitro recall responses were detected for all epitopesincluded in the construct (six A2.1-, three A11-restricted CTL epitopes, and one universal HTL epitope). Immunization with truncated forms of the decaepitope polypeptide was used to demonstrate that optimal immunogenicitywas associated with a size of at least 30–40 residues (3–4 epitopes). Solubility analyses of the truncated constructs were used to identify a correlation between immunogenicityfor IFN-γ responses and the propensity of these constructs to form particulate aggregates. Although the decaepitope polypeptide and a pool of epitopesemulsified in IFA elicited similar levels of CD8+ responses using fresh splenocytes, we found that the decaepitope polypeptide more effectively primed for in vitro recall CD8+ T cell responses. Finally, immunogenicitycomparisons were also made between the decaepitope polypeptide and a corresponding gene encoding the same polypeptide delivered by naked DNAimmunization. Although naked DNAimmunization induced somewhat greater direct ex vivo and in vitro recall responses 2 wk after a single immunization, only the polypeptide induced significant in vitro recall responses 6 wk following the priming immunization. These studies support further evaluation of multiepitope polypeptide vaccines for induction of CD8+ IFN-γ and HTL responses.