INDUCTION OF T-CELL RESPONSES BY CHIMERIC BACTERIAL PROTEINS EXPRESSING SEVERAL COPIES OF A VIRAL T-CELL EPITOPE

A viral T cell epitope was genetically inserted within the periplasmic MalE protein of Escherichia coli in two different permissive insertio n sites and resulting hybrid proteins were used to study the in vitro and in vivo immunogenicity of the foreign T cell epitope. Purified hyb rid MalE proteins containing the T cell epitope 120-132 (PreS:T) from PreS2 region of hepatitis B virus HBsAg inserted alone or with its adj acent B cell epitope (132-145) were able to induce strong peptide-spec ific T cell responses in mice. In vitro stimulation of primed lymph no de cells or specific T cell hybridomas by the hybrid proteins required processing of the inserted T cell epitope and was inhibited by antige n-presenting cells fixation. The inserted T cell epitope was presented in vitro, in association with appropriate major histocompatibility co mplex molecules, as efficiently as free synthetic peptide. The in vitr o immunogenicity of MalE hybrid proteins was increased by inserting fo ur tandemly repeated copies of PreS:T, either at site 133 or 303. Thes e results were confirmed in vivo by comparing the proliferative respon ses of lymph node cells from DBA/1 mice primed with MalE hybrid protei ns containing one or four copies of PreS:T, Thus, the use of MalE hybr id proteins expressing multiple copies of a given foreign T cell epito pe allows the induction of peptide-specific T cell response with a low er dose of priming antigen.