MOLECULAR CONTEXT OF A VIRAL T-CELL DETERMINANT WITHIN A CHIMERIC BACTERIAL PROTEIN ALTERS THE DIVERSITY OF ITS T-CELL RECOGNITION

We genetically introduced two different viral CD4(+) T cell epitopes w ithin two internal sites of the Escherichia coli maltose-binding (MalE ).protein. Affinity-purified hybrid MalE proteins were used to analyze the influence of the molecular environment on the presentation of ins erted epitope to T cells. In the first model, the 120 to 132 PreS T ce ll epitope was inserted alone or with its C-terminal B cell epitope (1 32-145) at site 133 or 303 of MalE. The maltose-binding protein with P reS peptide inserts expressing the 120 to 132 sequence were able to in duce in vivo and in vitro peptide-specific T cell response, whatever t he length and the position of the insert. In the second model, the 103 to 115 T cell epitope from the C3 region of poliovirus type 1 (PV1) w as inserted, with various flanking sequences, either at site 133 or 30 3 of MalE protein. The longer C3:86 to 115 insert induced poliovirus-s pecific T cell responses at both sites of MalE, whereas the C3:93 to 1 15 insert did it only at site 303 but not at site 133. Moreover, C3:10 3 to 115 specific T cell hybridomas discriminated between the processe d peptides generated from the different chimeric proteins, as a result of differences in the length and the position of the inserted sequenc e. Therefore, in this experimental model the loss of in vivo immunogen icity of an antigenic determinant within a chimeric protein is related to the activation of a reduced T cell repertoire. These observations involve important consequences for the engineering of recombinant vacc ines.