RECOGNITION OF OUT-OF-FRAME MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I-RESTRICTED EPITOPES IN-VIVO

In the course of constructing a recombinant vaccinia virus encoding th e influenza A nucleoprotein (NP) gene preceeded by the hemagglutinin l eader sequence, we isolated a single base-pair deletion mutant which g ave rise to L+NP(1-159) in which only the first 159 amino acids were i n frame. Despite this, when we infected target cells, we found that th e point mutant was able to sensitize them for lysis not only by cytoto xic T cells recognizing residues 50-58 (the in-frame portion), but als o by CTL to epitopes which are downstream of the mutation (365-374 and 378-386). Furthermore. normal C57BL/6 mice can be primed with the fra meshift NP to recognize the immunodominant Db-restricted epitope 366-3 74 (which is out of frame). Experiments in which the mutant gene produ ct was processed in the endoplasmic reticulum of target cells suggeste d that the apparent suppression occured during polypeptide extension.