Cutting edge: Induction of enhanced CTL-dependent protective immunity in vivo by N-end rule targeting of a model tumor antigen

There is much interest in vaccines that will enhance the induction of CTL. One mechanism to enhance Ag-specific CTL responses involves targeting Ag to undergo rapid cytoplasmic degradation by the N-end rule pathway. We have analyzed the ability of N-end rule targeting to confer protection in an immunization-challenge setting. Using the HIV-1 nef protein as a model tumor Ag, we found that in mice immunized with a vaccinia vector expressing a form of nef that is targeted for rapid cytoplasmic degradation, there was enhanced induction of nef-specific CTL and protection from a lethal challenge with the syngeneic CT26 tumor cells that had been transfected with nef. Protection from tumor challenge correlated with the magnitude of the CTL response. Thus, the targeting of tumor or viral Ags for rapid cytoplasmic degradation by the N-end rule pathway may represent a strategy for the induction of protective Ag-specific CTL responses in vivo.