very efficient since an sfv infection induces apoptotic cell death upon uptake of infected cell material exogenous antigen the recombinant protein will be processed and presented by mhc class ii molecules to activate cd4 t helper cells in addition dendritic cells and macrophages are able to present exogenous antigen in the context of mhc class i molecules for presentation to and activation of cd8 t cells thus both arms of the cellular immune system essential for the induction of an optimal immune response will be activated upon administration of recombinant sfv particles thus eliciting a potent ctl response moreover sfv immunization will introduce both class i and class ii antigenic epitopes into one and the same the apc which has recently been demonstrated to be required for a full activation of apcs as demonstrated by zhou et al immunization of mice with sfv particles encoding for the nucleoprotein of influenza virus not only induces influenza specific ctl activity but also a nucleoprotein specific antibody response this observation supports the hypothesis of cross priming and indirect presentation of antigenic peptides it has been demonstrated that immunization of mice with recombinant sfv e6e7 particles induces a potent ctl response against hpv transformed tumor cells this result combined with studies showing the high efficacy of the sfv system for priming the immune system of mice as.