Enhancement of Sindbis virus self-replicating RNA vaccine potency by targeting antigen to endosomal/lysosomal compartments

Self-replicating RNA vaccines (RNA replicons) have emerged as an attractive approach for tumor immunotherapy, RNA replicons do not integrate into host chromosomes, eliminating the concern for oncogenicity associated with a DN A vaccine. In this study, we used human papillomavirus type 16 (HPV-16) E7 as a model antigen and evaluated E7-specific immunity generated by a Sindbi s virus self-replicating RNA vector, SIN-rep5, Three different constructs w ere created to target E7 antigen to different cellular localizations: (1) E 7, a cytosolic/nuclear protein; (2) Sig/E7, a secretory protein; (3) Sig/E7 /LAMP-1, in which we linked the transmembrane and cytoplasmic regions of th e lysosome-associated membrane protein 1 (LAMP-1) to E7 protein to target E 7 to the endosomal/lysosomal compartment. We found that the RNA replicon va ccine containing the Sig/E7/LAMP-1 fusion gene generated the highest E7-spe cific T cell-mediated immune responses and antitumor effects relative to RN A vaccines containing either wild-type E7 or Sig/E7, Our in vitro studies d emonstrated that E7 antigen from Sig/E7/LAMP-1 RNA replicon-transfected apo ptotic cells can be taken up by bone marrow-derived dendritic cells (DCs) a nd presented more efficiently through the MHC class I pathway than wild-typ e E7 RNA replicon-transfected apoptotic cells. Furthermore, our data reveal ed that CD8(+) T cells, CD4(+) T cells, and NK cells were important for the antitumor effects generated by Sig/E7/LAMP-1 RNA vaccination. These result s indicate that targeting antigen to the endosomal/lysosomal compartment vi a fusion to LAMP-1 may greatly enhance the potency of self-replicating RNA vaccines.