The Murine Cell-Mediated Immune Response to Adenovirus Recombinant AdG12

Abstract

This study was undertaken to examine the specificity of the cell-mediated immune response to vesicular stomatitis virus in mice, using the recombinant adenovirus vector AdG12. AdG12 contains the coding region for VSV glycoprotein (G) within the genome of adenovirus type 5. Ultimately, these studies attempted to provide a model for the use of adenovirus vectors to elicit specific CTL responses in mice against an inserted foreign protein. Cell-mediated immunity was examined using a standard ⁵¹Cr release assay. Splenocyte effectors from VSV or AdG12 primed mice were tested for their ability to lyse labelled infected target cells. A number of target cell lines were analyzed for productive infection by AdG12 and expression of VSV-G. Of the lines tested, B10.D2 (H-2ᵈ) and PAK (H-2ᵇ) lines were shown to be infectible with AdG12 and expressed VSV-G 36 hours post infection. Cell lines P815 (H-2ᵈ) and EL-4 (H-2ᵇ) did not appear to be AdG12 infectible. Responses were measured in mice intravenously infected with AdG12. Results demonstrated that peak cytotoxic activity from AdG12 primed mice occurred six days post-infection against syngeneic target cells infected with AdG12, Ad5 wt or VSV. However, these effectors also significantly lysed allotargets infected with VSV, implying that VSV infected targets were lysed in a non-MHC restricted manner. In subsequent experiments, it was discovered that VSV infected B10.D2 and PAK targets were markedly lysed by effectors from immunized and non-immunized Balbic, C57B1/6 and CBA/J mice. Thus, it appeared that these mouse strains contained an inherent or natural cytotoxic activity against VSV infected targets that was unlike classical CTL killing. Depletion experiments showed that this activity was not due to adherent or Thy1 bearing cells within spleen cell populations. To further characterize this activity, splenocyte effectors were tested for their ability to lyse NK-sensitive YAC-1 targets, but no significant lysis was demonstrated. However, despite these results, it appeared that this activity was that of an NK-like effector. The presence of NK-like cytotoxicity against VSV infected targets precluded efforts to define specific anti-VSV responses in these mice.