Association of vaccinia virus-expressed adenovirus E3-19K glycoprotein with class I MHC and its effects on virulence in a murine pneumonia model.

The adenovirus type 2 (Ad2) early region 3 (E3) codes for a 19-kDa glycoprotein (gp19) that associates with the class I major histocompatibility (MHC) heavy chain in the endoplasmic reticulum (ER) and prevents the transport of class I MHC protein products to the cell surface. It has been shown previously in tissue culture that this reduction in class I MHC expression allows infected cells to escape detection by class I MHC restricted CD8+ cytotoxic T-lymphocytes (CTL). We now report the results of studies on the effects of Ad2/gp19 expression on virulence in vivo. Since we wanted to isolate the effect of Ad2/gp19 from the effects of other Ad E3 region gene products and human Ads do not replicate in the mouse, we cloned the Ad2/gp19 open reading frame (ORF) into the HindIII C region of WR vaccinia virus (VV). Two VV recombinants were constructed by inserting the Ad2/gp19 ORF in either an expressing (V-e19(+)) or a non-expressing (V-e19(-)) orientation under control of the VV P7.5 promoter. The V-e19(+)recombinant expressed Ad2/gp19 in infected tissue and could be co-precipitated with an antibody to the class I MHC antigen Kd. However, intracerebral or intranasal infections of BALB/c (H-2d), BALB.G (H-2g), or C3H (H-2k) mice showed that Ad2/gp19 expression by V-e19(+) had no significant effect either on viral lethality or on its ability to replicate in vivo when compared to V-e19(-). Furthermore, the nature of the CD8+ CTL response to a V-e19(+)-induced pneumonia in (H-2d) mice was unchanged by Ad2/gp19 expression. Modulating the CD8+ CTL response, by interfering with infected target presentation, may not be important in the control of VV replication or virulence in vivo when other aspects of the immune response to viral infection are not altered. However, the two VV recombinants V-e19(+) and V-e19(-) were both equally attenuated (10-fold) when compared to wild-type VV. This attenuation, which has been reported previously for an intracerebral infection, is believed to be caused by the disruption of a 37-kDa ORF in the VV HindIII C region. Interestingly, our studies showed that the attenuation is not accompanied by a reduction in viral titers in infected tissue.