EARLY REGION 3-REPLACEMENT ADENOVIRUS RECOMBINANTS ARE LESS PATHOGENIC IN COTTON RATS AND MICE THAN EARLY REGION 3-DELETED VIRUSES

BACKGROUND: Adenovirus type-5 (Ad5) recombinant viruses with replaceme nt of the 1.9 kb XbaI fragment in the early region 3 (E3) by foreign g enes have been constructed with the ultimate goal of inducing immune r esponses to the product of the inserted gene against a variety of viru s infections. The pathogenicity of these recombinants, however, has no t been studied. EXPERIMENTAL DESIGN: Histopathologic changes induced i n cotton rat and mouse lung by E3-replacement-Ad5 recombinant or wild- type Ad (Wt-Ad) or E3-deleted mutant (Ad5-Delta E3) viruses were compa red. Expression of viral mRNA and replication of these viruses in cott on rat and mouse lungs, as well as in human tissue culture cells, were assayed. Expression of class I major histocompatibility complex antig ens and the E3-14.7 kilodalton protein in virus-infected cells were al so analyzed. RESULTS: An Ad5 recombinant, Ad-human cytomegalovirus gly coprotein B (Ad-HCMV.gB), in which the E3 region is replaced by the fu ll-length gB gene of HCMV and with a genome size exceeding that of Wt- Ad, induced mild histopathologic responses in cotton rat and mouse lun gs, comparable with those of Wt-Ad, but less severe than those of Ad5- Delta E3. Analysis indicated that neither class I major histocompatibi lity complex expression on the cell surface nor differential expressio n of the protective E3-14.7 kilodalton protein underlies the pathologi c differences observed in cells infected with Ad5-Delta E3 or the Ad-H CMV.gB recombinant. In the mouse lung, another Ad-E3 replacement recom binant, Ad-herpes simplex glycoprotein B (HSV.gB), containing the comp lete HSV.gB gene and with a genome size larger than that of Wt-Ad, als o induced a very mild inflammatory response. However, two recombinants with truncated forms of the HCMV.gB (Ad-HCMV.gB.155) or HSV.gB genes (Ad-HSV.gB.147) produced more severe histopathologic changes than the Wt-Ad or the recombinants with the full complement of HCMV.gB or HSV.g B genes. Ad5 and some of the recombinants replicated in mouse and cott on rat lung, and the extent of replication was inversely proportional to genome size, both in the lung and in human tissue culture cells. In fectious virus titers were, however, higher in cotton rat than in mous e lung. In situ hybridization analysis of cotton rat and mouse lung in fected with Wt-Ad, Ad5-Delta E3, or Ad-HCMV.gB virus revealed expressi on of Ad early/late mRNA predominantly in bronchial epithelial cells. CONCLUSIONS: These data not only confirm that E3-deleted viruses induc e more severe pathologic changes in cotton rat lungs than Wt-Ad viruse s (Ginsberg et al., Proc Natl Acad Sci USA 1989;86:3823-7) but led to the observation that some E3 replacement recombinants also lacking the expression of the 19 and 14.7 kilodalton proteins are significantly l ess pathogenic in cotton rats and mice than an E3-deleted virus. Patho genicity and replication of the recombinant viruses inversely correlat e with the genomic size.