Implication of interfering antibody formation and apoptosis as two different mechanisms leading to variable duration of adenovirus-mediated transgeneexpression in immune-competent mice

This study explores the genetic and immunologic factors involved in the dif ferences in duration of transgene expression following in vivo transduction with recombinant adenoviruses, Different strains of mice (C3H/HeJ [C3H], C 57BL/6J [B6], BACB/cJ [Balb/c], C.B10-H2(b)/LiMcdJ [Balb.B], CB6F(1)/J [(Ba lbic x B6)F-1], B6C3F(1)/J [(B6 x C3H)F-1], and BALB/cj SCID) received 5 x 10(9) PFU of the first-generation adenovirus, which expresses human alpha(1 )-antitrypsin (Ad/RSVhAAT), While all strains studied showed similar patter ns of anti-adenovirus antibody formation, only Balbic and C3H mice develope d significant levels of anti-hAAT antibodies by 8 weeks posttransduction, I n addition, while all strains had quantitatively comparable amounts of aden ovirus genomes and hAAT mRNA transcripts in the liver 9 days posttransducti on, only Balbic mice had undetectable adenovirus vector genomes and hAAT mR NA in the liver 40 days posttransduction. Terminal deoxynucleotidyltransfer ase-mediated dUTP-biotin nick end labeling staining of liver sections from control and Ad/RSVAAT-infected mice 5, 9, and 40 days posttransduction sugg ested that apoptosis was involved in the rapid elimination of transduced he patocytes in Balb/c mice. Persistent expression of hAAT protein observed in BALB/cj SCID mice suggests that antigen-dependent immunity was essential f or this apoptotic process in transduced Balbic hepatocytes, In contrast to Balb/c mice, the loss of expression in C3H mice did not correlate with the loss of vector genomes or hAAT mRNA. Instead, the anti-hAAT antibodies in C 3H but not Balbic mice were found to interfere with detection of hAAT in th e serum. In Balb.B and B6 mice, vector genome, hAAT mRNA transcripts, and h AAT protein levels persisted for at least 40 days posttransduction, This pe rsistence correlated with poor anti-hAAT antibody formation and minimal hep atocyte toxicity, The expression of hAAT in (Balbic x B6)F-1 pups was found to be intermediate between the duration observed in the parental strains, while in (C3H x B6)F-1 pups hAAT expression was similar to that seen in the B6 parents, which together support polygenic control of the immune respons es in these mice, In summary, these findings suggest that there are three d ifferent profiles and at least two defined immune system-mediated mechanism s resulting in the loss of hAAT expression in mice and that different strai ns differ in the capacity to utilize these mechanisms.