HETEROLOGOUS EXPRESSION OF ADENOVIRUS E3-GP19K IN AN E1A-DELETED ADENOVIRUS VECTOR INHIBITS MHC-I EXPRESSION IN-VITRO, BUT DOES NOT PROLONGTRANSGENE EXPRESSION IN-VIVO

An E1a-deleted adenovirus vector constitutively expressing native aden ovirus E3-gp19K (Ad.RSV-gp19K) was constructed in order to determine w hether or not E3-gp19K mediated interference with antigen presentation would result in prolonged transgene expression in vivo. Cultured fibr oblasts infected with Ad.RSV-gp19K produced a native size gp19K protei n and had decreased cell surface levels of MHC I as shown by immunopre cipitation and flow cytometry. The congenic mouse strains Balb/b (H-2( b) MHC I with high gp19K affinity), Balb/k (H-2(k) MHC I with no gp19K affinity), and Balb/c (H-2(d) MHC I with moderate gp19K affinity) wer e chosen for in vivo experiments because of range of gp19K affinities. Following transduction of mice from each strain with Ad.RSV-gp19K and Ad/RSV-hAAT (a reporter adenovirus), or Ad/RSV-cFIX (control adenovir us) and Ad/RSV-hAAT, the level and duration of serum hAAT protein were unrelated to gp19K protein expression. Evaluation of MHC I abundance on hepatocytes following in vivo transduction demonstrated that recomb inant adenovirus rapidly increased the abundance of surface MHC I mole cules on hepatocytes, and surface MHC I molecules were reduced earlier and to a greater extent following wild-type adenovirus infection comp ared with hepatocytes transduced with control or Ad.RSV-gp19K recombin ant adenovirus. This difference in surface MHC I down-regulation may b e related to the different promoters (RSV-LTR versus the native E3 pro moter), and will be an important consideration in the development of n ewer generation adenovirus vectors designed to evade host immune respo nses.