991. Adenovirus-Mediated IL-12 Gene Transfer Increase Virus Specific CD8 T Cell Response in Aged Mice

Abstract

Top of pageAbstract Respiratory viral infection is a major cause of morbidity and mortality in the elderly population. IL-12 and other Th1 cytokines can prevent the age-related defect in the cytotoxic T lymphocyte (CTL) response by blocking the age-associated down modulation of CD28 and immune senescence of CD8+ T cells. Gene therapy is one method to restore defective Th1 cytokines and reverse immune senescence. However, the effect of IL-12 on the generation and effector function of the viral epitope-specific cytotoxic CD8 T cells (CTLs) after delivery by an adenovirus vector has been difficult to dissect due to the lack of appropriate tetramers capable of identifying the virus-specific CTL response. This limitation can now be overcome by the use of our recently developed MHC class I tetramer containing the adenovirus (Ad) epitope peptide E1Bp, referred to as Db-E1Bp, in combination with the use of an in vivo killing assay to analyze the virus specific CD8 T cell response in young and old mice after Ad administration. To determine the effect of IL-12 on the generation and effector function of the virus-specific CTLs, we utilized an recombinant Ad vector to deliver the IL-12 gene into aged (16-mo-old) and young (2-mo-old) C57BL/6 (B6; H-2b) mice before infected with a wild-type Ad5. The primary CTL response was assayed by the Db-E1Bp tetramer and E1Bp-specific in vivo killing assay. Our results indicate that there was a 58% decrease in the production of virus-specific Db-E1Bp+CD8+ T cells in aged mice at day 8 after Ad5 infection, compared with that from young mice (p<0.01; Table). This was associated with a 30% decrease in the specific killing activity by these CTLs in aged mice (p<0.01). In vivo pretreatment of aged mice with Ad-IL12 resulted in an increase in serum IL-12, from 18|[plusmn]|7 ng/ml before pretreatment to 96|[plusmn]|12 ng/ml at the time of Ad5 infection 3 days later. Ad-IL12 pretreatment also induced strong IFNg production of 34|[plusmn]|11 ng/ml at the time of Ad5 injection compared to the base line of 0.5|[plusmn]|0.2 ng/ml. There was only a moderate increase of these cytokines in young mice. However, the serum IL-12 correlated with IFNg production in both old (r2=0.889; p<0.001) and young (r2=0.946; p<0.001) mice. At day 8 after Ad5 infection, both the Db-E1Bp+CD8+ /total CD8+ T cells and E1Bp specific lysis efficiency in the spleen and liver of aged mice increased to levels comparable to those of young mice (Table). This was associated with an increased thymocyte proliferative response mediated through IL-2 and IL-7 in aged mice. Our results indicate that aged mice have a defect in the CTL response to Ad infection, and that Ad-IL12 treatment significantly enhances the Ad-specific CTL response in aged mice, partially by induction of IFN|[gamma]|.