1089. Examine the Cross-Reactivity of Vector-Specific T Cells between Human Adenoviral H5 and Simian Adenoviral C7 Vector in Mice (2005)

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Replication-defective adenoviral vectors based on human serotype 5 (H5) has emerged as very effective vaccine carriers. However, the neutralizing antibodies to AdH5 vector by previous natural infections will very likely impair its vaccine efficacy. Therefore, our lab developed replication-defective simian adenoviral C7 vectors to circumvent interference by pre-existing neutralizing antibodies to human AdH5. Nevertheless, cross-reactivity between virus-specifc T-cell has been identified in a variety of different forms in both human and murine models. Therefore, it is of interest to directly examine the cross-reactivity of vector-specific T cells. C57BL/6 mice were i.m. immunized with either AdH5Null or AdC7Null vector at the dose of 1011particles/mouse. Splenocytes were harvested after immunization. A small portion of splenocytes were stimulated with UV-inactivated AdH5 or AdC7 viral particles in vitro and supernatants were assayed for production of IFN-g by ELISA. The results suggested that there was cross reactivity of vector-specific Th1 subsets of T helper cells between AdH5 and AdC7 vector, since a significant level of IFN g was secreted when immunized splenocytes were stimulated with heterologous UV-inactivated viral particles in vitro. The majority of splenocytes were adoptively transferred into AdH5LacZ vector-i.v. injected Rag I mice. Two weeks after adoptive transfer, livers of Rag I mice were isolated and stained for LacZ expression. Stable lacZ expression was detected in Rag I received splenocytes from na|[iuml]|ve C57BL/6. In contrast, livers of Rag I received splenocytes from AdH5Null vector-immunized C57BL/6 showed dramatic diminution of LacZ expression. More importantly, splenocytes from AdC7Null vector-immunized C57BL/6 induced only marginal to intermediate reduction of LacZ expression after adoptive transferred into Rag I. The results suggested that there was some cross-reactivity of cytolytic T cells between AdH5 and AdC7 vector. Next, we studied the impact of pre-existing immunity against AdH5 vector on antigen-specific CD8 T cells response in mice. C57BL/6 mice were first i.m. injected with AdH5LacZ vector ranging from 1011 to109 particles/mouse. Two months later, mice in each dose group were divided into two sets, which were immunized with AdH5nSpike or AdC7nSpike, respectively, at the dose of 5|[times]|109 particles/ mouse. Two weeks after immunization, splenocytes were collected and subjected to intracellular IFN-g staining after stimulated with the identified spike-specific CD8 T-cell epitope. The results confirmed that pre-existing immunity against AdH5 vector can significantly reduce spike-specific CD8 T-cell response when AdH5nspike vector was used to immunize mice. More importantly, the inhibition of spike-specific CD8 T-cell response caused by pre-existing immunity against AdH5 vector can be sufficiently overcome when AdC7nSpike was used to immunize the mice. In summary, even though cross-reative vector-specific T cells were present between AdH5 and AdC7 vectors, pre-existing immunity against AdH5 vector, including AdH5-specific neutralizing antibodies and T cells, was not able to suppress the immunogenicity of AdC7 vaccine vector.