788 Direct Relationship Between Suppression of CMV-specific Immunity and Emergence of CMV End-organ Disease in AIDS N. Kassis1, C.L.Hale1, M. Simon1, M. Elliott1, J. Lifson2, A. Gomez-Yafal3, P. Barry4, M. Mach5, R. P. Johnson1, A. Kaur*1 1New England Regional Primate Res Ctr, Southborough, MA; 2Natl Cancer Inst, Frederick Cancer Res and Development Ctr, MD; 3Therion Biologics Corp, Cambridge, MA; 4Ctr for Comparative Med, Univ of California, Davis, CA; and 5Inst fur Klinische und Molekulare Virologie, Univ Erlangen-Nurnberg, Germany
Background: Although increased plasma CMV load is an independent risk factor for disease progression in HIV-infected individuals, the precise mechanisms underlying the occurrence of CMV disease in AIDS are not well characterized. We have used the SIV/rhesus macaque model to conduct a prospective, kinetic evaluation of CMV-specific immune responses and CMV load from the time of SIV infection until onset of AIDS.
Methods: Eleven (11) CMV-seropositive rhesus macaques inoculated intravenously with pathogenic SIVmac251 were monitored longitudinally. Plasma CMV DNA was quantitated by real time PCR. Binding and neutralizing antibodies (Ab) to rhesus CMV were measured by ELISA and an indirect immunofluorescence assay, respectively. CMV-specific CD4+ and CD8+ T-lymphocytes were quantitated by g-interferon Elispot assays using either whole rhesus CMV antigen or recombinant vaccinia expressing rhesus CMV proteins for antigen-specific stimulation. The nonparametric Mann Whitney U test and Spearman Rank Correlation test were used for statistical analysis.
Results: Six (6) of 11 rhesus macaques had histologic evidence of CMV disease at death. Macaques with CMV disease differed from macaques without CMV disease in having significantly higher levels of plasma SIV RNA and CMV DNA, and significantly lower titers of anti-CMV binding Ab titers at the time of death. Following SIV infection, a significant decline in anti-CMV Ab and CMV-specific CD4+ and CD8+ T-lymphocytes was observed in the macaques with CMV disease, but not in the macaques without CMV disease. Although plasma CMV DNA was inversely correlated with the frequency of CMV-specific CD4+ and CD8+ T-lymphocytes, and not with the titers of anti-CMV binding or neutralizing Ab, levels above 1000 copies/ml (seen in macaques with CMV disease) were only detected when the decline in cellular immunity was accompanied by a 2-fold or greater decline in anti-CMV neutralizing Ab. A significant direct correlation between loss of CMV-specific CD4+ T-lymphocytes and decline in anti-CMV neutralizing Ab was observed in the macaques with CMV disease.
Conclusions: Both humoral and cellular immune responses play a role in preventing CMV reactivation in AIDS. Although the importance of CD4+ T-cell help in maintaining an effective anti-viral CD8+ T-lymphocyte response is well established, our study also demonstrates a significant association between impaired CD4+ T-cell help and induction of memory B cell dysfunction.