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Pathogenicity and Mucosal Transmissibility of the R5-Tropic Simian/Human Immunodeficiency Virus SHIVAD8 in Rhesus Macaques: Implications for Use in Vaccine Studies

ABSTRACT There is an urgent need to develop new pathogenic R5 simian/human immunodeficiency viruses (SHIVs) for the evaluation of candidate anti-HIV vaccines in nonhuman primates. Here, we characterize swarm SHIVAD8 stocks, prepared from three infected rhesus macaques with documented immunodeficiency at the time of euthanasia, for their capacity to establish durable infections in macaques following inoculation by the intravenous (i.v.) or intrarectal (i.r.) route. All three viral stocks (SHIVAD8-CE8J, SHIVAD8-CK15, and SHIVAD8-CL98) exhibited robust replication in vivo and caused marked depletion of CD4+ T cells affecting both memory and naïve CD4+ T lymphocyte subsets following administration by either route. Eleven of 22 macaques inoculated with the new SHIVAD8 stocks were euthanized with clinical symptoms of immunodeficiency and evidence of opportunistic infections (Pneumocystis, Candida, and Mycobacterium). A single but unique founder virus, also present in the SHIVAD8-CE8J swarm stock, was transmitted to two animals following a single i.r. inoculation of approximately 3 50% animal infectious doses, which is close to the threshold required to establish infection in all exposed animals. Because the three new SHIVAD8 viruses are mucosally transmissible, exhibited tier 2 sensitivity to anti-HIV-1 neutralizing antibodies, deplete CD4+ T lymphocytes in vivo, and induce AIDS in macaques, they are eminently suitable as challenge viruses in vaccine experiments.