Pathogenicity and Mucosal Transmissibility of the R5-Tropic Simian/Human Immunodeficiency Virus SHIV _AD8 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 SHIV AD8 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 (SHIV AD8-CE8J , SHIV AD8-CK15 , and SHIV AD8-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 SHIV AD8 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 SHIV AD8-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 SHIV AD8 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.

Most rhesus macaques infected with the CCR5-tropic SHIV AD8 generate cross-reactive antibodies that neutralize multiple HIV-1 strains

“…We recently reported that only 3 of 19 monkeys inoculated with SHIV AD8 swarm stocks produced autologous neutralizing activity (13), and in the present study only 5 of 8 macaques inoculated with the SHIV AD8-EO molecular clone developed autologous NAbs ( Fig. 2A).…”

“…(5,000 or 500 TCID 50 ) and 7 by the intrarectal (5,000 or 1,000 TCID 50 ) routes. Similar to uncloned SHIV AD8 derivatives (13,14), the levels of set point viremia in macaques infected with the SHIV AD8-EO molecular clone varied widely (10 2 to >10 5 RNA copies/mL) (Fig. 1A).…”

“…We recently reported that only 3 of 19 macaques inoculated with SHIV AD8 swarm viruses developed sustained levels of autologous Nabs (13). In the current study, autologous NAbs, developing in eight of the macaques infected with the SHIV AD8-EO molecular clone were initially assessed using plasma samples diluted 1:20.…”

“…We next determined the cross-reactive IC 50 NAb titers directed against SHIV DH12 present in the plasmas of a different cohort of 11 macaques, which had been inoculated with molecularly cloned SHIV AD8 or recently described SHIV AD8 swarm stocks (13) (Fig. 3A).…”

Generation of a neutralization-resistant CCR5 tropic simian/human immunodeficiency virus (SHIV-MK38) molecular clone, a derivative of SHIV-89.6

“…It is important to consider the extensive mutation of the HIV-1 Env during monkey-to-monkey passages as frequently used SHIVs are adapted to the monkey in order to become pathogenic (Etemad-Moghadam et al, 2000;Hsu et al, 2003;Gautam et al, 2012). Boyd et al (2015) reported that SHIV adapted to utilize the monkey CD4 molecule, resulting in conformational changes that exposed epitopes in the variable regions.…”