Nonhuman primate (NHP) models are invaluable for HIV pathogenesis, intervention and cure studies. To enhance the translational potential of NHP HIV vaccine studies, clinically relevant R5-tropic, tier 2 neutralization sensitive, and mucosally transmissible simian-human immunodeficiency viruses (SHIVs) have been designed. Towards our goal of developing vaccines to prevent breastmilk transmission of HIV, we evaluated virological outcomes of three distinct SHIVs in repeated weekly oral exposure regimens in infant rhesus macaques. The selected strains SHIV-1157ipd3N4, SHIV-1157(QNE)Y173H, and SHIV CH505 375H.dCT express a clade C HIV Env, the clade most prevalent in regions with high pediatric HIV infections. All three SHIVs were orally transmissible. However, compared to the pediatric SIVmac251 model, SHIV replication was more attenuated. Some animals exposed to weekly low-dose (20 TCID50) SHIV-1157ipd3N4 had transient viremia blips associated with lack or delayed seroconversion. Animals with acute viremia 10,000 viral RNA copies/ml seroconverted. This finding was reminiscent of an earlier study suggesting to continue challenges until a threshold of 10,000 viral RNA copies/mlis surpassed to achieve seroconversion, one criterion of HIV diagnosis.All animals exposedweekly with higher doses (>104 TCID50) of SHIV-1157(QNE)Y173H or SHIV CH505 375h.dCT developed persistent infection with high peak viremia and seroconverted. Chronic viremia varied widely in all three SHIV infection models. Thus, although R5 clade C SHIVs are excellent tools to study prevention of virus acquisition, secondary virological outcomes of vaccine efficacy (e.g. risk of infection per exposure, modulation of peak viremia, viral set point) will require careful consideration and validation in SHIV challenge models.

Oral clade C SHIV challenge models to study pediatric HIV-1 infection by breastmilk transmission