Delayed vaginal SHIV infection in VRC01 and anti-α4β7 treated rhesus macaques

VRC01 protects macaques from vaginal SHIV infection after a single high-dose challenge. Infusion of a simianized anti-α₄β₇ mAb (Rh-α₄β₇) just prior to, and during repeated vaginal exposures to SIVmac251 partially protected macaques from vaginal SIV infection and rescued CD4⁺ T cells. To investigate the impact of combining VRC01 and Rh-α₄β₇ on SHIV infection, 3 groups of macaques were treated with a suboptimal dosing of VRC01 alone or in combination with Rh-α₄β₇ or with control antibodies prior to the initiation of weekly vaginal exposures to a high dose (1000 TCID₅₀) of SHIV_AD8-EO. The combination Rh-α₄β₇-VRC01 significantly delayed SHIV_AD8-EO vaginal infection. Following infection, VRC01-Rh-α₄β₇-treated macaques maintained higher CD4⁺ T cell counts and exhibited lower rectal SIV-DNA loads compared to controls. Interestingly, VRC01-Rh-α₄β₇-treated macaques had fewer IL-17-producing cells in the blood and the gut during the acute phase of infection. Moreover, higher T cell responses to the V2-loop of the SHIV_AD8-EO envelope in the VRC01-Rh-α₄β₇ group inversely correlated with set point viremia. The combination of suboptimal amounts of VRC01 and Rh-α₄β₇ delayed infection, altered antiviral immune responses and minimized CD4⁺ T cell loss. Further exploration of the effect of combining bNAbs with Rh-α₄β₇ on SIV/HIV infection and antiviral immune responses is warranted and may lead to novel preventive and therapeutic strategies.