An SAMT-247 Microbicide Provides Potent Protection against Intravaginal Simian Immunodeficiency Virus Infection of Rhesus Macaques, whereas an Added Vaccine Component Elicits Mixed Outcomes.

Because of microbicide noncompliance and lack of a durable, highly effective vaccine, a combined approach might improve HIV prophylaxis. We tested whether a vaccine-microbicide combination would enhance protection against SIV infection in rhesus macaques. Four macaque groups included vaccine only, vaccine-microbicide, microbicide only, and controls. Vaccine groups were primed twice mucosally with replicating adenovirus type 5 host range mutant SIV env/rev, gag, and nef recombinants and boosted twice i.m. with SIV gp120 proteins in alum. Controls and the microbicide-only group received adenovirus type 5 host range mutant empty vector and alum. The microbicide was SAMT-247, a 2-mercaptobenzamide thioester that targets the viral nucleocapsid protein NCp7, causing zinc ejection and preventing RNA encapsidation. Following vaccination, macaques were challenged intravaginally with repeated weekly low doses of SIVmac251 administered 3 h after application of 0.8% SAMT-247 gel (vaccine-microbicide and microbicide groups) or placebo gel (vaccine-only and control groups). The microbicide-only group exhibited potent protection; 10 of 12 macaques remained uninfected following 15 SIV challenges. The vaccine-only group developed strong mucosal and systemic humoral and cellular immunity but did not exhibit delayed acquisition compared with adjuvant controls. However, the vaccine-microbicide group exhibited significant acquisition delay compared with both control and vaccine-only groups, indicating further exploration of the combination strategy is warranted. Impaired protection in the vaccine-microbicide group compared with the microbicide-only group was not attributed to a vaccine-induced increase in SIV target cells. Possible Ab-dependent enhancement will be further investigated. The potent protection provided by SAMT-247 encourages its movement into human clinical trials.

TFH Cells Induced by Vaccination and Following SIV Challenge Support Env-Specific Humoral Immunity in the Rectal-Genital Tract and Circulation of Female Rhesus Macaques.

T follicular helper (TFH) cells are pivotal in lymph node (LN) germinal center (GC) B cell affinity maturation. Circulating CXCR5+ CD4+ T (cTFH) cells have supported memory B cell activation and broadly neutralizing antibodies in HIV controllers. We investigated the contribution of LN SIV-specific TFH and cTFH cells to Env-specific humoral immunity in female rhesus macaques following a mucosal Ad5hr-SIV recombinant priming and SIV gp120 intramuscular boosting vaccine regimen and following SIV vaginal challenge. TFH and B cells were characterized by flow cytometry. B cell help was evaluated in TFH-B cell co-cultures and by real-time PCR. Vaccination induced Env-specific TFH and Env-specific memory (ESM) B cells in LNs. LN Env-specific TFH cells post-priming and GC ESM B cells post-boosting correlated with rectal Env-specific IgA titers, and GC B cells at the same timepoints correlated with vaginal Env-specific IgG titers. Vaccination expanded cTFH cell responses, including CD25+ Env-specific cTFH cells that correlated negatively with vaginal Env-specific IgG titers but positively with rectal Env-specific IgA titers. Although cTFH cells post-2nd boost positively correlated with viral-loads following SIV challenge, cTFH cells of SIV-infected and protected macaques supported maturation of circulating B cells into plasma cells and IgA release in co-culture. Additionally, cTFH cells of naïve macaques promoted upregulation of genes associated with B cell proliferation, BCR engagement, plasma cell maturation, and antibody production, highlighting the role of cTFH cells in blood B cell maturation. Vaccine-induced LN TFH and GC B cells supported anti-viral mucosal immunity while cTFH cells provided B cell help in the periphery during immunization and after SIV challenge. Induction of TFH responses in blood and secondary lymphoid organs is likely desirable for protective efficacy of HIV vaccines.

Mucosal-associated invariant T (MAIT) cells provide B-cell help in vaccinated and subsequently SIV-infected Rhesus Macaques.

Mucosal-associated invariant T (MAIT) cells help combat opportunistic infections. Thus, MAIT cells are of interest in HIV/SIV vaccination and infection. We investigated MAIT cell dynamics and function in rhesus macaque blood and bronchoalveolar lavage (BAL) following mucosal adenovirus (Ad)-SIV recombinant priming, intramuscular SIV envelope boosting and infection following repeated low-dose intravaginal SIV exposures. Increased frequencies of blood MAIT cells over the course of vaccination were observed, which were maintained even 12-weeks post-SIV infection. BAL MAIT cells only increased after the first Ad immunization. Vaccination increased MAIT cell levels in blood and BAL expressing the antiviral cytokine IFN-γ and TNF-α and the proliferation marker Ki67. Upon T cell-specific α-CD3, α-CD28 stimulation, MAIT cells showed a greater capacity to secrete cytokines/chemokines associated with help for B cell activation, migration and regulation compared to CD3+MR1- cells. Culture of MAIT cell supernatants with B cells led to greater tissue like memory B cell frequencies. MAIT cell frequencies in blood and BAL correlated with SIV-specific antibody levels in rectal secretions and with SIV-specific tissue resident memory B cells. Overall, SIV vaccination influenced MAIT cell frequency and functionality. The potential for MAIT cells to provide help to B cells was evident during both vaccination and infection.