Polyinosinic-polycytidylic acid is the most effective TLR adjuvant for SIV Gag protein-induced T cell responses in nonhuman primates.

Prime-boost immunization with heterologous vaccines elicits potent cellular immunity. In this study, we assessed the influence of various TLR ligands on SIV Gag-specific T cell immunity and protection following prime-boost immunization. Rhesus macaques (RMs) were primed with SIV Gag protein emulsified in Montanide ISA51 with or without TLR3 (polyinosinic-polycytidylic acid [poly-IC]), TLR4 (monophosphoryl lipid A), TLR7/8 (3M-012), TLR9 (CpG), or TLR3 (poly-IC) combined with TLR7/8 ligands, then boosted with replication defective adenovirus 5 expressing SIV Gag (rAd5-Gag). After priming, RMs that received SIV Gag protein plus poly-IC developed significantly higher frequencies of SIV Gag-specific CD4(+) Th1 responses in blood and bronchoalveolar lavage (BAL) fluid lymphocytes compared with all other adjuvants, and low-level SIV Gag-specific CD8(+) T cell responses. After the rAd5-Gag boost, the magnitude and breadth of SIV Gag-specific CD8(+) T cell responses were significantly increased in RM primed with SIV Gag protein plus poly-IC, with or without the TLR7/8 ligand, or CpG. However, the anamnestic, SIV Gag-specific CD8(+) T cell response to SIVmac251 challenge was not significantly enhanced by SIV Gag protein priming with any of the adjuvants. In contrast, the anamnestic SIV Gag-specific CD4(+) T cell response in BAL was enhanced by SIV Gag protein priming with poly-IC or CpG, which correlated with partial control of early viral replication after SIVmac251 challenge. These results demonstrate that prime-boost vaccination with SIV Gag protein/poly-IC improves magnitude, breadth, and durability of CD4(+) T cell immune responses, which could have a role in the control of SIV viral replication.

Neutralizing polyclonal IgG present during acute infection prevents rapid disease onset in simian-human immunodeficiency virus SHIVSF162P3-infected infant rhesus macaques.

Simian-human immunodeficiency virus (SHIV) models for human immunodeficiency virus (HIV) infection have been widely used in passive studies with HIV neutralizing antibodies (NAbs) to test for protection against infection. However, because SHIV-infected adult macaques often rapidly control plasma viremia and any resulting pathogenesis is minor, the model has been unsuitable for studying the impact of antibodies on pathogenesis in infected animals. We found that SHIVSF162P3 infection in 1-month-old rhesus macaques not only results in high persistent plasma viremia but also leads to very rapid disease progression within 12 to 16 weeks. In this model, passive transfer of high doses of neutralizing IgG (SHIVIG) prevents infection. Here, we show that at lower doses, SHIVIG reduces both plasma and peripheral blood mononuclear cell (PBMC)-associated viremia and mitigates pathogenesis in infected animals. Moreover, production of endogenous NAbs correlated with lower set-point viremia and 100% survival of infected animals. New SHIV models are needed to investigate whether passively transferred antibodies or antibodies elicited by vaccination that fall short of providing sterilizing immunity impact disease progression or influence immune responses. The 1-month-old rhesus macaque SHIV model of infection provides a new tool to investigate the effects of antibodies on viral replication and clearance, mechanisms of B cell maintenance, and the induction of adaptive immunity in disease progression.

Cytomegalovirus vectors expressing Plasmodium knowlesi antigens induce immune responses that delay parasitemia upon sporozoite challenge.

The development of a sterilizing vaccine against malaria remains one of the highest priorities for global health research. While sporozoite vaccines targeting the pre-erythrocytic stage show great promise, it has not been possible to maintain efficacy long-term, likely due to an inability of these vaccines to maintain effector memory T cell responses in the liver. Vaccines based on human cytomegalovirus (HCMV) might overcome this limitation since vectors based on rhesus CMV (RhCMV), the homologous virus in rhesus macaques (RM), elicit and indefinitely maintain high frequency, non-exhausted effector memory T cells in extralymphoid tissues, including the liver. Moreover, RhCMV strain 68-1 elicits CD8+ T cells broadly recognizing unconventional epitopes exclusively restricted by MHC-II and MHC-E. To evaluate the potential of these unique immune responses to protect against malaria, we expressed four Plasmodium knowlesi (Pk) antigens (CSP, AMA1, SSP2/TRAP, MSP1c) in RhCMV 68-1 or in Rh189-deleted 68-1, which additionally elicits canonical MHC-Ia-restricted CD8+ T cells. Upon inoculation of RM with either of these Pk Ag expressing RhCMV vaccines, we obtained T cell responses to each of the four Pk antigens. Upon challenge with Pk sporozoites we observed a delayed appearance of blood stage parasites in vaccinated RM consistent with a 75-80% reduction of parasite release from the liver. Moreover, the Rh189-deleted RhCMV/Pk vectors elicited sterile protection in one RM. Once in the blood, parasite growth was not affected. In contrast to T cell responses induced by Pk infection, RhCMV vectors maintained sustained T cell responses to all four malaria antigens in the liver post-challenge. The delayed appearance of blood stage parasites is thus likely due to a T cell-mediated inhibition of liver stage parasite development. As such, this vaccine approach can be used to efficiently test new T cell antigens, improve current vaccines targeting the liver stage and complement vaccines targeting erythrocytic antigens.