Chronic HIV infection is associated with accumulation of germinal center T follicular helper cells (GC-Tfh) in the lymphoid tissue. The GC-Tfh cells can be heterogeneous based on the expression of chemokine receptors associated with T helper lineages such as CXCR3 (Th1), CCR4 (Th2), and CCR6 (Th17). However, the heterogeneous nature of GC-Tfh cells in the lymphoid tissue and its association with viral persistence and antibody production during chronic SIV/HIV infection is not known. To address this, here we characterized the expression of CXCR3, CCR4, and CCR6 on GC-Tfh in lymph nodes following SIVmac251 infection in rhesus macaques (RMs). In SIV naïve RM, only a small fraction of GC-Tfh expressed CXCR3, CCR4 and CCR6. However, during chronic SIV infection, the majority of GC-Tfh cells expressed CXCR3, while the proportion of CCR4+ cells did not change and CCR6+ cells decreased. CXCR3+ but not CXCR3− GC-Tfh produced IFN-γ (Th1 cytokine) and IL-21 (Tfh cytokine) while both subsets expressed CD40L following stimulation. Immunohistochemistry analysis demonstrated an accumulation of CD4+ IFN-γ+ T cells within the hyperplastic follicles during chronic SIV infection. CXCR3+ GC-Tfh also expressed higher levels of ICOS, CCR5 and α4β7, contained more copies of SIV DNA compared to CXCR3− GC-Tfh cells. However, both CXCR3+ and CXCR3− GC-Tfh delivered help to B cells in vitro for production of IgG. These data demonstrate that chronic SIV infection promotes expansion of Th1-biased GC-Tfh cells, which are phenotypically and functionally distinct from conventional GC-Tfh cells and contribute to hypergammaglobulinemia and viral reservoirs.

Recent efforts toward an HIV vaccine focus on inducing broadly neutralizing antibodies, but eliciting both neutralizing antibodies (nAbs) and cellular responses may be superior. Here, we immunized macaques with an HIV envelope trimer, either alone to induce nAbs, or together with a heterologous viral vector regimen to elicit nAbs and cellular immunity, including CD8 + tissue-resident memory T cells. After ten vaginal challenges with autologous virus, protection was observed in both vaccine groups at 53.3% and 66.7%, respectively. A nAb titer >300 was generally associated with protection but in the heterologous viral vector + nAb group, titers <300 were sufficient. In this group, protection was durable as the animals resisted six more challenges 5 months later. Antigen stimulation of T cells in ex vivo vaginal tissue cultures triggered antiviral responses in myeloid and CD4 + T cells. We propose that cellular immune responses reduce the threshold of nAbs required to confer superior and durable protection.

A combination of vaccination approaches will likely be necessary to fully control the SARS-CoV-2 pandemic. Here, we show that modified vaccinia Ankara (MVA) vectors expressing membrane anchored pre-fusion stabilized spike (MVA/S), but not secreted S1, induced strong neutralizing antibody responses against SARS-CoV-2 in mice. In macaques, the MVA/S vaccination induced strong neutralizing antibodies and CD8 + T cell responses, and showed protection from SARS-CoV-2 infection and virus replication in the lung as early as day 2 following intranasal or intratracheal challenge. Single-cell RNA sequencing analysis of lung cells at day 4 post-infection revealed that MVA/S vaccination also protected macaques from infection-induced inflammation and B cell abnormalities, and lowered induction of interferon stimulated genes. These results demonstrate that MVA/S vaccination induces both neutralizing antibodies and CD8 + T cells in the blood and lung and serves as a potential vaccine candidate against SARS-CoV-2.

It remains a challenge to develop a successful human immunodeficiency virus (HIV) vaccine that is capable of preventing infection. Here, we utilized the benefits of CD40L, a costimulatory molecule that can stimulate both dendritic cells (DCs) and B cells, as an adjuvant for our simian immunodeficiency virus (SIV) DNA vaccine in rhesus macaques. We coexpressed the CD40L with our DNA/SIV vaccine such that the CD40L is anchored on the membrane of SIV virus-like particle (VLP). These CD40L containing SIV VLPs showed enhanced activation of DCs in vitro. We then tested the potential of DNA/SIV-CD40L vaccine to adjuvant the DNA prime of a DNA/modified vaccinia virus Ankara (MVA) vaccine in rhesus macaques. Our results demonstrated that the CD40L adjuvant enhanced the functional quality of anti-Env antibody response and breadth of anti-SIV CD8 and CD4 T cell responses, significantly delayed the acquisition of heterologous mucosal SIV infection, and improved viral control. Notably, the CD40L adjuvant enhanced the control of viral replication in the gut at the site of challenge that was associated with lower mucosal CD8 immune activation, one of the strong predictors of disease progression. Collectively, our results highlight the benefits of CD40L adjuvant for enhancing antiviral humoral and cellular immunity, leading to enhanced protection against a pathogenic SIV. A single adjuvant that enhances both humoral and cellular immunity is rare and thus underlines the importance and practicality of CD40L as an adjuvant for vaccines against infectious diseases, including HIV-1. IMPORTANCEDespite many advances in the field of AIDS research, an effective AIDS vaccine that can prevent infection remains elusive. CD40L is a key stimulator of dendritic cells and B cells and can therefore enhance T cell and antibody responses, but its overly potent nature can lead to adverse effects unless used in small doses. In order to modulate local expression of CD40L at relatively lower levels, we expressed CD40L in a membrane-bound form, along with SIV antigens, in a nucleic acid (DNA) vector. We tested the immunogenicity and efficacy of the CD40L-adjuvanted vaccine in macaques using a heterologous mucosal SIV infection. The CD40L-adjuvanted vaccine enhanced the functional quality of anti-Env antibody response and breadth of anti-SIV T cell responses and improved protection. These results demonstrate that VLP-membrane-bound CD40L serves as a novel adjuvant for an HIV vaccine. N ovel vaccine approaches that elicit strong humoral and cellular immunity with high functional quality will aid HIV vaccine development. Here, we utilized the benefits of CD40L, a costimulatory molecule belonging to the tumor necrosis factor superfamily (TNFSF), that can stimulate both dendritic cells (DCs) and B cells for enhancing T cell and antibody (Ab) responses (1). CD40L activates DCs and enhances the priming of the cytotoxic CD8 T cell response (2-4). CD40L also enhances the survival and differentiation of activated B cells, leading to increased germinal c...

The goal of an HIV vaccine is to generate robust and durable protective antibody. Vital to this goal is the induction of CD4+ T follicular helper cells (TFH). However, very little is known about the TFH response to HIV vaccination and its relative contribution to magnitude and quality of vaccine-elicited antibody titers. Here, we investigated these questions in the context of a DNA/modified vaccinia virus Ankara (MVA) SIV vaccine with and without gp140 boost in alum in rhesus macaques. In addition, we determined the frequency of vaccine-induced CD4+ T cells co-expressing chemokine receptor, CXCR5 (facilitates migration to B cell follicles) in blood and whether these responses were representative of lymph node (LN) TFH responses. We show that booster MVA immunization induced a distinct and transient accumulation of proliferating CXCR5+ and CXCR5− CD4 T cells in blood at day 7-post immunization and the frequency of the former but not the latter correlated with TFH and B cell responses in germinal centers (GC) of LN. Interestingly, gp140 boost induced a skewing towards CXCR3 expression on GC TFH cells, which was strongly associated with longevity, avidity, and neutralization potential of vaccine-elicited antibody response. However, CXCR3+ cells preferentially expressed the HIV co-receptor CCR5 and vaccine-induced CXCR3+ CXCR5+ cells showed a moderate positive association with peak viremia following SIV251 infection. Taken together, our findings demonstrate that vaccine regimens that elicit CXCR3 biased TFH cell responses favor antibody persistence and avidity but may predispose to higher acute viremia in the event of breakthrough infections.

The rapid worldwide spread of human immunodeficiency virus (HIV) mandates the development of successful vaccination strategies. Since live attenuated HIV is not accepted as a vaccine due to safety concerns, virus-like particles (VLPs) offer an attractive safe alternative because they lack the viral genome yet they are perceived by the immune system as a virus particle. We hypothesized that adding immunostimulatory signals to VLPs would enhance their efficacy. To accomplish this we generated chimeric simian immunodeficiency virus (SIV) VLPs containing either glycosylphosphatidylinositol (GPI)-anchored granulocyte-macrophage colonystimulating factor (GM-CSF) or CD40 ligand (CD40L) and investigated their biological activity and ability to enhance immune responses in vivo. Immunization of mice with chimeric SIV VLPs containing GM-CSF induced SIV Env-specific antibodies as well as neutralizing activity at significantly higher levels than those induced by standard SIV VLPs, SIV VLPs containing CD40L, or standard VLPs mixed with soluble GM-CSF. In addition, mice immunized with chimeric SIV VLPs containing either GM-CSF or CD40L showed significantly increased CD4 ؉ -and CD8 ؉ -T-cell responses to SIV Env, compared to standard SIV VLPs. Taken together, these results demonstrate that the incorporation of immunostimulatory molecules enhances humoral and cellular immune responses. We propose that anchoring immunostimulatory molecules into SIV VLPs can be a promising approach to augmenting the efficacy of VLP antigens.

There is a great need for the development of vaccines that induce potent and long-lasting protective immunity against SARS-CoV-2. Multimeric display of the antigen combined with potent adjuvant can enhance the potency and longevity of the antibody response. The receptor binding domain (RBD) of the spike protein is a primary target of neutralizing antibodies. Here, we developed a trimeric form of the RBD and show that it induces a potent neutralizing antibody response against live virus with diverse effector functions and provides protection against SARS-CoV-2 challenge in mice and rhesus macaques. The trimeric form induces higher neutralizing antibody titer compared to monomer with as low as 1μg antigen dose. In mice, adjuvanting the protein with a TLR7/8 agonist formulation alum-3M-052 induces 100-fold higher neutralizing antibody titer and superior protection from infection compared to alum. SARS-CoV-2 infection causes significant loss of innate cells and pathology in the lung, and vaccination protects from changes in innate cells and lung pathology. These results demonstrate RBD trimer protein as a suitable candidate for vaccine against SARS-CoV-2.

The rapid spread of human immunodeficiency virus (HIV) worldwide makes it a high priority to develop an effective vaccine. Since live attenuated or inactivated HIV is not likely to be approved as a vaccine due to safety concerns, HIV virus like particles (VLPs) offer an attractive alternative because they are safe due to the lack of a viral genome. Although HIV VLPs have been shown to induce humoral and cellular immune responses, it is important to understand the mechanisms by which they induce such responses and to improve their immunogenicity. We generated HIV VLPs, and VLPs containing Flt3 ligand (FL), a dendritic cell growth factor, to target VLPs to dendritic cells, and investigated the roles of these VLPs in the initiation of adaptive immune responses in vitro and in vivo. We found that HIV-1 VLPs induced maturation of dendritic cells and monocyte/macrophage populations in vitro and in vivo, with enhanced expression of maturation markers and cytokines. Dendritic cells pulsed with VLPs induced activation of splenocytes resulting in increased production of cytokines. VLPs containing FL were found to increase dendritic cells and monocyte/macrophage populations in the spleen when administered to mice. Administration of VLPs induced acute activation of multiple types of cells including T and B cells as indicated by enhanced expression of the early activation marker CD69 and down-regulation of the homing receptor CD62L. VLPs containing FL were an effective form of antigen in activating immune cells via dendritic cells, and immunization with HIV VLPs containing FL resulted in enhanced T helper type 2-like immune responses.