SIV Antigens Research Articles

Lentiviral Infections Persist in Brain despite Effective Antiretroviral Therapy and Neuroimmune Activation.

ABSTRACTHIV infection persists in different tissue reservoirs among people with HIV (PWH) despite effective antiretroviral therapy (ART). In the brain, lentiviruses replicate principally in microglia and trafficking macrophages. The impact of ART on this viral reservoir is unknown. We investigated the activity of contemporary ART in various models of lentivirus brain infection. HIV-1 RNA and total and integrated DNA were detected in cerebral cortex from all PWH (n = 15), regardless of ART duration or concurrent plasma viral quantity and, interestingly, integrated proviral DNA levels in brain were significantly higher in the aviremic ART-treated group (P < 0.005). Most ART drugs tested (dolutegravir, ritonavir, raltegravir, and emtricitabine) displayed significantly lower 50% effective concentration (EC50) values in lymphocytes than in microglia, except tenofovir, which showed 1.5-fold greater activity in microglia (P < 0.05). In SIV-infected Chinese rhesus macaques, despite receiving suppressive (n = 7) or interrupted (n = 8) ART, brain tissues had similar SIV-encoded RNA and total and integrated DNA levels compared to brains from infected animals without ART (n = 3). SIV and HIV-1 capsid antigens were immunodetected in brain, principally in microglia/macrophages, regardless of ART duration and outcome. Antiviral immune responses were comparable in the brains of ART-treated and untreated HIV- and SIV-infected hosts. Both HIV-1 and SIV persist in brain tissues despite contemporary ART, with undetectable virus in blood. ART interruption exerted minimal effect on the SIV brain reservoir and did not alter the neuroimmune response profile. These studies underscore the importance of augmenting ART potency in different tissue compartments.

Localization and immunohistochemical detection of swine influenza A virus subtype H1N1 antigen in formalin-fixed, paraffin-embedded lung tissues from naturally infected pigs

BackgroundSwine influenza A viruses (SIV) infection is among the leading causes of respiratory diseases in a number of animal species and human, and has been reported to cause substantial losses to pig industry. Previous reports of serological, molecular, and surveillance studies in commercial piggeries in Nigeria indicated the presence of SIV subtypes H1N1 and H3N2 in infected pigs; hitherto, there exists lack of studies on the pulmonary pathology and pathogenicity of SIV in Nigeria. This study investigates the presence of SIV subtype H1N1 antigen in the formalin-fixed paraffin-embedded lung sections obtained from apparently healthy pigs slaughtered at abattoirs located in Lagos, Ogun, and Oyo States, Southwest Nigeria using a streptavidin-biotin (ABC) immunoperoxidase (IP) staining. Two hundred four lungs consisting of 144 grossly pneumonic lungs and 60 apparently normal lungs were randomly collected, fixed in 10% neutral-buffered formalin, embedded in paraffin wax, and processed for histopathological examination and immunohistochemistry.ResultsThe main gross lesions were marked pulmonary edema and mild bilateral consolidation of cranial lobes. Histopathology revealed suppurative bronchitis, and bronchiolitis with or without concurrent widespread degeneration and necrosis of epithelial cells (52.08%) and thickening of alveolar septa due to cellular infiltration consisting predominantly of neutrophils and mononuclear cells (macrophages and plasma cells) (39.58%). The lumina of most airways contained exudate consisting of neutrophils, desquamated epithelia cells, and necrotic debris. SIV antigen was immunohistochemically detected in 7/204 (3.43%) samples using SIV-specific (H1N1) monoclonal antibody. Positive cells exhibited a typical dark-brown reaction in the infected cells. A strong positive immunohistochemical staining was detected mainly in the alveolar macrophages and bronchial submucosal glandular epithelial cells while less intense staining was observed in the bronchiolar epithelial cells.ConclusionsThe present study describes the distribution and localization of SIV subtype H1N1 antigens in the lung tissues of the infected pigs and provides public awareness on the presence of the virus in pig population in Nigeria and the risk factors associated with the infection. Therefore, people working in pig farms should maintain high level of biosafety and personal hygiene. This is the first report of immunohistochemical detection of SIV subtype H1N1 antigen in naturally infected pigs in Nigeria and may indicate rapid dissemination of the virus in susceptible pigs in the study area. A further molecular epidemiological study to investigate other SIV subtypes circulating in Nigerian pig population is warranted.

Mucosal and systemic SIV-specific cytotoxic CD4+ T cell hierarchy in protection following intranasal/intramuscular recombinant pox-viral vaccination of pigtail macaques

A HIV vaccine that provides mucosal immunity is urgently needed. We evaluated an intranasal recombinant Fowlpox virus (rFPV) priming vaccine followed by intramuscular Modified Vaccinia Ankara (rMVA) booster vaccine, both expressing SIV antigens. The vaccination generated mucosal and systemic SIV-specific CD4+ T cell mediated immunity and was associated with partial protection against high-dose intrarectal SIVmac251 challenge in outbred pigtail macaques. Three of 12 vaccinees were completely protected and these animals elicited sustained Gag-specific poly-functional, cytotoxic mucosal CD4+ T cells, complemented by systemic poly-functional CD4+ and CD8+ T cell immunity. Humoral immune responses, albeit absent in completely protected macaques, were associated with partial control of viremia in animals with relatively weaker mucosal/systemic T cell responses. Co-expression of an IL-4R antagonist by the rFPV vaccine further enhanced the breadth and cytotoxicity/poly-functionality of mucosal vaccine-specific CD4+ T cells. Moreover, a single FPV-gag/pol/env prime was able to induce rapid anamnestic gp140 antibody response upon SIV encounter. Collectively, our data indicated that nasal vaccination was effective at inducing robust cervico-vaginal and rectal immunity, although cytotoxic CD4+ T cell mediated mucosal and systemic immunity correlated strongly with ‘complete protection’, the different degrees of protection observed was multi-factorial.

Human cytomegalovirus-vectored vaccines against HIV.

CMV-vectored vaccines expressing SIV antigens have mediated unprecedented levels of virus control following SIV challenge in rhesus macaques. Remarkably, protection was dependent on nonclassically restricted CD8 T cells. Here, we review the latest research in CMV-vectored vaccines in both humans and nonhuman primates as well as recent advances in the understanding nonclassically restricted T cells, particularly MHC-E-restricted CD8 T cells. Recent studies have investigated human translation of CMV-vectored vaccines including studies to ensure vaccine vector safety. Other work has focused on testing of animal models to investigate the relative contribution of MHC diversity and CMV strain on T-cell induction. Lastly, several groups have investigated MHC-E peptide binding, including HLA-E, have found that MHC-E can accommodate different peptide motifs, consistent with the original observations in CMV-vaccinated macaques. CMV remains a promising vaccine vector with the potential to be protective against multiple diseases, including HIV. However, CMV is highly species-specific and in humans, congenital infection can lead to serious birth defects. To ensure safe translation to humans, further clinical and animal studies are needed to better understand CMV-vectored immunity as well as more basic immunological questions relating to the induction of classical vs. nonclassical T cells.

Assessing non-classical antigen presentation in HIV-infected CD4+ T cells.

Abstract CD4+T cells recognize peptides presented by MHC Class II (MHC-II) molecules on B cells, dendritic cells, and macrophages. Interestingly, in humans, activated CD4+ T cells themselves express MHC-II molecules (HLA-DR, -DP, -DQ), but their potential role as antigen processing cells has not been well characterized. Recent promising data in a simian immunodeficiency (SIV) model suggest that antigen presentation by CD4+ T cells may be important in immunity. In these studies, a vaccine incorporating SIV antigens into a cytomegalovirus vector induced MHC-II restricted CD8+ T cells in macaques. Notably, these non-canonical cells were also observed in HIV patients. Clones generated from these MHC-II restricted CD8+ T cells killed autologous HIV-infected CD4+ T cells, suggesting that HIV is processed and presented on MHC-II on CD4+ T cells. To investigate this potentially novel form of antigen presentation, we eluted peptides from HLA-DR on activated CD4+T cells and sequenced them by LC-MS/MS. We show for the first time that human primary CD4+ T cells indeed process and present peptides on HLA-DR. We are currently applying this approach to HIV-infected cells to detect HIV peptides. Given the low sensitivity of untargeted MS for rare viral peptides, we are also generating a library of MHC-II HIV epitopes presented on HLA-DR to help guide more targeted MS analysis. To create this library, we are using a MHC-II cell-free processing system. We have already identified several epitopes from HIV Gag, Pol, Env, Vif, Rev, and Tat, some of which we show elicit memory responses in HIV patients. Our studies reveal a novel role for CD4+ T cells in antigen presentation and show that a cell-free processing system can predict HIV epitopes that may be presented on these cells.

Natural and cross-inducible anti-SIV antibodies in Mauritian cynomolgus macaques.

Cynomolgus macaques are an increasingly important nonhuman primate model for HIV vaccine research. SIV-free animals without pre-existing anti-SIV immune responses are generally needed to evaluate the effect of vaccine-induced immune responses against the vaccine epitopes. Here, in order to select such animals for vaccine studies, we screened 108 naïve female Mauritian cynomolgus macaques for natural (baseline) antibodies to SIV antigens using a Bio-Plex multiplex system. The antigens included twelve 20mer peptides overlapping the twelve SIV protease cleavage sites (-10/+10), respectively (PCS peptides), and three non-PCS Gag or Env peptides. Natural antibodies to SIV antigens were detected in subsets of monkeys. The antibody reactivity to SIV was further confirmed by Western blot using purified recombinant SIV Gag and Env proteins. As expected, the immunization of monkeys with PCS antigens elicited anti-PCS antibodies. However, unexpectedly, antibodies to non-PCS peptides were also induced, as shown by both Bio-Plex and Western blot analyses, while the non-PCS peptides do not share sequence homology with PCS peptides. The presence of natural and vaccine cross-inducible SIV antibodies in Mauritian cynomolgus macaques should be considered in animal selection, experimental design and result interpretation, for their best use in HIV vaccine research.

Abstract SY09-01: Next-generation anti-CTLA-4 antibodies

Abstract The activity of ipilimumab as a single agent and in combination with nivolumab (anti-PD-1) in melanoma, as well as the use of ipilimumab/nivolumab combinations in other malignancies, has confirmed the importance of CTLA-4 blockade in immunotherapy. The antitumor effect of this treatment also results in significant immune-related adverse events that limit dosing and result in patient discontinuation. We have taken two approaches to alter the activity of ipilimumab so as to improve its potency and its safety profile. One approach is to enhance the antibody-dependent cellular cytotoxicity (ADCC) activity of ipilimumab in order to increase the potential for Treg depletion at the tumor site; this would be expected to increase the activity of the antibody. The second approach is to produce a prodrug form of ipilimumab (an anti-CTLA-4 Probody therapeutic) that will have reduced activity systemically, but will become proteolytically cleaved at the tumor site to produce the fully functional antibody; the goal of this approach is to reduce the adverse event profile while retaining the antitumor activity of ipilimumab. It has previously been shown that antitumor activity of anti-CTLA-4 antibodies in mouse models of cancer is dependent on the ability of the antibody to bind activating FcγRs and mediate ADCC against Tregs at the tumor site (1, 2). Although human IgG1 Abs have been shown to be effective mediators of ADCC in patients with hematologic malignancies, it is still unclear whether ipilimumab mediates Treg depletion in solid tumors. Using in vitro ADCC assays, we have found that a nonfucosylated (NF) version of ipilimumab (ipilimumab-NF) has increased activity compared to ipilimumab. Ipilimumab-NF also demonstrates increased IL-2 secretion in peripheral mononuclear cells treated with the superantigen SEB as compared to ipilimumab. Transgenic mice that express human FcγRs in the place of mouse FcγRs were used to investigate the activity of anti-mouse surrogate CTLA-4 antibody engineered with either a human IgG1 or human IgG1-NF Fc region in a mouse tumor model. In these mice, the IgG1-NF version of anti-mouse CTLA-4 was found to significantly increase antitumor activity and Treg depletion at the tumor site compared to the IgG1. These data suggest that the clinical activity of ipilimumab could be enhanced by use of the nonfucosylated version of the Ab. In addition, ipilimumab-NF was tested for its ability to enhance a vaccine response in Mauritian cynomolgus macaques. Ipilimumab-NF was shown to result in increased vaccine-induced T-cell responses compared to ipilimumab using two replication-incompetent adenovirus serotype 5 viral vectors encoding SIV antigens as assessed by MHC-I tetramers and IFN-gamma ELISPOT in Mauritian cynomolgus macaques expressing the common allele, Mafa-A1*063. In a second approach, using Probody platform technology developed by CytomX, we have developed an anti-CTLA-4 Probody therapeutic (Probody Tx) based on ipilimumab. Probody Txs utilize a masking peptide that binds to the antigen-binding site of the Ab to reduce target binding. The mask extends from the light chain of the Ab via a linker sequence that contains cleavage sites for proteases preferentially active at the tumor site relative to healthy tissue. The ipilimumab Probody Tx binds to CTLA-4 with significantly lower affinity than the parental antibody and has reduced activity in in vitro assays. When tested in a mouse tumor model using human CTLA-4 KI mice, the ipilimumab-Probody Tx has comparable antitumor activity and Treg depletion at the tumor compared to ipilimumab. In contrast, ipilimumab-Probody Tx-treated mice show reduced levels of activated peripheral Tregs compared to ipilimumab-treated mice, even at doses 8-fold higher than are required for antitumor efficacy, consistent with reduced activity of the Probody Tx outside the tumor microenvironment. The development of next-generation anti-CTLA-4 antibodies holds promise for improving the utility of ipilimumab for single-agent or combination therapy. The two improvements to ipilimumab outlined above could each lead to a superior therapeutic outcome and merit further investigation.

Expression of complete SIV p27 Gag and HIV gp120 engineered outer domains targeted by broadly neutralizing antibodies in live rubella vectors

Infection with HIV or SIV often elicits a potent immune response to viral antigens. This includes T cells and antibodies specific for Gag and Env antigens. In contrast, when given as a vaccine, the same antigens have been weak immunogens, unable to elicit antibodies with comparable titer, durability, or neutralizing activity. We have used the live attenuated rubella vaccine strain RA27/3 as a viral vector to express HIV and SIV antigens. By mimicking an HIV infection, these vectors could elicit stronger and more durable immunity to HIV antigens. The vectors are based on the licensed rubella vaccine strain, which has demonstrated safety and potency in millions of children. One or two doses protect for life against rubella infection. The question was whether rubella vectors could similarly enhance the immunogenicity of a foreign vaccine insert.We have previously reported that rubella vectors can express small protein antigens in vitro and in vivo, where they elicit a strong immune response to the vaccine insert. The vectors have now expressed larger vaccine inserts that include epitope-rich fragments of the Gag matrix and capsid proteins (aa 41-211) or the complete p27 capsid protein with p2 (aa 136-381). These vectors have elicited a robust and durable immune response to Gag in rhesus macaques. This size range also encompasses the engineered outer domain (eOD) of HIV envelope gp120 (172 amino acids). The rubella/eOD-GT6 and GT8 vectors stably expressed glycoproteins that bind germline precursors and mature forms of VRC01-class broadly neutralizing antibodies. These vectors potentially could be used as part of a sequential immunization strategy to initiate the production of broadly neutralizing antibodies.

Development of novel replication-defective lymphocytic choriomeningitis virus vectors expressing SIV antigens

An important focus in vaccine research is the design of vaccine vectors with low seroprevalence and high immunogenicity. Replication-incompetent lymphocytic choriomeningitis virus (rLCMV) vectors do not elicit vector-neutralizing antibody responses, and homologous prime-boost regimens with rLCMV vectors induce boostable and protective T cell responses to model antigens in mice. However, cellular and humoral immune responses following homologous rLCMV vaccine regimens have not been rigorously evaluated in non-human primates (NHPs). To test whether rLCMV vectors constitute an effective vaccine platform in NHPs, we developed rLCMV vectors expressing SIVmac239 Env and Gag antigens and assessed their immunogenicity in mice and cynomolgus macaques. Immunization with rLCMV vaccine vectors expressing SIV Env and Gag was effective at generating SIV-specific T cell and antibody responses in both mice and NHPs. Epitope mapping using SIV Env in C57BL/6 mice demonstrated that rLCMV vectors induced sustained poly-functional responses to both dominant and subdominant epitopes. Our results suggest the potential of rLCMV vectors as vaccine candidates. Future SIV challenge experiments in rhesus macaques will be needed to assess immune protection by these vaccine vectors.

Responses to fibroblast-adapted human cytomegalovirus (HCMV) vaccines conform to CD8 T cell recognition paradigms

Abstract Recently, a rhesus CMV-based SIV vaccine that clears SIV from half of vaccinated monkeys was shown to elicit unconventional CD8 T cell responses to both SIV and RhCMV (IE1) antigens in all immunized monkeys. These responses were characterized by i) recognition of an unusually large number of peptide epitopes within each antigen, and ii) MHCII restriction by ~2/3 of responding CD8 T cells (Hansen et al, Science, 2013). Unconventional responses were only elicited by fibroblast-adapted rhCMV strain 68-1 that lacks ability to infect cells other than fibroblasts due to loss of pentameric viral glycoprotein expression. To determine whether fibroblast-adapted human CMV (HCMV) vaccines also elicit unconventional CD8 T cell responses, we exploited an ongoing phase I clinical trial of live HCMV vaccines. These vaccines have similar fibroblast-restricted tropism to rhCMV68-1, although the precise genetic lesions differ. We analyzed CD8 T cell responses in 12 seroconverters by stimulating PBMC with overlapping peptide pools covering 20 HCMV antigens. Seven subjects in this low dose trial (100 or 1000 pfu) made consistent, measurable CD8 T cell responses. All 7 responded to IE1; 3 also responded to 1–2 additional antigens. We have mapped responses to individual 15mers in 3 subjects, and all revealed highly focused responses to 1–3 epitopes within IE1. In one HLA-B08 positive subject, the two responses mapped to known immunodominant B08-restricted IE1 epitopes. We have mapped 4 other epitopes to date; of these, 3 are 9mers and are likely conventional, but one may be a 13mer. Thus far, in contrast to RhCMV in monkeys, the CD8 T cell response to fibroblast-adapted HCMV vaccines in humans appears to be predominantly conventional. Supported by NIH R21 AI116107

Mucosal Vaccination for Prevention of HIV Infection and AIDS.

Most of HIV infections occur via the genital tract or the rectum and HIV replicates at high levels in lymphoid organs and intestinal mucosa, likely requiring a more diversified immunity than pathogens restricted to a single mucosal site, such as the gastrointestinal tract for Vibrio cholera, or the respiratory airways for the influenza virus. Numerous AIDS vaccine candidates are under development and a general observation obtained from preclinical trials in non-human primates that failed to provide sterilizing immunity is that some infection protection or delayed onset of disease is observed in the presence of anti-SIV immunity. Recent clinical trials support difficulties to reproduce in humans the results observed in simian models, but at least one of them indicated that some protection of infection can be achieved. However, given the limited efficacy observed in the RV144 trial and concerns voiced in its statistical interpretation, preclinical trials should explore more effective immunogens, whether new or as combinations of existing ones, and mucosal routes of vaccinations in addition to the systemic routes, with the goal to maximize vaccination-mediated protection. The rationale for generating both strong mucosal and systemic immunity comes from animal experiments, recent clinical trials, and other successful vaccines currently in use. Mucosal responses against SIV have been induced with a variety of SIV antigens and via different mucosal routes with a spectrum of effects on protection. This review covers the rational and the experimental data that support the validity to explore mucosal immunization for HIV infection and AIDS prevention.

Modulation of SIV and HIV DNA vaccine immunity by Fas-FasL signaling.

Signaling through the Fas/Apo-1/CD95 death receptor is known to affect virus-specific cell-mediated immune (CMI) responses. We tested whether modulating the Fas-apoptotic pathway can enhance immune responses to DNA vaccination or lymphocytic choriomeningitis virus (LCMV) infection. Mice were electroporated with plasmids expressing a variety of pro- or anti-apoptotic molecules related to Fas signaling and then either LCMV-infected or injected with plasmid DNA expressing SIV or HIV antigens. Whereas Fas or FasL knockout mice had improved CMI, down-regulation of Fas or FasL by shRNA or antibody failed to improve CMI and was accompanied by increases in regulatory T cells (Treg). Two “adjuvant” plasmids were discovered that significantly enhanced plasmid immunizations. The adjuvant effects of Fas-associated death domain (FADD) and of cellular FLICE-inhibitory protein (cFLIP) were consistently accompanied by increased effector memory T lymphocytes and increased T cell proliferation. This adjuvant effect was also observed when comparing murine infections with LCMV-Armstrong and its persisting variant LCMV-Clone 13. LCMV-Armstrong was cleared in 100% of mice nine days after infection, while LCMV-Clone 13 persisted in all mice. However, half of the mice pre-electroporated with FADD or cFLIP plasmids were able to clear LCMV-Clone 13 by day nine, and, in the case of cFLIP, increased viral clearance was accompanied by higher CMI. Our studies imply that molecules in the Fas pathway are likely to affect a number of events in addition to the apoptosis of cells involved in immunity.

Which comes first: the antigen or the adjuvant?

Recent attempts to develop an HIV-1 vaccine indicate that viral replication can be limited by the induction of viral-specific T cell responses; however, recent trials of vaccine candidates designed to target CD8+ T cell responses were unsuccessful. In this issue, Sui and colleagues used a nonhuman primate model to investigate the effect of various vaccine adjuvants on the efficacy of SIV immunization. Unexpectedly, Sui et al. discovered that animals given adjuvant alone in the absence of SIV antigen exhibited a pronounced decrease in viral load following viral challenge. Vaccination with viral antigens combined with adjuvant correlated with the expansion of a population of cells with similarity to myeloid-derived suppressor cells (MDSCs) that may have suppressed vaccine-elicited T cell responses. Together, these results suggest that both innate and adaptive vaccine-elicited immune responses will need to be considered in future HIV-1 vaccine development.

Adenovirus Serotype 26 and 35 Vectors Induce Simian Immunodeficiency Virus-Specific T Lymphocyte Responses in Foreskin in Rhesus Monkeys

Foreskin is the principal site of heterosexual HIV-1 infection in men. However, little is known about HIV-1-specific immune responses or inflammation in foreskin. To the best of our knowledge, no previous studies have assessed immune responses to candidate HIV-1 vaccines in foreskin. Using the rhesus monkey model, we show that intramuscular immunization with adenovirus serotype 26 and 35 vectors expressing SIV antigens elicited durable SIV Gag-specific CD4(+) and CD8(+) T cell responses in foreskin that were detectable for more than 1 year following vaccination. Gag-specific CD4(+) and CD8(+) T cells were also detectable in foreskin of SIV- and SHIV-infected animals and were at least comparable in magnitude to those in peripheral blood. However, unlike peripheral blood T cells, the majority of foreskin T cells exhibited transitional memory or effector memory phenotype and expressed higher levels of the activation markers CD69, HLA-DR, and CCR5, although vaccination did not further enhance foreskin CD4(+) T cell activation. These findings suggest that systemic vaccination strategies can elicit potentially important SIV-specific cellular immunity in foreskin. Further characterization of vaccine-elicited immune responses and inflammation in foreskin is warranted. We demonstrate here the induction of SIV-specific cellular immune responses in foreskin by adenovirus serotype 26 and 35 vaccine vectors. Foreskin T cells were more activated than peripheral blood T cells, but foreskin T cells were not further activated by vaccination. These findings suggest that alternative serotype adenovirus vectors induce potentially important immune responses in foreskin.

Enhancement of SIV-specific cell mediated immune responses by co-administration of soluble PD-1 and Tim-3 as molecular adjuvants in mice

The development of an effective T cell based HIV vaccine would need to elicit cell mediated immune responses with superior magnitude, breadth, and quality. Since blocking the interactions between inhibitory receptors with their associated ligands using soluble PD-1 (sPD-1) and soluble Tim-3 (sTim-3) have been shown to reverse T cell exhaustion and enhance cell mediated immune responses, we tested if co-administration of sPD-1 and sTim-3 with an adenovirus vectored SIV vaccine (rAd5-SIV) can enhance cell mediated immune responses. The frequency of SIV antigen specific IFN-γ spot-forming cells and the secretion of IFN-γ and TNF-α by splenocytes from rAd5-SIV immunized mice was significantly increased when stimulated ex vivo with SIV peptides in the presence of sPD-1 or sTim-3 or both sPD-1 and sTim-3. The magnitude of cell mediated immune responses elicited by rAd5-SIV was enhanced by co-administration of sPD-1 and sTim-3. Co-administration of both sPD-1 and sTim-3 induced higher frequency of SIV antigen specific IFN-γ+ spot-forming cells to poorly immunogenic Vif and Tat. The percentage of cell mediated responses for each SIV antigen became more balanced, with reduction to Gag but induction to non-structural proteins. Furthermore, co-injection of rAd5-sPD1 and rAd5-sTim3 with rAd5-SIV in mice enhanced T cell proliferation capability and generated more antigen specific IFN-γ+ CD4+ and CD8+ T cells. Our study provided a new approach to enhance vaccine induced cell mediated immune responses, which may be applicable to improve the efficacy of vaccines against SIV/HIV.

Live attenuated rubella vectors expressing SIV and HIV vaccine antigens replicate and elicit durable immune responses in rhesus macaques

BackgroundLive attenuated viruses are among our most potent and effective vaccines. For human immunodeficiency virus, however, a live attenuated strain could present substantial safety concerns. We have used the live attenuated rubella vaccine strain RA27/3 as a vector to express SIV and HIV vaccine antigens because its safety and immunogenicity have been demonstrated in millions of children. One dose protects for life against rubella infection. In previous studies, rubella vectors replicated to high titers in cell culture while stably expressing SIV and HIV antigens. Their viability in vivo, however, as well as immunogenicity and antibody persistence, were unknown.ResultsThis paper reports the first successful trial of rubella vectors in rhesus macaques, in combination with DNA vaccines in a prime and boost strategy. The vectors grew robustly in vivo, and the protein inserts were highly immunogenic. Antibody titers elicited by the SIV Gag vector were greater than or equal to those elicited by natural SIV infection. The antibodies were long lasting, and they were boosted by a second dose of replication-competent rubella vectors given six months later, indicating the induction of memory B cells.ConclusionsRubella vectors can serve as a vaccine platform for safe delivery and expression of SIV and HIV antigens. By presenting these antigens in the context of an acute infection, at a high level and for a prolonged duration, these vectors can stimulate a strong and persistent immune response, including maturation of memory B cells. Rhesus macaques will provide an ideal animal model for demonstrating immunogenicity of novel vectors and protection against SIV or SHIV challenge.

SIV antigen-specific effects on immune responses induced by vaccination with DNA electroporation and plasmid IL-12

Molecular adjuvants are important for augmenting or modulating immune responses induced by DNA vaccination. Promising results have been obtained using IL-12 expression plasmids in a variety of disease models including the SIV model of HIV infection. We used a mouse model to evaluate plasmid IL-12 (pIL-12) in a DNA prime, recombinant adenovirus serotype 5 (rAd5) boost regimen specifically to evaluate the effect of IL-12 expression on cellular and humoral immunity induced against both SIVmac239 Gag and Env antigens. Priming with electroporated (EP) DNA+pIL-12 resulted in a 2–4-fold enhanced frequency of Gag-specific CD4 T cells which was maintained through the end of the study irrespective of the pIL-12 dose, while memory Env-specific CD4+T cells were maintained only at the low dose of pIL-12. There was little positive effect of pIL-12 on the humoral response to Env, and in fact, high dose pIL-12 dramatically reduced SIV Env-specific IgG. Additionally, both doses of pIL-12 diminished the frequency of CD8 T-cells after DNA prime, although a rAd5 boost recovered CD8 responses regardless of the pIL-12 dose. In this prime-boost regimen, we have shown that a high dose pIL-12 can systemically reduce Env-specific humoral responses and CD4T cell frequency, but not Gag-specific CD4+ T cells. These data indicate that it is important to independently characterize individual SIV or HIV antigen immunogenicity in multi-antigenic vaccines as a function of adjuvant dose.

ST108 Live, attenuated rubella viral vectors expressing SIV and HIV vaccine antigens grow well in vivo and are immunogenic

ST108 Live, attenuated rubella viral vectors expressing SIV and HIV vaccine antigens grow well in vivo and are immunogenic

CD8 down-regulation and functional impairment of SIV-specific cytotoxic T lymphocytes in lymphoid and mucosal tissues during SIV infection

Functional impairment of virus-specific T cells is a hallmark of HIV/SIV infection, but the underlying mechanisms of this dysfunction are not well understood. To address this, we simultaneously analyzed the expression and intensity of CD8 and inhibitory PD-1 on CTL in blood and lymphoid tissues in SIV-infected rhesus macaques. The intensity (mean channel fluorescence) of CD8 expression was transiently down-regulated in early SIV infection (10-14 dpi), despite an increase in CD8(+) T cell proliferation. In chronic infection, CD8 expression was maintained at low levels on CD8(+) T cells in all tissues. Interestingly, Gag-specific CTLs were clearly divided into CD8high- and CD8low-expressing populations in SIV-infected macaques, and CD8low Gag-specific cells increased with disease progression, especially in lymphoid tissues when compared with peripheral blood or in Gag-vaccinated controls. Moreover, the CD8low CTL population secreted lower levels of cytokines upon SIV antigen stimulation and exhibited lower proliferative capacity during infection compared with the CD8high CTL population. Meanwhile, intensity of PD-1 expression on Gag-specific CTL in chronic infection was significantly higher than in acute SIV infection, although the frequencies of PD-1+ Gag-specific cells were similar in acute and chronic stages. In summary, down-regulation of CD8 expression and higher expression of PD-1 on SIV-specific CTLs could coordinately attenuate SIV-specific CTL responses and their ability to recognize virus-infected target cells, especially in lymphoid tissues, resulting in failure to contain viremia, and continued persistence and replication of HIV in lymphoid tissue reservoirs.

Induction of CD8+ Regulatory T Cells Protects Macaques against SIV Challenge

Efforts to develop a vaccine against HIV have so far met with limited success. Given that CD4(+) T cell activation drives the initial burst of viral replication, we explored in macaques whether an oral vaccine comprised of Lactobacillus plantarum, a commensal bacterium that favors immune tolerance, and inactivated simian immunodeficiency virus mac239 (SIVmac239) would induce CD4(+) T cell unresponsiveness/tolerance toward SIV antigens and thereby prevent the establishment of SIV infection. The tolerogenic vaccine induced MHC-Ib/E-restricted CD8(+) regulatory T cells (Tregs) that suppressed SIV-harboring CD4(+) T cell activation and ex vivo SIV replication in 15 of 16 animals without inducing SIV-specific antibodies or cytotoxic T lymphocytes. Of 16 macaques that were intrarectally challenged with SIVmac239 or heterologous strain SIVB670, 15 were sterilely protected. In four macaques that were rechallenged intravenously, plasma SIV levels peaked slightly and then dropped to undetectable levels, although the animals subsequently harbored intracellular SIV DNA. Infusion of CD8 antibodies confirmed the role of CD8(+) Tregs in preventing/suppressing SIV in vivo. These findings suggest a new avenue of research toward developing an HIV-1 vaccine.