Immune Protection of SIV Challenge by PD-1 Blockade During Vaccination in Rhesus Monkeys

Mosaic neuraminidase-based vaccine induces antigen-specific T cell responses against homologous and heterologous influenza viruses

Seasonal influenza is an annually severe crisis for global public health, and an ideal influenza vaccine is expected to provide broad protection against constantly drifted strains. Compared to highly flexible hemagglutinin (HA), increasing data have demonstrated that neuraminidase (NA) might be a potential target against influenza variants. In the present study, a series of genetic algorithm-based mosaic NA were designed, and then cloned into recombinant DNA and replication-defective Vesicular Stomatitis Virus (VSV) vector as a novel influenza vaccine candidate. Our Results showed that DNA prime/VSV boost strategy elicited a robust NA-specific Th1-dominated immune response, but the traditional inactivated influenza vaccine elicited a Th2-dominated immune response. More importantly, the superior NA-specific immunity induced by our strategy could confer both a full protection against lethal homologous influenza challenge and a partial protection against heterologous influenza infection. These findings will provide insights on designing NA-based universal vaccine strategy against influenza variants.

Flt3 agonist enhances immunogenicity of arenavirus vector-based simian immunodeficiency virus vaccine in macaques

Arenaviral vaccine vectors encoding simian immunodeficiency virus (SIV) immunogens are capable of inducing efficacious humoral and cellular immune responses in nonhuman primates. Several studies have evaluated the use of immune modulators to further enhance vaccine-induced T-cell responses. The hematopoietic growth factor Flt3L drives the expansion of various bone marrow progenitor populations, and administration of Flt3L was shown to promote expansion of dendritic cell populations in spleen and blood, which are targets of arenaviral vectors. Therefore, we evaluated the potential of Flt3 signaling to enhance the immunogenicity of arenaviral vaccines encoding SIV immunogens (SIVSME543 Gag, Env, and Pol) in rhesus macaques, with a rhesus-specific engineered Flt3L-Fc fusion protein. In healthy animals, administration of Flt3L-Fc led to a 10- to 100-fold increase in type 1 dendritic cells 7 days after dosing, with no antidrug antibody (ADA) generation after repeated dosing. We observed that administration of Flt3L-Fc fusion protein 7 days before arenaviral vaccine increased the frequency and activation of innate immune cells and enhanced T-cell activation with no treatment-related adverse events. Flt3L-Fc administration induced early innate immune activation, leading to a significant enhancement in magnitude, breadth, and polyfunctionality of vaccine-induced T-cell responses. The Flt3L-Fc enhancement in vaccine immunogenicity was comparable to a combination with αCTLA-4 and supports the use of safe and effective variants of Flt3L to augment therapeutic vaccine-induced T-cell responses.IMPORTANCEInduction of a robust human immunodeficiency virus (HIV)-specific CD4+ and CD8+ T-cell response through therapeutic vaccination is considered essential for HIV cure. Arenaviral vaccine vectors encoding simian immunodeficiency virus (SIV) immunogens have demonstrated strong immunogenicity and efficacy in nonhuman primates. Here, we demonstrate that the immunogenicity of arenaviral vectors encoding SIV immunogens can be enhanced by administration of Flt3L-Fc fusion protein 7 days before vaccination. Flt3L-Fc-mediated increase in dendritic cells led to robust improvements in vaccine-induced T- and B-cell responses compared with vaccine alone, and Flt3L-Fc dosing was not associated with any treatment-related adverse events. Importantly, immune modulation by either Flt3L-Fc or αCTLA-4 led to comparable enhancement in vaccine response. These results indicate that the addition of Flt3L-Fc fusion protein before vaccine administration can significantly enhance vaccine immunogenicity. Thus, safe and effective Flt3L variants could be utilized as part of a combination therapy for HIV cure.

Inhibition of SFTSV replication in humanized mice by a subcutaneously administered anti-PD1 nanobody

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening disease caused by a novel bunyavirus (SFTSV), mainly transmitted by ticks. With no effective therapies or vaccines available, understanding the disease's mechanisms is crucial. Recent studies found increased expression of programmed cell death-1 (PD-1) on dysfunctional T cells in SFTS patients. However, the role of the PD-1/programmed cell death-ligand 1 (PD-L1) pathway in SFTS progression remains unclear. We investigated PD-1 blockade as a potential therapeutic strategy against SFTSV replication. Our study analyzed clinical samples and performed in vitro experiments, revealing elevated PD-1/PD-L1 expression in various immune cells following SFTSV infection. An anti-PD-1 nanobody, NbP45, effectively inhibited SFTSV infection in peripheral blood mononuclear cells (PBMCs), potentially achieved through the mitigation of apoptosis and the augmentation of T lymphocyte proliferation. Intriguingly, subcutaneous administration of NbP45 showed superior efficacy compared to a licensed anti-PD-1 antibody in an SFTSV-infected humanized mouse model. These findings highlight the involvement of the PD-1/PD-L1 pathway during acute SFTSV infection and suggest its potential as a host target for immunotherapy interventions against SFTSV infection.

Immune Checkpoint Inhibitors and Infection: What Is the Interplay?

Immune checkpoint molecules are receptors expressed on immune cells, especially T-cells, which activate immunosuppressive pathways and lead them to a state known as T-cell exhaustion. Immune checkpoint inhibitors (ICIs) constitute a group of specific antibodies that target these molecules, restoring T-cell effector function. Several ICIs have already been approved by the FDA as therapeutic options for certain malignancies. However, evidence in the literature remains unclear regarding the possible risk of infection in patients receiving this treatment. A thorough examination of existing literature was carried out to investigate whether the use of ICIs increases the likelihood of specific infections and to explore the potential beneficial effects of ICIs on the treatment of infections. Our review found most infectious complications are related to immunosuppressive therapy for immune-related adverse events caused by checkpoint blockade. Current evidence shows that ICIs per se do not seem to generally increase the risk of infection, yet they might increase susceptibility to certain infections, such as tuberculosis. On the other hand, reinvigoration of immune responses triggered by ICIs might play a significant role in pathogen clearance, establishing a possible positive impact of ICIs, especially on chronic infectious diseases, such as HIV infection. Data from preclinical models are limited and larger clinical trials are warranted to shed more light on the effect of immune checkpoint blockade on specific pathogens.

Arsenic trioxide-induced apoptosis contributes to suppression of viral reservoir in SIV-infected rhesus macaques

Latent viral reservoir is recognized as the major obstacle to achieving a functional cure for HIV infection. We previously reported that arsenic trioxide (As2O3) combined with antiretroviral therapy (ART) can reactivate the viral reservoir and delay viral rebound after ART interruption in chronically simian immunodeficiency virus (SIV)-infected macaques. In this study, we further investigated the effect of As2O3 independent of ART in chronically SIV-infected macaques. We found that As2O3-only treatment significantly increased the CD4/CD8 ratio, improved SIV-specific T cell responses, and reactivated viral latency in chronically SIVmac239-infected macaques. RNA-sequencing analysis revealed that As2O3 treatment downregulated the expression levels of genes related to HIV entry and infection, while the expression levels of genes related to transcription initiation, cell apoptosis, and host restriction factors were significantly upregulated. Importantly, we found that As2O3 treatment specifically induced apoptosis of SIV-infected CD4+ T cells. These findings revealed that As2O3 might not only impact viral latency, but also induce the apoptosis of HIV-infected cells and thus block the secondary infection of bystanders. Moreover, we investigated the therapeutic potential of this regimen in acutely SIVmac239-infected macaques and found that As2O3 + ART treatment effectively restored the CD4+ T cell count, delayed disease progression, and improved survival in acutely SIV-infected macaques. In sum, this work provides new insights to develop As2O3 as a component of the "shock-and-kill" strategy toward HIV functional cure. IMPORTANCE Although antiretroviral therapy (ART) can effectively suppress the viral load of AIDS patients, it cannot functionally cure HIV infection due to the existence of HIV reservoir. Strategies toward HIV functional cure are still highly anticipated to ultimately end the pandemic of AIDS. Herein, we investigated the direct role of As2O3 independent of ART in chronically SIV-infected macaques and explored the underlying mechanisms of the potential of As2O3 in the treatment of HIV/SIV infection. Meanwhile, we investigated the therapeutic effects of ART+As2O3 in acutely SIVmac239-infected macaques. This study showed that As2O3 has the potential to be launched into the "shock-and-kill" strategy to suppress HIV/SIV reservoir due to its latency-reversing and apoptosis-inducing properties.

ChAdOx1 nCoV-19 vaccination generates spike-specific CD8+ T cells in aged mice

Effective vaccines have reduced the morbidity and mortality caused by severe acute respiratory syndrome coronavirus-2 infection; however, the elderly remain the most at risk. Understanding how vaccines generate protective immunity and how these mechanisms change with age is key for informing future vaccine design. Cytotoxic CD8+ T cells are important for killing virally infected cells, and vaccines that induce antigen-specific CD8+ T cells in addition to humoral immunity provide an extra layer of immune protection. This is particularly important in cases where antibody titers are suboptimal, as can occur in older individuals. Here, we show that in aged mice, spike epitope-specific CD8+ T cells are generated in comparable numbers to younger animals after ChAdOx1 nCoV-19 vaccination, although phenotypic differences exist. This demonstrates that ChAdOx1 nCoV-19 elicits a good CD8+ T-cell response in older bodies, but that typical age-associated features are evident on these vaccine reactive T cells.

The implication of anti-PD-1 therapy in cancer patients for the vaccination against viral and other infectious diseases

The phenomenon of 'T cell exhaustion', a state of T cell dysfunction observed during chronic infections and cancers, has been a major obstacle in mounting appropriate immune responses against infectious agents or tumor antigens. The exhausted T cells are characterized by poor effector functions mainly due to the overexpression of inhibitory receptors such as programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), T cell immunoglobulin and mucin-domain containing 3 (TIM3), lymphocyte activation gene 3 (LAG3), and T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain (TIGIT), commonly referred to as immune checkpoint (ICP) molecules. ICP blockade, especially of PD-1 that can potentially reverse T cell exhaustion and thereby re-stimulate the impaired immune system, is widely used in clinics as a promising therapeutic strategy for various cancers and is more recently being investigated in infectious diseases as well. In fact, cancer patients represent a population of immunocompromised individuals who are more susceptible to infections and associated complications, and thus the need for protective vaccinations against these diseases is of prime importance in this category. When it comes to vaccinating anti-PD-1-treated cancer patients against infectious diseases including COVID-19 and influenza, a special focus should be brought on the revived immune cells, which could be dynamically affected by the antigenic stimulation. However, since cancer patients are not generally included in clinical trials for designing vaccines against infectious diseases, the possible interaction between vaccine immune responses and ICP therapy is largely unexplored. Mechanistically, the reversal of T cell exhaustion by ICP in an otherwise immunocompromised population could be beneficial for the vaccine's efficacy, helping the immune system to mount a robust immune response. Nevertheless, patients with cancer undergoing anti-PD-1 blockade are known to experience immune-related adverse effects (irAEs). The risk of increasing the irAEs due to the overstimulation of the immune system during vaccination is a major concern. Therefore, while routine vaccination is indispensable for the protection of cancer patients, the impact of PD-1 blockade on vaccine responses against infectious agents requires careful consideration to avoid undesirable adverse effects that could impair the efficacy of anti-cancer treatment.

The Combination of an mRNA Immunogen, a TLR7 Agonist and a PD1 Blocking Agent Enhances In-Vitro HIV T-Cell Immune Responses

The development of new strategies to achieve a functional cure for HIV remains a priority. We tested a novel HIV therapeutic vaccine using unmodified mRNA (TMEP-B) and mRNA modified by 1-methyl-3'-pseudouridylyl (TMEP-Bmod) expressing both a multiepitopic sequences from Gag, Pol, and Nef proteins, including different CD4 and CD8 T-cell epitopes functionally associated with HIV control in transfected monocyte-derived dendritic cells (MDDCs) obtained from HIV infected patients. In vitro assays were used to test the mRNAs alone and in combination with immunomodulator agents, such as the TLR-7 agonist Vesatolimod and the PD-1 antagonist Nivolumab to try to improve HIV-specific cellular immune responses. Combining the mRNAs with the immunomodulators enhanced HIV-specific T-cell responses, together with the secretion of IFNγ, IP10, MIP-1α, and MIP-1β, which are fundamental mediators of viral control. Our data suggest that the mRNA vaccine prototypes TMEP-B and TMEP-Bmod, when combined with Vesatolimod and/or Nivolumab, could achieve functional cure for patients with HIV.

Comparison of the Immunogenicity of HIV-1 CRF07_BC Gag Antigen With or Without a Seven Amino Acid Deletion in p6 Region

HIV-1 CRF07_BC-p6Δ7, a strain with a seven amino acid deletion in the p6 region of the Gag protein, is becoming the dominant strain of HIV transmission among men who have sex with men (MSM) in China. Previous studies demonstrated that HIV-1 patients infected by CRF07_BC-p6Δ7 strain had lower viral load and slower disease progression than those patients infected with CRF07_BC wild-type strain. However, the underlying mechanism for this observation is not fully clarified yet. In this study, we constructed the recombinant DNA plasmid and adenovirus type 2 (Ad2) vector-based constructs to express the HIV-1 CRF07_BC Gag antigen with or without p6Δ7 mutation and then investigated their immunogenicity in mice. Our results showed that HIV-1 CRF07_BC Gag antigen with p6Δ7 mutation induced a comparable level of Gag-specific antibodies but stronger CD4⁺ and CD8⁺ T-cell immune responses than that of CRF07_BC Gag (07_BC-wt). Furthermore, we identified a series of T-cell epitopes, which induced strong T-cell immune response and cross-immunity with CRF01_AE Gag. These findings implied that the p6^Gag protein with a seven amino acid deletion might enhance the Gag immunogenicity in particular cellular immunity, which provides valuable information to clarify the pathogenic mechanism of HIV-1 CRF07_BC-p6Δ7 and to develop precise vaccine strategies against HIV-1 infection.

Expression Profile and Biological Role of Immune Checkpoints in Disease Progression of HIV/SIV Infection

During HIV/SIV infection, the upregulation of immune checkpoint (IC) markers, programmed cell death protein-1 (PD-1), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), T cell immunoglobulin and ITIM domain (TIGIT), lymphocyte-activation gene-3 (LAG-3), T cell immunoglobulin and mucin domain-3 (Tim-3), CD160, 2B4 (CD244), and V-domain Ig suppressor of T cell activation (VISTA), can lead to chronic T cell exhaustion. These ICs play predominant roles in regulating the progression of HIV/SIV infection by mediating T cell responses as well as enriching latent viral reservoirs. It has been demonstrated that enhanced expression of ICs on CD4⁺ and CD8⁺ T cells could inhibit cell proliferation and cytokine production. Overexpression of ICs on CD4⁺ T cells could also format and prolong HIV/SIV persistence. IC blockers have shown promising clinical results in HIV therapy, implying that targeting ICs may optimize antiretroviral therapy in the context of HIV suppression. Here, we systematically review the expression profile, biological regulation, and therapeutic efficacy of targeted immune checkpoints in HIV/SIV infection.

Kynurenine-3-monooxygenase (KMO) broadly inhibits viral infections via triggering NMDAR/Ca2+ influx and CaMKII/ IRF3-mediated IFN-β production

Tryptophan (Trp) metabolism through the kynurenine pathway (KP) is well known to play a critical function in cancer, autoimmune and neurodegenerative diseases. However, its role in host-pathogen interactions has not been characterized yet. Herein, we identified that kynurenine-3-monooxygenase (KMO), a key rate-limiting enzyme in the KP, and quinolinic acid (QUIN), a key enzymatic product of KMO enzyme, exerted a novel antiviral function against a broad range of viruses. Mechanistically, QUIN induced the production of type I interferon (IFN-I) via activating the N-methyl-d-aspartate receptor (NMDAR) and Ca²⁺ influx to activate Calcium/calmodulin-dependent protein kinase II (CaMKII)/interferon regulatory factor 3 (IRF3). Importantly, QUIN treatment effectively inhibited viral infections and alleviated disease progression in mice. Furthermore, kmo^-/- mice were vulnerable to pathogenic viral challenge with severe clinical symptoms. Collectively, our results demonstrated that KMO and its enzymatic product QUIN were potential therapeutics against emerging pathogenic viruses.

The outbreaks of emerging infectious diseases have become a severe challenge worldwide, and therefore it is a public health priority to explore novel broad-spectrum antiviral agents with various mechanisms. This study reported that kynurenine-3-monooxygenase (KMO), a key rate-limiting enzyme during tryptophan metabolism, showed promise as a novel broad-spectrum antiviral factor against emerging pathogenic viruses. We further found that quinolinic acid (QUIN), an enzymatic product of KMO, could also act as a novel broad-spectrum antiviral agent. We then systematically studied the underlying mechanisms and broadly antiviral function of KMO and QUIN in vitro and in vivo. Our data highlight the importance of exploring novel antiviral targets from the key enzymes and their metabolites in tryptophan metabolism.

Immune checkpoint blockade in HIV

Antiretroviral therapy (ART) has dramatically improved life expectancy for people with HIV (PWH) and helps to restore immune function but is not curative and must be taken lifelong. Achieving long term control of HIV in the absence of ART will likely require potent T cell function, but chronic HIV infection is associated with immune exhaustion that persists even on ART. This is driven by elevated expression of immune checkpoints that provide negative signalling to T cells. In individuals with cancer, immune checkpoint blockade augments tumour-directed T-cell responses resulting in significant clinical cures. There is therefore high interest if ICB can contribute to HIV cure or remission by reversing HIV-latency and/or drive recovery of HIV-specific T-cells. We here review recent evidence on the role of immune checkpoints in persistent HIV infection and discuss the potential for employing immune checkpoint blockade as a therapeutic approach to target HIV persistence on ART.

Exacerbated AIDS progression by PD-1 blockade during therapeutic vaccination in chronically SIV-infected rhesus macaques after ART treatment interruption

The persistence of latent HIV-1-infected cells, named the latent reservoir, is the major barrier to HIV-1 eradication, and the formation and maintenance of latent reservoir might be exacerbated by activation of the immunoinhibitory pathway and dysfunction of CD8⁺ T cells during HIV-1 infection. Our previous findings demonstrated that prophylactic vaccination combined with PD-1 blockade generated distinct immune response profiles and conferred effective control of highly pathogenic SIVmac239 infection in rhesus macaques. However, to our surprise, herein we found that a therapeutic vaccination in combination with PD-1 blockade resulted in activation of the viral reservoir, faster viral rebound after treatment interruption, accelerated acquired immune deficiency syndrome (AIDS) progression and ultimately death in chronically SIV-infected macaques after ART treatment interruption. Our study further demonstrated that the SIV provirus was preferentially enriched in PD-1⁺CD4⁺ T cells due to their susceptibility to viral entry, potent proliferation ability and inability to perform viral transcription. In addition, the viral latency was effectively reactivated upon PD-1 blockade. Together, these results suggest that PD-1 blockade may be a double-edged sword for HIV-1 immunotherapy, and they provide important insight for the rational design of immunotherapy strategies toward an HIV-1 cure. Importance As one of the most challenging public health problems, there is no clinically effective cure strategies against HIV-1 infection yet. We have demonstrated that prophylactic vaccination combined with PD-1 blockade generated distinct immune response profiles and conferred better control of highly pathogenic SIVmac239 infection in rhesus macaques. In the present study, to our surprise, PD-1 blockade during therapeutic vaccination accelerated the reactivation of latent reservoir and then AIDS progression in chronically SIV-infected macaques after ART treatment interruption. Our further study demonstrated that the latent SIV provirus was preferentially enriched in PD-1⁺CD4⁺ T cells because of its susceptibility of viral entry, inhibition of SIV transcription and potent ability of proliferation, and the viral latency was effectively reactivated by PD-1 blockade. Therefore, PD-1 blockade might be a double-edged sword for AIDS therapy. These findings provoke extensive interests to further exploit novel therapeutic treatment against HIV-1 infection and other emerging infectious diseases.

Reversal of the CD8+ T-Cell Exhaustion Induced by Chronic HIV-1 Infection Through Combined Blockade of the Adenosine and PD-1 Pathways

Background

Targeting immune checkpoints for HIV treatment potentially provides a double benefit resulting from the ability to restore viral-specific CD8⁺ T-cell functions and enhance HIV production from reservoir cells. Despite promising pre-clinical data, PD-1 blockade alone in HIV-1-infected patients with advanced cancer has shown limited benefits in controlling HIV, suggesting the need for additional targets beyond PD-1. CD39 and PD-1 are highly co-expressed on CD8⁺ T cells in HIV-1 infection. However, the characteristics of CD39 and PD-1 dual-positive CD8⁺ T-cell subsets in chronic HIV-1 infection remain poorly understood.

Methods

This study enrolled 72 HIV-1-infected patients, including 40 treatment naïve and 32 ART patients. A total of 11 healthy individuals were included as controls. Different subsets of CD8⁺ T cells defined by CD39 and/or PD-1 expression were studied by flow cytometry. The relationships between the frequencies of the different subsets and parameters indicating HIV-1 disease progression were analyzed. Functional (i.e., cytokine secretion, viral inhibition) assays were performed to evaluate the impact of the blockade of adenosine and/or PD-1 signaling on CD8⁺ T cells.

Results

The proportions of PD-1⁺, CD39⁺, and PD-1⁺CD39⁺ CD8⁺ T cells were significantly increased in treatment naïve patients but were partially lowered in patients on antiretroviral therapy. In treatment naïve patients, the proportions of PD-1⁺CD39⁺ CD8⁺ T cells were negatively correlated with CD4⁺ T-cell counts and the CD4/CD8 ratio, and were positively correlated with viral load. CD39⁺CD8⁺ T cells expressed high levels of the A2A adenosine receptor and were more sensitive to 2-chloroadenosine-mediated functional inhibition than their CD39^- counterparts. In vitro, a combination of blocking CD39/adenosine and PD-1 signaling showed a synergic effect in restoring CD8⁺ T-cell function, as evidenced by enhanced abilities to secrete functional cytokines and to kill autologous reservoir cells.

Conclusion

In patients with chronic HIV-1 infection there are increased frequencies of PD-1⁺, CD39⁺, and PD-1⁺CD39⁺ CD8⁺ T cells. In treatment naïve patients, the frequencies of PD-1⁺CD39⁺ CD8⁺ T cells are negatively correlated with CD4⁺ T-cell counts and the CD4/CD8 ratio and positively correlated with viral load. Combined blockade of CD39/adenosine and PD-1 signaling in vitro may exert a synergistic effect in restoring CD8⁺ T-cell function in HIV-1-infected patients.

Modulation of Antiviral Immunity and Therapeutic Efficacy by 25-Hydroxycholesterol in Chronically SIV-Infected, ART-Treated Rhesus Macaques

Cholesterol-25-hydroxylase (CH25H) and its enzymatic product 25-hydroxycholesterol (25HC) exert broadly antiviral activity including inhibiting HIV-1 infection. However, their antiviral immunity and therapeutic efficacy in a nonhuman primate model are unknown. Here, we report that the regimen of 25HC combined with antiretroviral therapy (ART), provides profound immunological modulation towards inhibiting viral replication in chronically SIV_mac239-infected rhesus macaques (RMs). Compared to the ART alone, this regimen more effectively controlled SIV replication, enhanced SIV-specific cellular immune responses, restored the ratio of CD4/CD8 cells, reversed the hyperactivation state of CD4⁺ T cells, and inhibited the secretion of proinflammatory cytokines by CD4⁺ and CD8⁺ T lymphocytes in chronically SIV-infected RMs. Furthermore, the in vivo safety and the preliminary pharmacokinetics of the 25HC compound were assessed in this RM model. Taken together, these assessments help explain the profound relationship between cholesterol metabolism, immune modulation, and antiviral activities by 25HC. These results provide insight for developing novel therapeutic drug candidates against HIV-1 infection and other related diseases.

Early exposure to broadly neutralizing antibodies may trigger a dynamical switch from progressive disease to lasting control of SHIV infection

Antiretroviral therapy (ART) for HIV-1 infection is life-long. Stopping therapy typically leads to the reignition of infection and progressive disease. In a major breakthrough, recent studies have shown that early initiation of ART can lead to sustained post-treatment control of viremia, raising hopes of long-term HIV-1 remission. ART, however, elicits post-treatment control in a small fraction of individuals treated. Strikingly, passive immunization with broadly neutralizing antibodies (bNAbs) of HIV-1 early in infection was found recently to elicit long-term control in a majority of SHIV-infected macaques, suggesting that HIV-1 remission may be more widely achievable. The mechanisms underlying the control elicited by bNAb therapy, however, remain unclear. Untreated infection typically leads to progressive disease. We hypothesized that viremic control represents an alternative but rarely realized outcome of the infection and that early bNAb therapy triggers a dynamical switch to this outcome. To test this hypothesis, we constructed a model of viral dynamics with bNAb therapy and applied it to analyse clinical data. The model fit quantitatively the complex longitudinal viral load data from macaques that achieved lasting control. The model predicted, consistently with our hypothesis, that the underlying system exhibited bistability, indicating two potential outcomes of infection. The first had high viremia, weak cytotoxic effector responses, and high effector exhaustion, marking progressive disease. The second had low viremia, strong effector responses, and low effector exhaustion, indicating lasting viremic control. Further, model predictions suggest that early bNAb therapy elicited lasting control via pleiotropic effects. bNAb therapy lowers viremia, which would also limit immune exhaustion. Simultaneously, it can improve effector stimulation via cross-presentation. Consequently, viremia may resurge post-therapy, but would encounter a primed effector population and eventually get controlled. ART suppresses viremia but does not enhance effector stimulation, explaining its limited ability to elicit post-treatment control relative to bNAb therapy.

In a remarkable advance in HIV cure research, a recent study showed that 3 weekly doses of HIV-1 broadly neutralizing antibodies (bNAbs) soon after infection kept viral levels controlled for years in most macaques treated. If translated to humans, this bNAb therapy may elicit a functional cure, or long-term remission, of HIV-1 infection, eliminating the need for life-long antiretroviral therapy (ART). How early bNAb therapy works remains unknown. Here, we elucidate the mechanism using mathematical modeling and analysis of in vivo data. We predict that early bNAb therapy suppresses viremia, which reduces exhaustion of cytotoxic effector cells, and enhances antigen uptake and effector stimulation. Collectively, these effects drive infection to lasting control. Model predictions based on these effects fit in vivo data quantitatively. ART controls viremia but does not improve effector stimulation, explaining its weaker ability to induce lasting control post-treatment. Our findings may help improve strategies for achieving functional cure of HIV-1 infection.

Arsenic Trioxide Impacts Viral Latency and Delays Viral Rebound after Termination of ART in Chronically SIV-Infected Macaques

The latent viral reservoir is the source of viral rebound after interruption of antiretroviral therapy (ART) and is the major obstacle in eradicating the latent human immunodeficiency virus-1 (HIV-1). In this study, arsenic class of mineral, arsenic trioxide, clinically approved for treating acute promyelocytic leukemia, is demonstrated to reactivate latent provirus in CD4+ T cells from HIV-1 patients and Simian immunodeficiency virus (SIV)-infected macaques, without significant systemic T cell activation and inflammatory responses. In a proof-of-concept study using chronically SIVmac239-infected macaques, arsenic trioxide combined with ART delays viral rebound after ART termination, reduces the integrated SIV DNA copies in CD4+ T cells, and restores CD4+ T cells counts in vivo. Most importantly, half of arsenic trioxide-treated macaques show no detectable viral rebound in the plasma for at least 80 days after ART discontinuation. Mechanistically, the study reveals that CD4 receptors and CCR5 co-receptors of CD4+ T cells are significantly downregulated by arsenic trioxide treatment, which reduces susceptibility to infection after provirus reactivation. Furthermore, an increase in SIV-specific immune responses after arsenic trioxide treatment may contribute to suppression of viral rebound. This work suggests that arsenic trioxide in combination with ART is a novel regimen in down-sizing or even eradicating latent HIV-1 reservoir.

Preexisting Virus-Specific T Lymphocytes-Mediated Enhancement of Adenovirus Infections to Human Blood CD14+ Cells

Antigen-specific T lymphocytes play a critical role in controlling viral infections. However, we report here that preexisting virus-specific T cell responses also contribute to promoting adenovirus (Ad) infection. Previously, we found that CD14+ monocytes from Ad-seropositive individuals exhibited an increased susceptibility to Ad infection, when compared with that of Ad-seronegative individuals. But the underlying mechanisms for this enhancement of viral infection are not completely clarified. In this study, we found that the efficacy of Ad infection into CD14+ monocytes was significantly decreased after CD3+ T lymphocytes depletion from PBMC samples of Ad-seropositive individuals. In contrast, adding virus-specific CD3+ T lymphocytes into PBMC samples of Ad-seronegative individuals resulted in a significant increase of infection efficacy. CD3+ T lymphocytes in PBMC samples from Ad-seropositive individuals were more sensitive to be activated by adenovirus stimulus, characterized by upregulation of multiple cytokines and activation markers and also enhancement of cell proliferation. Further studies demonstrated that GM-CSF and IL-4 can promote Ad infection by up-regulating the expression of scavenger receptor 1 (SR-A) and integrins αVβ5 receptor of CD14+ cells. And taken together, these results suggest a novel role of virus-specific T cells in mediating enhancement of viral infection, and provide insights to understand the pathogenesis and complicated interactions between viruses and host immune cells.

Cytokine-Mediated Tissue Injury in Non-human Primate Models of Viral Infections

Viral infections trigger robust secretion of interferons and other antiviral cytokines by infected and bystander cells, which in turn can tune the immune response and may lead to viral clearance or immune suppression. However, aberrant or unrestricted cytokine responses can damage host tissues, leading to organ dysfunction, and even death. To understand the cytokine milieu and immune responses in infected host tissues, non-human primate (NHP) models have emerged as important tools. NHP have been used for decades to study human infections and have played significant roles in the development of vaccines, drug therapies and other immune treatment modalities, aided by an ability to control disease parameters, and unrestricted tissue access. In addition to the genetic and physiological similarities with humans, NHP have conserved immunologic properties with over 90% amino acid similarity for most cytokines. For example, human-like symptomology and acute respiratory syndrome is found in cynomolgus macaques infected with highly pathogenic avian influenza virus, antibody enhanced dengue disease is common in neotropical primates, and in NHP models of viral hepatitis cytokine-induced inflammation induces severe liver damage, fibrosis, and hepatocellular carcinoma recapitulates human disease. To regulate inflammation, anti-cytokine therapy studies in NHP are underway and will provide important insights for future human interventions. This review will provide a comprehensive outline of the cytokine-mediated exacerbation of disease and tissue damage in NHP models of viral infections and therapeutic strategies that can aid in prevention/treatment of the disease syndromes.