IL-15 induces CD4 effector memory T cell production and tissue emigration in nonhuman primates

Vaccine induced mucosal and systemic memory NK/ILCs elicit decreased risk of SIV/SHIV acquisition

SIV and HIV-based envelope V1-deleted (ΔV1) vaccines, delivered systemically by the DNA/ALVAC/gp120 platform, decrease the risk of mucosal SIV or SHIV acquisition more effectively than V1-replete vaccines. Here we investigated the induction of mucosal and systemic memory-like NK cells as well as antigen-reactive ILC response by DNA/ALVAC/gp120-based vaccination and their role against SIV/SHIV infection. ΔV1 HIV vaccination elicited a higher level of mucosal TNF-α+ and CD107+ memory-like NK cells than V1-replete vaccination, suggesting immunogen dependence. Mucosal memory-like NK cells, systemic granzyme B+ memory NK cells, and vaccine-induced mucosal envelope antigen-reactive IL-17+ NKp44+ ILCs, IL-17+ ILC3s, and IL-13+ ILC2 subsets were linked to a lower risk of virus acquisition. Additionally, mucosal memory-like NK cells and mucosal env-reactive IFN-γ+ ILC1s and env- reactive IL-13+ ILC2 subsets correlated with viral load control. We further observed a positive correlation between post-vaccination systemic and mucosal memory-like NK cells, suggesting vaccination enhances the presence of these cells in both compartments. Mucosal and systemic memory-like NK cells positively correlated with V2-specific ADCC responses, a reproducible correlate of reduced risk of SIV/HIV infection. In contrast, an increased risk was associated with the level of mucosal PMA/Ionomycin-induced IFN-γ+ and CD107+ NKG2A-NKp44- ILCs. Plasma proteomic analyses demonstrated that suppression of mucosal memory-like NK cells was linked to the level of CCL-19, LT-α, TNFSF-12, and IL-15, suppression of systemic env-reactive granzyme B+ memory-like NK cells was associated with the level of OLR1, CCL-3, and OSM, and suppression of IL-17+ ILCs immunity was correlated with the level of IL-6 and CXCL-9. In contrast, FLT3 ligand was associated with promotion of protective mucosal env-reactive IL-17+ responses. These findings emphasize the importance of mucosal memory-like NK cell and envelope- reactive ILC responses for protection against mucosal SIV/SHIV acquisition.

IL-15/IL-15Ra Synergies with IL-12 to Induce Functional CD8 T Cells and NK Cells During Chronic SHIV Infection

Cytokines are key mediators of immune regulation, orchestrate communication between immune cells, and play a pivotal role in shaping the immune landscape during chronic infection and cancer. The therapeutic potential of IL-15/IL-15Rα and IL-12 has been explored individually in various immunotherapeutic strategies, though not as a combination. Therefore, we investigated whether the combination of IL-15/IL-15Rα and IL-12 treatment would enhance the potency and quality of either NK cells, SIV-specific CD8 T cells, or both, compared with single cytokine treatment. Our findings reveal that in vitro IL-15/IL-15Rα and IL-15/IL-15Rα plus IL-12 treatment results in an expansion of functional CD8 T cells and NK cells from uninfected and chronically infected macaques with simian/human immunodeficiency virus. Additionally, the cytokine combination significantly reduced CCR5 expression on total CD4 T cells, limiting the number of viral targets. This study supports the potential utilization of combined IL-15/IL-15Rα plus IL-12 treatment for chronic viral infections and cancer.

Learning from Persistent Viremia: Mechanisms and Implications for Clinical Care and HIV-1 Cure

PURPOSE OF REVIEW

In this review, we discuss what persistent viremia has taught us about the biology of the HIV-1 reservoir during antiretroviral therapy (ART). We will also discuss the implications of this phenomenon for HIV-1 cure research and its clinical management.

RECENT FINDINGS

While residual viremia (RV, 1-3 HIV-1 RNA copies/ml) can be detected in most of people on ART, some individuals experience non-suppressible viremia (NSV, > 20-50 copies/mL) despite optimal adherence. When issues of drug resistance and pharmacokinetics are ruled out, this persistent virus in plasma is the reflection of virus production from clonally expanded CD4+ T cells carrying proviruses. Recent work has shown that a fraction of the proviruses source of NSV are not infectious, due to defects in the 5'-Leader sequence. However, additional viruses and host determinants of NSV are not fully understood. The study of NSV is of prime importance because it represents a challenge for the clinical care of people on ART, and it sheds light on virus-host interactions that could advance HIV-1 remission research.

Immunomodulation with IL-7 and IL-15 in HIV-1 infection

Immunomodulating agents are substances that modify the host immune responses in diseases such as infections, autoimmune conditions and cancers. Immunomodulators can be divided into two main groups: 1) immunostimulators that activate the immune system such as cytokines, toll-like receptor agonists and immune checkpoint blockers; and 2) immunosuppressors that dampen an overactive immune system such as corticosteroids and cytokine-blocking antibodies. In this review, we have focussed on the two primarily T and natural killer (NK) cell homeostatic cytokines: interleukin-7 (IL-7) and -15 (IL-15). These cytokines are immunostimulators which act on immune cells independently of the presence or absence of antigen. In vivo studies have shown that IL-7 administration enhances proliferation of circulating T cells whereas IL-15 agonists enhance the proliferation and function of NK and CD8+ T cells. Both IL-7 and IL-15 therapies have been tested as single interventions in HIV-1 cure-related clinical trials. In this review, we explore whether IL-7 and IL-15 could be part of the therapeutic approaches towards HIV-1 remission.

The Oxysterol Receptor EBI2 Links Innate and Adaptive Immunity to Limit IFN Response and Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with abnormal activation of the immune system. Recent attention is increasing about how aberrant lipid and cholesterol metabolism is linked together with type I interferon (IFN-I) signaling in the regulation of the pathogenesis of SLE. Here, a metabonomic analysis is performed and increased plasma concentrations of oxysterols, especially 7α, 25-dihydroxycholesterol (7α, 25-OHC), are identified in SLE patients. The authors find that 7α, 25-OHC binding to its receptor Epstein-Barr virus-induced gene 2 (EBI2) in macrophages can suppress STAT activation and the production of IFN-β, chemokines, and cytokines. Importantly, monocytes/macrophages from SLE patients and mice show significantly reduced EBI2 expression, which can be triggered by IFN-γ produced in activated T cells. Previous findings suggest that EBI2 enhances immune cell migration. Opposite to this effect, the authors demonstrate that EBI2-deficient macrophages produce higher levels of chemokines and cytokines, which recruits and activates myeloid cells,T and B lymphocytes to exacerbate tetramethylpentadecane-induced SLE. Together, via sensing the oxysterol 7α, 25-OHC, EBI2 in macrophages can modulate innate and adaptive immune responses, which may be used as a potential diagnostic marker and therapeutic target for SLE.

Recombinant BCG expressing the LTAK63 adjuvant increased memory T cells and induced long-lasting protection against Mycobacterium tuberculosis challenge in mice

Vaccine-induced protection against Mycobacterium tuberculosis (Mtb) is usually ascribed to the induction of Th1, Th17, and CD8⁺ T cells. However, protective immune responses should also involve other immune cell subsets, such as memory T cells. We have previously shown improved protection against Mtb challenge using the rBCG-LTAK63 vaccine (a recombinant BCG strain expressing the LTAK63 adjuvant, a genetically detoxified derivative of the A subunit from E. coli heat-labile toxin). Here we show that mice immunized with rBCG-LTAK63 exhibit a long-term (at least until 6 months) polyfunctional Th1/Th17 response in the draining lymph nodes and in the lungs. This response was accompanied by the increased presence of a diverse set of memory T cells, including central memory, effector memory and tissue-resident memory T cells. After the challenge, the T cell phenotype in the lymph nodes and lungs were characterized by a decrease in central memory T cells, and an increase in effector memory T cells and effector T cells. More importantly, when challenged 6 months after the immunization, this group demonstrated increased protection in comparison to BCG. In conclusion, this work provides experimental evidence in mice that the rBCG-LTAK63 vaccine induces a persistent increase in memory and effector T cell numbers until at least 6 months after immunization, which correlates with increased protection against Mtb. This improved immune response may contribute to enhance the long-term protection.

Virus-Specific T Cells: Promising Adoptive T Cell Therapy Against Infectious Diseases Following Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is a life-saving therapy for various hematologic disorders. Due to the bone marrow suppression and its long recovery period, secondary infections, like cytomegalovirus (CMV), Epstein-Bar virus (EBV), and adenovirus (AdV), are the leading causes of morbidity and mortality in HSCT cases. Drug resistance to the antiviral pharmacotherapies makes researchers develop adoptive T cell therapies like virus-specific T cell therapy. These studies have faced major challenges such as finding the most effective T cell expansion methods, isolating the expected subtype, defining the functionality of the end-cell population, product quality control, and clinical complications after the injection. This review discusses the viral infections after HSCT, T cells characteristics during chronic viral infection, application of virus-specific T cells (VSTs) for refractory infections, standard methods for producing VSTs and their limitation, clinical experiences on VSTs, focusing on outcomes and side effects that can be helpful in decision-making for patients and further researches.

Tissue-resident memory T cell maintenance during antigen persistence requires both cognate antigen and interleukin-15

Our understanding of tissue-resident memory T (TRM) cell biology has been largely developed from acute infection models in which antigen is cleared and sterilizing immunity is achieved. Less is known about TRM cells in the context of chronic antigen persistence and inflammation. We investigated factors that underlie TRM maintenance in a kidney transplantation model in which TRM cells drive rejection. In contrast to acute infection, we found that TRM cells declined markedly in the absence of cognate antigen, antigen presentation, or antigen sensing by the T cells. Depletion of graft-infiltrating dendritic cells or interruption of antigen presentation after TRM cells were established was sufficient to disrupt TRM maintenance and reduce allograft pathology. Likewise, removal of IL-15 transpresentation or of the IL-15 receptor on T cells during TRM maintenance led to a decline in TRM cells, and IL-15 receptor blockade prevented chronic rejection. Therefore, antigen and IL-15 presented by dendritic cells play nonredundant key roles in CD8 TRM cell maintenance in settings of antigen persistence and inflammation. These findings provide insights that could lead to improved treatment of chronic transplant rejection and autoimmunity.

Programming cytomegalovirus as an HIV vaccine

The initial development of cytomegalovirus (CMV) as a vaccine vector for HIV/simian immunodeficiency virus (SIV) was predicated on its potential to pre-position high-frequency, effector-differentiated, CD8+ T cells in tissues for immediate immune interception of nascent primary infection. This goal was achieved and also led to the unexpected discoveries that non-human primate (NHP) CMVs can be programmed to differentially elicit CD8+ T cell responses that recognize viral peptides via classical MHC-Ia, and/or MHC-II, and/or MHC-E, and that MHC-E-restricted CD8+ T cell responses can uniquely mediate stringent arrest and subsequent clearance of highly pathogenic SIV, an unprecedented type of vaccine-mediated protection. These discoveries delineate CMV vector-elicited MHC-E-restricted CD8+ T cells as a functionally distinct T cell response with the potential for superior efficacy against HIV-1, and possibly other infectious agents or cancers.

IL-15 Superagonist N-803 Enhances IFN-γ Production of MAIT Cells in SIV+ Macaques

Mucosal associated invariant T (MAIT) cells are innate T cells that recognize bacterial metabolites and secrete cytokines and cytolytic enzymes to destroy infected target cells. This makes MAIT cells promising targets for immunotherapy to combat bacterial infections. Here, we analyzed the effects of an immunotherapeutic agent, the IL-15 superagonist N-803, on MAIT cell activation, trafficking, and cytolytic function in macaques. We found that N-803 could activate MAIT cells in vitro and increase their ability to produce IFN-γ in response to bacterial stimulation. To expand upon this, we examined the phenotypes and functions of MAIT cells present in samples collected from PBMC, airways (bronchoalveolar lavage [BAL] fluid), and lymph nodes (LN) from rhesus macaques that were treated in vivo with N-803. N-803 treatment led to a transient 6 to 7-fold decrease in the total number of MAIT cells in the peripheral blood, relative to pre N-803 time points. Concurrent with the decrease in cells in the peripheral blood, we observed a rapid decline in the frequency of CXCR3⁺CCR6⁺ MAITs. This corresponded with an increase in the frequency of CCR6⁺ MAITs in the BAL fluid, and higher frequencies of ki-67⁺ and granzyme B⁺ MAITs in the blood, LN, and BAL fluid. Finally, N-803 improved the ability of MAIT cells collected from PBMC and airways to produce IFN-γ in response to bacterial stimulation. Overall, N-803 shows the potential to transiently alter the phenotypes and functions of MAIT cells, which could be combined with other strategies to combat bacterial infections.

Control of Simian Immunodeficiency Virus Infection in Prophylactically Vaccinated, Antiretroviral Treatment-Naive Macaques Is Required for the Most Efficacious CD8 T Cell Response during Treatment with the Interleukin-15 Superagonist N-803

The IL-15 superagonist N-803 has been shown to enhance the function of CD8 T cells and NK cells. We previously found that in a subset of vaccinated, ART-naive, SIV⁺ rhesus macaques, N-803 treatment led to a rapid but transient decline in plasma viremia that positively correlated with an increase in the frequency of CD8 T cells. Here, we tested the hypothesis that prophylactic vaccination was required for the N-803 mediated suppression of SIV plasma viremia. We either vaccinated rhesus macaques with a DNA prime/Ad5 boost regimen using vectors expressing SIVmac239 gag with or without a plasmid expressing IL-12 or left them unvaccinated. The animals were then intravenously infected with SIVmac239M. 6 months after infection, the animals were treated with N-803. We found no differences in the control of plasma viremia during N-803 treatment between vaccinated and unvaccinated macaques. Interestingly, when we divided the SIV⁺ animals based on their plasma viral load set-points prior to the N-803 treatment, N-803 increased the frequency of SIV-specific T cells expressing ki-67⁺ and granzyme B⁺ in animals with low plasma viremia (<10⁴ copies/mL; SIV controllers) compared to animals with high plasma viremia (>10⁴ copies/mL; SIV noncontrollers). In addition, Gag-specific CD8 T cells from the SIV⁺ controllers had a greater increase in CD8⁺CD107a⁺ T cells in ex vivo functional assays than did the SIV⁺ noncontrollers. Overall, our results indicate that N-803 is most effective in SIV⁺ animals with a preexisting immunological ability to control SIV replication. IMPORTANCE N-803 is a drug that boosts the immune cells involved in combating HIV/SIV infection. Here, we found that in SIV⁺ rhesus macaques that were not on antiretroviral therapy, N-803 increased the proliferation and potential capacity for killing of the SIV-specific immune cells to a greater degree in animals that spontaneously controlled SIV than in animals that did not control SIV. Understanding the mechanism of how N-803 might function differently in individuals that control HIV/SIV (for example, individuals on antiretroviral therapy or spontaneous controllers) compared to settings where HIV/SIV are not controlled, could impact the efficacy of N-803 utilization in the field of HIV cure.

Enhanced half-life and antitumor activity of Interleukin-15 through genetic fusion of a serum albumin-specific protein binder

Human interleukin-15 (hIL-15) has attracted a considerable attention as a promising cancer immunotherapeutic due to its function to directly stimulate the proliferation and cytotoxic activity of NK and T cells. Nevertheless, a relatively short half-life of hIL-15 requires repeated administration and higher doses, causing serious side effects. Here, we demonstrate an enhanced blood half-life and biological activity of hIL-15 through genetic fusion of a human serum albumin-specific protein binder (rHSA). The fusion construct (rHSA-IL15) was observed to maintain respective binding activities for both hIL-15 receptor α and human serum albumin. The rHSA-IL15 led to a significant increase in the secretion of Granzyme B and INF-γ by immune cells compare to free hIL-15, expanding the population of activated T cell subset such as CD4 ⁺ T and CD8⁺ T cells. The terminal half-life of the rHSA-IL15 was prolonged by around a 40-fold in transgenic mice expressing human serum albumin, compared to free hIL-15. The rHSA-IL15 resulted in distinct anti-tumor activities in xenograft SCC (squamous cell carcinoma) mouse and allograft melanoma mouse models through activation of NK and CD8⁺ T cells. The rHSA-IL15 is expected to be used in cancer immunotherapy, assisting in the development of other cytokines as immunotherapeutic agents with greater efficacy.

Increased Levels of Serum IL-15 and TNF-β Indicate the Progression of Human Intracranial Aneurysm

Objective

Existing evidence suggests that chronic inflammation promotes the progression of human intracranial aneurysm (IA) and many cytokines have been detected to participate in the process of inflammation. However, rare cytokines in plasma have been used as proxies for progression of IA. This study aimed to identify novel cytokines as biomarkers to predict the development of IA.

Methods

Patients with unruptured intracranial aneurysms (UIAs) undergoing microsurgical clipping were prospectively recruited from January 2017 to June 2020 and were separated into two groups based on their ELAPSS score (low risk group < 10, intermediate-high risk group ≥ 10). Propensity score matching (PSM) was used to reduce imbalances in the baseline characteristics between groups. All blood samples were collected before surgery. A human serum 48-cytokines examination was performed to analyze the concentrations of serological cytokines. Clinical data and cytokines were compared between groups.

Results

A total of 184 patients were enrolled in this study. The low risk group contained 77 patients and 107 patients were included in the intermediate-high risk group. Finally, there were 69 patients in each group after PSM with a matching rate of 1:1. The concentrations of 3 serum cytokines were significantly increased in intermediate-high risk patients, namely, interleukin-15 (IL-15), monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-β (TNF-β) (P < 0.05, |log₂ fold change| > 2). The result of receiver operator characteristic (ROC)curve revealed that TNF-β had the highest predictive accuracy, with an area under the curve (AUC) value of 0.725 [95% confidence interval (CI) 0.639–0.811, P < 0.001] followed by IL-15 (AUC = 0.691, 95% CI 0.602–0.781, P < 0.001) and MCP-1 (AUC = 0.661, 95% CI 0.569–0.753, P = 0.001). Multivariate logistic analysis demonstrated high IL-15 [odds ratio (OR), 3.23; 95% CI, 1.47–7.12; P = 0.004] and high TNF-β (OR, 8.30; 95% CI, 3.25–21.25; P < 0.001) as the risk factors that correlated with intermediate-high risk of IA progression.

Conclusion

UIA patients with intermediate-high growth risk exhibited increased serum levels of IL-15, MCP-1, and TNF-β. Serum IL-15, and TNF-β could serve as biomarkers to predict the progression of UIAs.

2022 update on the scientific premise and clinical trials for IL-15 agonists as cancer immunotherapy

Diverse cytokines and their receptors on immune cells constitute a highly complex network in the immune system. Some therapeutic cytokines and their derivatives have been approved for cancer treatment. IL-15 is an immune-regulating cytokine with multiple functions, among which the function of activating the immunity of cancer patients has great potential in cancer immunotherapy. In this review, we introduce the functions of IL-15 and discuss its role in regulating the immune system in different immune cells. Meanwhile, we will address the applications of IL-15 agonists in cancer immunotherapy and provide prospects for the next generation of therapeutic designs. Although many challenges remain, IL-15 agonists offer a new therapeutic option in the future direction of cancer immunotherapy.

Cytokine Adjuvants IL-7 and IL-15 Improve Humoral Responses of a SHIV LentiDNA Vaccine in Animal Models

HIV-1 remains a major public health issue worldwide in spite of efficacious antiviral therapies, but with no cure or preventive vaccine. The latter has been very challenging, as virus infection is associated with numerous escape mechanisms from host specific immunity and the correlates of protection remain incompletely understood. We have developed an innovative vaccine strategy, inspired by the efficacy of live-attenuated virus, but with the safety of a DNA vaccine, to confer both cellular and humoral responses. The CAL-SHIV-IN− lentiDNA vaccine comprises the backbone of the pathogenic SHIVKU2 genome, able to mimic the early phase of viral infection, but with a deleted integrase gene to ensure safety precluding integration within the host genome. This vaccine prototype, constitutively expressing viral antigen under the CAEV LTR promoter, elicited a variety of vaccine-specific, persistent CD4 and CD8 T cells against SIV-Gag and Nef up to 80 weeks post-immunization in cynomolgus macaques. Furthermore, these specific responses led to antiviral control of the pathogenic SIVmac251. To further improve the efficacy of this vaccine, we incorporated the IL-7 or IL-15 genes into the CAL-SHIV-IN− plasmid DNA in efforts to increase the pool of vaccine-specific memory T cells. In this study, we examined the immunogenicity of the two co-injected lentiDNA vaccines CAL-SHIV-IN− IRES IL-7 and CAL-SHIV-IN− IRES IL-15 in BALB/cJ mice and rhesus macaques and compared the immune responses with those generated by the parental vaccine CAL-SHIV-IN−. This co-immunization elicited potent vaccine-specific CD4 and CD8 T cells both in mice and rhesus macaques. Antibody-dependent cell-mediated cytotoxicity (ADCC) antibodies were detected up to 40 weeks post-immunization in both plasma and mucosal compartments of rhesus macaques and were enhanced by the cytokines.

Enhanced Cross-Reactive and Polyfunctional Effector-Memory T Cell Responses by ICVAX-a Human PD1-Based Bivalent HIV-1 Gag-p41 Mosaic DNA Vaccine

Vaccine-induced protective T cell immunity is necessary for HIV-1 functional cure. We previously reported that rhesus PD1-Gag-based DNA vaccination sustained simian-human immunodeficiency virus (SHIV) suppression by inducing effector-memory CD8⁺ T cells. Here, we investigated a human PD1-Gag-based DNA vaccine, namely, ICVAX, for clinical translation. PD1-based dendritic cell targeting and mosaic antigenic designs were combined to generate the ICVAX by fusing the human soluble PD1 domain with a bivalent HIV-1 Gag-p41 mosaic antigen. The mosaic antigen was cross-reactive with patients infected with B, CRF07/08_BC, and CRF01_AE variants. In mice, ICVAX elicited stronger, broader, and more polyfunctional T cell responses than mosaic Gag-p41 alone, and suppressed EcoHIV infection more efficiently. In macaques, ICVAX elicited polyfunctional effector-memory T cell responses that targeted multiple nonoverlapping epitopes of the Gag-p41 antigen. Furthermore, ICVAX manufactured following good manufacturing practices proved potent immunogenicity in macaques after biannual homologous vaccination, warranting clinical evaluation of ICVAX as an immunotherapy against HIV-1.

IMPORTANCE This study presents that ICVAX, a PD1-based DNA vaccine against HIV-1, could induce broad and polyfunctional T cell responses against different HIV-1 subtypes. ICVAX encodes a recombinant antigen consisting of the human soluble PD1 domain fused with two mosaic Gag-p41 antigens. The mosaic antigens cover more than 500 HIV-1 strains circulating in China including the subtypes B/B’, CRF01_AE, and CRF07/08_BC. In mice, ICVAX elicited stronger, broader, and more polyfunctional T cell responses, with better EcoHIV suppression than the nontargeting mosaic Gag-p41 DNA vaccine. Moreover, both lab-generated and GMP-grade ICVAX also elicited strong polyfunctional effector-memory T cell responses in rhesus macaques with good immunogenicity against multiple nonoverlapping epitopes of the Gag-p41 antigen. This study therefore highlights the great potential to translate the PD1-based DNA vaccine approach into clinical use, and opens up new avenues for alternative HIV-1 vaccine design for HIV-1 preventive and functional cure.

HIV-1 Genomes Are Enriched in Memory CD4+ T-Cells with Short Half-Lives

Future HIV-1 curative therapies require a thorough understanding of the distribution of genetically-intact HIV-1 within T-cell subsets during antiretroviral therapy (ART) and the cellular mechanisms that maintain this reservoir. Therefore, we sequenced near-full-length HIV-1 genomes and identified genetically-intact and genetically-defective genomes from resting naive, stem-cell memory, central memory, transitional memory, effector memory, and terminally-differentiated CD4⁺ T-cells with known cellular half-lives from 11 participants on ART. We find that a higher infection frequency with any HIV-1 genome was significantly associated with a shorter cellular half-life, such as transitional and effector memory cells. A similar enrichment of genetically-intact provirus was observed in these cells with relatively shorter half-lives. We found that effector memory and terminally-differentiated cells also had significantly higher levels of expansions of genetically-identical sequences, while only transitional and effector memory cells contained genetically-intact proviruses that were part of a cluster of identical sequences. Expansions of identical sequences were used to infer cellular proliferation from clonal expansion. Altogether, this indicates that specific cellular mechanisms such as short half-life and proliferative potential contribute to the persistence of genetically-intact HIV-1. IMPORTANCE The design of future HIV-1 curative therapies requires a more thorough understanding of the distribution of genetically-intact HIV-1 within T-cell subsets as well as the cellular mechanisms that maintain this reservoir. These genetically-intact and presumably replication-competent proviruses make up the latent HIV-1 reservoir. Our investigations into the possible cellular mechanisms maintaining the HIV-1 reservoir in different T-cell subsets have revealed a link between the half-lives of T-cells and the level of proviruses they contain. Taken together, we believe our study shows that more differentiated and proliferative cells, such as transitional and effector memory T-cells, contain the highest levels of genetically-intact proviruses, and the rapid turnover rate of these cells contributes to the expansion of genetically-intact proviruses within them. Therefore, our study delivers an in-depth assessment of the cellular mechanisms, such as cellular proliferation and half-life, that contribute to and maintain the latent HIV-1 reservoir.

Therapeutic Potential of IL-15 and N-803 in HIV/SIV Infection

IL-15, a proinflammatory cytokine critical for the generation, maintenance, and homeostasis of T cell responses, is produced naturally in response to HIV/SIV infection, but has also demonstrated therapeutic potential. IL-15 can boost CD4+ and CD8+ T cell and NK cell proliferation, activation, and function. However, IL-15 treatment may cause aberrant immune activation and accelerated disease progression in certain circumstances. Moreover, the relationship between the timing of IL-15 administration and disease progression remains unclear. The IL-15 superagonist N-803 was developed to expand the therapeutic potential of IL-15 by maximizing its tissue distribution and half-life. N-803 has garnered enthusiasm recently as a way to enhance the innate and cellular immune responses to HIV/SIV by improving CD8+ T cell recognition and killing of virus-infected cells and directing immune cells to mucosal sites and lymph nodes, the primary sites of virus replication. N-803 has also been evaluated in "shock and kill" strategies due to its potential to reverse latency (shock) and enhance antiviral immunity (kill). This review examines the current literature about the effects of IL-15 and N-803 on innate and cellular immunity, viral burden, and latency reversal in the context of HIV/SIV, and their therapeutic potential both alone and combined with additional interventions such as antiretroviral therapy (ART) and vaccination.

Systemic IL-15, IFN-γ, and IP-10/CXCL10 signature associated with effective immune response to SARS-CoV-2 in BNT162b2 mRNA vaccine recipients

Early responses to vaccination are important for shaping both humoral and cellular protective immunity. Dissecting innate vaccine signatures may predict immunogenicity to help optimize the efficacy of mRNA and other vaccine strategies. Here, we characterize the cytokine and chemokine responses to the 1^st and 2^nd dose of the BNT162b2 mRNA (Pfizer/BioNtech) vaccine in antigen-naive and in previously coronavirus disease 2019 (COVID-19)-infected individuals (NCT04743388). Transient increases in interleukin-15 (IL-15) and interferon gamma (IFN-γ) levels early after boost correlate with Spike antibody levels, supporting their use as biomarkers of effective humoral immunity development in response to vaccination. We identify a systemic signature including increases in IL-15, IFN-γ, and IP-10/CXCL10 after the 1^st vaccination, which were enriched by tumor necrosis factor alpha (TNF-α) and IL-6 after the 2^nd vaccination. In previously COVID-19-infected individuals, a single vaccination results in both strong cytokine induction and antibody titers similar to the ones observed upon booster vaccination in antigen-naive individuals, a result with potential implication for future public health recommendations.

Interleukin-15 response signature predicts RhCMV/SIV vaccine efficacy

Simian immunodeficiency virus (SIV) challenge of rhesus macaques (RMs) vaccinated with strain 68-1 Rhesus Cytomegalovirus (RhCMV) vectors expressing SIV proteins (RhCMV/SIV) results in a binary outcome: stringent control and subsequent clearance of highly pathogenic SIV in ~55% of vaccinated RMs with no protection in the remaining 45%. Although previous work indicates that unconventionally restricted, SIV-specific, effector-memory (EM)-biased CD8+ T cell responses are necessary for efficacy, the magnitude of these responses does not predict efficacy, and the basis of protection vs. non-protection in 68-1 RhCMV/SIV vector-vaccinated RMs has not been elucidated. Here, we report that 68-1 RhCMV/SIV vector administration strikingly alters the whole blood transcriptome of vaccinated RMs, with the sustained induction of specific immune-related pathways, including immune cell, toll-like receptor (TLR), inflammasome/cell death, and interleukin-15 (IL-15) signaling, significantly correlating with subsequent vaccine efficacy. Treatment of a separate RM cohort with IL-15 confirmed the central involvement of this cytokine in the protection signature, linking the major innate and adaptive immune gene expression networks that correlate with RhCMV/SIV vaccine efficacy. This change-from-baseline IL-15 response signature was also demonstrated to significantly correlate with vaccine efficacy in an independent validation cohort of vaccinated and challenged RMs. The differential IL-15 gene set response to vaccination strongly correlated with the pre-vaccination activity of this pathway, with reduced baseline expression of IL-15 response genes significantly correlating with higher vaccine-induced induction of IL-15 signaling and subsequent vaccine protection, suggesting that a robust de novo vaccine-induced IL-15 signaling response is needed to program vaccine efficacy. Thus, the RhCMV/SIV vaccine imparts a coordinated and persistent induction of innate and adaptive immune pathways featuring IL-15, a known regulator of CD8+ T cell function, that support the ability of vaccine-elicited unconventionally restricted CD8+ T cells to mediate protection against SIV challenge.

Sustained viremia suppression by SHIVSF162P3CN-recalled effector-memory CD8+ T cells after PD1-based vaccination

HIV-1 functional cure requires sustained viral suppression without antiretroviral therapy. While effector-memory CD8⁺ T lymphocytes are essential for viremia control, few vaccines elicit such cellular immunity that could be potently recalled upon viral infection. Here, we investigated a program death-1 (PD1)-based vaccine by fusion of simian immunodeficiency virus capsid antigen to soluble PD1. Homologous vaccinations suppressed setpoint viremia to undetectable levels in vaccinated macaques following a high-dose intravenous challenge by the pathogenic SHIV_SF162P3CN. Poly-functional effector-memory CD8⁺ T cells were not only induced after vaccination, but were also recalled upon viral challenge for viremia control as determined by CD8 depletion. Vaccine-induced effector memory CD8⁺ subsets displayed high cytotoxicity-related genes by single-cell analysis. Vaccinees with sustained viremia suppression for over two years responded to boost vaccination without viral rebound. These results demonstrated that PD1-based vaccine-induced effector-memory CD8⁺ T cells were recalled by AIDS virus infection, providing a potential immunotherapy for functional cure.

HIV-1/AIDS remains a major global pandemic although treatment regimen has improved. Identifying efficacious vaccines and therapeutics to achieve long-term viral control with very low/undetectable plasma viral loads in the absence of antiretroviral therapy, a status known as functional cure, would be highly beneficial. We previously demonstrated that antigens fused to a soluble program death-1 (PD1) domain could effectively bind and be cross-presented by dendritic cells that constitutively expressed PD1 ligands. When applied in the form of DNA vaccination, this antigen-targeting strategy was highly immunogenic in mice. Here, we investigated the efficacy of the PD1-based DNA vaccine approach against pathogenic simian-human immunodeficiency virus challenge in rhesus monkeys. Our results showed that homologous PD1-based DNA vaccinations induced highly functional effector-memory CD8⁺ T cells carrying a unique cytotoxicity gene expression profile. These T cells actively supressed viremia in monkeys and were re-activated via boost vaccination at 2 years after viral challenge without viral rebound. In summary, our study demonstrates the potential application of PD1-based DNA vaccination to control AIDS virus infection.

Nonsurgical Induction of Alopecia Areata in C3H/HeJ Mice via Adoptive Transfer of Cultured Lymphoid Cells

Surgical induction of alopecia areata (AA) via full-thickness grafting of spontaneous AA-affected C3H/HeJ mouse skin to naïve recipients has been a primary method of transferring the AA disease model phenotype. However, this method is associated with the need to perform an invasive procedure that could negatively impact animal wellbeing. Therefore, a rodent model that rapidly develops AA at a predictable rate and without the need to perform invasive surgical procedures on the mice is essential for studying the pathogenesis of AA. Here we describe a cell injection technique using cultured skin-draining lymph node cells (LNCs) injected intradermally into naïve recipients to induce rapid AA development. The cultured LNCs can reach ~ten fold expansion after 6 days with specific cytokine stimulation. The LNCs derived from a single AA affected mouse donor can induce AA development in more than 80 naïve mice within 2-18 weeks. For comparative control studies, mice receiving cultured LNCs from normal donors remain normally haired. The method enables the production of large numbers of AA mice for use in research and treatment development studies while avoiding the use of surgical procedures. We anticipate that the protocol can also be adapted for use in other mouse autoimmune disease models.

Heterodimeric IL-15 in Cancer Immunotherapy

Simple Summary

The rapidly expanding field of cancer immunotherapy uses diverse technologies, including cytokines, T cells, and antibody administration, with the aim to induce effective immune responses leading to tumor control. Interleukin-15 (IL-15), a cytokine discovered in 1994, supports the homeostasis of cytotoxic immune cells and shows promise as an anti-tumor agent. Many studies have elucidated IL-15 synthesis, regulation and biological function and explored its therapeutic efficacy in preclinical cancer models. Escherichia coli-derived single-chain IL-15 was tested in the first in-human trial in cancer patients. Its effects were limited by the biology of IL-15, which in vivo comprises a complex of the IL-15 chain with the IL-15 receptor alpha (IL-15Rα) chain, together forming the IL-15 heterodimer (hetIL-15). Currently, single-chain IL-15 and several heterodimeric IL-15:IL-15Rα variants (hetIL-15, N-803 and RLI) are being tested in clinical trials. This review presents a summary of contemporary preclinical and clinical research on IL-15.

Abstract

Immunotherapy has emerged as a valuable strategy for the treatment of many cancer types. Interleukin-15 (IL-15) promotes the growth and function of cytotoxic CD8⁺ T and natural killer (NK) cells. It also enhances leukocyte trafficking and stimulates tumor-infiltrating lymphocytes expansion and activity. Bioactive IL-15 is produced in the body as a heterodimeric cytokine, comprising the IL-15 and the so-called IL-15 receptor alpha chain that are together termed “heterodimeric IL-15” (hetIL-15). hetIL-15, closely resembling the natural form of the cytokine produced in vivo, and IL-15:IL-15Rα complex variants, such as hetIL-15Fc, N-803 and RLI, are the currently available IL-15 agents. These molecules have showed favorable pharmacokinetics and biological function in vivo in comparison to single-chain recombinant IL-15. Preclinical animal studies have supported their anti-tumor activity, suggesting IL-15 as a general method to convert “cold” tumors into “hot”, by promoting tumor lymphocyte infiltration. In clinical trials, IL-15-based therapies are overall well-tolerated and result in the expansion and activation of NK and memory CD8⁺ T cells. Combinations with other immunotherapies are being investigated to improve the anti-tumor efficacy of IL-15 agents in the clinic.

Antiretroviral therapy does not reduce tuberculosis reactivation in a tuberculosis-HIV coinfection model

While the advent of combination antiretroviral therapy (ART) has significantly improved survival, tuberculosis (TB) remains the leading cause of death in the HIV-infected population. We used Mycobacterium tuberculosis/simian immunodeficiency virus-coinfected (M. tuberculosis/SIV-coinfected) macaques to model M. tuberculosis/HIV coinfection and study the impact of ART on TB reactivation due to HIV infection. Although ART significantly reduced viral loads and increased CD4+ T cell counts in blood and bronchoalveolar lavage (BAL) samples, it did not reduce the relative risk of SIV-induced TB reactivation in ART-treated macaques in the early phase of treatment. CD4+ T cells were poorly restored specifically in the lung interstitium, despite their significant restoration in the alveolar compartment of the lung as well as in the periphery. IDO1 induction in myeloid cells in the inducible bronchus-associated lymphoid tissue (iBALT) likely contributed to dysregulated T cell homing and impaired lung immunity. Thus, although ART was indispensable for controlling viral replication, restoring CD4+ T cells, and preventing opportunistic infection, it appeared inadequate in reversing the clinical signs of TB reactivation during the relatively short duration of ART administered in this study. This finding warrants the modeling of concurrent treatment of TB and HIV to potentially reduce the risk of reactivation of TB due to HIV to inform treatment strategies in patients with M. tuberculosis/HIV coinfection.

Recombinant Human Interleukin-15 and Anti-PD-L1 Combination Therapy Expands a CXCR3+PD1-/low CD8 T-Cell Subset in Simian Immunodeficiency Virus-Infected Rhesus Macaques

BACKGROUND

The PD1/PD-L1 pathway contributes to the pathogenesis of human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infection, and blockade of this pathway may have potential to restore immune function and promote viral control or elimination. In this study, we combined a checkpoint inhibitor anti-PD-L1 (Avelumab) and recombinant human interleukin-15 (rhIL-15) in SIV-infected rhesus macaques (RM).

METHODS

The rhIL-15 was administered as continuous infusion in 2 cycles of 10 days in the context of weekly administration of anti-PD-L1 (Avelumab) in SIV-infected RM receiving combination antiretroviral therapy (cART). Safety, immunological parameters, and viral loads were monitored during the study.

RESULTS

Administration of rhIL-15/anti-PD-L1 was safe and well tolerated. Treatment resulted in transient increases in proliferating (Ki67+) natural killer and CD8 T cells. In addition, treatment expanded a CXCR3+PD1-/low CD8 T-cell subset with the ability to secrete cytokines. Despite these effects, no changes in plasma viremia were observed after cART interruption.

CONCLUSIONS

Expansion of the CXCR3+PD1-/low CD8 T-cell subset with functional capacity and potential to traffic to sites of viral reservoirs in SIV-infected rhesus macaques had no demonstrable effect on plasma viremia after cART interruption.

Rhesus Cytomegalovirus-Specific CD8+ Cytotoxic T Lymphocytes Do Not Become Functionally Exhausted in Chronic SIVmac239 Infection

CD8⁺ cytotoxic T lymphocytes (CTLs) exert potent antiviral activity after HIV/SIV infection. However, efforts to harness the antiviral efficacy of CTLs for HIV/SIV prophylaxis and therapy have been severely hindered by two major problems: viral escape and exhaustion. By contrast, CTLs directed against human cytomegalovirus (HCMV), a ubiquitous chronic herpesvirus, seldom select for escape mutations and remain functional and refractory to exhaustion during chronic HCMV and HIV infection. Recently, attempts have been made to retarget HCMV-specific CTLs for cancer immunotherapy. We speculate that such a strategy may also be beneficial in the context of HIV/SIV infection, facilitating CTL-mediated control of HIV/SIV replication. As a preliminary assessment of the validity of this approach, we investigated the phenotypes and functionality of rhesus CMV (RhCMV)-specific CTLs in SIVmac239-infected Indian rhesus macaques (RMs), a crucial HIV animal model system. We recently identified two immunodominant, Mamu-A^∗02-restricted CTL epitopes derived from RhCMV proteins and sought to evaluate the phenotypic and functional characteristics of these CTL populations in chronic SIVmac239 infection. We analyzed and directly compared RhCMV- and SIVmac239-specific CTLs during SIVmac239 infection in a cohort of Mamu-A^∗01 ⁺ and Mamu-A^∗02 ⁺ RMs. CTL populations specific for at least one of the RhCMV-derived CTL epitopes were detected in ten of eleven Mamu-A^∗02 ⁺ animals tested, and both populations were detected in five of these animals. Neither RhCMV-specific CTL population exhibited significant changes in frequency, memory phenotype, granzyme B expression, exhaustion marker (PD-1 and CTLA-4) expression, or polyfunctionality between pre- and chronic SIVmac239 infection timepoints. In chronic SIVmac239 infection, RhCMV-specific CTLs exhibited higher levels of granzyme B expression and polyfunctionality, and lower levels of exhaustion marker expression, than SIVmac239-specific CTLs. Additionally, compared to SIVmac239-specific CTLs, greater proportions of RhCMV-specific CTLs were of the terminally differentiated effector memory phenotype (CD28^- CCR7^-) during chronic SIVmac239 infection. These results suggest that, in contrast to SIVmac239-specific CTLs, RhCMV-specific CTLs maintain their phenotypes and cytolytic effector functions during chronic SIVmac239 infection, and that retargeting RhCMV-specific CTLs might be a promising SIV immunotherapeutic strategy.

Interleukin 15 upregulates the expression of PD-1 and TIM-3 on CD4+ and CD8+ T cells

Virus-specific T cell-mediated immunity is severely impaired in chronic hepatitis B virus (HBV) patients. HBV-specific T cells in chronic HBV patients show a low ability to produce cytokines and to exert their cytotoxic activity. A prominent characteristic of these exhausted T cells is overexpression of inhibitory receptor molecules which negatively regulate T cell function. In this study, we examined in vitro regulation of two inhibitory receptor expressions, programmed death 1 (PD-1) and T cell immunoglobulin mucin domain-containing molecule 3 (TIM-3). Peripheral blood mononuclear cells (PBMCs) obtained from healthy individuals were in vitro stimulated with a panel of cytokines. PD-1 and TIM-3 expression levels on CD4⁺ and CD8⁺ T cells were examined at days 2 and 7 post stimulation. We demonstrated that PD-1 and TIM-3 were induced via polyclonal (anti-CD3) and cytokine (interleukin 15 [IL-15]) stimulations. Noteworthy, there was a significantly increased induction of TIM-3 on CD8⁺ T cells as compared to CD4⁺ T cells. Our study thus contributes to further understanding the regulation of T cell exhaustion markers PD-1 and TIM-3.

Generation of high-affinity CMV-specific T cells for adoptive immunotherapy using IL-2, IL-15, and IL-21

Cytomegalovirus (CMV) infection remains a life-threatening condition in individuals with a suppressed immune system. CMV may also represent a clinically relevant target for immune responses in CMV-positive malignancies. We established a protocol to expand CMV-specific T cells (CMV-T) using peripheral blood mononuclear cells (PBMCs). PBMCs from 16 HLA-A*0201 donors were cultured with a cytokine cocktail comprising IL-2/IL-15/IL-21 along with overlapping peptides from CMV-pp65. Ten days later, T cells were stimulated with anti-CD3 (OKT3) and irradiated autologous PBMCs. CMV-T were detected by HLA-A*0201 CMV-pp65_NLVPMVATV wild type and q226a mutant tetramers (for high-affinity T cells), intracellular cytokine staining, a CD107a mobilization assays as well as IFN-γ and TNF-α production in cell culture supernatants. We reliably obtained 50.25 ± 27.27% of CD8+ and 22.08 ± 21.83% of CD4+ T cells post-CMV-pp65 stimulation of PBMCs with a Th1-polarized phenotype and decreased Th2/Th17 responses. Most CD3 + CD8 + tetramer+ T cells were effector-memory cells, particularly among high-affinity CMV-T (q226a CMV-tetramer+). High-affinity CMV-T cells, compared to WT-tetramer+ cells, expressed higher IL-21R and lower FasL post-stimulation with CMV-pp65. The IL-2/IL-15/IL-21 cocktail also promoted CCR6 and CXCR3 expression necessary for T-cell migration into tissues. We have optimized methods for generating high-affinity CMV-specific T cells that can be used for adoptive cellular therapy in clinical practice.

Protective Efficacy of Inhaled BCG Vaccination Against Ultra-Low Dose Aerosol M. tuberculosis Challenge in Rhesus Macaques

Ten million cases of tuberculosis (TB) were reported in 2018 with a further 1.5 million deaths attributed to the disease. Improved vaccination strategies are urgently required to tackle the ongoing global TB epidemic. In the absence of a validated correlate of protection, highly characterised pre-clinical models are required to assess the protective efficacy of new vaccination strategies. In this study, we demonstrate the application of a rhesus macaque ultra-low dose (ULD) aerosol M. tuberculosis challenge model for the evaluation of TB vaccination strategies by directly comparing the immunogenicity and efficacy of intradermal (ID) and aerosol BCG vaccination delivered using a portable vibrating mesh nebulizer (VMN). Aerosol- and ID-delivered Bacille Calmette-Guérin (BCG) induced comparable frequencies of IFN-γ spot forming units (SFU) measured in peripheral blood mononuclear cells (PBMCs) by ELISpot, although the induction of IFN-γ SFU was significantly delayed following aerosol immunisation. This delayed response was also apparent in an array of secreted pro-inflammatory and chemokine markers, as well as in the frequency of antigen-specific cytokine producing CD4 and CD8 T-cells measured by multi-parameter flow cytometry. Interrogation of antigen-specific memory T-cell phenotypes revealed that vaccination-induced CD4 and CD8 T-cell populations primarily occupied the central memory (TCM) and transitional effector memory (TransEM) phenotype, and that the frequency of CD8 TCM and TransEM populations was significantly higher in aerosol BCG-vaccinated animals in the week prior to M. tuberculosis infection. The total and lung pathology measured following M. tuberculosis challenge was significantly lower in vaccinated animals relative to the unvaccinated control group and pathology measured in extra-pulmonary tissues was significantly reduced in aerosol BCG-vaccinated animals, relative to the ID-immunised group. Similarly, significantly fewer viable M. tuberculosis CFU were recovered from the extra-pulmonary tissues of aerosol BCG-vaccinated macaques relative to unvaccinated animals. In this study, a rhesus macaque ULD M. tuberculosis aerosol challenge model was applied as a refined and sensitive system for the evaluation of TB vaccine efficacy and to confirm that aerosol BCG vaccination delivered by portable VMN can confer a significant level of protection that is equivalent, and by some measures superior, to intradermal BCG vaccination.

Circulating β cell-specific CD8+ T cells restricted by high-risk HLA class I molecules show antigen experience in children with and at risk of type 1 diabetes

In type 1 diabetes (T1D), autoreactive cytotoxic CD8+ T cells are implicated in the destruction of insulin-producing β cells. The HLA-B*3906 and HLA-A*2402 class I genes confer increased risk and promote early disease onset, suggesting that CD8+ T cells that recognize peptides presented by these class I molecules on pancreatic β cells play a pivotal role in the autoimmune response. We examined the frequency and phenotype of circulating preproinsulin (PPI)-specific and insulin B (InsB)-specific CD8+ T cells in HLA-B*3906+ children newly diagnosed with T1D and in high-risk HLA-A*2402+ children before the appearance of disease-specific autoantibodies and before diagnosis of T1D. Antigen-specific CD8+ T cells were detected using human leucocyte antigen (HLA) class I tetramers and flow cytometry was used to assess memory status. In HLA-B*3906+ children with T1D, we observed an increase in PPI5-12 -specific transitional memory CD8+ T cells compared to non-diabetic, age- and HLA-matched subjects. Furthermore, PPI5-12 -specific CD8+ T cells in HLA-B*3906+ children with T1D showed a significantly more antigen-experienced phenotype compared to polyclonal CD8+ T cells. In longitudinal samples from high-risk HLA-A*2402+ children, the percentage of terminal effector cells within the InsB15-24 -specific CD8+ T cells was increased before diagnosis relative to samples taken before the appearance of autoantibodies. This is the first study, to our knowledge, to report HLA-B*3906-restricted autoreactive CD8+ T cells in T1D. Collectively, our results provide evidence that β cell-reactive CD8+ T cells restricted by disease-associated HLA class I molecules display an antigen-experienced phenotype and acquire enhanced effector function during the period leading to clinical diagnosis, implicating these cells in driving disease.

The human IL-15 superagonist N-803 promotes migration of virus-specific CD8+ T and NK cells to B cell follicles but does not reverse latency in ART-suppressed, SHIV-infected macaques

Despite the success of antiretroviral therapy (ART) to halt viral replication and slow disease progression, this treatment is not curative and there remains an urgent need to develop approaches to clear the latent HIV reservoir. The human IL-15 superagonist N-803 (formerly ALT-803) is a promising anti-cancer biologic with potent immunostimulatory properties that has been extended into the field of HIV as a potential "shock and kill" therapeutic for HIV cure. However, the ability of N-803 to reactivate latent virus and modulate anti-viral immunity in vivo under the cover of ART remains undefined. Here, we show that in ART-suppressed, simian-human immunodeficiency virus (SHIV)SF162P3-infected rhesus macaques, subcutaneous administration of N-803 activates and mobilizes both NK cells and SHIV-specific CD8+ T cells from the peripheral blood to lymph node B cell follicles, a sanctuary site for latent virus that normally excludes such effector cells. We observed minimal activation of memory CD4+ T cells and no increase in viral RNA content in lymph node resident CD4+ T cells post N-803 administration. Accordingly, we found no difference in the number or magnitude of plasma viremia timepoints between treated and untreated animals during the N-803 administration period, and no difference in the size of the viral DNA cell-associated reservoir post N-803 treatment. These results substantiate N-803 as a potent immunotherapeutic candidate capable of activating and directing effector CD8+ T and NK cells to the B cell follicle during full ART suppression, and suggest N-803 must be paired with a bona fide latency reversing agent in vivo to facilitate immune-mediated modulation of the latent viral reservoir.

Memory CD4+ T Cells in Immunity and Autoimmune Diseases

CD4⁺ T helper (Th) cells play central roles in immunity in health and disease. While much is known about the effector function of Th cells in combating pathogens and promoting autoimmune diseases, the roles and biology of memory CD4⁺ Th cells are complex and less well understood. In human autoimmune diseases such as multiple sclerosis (MS), there is a critical need to better understand the function and biology of memory T cells. In this review article we summarize current concepts in the field of CD4⁺ T cell memory, including natural history, developmental pathways, subsets, and functions. Furthermore, we discuss advancements in the field of the newly-described CD4⁺ tissue-resident memory T cells and of CD4⁺ memory T cells in autoimmune diseases, two major areas of important unresolved questions in need of answering to advance new vaccine design and development of novel treatments for CD4⁺ T cell-mediated autoimmune diseases.

Role of IL-15 Signaling in the Pathogenesis of Simian Immunodeficiency Virus Infection in Rhesus Macaques

Although IL-15 has been implicated in the pathogenic hyperimmune activation that drives progressive HIV and SIV infection, as well as in the generation of HIV/SIV target cells, it also supports NK and T cell homeostasis and effector activity, potentially benefiting the host. To understand the role of IL-15 in SIV infection and pathogenesis, we treated two cohorts of SIVmac239-infected rhesus macaques (RM; Macaca mulatta), one with chronic infection, the other with primary infection, with a rhesusized, IL-15-neutralizing mAb (versus an IgG isotype control) for up to 10 wk (n = 7-9 RM per group). In both cohorts, anti-IL-15 was highly efficient at blocking IL-15 signaling in vivo, causing 1) profound depletion of NK cells in blood and tissues throughout the treatment period; 2) substantial, albeit transient, depletion of CD8+ effector memory T cells (TEM) (but not the naive and central memory subsets); and 3) CD4+ and CD8+ TEM hyperproliferation. In primary infection, reduced frequencies of SIV-specific effector T cells in an extralymphoid tissue site were also observed. Despite these effects, the kinetics and extent of SIV replication, CD4+ T cell depletion, and the onset of AIDS were comparable between anti-IL-15- and control-treated groups in both cohorts. However, RM treated with anti-IL-15 during primary infection manifested accelerated reactivation of RM rhadinovirus. Thus, IL-15 support of NK cell and TEM homeostasis does not play a demonstrable, nonredundant role in SIV replication or CD4+ T cell deletion dynamics but may contribute to immune control of oncogenic γ-herpesviruses.

Differentiation into an Effector Memory Phenotype Potentiates HIV-1 Latency Reversal in CD4+ T Cells

By performing phenotypic analysis of latency reversal in CD4⁺ T cells from virally suppressed individuals, we identify the T_EM subset as the largest contributor to the inducible HIV reservoir. Differential responses of memory CD4⁺ T cell subsets to latency-reversing agents (LRAs) demonstrate that HIV gene expression is associated with heightened expression of transcriptional pathways associated with differentiation, acquisition of effector function, and cell cycle entry. In vitro modeling of the latent HIV reservoir in memory CD4⁺ T cell subsets identify LRAs that reverse latency with ranges of efficiency and specificity. We found that therapeutic induction of latency reversal is associated with upregulation of identical sets of T_EM-associated genes and cell surface markers shown to be associated with latency reversal in our ex vivo and in vitro models. Together, these data support the idea that the effector memory phenotype supports HIV latency reversal in CD4⁺ T cells.

During antiretroviral therapy (ART), human immunodeficiency virus type 1 (HIV-1) persists as a latent reservoir in CD4⁺ T cell subsets in central memory (T_CM), transitional memory (T_TM), and effector memory (T_EM) CD4⁺ T cells. We have identified differences in mechanisms underlying latency and responses to latency-reversing agents (LRAs) in ex vivo CD4⁺ memory T cells from virally suppressed HIV-infected individuals and in an in vitro primary cell model of HIV-1 latency. Our ex vivo and in vitro results demonstrate the association of transcriptional pathways of T cell differentiation, acquisition of effector function, and cell cycle entry in response to LRAs. Analyses of memory cell subsets showed that effector memory pathways and cell surface markers of activation and proliferation in the T_EM subset are predictive of higher frequencies of cells carrying an inducible reservoir. Transcriptional profiling also demonstrated that the epigenetic machinery (known to control latency and reactivation) in the T_EM subset is associated with frequencies of cells with HIV-integrated DNA and inducible HIV multispliced RNA. T_CM cells were triggered to differentiate into T_EM cells when they were exposed to LRAs, and this increase of T_EM subset frequencies upon LRA stimulation was positively associated with higher numbers of p24⁺ cells. Together, these data highlight differences in underlying biological latency control in different memory CD4⁺ T cell subsets which harbor latent HIV in vivo and support a role for differentiation into a T_EM phenotype in facilitating latency reversal.

IMPORTANCE By performing phenotypic analysis of latency reversal in CD4⁺ T cells from virally suppressed individuals, we identify the T_EM subset as the largest contributor to the inducible HIV reservoir. Differential responses of memory CD4⁺ T cell subsets to latency-reversing agents (LRAs) demonstrate that HIV gene expression is associated with heightened expression of transcriptional pathways associated with differentiation, acquisition of effector function, and cell cycle entry. In vitro modeling of the latent HIV reservoir in memory CD4⁺ T cell subsets identify LRAs that reverse latency with ranges of efficiency and specificity. We found that therapeutic induction of latency reversal is associated with upregulation of identical sets of T_EM-associated genes and cell surface markers shown to be associated with latency reversal in our ex vivo and in vitro models. Together, these data support the idea that the effector memory phenotype supports HIV latency reversal in CD4⁺ T cells.

Adoptive lymphocyte transfer to an HIV-infected progressor from an elite controller

BACKGROUNDHIV-infected patients with poor virologic control and multidrug-resistant virus have limited therapeutic options. The current study was undertaken to evaluate the safety, immunologic effects, and antiviral activity of peripheral lymphocytes transferred from an elite controller, whose immune system is able to control viral replication without antiretroviral medications, to an HLA-B*2705-matched progressor.METHODSApproximately 22 billion cells were collected from an elite controller by lymphapheresis and infused within 6 hours into a recipient with a preinfusion CD4+ T cell count of 10 cells/μL (1%) and HIV plasma viral load of 114,993 copies/mL.RESULTSDonor cells were cleared from the recipient's peripheral blood by day 8. A transient decrease in viral load to 58,421 (day 3) was followed by a rebound to 702,972 (day 6) before returning to baseline values by day 8. The decreased viral load was temporally associated with peak levels of donor T cells, including CD8+ T cells that had high levels of expression of Ki67, perforin, and granzyme B. Notably, recipient CD8+ T cells also showed increased expression of these markers, especially in HIV-specific tetramer-positive cells.CONCLUSIONThese results suggest that the adoptive transfer of lymphocytes from an HIV-infected elite controller to an HIV-infected patient with progressive disease may be able to perturb the immune system of the recipient in both positive and negative ways.TRIAL REGISTRATIONClinicalTrials.gov NCT00559416.FUNDINGIntramural Research Programs of the US NIH Clinical Center and the National Institute of Allergy and Infectious Diseases (NIAID); the National Cancer Institute.

Simian-Human Immunodeficiency Virus SHIV.CH505 Infection of Rhesus Macaques Results in Persistent Viral Replication and Induces Intestinal Immunopathology

Simian-human immunodeficiency viruses (SHIVs) have been utilized to test vaccine efficacy and characterize mechanisms of viral transmission and pathogenesis. However, the majority of SHIVs currently available have significant limitations in that they were developed using sequences from chronically HIV-infected individuals or uncommon HIV subtypes or were optimized for the macaque model by serially passaging the engineered virus in vitro or in vivo Recently, a newly developed SHIV, SHIV.C.CH505.375H.dCT (SHIV.CH505), which incorporates vpu-env (gp140) sequences from a transmitted/founder HIV-1 subtype C strain, was shown to retain attributes of primary HIV-1 strains. However, a comprehensive analysis of the immunopathology that results from infection with this virus, especially in critical tissue compartments like the intestinal mucosa, has not been completed. In this study, we evaluated the viral dynamics and immunopathology of SHIV.CH505 in rhesus macaques. In line with previous findings, we found that SHIV.CH505 is capable of infecting and replicating efficiently in rhesus macaques, resulting in peripheral viral kinetics similar to that seen in pathogenic SIV and HIV infection. Furthermore, we observed significant and persistent depletions of CCR5⁺ and CCR6⁺ CD4⁺ T cells in mucosal tissues, decreases in CD4⁺ T cells producing Th17 cell-associated cytokines, CD8⁺ T cell dysfunction, and alterations of B cell and innate immune cell function, indicating that SHIV.CH505 elicits intestinal immunopathology typical of SIV/HIV infection. These findings suggest that SHIV.CH505 recapitulates the early viral replication dynamics and immunopathogenesis of HIV-1 infection of humans and thus can serve as a new model for HIV-1 pathogenesis, treatment, and prevention research.IMPORTANCE The development of chimeric SHIVs has been instrumental in advancing our understanding of HIV-host interactions and allowing for in vivo testing of novel treatments. However, many of the currently available SHIVs have distinct drawbacks and are unable to fully reflect the features characteristic of primary SIV and HIV strains. Here, we utilize rhesus macaques to define the immunopathogenesis of the recently developed SHIV.CH505, which was designed without many of the limitations of previous SHIVs. We observed that infection with SHIV.CH505 leads to peripheral viral kinetics and mucosal immunopathogenesis comparable with those caused by pathogenic SIV and HIV. Overall, these data provide evidence of the value of SHIV.CH505 as an effective model of SIV/HIV infection and an important tool that can be used in future studies, including preclinical testing of new therapies or prevention strategies.

Cytotoxic Activity and Memory T Cell Subset Distribution of in vitro-Stimulated CD8+ T Cells Specific for HER2/neu Epitopes

Minimal residual disease remaining after resection of primary tumors can lead to tumor recurrence and metastasis, increasing mortality and morbidity rates among cancer patients. Thus, there is a need for new technologies for recognition and elimination of single cancer cells remaining in a patient's body after radiation therapy, chemotherapy, or surgical resection. Effector CD8⁺ T cells, also commonly known as cytotoxic T lymphocytes (CTLs), play a key role in antitumor cellular immunity and, when properly activated, are able to effectively destroy tumor cells. The aims of this study were to obtain CD8⁺ CTLs specific for the HER2/neu epitopes E75 and E88 and to assess the cytotoxic activity and composition of these cells in terms of the distribution of memory T-cell subsets. We obtained HER2-specific CD8⁺ T cells and assessed T cell subset distribution among them including naive T cells (T_N), central memory T cells (T_CM), effector memory T cells (T_EM), stem cell-like memory T cells (T_SCM) and terminally-differentiated T cells (T_EMRA) via eight-color flow cytometry. HER2-specific CTLs were largely (~40–50%) represented by T_SCM cells, a population capable of mounting pronounced antitumor immune responses due to a combination of effector function and self-maintenance. In comparison with activated peripheral blood mononuclear cells (PBMCs) and bulk CD8⁺ T cells, HER2-specific CTLs exhibited greater cytotoxicity against the HER2-expressing human breast adenocarcinoma cell line MCF-7 and produced higher levels of IFN-γ in response to tumor cells. We also showed the presence of HER2-specific CTLs in healthy individuals and increase in them in HER2-positive breast cancer patients. Collectively, our results suggest that HER2-specific CD8⁺ T cells isolated using this approach could be used for adoptive T-cell transfer to eliminate tumor cells and prevent metastasis and relapse in patients with HER2-overexpressing cancers.

The Frequency of Vaccine-Induced T-Cell Responses Does Not Predict the Rate of Acquisition after Repeated Intrarectal SIVmac239 Challenges in Mamu-B*08+ Rhesus Macaques

Approximately 50% of rhesus macaques (RMs) expressing the major histocompatibility complex class I (MHC-I) allele Mamu-B*08 spontaneously control chronic-phase viremia after infection with the pathogenic simian immunodeficiency virus mac239 (SIVmac239) clone. CD8+ T-cell responses in these animals are focused on immunodominant Mamu-B*08-restricted SIV epitopes in Vif and Nef, and prophylactic vaccination with these epitopes increases the incidence of elite control in SIVmac239-infected Mamu-B*08-positive (Mamu-B*08+ ) RMs. Here we evaluated if robust vaccine-elicited CD8+ T-cell responses against Vif and Nef can prevent systemic infection in Mamu-B*08+ RMs following mucosal SIV challenges. Ten Mamu-B*08+ RMs were vaccinated with a heterologous prime/boost/boost regimen encoding Vif and Nef, while six sham-vaccinated MHC-I-matched RMs served as the controls for this experiment. Vaccine-induced CD8+ T cells against Mamu-B*08-restricted SIV epitopes reached high frequencies in blood but were present at lower levels in lymph node and gut biopsy specimens. Following repeated intrarectal challenges with SIVmac239, all control RMs became infected by the sixth SIV exposure. By comparison, four vaccinees were still uninfected after six challenges, and three of them remained aviremic after 3 or 4 additional challenges. The rate of SIV acquisition in the vaccinees was numerically lower (albeit not statistically significantly) than that in the controls. However, peak viremia was significantly reduced in infected vaccinees compared to control animals. We found no T-cell markers that distinguished vaccinees that acquired SIV infection from those that did not. Additional studies will be needed to validate these findings and determine if cellular immunity can be harnessed to prevent the establishment of productive immunodeficiency virus infection.IMPORTANCE It is generally accepted that the antiviral effects of vaccine-induced classical CD8+ T-cell responses against human immunodeficiency virus (HIV) are limited to partial reductions in viremia after the establishment of productive infection. Here we show that rhesus macaques (RMs) vaccinated with Vif and Nef acquired simian immunodeficiency virus (SIV) infection at a lower (albeit not statistically significant) rate than control RMs following repeated intrarectal challenges with a pathogenic SIV clone. All animals in the present experiment expressed the elite control-associated major histocompatibility complex class I (MHC-I) molecule Mamu-B*08 that binds immunodominant epitopes in Vif and Nef. Though preliminary, these results provide tantalizing evidence that the protective efficacy of vaccine-elicited CD8+ T cells may be greater than previously thought. Future studies should examine if vaccine-induced cellular immunity can prevent systemic viral replication in RMs that do not express MHC-I alleles associated with elite control of SIV infection.

Inoculation of fowlpox viruses coexpressing avian influenza H5 and chicken IL-15 cytokine gene stimulates diverse host immune responses

Fowlpox virus (FWPV) has been used as a recombinant vaccine vector to express antigens from several important avian pathogens. Attempts have been made to improve vaccine strains induced-host immune responses by coexpressing cytokines. This study describes the construction of recombinant FWPV (rFWPV) strain FP9 and immunological responses in specific-pathogen-free (SPF) chickens, co-expressing avian influenza virus (AIV) H5 of A/Chicken/Malaysia/5858/2004, and chicken IL-15 cytokine genes. Expression of H5 (50 kD) was confirmed by western blotting. Anti-H5 antibodies, which were measured by the haemagglutinin inhibition test, were at the highest levels at Week 3 post-inoculation in both rFWPV/H5- and rFWPV/H5/IL-15-vaccinated chickens, but decreased to undetectable levels from Week 5 onwards. CD3+/CD4+ or CD3+/CD8+T cell populations, assessed using flow cytometry, were significantly increased in both WT FP9- and rFWPV/H5-vaccinated chickens and were also higher than in rFWPV/H5/IL-15- vaccinated chickens, at Week 2. Gene expression analysis using real time quantitative polymerase chain reaction (qPCR) demonstrated upregulation of IL-15 expression in all vaccinated groups with rFWPV/H5/IL-15 having the highest fold change, at day 2 (117±51.53). Despite showing upregulation, fold change values of the IL-18 expression were below 1.00 for all vaccinated groups at day 2, 4 and 6. This study shows successful construction of rFWPV/H5 co-expressing IL-15, with modified immunogenicity upon inoculation into SPF chickens.

The human IL-15 superagonist ALT-803 directs SIV-specific CD8+ T cells into B-cell follicles

Sequestering of latent HIV in follicular helper T cells within B-cell follicles that largely exclude cytotoxic T cells is a major barrier to cellular immune-based approaches to eradicate HIV. Here, we show that the clinical-grade human interleukin-15 (IL-15) superagonist ALT-803 activates and redirects simian immunodeficiency virus (SIV)-specific CD8⁺ T cells from the peripheral blood into B-cell follicles. In agreement with the increased trafficking of SIV-specific cytotoxic T cells to sites of cryptic viral replication, lymph nodes of elite controlling macaques contained fewer cells expressing SIV RNA or harboring SIV DNA post-ALT-803 treatment. These data establish ALT-803 as an immunotherapeutic for HIV and other chronic viral pathogens that evade host immunity by persisting in B-cell follicles.

Nonhuman Primate Models of Immunosenescence

Due to a dramatic increase in life expectancy, the number of individuals aged 65 and older is rapidly rising. This presents considerable challenges to our health care system since advanced age is associated with a higher susceptibility to infectious diseases due to immune senescence. However, the mechanisms underlying age-associated dysregulated immunity are still incompletely understood. Advancement in our comprehension of mechanisms of immune senescence and development of interventions to improve health span requires animal models that closely recapitulate the physiological changes that occur with aging in humans. Nonhuman primates (NHPs) are invaluable preclinical models to study the underlying causal mechanism of pathogenesis due to their outbred nature, high degree of genetic and physiological similarity to humans, and their susceptibility to human pathogens. In this chapter, we review NHP models available for biogerontology research, advantages and challenges they present, and advances they facilitated. Furthermore, we emphasize the utility of NHPs in characterizing immune senescence, evaluating interventions to reverse aging of the immune system, and development of vaccine strategies that are better suited for this vulnerable population.

A recombinant herpesviral vector containing a near-full-length SIVmac239 genome produces SIV particles and elicits immune responses to all nine SIV gene products

The properties of the human immunodeficiency virus (HIV) pose serious difficulties for the development of an effective prophylactic vaccine. Here we describe the construction and characterization of recombinant (r), replication-competent forms of rhesus monkey rhadinovirus (RRV), a gamma-2 herpesvirus, containing a near-full-length (nfl) genome of the simian immunodeficiency virus (SIV). A 306-nucleotide deletion in the pol gene rendered this nfl genome replication-incompetent as a consequence of deletion of the active site of the essential reverse transcriptase enzyme. Three variations were constructed to drive expression of the SIV proteins: one with SIV's own promoter region, one with a cytomegalovirus (cmv) immediate-early promoter/enhancer region, and one with an RRV dual promoter (p26 plus PAN). Following infection of rhesus fibroblasts in culture with these rRRV vectors, synthesis of the early protein Nef and the late structural proteins Gag and Env could be demonstrated. Expression levels of the SIV proteins were highest with the rRRV-SIVcmv-nfl construct. Electron microscopic examination of rhesus fibroblasts infected with rRRV-SIVcmv-nfl revealed numerous budding and mature SIV particles and these infected cells released impressive levels of p27 Gag protein (>150 ng/ml) into the cell-free supernatant. The released SIV particles were shown to be incompetent for replication. Monkeys inoculated with rRRV-SIVcmv-nfl became persistently infected, made readily-detectable antibodies against SIV, and developed T-cell responses against all nine SIV gene products. Thus, rRRV expressing a near-full-length SIV genome mimics live-attenuated strains of SIV in several important respects: the infection is persistent; >95% of the SIV proteome is naturally expressed; SIV particles are formed; and CD8+ T-cell responses are maintained indefinitely in an effector-differentiated state. Although the magnitude of anti-SIV immune responses in monkeys infected with rRRV-SIVcmv-nfl falls short of what is seen with live-attenuated SIV infection, further experimentation seems warranted.

Optimized administration of hetIL-15 expands lymphocytes and minimizes toxicity in rhesus macaques

The common γ-chain cytokine interleukin-15 (IL-15) plays a significant role in regulating innate and adaptive lymphocyte homeostasis and can stimulate anti-tumor activity of leukocytes. We have previously shown that the circulating IL-15 in the plasma is the heterodimeric form (hetIL-15), produced upon co-expression of IL-15 and IL-15 Receptor alpha (IL-15Rα) polypeptides in the same cell, heterodimerization of the two chains and secretion. We investigated the pharmacokinetic and pharmacodynamic profile and toxicity of purified human hetIL-15 cytokine upon injection in rhesus macaques. We compared the effects of repeated hetIL-15 administration during a two-week dosing cycle, using different subcutaneous dosing schemata, i.e. fixed doses of 0.5, 5 and 50 μg/kg or a doubling step-dose scheme ranging from 2 to 64 μg/kg. Following a fixed-dose regimen, dose-dependent peak plasma IL-15 levels decreased significantly between the first and last injection. The trough plasma IL-15 levels measured at 48 h after injections were significantly higher after the first dose, compared to subsequent doses. In contrast, following the step-dose regimen, the systemic exposure increased by more than 1 log between the first injection given at 2 μg/kg and the last injection given at 64 μg/kg, and the trough levels were comparable after each injection. Blood lymphocyte cell count, proliferation, and plasma IL-18 levels peaked at day 8 when hetIL-15 was provided at fixed doses, and at the end of the cycle following a step-dose regimen, suggesting that sustained expansion of target cells requires increasing doses of cytokine. Macaques treated with a 50 μg/kg dose showed moderate and transient toxicity, including fever, signs of capillary leak syndrome and renal dysfunction. In contrast, these effects were mild or absent using the step-dose regimen. The results provide a new method of optimal administration of this homeostatic cytokine and may have applications for the delivery of other cytokines.

α4β7+ CD4+ Effector/Effector Memory T Cells Differentiate into Productively and Latently Infected Central Memory T Cells by Transforming Growth Factor β1 during HIV-1 Infection

HIV-1 transmission occurs mainly through mucosal tissues. During mucosal transmission, HIV-1 preferentially infects α₄β₇⁺ gut-homing CCR7^- CD4⁺ effector/effector memory T cells (T_EM) and results in massive depletion of these cells and other subsets of T_EM in gut-associated lymphoid tissues. However, besides being eliminated by HIV-1, the role of T_EM during the early stage of infection remains inconclusive. Here, using in vitro-induced α₄β₇⁺ gut-homing T_EM (α₄β₇⁺ T_EM), we found that α₄β₇⁺ T_EM differentiated into CCR7⁺ CD4⁺ central memory T cells (T_CM). This differentiation was HIV-1 independent but was inhibited by SB431542, a specific transforming growth factor β (TGF-β) receptor I kinase inhibitor. Consistently, T_EM-to-T_CM differentiation was observed in α₄β₇⁺ T_EM stimulated with TGF-β1 (TGF-β). The T_CM properties of the TGF-β-induced T_EM-derived T_CM (α₄β₇⁺ T_CM) were confirmed by their enhanced CCL19 chemotaxis and the downregulation of surface CCR7 upon T cell activation in vitro Importantly, the effect of TGF-β on T_CM differentiation also held in T_EM directly isolated from peripheral blood. To investigate the significance of the TGF-β-dependent T_EM-to-T_CM differentiation in HIV/AIDS pathogenesis, we observed that both productively and latently infected α₄β₇⁺ T_CM could differentiate from α₄β₇⁺ T_EM in the presence of TGF-β during HIV-1 infection. Collectively, this study not only provides a new insight for the plasticity of T_EM but also suggests that the TGF-β-dependent T_EM-to-T_CM differentiation is a previously unrecognized mechanism for the formation of latently infected T_CM after HIV-1 infection.IMPORTANCE HIV-1 is the causative agent of HIV/AIDS, which has led to millions of deaths in the past 30 years. Although the implementation of highly active antiretroviral therapy has remarkably reduced the HIV-1-related morbidity and mortality, HIV-1 is not eradicated in treated patients due to the presence of latent reservoirs. Besides, the pathogenesis in CD4 T cells early after infection still remains elusive. Immediately after HIV-1 mucosal infection, CD4 T cells are preferentially infected and depleted. However, in addition to being depleted, the other roles of the CD4 T cells, especially the effector/effector memory T cells (T_EM), in disease progression are not completely understood. The significance of this study is in revealing a novel mechanism for the formation of latently HIV-1-infected central memory CD4 T cells, a major latent reservoir from CD4 T_EM after infection. Our findings suggest previously unrecognized roles of CD4 T_EM in HIV-1 pathogenesis.

Treatment with native heterodimeric IL-15 increases cytotoxic lymphocytes and reduces SHIV RNA in lymph nodes

B cell follicles in secondary lymphoid tissues represent an immune privileged sanctuary for AIDS viruses, in part because cytotoxic CD8+ T cells are mostly excluded from entering the follicles that harbor infected T follicular helper (TFH) cells. We studied the effects of native heterodimeric IL-15 (hetIL-15) treatment on uninfected rhesus macaques and on macaques that had spontaneously controlled SHIV infection to low levels of chronic viremia. hetIL-15 increased effector CD8+ T lymphocytes with high granzyme B content in blood, mucosal sites and lymph nodes, including virus-specific MHC-peptide tetramer+ CD8+ cells in LN. Following hetIL-15 treatment, multiplexed quantitative image analysis (histo-cytometry) of LN revealed increased numbers of granzyme B+ T cells in B cell follicles and SHIV RNA was decreased in plasma and in LN. Based on these properties, hetIL-15 shows promise as a potential component in combination immunotherapy regimens to target AIDS virus sanctuaries and reduce long-term viral reservoirs in HIV-1 infected individuals.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02452268.

ALT-803 Transiently Reduces Simian Immunodeficiency Virus Replication in the Absence of Antiretroviral Treatment

Developing biological interventions to control human immunodeficiency virus (HIV) replication in the absence of antiretroviral therapy (ART) could contribute to the development of a functional cure. As a potential alternative to ART, the interleukin-15 (IL-15) superagonist ALT-803 has been shown to boost the number and function of HIV-specific CD8⁺ T and NK cell populations in vitro Four simian immunodeficiency virus (SIV)-positive rhesus macaques, three of whom possessed major histocompatibility complex alleles associated with control of SIV and all of whom had received SIV vaccine vectors that had the potential to elicit CD8⁺ T cell responses, were given ALT-803 in three treatment cycles. The first and second cycles of treatment were separated by 2 weeks, while the third cycle was administered after a 29-week break. ALT-803 transiently elevated the total CD8⁺ effector and central memory T cell and NK cell populations in peripheral blood, while viral loads transiently decreased by ∼2 logs in all animals. Virus suppression was not sustained as T cells became less responsive to ALT-803 and waned in numbers. No effect on viral loads was observed in the second cycle of ALT-803, concurrent with downregulation of the IL-2/15 common γC and β chain receptors on both CD8⁺ T cells and NK cells. Furthermore, populations of immunosuppressive T cells increased during the second cycle of ALT-803 treatment. During the third treatment cycle, responsiveness to ALT-803 was restored. CD8⁺ T cells and NK cells increased again 3- to 5-fold, and viral loads transiently decreased again by 1 to 2 logs.IMPORTANCE Overall, our data show that ALT-803 has the potential to be used as an immunomodulatory agent to elicit effective immune control of HIV/SIV replication. We identify mechanisms to explain why virus control is transient, so that this model can be used to define a clinically appropriate treatment regimen.

Novel mechanisms to inhibit HIV reservoir seeding using Jak inhibitors

Despite advances in the treatment of HIV infection with ART, elucidating strategies to overcome HIV persistence, including blockade of viral reservoir establishment, maintenance, and expansion, remains a challenge. T cell homeostasis is a major driver of HIV persistence. Cytokines involved in regulating homeostasis of memory T cells, the major hub of the HIV reservoir, trigger the Jak-STAT pathway. We evaluated the ability of tofacitinib and ruxolitinib, two FDA-approved Jak inhibitors, to block seeding and maintenance of the HIV reservoir in vitro. We provide direct demonstration for involvement of the Jak-STAT pathway in HIV persistence in vivo, ex vivo, and in vitro; pSTAT5 strongly correlates with increased levels of integrated viral DNA in vivo, and in vitro Jak inhibitors reduce the frequency of CD4+ T cells harboring integrated HIV DNA. We show that Jak inhibitors block viral production from infected cells, inhibit γ-C receptor cytokine (IL-15)-induced viral reactivation from latent stores thereby preventing transmission of infectious particles to bystander activated T cells. These results show that dysregulation of the Jak-STAT pathway is associated with viral persistence in vivo, and that Jak inhibitors target key events downstream of γ-C cytokine (IL-2, IL-7 and IL-15) ligation to their receptors, impacting the magnitude of the HIV reservoir in all memory CD4 T cell subsets in vitro and ex vivo. Jak inhibitors represent a therapeutic modality to prevent key events of T cell activation that regulate HIV persistence and together, specific, potent blockade of these events may be integrated to future curative strategies.

The potential and promise of IL-15 in immuno-oncogenic therapies

This review provides an in-depth description of the preclinical and clinical studies demonstrating the effectiveness and limitations of IL-15 and IL-15 analogs given as an exogenous immuno-oncology agent. IL-15 is a cytokine that primarily stimulates the proliferation and cytotoxic functions of CD8T cells and NK cells leading to enhanced anti-tumor responses. While initially showing promise as a cancer therapeutic, the efficacy of IL-15 was limited by its short in vivo half-life. More recently, various approaches have been developed to improve the in vivo half-life and efficacy of IL-15, largely by generating IL-15/IL-15Rα conjugates. These new IL-15 based agents renew the prospect of IL-15 as a cancer immunotherapeutic agent. While having some efficacy in inducing tumor regression as a monotherapy, IL-15 agents also show great potential in being used in combination with other immuno-oncological therapies. Indeed, IL-15 used in combination therapy yields even better anti-tumor responses and prolongs survival than IL-15 treatment alone in numerous murine cancer models. The promising results from these preclinical studies have led to the implementation of several clinical trials to test the safety and efficacy of IL-15-based agents as a stand-alone treatment or in conjunction with other therapies to treat both advanced solid tumors and hematological malignancies.

Vaccine-induced immune responses against both Gag and Env improve control of simian immunodeficiency virus replication in rectally challenged rhesus macaques

The ability to control lentivirus replication may be determined, in part, by the extent to which individual viral proteins are targeted by the immune system. Consequently, defining the antigens that elicit the most protective immune responses may facilitate the design of effective HIV-1 vaccines. Here we vaccinated four groups of rhesus macaques with a heterologous vector prime/boost/boost/boost (PBBB) regimen expressing the following simian immunodeficiency virus (SIV) genes: env, gag, vif, rev, tat, and nef (Group 1); env, vif, rev, tat, and nef (Group 2); gag, vif, rev, tat, and nef (Group 3); or vif, rev, tat, and nef (Group 4). Following repeated intrarectal challenges with a marginal dose of the neutralization-resistant SIVmac239 clone, vaccinees in Groups 1-3 became infected at similar rates compared to control animals. Unexpectedly, vaccinees in Group 4 became infected at a slower pace than the other animals, although this difference was not statistically significant. Group 1 exhibited the best post-acquisition virologic control of SIV infection, with significant reductions in both peak and chronic phase viremia. Indeed, 5/8 Group 1 vaccinees had viral loads of less than 2,000 vRNA copies/mL of plasma in the chronic phase. Vaccine regimens that did not contain gag (Group 2), env (Group 3), or both of these inserts (Group 4) were largely ineffective at decreasing viremia. Thus, vaccine-induced immune responses against both Gag and Env appeared to maximize control of immunodeficiency virus replication. Collectively, these findings are relevant for HIV-1 vaccine design as they provide additional insights into which of the lentiviral proteins might serve as the best vaccine immunogens.