PD-L1 Blockade Differentially Impacts Regulatory T Cells from HIV-Infected Individuals Depending on Plasma Viremia

Enhancement of Human Immunodeficiency Virus-Specific CD8+ T Cell Responses with TIGIT Blockade Involves Trogocytosis

Natural killer (NK) and CD8+ T cell function is compromised in human immunodeficiency virus type 1 (HIV-1) infection by increased expression of inhibitory receptors such as TIGIT (T cell immunoreceptor with Ig and ITIM domains). Blocking inhibitory receptors or their ligands with monoclonal antibodies (mAb) has potential to improve antiviral immunity in general and facilitate HIV eradication strategies. We assessed the impact of TIGIT engagement and blockade on cytotoxicity, degranulation, and interferon-gamma (IFN-γ) production by CD8+ T cells from persons living with HIV (PLWH). The effect of TIGIT engagement on non-specific anti-CD3-redirected cytotoxicity was assessed in redirected cytotoxicity assays, and the effect of TIGIT blockade on HIV-specific CD8+ T cell responses was assessed by flow cytometry. In 14/19 cases where peripheral blood mononuclear cells (PBMC) mediated >10% redirected cytotoxicity, TIGIT engagement reduced the level of cytotoxicity to <90% of control values. We selected PLWH with >1000 HIV Gag or Nef-specific IFN-γ spot forming cells per million PBMC to quantify the effects of TIGIT blockade on HIV-specific CD8+ T cell responses by flow cytometry. Cell surface TIGIT expression decreased on CD8+ T cells from 23/40 PLWH following TIGIT blockade and this loss was associated with increased anti-TIGIT mAb fluorescence on monocytes. In total, 6 of these 23 PLWH had enhanced HIV-specific CD8+ T cell degranulation and IFN-γ production with TIGIT blockade, compared to 0/17 with no decrease in cell surface TIGIT expression. Reduced CD8+ T cell TIGIT expression with TIGIT blockade involved trogocytosis by circulating monocytes, suggesting that an effector monocyte population and intact fragment crystallizable (Fc) functions are required for mAb-based TIGIT blockade to effectively enhance HIV-specific CD8+ T cell responses.

Prevalence of HPV in anal cancer: exploring the role of infection and inflammation

Anal cancer incidence is rising globally, driven primarily by human papillomavirus (HPV) infection. HPV, especially high-risk types 16 and 18, is considered a necessary cause of anal squamous cell carcinoma. Certain populations like people living with HIV, men who have sex with men, inflammatory bowel disease patients, smokers, and those with compromised immunity face elevated risk. Chronic inflammation facilitates viral persistence, cell transformation, and immune evasion through pathways involving the PD-1/PD-L1 axis. HIV coinfection further increases risk by impairing immune surveillance and epithelial integrity while promoting HPV oncogene expression. Understanding these inflammatory processes, including roles of CD8 + T cells and PD-1/PD-L1, could guide development of immunotherapies against anal cancer. This review summarizes current knowledge on inflammation's role in anal cancer pathogenesis and the interplay between HPV, HIV, and host immune factors.

Absence of PD-L1 signaling hinders macrophage defense against Mycobacterium tuberculosis via upregulating STAT3/IL-6 pathway

The blockade of programmed death-ligand 1 (PD-L1) pathway has been clinically used in cancer immunotherapy, while its effects on infectious diseases remain elusive. Roles of PD-L1 signaling in the macrophage-mediated innate immune defense against M.tb is unclear. In this study, the outcomes of tuberculosis (TB) in wild-type (WT) mice treated with anti-PD-1/PD-L1 therapy and macrophage-specific Pdl1-knockout (Pdl1ΔΜΦ) mice were compared. Treatment with anti-PD-L1 or anti-PD-1 benefited protection against M.tb infection in WT mice, while Pdl1ΔΜΦ mice exhibited the increased susceptibility to M.tb infection. Mechanistically, the absence of PD-L1 signaling impaired M.tb killing by macrophages. Furthermore, elevated STAT3 activation was found in PD-L1-deficient macrophages, leading to increased interleukin (IL)-6 production and reduced inducible nitric oxide synthase (iNOS) expression. Inhibiting STAT3 phosphorylation partially impeded the increase in IL-6 production and restored iNOS expression in these PD-L1-deficient cells. These findings provide valuable insights into the complexity and mechanisms underlying anti-PD-L1 therapy in the context of tuberculosis.

Expression and prognostic significance of the PD-1/PD-L1 pathway in AIDS-related non-Hodgkin lymphoma

OBJECTIVE

Immune tolerance and evasion play a critical role in virus-driven malignancies. However, the phenotype and clinical significance of programmed cell death 1 (PD-1) and its ligands, PD-L1 and PD-L2, in aggressive acquired immunodeficiency syndrome (AIDS)-related non-Hodgkin lymphoma (AR-NHL) remain poorly understood, particularly in the Epstein-Barr virus (EBV)-positive subset.

METHODS

We used in situ hybridization with EBV-encoded RNA (EBER) to assess the EBV status. We performed immunohistochemistry and flow cytometry analysis to evaluate components of the PD-1/PD-L1/L2 pathway in a multi-institutional cohort of 58 patients with AR-NHL and compared EBV-positive and EBV-negative cases.

RESULTS

The prevalence of EBV+ in AR-NHL was 56.9% and was associated with a marked increase in the expression of PD-1/PD-L1/PD-L2 in malignant cells. Patients with AR-NHLs who tested positive for both EBER and PD-1 exhibited lower survival rates compared to those negative for these markers (47.4% vs. 93.8%, p = 0.004). Similarly, patients positive for both EBER and PD-L1 also demonstrated poorer survival (56.5% vs. 93.8%, p = 0.043). Importantly, PD-1 tissue-expression demonstrated independent prognostic significance for overall survival in multivariate analysis and was correlated to elevated levels of LDH (r = 0.313, p = 0.031), increased PD-1+ Tregs (p = 0.006), and robust expression of EBER (r = 0.541, p < 0.001) and PD-L1 (r = 0.354, p = 0.014) expression.

CONCLUSIONS

These data emphasize the importance of PD-1-mediated immune evasion in the complex landscape of immune oncology in AR-NHL co-infected with EBV, and contribute to the diagnostic classification and possible definition of immunotherapeutic strategies for this unique subgroup.

Immune checkpoint inhibitors as potential therapy for reverting T-cell exhaustion and reverting HIV latency in people living with HIV

The immune system of people living with HIV (PLWH) is persistently exposed to antigens leading to systemic inflammation despite combination antiretroviral treatment (cART). This inflammatory milieu promotes T-cell activation and exhaustion. Furthermore, it produces diminished effector functions including loss of cytokine production, cytotoxicity, and proliferation, leading to disease progression. Exhausted T cells show overexpression of immune checkpoint molecules (ICs) on the cell surface, including programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT), and lymphocyte activation gene-3 (LAG-3). The ICs also play a crucial role in T-cell exhaustion by reducing the immune response to cancer antigens. Immunotherapy based on immune checkpoint inhibitors (ICIs) has changed the management of a diversity of cancers. Additionally, the interest in exploring this approach in the setting of HIV infection has increased, including AIDS-defining cancers and non-AIDS-defining cancers in PLWH. To date, research on this topic suggests that ICI-based therapies in PLWH could be a safe and effective approach. In this review, we provide an overview of the current literature on the potential role of ICI-based immunotherapy not only in cancer remission in PLWH but also as a therapeutic intervention to restore immune response against HIV, revert HIV latency, and attain a functional cure for HIV infection.

XCR1+ DCs are critical for T cell-mediated immunotherapy of chronic viral infections

The contribution of cross-presenting XCR1+ dendritic cells (DCs) and SIRPα+ DCs in maintaining T cell function during exhaustion and immunotherapeutic interventions of chronic infections remains poorly characterized. Using the mouse model of chronic LCMV infection, we found that XCR1+ DCs are more resistant to infection and highly activated compared with SIRPα+ DCs. Exploiting XCR1+ DCs via Flt3L-mediated expansion or XCR1-targeted vaccination notably reinvigorates CD8+ T cells and improves virus control. Upon PD-L1 blockade, XCR1+ DCs are not required for the proliferative burst of progenitor exhausted CD8+ T (TPEX) cells but are indispensable to sustain the functionality of exhausted CD8+ T (TEX) cells. Combining anti-PD-L1 therapy with increased frequency of XCR1+ DCs improves functionality of TPEX and TEX subsets, while increase of SIRPα+ DCs dampened their proliferation. Together, this demonstrates that XCR1+ DCs are crucial for the success of checkpoint inhibitor-based therapies through differential activation of exhausted CD8+ T cell subsets.

Functional cure of a chronic virus infection by shifting the virus - host equilibrium state

The clinical handling of chronic virus infections remains a challenge. Here we describe recent progress in the understanding of virus - host interaction dynamics. Based on the systems biology concept of multi-stability and the prediction of multiplicative cooperativity between virus-specific cytotoxic T cells and neutralising antibodies, we argue for the requirements to engage multiple immune system components for functional cure strategies. Our arguments are derived from LCMV model system studies and are translated to HIV-1 infection.

Hyperprogression: A novel response pattern under immunotherapy

Checkpoint blockade therapy has shown significant therapeutic benefits and resulted in durable responses in patients with various tumors. However, accumulating evidence has demonstrated that 4-29% of all patients with cancers with various histologies may suffer from tumor flare following such therapy. This novel tumor response pattern, termed hyperprogression, is a potentially deleterious side effect of checkpoint blockade therapy that accelerates disease progression in a subset of patients. In this review, we describe possible immune checkpoint blockade biomarkers and the epidemiology, different definitions, and predictors of hyperprogression based on the research findings and further present the available evidence supporting pathophysiological hypotheses that might explain hyperprogression during checkpoint blockade therapy. We also compare hyperprogression and pseudoprogression. Finally, we discuss areas requiring further study.

Targeting metabolism to reverse T-cell exhaustion in chronic viral infections

CD8 T-cells are an essential component of the adaptive immune response accountable for the clearance of virus-infected cells via cytotoxic effector functions. Maintaining a specific metabolic profile is necessary for these T-cells to sustain their effector functions and clear pathogens. When CD8 T-cells are activated via T-cell receptor recognition of viral antigen, they transition from a naïve to an effector state and eventually to a memory phenotype, and their metabolic profiles shift as the cells differentiate to accomidate different metabolic demands. However, in the context of particular chronic viral infections (CVIs), CD8 T-cells can become metabolically dysfunctional in a state known as T-cell exhaustion. In this state, CD8 T-cells exhibit reduced effector functions and are unable to properly control pathogens. Clearing these chronic infections becomes progressively difficult as increasing numbers of the effector T-cells become exhausted. Hence, reversal of this dysfunctional metabolic phenotype is vital when considering potential treatments of these infections and offers the opportunity for novel strategies for the development of therapies against CVIs. In this review we explore research implicating alteration of the metabolic state as a means to reverse CD8 T-cell exhaustion in CVIs. These findings indicate that strategies targeting dysfunctional CD8 T-cell metabolism could prove to be a promising option for successfully treating CVIs.

The Role of PD-1 in Acute and Chronic Infection

PD-1 as an immune checkpoint molecule down-regulates T cell activity during immune responses in order to prevent autoimmune tissue damage. In chronic infections or tumors, lasting antigen-exposure leads to permanent PD-1 expression that can limit immune-mediated clearance of pathogens or degenerated cells. Blocking PD-1 can enhance T cell function; in cancer treatment PD-1 blockade is already used as a successful therapy. However, the role of PD-1 expression and blocking in the context of acute and chronic infections is less defined. Building on its success in cancer therapy leads to the hypothesis that blocking PD-1 in infectious diseases is also beneficial in acute or chronic infections. This review will focus on the role of PD-1 expression in acute and chronic infections with virus, bacteria, and parasites, with a particular focus on recent studies regarding PD-1 blockade in infectious diseases.

Treating cancer with immunotherapy in HIV-positive patients: A challenging reality

Immunotherapy has widely changed the management of different malignancies. However, efficacy and safety of immune checkpoint inhibitors (ICIs) are not well established in people living with HIV (PLWH). Population of HIV-positive patients has deeply changed after the introduction of modern antiretroviral therapy (ART) and available data of immunotherapy in this subgroup are inadequate considering that cancer has become a leading cause of death and morbidity in this population. Moreover, there are many similarities between cancer and infectious antigen stimulation so that ICIs are even under evaluation as specific HIV treatment. Most of literature on this topic is based on small case series that suggest that immunotherapy for PLWH seems to be as effective as in HIV-negative population with a good safety profile. In this article we review literature on HIV and immunotherapy and we collect many case series available in different malignancies, with a brief focus on lung cancer.

Prediction of PD-L1 inhibition effects for HIV-infected individuals

The novel therapies with immune checkpoint inhibitors hold great promises for patients with chronic virus infections and cancers. This is based mainly on the partial reversal of the exhausted phenotype of antigen-specific cytotoxic CD8 T cells (CTL). Recently, we have shown that the restoration of HIV-specific T cell function depends on the HIV infection stage of an infected individual. Here we aimed to answer two fundamental questions: (i) Can one estimate growth parameters for the HIV-specific proliferative responsiveness upon PD-L1 blockade ex vivo? (ii) Can one use these parameter estimates to predict clinical benefit for HIV-infected individuals displaying diverse infection phenotypes? To answer these questions, we first analyzed HIV-1 Gag-specific CD8 T cell proliferation by time-resolved CFSE assays and estimated the effect of PD-L1 blockade on division and death rates, and specific precursor frequencies. These values were then incorporated into a model for CTL-mediated HIV control and the effects on CTL frequencies, viral loads and CD4 T cell counts were predicted for different infection phenotypes. The biggest absolute increase in CD4 T cell counts was in the group of slow progressors while the strongest reduction in virus loads was observed in progressor patients. These results suggest a significant clinical benefit only for a subgroup of HIV-infected individuals. However, as PD1 is a marker of lymphocyte activation and expressed on several lymphocyte subsets including also CD4 T cells and B cells, we subsequently examined the multiple effects of anti-PD-L1 blockade beyond those on CD8 T cells. This extended model then predicts that the net effect on HIV load and CD4 T cell number depends on the interplay between positive and negative effects of lymphocyte subset activation. For a physiologically relevant range of affected model parameters, PD-L1 blockade is likely to be overall beneficial for HIV-infected individuals.

Expression of costimulatory and inhibitory receptors in FoxP3+ regulatory T cells within the tumor microenvironment: Implications for combination immunotherapy approaches

The unprecedented success of immune checkpoint inhibitors has given rise to a rapidly growing number of immuno-oncology agents undergoing preclinical and clinical development and an exponential increase in possible combinations. Defining a clear rationale for combinations by identifying synergies between immunomodulatory pathways has therefore become a high priority. Immunosuppressive regulatory T cells (Tregs) within the tumor microenvironment (TME) represent a major roadblock to endogenous and therapeutic tumor immunity. However, Tregs are also essential for the maintenance of immunological self-tolerance, and share many molecular pathways with conventional T cells including cytotoxic T cells, the primary mediators of tumor immunity. Hence the inability to specifically target and neutralize Tregs within the TME of cancer patients without globally compromising self-tolerance poses a significant challenge. Here we review recent advances in the characterization of tumor-infiltrating Tregs with a focus on costimulatory and inhibitory receptors. We discuss receptor expression patterns, their functional role in Treg biology and mechanistic insights gained from targeting these receptors in preclinical models to evaluate their potential as clinical targets. We further outline a framework of parameters that could be used to refine the assessment of Tregs in cancer patients and increase their value as predictive biomarkers. Finally, we propose modalities to integrate our increasing knowledge on Treg phenotype and function for the rational design of checkpoint inhibitor-based combination therapies. Such combinations have great potential for synergy, as they could concomitantly enhance cytotoxic T cells and inhibit Tregs within the TME, thereby increasing the efficacy of current cancer immunotherapies.

GITR ligation enhances functionality of tumor-infiltrating T cells in hepatocellular carcinoma

No curative treatment options are available for advanced hepatocellular carcinoma (HCC). Anti-PD1 antibody therapy can induce tumor regression in 20% of advanced HCC patients, demonstrating that co-inhibitory immune checkpoint blockade has therapeutic potential for this type of cancer. However, whether agonistic targeting of co-stimulatory receptors might be able to stimulate anti-tumor immunity in HCC is as yet unknown. We investigated whether agonistic targeting of the co-stimulatory receptor GITR could reinvigorate ex vivo functional responses of tumor-infiltrating lymphocytes (TIL) freshly isolated from resected tumors of HCC patients. In addition, we compared GITR expression between TIL and paired samples of leukocytes isolated from blood and tumor-free liver tissues, and studied the effects of combined GITR and PD1 targeting on ex vivo TIL responses. In all three tissue compartments, CD4⁺ FoxP3⁺ regulatory T cells (Treg) showed higher GITR^- expression than effector T-cell subsets. The highest expression of GITR was found on CD4⁺ FoxP3^hi CD45RA^- activated Treg in tumors. Recombinant GITR-ligand as well as a humanized agonistic anti-GITR antibody enhanced ex vivo proliferative responses of CD4⁺ and CD8⁺ TIL to tumor antigens presented by mRNA-transfected autologous B-cell blasts, and also reinforced proliferation, IFN-γ secretion and granzyme B production in stimulations of TIL with CD3/CD28 antibodies. Combining GITR ligation with anti-PD1 antibody nivolumab further enhanced tumor antigen-specific responses of TIL in some, but not all, HCC patients, compared to either single treatment. In conclusion, agonistic targeting of GITR can enhance functionality of HCC TIL, and may therefore be a promising strategy for single or combinatorial immunotherapy in HCC.

Macrophage-Neisseria gonorrhoeae Interactions: A Better Understanding of Pathogen Mechanisms of Immunomodulation

Neisseria gonorrhoeae is a significant health problem worldwide due to multi-drug resistance issues and absence of an effective vaccine. Patients infected with N. gonorrhoeae have not shown a better immune response in successive infections. This might be explained by the fact that N. gonorrhoeae possesses several mechanisms to evade the innate and adaptative immune responses at different levels. Macrophages are a key cellular component in the innate immune response against microorganisms. The current information suggests that gonococcus can hijack the host response by mechanisms that involve the control of macrophages activity. In this mini review, we intend to condense the recent knowledge on the macrophage–N. gonorrhoeae interactions with a focus on strategies developed by gonococcus to evade or to exploit immune response to establish a successful infection. Finally, we discuss the opportunities and challenges of therapeutics for controlling immune manipulation by N. gonorrhoeae.

Cancer immunotherapy of patients with HIV infection

Cancer immunotherapy with antibodies against immune checkpoints has made impressive advances in the last several years. The most relevant drugs target programmed cell death 1 (PD-1) expressed on T cells or its ligand, the programmed cell death ligand 1 (PD-L1), expressed on cancer cells, and cytotoxic T lymphocyte-associated protein 4 (CTLA-4). Unfortunately, cancer patients with HIV infection are usually excluded from cancer clinical trials, because there are concerns about the safety and the anti-tumoral activity of these novel therapies in patients with HIV infection. Several retrospective studies and some case reports now support the notion that antibodies against immune checkpoints are safe and active in cancer patients with HIV infection, but prospective data in these patients are lacking. In addition, signs of antiviral activity with increase in CD4 T cell counts, plasma viremia reduction or decrease in the viral reservoir have been reported in some of the patients treated, although no patient achieved a complete clearance of the viral reservoir. Here we briefly summarize all clinical cases reported in the literature, as well as ongoing clinical trials testing novel immunotherapy drugs in cancer patients with HIV infection.

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

Though immune correlates for protection are still under investigation, potent cytotoxic T lymphocyte responses are desirable for an ideal HIV-1 vaccine. PD-1 blockade enhances SIV-specific CD8+ T cells. However, little information has been reported about how it affects the immunogenicity and protection of prophylactic SIV vaccines in nonhuman primates. Here, we show that PD-1 blockade during vaccination substantially improved protective efficacy in SIV challenged macaques. The PD-1 pathway was blocked using a monoclonal antibody specific to human PD-1. Administration of this antibody effectively augmented and sustained vaccine-induced SIV-specific T cell responses for more than 42 weeks after first immunization in rhesus monkeys, as compared with SIV vaccination only. Importantly, after intrarectally repeated low-dosage challenge with highly pathogenic SIVmac239, monkeys with PD-1 blockade during vaccination achieved full protection against incremental viral doses of up to 50,000 TICD₅₀. These findings highlight the importance of PD-1 blockade during vaccination for the development of HIV vaccines.

Peptide-based and small synthetic molecule inhibitors on PD-1/PD-L1 pathway: A new choice for immunotherapy?

Blockade the interaction of the programmed cell death protein 1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1) can prevent immune evasion of tumor cells and significantly prolong the survival of cancer patients. Currently marketed drugs targeting PD-1/PD-L1 pathway are all monoclonal antibodies (mAbs) that have achieved great success in clinical trials. With the constantly emerging problems of antibody drugs, small molecule inhibitors have attracted the attention of pharmaceutical chemists due to their controllable pharmacological and pharmacokinetic properties, which make them potential alternatives or supplements to mAbs to regulate PD-1/PD-L1 pathway. However, the insufficient target structure information hinders the development of small molecule inhibitors. Since the publication of human-PD-1/human-PD-L1 (hPD-1/hPD-L1) crystal structure, more and more cocrystal structures of mAbs, cyclopeptides and small molecules with PD-1 and PD-L1 have been resolved. These complexes provide a valuable starting point for the rational design of peptide-based and small synthetic molecule inhibitors. Here we reviewed the non-antibody inhibitors that have been published so far and analyzed their structure-activity relationships (SAR). We also summarized the cocrystal structures with hot spots identified, with the aim to provide reference for future drug discovery.

Plasmodium vivax Infection Impairs Regulatory T-Cell Suppressive Function During Acute Malaria

The balance between pro- and antiinflammatory mechanisms is essential to limit immune-mediated pathology, and CD4+ forkhead box P3 (Foxp3+) regulatory T cells (Treg) play an important role in this process. The expression of inhibitory receptors regulates cytokine production by Plasmodium vivax-specific T cells. Our goal was to assess the induction of programmed death-1 (PD-1) and cytotoxic T-lymphocyte antigen (CTLA-4) on Treg during malaria and to evaluate their function. We found that P. vivax infection triggered an increase in circulating Treg and their expression of CTLA-4 and PD-1. Functional analysis demonstrated that Treg from malaria patients had impaired suppressive ability and PD-1+Treg displayed lower levels of Foxp3 and Helios, but had higher frequencies of T-box transcription factor+ and interferon-gamma+ cells than PD-1-Treg. Thus malaria infection alters the function of circulating Treg by triggering increased expression of PD-1 on Treg that is associated with decreased regulatory function and increased proinflammatory characteristics.

Interplay between reaction and diffusion processes in governing the dynamics of virus infections

Spreading of viral infection in the tissues such as lymph nodes or spleen depends on virus multiplication in the host cells, their transport and on the immune response. Reaction-diffusion systems of equations with delays in cell proliferation and death by apoptosis represent an appropriate model to study this process. The properties of the cells of the immune system and the initial viral load determine the spatiotemporal regimes of infection spreading. Infection can be completely eliminated or it can persist at some level together with a certain chronic immune response in a spatially uniform or oscillatory mode. Finally, the immune cells can be completely exhausted leading to a high viral load persistence in the tissue. It has been found experimentally, that virus proteins can affect the immune cell migration. Our study shows that both the motility of immune cells and the virus infection spreading represented by the diffusion rate coefficients are relevant control parameters determining the fate of virus-host interaction.

Tristetraprolin Overexpression in Gastric Cancer Cells Suppresses PD-L1 Expression and Inhibits Tumor Progression by Enhancing Antitumor Immunity

The RNA-binding protein tristetraprolin (TTP) binds to adenosine-uridine AU-rich elements in the 3'-untranslated region of messenger RNAs and facilitates rapid degradation of the target mRNAs. Therefore, it regulates the expression of multiple cancer and immunity-associated transcripts. Furthermore, a lack of TTP in cancer cells influences cancer progression and predicts poor survival. Although the functions of TTP on cancer cells have previously been researched, the mechanism of TTP on the interaction between cancer cells with their microenvironment remains undiscovered. In this study, we admed to determine the role of cancer cell TTP during the interaction between tumor and immune cells, specifically regulatory T cells (Tregs). We evaluate the capability of TTP to modulate the antitumor immunity of GC and explored the underlying mechanism. The overexpression of TTP in GC cells dramatically increased peripheral blood mononuclear lymphocyte (PBML) -mediated cytotoxicity against GC cells. Increased cytotoxicity against TTP-overexpressed GC cells by PBMLs was determined by Treg development and infiltration. Surprisingly, we found the stabilization of programmed death-ligand 1 (PD-L1) mRNA was declining while TTP was elevated. The PD-L1 protein level was reduced in TTP-abundant GC cells. PD-L1 gas been found to play a pivotal role in Treg development and functional maintenance in immune system. Taken together, our results suggest the overexpression of TTP in GC cells not only affects cell survival and apoptosis but also increases PBMLs -mediated cytotoxicity against GC cells to decelerate tumor progression. Moreover, we identified PD-L1 as a critical TTP-regulated factor that contributes to inhibiting antitumor immunity.

Overexpression of programmed cell death-1 and human leucocyte antigen-DR on circulatory regulatory T cells in out-of-hospital cardiac arrest patients in the early period after return of spontaneous circulation

AIM

Whether regulatory T cells (Tregs) are involved in immune disorders of out-of-hospital cardiac arrest (OHCA) patients after return of spontaneous circulation (ROSC) is still unknown. We aimed to observe the expression of circulatory Tregs in OHCA patients and investigate programmed cell death-1 (PD-1) and human leucocyte antigen-DR (HLA-DR) on Tregs to evaluate the induction and activity of Tregs.

METHODS

Sixty-seven consecutive OHCA patients who recovered from spontaneous circulation over 12 h were enrolled. Clinical and 28-day outcome data were collected. Peripheral blood samples collected on days 1 and 3 after ROSC were analysed to evaluate PD-1 and HLA-DR expression on Tregs. Fifty healthy individuals were enrolled as healthy controls.

RESULTS

Compared with those in healthy individuals, circulatory Treg counts significantly decreased without changes of Treg/cluster-of-differentiation (CD)4+ lymphocyte ratios on day 1 after ROSC, and the percentage of PD-1+ Tregs and HLA-DR+ Tregs significantly rose. On day 3, Treg/CD4+ lymphocyte ratios rose with persistently low Treg counts, and the expression of PD-1 and HLA-DR on Tregs was not different from that on day 1. On day 1, both circulatory Treg counts and Treg/CD4+ lymphocyte ratios in non-survivors were lower than those in survivors, and Treg/CD4+ lymphocyte ratios increased in non-survivors on day 3. No significant difference of PD-1 and HLA-DR expression on Tregs was found between survivors and non-survivors on day 1.

CONCLUSIONS

After ROSC, despite decreased circulatory Treg counts, a relative increase of Treg percentage and enhanced activity of Tregs are involved in early immune regulation of OHCA patients.

The Significance of Tumor Necrosis Factor Receptor Type II in CD8+ Regulatory T Cells and CD8+ Effector T Cells

Tumor necrosis factor (TNF) is a pleiotropic cytokine that has both pro-inflammatory and anti-inflammatory functions. The biological functions of TNF are mediated by two receptors, TNF receptor type I (TNFR1) and TNF receptor type II (TNFR2). TNFR1 is expressed universally on almost all cell types and has been extensively studied, whereas TNFR2 is mainly restricted to immune cells and some tumor cells and its role is far from clarified. Studies have shown that TNFR2 mediates the stimulatory activity of TNF on CD4⁺Foxp3⁺ regulatory T cells (Tregs) and CD8⁺Foxp3⁺ Tregs, and is involved in the phenotypic stability, proliferation, activation, and suppressive activity of Tregs. TNFR2 can also be expressed on CD8⁺ effector T cells (Teffs), which delivers an activation signal and cytotoxic ability to CD8⁺ Teffs during the early immune response, as well as an apoptosis signal to terminate the immune response. TNFR2-induced abolition of TNF receptor-associated factor 2 (TRAF2) degradation may play an important role in these processes. Consequently, due to the distribution of TNFR2 and its pleiotropic effects, TNFR2 appears to be critical to keeping the balance between Tregs and Teffs, and may be an efficient therapeutic target for tumor and autoimmune diseases. In this review, we summarize the biological functions of TNFR2 expressed on CD8⁺Foxp3⁺ Tregs and CD8⁺ Teffs, and highlight how TNF uses TNFR2 to coordinate the complex events that ultimately lead to efficient CD8⁺ T cell-mediated immune responses.

Blockade of TNFR2 signaling enhances the immunotherapeutic effect of CpG ODN in a mouse model of colon cancer

Through the tumor necrosis factor (TNF) receptor type II (TNFR2), TNF preferentially activates, expands, and promotes the phenotypic stability of CD4⁺Foxp3⁺ regulatory T (T_reg) cells. Those T_reg cells that have a high abundance of TNFR2 have the maximal immunosuppressive capacity. We investigated whether targeting TNFR2 could effectively suppress the activity of T_reg cells and consequently enhance the efficacy of cancer immunotherapy. We found that, relative to a suboptimal dose of the immunostimulatory Toll-like receptor 9 ligand CpG oligodeoxynucleotide (ODN), the combination of the suboptimal dose of CpG ODN with the TNFR2-blocking antibody M861 more markedly inhibited the growth of subcutaneously grafted mouse CT26 colon tumor cells. This resulted in markedly fewer TNFR2⁺ T_reg cells and more interferon-γ-positive (IFN-γ⁺) CD8⁺ cytotoxic T lymphocytes infiltrating the tumor and improved long-term tumor-free survival in the mouse cohort. Tumor-free mice were resistant to rechallenge by the same but not unrelated (4T1 breast cancer) cells. Treatment with the combination of TNFR2-blocking antibody and a CD25-targeted antibody also resulted in enhanced inhibition of tumor growth in a syngeneic 4T1 mouse model of breast cancer. Thus, the combination of a TNFR2 inhibitor and an immunotherapeutic stimulant may represent a more effective treatment strategy for various cancers.

Increased Expression of Programmed Cell Death-1 in Regulatory T Cells of Patients with Severe Sepsis and Septic Shock: An Observational Clinical Study

While regulatory T cells (Tregs) constitutively express programmed cell death-1 (PD-1), the role of PD-1 expression in Tregs of patients with sepsis remains unclear. Thus, we determined PD-1 expression in Tregs from the peripheral blood of patients with severe sepsis and septic shock. Seventy-eight patients with severe sepsis and 40 with septic shock, as well as 21 healthy subjects, were enrolled in this study. The percentage of peripheral blood PD-1⁺ Tregs, as well as absolute Treg counts, were compared between these three groups. PD-1 expression in Tregs and absolute Treg counts were also compared between survivors and non-survivors in patients with sepsis. PD-1 expression in Tregs increased in patients with sepsis compared to healthy controls. Conversely, absolute Treg counts were significantly decreased in patients with sepsis compared to healthy controls; patients with septic shock had the lowest absolute Treg counts. Among patients with sepsis, survivors had lower levels of PD-1 expression in Tregs, as well as higher absolute Treg counts, than non-survivors. Additionally, the percentage of PD-1⁺ Tregs correlated positively with lactate levels as well as the Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment scores in patients with sepsis. PD-1 was upregulated in Tregs of patients with sepsis and may indicate a state of immune dysfunction. Overexpression of PD-1 in Tregs was associated with more severe sepsis as well as poor outcomes.

Cell and gene therapy strategies to eradicate HIV reservoirs

PURPOSE OF REVIEW

Highly active antiretroviral treatment has dramatically improved the prognosis for people living with HIV by preventing AIDS-related morbidity and mortality through profound suppression of viral replication. However, a long-lived viral reservoir persists in latently infected cells that harbor replication-competent HIV genomes. If therapy is discontinued, latently infected memory cells inevitably reactivate and produce infectious virus, resulting in viral rebound. The reservoir is the biggest obstacle to a cure of HIV.

RECENT FINDINGS

This review summarizes significant advances of the past year in the development of cellular and gene therapies for HIV cure. In particular, we highlight work done on suppression or disruption of HIV coreceptors, vectored delivery of antibodies and antibody-like molecules, T-cell therapies and HIV genome disruption.

SUMMARY

Several recent advancements in cellular and gene therapies have emerged at the forefront of HIV cure research, potentially having broad implications for the future of HIV treatment.

Immunological strategies to target HIV persistence

PURPOSE OF REVIEW

The purpose of this article is to review recent advances in immunotherapeutic approaches aiming at reducing the latent HIV reservoir.

RECENT FINDINGS

HIV-1 establishes early during infection a pool of latently infected cells that persist long term and are largely undetectable to the immune system. Highly active antiretroviral therapy has dramatically improved the life expectancy and life quality of HIV-1-infected individuals, but is incapable of eliminating the pool of latently HIV-1-infected cells. Recent studies have started to test immunotherapeutic interventions in combination with latency reversing agents to reduce the latent HIV-1 reservoir, including approaches aimed at enhancing antiviral T-cell immunity, innate immunity, and virus-specific antibodies.

SUMMARY

The better understanding of virus-specific immunity and the pathways used by HIV-1 to evade host immune responses have enabled the development of new strategies focusing on targeting latently HIV-1-infected cells, with the goal to reduce the HIV-1 reservoir. Here, we will review recent advances in harnessing effector cells of the immune system, including CD8 T cells and natural killer cells, antiviral antibodies and new immunomodulatory molecules, to target HIV-1 persistence.

CD8 T-cell regulation by T regulatory cells and the programmed cell death protein 1 pathway

The primary function of the immune system is to protect the host from infectious microorganisms and cancers. However, a major component of the immune response involves the direct elimination of cells in the body and the induction of systemic inflammation, which may result in life-threatening immunopathology. Therefore, the immune system has developed complex mechanisms to regulate itself with a specialized subset of CD4 T lymphocytes (referred to as regulatory T cells) and immune checkpoint pathways, such as the programmed cell death protein 1 pathway. These immune regulatory mechanisms can be exploited by pathogens and tumours to establish persistence in the host, warranting a deeper understanding of how to fine-tune immune responses during these chronic diseases. Here, I discuss various features of immune regulatory pathways and what important aspects must be considered in the next generation of therapies to reverse immune exhaustion, understanding that this process is a natural mechanism to prevent the host from destroying itself.

Anti-PD-1/PD-L1 therapy for infectious diseases: learning from the cancer paradigm

OBJECTIVES

Immune checkpoint pathways regulate optimal host immune responses against transformed cells, induce immunological memory, and limit tissue pathology. Conversely, aberrant immune checkpoint activity signifies a poor prognosis in cancer and infectious diseases. Host-directed therapy (HDT) via immune checkpoint blockade has revolutionized cancer treatment with therapeutic implications for chronic infections, thus laying the foundation for this review.

METHODS

Online literature searches were performed via PubMed, PubMed Central, and Google using the keywords "immune checkpoint inhibition"; "host-directed therapy"; "T cell exhaustion"; "cancer immunotherapy"; "anti-PD-1 therapy"; "anti-PD-L1 therapy"; "chronic infections"; "antigen-specific cells"; "tuberculosis"; "malaria"; "viral infections"; "human immunodeficiency virus"; "hepatitis B virus"; "hepatitis C virus"; "cytomegalovirus" and "Epstein-Barr virus". Search results were filtered based on relevance to the topics covered in this review.

RESULTS

The use of monoclonal antibodies directed against the antigen-experienced T-cell marker programmed cell death 1 (PD-1) and its ligand PD-L1 in the context of chronic infectious diseases is reviewed. The potential pitfalls and precautions, based on clinical experience from treating patients with cancer with PD-1/PD-L1 pathway inhibitors, are also described.

CONCLUSIONS

Anti-PD-1/PD-L1 therapy holds promise as adjunctive therapy for chronic infectious diseases such as tuberculosis and HIV, and must therefore be tested in randomized clinical trials.

Perturbed CD8+ T cell TIGIT/CD226/PVR axis despite early initiation of antiretroviral treatment in HIV infected individuals

HIV-specific CD8⁺ T cells demonstrate an exhausted phenotype associated with increased expression of inhibitory receptors, decreased functional capacity, and a skewed transcriptional profile, which are only partially restored by antiretroviral treatment (ART). Expression levels of the inhibitory receptor, T cell immunoglobulin and ITIM domain (TIGIT), the co-stimulatory receptor CD226 and their ligand PVR are altered in viral infections and cancer. However, the extent to which the TIGIT/CD226/PVR-axis is affected by HIV-infection has not been characterized. Here, we report that TIGIT expression increased over time despite early initiation of ART. HIV-specific CD8⁺ T cells were almost exclusively TIGIT⁺, had an inverse expression of the transcription factors T-bet and Eomes and co-expressed PD-1, CD160 and 2B4. HIV-specific TIGIT^hi cells were negatively correlated with polyfunctionality and displayed a diminished expression of CD226. Furthermore, expression of PVR was increased on CD4⁺ T cells, especially T follicular helper (Tfh) cells, in HIV-infected lymph nodes. These results depict a skewing of the TIGIT/CD226 axis from CD226 co-stimulation towards TIGIT-mediated inhibition of CD8⁺ T cells, despite early ART. These findings highlight the importance of the TIGIT/CD226/PVR axis as an immune checkpoint barrier that could hinder future “cure” strategies requiring potent HIV-specific CD8⁺ T cells.

Subset- and Antigen-Specific Effects of Treg on CD8+ T Cell Responses in Chronic HIV Infection

We, and others, have reported that in the HIV-negative settings, regulatory CD4+CD25highFoxP3+ T cells (Treg) exert differential effects on CD8 subsets, and maintain the memory / effector CD8+ T cells balance, at least in part through the PD-1/PD-L1 pathway. Here we investigated Treg-mediated effects on CD8 responses in chronic HIV infection. As compared to Treg from HIV negative controls (Treg/HIV-), we show that Treg from HIV infected patients (Treg/HIV+) did not significantly inhibit polyclonal autologous CD8+ T cell function indicating either a defect in the suppressive capacity of Treg/HIV+ or a lack of sensitivity of effector T cells in HIV infection. Results showed that Treg/HIV+ inhibited significantly the IFN-γ expression of autologous CD8+ T cells stimulated with recall CMV/EBV/Flu (CEF) antigens, but did not inhibit HIV-Gag-specific CD8+ T cells. In cross-over cultures, we show that Treg/HIV- inhibited significantly the differentiation of either CEF- or Gag-specific CD8+ T cells from HIV infected patients. The expression of PD-1 and PD-L1 was higher on Gag-specific CD8+ T cells as compared to CEF-specific CD8+ T cells, and the expression of these markers did not change significantly after Treg depletion or co-culture with Treg/HIV-, unlike on CEF-specific CD8+ T cells. In summary, we show a defect of Treg/HIV+ in modulating both the differentiation and the expression of PD-1/PD-L1 molecules on HIV-specific CD8 T cells. Our results strongly suggest that this particular defect of Treg might contribute to the exhaustion of HIV-specific T cell responses.