PD-1 Upregulation Is Associated with Exhaustion of Regulatory T Cells and Reflects Immune Activation in HIV-1-Infected Individuals

The Complex Dysregulations of CD4 T Cell Subtypes in HIV Infection

Human immunodeficiency virus (HIV) infection remains an important global public health problem. About 40 million people are infected with HIV, and this infection caused about 630,000 deaths in 2022. The hallmark of HIV infection is the depletion of CD4+ T helper lymphocytes (Th cells). There are at least seven different Th subtypes, and not all are the main targets of HIV. Moreover, the effect of the virus in a specific subtype can be completely different from that of the others. Although the most compromised Th subtype in HIV infection is Th17, HIV can induce important dysregulations in other subtypes, such as follicular Th (Tfh) cells and regulatory Th cells (Treg cells or Tregs). Several studies have shown that HIV can induce an increase in the immunosuppressive activity of Tregs without causing a significant reduction in their numbers, at least in the early phase of infection. The increased activity of this Th subtype seems to play an important role in determining the immunodeficiency status of HIV-infected patients, and Tregs may represent a new target for innovative anti-HIV therapies, including the so-called "Kick and Kill" therapeutic method whose goal is the complete elimination of the virus and the healing of HIV infection. In this review, we report the most important findings on the effects of HIV on different CD4+ T cell subtypes, the molecular mechanisms by which the virus impairs the functions of these cells, and the implications for new anti-HIV therapeutic strategies.

Novel Strategies in Transplantation: Genetic Engineering and Vascularized Composite Allotransplantation

INTRODUCTION

Despite the clinical success in vascularized composite allotransplantation (VCA), systemic immunosuppression remains necessary to prevent allograft rejection. Even with potent immunosuppressive regimens (tacrolimus, mycophenolate mofetil, and steroids), most patients experience several rejection episodes, often within the same year. The risk of systemic side effects must constantly be weighed against the risk of under-immunosuppression and, thus, acute and chronic rejection. In this context, genomic editing has emerged as a potential tool to minimize the need for toxic immunosuppressive regimens and has gained attention in the fields of solid organ transplantation and xenotransplantation. This strategy may also be relevant for the future of VCA.

METHODS

We discuss the topic of genetic engineering and review recent developments in this field that justify investigating tools such as clustered regularly interspaced short palindromic repeats/Cas9 in the context of VCA.

RESULTS

We propose specific strategies for VCA based on the most recent gene expression data. This includes the well-known strategy of tolerance induction. Specifically, targeting the interaction between antigen-presenting cells and recipient-derived T cells by CD40 knockout may be effective. The novelty for VCA is a discovery that donor-derived T lymphocytes may play a special role in allograft rejection of facial transplants. We suggest targeting these cells prior to transplantation (e.g., by ex vivo perfusion of the transplant) by knocking out genes necessary for the long-term persistence of donor-derived immune cells in the allograft.

CONCLUSION

Despite the demonstrated feasibility of VCA in recent years, continued improvements to immunomodulatory strategies using tools like clustered regularly interspaced short palindromic repeats/Cas9 could lead to the development of approaches that mitigate the limitations associated with rejection of this life-giving procedure.

Circulating (1 → 3)-β-D-Glucan as an immune activation marker decreased after ART in people living with HIV

Background

Plasma level of polysaccharide (1 → 3)-β-D-Glucan (βDG), as a diagnostic marker of invasive fungal infection has been reported to be elevated in people living with HIV (PLWH). We assessed the association of circulating βDG to inflammation and systemic immune activation and the effect of antiretroviral therapy (ART) on βDG in PLWH.

Method

Plasma and peripheral blood monocular cell samples from 120 PLWH naive to ART and after 1 year's ART were collected. Plasma levels of βDG, markers of bacterial translocation, gut damage, and cellular immune activation were quantified.

Result

The plasma βDG levels were negatively correlated with CD4+ T cells count (r = -0.25, p = 0.005) and positively with HIV viral load (r = 0.28, p = 0.002) before ART. It was also positively correlated with immune activation markers, including PD-1 expression on CD4+ T cell (r = 0.40, p = 0.01) and CD8+ T cell (r = 0.47, p = 0.002), as well as HLADR+CD38+ co-expression on CD8+ T cell (r = 0.56, p = 0.0002), but not with the plasma levels of LPS (r = 0.02, p = 0.84), LPS binding protein (LBP, r = 0.11, p = 0.36), soluble LPS receptor sCD14 (r = 0.04, p = 0.68), intestinal fatty acid binding protein (IFABP, r = -0.12, p = 0.18), and regenerating islet-derived protein 3α (REG3α, r = 0.18, p = 0.06). After 1 year's ART, the levels of βDG were significantly decreased compared to that in pre-ART (1.31 ± 0.24 Log10 pg/ml vs. 1.39 ± 0.18 Log10 pg/ml, p < 0.001).

Conclusion

The level of plasma βDG was associated with cellular immune activation and decreased after ART in PLWH, suggesting it could serve as a biomarker of immune activation and efficacy monitoring.

Emerging strategies for treating autoimmune disorders with genetically modified Treg cells

Gene editing of living cells is a cornerstone of present-day medical research that has enabled scientists to address fundamental biologic questions and identify novel strategies to treat diseases. The ability to manipulate adoptive cell therapy products has revolutionized cancer immunotherapy and promises similar results for the treatment of autoimmune diseases, inflammatory disorders, and transplant rejection. Clinical trials have recently deemed polyclonal regulatory T (Treg) cell therapy to be a safe therapeutic option, but questions remain regarding the efficacy of this approach. In this review, we discuss how gene editing technologies are being applied to transform the future of Treg cell therapy, focusing on the preclinical strategies that are currently being investigated to enhance the efficacy, function, and survival of human Treg cells. We explore approaches that may be used to generate immunoregulatory cells ex vivo, detail emerging strategies that are being used to modify these cells (such as using chimeric antigen receptors to confer antigen specificity), and outline concepts that have been explored to repurpose conventional T cells to target and destroy autoreactive and alloreactive lymphocytes. We also describe the key hurdles that currently hinder the clinical adoption of Treg cell therapy and propose potential future avenues of research for this field.

Dynamics and epigenetic signature of regulatory T-cells following antiretroviral therapy initiation in acute HIV infection

BACKGROUND

HIV infection promotes the expansion of immunosuppressive regulatory T-cells (Tregs), contributing to immune dysfunction, tissue fibrosis and disease progression. Early antiretroviral treatment (ART) upon HIV infection improves CD4 count and decreases immune activation. However, Treg dynamics and their epigenetic regulation following early ART initiation remain understudied.

METHODS

Treg subsets were characterized by flow cytometry in 103 individuals, including untreated HIV-infected participants in acute and chronic phases, ART-treated in early infection, elite controllers (ECs), immunological controllers (ICs), and HIV-uninfected controls. The methylation status of six regulatory regions of the foxp3 gene was assessed using MiSeq technology.

FINDINGS

Total Treg frequency increased overtime during HIV infection, which was normalized in early ART recipients. Tregs in untreated individuals expressed higher levels of activation and immunosuppressive markers (CD39, and LAP(TGF-β1)), which remained unchanged following early ART. Expression of gut migration markers (CCR9, Integrin-β7) by Tregs was elevated during untreated HIV infection, while they declined with the duration of ART but not upon early ART initiation. Notably, gut-homing Tregs expressing LAP(TGF-β1) and CD39 remained higher despite early treatment. Additionally, the increase in LAP(TGF-β1)⁺ Tregs overtime were consistent with higher demethylation of conserved non-coding sequence (CNS)-1 in the foxp3 gene. Remarkably, LAP(TGF-β1)-expressing Tregs in ECs were significantly higher than in uninfected subjects, while the markers of Treg activation and gut migration were not different.

INTERPRETATION

Early ART initiation was unable to control the levels of immunosuppressive Treg subsets and their gut migration potential, which could ultimately contribute to gut tissue fibrosis and HIV disease progression.

FUNDING

This study was funded by the Canadian Institutes of Health Research (CIHR, grant MOP 142294) and in part by the AIDS and Infectious Diseases Network of the Réseau SIDA et maladies infectieuses du Fonds de recherche du Québec-Santé (FRQ-S).

Oral immune dysfunction is associated with the expansion of FOXP3+PD-1+Amphiregulin+ T cells during HIV infection

Residual systemic inflammation and mucosal immune dysfunction persist in people living with HIV, despite treatment with combined anti-retroviral therapy, but the underlying immune mechanisms are poorly understood. Here we report that the altered immune landscape of the oral mucosa of HIV-positive patients on therapy involves increased TLR and inflammasome signaling, localized CD4+ T cell hyperactivation, and, counterintuitively, enrichment of FOXP3+ T cells. HIV infection of oral tonsil cultures in vitro causes an increase in FOXP3+ T cells expressing PD-1, IFN-γ, Amphiregulin and IL-10. These cells persist even in the presence of anti-retroviral drugs, and further expand when stimulated by TLR2 ligands and IL-1β. Mechanistically, IL-1β upregulates PD-1 expression via AKT signaling, and PD-1 stabilizes FOXP3 and Amphiregulin through a mechanism involving asparaginyl endopeptidase, resulting in FOXP3+ cells that are incapable of suppressing CD4+ T cells in vitro. The FOXP3+ T cells that are abundant in HIV-positive patients are phenotypically similar to the in vitro cultured, HIV-responsive FOXP3+ T cells, and their presence strongly correlates with CD4+ T cell hyper-activation. This suggests that FOXP3+ T cell dysregulation might play a role in the mucosal immune dysfunction of HIV patients on therapy.

Prostaglandin I2 signaling licenses Treg suppressive function and prevents pathogenic reprogramming

Tregs restrain both the innate and adaptive immune systems to maintain homeostasis. Allergic airway inflammation, characterized by a Th2 response that results from a breakdown of tolerance to innocuous environmental antigens, is negatively regulated by Tregs. We previously reported that prostaglandin I2 (PGI2) promoted immune tolerance in models of allergic inflammation; however, the effect of PGI2 on Treg function was not investigated. Tregs from mice deficient in the PGI2 receptor IP (IP KO) had impaired suppressive capabilities during allergic airway inflammatory responses compared with mice in which PGI2 signaling was intact. IP KO Tregs had significantly enhanced expression of immunoglobulin-like transcript 3 (ILT3) compared with WT Tregs, which may contribute to the impairment of the IP KO Treg's ability to suppress Th2 responses. Using fate-mapping mice, we reported that PGI2 signaling prevents Treg reprogramming toward a pathogenic phenotype. PGI2 analogs promoted the differentiation of naive T cells to Tregs in both mice and humans via repression of β-catenin signaling. Finally, a missense variant in IP in humans was strongly associated with chronic obstructive asthma. Together, these data support that PGI2 signaling licenses Treg suppressive function and that PGI2 is a therapeutic target for enhancing Treg function.

Emerging patterns of regulatory T cell function in tuberculosis

Tuberculosis (TB) is one of the top 10 causes of mortality worldwide from a single infectious agent and has significant implications for global health. A major hurdle in the development of effective TB vaccines and therapies is the absence of defined immune‐correlates of protection. In this context, the role of regulatory T cells (T_reg), which are essential for maintaining immune homeostasis, is even less understood. This review aims to address this knowledge gap by providing an overview of the emerging patterns of T_reg function in TB. Increasing evidence from studies, both in animal models of infection and TB patients, points to the fact the role of T_regs in TB is dependent on disease stage. While T_regs might expand and delay the appearance of protective responses in the early stages of infection, their role in the chronic phase perhaps is to counter‐regulate excessive inflammation. New data highlight that this important homeostatic role of T_regs in the chronic phase of TB may be compromised by the expansion of activated human leucocyte antigen D‐related (HLA‐DR)⁺CD4⁺ suppression‐resistant effector T cells. This review provides a comprehensive and critical analysis of the key features of T_reg cells in TB; highlights the importance of a balanced immune response as being important in TB and discusses the importance of probing not just T_reg frequency but also qualitative aspects of T_reg function as part of a comprehensive search for novel TB treatments.

Programmed death-1 expression and regulatory T cells increase in the Intestinal mucosa of cytomegalovirus colitis in patients with HIV/AIDS

BACKGROUND

Cytomegalovirus (CMV) is among the most common opportunistic infections identified in patients with HIV/AIDS. CMV often targets the colon in such patients. However, the role of regulatory T cells (T_regs) and Programmed death-1 (PD-1) in intestinal CMV infection is unclear. In this study, we evaluate the expression of programmed death -1 (PD-1) and its association with regulatory T cells (T_regs) in patients with HIV/AIDS having CMV colitis.

METHODS

CMV was detected in the intestinal mucosal biopsy samples via nucleic acid in situ hybridization. PD-1, CD4, CD8, and T_reg-specific marker as well as the winged-helix transcription factor and forkhead box P3 (FoxP3) were detected by immunohistochemical methods.

RESULTS

Intestinal CMV diease was identified in 20 out of 195 patients with HIV/AIDS enrolled in our study. CMV was diagnosed microscopically by the presence of giant cell inclusion bodies in epithelial cells, histiocytes, and fibroblasts. Levels of immunoreactive PD-1 detected in mucosal biopsies from patients with HIV/AIDS having CMV colitis were significantly higher than CMV-negative control group (p = 0.023). FoxP3⁺ cells were detected in the CMV colitis group slight more than that in the control group. CD4⁺ T lymphocyte counts in the peripheral blood and intestinal mucosal biopsies from CMV colitis group were all notably decreased compared with those with control group (p < 0.001 for both). PD-1 had a significant negative correlation with CD4 counts in intestinal mucosa (p = 0.016). CD8⁺T lymphocyte counts in peripheral blood and intestinal mucosa were slightly lower than those in the control group, although the differences were not statistically significant.

CONCLUSIONS

CMV colitis with HIV/AIDS is associated with significant changes in T lymphocyte populations. These findings may have important implications for disease pathogenesis and progression.