Immune-related adverse events in various organs caused by immune checkpoint inhibitors

Current cancer immunotherapies target immune checkpoint molecules such as the inhibitory receptor programmed cell death-1 (PD-1), one of its ligands, programmed cell death ligand-1 (PD-L1), and cytotoxic T-lymphocyte antigen 4 (CTLA-4), a competitive ligand for CD28 binding to stimulatory receptors CD80 and CD86. Multiple biological drugs use monoclonal antibodies targeting PD-1, PD-L1 and CTLA-4 as cancer immunotherapies. These are termed immune checkpoint inhibitors (ICIs). However, activation of the immune system by ICIs can induce the development of immune-related adverse events (irAEs), which can affect multiple organ systems. The most frequent irAEs are cutaneous and mimic various types of spontaneous skin disorders. Most irAEs are classified as autoimmune conditions mediated by ICI-activated CD8⁺ cytotoxic T cells, some of which are also related to activated B cells and production of pathogenic antibodies. Interestingly, blockade of CTLA-4 mainly induces activation of T cells and inhibition of T_reg cells. On the other hand, the mechanisms underlying anti-PD-1/PD-L1 ICI-induced irAEs are more complicated. PD-1 is a receptor expressed on T and B cells, which binds not only PD-L1, but also PD-L2. The role of PD-L1 is dominant in Th1 and Th17 immunity, while PD-L2 works mainly in Th2 immunity. Better understanding of the mechanisms underlying irAEs will allow for better management of irAEs and improve outcomes and quality of life in cancer patients.     

Increased frequency of CD4+PD-1+HLA-DR+ T cells is associated with disease progression in CLL

Chronic lymphocytic leukaemia (CLL) patients often have abnormal expansions of CD4⁺ and CD8⁺ T cells and this can be associated with progressive disease. To characterise the key T-cell populations involved in this phenomenon, we used flow cytometry and 11 phenotypic markers to study 74 CLL patients and 14 controls. T cells of CLL patients were more phenotypically complex than those of healthy controls with significant increases in the frequencies of CD4 and CD8 memory T cells expressing exhaustion-, activation- and senescence-associated markers. Multivariate analysis of 111 different T-cell subsets showed that high frequencies of four subsets (three CD8 and one CD4) were associated with shorter progression-free survival. The most significant association was with CD4⁺HLA-DR⁺PD-1⁺ T cells, and patients could be stratified into high- and low-risk groups based on the frequency of these T cells. The expansion of this CD4⁺ subset could not be accounted for by age, cytomegalovirus infection or increases in Treg cells. Overall, these results highlight two relatively simple biomarkers, percentage CD8⁺ and percentage CD4⁺PD-1⁺HLA-DR⁺ T cells, which can be used to risk-stratify CLL patients, independent of other tumour-associated markers. They also provide further evidence for the pivotal role of T cells in modulating the pathology of CLL.     

B7-H1 expression is associated with expansion of regulatory T cells in colorectal carcinoma

AIM: To investigate the expression of B7-H1 in human colorectal carcinoma (CRC) to define its regulating effects on T cells in tumor microenvironment.METHODS: One hundred and two paraffin blocks and 33 fresh samples of CRC tissues were subject to this study. Immunohistochemistry was performed for B7-H1 and CD3 staining in CRC tissues. Ficoll-Hypaque density gradient centrifugation was used to isolate peripheral blood mononuclear cells of fresh CRC tissues; flow cytometry and immunofluorescence staining were used for detection of regulatory T cells. Data was analyzed with statistical software.RESULTS: Costimulatory molecule B7-H1 was found strongly expressed in CRC tissues, localized in tumor cell membrane and cytoplasm, while weak or none expression of B7-H1 was detected in pared normal colorectal tissues. Meanwhile, CD3 positive T cells were found congregated in CRC tumor nest and stroma. Statistic analysis showed that B7-H1 expression level was negatively correlated to the total T cell density in tumor nest (P < 0.0001) and tumor stroma (P = 0.0200) of 102 cases of CRC tissues. Among the total T cells, a variable amount of regulatory T cells with a clear Foxp3⁺ (forkhead box P3) staining could be detected in CRC tissues and patients’ blood. Interestingly, in the 33 samples (15 cases of B7-H1^high CRC tissues and 18 cases of B7-H1^low CRC tissues) of freshly isolated mononuclear cells from CRC tissues, the percentages of CD4⁺Foxp3⁺ and CD8⁺Foxp3⁺ regulatory T cells were found remarkably higher in B7-H1^high CRC tissues than in B7-H1^low CRC tissues (P = 0.0024, P = 0.0182), indicating that B7-H1 expression was involved in proliferation of regulatory T cell. No significant difference was found in CRC peripheral blood (P = 0.0863, P = 0.0678). PD-1 is the specific ligand for B7-H1 pathway transferring inhibitory signal to T cell, which is expressed by activated T cell. Our further analysis of PD-1 expression on T cells in CRC tissues showed that conventional T cells (CD4⁺Foxp3^-/CD8⁺Foxp3^-), which was thought to contribute to the anti-tumor immune response, highly expressed PD-1; while regulatory T cells (CD4⁺Foxp3⁺/CD8⁺Foxp3^-) almost failed to express PD-1. The average percentage of PD-1 expression on regulatory T cells was significantly higher than the percentage of PD-1 on conventional T cells (CD4⁺Foxp3^- T cell, P < 0.0001; CD8⁺Foxp3^- T cell, P < 0.0001). The diverse expression of PD-1 might lead to different fate of T cell subsets in B7-H1 over-expression CRC tumor microenvironment.CONCLUSION: B7-H1 expression in tumor cells can inhibit the conventional T cell proliferation in tumor microenvironment through the PD-1 expression on conventional T cells.     

Associations of circulating CXCR3–PD-1+CD4+T cells with disease activity of systemic lupus erythematosus

Abstract

Objectives: Which helper CD4⁺ T cell subset contributes to autoantibodies generation and severity of end-organ involvement in lupus patients remains to be explored. Our research aims to investigate the roles of circulating Tfh (cTfh) cell subsets and corresponding CXCR5^– Th cells in lupus patients and their correlation with SLE disease activity index 2000 (SLEDAI).

Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from blood of systemic lupus erythematosus (SLE) patients as well as healthy donors. The proportion of Th cell subsets classified from cell surface markers (CD45RO, CXCR5, CXCR3, CCR6, PD-1, ICOS, and CCR7) is detected by flow cytometry.

Results: We found no difference in the frequency of CD45RO⁺CXCR5⁺CD4⁺ T cells between SLE patients and health controls. As previously reported, SLE patients showed an increase in the percentage of CXCR5⁺PD-1⁺, CXCR5⁺ICOS⁺PD-1⁺ and CXCR5⁺CCR7^loPD-1^hi cTfh subset, however, none of these populations had correlation with SLEDAI. Therefore, we further investigated the CXCR5^– subsets, and surprisingly we found that the frequency of CXCR3^–PD-1⁺ subset was correlated with SLEDAI, ds-DNA IgG, anti-nucleosome antibody, C3, and C4 independent of CXCR5. Consistently, CXCR3^–PD-1⁺CD45RO⁺CD4⁺T cells expressed factors associated with B-cell-help for the autoantibody production.

Conclusion: CXCR3^–PD-1⁺CD4⁺T cells are a sensitive indicator to assess SLE disease activity and might contribute B cell help and the generation of autoantibodies in patients.     

Differential effects of PD-1 and CTLA-4 blockade on the melanoma-reactive CD8 T cell response

Immune checkpoint inhibitors targeting programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) have revolutionized the treatment of melanoma patients. Based on early studies addressing the mechanism of action, it was assumed that PD-1 blockade mostly influences T cell responses at the tumor site. However, recent work has demonstrated that PD-1 blockade can influence the T cell compartment in peripheral blood. If the activation of circulating, tumor-reactive T cells would form an important mechanism of action of PD-1 blockade, it may be predicted that such blockade would alter either the frequency and/or the breadth of the tumor-reactive CD8 T cell response. To address this question, we analyzed CD8 T cell responses toward 71 melanoma-associated epitopes in peripheral blood of 24 melanoma patients. We show that both the frequency and the breadth of the circulating melanoma-reactive CD8 T cell response was unaltered upon PD-1 blockade. In contrast, a broadening of the circulating melanoma-reactive CD8 T cell response was observed upon CTLA-4 blockade, in concordance with our prior data. Based on these results, we conclude that PD-1 and CTLA-4 blockade have distinct mechanisms of action. In addition, the data provide an argument in favor of the hypothesis that anti–PD-1 therapy may primarily act at the tumor site.

Immune checkpoint–targeting therapies, in particular those targeting the programmed cell death protein 1/ligand 1 (PD-1/PD-L1) axis, now form the standard of care for advanced melanoma (1) and a number of other solid cancers including non–small cell lung cancer (NSCLC) (2), renal cell carcinoma (3), and urothelial carcinoma (4). Despite the widespread clinical use of PD-1/PD-L1 blocking agents, the mechanism by which these therapies enhance immune-mediated tumor control remains incompletely understood. Early work addressing the mechanism of action of PD-1 blockade showed increased numbers of intratumoral proliferating (Ki-67⁺) CD8 T cells and T cell receptor (TCR) clones after treatment (5). These findings provide evidence for a boosting effect on tumor-infiltrating CD8 T cells. In line with these findings, PD-L1 expression on tumor cells has been shown to have predictive value for therapy outcome (5–7) and influence the activity of PD-1 blockade in at least some mouse models (8, 9). Other studies, however, have suggested that PD-1 blockade may also exert its effect through activation of circulating tumor-reactive CD8 T cell responses. First, studies in mouse models of chronic viral infection have shown the recruitment of CXCR5⁺ Tim-3⁻ CD8 T cells from the white pulp of the spleen upon PD-1 blockade (10, 11). Second, data obtained using mouse tumor models demonstrated that the proliferative response to anti–PD-1 therapy is dependent on CD28-mediated costimulation (12), and these findings are in line with a mechanistic study showing that PD-1 signaling inhibits T cell functionality through attenuation of CD28 costimulation (13). Collectively, the latter findings have been interpreted as PD-1 blockade potentially having a role in inducing proliferation of the tumor-reactive CD8 T cell pool. Recent data from clinical studies in patients provide evidence supporting such a hypothesis. First, NSCLC and melanoma patients treated with PD-1 blockade showed an increase in proliferating (Ki-67⁺) CD8 T cell subsets (14–17). Second, PD-1 blockade was shown to result in clonal replacement of tumor-infiltrating CD8 T cells in patients with squamous cell carcinoma (18). In contrast, however, an analysis of peripheral blood from melanoma patients showed no consistent increase in TCR diversity after treatment (19). Although the current knowledge suggests that PD-1 blockade may alter the circulating tumor-reactive CD8 T cell compartment, direct evidence for such a hypothesis is currently lacking.Importantly, most studies that have addressed the impact of PD-1 blockade on CD8 T cells focused the analyses on bulk CD8 T cells without assessing the T cell specificity. However, work from Schreiber and colleagues has shown that “bystander” CD8 T cells respond differentially to checkpoint-targeting therapies compared to tumor-reactive CD8 T cells in their mouse model (20). These findings demonstrate the importance of dissecting the mechanism of action of checkpoint-targeting therapies on the tumor-reactive CD8 T cell response rather than the bulk CD8 T cell compartment. In this study, we assessed whether PD-1 blockade can increase the magnitude of preexisting melanoma-reactive CD8 T cells (boosting) and/or lead to newly detectable tumor-reactive CD8 T cell responses (broadening) in peripheral blood of melanoma patients (Fig. 1A).Open in a separate windowFig. 1.Hypothesis and kinetics of melanoma-reactive CD8 T cell responses during anti–PD-1 therapy. (A) Potential mechanisms of anti–PD-1 therapy include expansion of preexisting tumor-reactive CD8 T cells (boosting) and induction of novel, tumor-reactive CD8 T cell responses (broadening). (B) Overview of the HLA-A*02:01–restricted epitope panel. A total of 71 shared melanoma-associated epitopes were included to analyze the tumor-reactive CD8 T cell responses. Viral epitopes served as positive control for the generation of pMHC multimers. Detailed information about the epitopes is provided in SI Appendix, Table S1. (C) Representative flow cytometry plots of melanoma-reactive CD8 T cell responses (blue, located in the diagonal of the plot because of the dual coding strategy) before and during anti–PD-1 therapy. The magnitude of melanoma-reactive CD8 T cell responses (blue, upper right corner) represents the percentage of total CD8 T cells (gray). A representative example of the full gating strategy is provided in SI Appendix, Fig. S1. (D) Kinetics of melanoma-reactive CD8 T cell responses detected in melanoma patients (n = 5) following anti–PD-1 therapy. A ≥twofold increase (on-therapy versus pretherapy) in magnitude is indicated (*).     

The Expression of Programmed Death-1 in Circulating CD4+ and CD8+ T Cells during Hepatitis B Virus Infection Progression and Its Correlation with Clinical Baseline Characteristics

Background/Aims

Programmed death-1 (PD-1) expression was investigated in CD4⁺ and CD8⁺ T cells from hepatitis B virus (HBV)-infected patients at the chronic hepatitis B (CHB) infection, liver cirrhosis (LC), and hepatocellular carcinoma (HCC) stages.

Methods

PD-1 expression in circulating CD4⁺ and CD8⁺ T cells was detected by flow cytometry. The correlations between PD-1 expression and HBV viral load, alanine aminotransaminase (ALT) levels and aspartate aminotransferase (AST) levels were analyzed using GraphPad Prism 5.0.

Results

PD-1 expression in CD4⁺ and CD8⁺ T cells was significantly increased in both the CHB group and advanced-stage group (LC plus HCC). In the CHB group, PD-1 expression in both CD4⁺ and CD8⁺ T cells was positively correlated with the HBV viral load, ALT, and AST levels. However, in the LC plus HCC group, significant correlations between PD-1 expression and the clinical parameters were nearly absent.

Conclusions

PD-1 expression in peripheral CD4⁺ and CD8⁺ T cells is dynamic, changes with HBV infection progression, and is related to HBV viral load and liver function, especially in CHB. PD-1 expression could be utilized as a potential clinical indicator to determine the extent of virus replication and liver injury.     

Resistance to age-dependent thymic atrophy in long-lived mice that are deficient in pregnancy-associated plasma protein A

Pregnancy-associated plasma protein A (PAPPA) is a metalloproteinase that controls the tissue availability of insulin-like growth factor (IGF). Homozygous deletion of PAPPA in mice leads to lifespan extension. Since immune function is an important determinant of individual fitness, we examined the natural immune ecology of PAPPA^−/− mice and their wild-type littermates reared under specific pathogen-free condition with aging. Whereas wild-type mice exhibit classic age-dependent thymic atrophy, 18-month-old PAPPA^−/− mice maintain discrete thymic cortex and medulla densely populated by CD4⁺CD8⁺ thymocytes that are capable of differentiating into single-positive CD4 and CD8 T cells. Old PAPPA^−/− mice have high levels of T cell receptor excision circles, and have bone marrows enriched for subsets of thymus-seeding progenitors. PAPPA^−/− mice have an overall larger pool of naive T cells, and also exhibit an age-dependent accumulation of CD44⁺CD43⁺ memory T cells similar to wild-type mice. However, CD43⁺ T cell subsets of old PAPPA^−/− mice have significantly lower prevalence of 1B11 and S7, glycosylation isoforms known to inhibit T cell activation with normal aging. In bioassays of cell activation, splenic T cells of old PAPPA^−/− mice have high levels of activation antigens and cytokine production, and also elicit Ig production by autologous B cells at levels equivalent to young wild-type mice. These data suggest an IGF-immune axis of healthy longevity. Controlling the availability of IGF in the thymus by targeted manipulation of PAPPA could be a way to maintain immune homeostasis during postnatal development and aging.     

T-cell co-stimulation by CD28–CD80/86 and its negative regulator CTLA-4 strongly influence accelerated atherosclerosis development

Objective

T-cells are central to the immune response responsible for native atherosclerosis. The objective of this study is to investigate T-cell contribution to post-interventional accelerated atherosclerosis development, as well as the role of the CD28–CD80/86 co-stimulatory and Cytotoxic T-Lymphocyte Antigen (CTLA)-4 co-inhibitory pathways controlling T-cell activation status in this process.

Methods and results

The role of T-cells and the CD28–CD80/86 co-stimulatory and CTLA-4 co-inhibitory pathways were investigated in a femoral artery cuff mouse model for post-interventional remodeling, with notable intravascular CTLA-4 + T-cell infiltration. Reduced intimal lesions developed in CD4^−/− and CD80^−/−CD86^−/− mice compared to normal C57Bl/6J controls. Systemic abatacept-treatment, a soluble CTLA-4Ig fusion protein that prevents CD28–CD80/86 co-stimulatory T-cell activation, prevented intimal thickening by 58.5% (p = 0.029).Next, hypercholesterolemic ApoE3*Leiden mice received abatacept-treatment which reduced accelerated atherosclerosis development by 78.1% (p = 0.040) and prevented CD4 T-cell activation, indicated by reduced splenic fractions of activated KLRG1 +, PD1 +, CD69 + and CTLA-4 + T-cells. This correlated with reduced plasma interferon-γ and elevated interleukin-10 levels. The role of CTLA-4 was confirmed using CTLA-4 blocking antibodies, which strongly increased vascular lesion size by 66.7% (p = 0.008), compared to isotype-treated controls.

Conclusions

T-cell CD28–CD80/86 co-stimulation is vital for post-interventional accelerated atherosclerosis development and is regulated by CTLA-4 co-inhibition, indicating promising clinical potential for prevention of post-interventional remodeling by abatacept.     

A dominant,coordinated T regulatory cell-IgA response to the intestinal microbiota

A T cell receptor transgenic mouse line reactive to a microbiota flagellin, CBir1, was used to define mechanisms of host microbiota homeostasis. Intestinal IgA, but not serum IgA, was found to block mucosal flagellin uptake and systemic T cell activation in mice. Depletion of CD4⁺CD25⁺ Tregs decreased IgA⁺ B cells, total IgA, and CBir1-specific IgA in gut within days. Repletion of T cell-deficient mice with either CD4⁺CD25⁺ or CD4⁺foxp3⁺ Tregs restored intestinal IgA to a much greater extent than their reciprocal CD4⁺ subsets, indicating that Tregs are the major helper cells for IgA responses to microbiota antigens such as flagellin. We propose that the major role of this coordinated Treg-IgA response is to maintain commensalism with the microbiota.     

A case of bronchial asthma as an immune-related adverse event of pembrolizumab treatment for bladder cancer: A case report

Rationale:Bladder cancer is one of the most common cancers worldwide. The anti-programmed cell death protein 1 (PD-1) antibody pembrolizumab, which is an immune checkpoint inhibitor (ICI), has improved survival in bladder cancer. We report a case of bladder cancer that had a high antitumor effect with anti-programmed cell death PD-1 antibody pembrolizumab, an ICI, but asthma occurred an immune-related adverse event (irAE).Patient concerns:A 70-year-old female patient was diagnosed as unresectable bladder cancer who was indicated for ICI treatment.Diagnosis:After ICI administration as a treatment for bladder cancer, the patient had a grade 3 asthma attack. Cytotoxic T lymphocyte antigen 4 (CTLA-4) in CD4⁺ FOX3⁺ T cells was upregulated in the early phase before the development of asthma attacks. Moreover, T-cell immunoglobulin and mucin domain 3 (TIM-3) was upregulated in all memory T cells among CD4⁺ T cells. However, no change in the expression of TIM-3 was observed in any CD8⁺ T-cell subtype. In contrast, the proportion of CD161^- T helper 17 cell (Th17) cells increased.Interventions:The patient was treated with betamethasone, montelukast, salbutamol nebulization, and a combination of salmeterol (50 μg) and fluticasone (500 μg) (SFC).Outcomes:The patient''s wheezing resolved, and her peak flow rate reached 100% of the predicted value; therefore, the patient continued treatment with SFC and montelukast and was discharged from the hospital.Conclusion:Increases in CTLA-4 and TIM-3 expression in CD4⁺ T cells (not CD8⁺), as well as an increase in Th17 cells, may reflect asthma-related inflammation activity. Immune-related adverse events during immune checkpoint inhibitor administration may be predictive markers of antitumor efficacy.     

PD-1 and CTLA-4 combination blockade expands infiltrating T cells and reduces regulatory T and myeloid cells within B16 melanoma tumors

Vaccination with irradiated B16 melanoma cells expressing either GM-CSF (Gvax) or Flt3-ligand (Fvax) combined with antibody blockade of the negative T-cell costimulatory receptor cytotoxic T-lymphocyte antigen-4 (CTLA-4) promotes rejection of preimplanted tumors. Despite CTLA-4 blockade, T-cell proliferation and cytokine production can be inhibited by the interaction of programmed death-1 (PD-1) with its ligands PD-L1 and PD-L2 or by the interaction of PD-L1 with B7-1. Here, we show that the combination of CTLA-4 and PD-1 blockade is more than twice as effective as either alone in promoting the rejection of B16 melanomas in conjunction with Fvax. Adding αPD-L1 to this regimen results in rejection of 65% of preimplanted tumors vs. 10% with CTLA-4 blockade alone. Combination PD-1 and CTLA-4 blockade increases effector T-cell (Teff) infiltration, resulting in highly advantageous Teff-to-regulatory T-cell ratios with the tumor. The fraction of tumor-infiltrating Teffs expressing CTLA-4 and PD-1 increases, reflecting the proliferation and accumulation of cells that would otherwise be anergized. Combination blockade also synergistically increases Teff-to-myeloid-derived suppressor cell ratios within B16 melanomas. IFN-γ production increases in both the tumor and vaccine draining lymph nodes, as does the frequency of IFN-γ/TNF-α double-producing CD8⁺ T cells within the tumor. These results suggest that combination blockade of the PD-1/PD-L1- and CTLA-4-negative costimulatory pathways allows tumor-specific T cells that would otherwise be inactivated to continue to expand and carry out effector functions, thereby shifting the tumor microenvironment from suppressive to inflammatory.     

CTLA-4 blockade enhances polyfunctional NY-ESO-1 specific T cell responses in metastatic melanoma patients with clinical benefit

Blockade of inhibitory signals mediated by cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) has been shown to enhance T cell responses and induce durable clinical responses in patients with metastatic melanoma. The functional impact of anti-CTLA-4 therapy on human immune responses is still unclear. To explore this, we analyzed immune-related adverse events and immune responses in metastatic melanoma patients treated with ipilimumab, a fully human anti-CTLA-4 monoclonal antibody. Fifteen patients were selected on the basis of availability of suitable specimens for immunologic monitoring, and eight of these showed evidence of clinical benefit. Five of the eight patients with evidence of clinical benefit had NY-ESO-1 antibody, whereas none of seven clinical non-responders was seropositive for NY-ESO-1. All five NY-ESO-1 seropositive patients had clearly detectable CD4⁺ and CD8⁺ T cells against NY-ESO-1 following treatment with ipilimumab. One NY-ESO-1 seronegative clinical responder also had a NY-ESO-1 CD4⁺ and CD8⁺ T cell response, possibly related to prior vaccination with NY-ESO-1. Among five clinical non-responders analyzed, only one had a NY-ESO-1 CD4⁺ T cell response and this patient did not have detectable anti-NY-ESO-1 antibody. Overall, NY-ESO-1-specific T cell responses increased in frequency and functionality during anti-CTLA-4 treatment, revealing a polyfunctional response pattern of IFN-γ, MIP-1β and TNF-α. We therefore suggest that CTLA-4 blockade enhanced NY-ESO-1 antigen-specific B cell and T cell immune responses in patients with durable objective clinical responses and stable disease. These data provide an immunologic rationale for the efficacy of anti-CTLA-4 therapy and call for immunotherapeutic designs that combine NY-ESO-1 vaccination with CTLA-4 blockade.     

Phenotypic and genetic analyses of T-cell-mediated immunoregulation in patients with Type 1 diabetes.

AIMS: To investigate the contribution of regulatory T cells and co-stimulatory molecules in CD4(+) T cells to the development of Type 1 diabetes (T1D). METHODS: Twelve patients with T1D, nine patients with systemic lupus erythematosus (SLE), and 12 age-matched healthy control subjects participated. We analysed the proportions of CD25(+)CD4(+) T cells and natural killer T cells (NKT cells), and the expression levels of Foxp3, CTLA-4, CD28, ICOS, PD-1 and BTLA in peripheral blood mononuclear cells and purified CD4(+) T cells. RESULTS: There were no significant differences in the proportions of CD25(+) CD4(+) T cells or NKT cells among the three groups. PD-1 expression levels of peripheral CD4(+) T cells from T1D patients were significantly lower than those from healthy control subjects (P = 0.00066). In contrast, PD-1 expression levels were similar in SLE patients and healthy control subjects. The expression levels of Foxp3, CTLA-4, CD28, ICOS and BTLA were similar in the three groups. CONCLUSIONS: Decreased expression of the PD-1 gene in CD4(+) T cells may contribute to the development and/or maintenance of autoimmune T1D. As the population studied was small and heterogeneous, further studies are required to confirm the findings.     

Programmed death-1/programmed death-L1 signaling pathway and its blockade in hepatitis C virus immunotherapy

Chronic hepatitis C virus (HCV) infection is a public health issue that often progresses to life-threatening complications, including liver cirrhosis, fibrosis, and hepatocellular carcinoma. Impaired immune responses to HCV are key features of chronic HCV infection. Therefore, intervention strategies usually involve enhancing the immune responses against HCV. Cytotoxic CD8⁺ T lymphocytes (CTLs) play a critical role in the control of HCV infection. However, their cytolytic function can be impaired by the expression of co-inhibitory molecules. Programmed death-1 (PD-1) receptor and its ligand PD-L1 function in a T cell co-inhibitory pathway, which either blocks the function of CTLs or the differentiation of CD8⁺ T cells. During chronic HCV infection, the immune inhibitory receptor PD-1 is upregulated on dysfunctional HCV-specific CD8⁺ T cells. As such, blockade of the PD-1/PD-L1 pathway in these CD8⁺ T cells might restore their functional capabilities. Indeed, clinical trials using therapies to block this pathway have shown promise in the fostering of anti-HCV immunity. Understanding how chronic HCV infection induces upregulation of PD-1 on HCV specific T cells and how the PD-1/PD-L1 interaction develops HCV specific T cell dysfunction will accelerate the development of an efficacious prophylactic and therapeutic vaccination against chronic HCV infections, which will significantly improve HCV treatments and patient survival. In this review, we discuss the relationship between PD-1 expression and clinical responses and the potential use of PD-1 blockade for anti-HCV therapy.     

Dendritic Cell-Targeted Pancreatic ��-Cell Antigen Leads to Conversion of Self-Reactive CD4+ T Cells Into Regulatory T Cells and Promotes Immunotolerance in NOD Mice

Studies employing T cell receptor transgenic T cells have convincingly shown that selective delivery of non-self model antigens to DEC-205⁺ dendritic cells (DCs) in the steady-state can induce Foxp3-expressing CD4⁺CD25⁺ regulatory T (Treg) cells from conventional CD4⁺CD25^-Foxp3^- T cells. Although of considerable clinical interest, the concept of DC-targeted de novo generation of antigen-specific Treg cells has not yet been evaluated for self-antigens and self-reactive CD4⁺ T cells in the non-obese diabetic (NOD) mouse model of type 1 diabetes (T1D). Here, we show in proof-of-principle experiments that targeting a mimotope peptide to the endocytic receptor DEC-205 on DCs in NOD mice induces efficient conversion of pancreatic β-cell-reactive BDC2.5 CD4⁺ T cells into long-lived Foxp3⁺ Treg cells. Of note, conversion efficiency in normoglycemic and hyperglycemic mice with early diabetes onset was indistinguishable. While de novo generation of BDC2.5 Treg cells did not interfere with disease progression, anti-DEC-205-mediated targeting of whole proinsulin in prediabetic NOD mice substantially reduced the incidence of diabetes. These results suggest that promoting antigen-specific Treg cells in vivo might be a feasible approach towards cellular therapy in T1D.     

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

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

Enhanced selection of FoxP3+ T-regulatory cells protects CTLA-4-deficient mice from CNS autoimmune disease

It is generally acknowledged that cytotoxic T-lymphocyte–associated antigen-4 (CTLA-4/CD152) plays a pivotal role in the regulation of T-cell activation and the establishment of self-tolerance in the periphery. CTLA-4–deficient (CTLA-4KO) mice develop a lymphoproliferative disorder and die within 4 weeks of birth, suggesting a role for CTLA-4 in T-cell homeostasis or the development and activity of T-regulatory (Treg) cells. To study the role of CTLA-4 in the control of experimental autoimmune encephalomyelitis (EAE), we have generated a CTLA-4KO mouse in which >90% of all CD4⁺ T cells bear a Vβ8.2 transgenic T-cell receptor that is specific for myelin basic protein peptide Ac1–9 (ASQKRPSQR). These mice do not develop spontaneous lymphoproliferative disease or EAE and are resistant to disease induction. This correlates with a higher frequency of functional FoxP3⁺ Treg cells in the spleen and thymus of CTLA-4KO mice. The absence of CTLA-4–mediated suppression of CD28 signaling resulted in the early expression of FoxP3 on double-positive cells in the thymic cortex. We conclude that CTLA-4 is not essential for the peripheral function of FoxP3⁺ Treg cells but plays a pivotal role in their thymic selection.     

PD-1+ memory phenotype CD4+ T cells expressing C/EBPα underlie T cell immunodepression in senescence and leukemia

Although altered T cell function plays a part in immunosenescence, the mechanisms remain uncertain. Here we identify a bona fide age-dependent PD-1⁺ memory phenotype (MP) CD4⁺ T cell subpopulation that hardly proliferates in response to T cell receptor (TCR) stimulation and produces abundant osteopontin at the cost of typical T cell lymphokines. These T cells demonstrate impaired repopulation in Rag2^−/− mice, but a homeostatic proliferation in γ-ray–irradiated mice. These T cells also reveal a unique molecular signature, including a strong expression of C/EBPα normally expressed in myeloid-lineage cells, with diminished c-Myc and cyclin D1. Transduction of Cebpa in regular CD4⁺ T cells inhibited the TCR-mediated proliferation with c-Myc and cyclin D1 repression and caused a striking activation of Spp1 encoding osteopontin along with concomitant repression of T cell lymphokine genes. Although these T cells gradually increase in number with age and become predominant at the senescent stage in normal mice, the generation is robustly accelerated during leukemia. In both conditions, their predominance is associated with the diminution of specific CD4⁺ T cell response. The results suggest that global T cell immunodepression in senescence and leukemia is attributable to the increase in PD-1⁺ MP CD4⁺ T cells expressing C/EBPα.