Interleukin-21 and cellular activation concurrently induce potent cytotoxic function and promote antiviral activity in human CD8 T cells

Human innate lymphoid cell activation by adenoviruses is modified by host defense proteins and neutralizing antibodies

Innate lymphoid cells (ILCs), the complements of diverse CD4 T helper cells, help maintain tissue homeostasis by providing a link between innate and adaptive immune responses. While pioneering studies over the last decade have advanced our understanding how ILCs influence adaptive immune responses to pathogens, far less is known about whether the adaptive immune response feeds back into an ILC response. In this study, we isolated ILCs from blood of healthy donors, fine-tuned culture conditions, and then directly challenged them with human adenoviruses (HAdVs), with HAdVs and host defense proteins (HDPs) or neutralizing antibodies (NAbs), to mimic interactions in a host with pre-existing immunity. Additionally, we developed an ex vivo approach to identify how bystander ILCs respond to the uptake of HAdVs ± neutralizing antibodies by monocyte-derived dendritic cells. We show that ILCs take up HAdVs, which induces phenotypic maturation and cytokine secretion. Moreover, NAbs and HDPs complexes modified the cytokine profile generated by ILCs, consistent with a feedback loop for host antiviral responses and potential to impact adenovirus-based vaccine efficacy.

T Cell Roles and Activity in Chronic Sclerosing Sialadenitis as IgG4-Related Disease: Current Concepts in Immunopathogenesis

IgG4-related disease is a multiorgan immunological fibroinflammatory disorder characterized by lymphoplasmacytic infiltration and fibrosis in multiple organs accompanied by high serum IgG4 levels. The salivary glands are the most common organs involved in this disease. Recently, chronic sclerosing sialadenitis affecting salivary glands, formerly known as Küttner's tumor, and Mikulicz's disease have been classified as a class of IgG4-related diseases. The etiopathobiology of IgG4-related disease is not fully understood. It has recently been hypothesized that the inflammatory and fibrotic process and the increased serum IgG4⁺ levels in IgG4-related disease are the result of an interaction between B cells and T helper cells, suggesting that T cells may play a key role in the pathogenesis of this disease. The aim of this review is to discuss the proposed roles of different T cell subsets in the pathogenesis of IgG4-related disease focusing on their roles in immunopathogenesis of IgG4-related sialadenitis.

High Tacrolimus Intrapatient Variability and Subtherapeutic Immunosuppression are Associated With Adverse Kidney Transplant Outcomes

BACKGROUND

Kidney transplant recipients with high intrapatient variability (IPV) in tacrolimus (Tac) exposure experience more rejection and reduced graft survival. To understand the underlying pathophysiology of this association, the authors investigated whether patients with high tacrolimus IPV have a more activated immune system than patients with low IPV. In addition, exposure to tacrolimus and mycophenolic acid (MPA) was studied in relation to rejection and graft survival.

METHODS

At the time of patient inclusion (5-7 years post-transplantation), the frequency of donor-reactive cells was determined by enzyme-linked immunosorbent assay, and the development of donor-specific anti-Human Leukocyte Antigen antibodies (DSA) was measured by Luminex Single Antigen assay. Tacrolimus IPV was retrospectively calculated between 6 and 12 months and the exposure to tacrolimus and MPA was determined between 1 and 5 years post-transplantation.

RESULTS

A total of 371 kidney transplant recipients were included in this study, of whom 56 developed a rejection episode after 12 months and 60 experienced graft failure after 5-7 years. No correlations were found between tacrolimus IPV or immunosuppression exposure and the number of donor-reactive cells after 5 years of transplantation. DSA were detected more often in patients with low exposure to both tacrolimus and MMF [4/21 (19%) versus 17/350 (4.9%), P = 0.04]. In this cohort, neither tacrolimus IPV nor low overall immunosuppression exposure was associated with a higher incidence of rejection. However, regression analysis showed that a higher tacrolimus IPV was associated with an increased incidence of graft failure (odds ratio = 1.03, P = 0.02).

CONCLUSIONS

This study verifies the relationship between high tacrolimus IPV and impaired kidney allograft survival in long-term follow-up. DSA was also found to be more prevalent in patients with subtherapeutic concentrations of tacrolimus and MPA. An increased prevalence of donor-specific alloreactivity is yet to be demonstrated in patients with high IPV.

A T-Cell Epitope-Based Multi-Epitope Vaccine Designed Using Human HLA Specific T Cell Epitopes Induces a Near-Sterile Immunity against Experimental Visceral Leishmaniasis in Hamsters

Visceral leishmaniasis is a neglected tropical disease affecting 12 million people annually. Even in the second decade of the 21st century, it has remained without an effective vaccine for human use. In the current study, we designed three multiepitope vaccine candidates by the selection of multiple IFN-γ inducing MHC-I and MHC-II binder T-cell specific epitopes from three previously identified antigen genes of Leishmania donovani from our lab by an immuno-informatic approach using IFNepitope, the Immune Epitope Database (IEDB) T cell epitope identification tools, NET-MHC-1, and NET MHC-2 webservers. We tested the protective potential of these three multiepitope proteins as a vaccine in a hamster model of visceral leishmaniasis. The immunization data revealed that the vaccine candidates induced a very high level of Th1 biased protective immune response in-vivo in a hamster model of experimental visceral leishmaniasis, with one of the candidates inducing a near-sterile immunity. The vaccinated animals displayed highly activated monocyte macrophages with the capability of clearing intracellular parasites due to increased respiratory burst. Additionally, these proteins induced activation of polyfunctional T cells secreting INF-γ, TNF-α, and IL-2 in an ex-vivo stimulation of human peripheral blood mononuclear cells, further supporting the protective nature of the designed candidates.

IL-21 Prevents Expansion of CD8+CD28- T Cells Stimulated by IL-15 and Changes Their Subset Distribution

BACKGROUND

To examine the effect of interleukin (IL)-21 on the proliferation, subsets, and immunological characteristics of CD8⁺CD28^- T cells stimulated by IL-15 in vitro.

METHODS

Purified CD8⁺ T cells stimulated with allogeneic CD2^- cells obtained from the peripheral blood mononuclear cells of healthy volunteers were cocultured in the presence of IL-15 alone or IL-21 and IL-15 combined. The dynamic changes in the proliferation, subsets, and phenotypic characteristics of CD8⁺CD28^- T cells were detected. Our work, involving human participants, complied with the Declaration of Helsinki and the Declaration of Istanbul.

RESULTS

IL-21 prevented the expansion of CD8⁺CD28^- T cells stimulated by IL-15 by sustaining CD28 expression at the mRNA level. IL-15 altered the expanded CD8⁺CD28^- T cell memory subsets over the coculture duration, but the addition of IL-21 could change the subset distribution. In the presence of IL-15, the in vitro-expanded CD8⁺CD28^- T cells were mainly intermediately differentiated cells, but they were mainly late differentiated cells in the presence of IL-21 plus IL-15. Moreover, IL-21 upregulated the expression of toxic molecules in the IL-15-expanded CD8⁺CD28^- T cells.

CONCLUSIONS

IL-21 prevents IL-15-induced CD8⁺CD28^- T cell amplification by downregulating CD28 at the transcriptional level. IL-21 can alter the subpopulation distribution and phenotypic characteristics of CD8⁺CD28^- T cells stimulated by IL-15.

HIV-1 infection and the lack of viral control are associated with greater expression of interleukin-21 receptor on CD8+ T cells

OBJECTIVES

Interleukin-21 (IL-21) has been linked with the generation of virus-specific memory CD8+ T cells following acute infection with HIV-1 and reduced exhaustion of CD8+ T cells. IL-21 has also been implicated in the promotion of CD8+ T-cell effector functions during viral infection. Little is known about the expression of interleukin-21 receptor (IL-21R) during HIV-1 infection or its role in HIV-1-specific CD8+ T-cell maintenance and subsequent viral control.

METHODS

We compared levels of IL-21R expression on total and memory subsets of CD8+ T cells from HIV-1-negative and HIV-1-positive donors. We also measured IL-21R on antigen-specific CD8+ T cells in volunteers who were positive for HIV-1 and had cytomegalovirus-responding T cells. Finally, we quantified plasma IL-21 in treatment-naive HIV-1-positive individuals and compared this with IL-21R expression.

RESULTS

IL-21R expression was significantly higher on CD8+ T cells (P = 0.0256), and on central memory (P = 0.0055) and effector memory (P = 0.0487) CD8+ T-cell subsets from HIV-1-positive individuals relative to HIV-1-negative individuals. For those infected with HIV-1, the levels of IL-21R expression on HIV-1-specific CD8+ T cells correlated significantly with visit viral load (r = 0.6667, P = 0.0152, n = 13) and inversely correlated with plasma IL-21 (r = -0.6273, P = 0.0440, n = 11). Lastly, CD8+ T cells from individuals with lower set point viral load who demonstrated better viral control had the lowest levels of IL-21R expression and highest levels of plasma IL-21.

CONCLUSION

Our data demonstrates significant associations between IL-21R expression on peripheral CD8+ T cells and viral load, as well as disease trajectory. This suggests that the IL-21 receptor could be a novel marker of CD8+ T-cell dysfunction during HIV-1 infection.

Pre-transplant donor-reactive IL-21 producing T cells as a tool to identify an increased risk for acute rejection

Pre-transplant screening focuses on the detection of anti-HLA alloantibodies. Previous studies have shown that IFN-γ and IL-21 producing T cells are associated with the development of acute rejection (AR). The aim of this study, was to assess whether pre-transplant donor-reactive T cells and/or B cells are associated with increased rejection risk. Samples from 114 kidney transplant recipients (transplanted between 2010 and 2013) were obtained pre-transplantation. The number of donor-reactive IFN-γ and IL-21 producing cells was analyzed by ELISPOT assay. The presence of donor specific antibodies (DSA) was also determined before transplantation. Numbers of donor-reactive IFN-γ producing cells were similar in patients with or without AR whereas those of IL-21 producing cells were higher in patients with AR (p = 0.03). Significantly more patients with AR [6/30(20%)] had detectable DSA compared to patients without AR [5/84(5.9%), p = 0.03]. Multivariate logistic regression showed that donor age (OR 1.06), pre-transplant DSA (OR 5.61) and positive IL-21 ELISPOT assay (OR 2.77) were independent predictors of an increased risk for the development of AR. Aside from an advanced donor-age and pre-transplant DSA, also pre-transplant donor-reactive IL-21 producing cells are associated with the development of AR after transplantation.

The CD8+ T Cell Noncytotoxic Antiviral Responses

The CD8+ T cell noncytotoxic antiviral response (CNAR) was discovered during studies of asymptomatic HIV-infected subjects more than 30 years ago. In contrast to CD8+ T cell cytotoxic lymphocyte (CTL) activity, CNAR suppresses HIV replication without target cell killing. This activity has characteristics of innate immunity: it acts on all retroviruses and thus is neither epitope specific nor HLA restricted. The HIV-associated CNAR does not affect other virus families. It is mediated, at least in part, by a CD8+ T cell antiviral factor (CAF) that blocks HIV transcription. A variety of assays used to measure CNAR/CAF and the effects on other retrovirus infections are described. Notably, CD8+ T cell noncytotoxic antiviral responses have now been observed with other virus families but are mediated by different cytokines. Characterizing the protein structure of CAF has been challenging despite many biologic, immunologic, and molecular studies. It represents a low-abundance protein that may be identified by future next-generation sequencing approaches. Since CNAR/CAF is a natural noncytotoxic activity, it could provide promising strategies for HIV/AIDS therapy, cure, and prevention.

The role of Th17 cells in viral infections

The present review provides an overview of recent advances regarding the function of Th17 cells and their produced cytokines in the progression of viral diseases. Viral infections alone do not lead to virus-induced malignancies, as both genetic and host safety factors are also involved in the occurrence of malignancies. Acquired immune responses, through the differentiation of Th17 cells, form the novel components of the Th17 cell pathway when reacting with viral infections all the way from the beginning to its final stages. As a result, instead of inducing the right immune responses, these events lead to the suppression of the immune system. In fact, the responses from Th17 cells during persistent viral infections causes chronic inflammation through the production of IL-17 and other cytokines which provide a favorable environment for tumor growth and its development. Additionally, during the past decade, these cells have been understood to be involved in tumor progression and metastasis. However, further research is required to understand Th17 cells' immune mechanisms in the vast variety of viral diseases. This review aims to determine the roles and effects of the immune system, especially Th17 cells, in the progression of viral diseases; which can be highly beneficial for the diagnosis and treatment of these infections.

Different Effects of Interleukin 21 and Interleukin 15 on In Vitro Expanded CD8+ T Cells Stimulated by Alloantigen

OBJECTIVE

To investigate the effects of IL (interleukin) 21 on CD8⁺ T cells stimulated by alloantigen in the presence of IL-15 in vitro.

METHODS

CD8⁺ T cells sorted with MicroBeads from fresh human peripheral blood mononuclear cells were cocultured with antigen-presenting cells derived from HLA-A, -B, and -DR full-mismatched individuals for 9 days without any cytokines, in the presence of IL-15, IL-21, and IL-15 combined with IL-21, respectively. The proliferation and phenotypic characteristics of CD28⁺ and CD28^- subsets were measured after 9 days of culture.

RESULTS

The proliferation of CD8⁺ T cells can be promoted either by IL-15 alone or in combination with IL-21 compared with IL-21. Cells expanded in the presence of IL-15 are mainly CD8⁺CD28^- T cells, while those expanded in the presence of IL-15 combined with IL-21 are mostly CD8⁺CD28⁺ T cells. In the presence of IL-15, most CD8⁺CD28⁺ T cells shifted to CD8⁺CD28^- T cells during the process of proliferation, but In the presence of IL-15 combined with IL-21, CD8⁺CD28⁺ T cells didn't shift to CD8⁺CD28^- T cells during proliferation, moreover, CD8⁺CD28^- T cells cannot transform in reverse to CD8⁺CD28⁺ T cells. IL-21 combined with IL-15 can promote the expression of granzyme B and perforin in CD8⁺CD28⁺ and/or CD8⁺CD28^- T cells compared with IL-15 alone.

CONCLUSION

IL-21 cannot promote the proliferation of CD8⁺ T cells under allogeneic stimulation unless combined with IL-15. IL-21 prevents the loss of CD28 molecules caused by IL-15 but cannot promote its re-expression in CD28^- T cells. CD8⁺ T cells expanded by IL-21 combined with IL-15 is characterized by cytotoxic phenotype.

The Number of Donor-Specific IL-21 Producing Cells Before and After Transplantation Predicts Kidney Graft Rejection

Interleukin (IL)-21 supports induction and expansion of CD8⁺ T cells, and can also regulate the differentiation of B cells into antibody-producing plasma cells. We questioned whether the number of circulating donor-specific IL-21 producing cells (pc) can predict kidney transplant rejection, and evaluated this in two different patient cohorts. The first analysis was done on pre-transplantation samples of 35 kidney transplant recipients of whom 15 patients developed an early acute rejection. The second study concerned peripheral blood mononuclear cell (PBMC) samples from 46 patients obtained at 6 months after kidney transplantation of whom 13 developed late rejection. Significantly higher frequencies of donor-specific IL-21 pc were found by Elispot assay in both patients who developed early and late rejection compared to those without rejection. In addition, low frequencies of donor-specific IL-21 pc were associated with higher rejection-free survival. Moreover, low pre-transplant donor-specific IL-21 pc numbers were associated with the absence of anti-HLA antibodies. Donor-reactive IL-21 was mainly produced by CD4⁺ T cells, including CD4⁺ follicular T helper cells. In conclusion, the number of donor-specific IL-21 pc is associated with an increased risk of both early and late rejection, giving it the potential to be a new biomarker in kidney transplantation.

Interleukin-21 receptor gene polymorphism is associated with hepatitis B virus-related hepatocellular carcinoma in Chinese patients

Background

We investigated the relationship between hepatitis B virus (HBV)‐related pathogenesis and single nucleotide polymorphisms (SNPs) in interleukin‐21 (IL‐21)‐JAK‐STAT signaling pathway genes.

Methods

We used the high‐resolution melting (HRM) method to genotype five SNPs (IL‐21 rs2221903, IL‐21 rs4833837, IL‐21 receptor (IL‐21R) rs2285452, JAK3 rs3008, and STAT3 rs1053023) in 546 HBV‐infected patients and 353 healthy Chinese subjects. The HBV‐infected patients were further divided into subgroups based on the HBV‐related pathologies: chronic hepatitis B (CHB), HBV‐related liver cirrhosis (LC), and HBV‐related hepatocellular carcinoma (HCC).

Results

There were no significant differences in the genotype and allele distributions of the five SNPs between the HBV‐infected patients and healthy subjects. The genotype and allele frequencies were similar in the two groups for IL‐21 rs2221903 (A>G, P = 0.83 and 0.67), rs4833837 (A>G, P = 0.80 and 0.49), IL‐21R rs2285452 (G>A, P = 0.25 and 0.68), STAT3 rs1053023 (A>G, P = 1.00 and 0.96), and JAK3 rs3008 (C>T, P = 0.32 and 0.54). However, patients with the IL‐21R rs2285452 AA genotype were more susceptible to HBV‐related HCC than those with the IL‐21R rs2285452 GA/GG genotype (P = 0.03, OR = 3.27, 95% CI = 1.16‐9.20). The serological marker model of “HBsAg+, HBeAg+, HBcAb+” was predominant among patients with HBV infection. However, there was no association between the genotype's distribution of the five SNPs and the serological marker models (P > 0.05).

Conclusions

These findings demonstrate that the IL‐21R rs2285452 AA genotype increases the risk of HBV‐related HCC in Chinese patients.

The proportion of different interleukin-17-producing T-cell subsets is associated with liver fibrosis in chronic hepatitis C

Studies have suggested the pivotal role of T helper type 1 (Th1) -related cytokines on the outcome of hepatitis C virus (HCV) infection. Nevertheless, the role of different interleukin-17 (IL-17) -secreting T cells on chronic hepatitis C (CHC) is less clear. Here, the in vivo IL-1β, IL-6, and IL-17 levels were positively correlated with both alanine transaminase (ALT) levels and hepatic lesions. When compared with the control group, CHC patients showed a lower proportion of IL-17-secreting (CD4⁺ and CD8⁺ ) T cells capable of simultaneously producing IL-21. Moreover, the percentage of IL-10-secreting Th17 cells was also lower in CHC patients. Notably, advanced liver lesions were observed among those patients with lower percentage levels of IL-17-producing T cells positive for IL-21, interferon-γ (IFN-γ) and IL-10. In contrast, the severity of hepatic damage was associated with peripheral single IL-17⁺ T cells. The percentage of IL-17⁺ IL-21^- IFN-γ⁺ (CD4⁺ and CD8⁺ ) T-cell phenotypes was positively associated with plasma CD14 levels. Finally, elevated levels of circulating CD14 were detected among CHC patients with extensive liver damage. In summary, although preliminary, our results suggest that a balance between different IL-17-producing T cells, associated with peripheral levels of CD14, may be a progress marker for liver disease in chronically HCV-infected patients.

CD4+IL-21+T cells are correlated with regulatory T cells and IL-21 promotes regulatory T cells survival during HIV infection

INTRODUCTION

IL-21 enhances T and natural killer cells survival and antiviral functions without promoting T cell activation during HIV infection, which makes it a better adjuvant in anti-HIV immunotherapy. Due to the pleiotropy and redundancy of cytokines, it is vital to have a comprehensive knowledge of the role of IL-21 in the regulation of immune responses. Regulatory T cells (Tregs) play an important role in immune regulation and are a determinant of immune therapeutic efficacy in certain circumstances. In this study, we explored the direct effect of IL-21 on Tregs during HIV infection, which has not been addressed before.

METHODS

Thirty-four HIV treatment-naïve patients were enrolled and the relationship between CD4⁺IL-21⁺T cells and Tregs were studied. The effects of IL-21 on CD4⁺CD25⁺CD127^low Tregs' apoptosis, proliferation, and CTLA-4 and TGF-β expression in HIV-infected patients was investigated and compared with the effect of other common γ-chain cytokines.

RESULTS

We found the percentage and absolute numbers of CD4⁺IL-21⁺T cells were positively related to the frequency or absolute numbers of CD4⁺CD25⁺ or CD4⁺CD25⁺CD127^low Tregs. Compared with the media-alone control, IL-21, IL-7, and IL-15 could significantly reduce apoptosis of Tregs (p<0.05). IL-21 did not promote the proliferation of Tregs as compared with media alone, while IL-2, IL-7, and IL-15 could significantly increase the proliferation of Tregs (p<0.05). IL-21 enhanced CTLA-4 expression by Tregs (p<0.05), but could not induce TGF-β secretion of Tregs from HIV infected patients. There were no significant differences of the fold induction of apoptosis, proliferation, or CTLA-4 and TGF-β expression by Tregs from HIV-infected patients and normal controls after IL-21 treatment. In vitro experiment showed that pretreatment with IL-21 significantly enhanced the suppressive effect of Tregs on CD8+ T cells' IFN-γ expression.

CONCLUSION

We conclude that IL-21 promotes the survival and CTLA-4 expression of Tregs and enhanced the suppressive capacity of Tregs during HIV infection. These results broaden the understanding of HIV pathogenesis and provide critical information for HIV interventions.

Signal transducer and activator of transcription 3: a year in review

PURPOSE OF REVIEW

Signal transducer and activator of transcription 3 (STAT3) is an important transcription factor involved in a wide variety of cellular functions. Germline loss-of-function mutations are known to cause hyper-IgE immunodeficiency (autosomal dominant hyper IgE syndrome), whereas somatic gain-of-function mutations have been described in large granular cell leukemia, and polymorphisms in STAT3 have been associated with inflammatory bowel disease and other solid organ tumors. The review examines recent discoveries in our understanding of the nonmalignant disease processes affected by STAT3 mutations in human disease.

RECENT FINDINGS

Germline STAT3 gain-of-function mutations have recently been identified in patients with an early-onset autoimmunity/lymphoproliferative syndrome. STAT3 plays a previously unrecognized role in several facets of the pathogenesis of allergy. Loss-of-function STAT3 mutations revealed critical roles for STAT3 in the development and function of several lymphocyte populations and in their role in host defense.

SUMMARY

The discovery of new gain-of-function mutations in STAT3, as well as new studies among patients with loss-of-function mutations, expand the understanding of the pathophysiology of STAT3 function and its importance in regulating the immune system. These findings contribute to elucidating STAT3 biology and clinical symptoms in patients with the different disease phenotypes.

Regulation of CD8+ T-cell cytotoxicity in HIV-1 infection

Understanding the mechanisms involved in cellular immune responses against control of human immunodeficiency virus (HIV) infection is key to development of effective immunotherapeutic strategies against viral proliferation. Clear insights into the regulation of cytotoxic CD8+ T cells is crucial to development of effective immunotherapeutic strategies due to their unique ability to eliminate virus-infected cells during the course of infection. Here, we reviewed the roles of transcription factors, co-inhibitory molecules and regulatory cytokines following HIV infection and their potential significance in regulating the cytotoxic potentials of CD8+ T cells.

IL-21 induces antiviral microRNA-29 in CD4 T cells to limit HIV-1 infection

Initial events after exposure determine HIV-1 disease progression, underscoring a critical need to understand host mechanisms that interfere with initial viral replication. Although associated with chronic HIV-1 control, it is not known whether interleukin-21 (IL-21) contributes to early HIV-1 immunity. Here we take advantage of tractable primary human lymphoid organ aggregate cultures to show that IL-21 directly suppresses HIV-1 replication, and identify microRNA-29 (miR-29) as an antiviral factor induced by IL-21 in CD4 T cells. IL-21 promotes transcription of all miR-29 species through STAT3, whose binding to putative regulatory regions within the MIR29 gene is enriched by IL-21 signalling. Notably, exogenous IL-21 limits early HIV-1 infection in humanized mice, and lower viremia in vivo is associated with higher miR-29 expression. Together, these findings reveal a novel antiviral IL-21-miR-29 axis that promotes CD4 T-cell-intrinsic resistance to HIV-1 infection, and suggest a role for IL-21 in initial HIV-1 control in vivo.

HIV-infected patients who maintain undetectable virus levels possess elevated plasma concentrations of IL-21. Here, Adoro et al. show that IL-21 inhibits early viral infection in humanized mice and suppresses HIV-1 replication in vitro by upregulating a microRNA via the regulatory protein STAT3.

CD4⁺CD28null T lymphocytes resemble CD8⁺CD28null T lymphocytes in their responses to IL-15 and IL-21 in HIV-infected patients

HIV-infected individuals suffer from accelerated immunologic aging. One of the most prominent changes during T lymphocyte aging is the accumulation of CD28(null) T lymphocytes, mainly CD8(+) but also CD4(+) T lymphocytes. Enhancing the functional properties of these cells may be important because they provide antigen-specific defense against chronic infections. The objective of this study was to compare the responses of CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes from HIV-infected patients to the immunomodulatory effects of cytokines IL-15 and IL-21. We quantified the frequencies of CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes in peripheral blood from 110 consecutive, HIV-infected patients and 25 healthy controls. Patients showed increased frequencies of CD4(+)CD28(null) and CD8(+)CD28(null). Both subsets were positively correlated to each other and showed an inverse correlation with the absolute counts of CD4(+) T lymphocytes. Higher frequencies of HIV-specific and CMV-specific cells were found in CD28(null) than in CD28(+) T lymphocytes. Activation of STAT5 by IL-15 and STAT3 by IL-21 was higher in CD28(null) compared with CD28(+) T lymphocytes. Proliferation, expression of CD69, and IFN-γ production in CD28(null) T lymphocytes were increased after treatment with IL-15, and IL-21 potentiated most of those effects. Nevertheless, IL-21 alone reduced IFN-γ production in response to anti-CD3 stimulation but increased CD28 expression, even counteracting the inhibitory effect of IL-15. Intracytoplasmic stores of granzyme B and perforin were increased by IL-15, whereas IL-21 and simultaneous treatment with the 2 cytokines also significantly enhanced degranulation in CD4(+)CD28(null) and CD8(+)CD28(null) T lymphocytes. IL-15 and IL-21 could have a role in enhancing the effector response of CD28(null) T lymphocytes against their specific chronic antigens in HIV-infected patients.

Elevation of Tim-3 and PD-1 expression on T cells appears early in HIV infection, and differential Tim-3 and PD-1 expression patterns can be induced by common γ -chain cytokines

Purpose. To explore the association between differential Tim-3 and PD-1 expression patterns and HIV disease progression, and to investigate the impact of common γ-chain cytokines on Tim-3 and PD-1 expression patterns on T cells. Methods. Tim-3/PD-1 expression on the T cells of patients with early and chronic HIV infections was detected. The expression levels and functional profiles of T cells with differential Tim-3 and PD-1 expression patterns induced by γ-chain cytokines were studied. Results. The elevation of differential Tim-3 and PD-1 expression patterns on T cells appeared early in HIV infection. Co-expression of Tim-3 and PD-1 (Tim-3+PD-1+) correlates with more severe exhaustion of T cells during HIV infection. In vitro stimulation of common γ-chain cytokines can induce differential expression patterns of Tim-3 and PD-1 on T cells. The enhancement of Tim-3 and PD-1 expression by common γ-chain IL-2 can inhibit the function of T cells re-stimulated by HIV gag and TCR, not by the re-stimulation of IL-2. Conclusions. The elevation of differential Tim-3 and PD-1 expression patterns on T cells represents a state of T cell exhaustion and can be induced by common γ-chain cytokines. These findings provide insights into HIV pathogenesis and help inform immune intervention strategies.

Interleukin-21 responses in patients with chronic hepatitis B

Interleukin (IL)-21 has been demonstrated to play a pivotal role in controlling chronic viral infections. However, little is known about the regulatory role of IL-21 in T cell immunity during the process of chronic hepatitis B (CHB). In the present study, the levels of serum IL-21 in 77 patients with various degrees of CHB in immune clearance phase (IC), 25 patients infected with hepatitis B virus (HBV) in immune tolerance phase (IT), and 25 healthy controls (HC) were measured and their potential association with major clinic indexes was examined. Peripheral blood mononuclear cells from CHB patients were stimulated with hepatitis B core antigen (HBcAg) in the presence or absence of anti-IL-21 antibody or recombinant IL-21, and the frequency of HBcAg-specific IL-21(+)CD4(+) and interferon (IFN)-γ(+)CD8(+) T cells was characterized by flow cytometry. Our data indicated that the levels of serum IL-21 were significantly higher in the IC CHB patients than that in the other groups and were positively correlated with the levels of serum HBV DNA and HBeAg in the IC patients. There was a low frequency of HBcAg-specific IL-21(+)CD4(+) T cells in IC CHB patients. Further, IL-21 enhanced HBcAg-specific IFN-γ(+)CD8(+) T cell proliferation, while treatment with anti-IL-21 inhibited antigen-specific IFN-γ(+)CD8(+) T cell expansion in vitro. Our findings imply that IL-21 positively regulates proinflammatory IFN-γ(+)CD8(+) T cell responses during the process of chronic HBV infection in humans.

Interleukin-21 and T follicular helper cells in HIV infection: research focus and future perspectives

Interleukin (IL)-21 is a member of the γ chain-receptor cytokine family along with IL-2, IL-4, IL-7, IL-9, and IL-15. The effects of IL-21 are pleiotropic, owing to the broad cellular distribution of the IL-21 receptor. IL-21 is secreted by activated CD4 T cells and natural killer T cells. Within CD4 T cells, its secretion is restricted mainly to T follicular helper (Tfh) cells and Th17 cells to a lesser extent. Our research focus has been on the role of IL-21 and more recently of Tfh in immunopathogenesis of HIV infection. This review focuses on first the influence of IL-21 in regulation of T cell, B cell, and NK cell responses and its immunotherapeutic potential in viral infections and as a vaccine adjuvant. Second, we discuss the pivotal role of Tfh in generation of antibody responses in HIV-infected persons in studies using influenza vaccines as a probe. Lastly, we review data supporting ability of HIV to infect Tfh and the role of these cells as reservoirs for HIV and their contribution to viral persistence.

Developing Combined HIV Vaccine Strategies for a Functional Cure

Increasing numbers of HIV-infected individuals have access to potent antiretroviral drugs that control viral replication and decrease the risk of transmission. However, there is no cure for HIV and new strategies have to be developed to reach an eradication of the virus or a natural control of viral replication in the absence of drugs (functional cure). Therapeutic vaccines against HIV have been evaluated in many trials over the last 20 years and important knowledge has been gained from these trials. However, the major obstacle to HIV eradication is the persistence of latent proviral reservoirs. Different molecules are currently tested in ART-treated subjects to reactivate these latent reservoirs. Such anti-latency agents should be combined with a vaccination regimen in order to control or eradicate reactivated latently-infected cells. New in vitro assays should also be developed to assess the success of tested therapeutic vaccines by measuring the immune-mediated killing of replication-competent HIV reservoir cells. This review provides an overview of the current strategies to combine HIV vaccines with anti-latency agents that could act as adjuvant on the vaccine-induced immune response as well as new tools to assess the efficacy of these approaches.

T cell replicative senescence in human aging

The decline of the immune system appears to be an intractable consequence of aging, leading to increased susceptibility to infections, reduced effectiveness of vaccination and higher incidences of many diseases including osteoporosis and cancer in the elderly. These outcomes can be attributed, at least in part, to a phenomenon known as T cell replicative senescence, a terminal state characterized by dysregulated immune function, loss of the CD28 costimulatory molecule, shortened telomeres and elevated production of proinflammatory cytokines. Senescent CD8 T cells, which accumulate in the elderly, have been shown to frequently bear antigen specificity against cytomegalovirus (CMV), suggesting that this common and persistent infection may drive immune senescence and result in functional and phenotypic changes to the T cell repertoire. Senescent T cells have also been identified in patients with certain cancers, autoimmune diseases and chronic infections, such as HIV. This review discusses the in vivo and in vitro evidence for the contribution of CD8 T cell replicative senescence to a plethora of age-related pathologies and a few possible therapeutic avenues to delay or prevent this differentiative end-state in T cells. The age-associated remodeling of the immune system, through accumulation of senescent T cells has farreaching consequences on the individual and society alike, for the current healthcare system needs to meet the urgent demands of the increasing proportions of the elderly in the US and abroad.

Signal transducer and activator of transcription 3 (STAT3) mutations underlying autosomal dominant hyper-IgE syndrome impair human CD8(+) T-cell memory formation and function

BACKGROUND

The capacity of CD8(+) T cells to control infections and mediate antitumor immunity requires the development and survival of effector and memory cells. IL-21 has emerged as a potent inducer of CD8(+) T-cell effector function and memory development in mouse models of infectious disease. However, the role of IL-21 and associated signaling pathways in protective CD8(+) T-cell immunity in human subjects is unknown.

OBJECTIVE

We sought to determine which signaling pathways mediate the effects of IL-21 on human CD8(+) T cells and whether defects in these pathways contribute to disease pathogenesis in patients with primary immunodeficiencies caused by mutations in components of the IL-21 signaling cascade.

METHODS

Human primary immunodeficiencies resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Lymphocytes from patients with loss-of-function mutations in signal transducer and activator of transcription 1 (STAT1), STAT3, or IL-21 receptor (IL21R) were used to assess the respective roles of these genes in human CD8(+) T-cell differentiation in vivo and in vitro.

RESULTS

Mutations in STAT3 and IL21R, but not STAT1, led to a decrease in multiple memory CD8(+) T-cell subsets in vivo, indicating that STAT3 signaling, possibly downstream of IL-21R, regulates the memory cell pool. Furthermore, STAT3 was important for inducing the lytic machinery in IL-21-stimulated naive CD8(+) T cells. However, this defect was overcome by T-cell receptor engagement.

CONCLUSION

The IL-21R/STAT3 pathway is required for many aspects of human CD8(+) T-cell behavior but in some cases can be compensated by other signals. This helps explain the relatively mild susceptibility to viral disease observed in STAT3- and IL-21R-deficient subjects.

Galectin-9 and IL-21 mediate cross-regulation between Th17 and Treg cells during acute hepatitis C

Loss of CD4 T cell help correlates with virus persistence during acute hepatitis C virus (HCV) infection, but the underlying mechanism(s) remain unknown. We developed a combined proliferation/intracellular cytokine staining assay to monitor expansion of HCV-specific CD4 T cells and helper cytokines expression patterns during acute infections with different outcomes. We demonstrate that acute resolving HCV is characterized by strong Th1/Th17 responses with specific expansion of IL-21-producing CD4 T cells and increased IL-21 levels in plasma. In contrast, viral persistence was associated with lower frequencies of IL-21-producing CD4 T cells, reduced proliferation and increased expression of the inhibitory receptors T cell immunoglobulin and mucin-domain-containing-molecule-3 (Tim-3), programmed death 1 (PD-1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4) on HCV-specific CD8 T cells. Progression to persistent infection was accompanied by increased plasma levels of the Tim-3 ligand Galectin-9 (Gal-9) and expansion of Gal-9 expressing regulatory T cells (Tregs). In vitro supplementation of Tim-3(high) HCV-specific CD8 T cells with IL-21 enhanced their proliferation and prevented Gal-9 induced apoptosis. siRNA-mediated knockdown of Gal-9 in Treg cells rescued IL-21 production by HCV-specific CD4 T cells. We propose that failure of CD4 T cell help during acute HCV is partially due to an imbalance between Th17 and Treg cells whereby exhaustion of both CD4 and CD8 T cells through the Tim-3/Gal-9 pathway may be limited by IL-21 producing Th17 cells or enhanced by Gal-9 producing Tregs.

IL-21 promotes the expansion of CD27+ CD28+ tumor infiltrating lymphocytes with high cytotoxic potential and low collateral expansion of regulatory T cells

Background

Adoptive cell transfer of tumor infiltrating lymphocytes has shown clinical efficacy in the treatment of melanoma and is now also being explored in other tumor types. Generation of sufficient numbers of effector T cells requires extensive ex vivo expansion, often at the cost of T cell differentiation and potency. For the past 20 years, IL-2 has been the key cytokine applied in the expansion of TIL for ACT. However, the use of IL-2 has also led to collateral expansion of regulatory T cells (Tregs) and progressive T cell differentiation, factors known to limit in vivo persistence and activity of transferred TIL. The use of alternative T cell growth factors is therefore warranted. Here, we have compared the effects of IL-2, -15 and −21 cytokines on the expansion and activation of TIL from single-cell suspensions of non-small cell lung cancer, ovarian cancer and melanoma.

Methods

We applied the K562-based artificial APC (aAPC) platform for the direct and rapid expansion of tumor infiltrating lymphocytes isolated from primary cancer specimens. These aAPC were engineered to express the Fc-γ receptor CD32 (for anti-CD3 antibody binding), the co-stimulatory molecule 4-1BBL, and to secrete either IL-2, IL-15 or IL-21 cytokine.

Results

Although IL-2 aAPC induced the greatest overall TIL expansion, IL-21 aAPC induced superior expansion of CD8⁺ T cells with a CD27⁺CD28⁺ “young” phenotype and superior functional cytotoxic effector characteristics, without collateral expansion of Tregs.

Conclusion

Our data rationalize the clinical application of IL-21-secreting aAPC as a standardized cell-based platform in the expansion of “young” effector TIL for ACT.

Anti-viral CD8 T cells and the cytokines that they love

Viral infections cause an immunological disequilibrium that provokes CD8 T cell responses. These cells play critical roles in purging acute infections, limiting persistent infections, and conferring life-long protective immunity. At every stage of the response anti-viral CD8 T cells are sensitive to signals from cytokines. Initially cytokines operate as immunological warning signs that inform of the presence of an infection, and also influence the developmental choices of the responding cells. Later during the course of the response other sets of cytokines support the survival and maintenance of the differentiated anti-viral CD8 T cells. Although many cytokines promote virus-specific CD8 T cells, other cytokines can suppress their activities and thus favor viral persistence. In this review we discuss how select cytokines act to regulate anti-viral CD8 T cells throughout the response and influence the outcome of viral infections.

T cell replicative senescence in human aging

The decline of the immune system appears to be an intractable consequence of aging, leading to increased susceptibility to infections, reduced effectiveness of vaccination and higher incidences of many diseases including osteoporosis and cancer in the elderly. These outcomes can be attributed, at least in part, to a phenomenon known as T cell replicative senescence, a terminal state characterized by dysregulated immune function, loss of the CD28 costimulatory molecule, shortened telomeres and elevated production of proinflammatory cytokines. Senescent CD8 T cells, which accumulate in the elderly, have been shown to frequently bear antigen specificity against cytomegalovirus (CMV), suggesting that this common and persistent infection may drive immune senescence and result in functional and phenotypic changes to the T cell repertoire. Senescent T cells have also been identified in patients with certain cancers, autoimmune diseases and chronic infections, such as HIV. This review discusses the in vivo and in vitro evidence for the contribution of CD8 T cell replicative senescence to a plethora of age-related pathologies and a few possible therapeutic avenues to delay or prevent this differentiative end-state in T cells. The age-associated remodeling of the immune system, through accumulation of senescent T cells has farreaching consequences on the individual and society alike, for the current healthcare system needs to meet the urgent demands of the increasing proportions of the elderly in the US and abroad.

Can immunotherapy be useful as a "functional cure" for infection with Human Immunodeficiency Virus-1?

Immunotherapy aims to assist the natural immune system in achieving control over viral infection. Various immunotherapy formats have been evaluated in either therapy-naive or therapy-experienced HIV-infected patients over the last 20 years. These formats included non-antigen specific strategies such as cytokines that stimulate immunity or suppress the viral replication, as well as antibodies that block negative regulatory pathways. A number of HIV-specific therapeutic vaccinations have also been proposed, using in vivo injection of inactivated virus, plasmid DNA encoding HIV antigens, or recombinant viral vectors containing HIV genes. A specific format of therapeutic vaccines consists of ex vivo loading of autologous dendritic cells with one of the above mentioned antigenic formats or mRNA encoding HIV antigens.This review provides an extensive overview of the background and rationale of these different therapeutic attempts and discusses the results of trials in the SIV macaque model and in patients. To date success has been limited, which could be explained by insufficient quality or strength of the induced immune responses, incomplete coverage of HIV variability and/or inappropriate immune activation, with ensuing increased susceptibility of target cells.Future attempts at therapeutic vaccination should ideally be performed under the protection of highly active antiretroviral drugs in patients with a recovered immune system. Risks for immune escape should be limited by a better coverage of the HIV variability, using either conserved or mosaic sequences. Appropriate molecular adjuvants should be included to enhance the quality and strength of the responses, without inducing inappropriate immune activation. Finally, to achieve a long-lasting effect on viral control (i.e. a "functional cure") it is likely that these immune interventions should be combined with anti-latency drugs and/or gene therapy.

[Interleukin-21: a key cytokine for controlling HIV and other chronic viral infections]

The differentiation, homeostatic proliferation and effector functions of different immune cells are controlled, to a large extent, by cytokines. Viruses often cause immune response dysfunctions by causing defects in the cytokine networks. The defects are often manifested by altered cytokine secretion and/or responsiveness to the cytokine. Among these cytokines, Interleukin-21 (IL-21) is a relatively recently discovered cytokine, which is mainly produced by CD4(+) T cells in the body, and exerts multiple and pleiotropic effects on various immune cells. Recent studies have shown that the cytokine is indispensable for controlling chronic viral infections. This review summarizes current knowledges concerning the biological effects of this cytokine on different components of the immune system. We also discuss how it contributes toward mounting efficient antiviral immunity and controlling chronic viral infections, especially HIV-1. The IL-1 cytokine represents a novel therapeutic agent for virus-infected patients as well as an adjuvant in antiviral vaccination strategies.

The role of interleukin-21 in HIV infection

Interleukin (IL)-21 is one of a group of cytokines including IL-2, IL-4, IL-7, IL-9 and IL-15 whose receptor complexes share the common γ chain (γ(c)). Secretion of IL-21 is restricted mainly to T follicular helper (TFH) CD4 T cell subset with contributions from Th17, natural killer (NK) T cells, but the effects of IL-21 are pleiotropic, owing to the broad cellular distribution of the IL-21 receptor. The role of IL-21 in sustaining and regulating T cell, B cell and NK cell responses during chronic viral infections has recently come into focus. This chapter reviews current knowledge about the biology of IL-21 in the context of HIV infection.

Cytokine production and dysregulation in HIV pathogenesis: lessons for development of therapeutics and vaccines

Numerous studies have characterized the cytokine modulation observed in human immunodeficiency virus (HIV) infected individuals, from initial infection through chronic disease. Progressive and non-progressive HIV infection models show the cytokine milieu differs in terms of production and responsiveness in these two groups, suggesting an understanding of the role cytokines play during infection is necessary for directing the immune response toward viral control. This review will cover cytokine induction and dysfunction during HIV pathogenesis, with a focus on the interplay between cytokines and transcription factors, T cell activation, and exhaustion. We highlight cytokines that have either vaccine adjuvant or therapeutic potential and discuss the need to identify key factors required for prevention of progression, clearance of infection, or protection from acquisition.

Interleukin-21 administration to rhesus macaques chronically infected with simian immunodeficiency virus increases cytotoxic effector molecules in T cells and NK cells and enhances B cell function without increasing immune activation or viral replication

We have previously shown that interleukin-21, a pleiotropic C γ-chain signaling cytokine, induces the expression of the cytotoxic molecules granzyme B (GrB) and perforin in vitro in CD8 T cells and NK cells of chronically HIV infected individuals. In this pilot study, four chronically SIV infected rhesus macaques (RM) in late-stage disease were given two doses of recombinant MamuIL-21, 50 μg/kg, intravenously 7 days apart, followed by one subcutaneous dose, 100 μg/kg, 23 days after the second dose. Three animals served as controls. After each dose of IL-21, increases were noted in frequency and mean fluorescence intensity of GrB and perforin expression in memory and effector subsets of CD8 T cells in peripheral blood (PB), in peripheral and mesenteric lymph node (LN) cells, in PB memory and effector CD4 T cells and in NK cells. Frequencies of SIV-gag specific CD107a(+)IFN-γ(+) CD8 T cells increased 3.8-fold in PB and 1.8-fold in LN. In addition, PB CD27(+) memory B cells were 2-fold higher and serum SIV antibodies increased significantly after IL-21 administration. No changes were observed in markers of T cell activation, T cell proliferation or plasma virus load. Thus, administration of IL-21 to chronically SIV infected viremic animals was safe, well tolerated and could augment the cytotoxic potential of T cells and NK cells, promote B cell differentiation with increases in SIV antibody titers without discernable increase in cellular activation. Further studies are warranted to elucidate the effects and potential benefit of IL-21 administration in the context of SIV/HIV infection and in SIV/HIV vaccine design.

Expression of γ-chain cytokine receptors on CD8+ T cells in HIV infection with a focus on IL-7Rα (CD127)

When interleukin-2 (IL-2) receptor γ-chain (γ(C))-sharing cytokine receptors on T cells bind their specific ligands (IL-2, -4, -7, -9, -15 or -21), they initiate a variety of cell signals that promote survival, differentiation or antiviral or antitumor cytolytic functions. Although expression of the γ(C) is constitutive across T-cell subsets, the varying expression of other receptor complex components can regulate cytokine signalling and function. Impaired γ(C) cytokine activity in HIV infection, and the role of γ(C) cytokines in CD8(+) T-cell function and homeostasis, implicates these molecules among potential contributors to the observed decline of cytolytic activity (CTL) in HIV disease. In particular, this review will be highlighting information about the IL-7 receptor (IL-7R) complex, which is composed of the γ(C) and the IL-7Rα (CD127) chains. There has been an abundance of HIV-related CD127 research and its important role in CD8(+) T-cell survival and function. The expression of CD127 undergoes dramatic changes throughout the course of T-cell responses in HIV infection. The expression of CD127 is significantly decreased in progressive HIV disease, whereas effective antiretroviral therapy results in its recovery. Observations of impaired IL-7 activity in HIV(+) individuals have suggested that CD127 has an important role in HIV immunopathogenesis. In addition, a soluble form of CD127 (sCD127) is upregulated in the plasma of HIV(+) individuals. Hence, CD127 is being increasingly considered as a marker of disease prognosis, and related information may provide insight into understanding the expression and role of other γ(C) receptors in HIV disease and contribute to the development of novel cytokine-based therapeutics.

IL-15 ex vivo overcomes CD4+ T cell deficiency for the induction of human antigen-specific CD8+ T cell responses

CD4(+) Th cells are important for the induction and maintenance of antigen-specific CD8(+) T cell function, so their loss or dysfunction in HIV-infected or cancer patients could reduce the patients' ability to control viral infection. Previous work in murine systems indicated that IL-15 codelivered with vaccines could overcome CD4(+) Th cell deficiency for induction of functionally efficient CD8(+) T cells and maintenance of viral-specific CTLs, but its efficacy in helping primary human CD8(+) T cell responses is unknown. In the present study, a peptide-pulsed, DC-based human coculture ex vivo system was used to study the role of IL-15 in overcoming CD4(+) Th deficiency to elicit CD8(+) T cell responses in CD4-depleted PBMCs from healthy individuals and PBMCs from HIV-1-infected patients. We found that IL-15 could overcome CD4(+) Th deficiency to induce primary and recall memory CD8(+) T cell responses in healthy individuals. Moreover, in CD4-deficient, HIV-1-infected patients with diminished CD8(+) T cell responses, IL-15 greatly enhanced CD8(+) T cell responses to alloantigen. These results suggest that IL-15 may be useful in the development of therapeutic and preventive vaccines against cancers and viral infections in patients defective in CD4(+) Th cell.