Th2 immune regulation induced by T cell vaccination in patients with multiple sclerosis

T cell responses to myelin basic protein (MBP) are potentially involved in the pathogenesis of multiple sclerosis (MS). In this study, we demonstrated that subcutaneous inoculations with irradiated autologous MBP-reactive T cell clones (T cell vaccination) elicited CD8+ anti-idiotypic T cell responses and CD4+ Th2 cell responses in patients with MS. Both regulatory cell types induced by T cell vaccination contributed to the inhibition of MBP-reactive T cells while they differed in the recognition pattern and functional properties. We describe for the first time that the Th2 regulatory cells reacted with activated but not resting T cells in the context of MHC class II molecules and inhibited the proliferation of MBP-reactive T cells through the secretion of IL-4 and IL-10. The T-T cell interaction mediated by Th2 regulatory cells was independent of the antigen specificity of activated T cells. The findings have important implications for our understanding of the regulatory mechanism induced by T cell vaccination.     

The spectrum of Merkel cell polyomavirus expression in Merkel cell carcinoma, in a variety of cutaneous neoplasms, and in neuroendocrine carcinomas from different anatomical sites

Most Merkel cell carcinomas display pure neuroendocrine differentiation (pure Merkel cell carcinoma), whereas a minority show combined neuroendocrine and nonneuroendocrine elements (combined Merkel cell carcinoma). Recent identification of Merkel cell polyomavirus DNA and Merkel cell polyomavirus large T antigen expression in a proportion of Merkel cell carcinomas has suggested viral-induced oncogenesis. To date, Merkel cell polyomavirus immunohistochemistry has shown an absence of viral large T antigen expression in combined Merkel cell carcinoma as well as select non-Merkel cell carcinoma cutaneous lesions and visceral neuroendocrine tumors. In our series, we aimed to further characterize the frequency and pattern of Merkel cell polyomavirus large T antigen expression by CM2B4 immunohistochemistry in primary and metastatic Merkel cell carcinoma (pure Merkel cell carcinoma and combined Merkel cell carcinoma) and various non-Merkel cell carcinoma lesions from patients with Merkel cell carcinoma, patients without Merkel cell carcinoma, and individuals with altered immune function. Merkel cell polyomavirus large T antigen was detected in 17 (63%) of 27 pure Merkel cell carcinomas and absent in all 15 (0%) combined Merkel cell carcinomas. Furthermore, complete concordance (100%) of Merkel cell polyomavirus large T antigen expression was observed in 10 cases of primary Merkel cell carcinoma and subsequent tumor metastases. We also evaluated 70 non-Merkel cell carcinoma lesions including 15 cases each of pulmonary and gastrointestinal neuroendocrine tumors. All 70 non-Merkel cell carcinoma lesions were negative for Merkel cell polyomavirus by CM2B4 immunohistochemistry, irrespective of any known Merkel cell carcinoma diagnosis and immune status. In summary, our identification of Merkel cell polyomavirus large T antigen expression in a subset of Merkel cell carcinoma and lack of findings in combined Merkel cell carcinomas and non-Merkel cell carcinoma lesions concur with earlier findings and implicate Merkel cell polyomavirus-independent pathogenesis in these cases. Overall, CM2B4 immunohistochemistry appears to be a specific method for Merkel cell polyomavirus detection and has the potential to play an important role in the diagnosis and classification of Merkel cell carcinoma in the future.     

Immune status of the murine 22q11.2 deletion syndrome model

Mice modeling the hemizygous deletion of chromosome 22q11.2 (22qMc) have been utilized to address various clinical phenotypes associated with the disease, including cardiac malformations, altered neural circuitry, and behavioral deficits. Yet, the status of the T cell compartment, an important clinical concern among 22q11.2 deletion syndrome (22qDS) patients, has not been addressed. While infancy and early childhood in 22qDS are associated with deficient T cell numbers and thymic hypoplasia, which can be severe in a small subset of patients, studies suggest normalization of the T cell counts by adulthood. We found that adult 22qMc do not exhibit thymic hypoplasia or altered thymic T cell development. Our findings that immune cell counts and inflammatory T cell activation are unaffected in 22qMc lend support to the hypothesis that human 22qDS immunodeficiencies are secondary to thymic hypoplasia, rather than intrinsic effects due to the deletion. Furthermore, the 22q11.2 deletion does not impact the differentiation capacity of T cells, nor their activity and response during inflammatory activation. Thus, 22qMc reflects the T cell compartment in adult 22qDS patients, and our findings suggest that 22qMc may serve as a novel model to address experimental and translational aspects of immunity in 22qDS.     

Heterogeneity and cell-fate decisions in effector and memory CD8+ T cell differentiation during viral infection

Heterogeneity is a hallmark of the adaptive immune system. This is most evident in the enormous diversity of B and T cell antigen receptors. There is also heterogeneity within antiviral T cell populations, and subsets of effector and memory T cells now permeate our thinking about specialization of T cell responses to pathogens. It has been less clear, however, how heterogeneity in developing virus-specific effector and memory T cells is related to cell-fate decisions in the immune response, such as the generation long-lived memory T cells. Here we discuss recent findings that might help redefine how heterogeneity in antiviral T cell populations gives rise to T cell subsets with short- and long-lived cell fates.     

CD4 and IL-2 mediated NK cell responses after COVID-19 infection and mRNA vaccination in adults

A detailed understanding of protective immunity against SARS-CoV-2 is incredibly important in fighting the pandemic. Central to protective immunity is the ability of the immune system to recall previous exposures. Although antibody and T cell immunity have gained considerable attention, the contribution of the NK cell compartment to immune recall and protection from SARS-CoV-2 has not been explored. In this study, we investigate the NK cell responses to stimulation with SARS-CoV-2 in previously exposed and non-exposed individuals. We show that NK cells demonstrate an enhanced CD4+ T cell dependent response when re-exposed to SARS-CoV-2 antigen. The enhanced response is dependent on T cells and correlates with the number of SARS-CoV-2 specific CD4 T cells. We find that IL-2 is a critical mediator of NK cell function. These findings suggest that NK cells contribute to the protective responses against SARS-CoV-2 through a cooperation with antigen-specific CD4 T cells and have significant implications on our understanding of protective immunity in SARS-CoV-2.     

Scant activation of CD8 T cells by antigen loaded on heat shock protein

Heat shock proteins (HSP) not only function as chaperones for denatured proteins but also for antigenic peptides, thus inducing protective T cell responses. Here we show that vaccination with peptide-loaded HSP70 causes initial interferon-gamma production by murine CD8 T cells but no T cell expansion. These CD8 T cells lacked cytotoxic activity in vitro and in vivo, which was not due to apoptosis. Restimulation with peptide-pulsed dendritic cells both bypassed the proliferative block and suspended the non-protective state of CD8 T lymphocytes in an infection model with the bacterial pathogen, Listeria monocytogenes. Cotransfer of antigen-specific CD4 T cells circumvented the proliferative arrest of CD8 T cells. Our data suggest that HSP vaccines induce CD8 T cell unresponsiveness unless proficient help is provided. Assuming that this model reflects the antigenically experienced human condition where immunological space is restricted and any T cell response possibly leads to suppression of heterologous reactions, our findings bear implications for rational vaccination protocols including those for immunocompromised patients.     

Permanent effector phenotype of neuroantigen-specific T cells acquired in the central nervous system during experimental allergic encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is regarded as an animal model of the human autoimmune disease multiple sclerosis (MS). Autoreactive T cells are present in the peripheral T cell repertoire of healthy mice and mediate clinical autoimmune disease only after activation by immunization or pathogens and migrate into the central nervous system (CNS). Because it is not known whether autoreactive T cells are regulated differentially once entering the CNS we investigated cytokine regulation in T cells from peripheral lymphatic organs and from the inflamed CNS ex vivo obtained from SJL mice after inducing relapsing-remitting EAE with PLP peptide 139–151. We show here that during acute EAE, an interleukin-2 (IL-2) biased T cell response exists in the spleen, while an interferon-γ (IFN-γ) biased T cell response prevails in the CNS of mice with acute EAE. The IFN-γ biased phenotype was stable with optimized costimulation and even after in vitro stimulation with IL-2. After adoptive transfer into naïve syngeneic mice these T cells were only partially reversed to an IL-2 biased phenotype. These findings of our work suggest that a permanent effector phenotype of neuroantigen-specific T cells is finally acquired in the CNS in EAE.     

Functionally Diverse Subsets in CD4 T Cell Responses Against Influenza

Background  Antibody alone cannot provide optimal protection against many infectious diseases impacting global heath. In these cases, our challenge is to develop innovative vaccines that generate protective populations of memory T cells. However, our studies suggest that current paradigms explaining how memory CD4 T cells provide protection are inadequate. This is likely due to both the paucity of and heterogeneity of memory CD4 T cells observed in vivo, which make analysis extremely difficult. Summary  Here, we discuss new findings that indicate there is extensive functional heterogeneity within effector and memory CD4 T cell populations both in vivo and in vitro. Using influenza as an example, we also discuss the merits of employing reductionist approaches to explore how unique subsets of CD4 T cells are generated, what mechanisms of protection they use, and where they stand on the axes of differentiation that define T cell subsets.     

ICOStomizing immunotherapies with T(H)17

New insights on the role of costimulatory molecules in T helper cell function have yielded exciting alternatives to the development of therapeutic strategies that target T cell costimulatory pathways. Inducible costimulatory molecule (ICOS) signaling is now shown by Paulos and colleagues to support expansion of human T helper 17 (T(H)17) cells that could exert antitumor activity. Here we discuss (i) how these findings aid in our understanding of mechanisms that govern T(H)17 cell functions and (ii) the potential application of these new insights to the development of immunotherapies.     

Further characterization of memory T cells existing in a case of CD8 deficiency

CD8 deficiency is a rare primary immunodeficiency caused by a defect of ZAP-70, which plays a pivotal role in T cell activation. We previously reported the existence of memory phenotype-CD4+ T cells in a case of CD8 deficiency, which demonstrates that activation signals through ZAP-70 are not essential to the phenotypic conversion of T cells from "naive" to "memory." In this study, we further characterized CD45RO+ T cells in a CD8 deficient patient. We showed that the patient's CD45RO+ T cell population had a wide variety of T cell receptor Vbeta-chain gene usage, and contained few clonally expanded T cells, while many clonally expanded T cells were present in the memory T cell population of age-matched healthy children. These results suggest that various kinds of antigens were involved in the differentiation of the patient's T cells, and that the differentiation into memory T cells was not accompanied by profound T cell proliferation. Moreover, our findings confirmed that the patient's CD45RO+CD4+ T cells had acquired effector-cytokine producing ability, indicating that there exists an alternative activation pathway which is independent of ZAP-70 for the acquisition of effector-cytokine producing ability.     

T cell tolerance to the skin: a central role for central tolerance

T cell tolerance to self-antigens is believed to be achieved in a two-step process. The first step, called central tolerance, takes place in the thymus. The second step takes place outside the thymus in secondary lymphoid organs. One may ask why two mechanisms are needed to insure T cell tolerance. These two mechanisms share redundant functions and dysfunctions, leading to T cell-mediated autoimmune syndromes. By reviewing the literature on relevant animal models for T cell tolerance and our own recent findings, we are providing evidences that only central tolerance is acting for the skin.     

Regulation of TCR-mediated T cell activation by TNF-RII

In the present study, we investigated the role of tumor necrosis factor receptor II (TNF-RII) in human T cell activation induced via the T cell receptor (TCR) in an antigen-presenting cell-independent system. Our results confirm that interaction of TNF-alpha with TNF-RII but not TNF-RI is directly costimulatory to TCR-mediated T cell activation, thereby augmenting T cell proliferation, expression of T cell activation markers (CD25, human leukocyte antigen-DR, TNF-RII), and secretion of cytokines such as interferon-gamma and TNF-alpha. In contrast to the well-defined costimulatory molecule CD28, costimulation via TNF-RII showed significant differences in kinetics, requirement for cross-linking, redundancy of intracellular signaling pathways involved, and the capacity to induce interleukin (IL)-2, IL-10, and IL-13 secretion. In addition, cross-linking TNF-RII had the capacity to down-regulate TCR/CD28-induced Ca++ mobilization, IL-2 mRNA expression, and IL-2 and IL-10 secretion. Taken together, our findings demonstrate that TNF-RII plays a unique role among the T cell costimulatory molecules, as TNF-RII ligation can have positive and negative effects on TCR-dependent signaling. TNF-RII cross-linking has an inhibitory effect on early TCR signaling events proximal to induction of Ca++ flux, which ultimately leads to modulation of the T cell cytokine pattern expressed.     

Angiotensin-converting enzyme inhibitor captopril prevents activation-induced apoptosis by interfering with T cell activation signals

Captopril is an orally active inhibitor of angiotensin-converting enzyme (ACE) which is widely used as an anti-hypertensive agent. In addition to its ability to reduce blood pressure, captopril has a number of other biological activities. Recently the drug was shown to inhibit Fas-induced apoptosis in human activated peripheral T cells and human lung epithelial cells. In this study, we investigated whether captopril blocks activation-induced apoptosis in murine T cell hybridomas, and found that captopril inhibited IL-2 synthesis and apoptotic cell death upon activation with anti-CD3 antibody. In addition, captopril inhibited an inducible caspase-3-like activity during activation-induced apoptosis. On the other hand, captopril did not interfere with Fas signalling, since anti-Fas antibody-induced apoptosis in Fas+ Jurkat cells was unaffected by the drug. Furthermore, we examined whether captopril blocks activation-induced apoptosis by interfering with expression of Fas, Fas ligand (FasL), or both on T cell hybridomas. FasL expression on activated T cells was significantly inhibited by captopril, whereas up-expression of Fas was partially inhibited, as assessed by cell surface staining. Taking all data together, we conclude that captopril prevents activation-induced apoptosis in T cell hybridomas by interfering with T cell activation signals. Captopril has been reported to induce systemic lupus erythematosus syndrome, and our findings may be useful for elucidating the mechanism of captopril-induced autoimmunity.     

Functions of thymic stromal lymphopoietin in immunity and disease

Thymic stromal lymphopoietin (TSLP) is an interleukin 7-like cytokine expressed mainly by epithelial cells. Current studies provide compelling evidence that TSLP is capable of activating dendritic cells to promote T helper (Th) 2 immune responses. TSLP has also been shown to directly promote Th2 differentiation of na?ve CD4(+) T cell and activate natural killer T cells, basophils and other innate immune cells at the initial stage of inflammation. In addition, TSLP affects B cell maturation and activation and can also influence regulatory T (Treg) cell differentiation and development. TSLP-induced Th2 responses are associated with the pathogenesis of allergic inflammatory diseases, including atopic dermatitis, asthma, and rhinitis. Based on recent findings in humans and mouse models, TSLP might also be involved in the pathogenesis of inflammatory bowel disease and progression of cancer. In this review, we will summarize our current understanding of the biology of TSLP and highlight the important issues for future investigations.     

Further evidence for T cell abnormalities in chronic lymphocytic leukaemia of the B cell type.

Functional properties were studied in the purified T cell fraction of patients with chronic lymphocytic leukaemia of the B cell type (B-CLL). This analysis included the evaluation of T suppressor activity when investigated patients' T cells were co-cultured together with allogenic normal B and OKT4 enriched T cells in the presence of pokeweed mitogen (PWM). The Ig secreting cells (ISC) were assessed in a reverse haemolytic plaque assay (RHPA). Antibody-dependent cytotoxicity (ADCC) and natural killer activity (NK) were determined in a 51Cr release assay. Furthermore, purified T cells reactive with the monoclonal antibody HNK1, known to recognize most effector cells in ADCC and NK, were enumerated using an indirect immunofluorescence. Our results revealed increased T suppressor cell activity and markedly deficient NK activity in peripheral blood lymphocytes (PBL), T cell and T gamma cell fractions from B-CLL patients, whereas ADCC potential was only increased in T cells and T gamma cells. Accordingly, T cells were recognized by HNK1 in greater numbers in B-CLL patients than in healthy subjects. Our data suggest that there may be a link between our findings and the hypogammaglobulinaemia as well as the increased incidence of second neoplasias reported in CLL.     

Contact Between Good Friends: What Limiting Dilution Analysis Taught Us

The demonstration in the 1960s that T cells collaborated with B cells in enabling antibody responses to simple protein antigens opened up the challenge of how to investigate the interactions of two rare antigen-specific lymphocytes within a vast population. One idea was that T cells made soluble factors that could activate B cells at a distance; the other was that rare T cells and B cells came into contact. Using limiting dilution analysis, we asked the question 'How many B cells could a single T cell collaborate with in the short term?' Unequivocally, the answer was just one. This implied a need for cell contact, and coupled with the observation for genetic restriction in T-cell/B-cell co-operation, seemed to make a watertight case for direct coupling. Claims of diffusible antigen-specific factors undermined the importance of our findings at that time. Remarkably, those claims have not yet been retracted and our original findings that collaborating T cells and B cells must come into contact have never achieved the recognition that they deserved.     

Development of a Unique T Cell Receptor Gene-Transferred Tax-Redirected T Cell Immunotherapy for Adult T Cell Leukemia

Adult T cell leukemia/lymphoma (ATL) is an aggressive peripheral T cell neoplasm caused by infection with human T cell lymphotropic virus type-1 (HTLV-1). Its prognosis remains extremely poor. Tax, the most important regulatory protein for HTLV-1, is associated with the aggressive proliferation of host cells and is also a major target antigen for CD8⁺ cytotoxic T cells (CTLs). Based on our previous findings that Tax-specific CTLs with a T cell receptor (TCR) containing a unique amino-acid sequence motif exhibit strong HLA-A*24:02-restricted, Tax_301-309-specific activity against HTLV-1, we aimed to develop a Tax-redirected T cell immunotherapy for ATL. TCR-ɑ/β genes were cloned from a previously established CTL clone and transduced into peripheral blood mononuclear cells (PBMCs) of healthy volunteers using a retroviral siTCR vector. Then the cytotoxic efficacy against HTLV-1-infected T cells or primary ATL cells was assessed both in vitro and in vivo. The redirected CTLs (Tax-siCTLs) produced a large amount of cytokines and showed strong killing activity against ATL/HTLV-1-infected T cells in vitro, although they did not have universal activity against ATL cells. Next, in a xenograft mouse model using an HTLV-1-infected T cell line (MT-2), in all mice treated with Tax-siCTLs, the tumor rapidly diminished and finally disappeared without normal tissue damage, although all mice that were untreated or treated with non-gene-modified PBMCs died because of tumor progression. Our findings confirm that Tax-siCTLs can exert strong anti-ATL/HTLV-1 effects without a significant reaction against normal cells and have the potential to be a novel immunotherapy for ATL patients.     

CTLA-4: new insights into its biological function and use in tumor immunotherapy

The discovery of multiple costimulatory cell surface molecules that influence the course of T cell activation has increased our appreciation of the complexity of the T cell response. It remains clear, however, that CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) are the critical costimulatory receptors that determine the early outcome of stimulation through the T cell antigen receptor (TCR). Details of how the T cell integrates TCR stimulation with the costimulatory signals of CD28 and the inhibitory signals of CTLA-4 remain to be established, but unique features of the cell biology of CTLA-4 provide important insights into its function. We summarize here recent findings that suggest a previously unrecognized role for CTLA-4 in the regulation of T cell responses. We also describe preclinical and clinical results that indicate manipulation of CTLA-4 has considerable promise as a strategy for the immunotherapy of cancer.     

Degenerate recognition and response of human CD4+ Th cell clones: implications for basic and applied immunology

It was once considered that the T cell response is an all or nothing type event, but recent studies have clearly indicated that T cells show many different types of activation in recognition of altered ligands for T cell receptors (TCR). In this review, we summarize our recent findings on the response of human CD4+ helper T (Th) cell clones to altered peptide ligands (APL); peptides carrying single or multiple residue substitutions in antigenic peptides. The extensive analyses revealed that TCR-antagonism and partial agonism are frequently observed by the stimulation with APLs substituted at particular amino acid residues of antigenic peptides. We observed unique partially agonistic APLs inducing prolongation of T cell survival without cell proliferation. Superagonistic APLs stimulated enhanced proliferation and production of cytokines in Th cell clones reactive to tumor-associated antigens. The other APL induced enhanced production of interleukin-12 by antigen presenting cells and subsequent enhancement of IFN-gamma production by T cells reactive to allergens. By utilizing an HLA-DR-restricted T cell epitope library generated by mutated invariant chain genes, it was revealed that human Th cell clones recognize a more diverse array of peptides with multiple and simultaneous amino acid substitutions in an antigenic peptide. APLs also induced altered intracellular signaling events including intracellular calcium increase and phosphorylation of signaling molecules. This information provides basic knowledge regarding the characteristics of antigen recognition by human Th cells and the subsequent activation, and a novel method for manipulation of human Th cell responses by APLs, as a possible candidate for antigen-specific immuno-potentiating or immunosuppressive therapy.