Induced regulatory T cells in inhibitory microenvironments created by cancer

Introduction: Regulatory T cells (Tregs) accumulating in the peripheral circulation and tumor sites of patients contribute to tumor escape from the host immune system. Tregs encompass subsets of immune cells with distinct phenotypic and functional properties. Whereas natural (n) or thymic-derived (t) Tregs regulate responses to self-antigens, inducible (i) or peripheral (p) Tregs generated and expanded in regulatory microenvironments control immune responses to a broad variety of antigens.

Areas covered: Tregs accumulating in the tumor microenvironment (TME) are contextually regulated. They acquire phenotypic and functional attributes imposed by the inhibitory molecular pathways operating in situ. Several molecular pathways active in human cancer are reviewed. The pathways may differ from one tumor to another, and environmentally induced Tregs may be functionally distinct. Potential therapeutic strategies for selective silencing of iTregs are considered in the light of the newly acquired understanding of their phenotypic and functional diversity.

Expert opinion: Human Tregs accumulating in cancer comprise ‘bad’ subsets, which inhibit antitumor immunity, and ‘good’ anti-inflammatory subsets, which maintain tolerance to self and benefit the host. Future therapeutic strategies targeting Tregs will need to discriminate between these Treg subsets and will need to consider reprogramming strategies instead of Treg elimination. Re-establishment of effective antitumor immune responses in cancer patients without disturbing a normal homeostatic T-cell balance will greatly benefit from insights into inhibitory pathways engaged by human tumors.     

Immune responses in healthy and allergic individuals are characterized by a fine balance between allergen-specific T regulatory 1 and T helper 2 cells

The mechanisms by which immune responses to nonpathogenic environmental antigens lead to either allergy or nonharmful immunity are unknown. Single allergen-specific T cells constitute a very small fraction of the whole CD4+ T cell repertoire and can be isolated from the peripheral blood of humans according to their cytokine profile. Freshly purified interferon-gamma-, interleukin (IL)-4-, and IL-10-producing allergen-specific CD4+ T cells display characteristics of T helper cell (Th)1-, Th2-, and T regulatory (Tr)1-like cells, respectively. Tr1 cells consistently represent the dominant subset specific for common environmental allergens in healthy individuals; in contrast, there is a high frequency of allergen-specific IL-4-secreting T cells in allergic individuals. Tr1 cells use multiple suppressive mechanisms, IL-10 and TGF-beta as secreted cytokines, and cytotoxic T lymphocyte antigen 4 and programmed death 1 as surface molecules. Healthy and allergic individuals exhibit all three allergen-specific subsets in different proportions, indicating that a change in the dominant subset may lead to allergy development or recovery. Accordingly, blocking the suppressor activity of Tr1 cells or increasing Th2 cell frequency enhances allergen-specific Th2 cell activation ex vivo. These results indicate that the balance between allergen-specific Tr1 cells and Th2 cells may be decisive in the development of allergy.     

Pre-conditioning modifies the TME to enhance solid tumor CAR T cell efficacy and endogenous protective immunity

1. Download : Download high-res image (108KB)
2. Download : Download full-size image

     

Regulatory T cells, a potent immunoregulatory target for CAM researchers: modulating tumor immunity, autoimmunity and alloreactive immunity (III)

Regulatory T (T(reg)) cells are the major arbiter of immune responses, mediating actions through the suppression of inflammatory and destructive immune reactions. Inappropriate T(reg) cell frequency or functionality potentiates the pathogenesis of myriad diseases with ranging magnitudes of severity. Lack of suppressive capability hinders restraint on immune responses involved in autoimmunity and alloreactivity, while excessive suppressive capacity effectively blocks processes necessary for tumor destruction. Although the etiology of dysfunctional T(reg) cell populations is under debate, the ramifications, and their mechanisms, are increasingly brought to light in the medical community. Methods that compensate for aberrant immune regulation may not address the underlying complications; however, they hold promise for the alleviation of debilitating immune system-related disorders. The dominant immunoregulatory nature of T(reg) cells, coupled with recent mechanistic knowledge of natural immunomodulatory compounds, highlights the importance of T(reg) cells to practitioners and researchers of complementary and alternative medicine (CAM).     

Complement C3 depletion links to the expansion of regulatory T cells and compromises T-cell immunity in human abdominal sepsis: A prospective pilot study

Purpose

Complement depletion commonly occurred in septic patients, but this problem was often underestimated during the treatment process. This study was designed to determine the association between complement depletion and T-cell immunosuppression.

Methods

From November 2011 to March 2012, patients with severe abdominal sepsis were prospectively enrolled in a single center. The baseline levels of complement C3 were used to stratify subjects into 2 groups. Plasma levels of complement components, percentage of regulatory T cells (Tregs), and T-cell immunity indexes were monitored at times after admission. The relationship between C3 depletion and T-cell response was investigated, with clinical outcomes explored meanwhile.

Results

A total of 60 patients aged 43.9 ± 11.3 years were included within the period. C3 depletion, occurring in 65% of enrolled subjects, was strongly correlated with Treg expansion (P = .001) and decreased CD4⁺/CD8⁺ ratio (P = .008). This depletion was also related to prolonged hospital stay (P = .001), delayed time to operation (P < .001), increased postoperative complications (P = .036), and hospital expenditure (P < .001).

Conclusions

Complement C3 depletion was found to be linked to the expansion of Tregs during abdominal sepsis. Such depletion and associated immunosuppression should be paid close attention in the critical care.     

流式细胞术检测RA患者外周血CD4^＋CD25^＋FOXP3^＋ Treg细胞及其GITR表达

目的研究FOXP3和糖皮质激素诱导的肿瘤坏死因子受体(GITR)在类风湿关节炎(RA)患者外周血Treg细胞的表达并探讨其临床意义。方法用五色流式细胞术(FCM)检测40例健康体检者、61例RA患者外周血CD4 CD25 FOXP3 调节性T细胞(Treg)及其中GITR的表达情况。结果RA患者组FOXP3的平均荧光强度(MFI)低于健康对照组(P<0.05),CD4 CD25 FOXP3 Treg占CD4 T细胞的比例、CD4 CD25 FOXP3 Treg中GITR的表达率、GITR MFI和健康对照组相比无统计学差异(P>0.05);活动期RA患者的FOXP3 MFI和GITR MFI均显著低于非活动期组(P<0.01和P=0.032),CD4 CD25 FOXP3 Treg占CD4 T细胞中的比例、CD4 CD25 FOXP3 Treg中GITR的表达率与非活动期组相比无统计学差异(P>0.05)。结论RA患者的FOXP3表达低下,活动期组的FOXP3表达低于非活动期组,为其作为RA病情变化的判断指标提供进一步的证据。     

Enhanced therapeutic potential of adoptive immunotherapy by in vitro CD28/4-1BB costimulation of tumor-reactive T cells against a poorly immunogenic, major histocompatibility complex class I-negative A9P melanoma

Costimulation plays a critical role in T-cell activation and amplification of anti-tumor immunity. Although CD28 engagement triggers an early activation signal, activation-induced 4-1BB molecule on T cells transmits a crucial signal for further expansion and maturation of effector cells. In this report, the authors show that costimulation through CD28 and 4-1BB pathways synergistically enhances the therapeutic efficacy of T cells from tumor-draining lymph nodes. Intravenous adoptive transfer of costimulated T cells into mice bearing disseminated micrometastasis of a poorly immunogenic, major histocompatibility complex class I-negative A9P melanoma results in a 60% cure rate. Autopsy of mice that died after unsuccessful treatment revealed tumor growth in the liver, spleen, and skin with minimal or no evidence of pulmonary disease. In contrast, mice that received no treatment or noncostimulated T cells had massive pulmonary tumors, suggesting that adoptively transferred T cells are less effective against growth of extrapulmonary tumors. These results show that costimulation of tumor-draining lymph node T cells through CD28 and 4-1BB increases their potential for cancer immunotherapy and suggests that improper trafficking of tumor-reactive T cells to extrapulmonary sites must be improved to enhance clinical efficacy.     

The intestinal T cell response to alpha-gliadin in adult celiac disease is focused on a single deamidated glutamine targeted by tissue transglutaminase

The great majority of patients that are intolerant of wheat gluten protein due to celiac disease (CD) are human histocompatibility leukocyte antigen (HLA)-DQ2(+), and the remaining few normally express HLA-DQ8. These two class II molecules are chiefly responsible for the presentation of gluten peptides to the gluten-specific T cells that are found only in the gut of CD patients but not of controls. Interestingly, tissue transglutaminase (tTG)-mediated deamidation of gliadin plays an important role in recognition of this food antigen by intestinal T cells. Here we have used recombinant antigens to demonstrate that the intestinal T cell response to alpha-gliadin in adult CD is focused on two immunodominant, DQ2-restricted peptides that overlap by a seven-residue fragment of gliadin. We show that tTG converts a glutamine residue within this fragment into glutamic acid and that this process is critical for T cell recognition. Gluten-specific T cell lines from 16 different adult patients all responded to one or both of these deamidated peptides, indicating that these epitopes are highly relevant to disease pathology. Binding studies showed that the deamidated peptides displayed an increased affinity for DQ2, a molecule known to preferentially bind peptides containing negatively charged residues. Interestingly, the modified glutamine is accommodated in different pockets of DQ2 for the different epitopes. These results suggest modifications of anchor residues that lead to an improved affinity for major histocompatibility complex (MHC), and altered conformation of the peptide-MHC complex may be a critical factor leading to T cell responses to gliadin and the oral intolerance of gluten found in CD.     

Low dose Leishmania major promotes a transient T helper cell type 2 response that is down-regulated by interferon gamma-producing CD8+ T cells

An unresolved issue in the field of T helper (Th) cell development relates to the findings that low doses of antigen promote Th2 cell development in vitro, whereas several classic in vivo studies suggest the opposite. Here we resolve this paradox by studying the early immune response in mice after infection with different doses of Leishmania major. We found that low parasite doses induced a Th2 response in C57BL/6 (B6) mice, whereas high doses induced a Th1 response. However, the Th2 response in low dose-infected mice was transient and the animals healed. The appearance of a Th1 response after low dose infection was dependent upon the concomitant activation of interferon gamma-producing CD8+ T cells. In the absence of CD8+ T cells, the Th2 response was maintained. However, either neutralization of interleukin (IL)-4 or administration of IL-12 promoted a Th1 response after low dose infection of CD8-deficient mice, indicating that the required role for CD8+ T cells was limited to modulation of CD4+ T cell responses. Thus, the discrepant results seen between in vivo and in vitro studies on the effects of antigen dose on Th cell differentiation may depend upon whether CD8+ T cells participate in the immune response.