T regulatory cells, the evolution of targeted immunotherapy

"To be or not to Be": Regulatory T cells in melanoma

In spite of progresses in the therapy of different malignancies, melanoma still remains as one of lethal types of skin tumor. Melanoma is almost easily treatable by surgery alone with higher overall survival rates when it is diagnosed at early stages. However, survival rates are decreased remarkably upon survival if the tumor is progressed to advanced metastatic stages. Immunotherapeutics have been prosperous in the development of anti-tumor responses in patients with melanoma through promotion of the tumor-specific effector T cells in vivo; nonetheless, suitable clinical outcomes have not been satisfactory. One of the underlying causes of the unfavorable clinical outcomes might stem from adverse effects of regulatory T (Treg) cell, which is a prominent mechanism of tumor cells to escape from tumor-specific immune responses. Evidence shows that a poor prognosis and low survival rate in patients with melanoma can be attributed to a higher Treg cell number and function in these subjects. As a result, to promote melanoma-specific anti-tumor responses, depletion of Treg cells appears to be a promising approach; even though the clinical efficacy of different approaches to attain appropriate Treg cell depletion has been inconsistent. Here in this review, the main purpose is to assess the role of Treg cells in the initiation and perpetuation of melanoma and to discuss effective strategies for Treg cell modulation with the aim of melanoma therapy.

Identification of Age-Associated Transcriptomic Changes Linked to Immunotherapy Response in Primary Melanoma

Melanoma is a lethal form of skin cancer. Immunotherapeutic agents such as anti-PD-1 (pembrolizumab and nivolumab) and anti-CTLA-4 (ipilimumab) have revolutionized melanoma treatment; however, drug resistance is rapidly acquired. Several studies have reported an increase in melanoma rates in older patients. Thus, the impact of ageing on transcriptional profiles of melanoma and response to immunotherapy is essential to understand. In this study, the bioinformatic analysis of RNA seq data of old and young melanoma patients receiving immunotherapy identifies the significant upregulation of extra-cellular matrix and cellular adhesion genes in young cohorts, while genes involved in cell proliferation, inflammation, non-canonical Wnt signaling and tyrosine kinase receptor ROR2 are significantly upregulated in the old cohort. Several Treg signature genes as well as transcription factors that are associated with dysfunctional T cell tumor infiltration are differentially expressed. The differential expression of several genes involved in oxidative phosphorylation, glycolysis and glutamine metabolism is also observed. Taken together, this study provides novel findings on the impact of ageing on transcriptional changes in melanoma, and novel therapeutic targets for future studies.

Immune Evasion Mechanism and AXL

Extensive interest in cancer immunotherapy is reported according to the clinical importance of CTLA-4 and (PD-1/PD-L1) [programmed death (PD) and programmed death-ligand (PD-L1)] in immune checkpoint therapies. AXL is a receptor tyrosine kinase expressed in different types of cancer and in relation to resistance against various anticancer therapeutics due to poor clinical prognosis. AXL and its ligand, i.e., growth arrest-specific 6 (GAS6) proteins, are expressed on many cancer cells, and the GAS6/AXL pathway is reported to promote cancer cell proliferation, survival, migration, invasion, angiogenesis, and immune evasion. AXL is an attractive and novel therapeutic target for impairing tumor progression from immune cell contracts in the tumor microenvironment. The GAS6/AXL pathway is also of interest immunologically because it targets fewer antitumor immune responses. In effect, several targeted therapies are selective and nonselective for AXL, which are in preclinical and clinical development in multiple cancer types. Therefore, this review focuses on the role of the GAS6/AXL signaling pathway in triggering the immunosuppressive tumor microenvironment as immune evasion. This includes regulating its composition and activating T-cell exclusion with the immune-suppressive activity of regulatory T cells, which is related to one of the hallmarks of cancer survival. Finally, this article discusses the GAS6/AXL signaling pathway in the context of several immune responses such as NK cell activation, apoptosis, and tumor-specific immunity, especially PD-1/PDL-1 signaling.

T cell receptor therapy against melanoma-Immunotherapy for the future?

Malignant melanoma has seen monumental changes in treatment options the last decade from the very poor results of dacarbazine treatment to the modern-day use of targeted therapies and immune checkpoint inhibitors. Melanoma has a high mutational burden making it more capable of evoking immune responses than many other tumours. Even when considering double immune checkpoint blockade with anti-CTLA-4 and anti-PD-1, we still have far to go in melanoma treatment as 50% of patients with metastatic disease do not respond to current treatment. Alternative immunotherapy should therefore be considered. Since melanoma has a high mutational burden, it is considered more immunogenic than many other tumours. T cell receptor (TCR) therapy could be a possible way forward, either alone or in combination, to improve the response rates of this deadly disease. Melanoma is one of the cancers where TCR therapy has been frequently applied. However, the number of antigens targeted remains fairly limited, although advanced personalized therapies aim at also targeting private mutations. In this review, we look at possible aspects of targeting TCR therapy towards melanoma and provide an implication of its use in the future.

Mechanisms of Epstein-Barr virus nuclear antigen 1 favor Tregs accumulation in nasopharyngeal carcinoma

Background

Documented reports proved that Epstein‐Barr virus (EBV) infection increased infiltration of Tregs in malignancy. However, the mechanism of EBV recruitment Tregs into nasopharyngeal carcinoma (NPC) tissues has not been detailed discussion.

Methods

Expression of EBV nuclear antigen 1 (EBNA1) and Foxp3 in NPC tissue samples was detected by immunohistochemistry. EBNA1+ NPC cell lines were used to coculture with PBMC, naïve T cells, Tregs, and monocytes. Percent of Treg was detected by flow cytometry.

Results

EBNA1 protein was overexpressed in NPC tissues, and was associated with a number of infiltrated Tregs. EBNA1+ NPC cells converted naïve T cells into Tregs by up‐regulated TGF‐β1. Enhanced CCL20 production in EBNA1‐expressed tumor cells increased Tregs migration. Polarized‐M2 macrophages by EBNA1 expression cells converted naïve T cells into Tregs.

Conclusions

EBNA1 favors accumulation of Tregs in NPC through: (a) upregulated TGF‐β1 converted naïve T cell into Treg; (b) upregulated CCL20 increased Treg migration; and (c) polarized‐M2 macrophage converted naïve T cell into Treg.

T cell pathology in skin inflammation

Forming the outer body barrier, our skin is permanently exposed to pathogens and environmental hazards. Therefore, skin diseases are among the most common disorders. In many of them, the immune system plays a crucial pathogenetic role. For didactic and therapeutic reasons, classification of such immune-mediated skin diseases according to the underlying dominant immune mechanism rather than to their clinical manifestation appears to be reasonable. Immune-mediated skin diseases may be mediated mainly by T cells, by the humoral immune system, or by uncontrolled unspecific inflammation. According to the involved T cell subpopulation, T cell–mediated diseases may be further subdivided into T1 cell–dominated (e.g., vitiligo), T2 cell–dominated (e.g., acute atopic dermatitis), T17/T22 cell–dominated (e.g., psoriasis), and Treg cell–dominated (e.g., melanoma) responses. Moreover, T cell–dependent and -independent responses may occur simultaneously in selected diseases (e.g., hidradenitis suppurativa). The effector mechanisms of the respective T cell subpopulations determine the molecular changes in the local tissue cells, leading to specific microscopic and macroscopic skin alterations. In this article, we show how the increasing knowledge of the T cell biology has been comprehensively translated into the pathogenetic understanding of respective model skin diseases and, based thereon, has revolutionized their daily clinical management.

Anti-regulatory T cell vaccines in immunotherapy: focusing on FoxP3 as target

Anti- tumor vaccination elicits imperfect immune responses against tumor cells; that is related to the presence of suppressive obstacles in the tumor microenvironment. The main members of suppressive milieu of tumor are heteroogenous groups of immune cells in which regulatory T cell is a substantial component. Tregs express different immunomodulatory molecules such as FoxP3. Transcription factor, FoxP3, is a specific intracellular marker of Treg and crucial for Treg development. Therefore it is an attractive target for cancer treatment. This article reviews some recent anti-Treg vaccine focusing on FoxP3 to ameliorate anti-tumor immune responses. Among them, fusion vaccine of FoxP3-Fc(IgG) recombinant DNA vaccine and its accordant protein vaccine represents effective results.

Phenotypic and Functional Properties of Tumor-Infiltrating Regulatory T Cells

Regulatory T (Treg) cells maintain immune homeostasis by suppressing excessive immune responses. Treg cells induce tolerance against self- and foreign antigens, thus preventing autoimmunity, allergy, graft rejection, and fetus rejection during pregnancy. However, Treg cells also infiltrate into tumors and inhibit antitumor immune responses, thus inhibiting anticancer therapy. Depleting whole Treg cell populations in the body to enhance anticancer treatments will produce deleterious autoimmune diseases. Therefore, understanding the precise nature of tumor-infiltrating Treg cells is essential for effectively targeting Treg cells in tumors. This review summarizes recent results relating to Treg cells in the tumor microenvironment, with particular emphasis on their accumulation, phenotypic, and functional properties, and targeting to enhance the efficacy of anticancer treatment.

A multi-antigen vaccine in combination with an immunotoxin targeting tumor-associated fibroblast for treating murine melanoma

A therapeutically effective cancer vaccine must generate potent antitumor immune responses and be able to overcome tolerance mechanisms mediated by the progressing tumor itself. Previous studies showed that glycoprotein 100 (gp100), tyrosinase-related protein 1 (TRP1), and tyrosinase-related protein 2 (TRP2) are promising immunogens for melanoma immunotherapy. In this study, we administered these three melanoma-associated antigens via lentiviral vectors (termed LV-3Ag) and found that this multi-antigen vaccine strategy markedly increased functional T-cell infiltration into tumors and generated protective and therapeutic antitumor immunity. We also engineered a novel immunotoxin, αFAP-PE38, capable of targeting fibroblast activation protein (FAP)-expressing fibroblasts within the tumor stroma. When combined with αFAP-PE38, LV-3Ag exhibited greatly enhanced antitumor effects on tumor growth in an established B16 melanoma model. The mechanism of action underlying this combination treatment likely modulates the immune suppressive tumor microenvironment and, consequently, activates cytotoxic CD8⁺ T cells capable of specifically recognizing and destroying tumor cells. Taken together, these results provide a strong rationale for combining an immunotoxin with cancer vaccines for the treatment of patients with advanced cancer.

Regulatory T cells in the immunotherapy of melanoma

Patients with melanoma are supposed to develop spontaneous immune responses against specific tumor antigens. However, several mechanisms contribute to the failure of tumor antigen-specific T cell responses, inducing immune escape. Importantly, immunosuppression mediated by regulatory T cells (Tregs) in tumor lesions is a dominant mechanism of tumor immune evasion. Based on this information, several therapies targeting Tregs such as cyclophosphamide, IL-2-based therapies, and antibodies against the surface molecular of Tregs have been developed. However, only some of these strategies showed clinical efficacy in patients with melanoma in spite of their success in shifting immune systems to antitumor responses in animal models. In the future, strategies specifically depleting local Tregs, inhibiting Treg migration to the tumor lesion, and Treg depletion in combination with other chemotherapies or immune modulation will hopefully bring benefits to melanoma patients.

Melanoma expression of matrix metalloproteinase-23 is associated with blunted tumor immunity and poor responses to immunotherapy

BACKGROUND

Matrix metalloproteinase-23 (MMP-23) can block the voltage-gated potassium channel Kv1.3, whose function is important for sustained Ca(2+) signaling during T cell activation. MMP-23 may also alter T cell activity and phenotype through cleavage of proteins affecting cytokine and chemokine signaling. We therefore tested the hypothesis that MMP-23 can negatively regulate the anti-tumor T cell response in human melanoma.

METHODS

We characterized MMP-23 expression in primary melanoma patients who received adjuvant immunotherapy. We examined the association of MMP-23 with the anti-tumor immune response - as assessed by the prevalence of tumor-infiltrating lymphocytes and Foxp3(+) regulatory T cells. Further, we examined the association between MMP-23 expression and response to immunotherapy. Considering also an in trans mechanism, we examined the association of melanoma MMP-23 and melanoma Kv1.3 expression.

RESULTS

Our data revealed an inverse association between primary melanoma MMP-23 expression and the anti-tumor T cell response, as demonstrated by decreased tumor-infiltrating lymphocytes (TIL) (P = 0.05), in particular brisk TILs (P = 0.04), and a trend towards an increased proportion of immunosuppressive Foxp3(+) regulatory T cells (P = 0.07). High melanoma MMP-23 expression is also associated with recurrence in patients treated with immune biologics (P = 0.037) but not in those treated with vaccines (P = 0.64). Further, high melanoma MMP-23 expression is associated with shorter periods of progression-free survival for patients receiving immune biologics (P = 0.025). On the other hand, there is no relationship between melanoma MMP-23 and melanoma Kv1.3 expression (P = 0.27).

CONCLUSIONS

Our data support a role for MMP-23 as a potential immunosuppressive target in melanoma, as well as a possible biomarker for informing melanoma immunotherapies.

Depletion of CD4+ CD25+ regulatory T cells promotes CCL21-mediated antitumor immunity

CCL21 is known to attract dendritic cells (DCs) and T cells that may reverse tumor-mediated immune suppression. The massive infiltration of tumors by regulatory T cells (Tregs) prevents the development of a successful helper immune response. In this study, we investigated whether elimination of CD4(+) CD25(+) Tregs in the tumor microenvironment using anti-CD25 monoclonal antibodies (mAbs) was capable of enhancing CCL21-mediated antitumor immunity in a mouse hepatocellular carcinoma (HCC) model. We found that CCL21 in combination with anti-CD25 mAbs (PC61) resulted in improved antitumor efficacy and prolonged survival, not only inhibited tumor angiogenesis and cell proliferation, but also led to significant increases in the frequency of CD4(+), CD8(+) T cells and CD11c(+) DCs within the tumor, coincident with marked induction of tumor-specific CD8(+) cytotoxic T lymphocytes (CTLs) at the local tumor site. The intratumoral immune responses were accompanied by the enhanced elaboration of IL-12 and IFN-γ, but reduced release of the immunosuppressive mediators IL-10 and TGF-β1. The results indicated that depletion of Tregs in the tumor microenvironment could enhance CCL21-mediated antitumor immunity, and CCL21 combined with anti-CD25 mAbs may be a more effective immunotherapy to promote tumor rejection.

Inflammatory monocytes are potent antitumor effectors controlled by regulatory CD4+ T cells

The present study evaluates the impact of immune cell populations on metastatic development in a model of spontaneous melanoma [mice expressing the human RET oncogene under the control of the metallothionein promoter (MT/ret mice)]. In this model, cancer cells disseminate early but remain dormant for several weeks. Then, MT/ret mice develop cutaneous metastases and, finally, distant metastases. A total of 35% of MT/ret mice develop a vitiligo, a skin depigmentation attributable to the lysis of normal melanocytes, associated with a delay in tumor progression. Here, we find that regulatory CD4(+) T cells accumulate in the skin, the spleen, and tumor-draining lymph nodes of MT/ret mice not developing vitiligo. Regulatory T-cell depletion and IL-10 neutralization led to increased occurrence of vitiligo that correlated with a decreased incidence of melanoma metastases. In contrast, inflammatory monocytes/dendritic cells accumulate in the skin of MT/ret mice with active vitiligo. Moreover, they inhibit tumor cell proliferation in vitro through a reactive oxygen species-dependent mechanism, and both their depletion and reactive oxygen species neutralization in vivo increased tumor cell dissemination. Altogether, our data suggest that regulatory CD4(+) T cells favor tumor progression, in part, by inhibiting recruitment and/or differentiation of inflammatory monocytes in the skin.

CD4+ CD25- FoxP3+ regulatory cells are the predominant responding regulatory T cells after human rotavirus infection or vaccination in gnotobiotic pigs

The distribution and dynamic changes of CD4(+) CD25(+) FoxP3(+) and CD4(+) CD25(-) FoxP3(+) regulatory T (Treg) cells induced by human rotavirus (HRV) infection and vaccination were examined in neonatal gnotobiotic pigs infected with virulent HRV (VirHRV) or vaccinated with attenuated HRV (AttHRV). Subsets of gnotobiotic pigs in the AttHRV and control groups were challenged with VirHRV at post-inoculation day (PID) 28. We demonstrated that VirHRV infection or AttHRV vaccination reduced frequencies and numbers of tissue-residing Treg cells, and decreased the frequencies of interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) producing CD4(+) CD25(-) Treg cells in ileum, spleen and blood at PID 28. The frequencies of IL-10 and TGF-β producing CD4(+) CD25(-) Treg cells in all sites at PID 28 were significantly inversely correlated with the protection rate against VirHRV-caused diarrhoea (r = -1, P < 0.0001). Hence, higher frequencies of functional CD4(+) CD25(-) Treg cells can be an indicator for poorer protective immunity against rotavirus. Our results highlighted the importance of CD4(+) CD25(-) Treg cells over CD4(+) CD25(+) Treg cells in rotavirus infection and immunity. AttHRV vaccination (induction of immune effector responses) reduced the expansion of CD4(+) CD25(-) Treg cells in ileum seen in the challenged naive pigs during the acute phase of VirHRV infection and preserved normal levels of intestinal TGF-β producing Treg cells post-challenge. The reduced suppressive effect of Treg cells in AttHRV-vaccinated pigs would unleash effector/memory T-cell activation upon challenge. Preserving TGF-β producing CD4(+) CD25(-) Treg cells is important in maintaining homeostasis. Based on our findings, a model is proposed to depict the dynamic equilibrium course of Treg and effector T-cell responses after primary rotavirus infection/vaccination and challenge.

Cancer-associated fibroblasts as targets for immunotherapy

Immunotherapy for solid tumors has shown promise in preclinical as well as early clinical studies. However, its efficacy remains limited. The hindrance to achieving objective, long-lasting therapeutic responses in solid tumors is, in part, mediated by the dynamic nature of the tumor and its complex microenvironment. Tumor-directed therapies fail to eliminate components of the microenvironment, which can reinstate a tumorigenic milieu and contribute to recurrence. Cancer-associated fibroblasts (CAFs) form the most preponderant cell type in the solid tumor microenvironment. Given their pervasive role in facilitating tumor growth and metastatic dissemination, CAFs have emerged as attractive therapeutic targets in the tumor microenvironment. In this article, we highlight the cross-talk between CAFs and cancer cells, and discuss how targeting CAFs has the potential to improve current immunotherapy approaches for cancer.

Tumor-infiltrating regulatory T cells: phenotype, role, mechanism of expansion in situ and clinical significance

In immunocompetent individuals, the immune system initially eradicates potentially tumorigenic cells as they develop, a capacity that is progressively lost when malignant cells acquire alterations that sustain immunosubversion and/or immunoevasion. One of the major mechanisms whereby cancer cells block antitumor immune responses involves a specific class of immunosuppressive T cells that-in the vast majority of cases-express the Forkhead box P3 (FOXP3) transcription factor. Such FOXP3(+) regulatory T cells (Tregs) accumulate within neoplastic lesions as a result of several distinct mechanisms, including increased infiltration, local expansion, survival advantage and in situ development from conventional CD4(+) cells. The prognostic/predictive significance of tumor infiltration by Tregs remains a matter of debate. Indeed, high levels of intratumoral Tregs have been associated with poor disease outcome in cohorts of patients affected by multiple, but not all, tumor types. This apparent discrepancy may relate to the existence of functionally distinct Treg subsets, to the fact that Tregs near-to-invariably infiltrate neoplastic lesions together with other cells from the immune system, notably CD4(+) and CD8(+) T lymphocytes and/or to peculiar features of some oncogenic programs that involve a prominent pro-inflammatory component. In this review, we will discuss the phenotype, function and clinical significance of various Treg subsets.

The tipping point for combination therapy: cancer vaccines with radiation, chemotherapy, or targeted small molecule inhibitors

Therapeutic cancer vaccines are a unique treatment modality in that they initiate a dynamic process of activating the host immune system, which can then be exploited by concurrent or subsequent therapies. The addition of immunotherapy to standard-of-care cancer therapies has shown evidence of efficacy in preclinical models and in the clinical setting. This review examines the preclinical and clinical interactions between vaccine-mediated tumor-specific immune responses and local radiation, systemic chemotherapy, or select small molecule inhibitors, as well as the potential synergy between these modalities.

High dose and low dose Lactobacillus acidophilus exerted differential immune modulating effects on T cell immune responses induced by an oral human rotavirus vaccine in gnotobiotic pigs

BACKGROUND

Strain-specific effects of probiotics in pro- or anti-inflammatory immune responses have been well recognized. Several proinflammatory Lactobacillus strains have been shown to act as adjuvants to enhance the immunogenicity of vaccines. However, dose effects of probiotics in modulating immune responses are not clearly understood. This study examined the dose effects of Lactobacillus acidophilus (LA) NCFM strain on T cell immune responses to rotavirus vaccination in a gnotobiotic (Gn) pig model.

METHODS

Frequencies of IFN-γ producing CD4+ and CD8+ T cell and IL-10 and TGF-β producing CD4+CD25+ and CD4+CD25- regulatory T (Treg) cell responses were determined in the intestinal and systemic lymphoid tissues of Gn pigs vaccinated with an oral human rotavirus vaccine in conjunction with low dose (5 feedings; up to 10(6) colony forming units [CFU]/dose) or high dose (14 feedings; up to 10(9)CFU/dose) or without LA feeding.

RESULTS

Low dose LA significantly promoted IFN-γ producing T cell responses and down-regulated Treg cell responses and their TGF-β and IL-10 productions in all the tissues compared to the high dose LA and control groups. To the contrary, high dose LA increased the frequencies of Treg cells in most of the tissues compared to the control groups. The dose effects of LA on IFN-γ producing T cell and CD4+CD25- Treg cell immune responses were similar in the intestinal and systemic lymphoid tissues and were independent from the vaccination.

CONCLUSION

Thus the same probiotic strain in different doses can either promote or suppress IFN-γ producing T cell or Treg cell immune responses. These findings have significant implications in the use of probiotic lactobacilli as immunostimulatory versus immunoregulatory agents. Probiotics can be ineffective or even detrimental if not used at the optimal dosage for the appropriate purposes.