S-adenosylmethionine blocks tumorigenesis and with immune checkpoint inhibitor enhances anti-cancer efficacy against BRAF mutant and wildtype melanomas.

Despite marked success in treatment with immune checkpoint inhibitor (CPI), only a third of patients are responsive. Thus, melanoma still has one of the highest prevalence and mortality rates; which has led to a search for novel combination therapies that might complement CPI. Aberrant methylomes are one of the mechanisms of resistance to CPI therapy. S-adenosylmethionine (SAM), methyl donor of important epigenetic processes, has significant anti-cancer effects in several malignancies; however, SAM's effect has never been extensively investigated in melanoma. We demonstrate that SAM modulates phenotype switching of melanoma cells and directs the cells towards differentiation indicated by increased melanogenesis (melanin and melanosome synthesis), melanocyte-like morphology, elevated Mitf and Mitf activators' expression, increased antigen expression, reduced proliferation, and reduced stemness genes' expression. Consistently, providing SAM orally, reduced tumor growth and progression, and metastasis of syngeneic BRAF mutant and wild-type (WT) melanoma mouse models. Of note, SAM and anti-PD-1 antibody combination treatment had enhanced anti-cancer efficacy compared to monotherapies, showed significant reduction in tumor growth and progression, and increased survival. Furthermore, SAM and anti-PD-1 antibody combination triggered significantly higher immune cell infiltration, higher CD8+ T cells infiltration and effector functions, and polyfunctionality of CD8+ T cells in YUMMER1.7 tumors. Therefore, SAM combined with CPI provides a novel therapeutic strategy against BRAF mutant and WT melanomas and provides potential to be translated into clinic.

Mechanisms of human FoxP3+ Treg cell development and function in health and disease.

Regulatory T (Treg ) cells represent an essential component of peripheral tolerance. Given their potently immunosuppressive functions that is orchestrated by the lineage-defining transcription factor forkhead box protein 3 (FoxP3), clinical modulation of these cells in autoimmunity and cancer is a promising therapeutic target. However, recent evidence in mice and humans indicates that Treg cells represent a phenotypically and functionally heterogeneic population. Indeed, both suppressive and non-suppressive Treg cells exist in human blood that are otherwise indistinguishable from one another using classical Treg cell markers such as CD25 and FoxP3. Moreover, murine Treg cells display a degree of plasticity through which they acquire the trafficking pathways needed to home to tissues containing target effector T (Teff ) cells. However, this plasticity can also result in Treg cell lineage instability and acquisition of proinflammatory Teff cell functions. Consequently, these dysfunctional CD4+ FoxP3+ T cells in human and mouse may fail to maintain peripheral tolerance and instead support immunopathology. The mechanisms driving human Treg cell dysfunction are largely undefined, and obscured by the scarcity of reliable immunophenotypical markers and the disregard paid to Treg cell antigen-specificity in functional assays. Here, we review the mechanisms controlling the stability of the FoxP3+ Treg cell lineage phenotype. Particular attention will be paid to the developmental and functional heterogeneity of human Treg cells, and how abrogating these mechanisms can lead to lineage instability and Treg cell dysfunction in diseases like immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome, type 1 diabetes, rheumatoid arthritis and cancer.

An ENU-induced splicing mutation reveals a role for Unc93b1 in early immune cell activation following influenza A H1N1 infection.

Genetic and immunological analysis of host-pathogen interactions can reveal fundamental mechanisms of susceptibility and resistance to infection. Modeling human infectious diseases among inbred mouse strains is a proven approach but is limited by naturally occurring genetic diversity. Using N-ethyl-N-nitrosourea mutagenesis, we created a recessive loss-of-function point mutation in Unc93b1 (unc-93 homolog B1 (C. elegans)), a chaperone for endosomal Toll-like receptors (TLR)3, TLR7 and TLR9, which we termed Letr for 'loss of endosomal TLR response'. We used Unc93b1(Letr/Letr) mice to study the role of Unc93b1 in the immune response to influenza A/PR/8/34 (H1N1), an important global respiratory pathogen. During the early phase of infection, Unc93b1(Letr/Letr) mice had fewer activated exudate macrophages and decreased expression of CXCL10, interferon (IFN)-γ and type I IFN. Mutation of Unc93b1 also led to reduced expression of the CD69 activation marker and a concomitant increase in the CD62L naive marker on CD4(+) and CD8(+) T cells in infected lungs. Finally, loss of endosomal TLR signaling resulted in delayed viral clearance that coincided with increased tissue pathology during infection. Taken together, these findings establish a role for Unc93b1 and endosomal TLRs in the activation of both myeloid and lymphoid cells during the innate immune response to influenza.

Functional evaluation of the role of C-type lectin domain family 16A at the chromosome 16p13 locus.

The type 1 diabetes-associated 16p13 locus contains the CLEC16A gene. Its preferential immune cell expression suggests involvement in autoimmunity. Given its elevated expression in dendritic and B cells - known professional antigen-presenting cells (APCs) - we hypothesize that C-type lectin domain family 16 member A (CLEC16A) may be involved in T cell co-stimulation and consequent activation and proliferation. We also sought to identify CLEC16A's subcellular localization. The effect of the CLEC16A knock-down (KD) on B cell co-stimulation and activation of T cells was tested in human lymphoblastoid cell lines (LCLs) by co-culture with CD4(+) T cells. T cell activation and proliferation were determined by flow-cytometric analysis of CD69 and CD25 expression and carboxyfluorescein succinimidyl ester (CFSE) dilution, respectively. CLEC16A subcellular localization in K562 cells was examined by immunofluorescence. We show that the CLEC16A KD did not affect the tested indices of lymphoblastoid cell line (LCL) APC capacity. Additionally, the percentage of activated T cells following LCL co-culture was not affected significantly by the CLEC16A KD. T cells co-cultured with KD or control LCLs also exhibited similar cell division profiles. CLEC16A co-localized with an endoplasmic reticulum (ER) marker, suggesting that it may be an ER protein. In conclusion, CLEC16A may not be involved in T cell co-stimulation. Additional studies on CLEC16A, accounting for its ER localization, are needed to uncover its biological role.

Transfer of cell membrane components via trogocytosis occurs in CD4+ Foxp3+ CD25+ regulatory T-cell contact-dependent suppression.

A key component of the immune system is its ability to establish and maintain peripheral tolerance. Naturally occurring CD4+ CD25+ Foxp3+ regulatory T (nTreg) cells represent an important means by which this is accomplished, through their potent ability to suppress the actions of both CD4+ and CD8+ effector (Teff) cells in vitro and in vivo. We hypothesized that direct contact between nTreg and Teff cells is sufficient for nTreg cell-contact suppression. We first show that nTreg cell suppression is independent of APCs and their derived co-stimulatory signals. We then used a two-colour, lipid dye labelling and quantification approach to formally demonstrate that nTreg cells specifically form cell conjugates with responding T (Tresp) cells only under TCR activating conditions. Strikingly, activated CD4+ nTreg cells undergo progressive trogocytosis, a process by which membrane fragments are transferred from one cell subset to another, with Tresp cells more readily than Teff cells. These results are the first to show that nTreg cell cognate interactions with Tresp cells leads to trogocytosis between the cells, and the first to relate the degree of trogocytosis with the level of nTreg-mediated suppression.

Intravenous immunoglobulin attenuates airway hyperresponsiveness in a murine model of allergic asthma.

BACKGROUND: Intravenous immunoglobulin (IVIG) has potent anti-inflammatory and immune-modulating properties. IVIG has been utilized as a steroid-sparing agent in severe asthma, but the results of clinical trials have been conflicting. OBJECTIVE: To determine whether IVIG is able to attenuate bronchial reactivity, pulmonary inflammation and T cell function using a murine model of allergic airways disease. METHODS: BALB/c or C57BL/6 mice were sensitized to ovalbumin (OVA) or a phosphate-buffered saline control using local nasal sensitization, and then received five intranasal challenges on days 28-32 before sacrifice. Mice were treated intraperitoneally with either IVIG (1-2 g/kg) or equivalent human serum albumin 24 h before the first OVA challenge. Bronchial reactivity to methacholine was examined using the FlexiVent small animal ventilator. We evaluated pulmonary histology, mRNA from lung digests for T-helper type 2 (Th2)-related genes and bronchoalveolar lavage for cell counts and cytokines. Splenocytes were utilized to study OVA-induced cell proliferation, cytokine production and dendritic cell maturation. RESULTS: IVIG markedly attenuated the perivascular and peribronchial pulmonary inflammation, and decreased bronchial hyperresponsiveness to methacholine. IVIG treatment of splenocytes from sensitized animals diminished cellular proliferation to OVA, whereas IVIG treatment in vivo markedly attenuated OVA-driven splenocyte proliferation. This is accompanied by diminished IL-13 and TNF-α levels in splenocyte culture, decreased expression of Jagged-1, increased Delta-4 and decreased GATA-3 mRNA levels, signs that IVIG has suppressed the expected Th2 response that accompanies repeated allergen exposure. Increased regulatory T cells were found in draining pulmonary lymph nodes in IVIG-treated mice but not in controls. CONCLUSIONS AND CLINICAL RELEVANCE: IVIG was effective in ameliorating allergic airway disease in our model. IVIG may be a promising adjunct therapy requiring further study for patients with severe asthma.

TGF-beta1 modulates Foxp3 expression and regulatory activity in distinct CD4+ T cell subsets.

Although forkhead box p3 (Foxp3) expression is restricted to naturally occurring CD4(+) regulatory T cells (T(REG)), little is known about the various signals that regulate it in T cells. As TGF-beta has been reported to modulate Foxp3 expression in T cells, we investigated its effects on the induction or maintenance of regulatory functions in different CD4(+) T cell subsets. TGF-beta1 priming was able to promote differentiation of T(REG) cells from nonregulatory CD4(+)CD25(-) T cells in a concentration-dependent manner through Foxp3 induction. As CD4(+)CD25(-) T cells remain a highly heterogeneous population with variable degrees of antigen experience, we then examined the effect of TGF-beta1 on naive CD4(+)CD25(-)CD45RB(HIGH) T cells. Freshly isolated or TGF-beta1-treated CD4(+)CD25(-)CD45RB(HIGH) T cells never displayed any regulatory functions or significant Foxp3 expression following TCR activation. In stark contrast, freshly isolated CD4(+)CD25(-)CD45RB(LOW) cells, albeit expressing low levels of Foxp3 mRNA and protein, were unable to suppress CD4(+) effector T cell proliferation but acquired regulatory activity and de novo Foxp3 expression following TGF-beta1 exposure. Furthermore, suppression was IL-10-dependent, as anti-IL-10 receptor antibody treatment abrogated this suppression completely, consistent with the ability of TGF-beta1-treated CD4(+)CD25(-)CD45RB(LOW) to synthesize IL-10 upon restimulation in vitro. Last, we show that TGF-beta1 treatment or blockade did not lead to enhanced expansion or function of naturally occurring CD4(+)CD25(+) T(REG) cells, although it maintained Foxp3 mRNA and protein expression. Altogether, TGF-beta1 promotes the induction of IL-10-secreting CD4(+) T(REG) cells from CD4(+)CD25(-)CD45RB(LOW) precursors through de novo Foxp3 production and maintains natural T(REG) cell peripheral homeostasis by sustaining Foxp3 expression.

Control of type 1 autoimmune diabetes by naturally occurring CD4+CD25+ regulatory T lymphocytes in neonatal NOD mice.

Nonobese diabetic (NOD) mice serve as a model of spontaneous type 1 diabetes (T1D), a T cell-mediated autoimmune disease leading to the destruction of pancreatic insulin-producing beta islet cells. A possible deficiency in regulatory T (T(reg)) cell development or function may promote the activation, expansion, and recruitment of autoreactive T cells and the onset of T1D. Naturally occurring CD4(+)CD25(+) T(reg) (nT(reg)) cells, which typically display potent inhibitory effects on T cell functions in vitro and in vivo, may be defective at controlling autoimmunity in T1D. We have examined the relative contribution of CD4(+)CD25(+) nT(reg) cells in the immune regulation of T1D in the NOD mouse model. CD4(+)CD25(+) T cells represent 5-10% of CD4(+) thymocytes or peripheral T cells from prediabetic neonatal NOD mice, are anergic to TCR signals, and potently suppress activated T cells in a contact-dependent and cytokine-independent fashion in vitro. Unlike total CD4(+) T cells, prediabetic CD25(+)-depleted CD4(+) T cells are potently diabetogenic when transferred in immunodeficient NOD mice. Co-transfer of CD4(+)CD25(+) T cells from thymocytes or peripheral lymphoid tissues of neonatal NOD mice dramatically halts disease development and beta-islet cell lymphocytic infiltration, even when T1D is induced by CD4(+) T cells from BDC2.5 transgenic or diabetic NOD mice. Finally, we show that CD4(+)CD25(+) T(reg) preferentially accumulate in inflamed pancreatic environments, where they potently inhibit the antigen-specific expansion and cytokine effector functions of diabetogenic T cells. Thus, CD4(+)CD25(+) T cell-mediated regulation is operative in the prediabetic neonatal T cell repertoire and can suppress the diabetogenic process and control the onset of T1D.

Control of T-cell activation by CD4+ CD25+ suppressor T cells.

Depletion of the minor ( approximately 10%) subpopulation of CD4+ T cells that co-expresses CD25 (interleukin (IL)-2 receptor alpha-chain) by thymectomy of neonates on the third day of life or by treatment of adult CD4+ T cells with anti-CD25 and complement results in the development of organ-specific autoimmunity. Autoimmune disease can be prevented by reconstitution of the animals with CD4+ CD25+ cells. CD4+ CD25+-mediated protection of autoimmune gastritis does not require the suppressor cytokines IL-4, IL-10, or transforming growth factor (TGF)-beta. Mice that express a transgenic T-cell receptor (TCR) derived from a thymectomized newborn that recognizes the gastric parietal cell antigen H/K ATPase all develop severe autoimmune gastritis very early in life. CD4+ CD25+ T cells are also powerful suppressors of the activation of both CD4+ and CD8+ T cells in vitro. Suppression is mediated by a cell contact-dependent, cytokine-independent T-T interaction. Activation of CD4+ CD25+ via their TCR generates suppressor effector cells that are capable of non-specifically suppressing the activation of any CD4+ or CD8+ T cell. Activation of suppressor effector function is independent of co-stimulation mediated by CD28/CTLA-4 interactions with CD80/CD86. We propose that CD4+ CD25+ T cells recognize organ-specific antigens, are recruited to sites of autoimmune damage where they are activated by their target antigen, and then physically interact with autoreactive CD4+ or CD8+ effector cells to suppress the development of autoimmune disease.

Cutting edge: control of CD8+ T cell activation by CD4+CD25+ immunoregulatory cells.

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of CD4(+)CD25(-) T cell activation in vitro. We demonstrate that CD4(+)CD25(+) T cells also suppress both proliferation and IFN-gamma production by CD8(+) T cells induced either by polyclonal or Ag-specific stimuli. CD4(+)CD25(+) T cells inhibit the activation of CD8(+) responders by inhibiting both IL-2 production and up-regulation of IL-2Ralpha-chain (CD25) expression. Suppression is mediated via a T-T interaction as activated CD4(+)CD25(+) T cells suppress the responses of TCR-transgenic CD8(+) T cells stimulated with soluble peptide-MHC class I tetramers in the complete absence of APC. These results broaden the immunoregulatory role played by CD4(+)CD25(+) T cells in the prevention of autoimmune diseases, but also raise the possibility that they may hinder the induction of effector CD8(+) T cells to tumor or foreign Ags.

The inhibitory effects of transforming growth factor-beta-1 (TGF-beta1) in autoimmune diseases.

The importance of transforming growth factor-beta-1 (TGF-beta1) in immunoregulation and tolerance has been increasingly recognized. It is now proposed that there are populations of regulatory T cells (T-reg), some designated T-helper type 3 (Th3), that exert their action primarily by secreting this cytokine. Here, we emphasize the following concepts: (1) TGF-beta1 has multiple suppressive actions on T cells, B cells, macrophages, and other cells, and increased TGF-beta1 production correlates with protection and/or recovery from autoimmune diseases; (2) TGF-beta1 and CTLA-4 are molecules that work together to terminate immune responses; (3) Th0, Th1 and Th2 clones can all secrete TGF-beta1 upon cross-linking of CTLA-4 (the functional significance of this in autoimmune diseases has not been reported, but TGF-beta1-producing regulatory T-cell clones can produce type 1 inflammatory cytokines); (4) TGF-beta1 may play a role in the passage from effector to memory T cells; (5) TGF-beta1 acts with some other inhibitory molecules to maintain a state of tolerance, which is most evident in immunologically privileged sites, but may also be important in other organs; (6) TGF-beta1 is produced by many cell types, is always present in the plasma (in its latent form) and permeates all organs, binding to matrix components and creating a reservoir of this immunosuppressive molecule; and (7) TGF-beta1 downregulates adhesion molecules and inhibits adhesion of leukocytes to endothelial cells. We propose that rather than being passive targets of autoimmunity, tissues and organs actively suppress autoreactive lymphocytes. We review the beneficial effects of administering TGF-beta1 in several autoimmune diseases, and show that it can be effectively administered by a somatic gene therapy approach, which results in depressed inflammatory cytokine production and increased endogenous regulatory cytokine production.

Prevention of experimental allergic encephalomyelitis by intramuscular gene transfer with cytokine-encoding plasmid vectors.

Antiinflammatory cytokines such as transforming growth factor beta1 (TGF-beta1) and interleukin 4 (IL-4) can protect from autoimmune diseases. To study the immunoregulatory effects of these cytokines in vivo, we used a method of gene therapy that permits continuous cytokine delivery over a period of weeks. We injected naked plasmid DNA expression vectors encoding either TGF-beta1 (pVR-TGF-beta1) or an IL-4-IgG1 chimeric protein (pVR-IL-4-IgG1) intramuscularly. This resulted in production of TGF-beta1 or IL-4-IgG1, respectively, and protection from myelin basic protein (MBP)-induced experimental allergic encephalomyelitis (EAE). TGF-beta1 gene delivery had pronounced downregulatory effects on T cell proliferation and production of interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha), on in vitro restimulation with MBP. IL-4-IgG1 vector administration also suppressed these responses, although much less than TGF-beta1, and enhanced secretion of endogenous IL-4. Therapy resulted in a significant decrease in the severity of histopathologic inflammatory lesions. In the CNS, treatment with either vector suppressed IL-12 and IFN-gamma mRNA expression, while IL-4 and TGF-beta1 mRNA levels were increased compared with control mice. Thus, cytokine plasmid treatment appeared to inhibit MBP-specific pathogenic Thl responses, while enhancing endogenous secretion of protective cytokines. We demonstrate that gene therapy with these vectors is an effective therapeutic strategy for EAE.

TGF-beta1 somatic gene therapy prevents autoimmune disease in nonobese diabetic mice.

Nonobese diabetic (NOD) mice develop insulitis and diabetes through an autoimmune process. Since TGF-beta1 down-regulates many immune responses, we hypothesized that TGF-beta1 could prevent disease in NOD mice and that there would be several advantages to cytokine delivery by a somatic gene therapy approach. We opted for i.m. injection of a naked plasmid DNA expression vector encoding murine TGF-beta1 (pCMV-TGF-beta1). Treatment with pCMV-TGF-beta1 resulted in the retention and expression of the vector in muscle cells, associated with a considerable elevation in the plasma levels of TGF-beta1, that was not observed in control vector-treated mice. The levels of TGF-beta1 produced were sufficient to exert immunosuppressive effects. Delayed-type hypersensitivity responses were suppressed, and autoimmunity-prone NOD mice were protected from insulitis and diabetes in models of cyclophosphamide-accelerated and natural course disease. In pCMV-TGF-beta1-treated mice, pancreatic IL-12 and IFN-gamma mRNA expression was depressed, and the ratio of IFN-gamma to IL-4 mRNA was decreased, as determined by semiquantitative reverse-transcription PCR. In contrast, NOD mice injected with a vector encoding the proinflammatory cytokine IFN-gamma developed diabetes earlier. Intramuscular administration of cytokine-encoding plasmid vectors proved to be an effective method of cytokine delivery in these mice, and altered autoimmune disease expression.