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.

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.