VISTA checkpoint inhibition by pH-selective antibody SNS-101 with optimized safety and pharmacokinetic profiles enhances PD-1 response.

VISTA, an inhibitory myeloid-T-cell checkpoint, holds promise as a target for cancer immunotherapy. However, its effective targeting has been impeded by issues such as rapid clearance and cytokine release syndrome observed with previous VISTA antibodies. Here we demonstrate that SNS-101, a newly developed pH-selective VISTA antibody, addresses these challenges. Structural and biochemical analyses confirmed the pH-selectivity and unique epitope targeted by SNS-101. These properties confer favorable pharmacokinetic and safety profiles on SNS-101. In syngeneic tumor models utilizing human VISTA knock-in mice, SNS-101 shows in vivo efficacy when combined with a PD-1 inhibitor, modulates cytokine and chemokine signaling, and alters the tumor microenvironment. In summary, SNS-101, currently in Phase I clinical trials, emerges as a promising therapeutic biologic for a wide range of patients whose cancer is refractory to current immunotherapy regimens.

Myeloid and dendritic cells enhance therapeutics-induced cytokine release syndrome features in humanized BRGSF-HIS preclinical model.

Objectives: Despite their efficacy, some immunotherapies have been shown to induce immune-related adverse events, including the potentially life-threatening cytokine release syndrome (CRS), calling for reliable and translational preclinical models to predict potential safety issues and investigate their rescue. Here, we tested the reliability of humanized BRGSF mice for the assessment of therapeutics-induced CRS features in preclinical settings. Methods: BRGSF mice reconstituted with human umbilical cord blood CD34+ cells (BRGSF-CBC) were injected with anti-CD3 antibody (OKT3), anti-CD3/CD19 bispecific T-cell engager Blinatumomab, or VISTA-targeting antibody. Human myeloid and dendritic cells' contribution was investigated in hFlt3L-boosted BRGSF-CBC mice. OKT3 treatment was also tested in human PBMC-reconstituted BRGSF mice (BRGSF-PBMC). Cytokine release, immune cell distribution, and clinical signs were followed. Results: OKT3 injection in BRGSF-CBC mice induced hallmark features of CRS, specifically inflammatory cytokines release, modifications of immune cell distribution and activation, body weight loss, and temperature drop. hFlt3L-boosted BRGSF-CBC mice displayed enhanced CRS features, revealing a significant role of myeloid and dendritic cells in this process. Clinical CRS-managing treatment Infliximab efficiently attenuated OKT3-induced toxicity. Comparison of OKT3 treatment's effect on BRGSF-CBC and BRGSF-PBMC mice showed broadened CRS features in BRGSF-CBC mice. CRS-associated features were also observed in hFlt3L-boosted BRGSF-CBC mice upon treatment with other T-cell or myeloid-targeting compounds. Conclusions: These data show that BRGSF-CBC mice represent a relevant model for the preclinical assessment of CRS and CRS-managing therapies. They also confirm a significant role of myeloid and dendritic cells in CRS development and exhibit the versatility of this model for therapeutics-induced safety assessment.

Tissue-restricted control of established central nervous system autoimmunity by TNF receptor 2-expressing Treg cells.

CD4+Foxp3+ regulatory T (Treg) cells are central modulators of autoimmune diseases. However, the timing and location of Treg cell-mediated suppression of tissue-specific autoimmunity remain undefined. Here, we addressed these questions by investigating the role of tumor necrosis factor (TNF) receptor 2 (TNFR2) signaling in Treg cells during experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. We found that TNFR2-expressing Treg cells were critical to suppress EAE at peak disease in the central nervous system but had no impact on T cell priming in lymphoid tissues at disease onset. Mechanistically, TNFR2 signaling maintained functional Treg cells with sustained expression of CTLA-4 and Blimp-1, allowing active suppression of pathogenic T cells in the inflamed central nervous system. This late effect of Treg cells was further confirmed by treating mice with TNF and TNFR2 agonists and antagonists. Our findings show that endogenous Treg cells specifically suppress an autoimmune disease by acting in the target tissue during overt inflammation. Moreover, they bring a mechanistic insight to some of the adverse effects of anti-TNF therapy in patients.

Hematopoietic Stem and Progenitor Cells Exhibit Stage-Specific Translational Programs via mTOR- and CDK1-Dependent Mechanisms.

Hematopoietic stem cells (HSCs) require highly regulated rates of protein synthesis, but it is unclear if they or lineage-committed progenitors preferentially recruit transcripts to translating ribosomes. We utilized polysome profiling, RNA sequencing, and whole-proteomic approaches to examine the translatome in LSK (Lin-Sca-1+c-Kit+) and myeloid progenitor (MP; Lin-Sca-1-c-Kit+) cells. Our studies show that LSKs exhibit low global translation but high translational efficiencies (TEs) of mRNAs required for HSC maintenance. In contrast, MPs activate translation in an mTOR-independent manner due, at least in part, to proteasomal degradation of mTOR by the E3 ubiquitin ligase c-Cbl. In the near absence of mTOR, CDK1 activates eIF4E-dependent translation in MPs through phosphorylation of 4E-BP1. Aberrant activation of mTOR expression and signaling in c-Cbl-deficient MPs results in increased mature myeloid lineage output. Overall, our data demonstrate that hematopoietic stem and progenitor cells (HSPCs) undergo translational reprogramming mediated by previously uncharacterized mechanisms of translational regulation.

VISTA is an acidic pH-selective ligand for PSGL-1.

Co-inhibitory immune receptors can contribute to T cell dysfunction in patients with cancer1,2. Blocking antibodies against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1) partially reverse this effect and are becoming standard of care in an increasing number of malignancies3. However, many of the other axes by which tumours become inhospitable to T cells are not fully understood. Here we report that V-domain immunoglobulin suppressor of T cell activation (VISTA) engages and suppresses T cells selectively at acidic pH such as that found in tumour microenvironments. Multiple histidine residues along the rim of the VISTA extracellular domain mediate binding to the adhesion and co-inhibitory receptor P-selectin glycoprotein ligand-1 (PSGL-1). Antibodies engineered to selectively bind and block this interaction in acidic environments were sufficient to reverse VISTA-mediated immune suppression in vivo. These findings identify a mechanism by which VISTA may engender resistance to anti-tumour immune responses, as well as an unexpectedly determinative role for pH in immune co-receptor engagement.

CD97 is a critical regulator of acute myeloid leukemia stem cell function.

Despite significant efforts to improve therapies for acute myeloid leukemia (AML), clinical outcomes remain poor. Understanding the mechanisms that regulate the development and maintenance of leukemic stem cells (LSCs) is important to reveal new therapeutic opportunities. We have identified CD97, a member of the adhesion class of G protein-coupled receptors (GPCRs), as a frequently up-regulated antigen on AML blasts that is a critical regulator of blast function. High levels of CD97 correlate with poor prognosis, and silencing of CD97 reduces disease aggressiveness in vivo. These phenotypes are due to CD97's ability to promote proliferation, survival, and the maintenance of the undifferentiated state in leukemic blasts. Collectively, our data credential CD97 as a promising therapeutic target on LSCs in AML.

Meddling with METTLs in Normal and Leukemia Stem Cells.

Three recent studies independently identified the m6A RNA modifying enzymes METTL3 and METTL14 as critical regulators of differentiation in both normal hematopoiesis and AML pathogenesis. These studies expand the described roles of the epitranscriptome in maintaining the undifferentiated state in somatic stem cells and human cancer.

Restoration of TET2 Function Blocks Aberrant Self-Renewal and Leukemia Progression.

Loss-of-function mutations in TET2 occur frequently in patients with clonal hematopoiesis, myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML) and are associated with a DNA hypermethylation phenotype. To determine the role of TET2 deficiency in leukemia stem cell maintenance, we generated a reversible transgenic RNAi mouse to model restoration of endogenous Tet2 expression. Tet2 restoration reverses aberrant hematopoietic stem and progenitor cell (HSPC) self-renewal in vitro and in vivo. Treatment with vitamin C, a co-factor of Fe2+ and α-KG-dependent dioxygenases, mimics TET2 restoration by enhancing 5-hydroxymethylcytosine formation in Tet2-deficient mouse HSPCs and suppresses human leukemic colony formation and leukemia progression of primary human leukemia PDXs. Vitamin C also drives DNA hypomethylation and expression of a TET2-dependent gene signature in human leukemia cell lines. Furthermore, TET-mediated DNA oxidation induced by vitamin C treatment in leukemia cells enhances their sensitivity to PARP inhibition and could provide a safe and effective combination strategy to selectively target TET deficiency in cancer. PAPERCLIP.

Control of GVHD by regulatory T cells depends on TNF produced by T cells and TNFR2 expressed by regulatory T cells.

Therapeutic CD4(+)Foxp3(+) natural regulatory T cells (Tregs) can control experimental graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HCT) by suppressing conventional T cells (Tconvs). Treg-based therapies are currently tested in clinical trials with promising preliminary results in allo-HCT. Here, we hypothesized that as Tregs are capable of modulating Tconv response, it is likely that the inflammatory environment and particularly donor T cells are also capable of influencing Treg function. Indeed, previous findings in autoimmune diabetes revealed a feedback mechanism that renders Tconvs able to stimulate Tregs by a mechanism that was partially dependent on tumor necrosis factor (TNF). We tested this phenomenon during alloimmune response in our previously described model of GVHD protection using antigen specific Tregs. Using different experimental approaches, we observed that control of GVHD by Tregs was fully abolished by blocking TNF receptor type 2 (TNFR2) or by using TNF-deficient donor T cells or TNFR2-deficient Tregs. Thus, our results show that Tconvs exert a powerful modulatory activity on therapeutic Tregs and clearly demonstrate that the sole defect of TNF production by donor T cells was sufficient to completely abolish the Treg suppressive effect in GVHD. Importantly, our findings expand the understanding of one of the central components of Treg action, the inflammatory context, and support that targeting TNF/TNFR2 interaction represents an opportunity to efficiently modulate alloreactivity in allo-HCT to either exacerbate it for a powerful antileukemic effect or reduce it to control GVHD.

Treatment of Uveitis by In Situ Administration of Ex Vivo-Activated Polyclonal Regulatory T Cells.

CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cell therapy is a promising approach for the treatment of autoimmune diseases. To be effective, Treg cells should be in an activated state in the target tissue. This can be achieved by systemic administration of Ag-specific Treg cells, which are difficult to produce in conditions that can be translated to the clinic. In this paper, we propose an alternative approach consisting of in situ injection of preactivated polyclonal Treg cells that would exert bystander suppression in the target tissue. We show that polyclonal Treg cells suppressed uveitis in mice as efficiently as Ag-specific Treg cells but only when preactivated and administered in the vitreous. Uveitis control was correlated with an increase of IL-10 and a decrease of reactive oxygen species produced by immune cell infiltrates in the eye. Thus, our results reveal a new mechanism of Treg cell-mediated suppression and a new Treg cell therapy approach.

Immunoendocrine dysbalance during uncontrolled T. cruzi infection is associated with the acquisition of a Th-1-like phenotype by Foxp3(+) T cells.

We previously showed that Trypanosomacruzi infection in C57BL/6 mice results in a lethal infection linked to unbalanced pro- and anti-inflammatory mediators production. Here, we examined the dynamics of CD4(+)Foxp3(+) regulatory T (Treg) cells within this inflammatory and highly Th1-polarized environment. Treg cells showed a reduced proliferation rate and their frequency is progressively reduced along infection compared to effector T (Teff) cells. Also, a higher fraction of Treg cells showed a naïve phenotype, meanwhile Teff cells were mostly of the effector memory type. T. cruzi infection was associated with the production of pro- and anti-inflammatory cytokines, notably IL-27p28, and with the induction of T-bet and IFN-γ expression in Treg cells. Furthermore, endogenous glucocorticoids released in response to T. cruzi-driven immune activation were crucial to sustain the Treg/Teff cell balance. Notably, IL-2 plus dexamethasone combined treatment before infection was associated with increased Treg cell proliferation and expression of GATA-3, IL-4 and IL-10, and increased mice survival time. Overall, our results indicate that therapies aimed at specifically boosting Treg cells, which during T. cruzi infection are overwhelmed by the effector immune response, represent new opportunities for the treatment of Chagas disease, which is actually only based on parasite-targeted chemotherapy.

Potential limitations of IL-2 administration for the treatment of experimental acute graft-versus-host disease.

Low-dose IL-2 administration can control autoimmunity by specifically activating CD4(+) Foxp3(+) regulatory T cells (Tregs). Here, we studied IL-2-based immunotherapy in experimental graft-versus-host disease (GVHD). IL-2 administration to donor mice induced a dose-dependent expansion of Tregs in the graft but was insufficient to control GVHD. IL-2 administration to allogeneic-grafted recipient mice activated T-conventional cells (Tcons) and did not prevent GVHD. This loss of IL-2 selectivity toward Tregs was explained by an IL-2-induced increase in the IL-2 receptor α-chain expression on Tcons. Finally, in xeno-GVHD generated by human PBMCs transplanted into immunodeficient mice, low-dose IL-2 increased Treg frequencies but did neither control pro-inflammatory cytokine production by pathogenic Tcons, nor prevented GVHD. Furthermore, combination of low-dose IL-2 with rapamycin was ineffective in this model. Our results indicate that limitations on the use of IL-2 during acute GVHD are likely due to the massive activation of the allogeneic T cells unique to this setting.

In vivo activation of transferred regulatory T cells specific for third-party exogenous antigen controls GVH disease in mice.

Treg cells hold enormous promise for therapeutic application in GVH disease, a lethal complication of allogeneic HSC transplantation. Mouse studies showed that donor-derived recipient-specific Treg (rsTreg) cells are far more efficient than polyclonal Treg cells in suppressing GVH disease. However, clinical grade preparations of rsTreg cells carries the risk of containing significant numbers of highly pathogenic recipient-specific effector T cells. We hypothesized that an alternative approach using Treg cells specific for an exogenous (i.e. nondonor, nonrecipient) Ag (exoTreg cells) can overcome this risk by taking advantage of the bystander suppressive effect of Treg cells. For this, we used a murine model for aggressive GVH disease. We expanded ex vivo exoTreg cells that are primed against the HY Ag, which is only expressed in males. ExoTreg cells supressed GVH disease as efficiently as rsTreg cells in recipient male mice. We also applied this strategy in female mice that do not express this Ag. While exoTreg cells were not effective in female recipients when applied alone, providing the cognate HY Ag in vivo along side effectively activated exoTreg cells and completely abrogated GVH disease, establishing a targeted on/off system to provide a suppressive effect on alloreactive effector T cells.

Pathogenic T cells have a paradoxical protective effect in murine autoimmune diabetes by boosting Tregs.

CD4+CD25+Foxp3+ Tregs play a major role in prevention of autoimmune diseases. The suppressive effect of Tregs on effector T cells (Teffs), the cells that can mediate autoimmunity, has been extensively studied. However, the in vivo impact of Teff activation on Tregs during autoimmunity has not been explored. In this study, we have shown that CD4+ Teff activation strongly boosts the expansion and suppressive activity of Tregs. This helper function of CD4+ T cells, which we believe to be novel, was observed in the pancreas and draining lymph nodes in mouse recipients of islet-specific Teffs and Tregs. Its physiological impact was assessed in autoimmune diabetes. When islet-specific Teffs were transferred alone, they induced diabetes. Paradoxically, when the same Teffs were cotransferred with islet-specific Tregs, they induced disease protection by boosting Treg expansion and suppressive function. RNA microarray analyses suggested that TNF family members were involved in the Teff-mediated Treg boost. In vivo experiments showed that this Treg boost was partially dependent on TNF but not on IL-2. This feedback regulatory loop between Teffs and Tregs may be critical to preventing or limiting the development of autoimmune diseases.