Atsushi Satake

Cutting Edge: IL-2 Signals Determine the Degree of TCR Signaling Necessary To Support Regulatory T Cell Proliferation In Vivo

To ensure immune tolerance, regulatory T cell (Treg) numbers must be maintained by cell division. This process has been thought to be strictly dependent on the Treg TCR interacting with MHC class II. In this study, we report that Treg division does not absolutely require cell-autonomous TCR signaling in vivo, depending on the degree of IL-2–mediated stimulation provided. At steady state IL-2 levels, Tregs require cell-autonomous TCR signaling to divide. However, when given exogenous IL-2 or when STAT5 is selectively activated in Tregs, Treg division can occur independently of MHC class II and TCR signaling. Thus, depending on the amount of IL-2R stimulation, a wide range of TCR signals supports Treg division, which may contribute to preservation of a diverse repertoire of Treg TCR specificities. These findings also have therapeutic implications, as TCR signaling by Tregs may not be required when using IL-2 to increase Treg numbers for treatment of inflammatory disorders.

Cell-autonomous role of TGFβ and IL-2 receptors in CD4+ and CD8+ inducible regulatory T-cell generation during GVHD

FoxP3(+) regulatory T cells (Tregs) suppress GVHD while preserving graft-versus-tumor effects, making them an attractive target for GVHD therapy. The donor-derived Treg pool can potentially be derived from the expansion of preexisting natural Tregs (nTregs) or from de novo generation of inducible Tregs (iTregs) from donor Tconvs in the transplantation recipient. Using an MHC-mismatched model of acute GVHD, in the present study we found that the Treg pool was comprised equally of donor-derived nTregs and iTregs. Experiments using various combinations of T cells from wild-type and FoxP3-deficient mice suggested that both preexisting donor nTregs and the generation of iTregs in the recipient mice contribute to protection against GVHD. Surprisingly, CD8(+)FoxP3(+) T cells represented approximately 70% of the iTreg pool. These CD8(+)FoxP3(+) T cells shared phenotypic markers with their CD4(+) counterparts and displayed suppressive activity, suggesting that they were bona fide iTregs. Both CD4(+) and CD8(+) Tregs appeared to be protective against GVHD-induced lethality and required IL-2 and TGFβ receptor expression for their generation. These data illustrate the complex makeup of the donor-derived FoxP3(+) Treg pool in allogeneic recipients and their potential role in protection against GVHD.

Inhibition of calcineurin abrogates while inhibition of mTOR promotes regulatory T cell expansion and graft-versus-host disease protection by IL-2 in allogeneic bone marrow transplantation.

Regulatory T cells (Treg)s attenuate excessive immune responses, making their expansion beneficial in immune-mediated diseases including allogeneic bone marrow transplantation (BMT)-associated graft-versus-host disease (GVHD). We have recently reported that Treg expansion does not require phospholipase Cγ activation when IL-2 is provided. As such, the combination of IL-2 and a calcineurin inhibitor (Cyclosporine A; CsA) expands Tregs while inhibiting Tconv proliferation and protects against a mouse model of multiple sclerosis. However, CsA inhibits Treg proliferation in the presence of a TCR stimulus, suggesting that CsA may negatively impact Treg proliferation when they receive strong allogeneic MHC-mediated TCR signals. In this study, we show that CsA inhibits Treg proliferation and inducible Treg generation in allogeneic but not in syngeneic BMT when IL-2 is provided. In contrast to CsA, the mTOR inhibitor (Rapamycin) almost completely suppressed IL-2-mediated Treg proliferation. However, CsA and Rapamycin inhibited Treg proliferation to a similar extent when TCR stimulation was provided. Furthermore, Rapamycin promoted Treg expansion and inducible Treg generation in allogeneic BMT recipients treated with IL-2. Consistent with these observations, CsA abrogated while Rapamycin promoted the protective effect of IL-2 on allogeneic BMT-induced GVHD. These results suggest that while CsA permits IL-2-induced Treg proliferation in the syngeneic setting (absence of strong TCR signals), CsA in combination with IL-2 may be detrimental for Treg proliferation in an allogeneic setting. Thus, in allogeneic settings, an mTOR inhibitor such as Rapamycin is a better choice for adjunct therapy with IL-2 in expansion of Tregs and protection against allogeneic BMT-induced GVHD.

NKG2D expression by CD8 + T-cells contributes to GVHD and GVT effects in a murine model of allogeneic HSCT

In allogeneic hematopoietic stem cell transplantation (HSCT), controlling graft-versus-host disease (GVHD) while maintaining graft-versus-tumor (GVT) responses is of critical importance. Using a mouse model of allogeneic HSCT, we hereby demonstrate that NKG2D expression by CD8(+) T cells plays a major role in mediating GVHD and GVT effects by promoting the survival and cytotoxic function of CD8(+) T cells. The expression of NKG2D ligands was not induced persistently on normal tissues of allogeneic HSCT-recipient mice treated with anti-NKG2D antibody, suggesting that transient NKG2D blockade might be sufficient to attenuate GVHD and allow CD8(+) T cells to regain their GVT function. Indeed, short-term treatment with anti-NKG2D antibody restored GVT effects while maintaining an attenuated GVHD state. NKG2D expression was also detected on CD8(+) T cells from allogeneic HSCT patients and trended to be higher in those with active GVHD. Together, these data support a novel role for NKG2D expression by CD8(+) T cells during allogeneic HSCT, which could be potentially therapeutically exploited to separate GVHD from GVT effects.

Cellular therapies supplement: the role of granulocyte macrophage colony-stimulating factor and dendritic cells in regulatory T-cell homeostasis and expansion

Regulatory T cells are a subset of T cells with inhibitory function that are critical for protection against autoimmunity and immunopathology. A failure to maintain adequate regulatory T‐cell numbers in the periphery results in autoimmune manifestations, highlighting the importance of the continuous maintenance of peripheral regulatory T cells. The cellular and molecular requirements for regulatory T‐cell homeostasis and expansion are not fully understood but involve a complex interplay among dendritic cells, conventional T cells, and regulatory T cells. In addition, soluble factors such as the cytokine granulocyte macrophage colony‐stimulating factor may play a role in enhancing these interactions. In this review, we discuss our National Blood Foundation‐funded studies relating to the role of granulocyte macrophage colony‐stimulating factor and dendritic cells in controlling regulatory T‐cell homeostasis and expansion.

Skin-derived TSLP systemically expands regulatory T cells

Regulatory T cells (Tregs) are a subset of CD4+ T cells with suppressive function and are critical for limiting inappropriate activation of T cells. Hence, the expansion of Tregs is an attractive strategy for the treatment of autoimmune diseases. Here, we demonstrate that the skin possesses the remarkable capacity to systemically expand Treg numbers by producing thymic stromal lymphopoietin (TSLP) in response to vitamin D receptor stimulation. An ∼2-fold increase in the proportion and absolute number of Tregs was observed in mice treated topically but not systemically with the Vitamin D3 analog MC903. This expansion of Tregs was dependent on TSLP receptor signaling but not on VDR signaling in hematopoietic cells. However, TSLP receptor expression by Tregs was not required for their proliferation. Rather, skin-derived TSLP promoted Treg expansion through dendritic cells. Importantly, treatment of skin with MC903 significantly lowered the incidence of autoimmune diabetes in non-obese diabetic mice and attenuated disease score in experimental autoimmune encephalomyelitis. Together, these data demonstrate that the skin has the remarkable potential to control systemic immune responses and that Vitamin D-mediated stimulation of skin could serve as a novel strategy to therapeutically modulate the systemic immune system for the treatment of autoimmunity.

Delayed HBV reactivation in rituximab-containing chemotherapy: How long should we continue anti-virus prophylaxis or monitoring HBV-DNA?

Reactivation of hepatitis B virus (HBV) infection is a well-recognized and potentially fatal complication in patients treated with chemotherapy for lymphoid malignancies. Although several guidelines recommend antiviral prophylaxis and/or monitoring for HBV-DNA, there is no consensus over what time period these should occur. Clinically, we have encountered delayed reactivation of HBV infections and have reported 12 cases of reactivation in patients. Among them, five patients developed HBV reactivation more than a year after they completed their chemotherapy. This means there can be a delayed HBV reactivation and prolonged monitoring of more than a year after cessation of chemotherapy may be needed. Hence, the current recommendation of stopping antiviral prophylaxis 6-12 months after the cessation of chemotherapy may not fully protect all patients from HBV reactivation. The optimal duration of follow-up needs to be determined, and until better guidelines are set, there is no choice but to keep monitoring patients for reactivation for as long as practicable.

Relationship between HMGB1 and PAI-1 after allogeneic hematopoietic stem cell transplantation

Background Conditioning regimens including total body irradiation (TBI) or cyclophosphamide can mobilize high-mobility group box 1 (HMGB1) to peripheral blood. Additionally, increased plasminogen activator inhibitor (PAI)-1 levels are associated with post-allogeneic hematopoietic stem cell transplantation (aHSCT). However, changes to circulating levels of HMGB1 after aHSCT are poorly understood. Materials and methods The study cohort included 289 patients who underwent aHSCT at one of 25 institutions in Japan. We have investigated the relationship between HMGB1 and PAI-1 following aHSCT. A significant increase in HMGB1 levels occurred after conditioning treatment. Additionally, levels of HMGB1 at day 0 were significantly increased in TBI+ patients and cyclophosphamide/TBI patients. Conclusion Our data revealed that an increased level of HMGB1 at day 0 following aHSCT correlates with increased PAI-1 after aHSCT, which is consistent with previous reports. Increased HMGB1 at day 0 after a conditioning regimen may play a role in transplantation-associated coagulopathy following aHSCT, because PAI-1 can accelerate procoagulant activity.

Successful treatment with mogamulizumab followed by allogeneic hematopoietic stem-cell transplantation in adult T-cell leukemia/lymphoma: a report of two cases.

A humanized anti-CC chemokine receptor 4 (CCR4) monoclonal antibody, mogamulizumab (MOG), has been shown to be safe and effective in the treatment of relapsed/refractory adult T-cell leukemia/lymphoma (ATLL). MOG depletes ATLL cells as well as regulatory T cells (Tregs), as CCR4 is expressed on these cells as well. In this context, pretransplant treatment with MOG may induce severe graft-versus-host disease (GVHD) in allogeneic hematopoietic stem-cell transplantation (HSCT). However, the influence of MOG on allogeneic HSCT, including its induction of GVHD, is unclear. In this report, we describe two patients treated with MOG who subsequently underwent allogeneic HSCT. They did not develop severe GVHD or treatment-related complications. In addition, we examined the kinetics of Tregs in the second case. Finally, we suggest that the detrimental effects of MOG can be avoided, which should be prospectively evaluated in future studies.

Impact of CRAB symptoms in survival of patients with symptomatic myeloma in novel agent era

The acronym CRAB summarizes the most typical clinical manifestations of multiple myeloma, these being hypercalcemia, renal failure, anemia, and bone disease. CRAB can be used to distinguish between active, symptomatic multiple myeloma and monoclonal gammopathy of undermined significance or smoldering myeloma. The distinction is relevant not only for classification and diagnosis but also for therapy. CRAB factors influence the prognosis of multiple myeloma. However, it is unclear whether the presence of CRAB factors has an influence on the prognosis of myeloma treated with novel agents. In the current study, patients with hypercalcemia and bone disease showed a significantly worse prognosis, whereas anemia and renal failure showed no difference in survival. Novel agents used for treatment of patients with renal failure suggested a favorable outcome compared with conventional therapy. Bone disease was the most common factor and may have the strongest prognostic value in symptomatic myeloma patients using novel agents.