Jaebok Choi

In vivo administration of hypomethylating agents mitigate graft-versus-host disease without sacrificing graft-versus-leukemia

Regulatory T cells (Tregs) suppress graft-versus-host disease (GVHD) while preserving a beneficial graft-versus-leukemia (GVL) effect. Thus, their use in allogeneic stem cell transplantation (SCT) provides a promising strategy to treat GVHD. However, 3 obstacles prevent their routine use in human clinical trials: (1) low circulating number of Tregs in peripheral blood, (2) loss of suppressor function after in vitro expansion, and (3) lack of Treg-specific surface markers necessary for efficient purification. FOXP3 is exclusively expressed in Tregs and forced expression in CD4(+)CD25(-) T cells can convert these non-Tregs into Tregs with functional suppressor function. Here, we show that the FDA-approved hypomethylating agents, decitabine (Dec) and azacitidine (AzaC), induce FOXP3 expression in CD4(+)CD25(-) T cells both in vitro and in vivo. Their suppressor function is dependent on direct contact, partially dependent on perforin 1 (Prf1), but independent of granzyme B (GzmB), and surprisingly, Foxp3. Independence of Foxp3 suggests that genes responsible for the suppressor function are also regulated by DNA methylation. We have identified 48 candidate genes for future studies. Finally, AzaC treatment of mice that received a transplant of major histocompatibility complex mismatched allogeneic bone marrow and T cells mitigates GVHD while preserving GVL by peripheral conversion of alloreactive effector T cells into FOXP3(+) Tregs and epigenetic modulation of genes downstream of Foxp3 required for the suppressor function of Tregs.

IFNγR signaling mediates alloreactive T-cell trafficking and GVHD

The clinical goal of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is to minimize GVHD while maintaining GvL. Here, we show that interferon γ receptor-deficient (IFNγR(-/-)) allogeneic Tconv, which possess normal alloreactivity and cytotoxicity, induce significantly less GVHD than wild-type (WT) Tconv. This effect is mediated by altered trafficking of IFNγR(-/-) Tconv to GVHD target organs, especially the gastrointestinal (GI) tract. We show that the chemokine receptor CXCR3 is induced via IFNγR-mediated signaling and partially contributes to the trafficking of WT Tconv to GVHD target organs. Indeed, CXCR3(-/-) Tconv recapitulate the reduced GVHD potential of IFNγR(-/-) Tconv in a minor-mismatched GVHD model. Most importantly, IFNγR(-/-) (and CXCR3(-/-)) Tconv mediate a robust and beneficial GvL effect. In addition, we show that IFNγR(-/-) regulatory T cells (Tregs) are fully suppressive in vitro although defective in suppressor function in vivo and that WT Tregs suppress GVHD in vivo only when allogeneic Tconv produce interferon γ (IFNγ), suggesting that the IFNγR signaling pathway is the major mechanism for both Tregs and Tconv to migrate to GVHD target organs. Finally, pharmacologic inhibition of IFNγR signaling with inhibitors of JAK1/JAK2, which are mediators of IFNγR signaling, results in the decreased expression of CXCR3 and reduced GVHD and improved survival after allo-HSCT and this effect is mediated by altered trafficking of Tconv to GVHD target organs.

Maintenance Therapy with Decitabine after Allogeneic Stem Cell Transplantation for Acute Myelogenous Leukemia and Myelodysplastic Syndrome

Decitabine is a hypomethylating agent that irreversibly inhibits DNA methyltransferase I, inducing leukemic differentiation and re-expression of epigenetically silenced putative tumor antigens. We assessed safety and efficacy of decitabine maintenance after allogeneic transplantation for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Decitabine maintenance may help eradicate minimal residual disease, decrease the incidence of graft-versus-host disease (GVHD), and facilitate a graft-versus-leukemia effect by enhancing the effect of T regulatory lymphocytes. Patients with AML/MDS in complete remission (CR) after allotransplantation started decitabine between day +50 and +100. We investigated 4 decitabine doses in cohorts of 4 patients: 5, 7.5, 10, and 15 mg/m(2)/day × 5 days every 6 weeks, for a maximum 8 cycles. The maximum tolerated dose (MTD) was defined as the maximum dose at which ≤ 25% of people experience dose-limiting toxicities during the first cycle of treatment. Twenty-four patients were enrolled and 22 were evaluable. All 4 dose levels were completed and no MTD was reached. Overall, decitabine maintenance was well tolerated. Grade 3 and 4 hematological toxicities were experienced by 75% of patients, including all patients treated at the highest dose level. Nine patients completed all 8 cycles and 8 of them remain in CR. Nine patients died from relapse (n = 4), infectious complications (n = 3), and GVHD (n = 2). Most occurrences of acute GVHD were mild and resolved without interruption of treatment; 1 patient died of acute gut GVHD. Decitabine maintenance did not clearly impact the rate of chronic GVHD. Although there was a trend of increased FOXP3 expression, results were not statistically significant. In conclusion, decitabine maintenance is associated with acceptable toxicities when given in the post-allotransplantation setting. Although the MTD was not reached, the dose of 10 mg/m(2) for 5 days every 6 weeks appeared to be the optimal dose rather than 15 mg/m(2), where most hematological toxicities occurred.

Pharmacologic blockade of JAK1/JAK2 reduces GvHD and preserves the graft-versus-leukemia effect

We have recently reported that interferon gamma receptor deficient (IFNγR−/−) allogeneic donor T cells result in significantly less graft-versus-host disease (GvHD) than wild-type (WT) T cells, while maintaining an anti-leukemia or graft-versus-leukemia (GvL) effect after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We demonstrated that IFNγR signaling regulates alloreactive T cell trafficking to GvHD target organs through expression of the chemokine receptor CXCR3 in alloreactive T cells. Since IFNγR signaling is mediated via JAK1/JAK2, we tested the effect of JAK1/JAK2 inhibition on GvHD. While we demonstrated that pharmacologic blockade of JAK1/JAK2 in WT T cells using the JAK1/JAK2 inhibitor, INCB018424 (Ruxolitinib), resulted in a similar effect to IFNγR−/− T cells both in vitro (reduction of CXCR3 expression in T cells) and in vivo (mitigation of GvHD after allo-HSCT), it remains to be determined if in vivo administration of INCB018424 will result in preservation of GvL while reducing GvHD. Here, we report that INCB018424 reduces GvHD and preserves the beneficial GvL effect in two different murine MHC-mismatched allo-HSCT models and using two different murine leukemia models (lymphoid leukemia and myeloid leukemia). In addition, prolonged administration of INCB018424 further improves survival after allo-HSCT and is superior to other JAK1/JAK2 inhibitors, such as TG101348 or AZD1480. These data suggest that pharmacologic inhibition of JAK1/JAK2 might be a promising therapeutic approach to achieve the beneficial anti-leukemia effect and overcome HLA-barriers in allo-HSCT. It might also be exploited in other diseases besides GvHD, such as organ transplant rejection, chronic inflammatory diseases and autoimmune diseases.

F11R Is a Novel Monocyte Prognostic Biomarker for Malignant Glioma

Objective Brain tumors (gliomas) contain large populations of infiltrating macrophages and recruited microglia, which in experimental murine glioma models promote tumor formation and progression. Among the barriers to understanding the contributions of these stromal elements to high-grade glioma (glioblastoma; GBM) biology is the relative paucity of tools to characterize infiltrating macrophages and resident microglia. In this study, we leveraged multiple RNA analysis platforms to identify new monocyte markers relevant to GBM patient outcome. Methods High-confidence lists of mouse resident microglia- and bone marrow-derived macrophage-specific transcripts were generated using converging RNA-seq and microarray technologies and validated using qRT-PCR and flow cytometry. Expression of select cell surface markers was analyzed in brain-infiltrating macrophages and resident microglia in an induced GBM mouse model, while allogeneic bone marrow transplantation was performed to trace the origins of infiltrating and resident macrophages. Glioma tissue microarrays were examined by immunohistochemistry, and the Gene Expression Omnibus (GEO) database was queried to determine the prognostic value of identified microglia biomarkers in human GBM. Results We generated a unique catalog of differentially-expressed bone marrow-derived monocyte and resident microglia transcripts, and demonstrated that brain-infiltrating macrophages acquire F11R expression in GBM and following bone-marrow transplantation. Moreover, mononuclear cell F11R expression positively correlates with human high-grade glioma and additionally serves as a biomarker for GBM patient survival, regardless of GBM molecular subtype. Significance These studies establish F11R as a novel monocyte prognostic marker for GBM critical for defining a subpopulation of stromal cells for future potential therapeutic intervention.

An “off-the-shelf” fratricide-resistant CAR-T for the treatment of T cell hematologic malignancies

T cell malignancies represent a group of hematologic cancers with high rates of relapse and mortality in patients for whom no effective targeted therapies exist. The shared expression of target antigens between chimeric antigen receptor (CAR) T cells and malignant T cells has limited the development of CAR-T because of unintended CAR-T fratricide and an inability to harvest sufficient autologous T cells. Here, we describe a fratricide-resistant “off-the-shelf” CAR-T (or UCART7) that targets CD7+ T cell malignancies and, through CRISPR/Cas9 gene editing, lacks both CD7 and T cell receptor alpha chain (TRAC) expression. UCART7 demonstrates efficacy against human T cell acute lymphoblastic leukemia (T-ALL) cell lines and primary T-ALL in vitro and in vivo without the induction of xenogeneic GvHD. Fratricide-resistant, allo-tolerant “off-the-shelf” CAR-T represents a strategy for treatment of relapsed and refractory T-ALL and non-Hodgkin’s T cell lymphoma without a requirement for autologous T cells.

Phase I study of azacitidine following donor lymphocyte infusion for relapsed acute myeloid leukemia post allogeneic stem cell transplantation

Donor lymphocyte infusion (DLI) without prophylactic immunosuppression has been used for relapsed AML after allogeneic stem cell transplant (allo-SCT). However DLI is associated with an increased incidence of acute Graft vs. Host Disease (aGVHD). In mice, administration of azacitidine (AzaC) on days 4, 6, 8, and 10 post DLI increases regulatory T cell (Treg) numbers and prevents GVHD without hindering Graft vs. Leukemia (GVL). Based on these findings, we conducted a phase 1 study of AzaC post DLI for AML relapse post allo-SCT. AzaC was administered on days 4, 6, 8 and 10 post-DLI. Dose escalation was done using a 3+3 design with three AzaC dose levels: 30mg/m(2) (level -1), 45mg/m(2) (level 1) and 75mg/m(2) (level 2). Three patients were treated in the 45mg/m(2) dose level and 5 patients were treated in the 75mg/m(2) dose level; no DLTs or grade 3-5 treatment related toxicities were observed. After a median follow-up of 5.2 months, no patients developed grade III-IV aGVHD and no patients died of aGVHD. Six out of 8 patients in the treatment group responded to treatment including two cytogenetic complete remissions, one hematologic complete remission, and three complete remissions with incomplete count recovery. In conclusion, administration of AzaC early post DLI is well tolerated and can potentially prevent GVHD after DLI. Further studies are required to evaluate the effect of azacitidine early post DLI on GVHD and GVL.

GPR18 Controls Reconstitution of Mouse Small Intestine Intraepithelial Lymphocytes following Bone Marrow Transplantation

Specific G protein coupled receptors (GPRs) regulate the proper positioning, function, and development of immune lineage subsets. Here, we demonstrate that GPR18 regulates the reconstitution of intraepithelial lymphocytes (IELs) of the small intestine following bone marrow transplantation. Through analysis of transcriptional microarray data, we find that GPR18 is highly expressed in IELs, lymphoid progenitors, and mature follicular B cells. To establish the physiological role of this largely uncharacterized GPR, we generated Gpr18-/- mice. Despite high levels of GPR18 expression in specific hematopoietic progenitors, Gpr18-/- mice have no defects in lymphopoiesis or myelopoiesis. Moreover, antibody responses following immunization with hapten-protein conjugates or infection with West Nile virus are normal in Gpr18-/- mice. Steady-state numbers of IELs are also normal in Gpr18-/- mice. However, competitive bone marrow reconstitution experiments demonstrate that GPR18 is cell-intrinsically required for the optimal restoration of small intestine TCRγδ+ and TCRαβ+ CD8αα+ IELs. In contrast, GPR18 is dispensable for the reconstitution of large intestine IELs. Moreover, Gpr18-/- bone marrow reconstitutes small intestine IELs similarly to controls in athymic recipients. Gpr18-/- chimeras show no changes in susceptibility to intestinal insults such as Citrobacter rodentium infections or graft versus host disease. These data reveal highly specific requirements for GPR18 in the development and reconstitution of thymus-derived intestinal IEL subsets in the steady-state and after bone marrow transplantation.

The Role of Janus Kinase Signaling in Graft-Versus-Host Disease and Graft Versus Leukemia

For patients with hematologic malignancies, allogeneic hematopoietic cell transplantation (alloHCT) offers a potential curative treatment option, primarily due to an allogeneic immune response against recipient tumor cells (ie, graft-versus-leukemia [GVL] activity). However, many recipients of alloHCT develop graft-versus-host disease (GVHD), in which allogeneic immune responses lead to the damage of healthy tissue. GVHD is a leading cause of nonrelapse mortality and a key contributor to morbidity among patients undergoing alloHCT. Therefore, improving alloHCT outcomes will require treatment strategies that prevent or mitigate GVHD without disrupting GVL activity. Janus kinases (JAKs) are intracellular signaling molecules that are well positioned to regulate GVHD. A variety of cytokines that signal through the JAK signaling pathways play a role in regulating the development, proliferation, and activation of several immune cell types important for GVHD pathogenesis, including dendritic cells, macrophages, T cells, B cells, and neutrophils. Importantly, despite JAK regulation of GVHD, preclinical evidence suggests that JAK inhibition preserves GVL activity. Here we provide an overview of potential roles for JAK signaling in the pathogenesis of acute and chronic GVHD as well as effects on GVL activity. We also review preclinical and clinical results with JAK inhibitors in acute and chronic GVHD settings, with added focus on those actively being evaluated in patients with acute and chronic GVHD.

Baricitinib-induced blockade of interferon gamma receptor and interleukin-6 receptor for the prevention and treatment of graft-versus-host disease

The therapeutic benefits of allogeneic hematopoietic stem cell transplantation (allo-HSCT) are derived from the graft-versus-leukemia (GvL) effects of the procedure. There is a strong association between the GvL effects and graft-versus-host disease (GvHD), a major life-threatening complication of allo-HSCT. The limiting of GvHD while maintaining the GvL effect remains the goal of allo-HSCT. Therefore, identifying optimal therapeutic targets to selectively suppress GvHD while maintaining the GvL effects represents a significant unmet medical need. We demonstrate that the dual inhibition of interferon gamma receptor (IFNγR) and interleukin-6 receptor (IL6R) results in near-complete elimination of GvHD in a fully major histocompatibility complex–mismatched allo-HSCT model. Furthermore, baricitinib (an inhibitor of Janus kinases 1 and 2 (JAK1/JAK2) downstream of IFNγR/IL6R) completely prevented GvHD; expanded regulatory T cells by preserving JAK3-STAT5 signaling; downregulated CXCR3 and helper T cells 1 and 2 while preserving allogeneic antigen-presenting cell-stimulated T-cell proliferation; and suppressed the expression of major histocompatibility complex II (I-Ad), CD80/86, and PD-L1 on host antigen-presenting cells. Baricitinib also reversed established GvHD with 100% survival, thus demonstrating both preventive and therapeutic roles for this compound. Remarkably, baricitinib enhanced the GvL effects, possibly by downregulating tumor PD-L1 expression.