Letter to Blood| January 19, 2023 Lithium attenuates graft-versus-host disease via effects on the intestinal stem cell niche Motoko Koyama, Motoko Koyama 1Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA Search for other works by this author on: This Site PubMed Google Scholar Luke Samson, Luke Samson 1Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA Search for other works by this author on: This Site PubMed Google Scholar Kathleen S. Ensbey, Kathleen S. Ensbey 1Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA Search for other works by this author on: This Site PubMed Google Scholar Shuichiro Takahashi, Shuichiro Takahashi 1Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA Search for other works by this author on: This Site PubMed Google Scholar Andrew D. Clouston, Andrew D. Clouston 3Department of Medicine, University of Washington, Seattle, WA Search for other works by this author on: This Site PubMed Google Scholar Paul J. Martin, Paul J. Martin 1Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA2Envoi Specialist Pathologists, Brisbane, QLD, Australia https://orcid.org/0000-0001-9051-1215 Search for other works by this author on: This Site PubMed Google Scholar Geoffrey R. Hill Geoffrey R. Hill 1Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA2Envoi Specialist Pathologists, Brisbane, QLD, Australia Search for other works by this author on: This Site PubMed Google Scholar Blood (2023) 141 (3): 315–319. https://doi.org/10.1182/blood.2022015808 Article history Submitted: February 4, 2022 Accepted: September 21, 2022 First Edition: October 6, 2022 Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Request Permissions Cite Icon Cite Search Site Citation Motoko Koyama, Luke Samson, Kathleen S. Ensbey, Shuichiro Takahashi, Andrew D. Clouston, Paul J. Martin, Geoffrey R. Hill; Lithium attenuates graft-versus-host disease via effects on the intestinal stem cell niche. Blood 2023; 141 (3): 315–319. doi: https://doi.org/10.1182/blood.2022015808 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBlood Search Subjects: Immunobiology and Immunotherapy, Transplantation TO THE EDITOR: Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative therapy for the majority of hematological malignancies but is limited by graft-versus-host disease (GVHD) and opportunistic infections. Severe acute GVHD in the gastrointestinal (GI) tract is a major determinant of mortality1 and causes progressive epithelial and crypt loss, leading to denudation of intestinal mucosa.1-3 Approaches to prevent severe GVHD to date focus on the immune suppression of T cells with calcineurin inhibitors, antimetabolites, or alkylating agents.3 Intestinal stem cell (ISC) function and associated intestinal epithelial cell (IEC) renewal are regulated by signaling pathways of WNT, R-spondin, Notch, bone morphogenetic proteins, and epidermal growth factor.4 Stem cell populations expressing leucine-rich repeat-containing G protein−coupled receptor 5 (LGR5) are essential in the renewal of intestinal epithelium during homeostasis. R-spondins are encoded by 4 genes (rspo1, 2, 3, and... References 1.Naymagon S, Naymagon L, Wong SY, et al. Acute graft-versus-host disease of the gut: considerations for the gastroenterologist. 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The Wnt agonist R-spondin1 regulates systemic graft-versus-host disease by protecting intestinal stem cells. J Exp Med. 2011. ;208(2):285-294.Google ScholarCrossrefSearch ADS 7.Harnack C, Berger H, Antanaviciute A, et al. R-spondin 3 promotes stem cell recovery and epithelial regeneration in the colon. Nat Commun. 2019. ;10(1):4368.Google ScholarCrossrefSearch ADS PubMed 8.Ogasawara R, Hashimoto D, Kimura S, et al. Intestinal lymphatic endothelial cells produce R-Spondin3. Sci Rep. 2018. ;8(1):10719.Google ScholarCrossrefSearch ADS PubMed 9.Ter Steege EJ, Bakker ERM. The role of R-spondin proteins in cancer biology. Oncogene. 2021. ;40(47):6469-6478.Google ScholarCrossrefSearch ADS PubMed 10.Snitow ME, Bhansali RS, Klein PS. Lithium and therapeutic targeting of GSK-3. Cells. 2021. ;10(2):255.Google ScholarCrossrefSearch ADS PubMed 11.Gould TD, Manji HK. Glycogen synthase kinase-3: a putative molecular target for lithium mimetic drugs. Neuropsychopharmacology. 2005. ;30(7):1223-1237.Google ScholarCrossrefSearch ADS PubMed 12.Pottegard A, Ennis ZN, Hallas J, Jensen BL, Madsen K, Friis S. Long-term use of lithium and risk of colorectal adenocarcinoma: a nationwide case-control study. Br J Cancer. 2016. ;114(5):571-575.Google ScholarCrossrefSearch ADS PubMed 13.Steinbach G, Hockenbery DM, Huls G, et al. Pilot study of lithium to restore intestinal barrier function in severe graft-versus-host disease. PLoS One. 2017. ;12(8):e0183284.Google ScholarCrossrefSearch ADS PubMed 14.van Es JH, Jay P, Gregorieff A, et al. Wnt signalling induces maturation of Paneth cells in intestinal crypts. Nat Cell Biol. 2005. ;7(4):381-386.Google ScholarCrossrefSearch ADS PubMed 15.Clevers HC, Bevins CL. Paneth cells: maestros of the small intestinal crypts. Annu Rev Physiol. 2013. ;75:289-311.Google ScholarCrossrefSearch ADS PubMed 16.Hanash AM, Dudakov JA, Hua G, et al. Interleukin-22 protects intestinal stem cells from immune-mediated tissue damage and regulates sensitivity to graft versus host disease. Immunity. 2012. ;37(2):339-350.Google ScholarCrossrefSearch ADS PubMed 17.Zhao D, Kim YH, Jeong S, et al. Survival signal REG3alpha prevents crypt apoptosis to control acute gastrointestinal graft-versus-host disease. J Clin Invest. 2018. ;128(11):4970-4979.Google ScholarCrossrefSearch ADS 18.Eriguchi Y, Takashima S, Oka H, et al. Graft-versus-host disease disrupts intestinal microbial ecology by inhibiting Paneth cell production of alpha-defensins. Blood. 2012. ;120(1):223-231.Google ScholarCrossrefSearch ADS PubMed 19.Levine JE, Huber E, Hammer ST, et al. Low Paneth cell numbers at onset of gastrointestinal graft-versus-host disease identify patients at high risk for nonrelapse mortality. Blood. 2013. ;122(8):1505-1509.Google ScholarCrossrefSearch ADS PubMed 20.Sato T, van Es JH, Snippert HJ, et al. Paneth cells constitute the niche for Lgr5 stem cells in intestinal crypts. Nature. 2011. ;469(7330):415-418.Google ScholarCrossrefSearch ADS PubMed 21.Henden AS, Koyama M, Robb RJ, et al. IFN-lambda therapy prevents severe gastrointestinal graft-versus-host disease. Blood. 2021. ;138(8):722-737.Google ScholarCrossrefSearch ADS PubMed © 2023 by The American Society of Hematology2023 © 2023 by The American Society of Hematology2023 You do not currently have access to this content. Sign in via your Institution

Some hematological malignancies such as multiple myeloma are inherently resistant to immune-mediated antitumor responses, the cause of which remains unknown. Allogeneic bone marrow transplantation (alloBMT) is the only curative immunotherapy for hematological malignancies due to profound graft-versus-tumor (GVT) effects, but relapse remains the major cause of death. We developed murine models of alloBMT where the hematological malignancy is either sensitive [acute myeloid leukemia (AML)] or resistant (myeloma) to GVT effects. We found that CD8 + T cell exhaustion in bone marrow was primarily alloantigen-driven, with expression of inhibitory ligands present on myeloma but not AML. Because of this tumor-independent exhaustion signature, immune checkpoint inhibition (ICI) in myeloma exacerbated graft-versus-host disease (GVHD) without promoting GVT effects. Administration of post-transplant cyclophosphamide (PT-Cy) depleted donor T cells with an exhausted phenotype and spared T cells displaying a stem-like memory phenotype with chromatin accessibility present in cytokine signaling genes, including the interleukin-18 (IL-18) receptor. Whereas ICI with anti–PD-1 or anti–TIM-3 remained ineffective after PT-Cy, administration of a decoy-resistant IL-18 (DR-18) strongly enhanced GVT effects in both myeloma and leukemia models, without exacerbation of GVHD. We thus defined mechanisms of resistance to T cell–mediated antitumor effects after alloBMT and described an immunotherapy approach targeting stem-like memory T cells to enhance antitumor immunity.

Donor and recipient cytomegalovirus (CMV) serostatus correlate with transplant-related mortality that is associated with reduced survival following allogeneic stem cell transplant (SCT). Prior epidemiologic studies have suggested that CMV seronegative recipients (R-) receiving a CMV-seropositive graft (D+) experience inferior outcomes compared with other serostatus combinations, an observation that appears independent of viral reactivation. We therefore investigated the hypothesis that prior donor CMV exposure irreversibly modifies immunologic function after SCT. We identified a CD4(+)/CD57(+)/CD27(-) T-cell subset that was differentially expressed between D+ and D- transplants and validated results with 120 patient samples. This T-cell subset represents an average of 2.9% (D-/R-), 18% (D-/R+), 12% (D+/R-), and 19.6% (D+/R+) (P < .0001) of the total CD4(+) T-cell compartment and stably persists for at least several years post-SCT. Even in the absence of CMV reactivation postSCT, D+/R- transplants displayed a significant enrichment of these cells compared with D-/R- transplants (P = .0078). These are effector memory cells (CCR7-/CD45RA(+/-)) that express T-bet, Eomesodermin, granzyme B, secrete Th1 cytokines, and are enriched in CMV-specific T cells. These cells are associated with decreased T-cell receptor diversity (P < .0001) and reduced proportions of major histocompatibility class (MHC) II expressing classical monocytes (P < .0001), myeloid (P = .024), and plasmacytoid dendritic cells (P = .0014). These data describe a highly expanded CD4(+) T-cell population and putative mechanisms by which prior donor or recipient CMV exposure may create a lasting immunologic imprint following SCT, providing a rationale for using D- grafts for R- transplant recipients.

Patients with acute leukemia who are unable to achieve complete remission prior to allogeneic hematopoietic stem cell transplantation (SCT) have dismal outcomes, with relapse rates well in excess of 60%. Haplo-identical SCT (haplo-SCT) may allow enhanced graft-versus-leukemia (GVL) effects by virtue of HLA class I/II donor-host disparities, but it typically requires intensive immunosuppression with posttransplant cyclophosphamide (PT-Cy) to prevent lethal graft-versus-host disease (GVHD). Here, we demonstrate in preclinical models that glucocorticoid administration from days –1 to +5 inhibits alloantigen presentation by professional recipient antigen presenting cells in the gastrointestinal tract and prevents donor T cell priming and subsequent expansion therein. In contrast, direct glucocorticoid signaling of donor T cells promotes chemokine and integrin signatures permissive of preferential circulation and migration into the BM, promoting donor T cell residency. This results in significant reductions in GVHD while promoting potent GVL effects; relapse in recipients receiving glucocorticoids, vehicle, or PT-Cy was 12%, 56%, and 100%, respectively. Intriguingly, patients with acute myeloid leukemia not in remission who received unmanipulated haplo-SCT and peritransplant glucocorticoids also had an unexpectedly low relapse rate at 1 year (32%; 95% CI, 18%–47%) with high overall survival at 3 years (58%; 95% CI, 38%–74%). These data highlight a potentially simple and effective approach to prevent relapse in patients with otherwise incurable leukemia that could be studied in prospective randomized trials.

Allogeneic stem cell transplantation (alloSCT) is a highly effective, curative therapy for leukemia yet does not provide a survival benefit above autologous SCT in patients with multiple myeloma (MM). To explore this, we developed preclinical models of SCT using C57Bl/6 recipient mice and either C57Bl/6 (ASCT) or C3H.SW (alloSCT) donor grafts. Importantly, these models recapitulated the clinical setting whereby alloSCT provided superior outcomes, compared to ASCT, in recipients bearing MLL-AF9-driven acute myeloid leukemia (AML) but not in those bearing Vk*MYC-MM. Interestingly, we found that MM-specific, T cell-mediated immunity was generated after ASCT, which failed due to MM-induced T cell exhaustion. MM relapse after ASCT could be prevented by TIGIT or PD-1 targeted immune checkpoint inhibition or via depletion of suppressive CSF1-R+ myeloid cells. Conversely, after alloSCT, T cell exhaustion was driven principally by alloantigen and CD8 T cells expressed high levels of PD-1, TIGIT and TIM-3. Furthermore, Vk*MYC myeloma exploited this alloantigen-driven T cell exhaustion via expression of high levels of PD-L1 and CD155 (the cognate ligands for PD-1 and TIGIT), which were expressed minimally on MLL-AF9 AML. To exploit alloSCT in MM, we used post-transplant cyclophosphamide (PT-Cy) to delete high affinity alloreactive T cells that generate the exhausted donor T cell pool. Subsequent administration of CD137 agonists enhanced T cell activation and cytolytic activity within bone marrow, without exacerbating GVHD. Thus, PT-Cy provides a platform for optimizing immunotherapy after alloSCT.

Allogeneic stem cell transplantation (SCT) is a curative therapy for patients with hematological malignancies related largely to an immunological graft-versus-leukemia (GVL) effect mediated by donor T cells and natural killer cells. Relapse of disease after SCT represents failure of GVL and is now the major cause of treatment failure. We sought to augment GVL effects in patients (n = 29) relapsing after SCT in a prospective phase I/II clinical trial of dose-escalated pegylated interferon-2α (peg-IFNα). The administration of peg-IFNα after reinduction chemotherapy, with or without subsequent donor lymphocyte infusion (DLI), resulted in a 2-year overall survival (OS) of 31% (95% confidence interval, 17.3%-49.2%), which rejects the null hypothesis of 7% generated by observations in an institutional historical cohort. As expected, peg-IFNα was associated with graft-versus-host disease (GVHD) and hematological toxicity, which was manageable with scheduled dose modifications. Progression-free survival (PFS) was greatest in patients who experienced GVHD, although the majority of those patients still eventually progressed. Higher PFS and OS were associated with pretreatment proportions of immune cell populations with regulatory function, including mucosal invariant T cells, regulatory T cells, and plasmacytoid dendritic cells, independent of any association with GVHD. Peg-IFNα administration after relapse thus constitutes a logical strategy to invoke GVL effects and should be studied in a larger, multicenter cohort. This trial was registered at www.anzctr.org.au as #ACTRN12612000728831.

Andrea S. Henden, Antiopi Varelias, Justine Leach, Elise Sturgeon, Judy Avery, Jessica Kelly, Stuart Olver, Luke Samson, Gunter Hartel, Simon Durrant, Jason Butler, Anthony J. Morton, Ashish Misra, Siok-Keen Tey, Elango Subramoniapillai, Cameron Curley, Glen Kennedy,* and Geoffrey R. Hill* Department of Haematology and Bone Marrow Transplantation, Royal Brisbane and Women’s Hospital, Brisbane, QLD, Australia; Bone Marrow Transplantation Laboratory, Queensland Institute of Medical Research (QIMR) Berghofer Medical Research Institute, Brisbane, QLD, Australia; Faculty of Medicine, University of Queensland, Herston, QLD, Australia; Statistics Unit, QIMR Berghofer Medical Research Institute, Brisbane, QLD, Australia; Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA; and Division of Medical Oncology, The University of Washington, Seattle, WA

Key Points Stem cell mobilization with G-CSF promotes IL-17A secretion by donor CD8+ MAIT cells. Tbet and RORγt coexpression identifies potential IL-17A–secreting proinflammatory populations after allogeneic stem cell transplantation.

Abstract Purpose: Inducible caspase 9 (iCasp9) is a cellular safety switch that can make T-cell therapy safer. The purpose of this phase I trial was to investigate the use of iCasp9-transduced T-cell addback in adult patients undergoing haploidentical stem cell transplantation for high-risk hematologic malignancies. Patients and Methods: Patients undergoing myeloablative, CD34-selected haploidentical stem cell transplantation were treated with 0.5−1.0 × 106/kg donor-derived iCasp9-transduced T cells on day +25 or 26 post-transplant, with additional doses allowed for disease relapse, infection, or mixed chimerism. Results: Three patients were enrolled. iCasp9-transduced T cells were readily detectable by 4 weeks post-infusion in all patients and remained at high level (114 cells/μL, 11% of T cells) in 1 patient alive at 3.6 years. One patient developed donor-derived Epstein–Barr virus-associated post-transplant lymphoproliferative disease (EBV-PTLD), which was followed by a marked expansion of iCasp9 T cells and cytokine release syndrome (CRS). These iCasp9-transduced T cells infiltrated the affected lymph nodes and secreted IFNγ and IL-10. They peaked at 1,848 cells/μL and were found to be monoclonal by T-cell receptor (TCR) clonotype and oligoclonal by viral integrant analysis, representing a 6-log in vivo expansion of the dominant T-cell clone. These T cells were not autonomous and contracted with the resolution of EBV-PTLD, which did not recur. Conclusions: iCasp9-transduced T cells could persist long-term. They retained very high in vivo clonotypic proliferative capacity and function, and could cause CRS in response to de novo lymphoma development.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has recently emerged as an important pathogenic cytokine in acute graft-versus-host disease (GVHD), but the nature of the T-cell lineages secreting the cytokine and the mechanisms of action are less clear. Here we used interleukin 17A-fate reporter systems with transcriptional analysis and assays of alloantigen presentation to interrogate the origins of GM-CSF-secreting T cells and the effects of the cytokine on antigen-presenting cell (APC) function after experimental allogeneic stem cell transplantation (SCT). We demonstrated that although GM-CSF-secreting Th17 and non-Th17 cells expanded in the colon over time after SCT, the Th17 lineage expanded to represent 10% to 20% of the GM-CSF secreting T cells at this site by 4 weeks. Donor T-cell-derived GM-CSF expanded alloantigen-presenting donor dendritic cells (DCs) in the colon and lymph nodes. In the mesenteric lymph nodes, GM-CSF-dependent DCs primed donor T cells and amplified acute GVHD in the colon. We thus describe a feed-forward cascade whereby GM-CSF-secreting donor T cells accumulate and drive alloantigen presentation in the colon to amplify GVHD severity. GM-CSF inhibition may be a tractable clinical intervention to limit donor alloantigen presentation and GVHD in the lower gastrointestinal tract.

Leukemia relapse represents a failure of graft-versus-leukemia (GVL) and remains the major limitation of allogeneic stem cell/bone marrow transplantation (BMT). Graft-versus-host disease (GVHD) within the gastrointestinal (GI) tract is the principal determinant of transplant-related mortality and is initiated by a network of alloantigen presentation by professional and non-professional APC that prime donor T cells in the GI tract and related lymphoid structures. Since GVL and lethal GVHD are mediated by donor T cells at spatially distinct sites; bone marrow (BM) and the GI tract respectively, we sought tractable approaches to spatially separate alloreactive responses at these two locations. The administration of high dose steroids in the peri-transplant period is permissive of T cell replete HLA-haploidentical BMT and significant GVL effects (Ogawa H, et al. BBMT. 2006). We utilized murine haploidentical BMT models (B6D2F1 → B6C3F1, B6 → B6D2F1) with recipient background MLL/AF9 primary acute myeloid leukemia (AML), with or without dexamethasone (Dex) administration (5 mg/kg/day i.p., days -1 to +5). Dex-treatment improved transplant survival (from 25% to 68% at day 100, P=0.0012) with significant reductions in GVHD histopathology specifically in the colon (histopathology scores 8.7±1.0 vs 4.6±0.8, P< 0.05), despite excellent leukemia control. To understand this paradox, we analyzed the kinetics of donor T cell expansion after BMT. In the mesenteric lymph node (mLN), Dex treatment significantly suppressed the expansion of both CD4 and CD8 T cells (3.3±0.3 x 105 vs 1.4±0.3 x 105, P< 0.001 and 4.2±0.4 x 105 vs 2.1±0.4 x 105, P< 0.01 respectively) and the activation of CD4 T cells (CD25 MFI: 2021±146 vs 1056±102, P< 0.01). In contrast, donor effector/memory CD44+ CD8 T cells were expanded in the BM of Dex treated recipients (1.9±0.3 x 105 vs 3.1±0.4 x 105, P< 0.05) that demonstrated high per cell cytolytic activity against leukemia (specific lysis: 65±2.4 % vs 62±2.6 % in untreated vs Dex-treated, P> 0.05). Surprisingly, there was no difference in proliferation (cell tracking dye dilution: 63±5.5 % vs 57±5.5 % in untreated vs Dex-treated, P> 0.05) or apoptosis (caspase-3: 6.6±0.4 % vs 6.1±0.6 %, caspase-8: 20±1.6 % vs 17±3.3 % in untreated vs Dex-treated, respectively, P> 0.05) of CD4 T cells in the mLN between the two groups. We undertook experiments with luciferase expressing T cells and noted that Dex-treatment preferentially inhibited T cell accumulation in the GI tract, but not marrow after BMT. Thus, it appeared that Dex treatment preferentially re-distributed donor T cells from the GI tract to the bone marrow. We next determined if Dex exerted effects via direct signaling to the donor T cell. We thus transplanted glucocorticoid receptor (GR)-deficient or intact T cells (GRfl/fl lck-Cre mice). Dex-treatment reduced donor CD4 T cell expansion in the mLN independent of their expression of the GR (untreated vs Dex-treated: 2.8±0.6 x 105 vs 1.2±0.3 x 105, lckCREGRfl/fl and 2.4±0.3 x 105 vs 1.4±0.4 x 105, GRfl/fl littermates, P< 0.05 both groups). Thus steroid effects were mediated indirectly, putatively via effects on recipient alloantigen presentation. There was a marked reduction in recipient dendritic cells (DC) and macrophages expressing the Ea peptide within MHC class II in the GI tract of Dex-treated recipients (terminal Ileum YAe+ DC number 896±93 vs 356±40, P< 0.01, YAe+ macrophage number 1035±136 vs 355±97, P< 0.01). In conjunction with this, expression of the gut homing integrin a4b7 expression was reduced in CD4 T cells from Dex treated recipient mLN (25±1.6 % vs 17±1.7 %, P< 0.01), while the marrow homing integrin VLA-4 (a4b1) was increased (a4: 62±2.2 % vs 75±1.6 %, P< 0.001, b1: 52±2.5 % vs 61±1.6 %, P< 0.05) in donor CD8 T cells from Dex treated recipient BM. Finally, Dex treatment enhanced GVL against a second primary AML (BCR/ABL-NUP98/HOXA9) relative to untreated recipients and those receiving post-transplant cyclophosphamide (PT-Cy) (relapse rate: 0% vs 40% vs 100% at day 35 in Dex vs untreated vs PT-Cy, PT-Cy vs Dex-treated, P< 0.0001; untreated vs Dex-treated, P=0.029). These data suggest a potential therapeutic strategy to modulate antigen presentation in the GI tract and consequent integrin imprinting that minimizes GVHD lethality whilst enhancing GVL within BM. Disclosures No relevant conflicts of interest to declare.

Autologous stem cell transplantation (SCT) remains a standard of care for multiple myeloma (MM) patients and prolongs progression-free survival. A small cohort of patients achieve long-term control of disease, but the majority of patients ultimately relapse, and the mechanisms permitting disease progression remain unclear. In this study, we used a preclinical model of autologous SCT for myeloma where the disease either progressed (MM relapsed) or was controlled. In the bone marrow (BM), inhibitory receptor expression on CD8+ T cells correlated strongly with myeloma progression after transplant. In conjunction, the costimulatory/adhesion receptor CD226 (DNAM-1) was markedly downregulated. Interestingly, DNAM-1- CD8+ T cells in MM-relapsed mice had an exhausted phenotype, characterized by upregulation of multiple inhibitory receptors, including T-cell immunoglobulin and ITIM domains (TIGIT) and programmed cell death protein 1 (PD-1) with decreased T-bet and increased eomesodermin expression. Immune checkpoint blockade using monoclonal antibodies against PD-1 or TIGIT significantly prolonged myeloma control after SCT. Furthermore, CD8+ T cells from MM-relapsed mice exhibited high interleukin-10 (IL-10) secretion that was associated with increased TIGIT and PD-1 expression. However, while donor-derived IL-10 inhibited myeloma control post-SCT, this was independent of IL-10 secretion by or signaling to T cells. Instead, the donor myeloid compartment, including colony-stimulating factor 1 receptor-dependent macrophages and an IL-10-secreting dendritic cell population in the BM, promoted myeloma progression. Our findings highlight PD-1 or TIGIT blockade in conjunction with SCT as a potent combination therapy in the treatment of myeloma.

IL-6 mediates broad physiological and pathological effects through its receptor signal transducing unit gp130. Due to the reportedly wide cellular expression of gp130, IL-6 is thought to signal ubiquitously via gp130 complex formation with membrane-bound IL-6Rα or soluble IL-6Rα. gp130 signaling primarily induces p-STAT3 and p-STAT1. In contrast to the previous dogma, we show in this article that circulating mouse and human granulocytes are unable to induce p-STAT3 or p-STAT1 after stimulation with IL-6 or an IL-6/soluble IL-6R complex. Furthermore, we demonstrate that this is due to a lack of gp130 expression on mouse and human granulocytes, despite their expression of membrane-bound IL-6R. Importantly, the absence of gp130 is not only a feature of mature granulocytes in healthy individuals, it is also observed after allogeneic stem cell transplantation. Moreover, granulocyte gp130 expression is lost during maturation, because granulocyte-monocyte progenitor cells express gp130 and respond to IL-6. Given that granulocytes constitute 50–70% of circulating leukocytes, this indicates a significantly smaller scope of IL-6 signaling than previously anticipated and has important implications for therapeutic IL-6 inhibition and the mechanisms of action thereof.

Type 1 regulatory T (T(R)1) cells are Foxp3(-) interleukin-10 (IL-10)-producing CD4(+) T cells with potent immunosuppressive properties, but their requirements for lineage development have remained elusive. We show that T(R)1 cells constitute the most abundant regulatory population after allogeneic bone marrow transplantation (BMT), express the transcription factor Eomesodermin (Eomes), and are critical for the prevention of graft-versus-host disease. We demonstrate that Eomes is required for T(R)1 cell differentiation, during which it acts in concert with the transcription factor B lymphocyte-induced maturation protein-1 (Blimp-1) by transcriptionally activating IL-10 expression and repressing differentiation into other T helper cell lineages. We further show that Eomes induction in T(R)1 cells requires T-bet and donor macrophage-derived IL-27. Thus, we define the cellular and transcriptional control of T(R)1 cell differentiation during BMT, opening new avenues to therapeutic manipulation.