Depletion of exhausted alloreactive T cells enables targeting of stem-like memory T cells to generate tumor-specific immunity.

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 T-cell-derived GM-CSF drives alloantigen presentation by dendritic cells in the gastrointestinal tract.

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.

Phase I Trial of Inducible Caspase 9 T Cells in Adult Stem Cell Transplant Demonstrates Massive Clonotypic Proliferative Potential and Long-term Persistence of Transgenic T Cells.

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.

Granulocytes Are Unresponsive to IL-6 Due to an Absence of gp130.

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.

Eomesodermin promotes the development of type 1 regulatory T (TR1) cells.

Type 1 regulatory T (TR1) 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 TR1 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 TR1 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 TR1 cells requires T-bet and donor macrophage-derived IL-27. Thus, we define the cellular and transcriptional control of TR1 cell differentiation during BMT, opening new avenues to therapeutic manipulation.