In the clinic, chimeric antigen receptor-modified T (CAR T) cell therapy is frequently associated with life-threatening cytokine-release syndrome (CRS) and neurotoxicity. Understanding the nature of these pathologies and developing treatments for them are hampered by the lack of appropriate animal models. Herein, we describe a mouse model recapitulating key features of CRS and neurotoxicity. In humanized mice with high leukemia burden, CAR T cell-mediated clearance of cancer triggered high fever and elevated IL-6 levels, which are hallmarks of CRS. Human monocytes were the major source of IL-1 and IL-6 during CRS. Accordingly, the syndrome was prevented by monocyte depletion or by blocking IL-6 receptor with tocilizumab. Nonetheless, tocilizumab failed to protect mice from delayed lethal neurotoxicity, characterized by meningeal inflammation. Instead, the IL-1 receptor antagonist anakinra abolished both CRS and neurotoxicity, resulting in substantially extended leukemia-free survival. These findings offer a therapeutic strategy to tackle neurotoxicity and open new avenues to safer CAR T cell therapies.

Key Points T cells genetically targeted to the tumor-promoting antigen CD44v6 are effective against AML and MM. CD44v6-targeted T cells do not recognize hematopoietic stem cells and keratinocytes but cause reversible monocytopenia.

Chimeric antigen receptor (CAR)-T cell immunotherapy is at the forefront of innovative cancer therapeutics. However, lack of standardization of cellular products within the same clinical trial and lack of harmonization between different trials have hindered the clear identification of efficacy and safety determinants that should be unveiled in order to advance the field. With the aim of facilitating the isolation and in vivo tracking of CAR-T cells, we here propose the inclusion within the CAR molecule of a novel extracellular spacer based on the low-affinity nerve-growth-factor receptor (NGFR). We screened four different spacer designs using as target antigen the CD44 isoform variant 6 (CD44v6). We successfully generated NGFR-spaced CD44v6 CAR-T cells that could be efficiently enriched with clinical-grade immuno-magnetic beads without negative consequences on subsequent expansion, immuno-phenotype, in vitro antitumor reactivity, and conditional ablation when co-expressing a suicide gene. Most importantly, these cells could be tracked with anti-NGFR monoclonal antibodies in NSG mice, where they expanded, persisted, and exerted potent antitumor effects against both high leukemia and myeloma burdens. Similar results were obtained with NGFR-enriched CAR-T cells specific for CD19 or CEA, suggesting the universality of this strategy. In conclusion, we have demonstrated that the incorporation of the NGFR marker gene within the CAR sequence allows for a single molecule to simultaneously work as a therapeutic and selection/tracking gene. Looking ahead, NGFR spacer enrichment might allow good manufacturing procedures-manufacturing of standardized CAR-T cell products with high therapeutic potential, which could be harmonized in different clinical trials and used in combination with a suicide gene for future application in the allogeneic setting.

Immunotherapy is emerging as a new pillar of cancer treatment with potential to cure. However, many patients still fail to respond to these therapies. Among the underlying factors, an immunosuppressive tumor microenvironment (TME) plays a major role. Here we show that monocyte-mediated gene delivery of IFNα inhibits leukemia in a mouse model. IFN gene therapy counteracts leukemia-induced expansion of immunosuppressive myeloid cells and imposes an immunostimulatory program to the TME, as shown by bulk and single-cell transcriptome analyses. This reprogramming promotes T-cell priming and effector function against multiple surrogate tumor-specific antigens, inhibiting leukemia growth in our experimental model. Durable responses are observed in a fraction of mice and are further increased combining gene therapy with checkpoint blockers. Furthermore, IFN gene therapy strongly enhances anti-tumor activity of adoptively transferred T cells engineered with tumor-specific TCR or CAR, overcoming suppressive signals in the leukemia TME. These findings warrant further investigations on the potential development of our gene therapy strategy towards clinical testing.

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Activating mutations in the BRAF-MAPK pathway have been reported in histiocytoses, hematological inflammatory neoplasms characterized by multi-organ dissemination of pro-inflammatory myeloid cells. Here, we generate a humanized mouse model of transplantation of human hematopoietic stem and progenitor cells (HSPCs) expressing the activated form of BRAF (BRAFV600E). All mice transplanted with BRAFV600E-expressing HSPCs succumb to bone marrow failure, displaying myeloid-restricted hematopoiesis and multi-organ dissemination of aberrant mononuclear phagocytes. At the basis of this aggressive phenotype, we uncover the engagement of a senescence program, characterized by DNA damage response activation and a senescence-associated secretory phenotype, which affects also non-mutated bystander cells. Mechanistically, we identify TNFα as a key determinant of paracrine senescence and myeloid-restricted hematopoiesis and show that its inhibition dampens inflammation, delays disease onset and rescues hematopoietic defects in bystander cells. Our work establishes that senescence in the human hematopoietic system links oncogene-activation to the systemic inflammation observed in histiocytic neoplasms.

BackgroundMultisystemic Langerhans cell histiocytosis (mLCH) is an aggressive disease characterized by the accumulation of mononuclear phagocytes with immunohistochemical features of dendritic cell (histiocytes)1. Histiocytes infiltrate mostly the skin, bone marrow (BM), lung and spleen, and produce high levels of proinflammatory cyto/chemokines, leading to organ dysfunction2,3. In patients, around 10% of cells in lesions carries an oncogenic mutation in the MAPK pathway, mostly BRAFV600E (70% of cases). BRAFV600E can be detected also in monocytes and BM progenitors (HSPC) from these patients, whereas only a fraction of them carries a mutation in B cells and none in T cells4.ObjectivesTo study the role of BRAFV600E in the pathogenesis of mLCH, we set up a humanized mouse model of mLCH based on the transplantation into immunodeficient mice (NSG) of human HSPC expressing BRAFV600E.MethodsWe isolated HSPC from human cord blood and transduced them at two different levels (50% and 20%) with lentiviral vectors that ubiquitously express BRAFV600E, BRAFWT or GFP.ResultsAll BRAFV600E mice manifested severe weight loss within 7 weeks with a median of 3 and 5 weeks for 50% and 20% transduction groups, respectively. Mice showed dysplastic bone marrow (BM) with infiltration of histiocytes; lesions were present also in lungs, kidneys, CNS, spleen and liver. Immunophenotype of infiltrating histiocytes closely resembles mLCH, staining positive for CD14, CD68, S-100 and langerin. None of the control mice lost weight nor displayed organ alteration. Flow cytometry analyses of BM showed 5- to 7-fold reduction in engraftment of human cells in BRAFV600E vs GFP groups (p<0,001). Percentage of myeloid cells increased by 3- to 4-fold in BRAFV600E vs GFP groups (p<0,001). On the contrary, percentage of B cells was reduced by 3- to 6,5-fold in BRAFV600E vs GFP groups (p<0,001). Moreover, there was no difference in the percentage of GFP-positive cells between myeloid cells, whole BM and in vitro sample, suggesting a non-cell autonomous mechanism underlying this myeloid phenotype.ConclusionsIn summary, we generated for the first time a human xenogeneic transplantation mouse model of mLCH, showing that BRAFV600E in human HSPC promotes myeloid skewing rather than proliferation.References Wilejto et al. Curr Opin Rheumatol 2012. DOI: 10.1097/BOR.0b013e32834db53e.Donadieu et al. Histiocytic Disorders of Children and Adults 2005.Kannourakis et al. Br J Cancer 1994, Sep;23:S37–40.Berres et al. J Exp Med 2014, DOI: 10.1084/jem.20130977. Disclosure of InterestNone declared

Hematopoietic stem cell transplantation (HSCT) from an allogeneic donor is an effective form of cancer immunotherapy, especially for acute leukemias. HSCT is however frequently complicated by the occurrence of graft-versus-host disease (GVHD). Immunocompromised mice infused with human T cells often develop a clinical syndrome resembling human GVHD (xenogeneic or X-GVHD). Herein, we describe a method for inducing X-GVHD in a highly reproducible manner. Given the human nature of immune effectors, this xenogeneic model can be routinely adopted for screening the efficacy of new treatments for GVHD.