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The mechanisms underlying operational tolerance after hematopoietic stem cell transplantation in humans are poorly understood. We studied two independent cohorts of patients who underwent allogeneic hematopoietic stem cell transplantation from human leukocyte antigen–identical siblings. Primary tolerance was associated with long-lasting reshaping of the recipients' immune system compared to their healthy donors with an increased proportion of regulatory T cell subsets and decreased T cell activation, proliferation, and migration. Transcriptomics profiles also identified a role for nicotinamide adenine dinucleotide biosynthesis in the regulation of immune cell functions. We then compared individuals with operational tolerance and nontolerant recipients at the phenotypic, transcriptomic, and metabolomic level. We observed alterations centered on CD38+-activated T and B cells in nontolerant patients. In tolerant patients, cell subsets with regulatory functions were prominent. RNA sequencing analyses highlighted modifications in the tolerant patients' transcriptomic profiles, particularly with overexpression of the ectoenzyme NT5E (encoding CD73), which could counterbalance CD38 enzymatic functions by producing adenosine. Further, metabolomic analyses suggested a central role of androgens in establishing operational tolerance. These data were confirmed using an integrative approach to evaluating the immune landscape associated with operational tolerance. Thus, balance between a CD38-activated immune state and CD73-related production of adenosine may be a key regulator of operational tolerance. Understanding operational tolerance: Operational tolerance describes a spontaneous lack of alloreactivity to donor cells or tissue in the absence of immunosuppressive drugs. Although operational tolerance has been observed in solid organ transplantation and hematopoietic stem cell transplantation (HSCT), the features underlying operational tolerance are not clear. Here, Dubouchet et al. characterized the transcriptional, immunological, and metabolomic features of operational tolerance in two cohorts of individuals who received HSCT from an HLA-matched sibling donor. The authors found that operational tolerance was distinguished by expression of immunosuppressive markers, including CD73, as well as androgens. Together, these findings shed light on potential drivers of operational tolerance. [ABSTRACT FROM AUTHOR]

The use of chimeric antigen receptor (CAR)-engineered regulatory T cells (Tregs) has emerged as a promising strategy to promote immune tolerance. However, in conventional T cells (Tconvs), CAR expression is often associated with tonic signaling, which can induce CAR-T cell dysfunction. The extent and effects of CAR tonic signaling vary greatly according to the expression intensity and intrinsic properties of the CAR. Here, we show that the 4-1BB CSD-associated tonic signal yields a more dramatic effect in CAR-Tregs than in CAR-Tconvs with respect to activation and proliferation. Compared to CD28 CAR-Tregs, 4-1BB CAR-Tregs exhibit decreased lineage stability and reduced in vivo suppressive capacities. Transient exposure of 4-1BB CAR-Tregs to a Treg stabilizing cocktail, including an mTOR inhibitor and vitamin C, during ex vivo expansion sharply improves their in vivo function and expansion after adoptive transfer. This study demonstrates that the negative effects of 4-1BB tonic signaling in Tregs can be mitigated by transient mTOR inhibition. Chimeric antigen receptor engineering in T cells has been shown to be of great potential therapeutic benefit in a range of immune pathologies, although the functionality of such cell therapies can be limited due to tonic signalling and the induction of dysfunction. Here the authors show transient inhibition of mTOR can rescue their 41-BB-CAR-Tregs from tonic signalling-induced dysfunction. [ABSTRACT FROM AUTHOR]

Mechanisms driving acute graft-versus-host disease (aGVHD) onset in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) are still poorly understood. To provide a detailed characterization of tissue-infiltrating T lymphocytes (TL) and search for eventual site-specific specificities, we developed a xenogeneic model of aGVHD in immunodeficient mice. Phenotypic characterization of xenoreactive T lymphocytes (TL) in diseased mice disclosed a massive infiltration of GVHD target organs by an original CD4+CD8+ TL subset. Immunophenotypic and transcriptional profiling shows that CD4+CD8+ TL comprise a major PD1+CD62L−/+ transitional memory subset (>60%) characterized by low level expression of cytotoxicity-related transcripts. CD4+CD8+ TL produce high IL-10 and IL-13 levels, and low IL-2 and IFN-γ, suggestive of regulatory function. In vivo tracking of genetically labeled CD4+ or CD8+ TL subsequently found that CD4+CD8+ TL mainly originate from chronically activated cytotoxic TL (CTL). On the other hand, phenotypic profiling of CD3+ TL from blood, duodenum or rectal mucosa in a cohort of allo-HSCT patients failed to disclose abnormal expansion of CD4+CD8+ TL independent of aGVHD development. Collectively, our results show that acquisition of surface CD4 by xenoreactive CD8+ CTL is associated with functional diversion toward a regulatory phenotype, but rule out a central role of this subset in the pathogenesis of aGVHD in allo-HSCT patients. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 44-year-old man with asymptomatic Binet stage A chronic lymphocytic leukaemia (CLL). It mentions administration of courses of fludarabine, cyclophosphamide, alemtuzumab and high-dose methylprednisolone because of insufficient response and immune thrombocytopenia. It also mentions ibrutinib have the ability to enhance the activity of donor T cells in the context of relapse after haematopoietic stem cell transplantation (HSCT).

The preimmune repertoire consists of mature T lymphocytes that have not yet been stimulated in the periphery. Memory phenotype (MP) cells have been reported as part of the preimmune repertoire (i.e., T cells bearing memory markers despite lack of engagement with cognate Ag); however, little is known about their trafficking and function. In this study, we hypothesized that MP cells, naive to TCR stimulation, constitute a transient population that traffics to tissues during development. Using mutant and transgenic animals with a monospecific TCR, we discovered increased numbers of MP CD8+ T cells circulating in nonimmunized Cxcr3-/- and Cxcl10-/- mice compared with wild-type animals. Phenotypic differences included decreased numbers of preimmune MP Ag-specific T cells in the skin and thymus and a distinct pattern of activation upon TCR engagement. Our results show for the first time, to our knowledge, an important role for CXCR3 and CXCL10 in the tissue distribution of preimmune MP cells. [ABSTRACT FROM AUTHOR]