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CD4 + regulatory T (T reg ) cells accumulate in the tumor microenvironment (TME) and suppress the immune system. Whether and how metabolite availability in the TME influences T reg cell differentiation is not understood. Here, we measured 630 metabolites in the TME and found that serine and palmitic acid, substrates required for the synthesis of sphingolipids, were enriched. A serine-free diet or a deficiency in Sptlc2, the rate-limiting enzyme catalyzing sphingolipid synthesis, suppressed T reg cell accumulation and inhibited tumor growth. Sphinganine, an intermediate metabolite in sphingolipid synthesis, physically interacted with the transcription factor c-Fos. Sphinganine c-Fos interactions enhanced the genome-wide recruitment of c-Fos to regions near the transcription start sites of target genes including Pdcd1 (encoding PD-1), which promoted Pdcd1 transcription and increased inducible T reg cell differentiation in vitro in a PD-1-dependent manner. Thus, Sptlc2-mediated sphingolipid synthesis translates the extracellular information of metabolite availability into nuclear signals for T reg cell differentiation and limits antitumor immunity.

The malate shuttle is traditionally understood to maintain NAD + /NADH balance between the cytosol and mitochondria. Whether the malate shuttle has additional functions is unclear. Here we show that chronic viral infections induce CD8 + T cell expression of GOT1, a central enzyme in the malate shuttle. Got1 deficiency decreased the NAD + /NADH ratio and limited antiviral CD8 + T cell responses to chronic infection; however, increasing the NAD + /NADH ratio did not restore T cell responses. Got1 deficiency reduced the production of the ammonia scavenger 2-ketoglutarate (2-KG) from glutaminolysis and led to a toxic accumulation of ammonia in CD8 + T cells. Supplementation with 2-KG assimilated and detoxified ammonia in Got1-deficient T cells and restored antiviral responses. These data indicate that the major function of the malate shuttle in CD8 + T cells is not to maintain the NAD + /NADH balance but rather to detoxify ammonia and enable sustainable ammonia-neutral glutamine catabolism in CD8 + T cells during chronic infection., (© 2023. The Author(s).)

While the immunosuppressive function of regulatory T (Treg) cells has been extensively studied, their immune-supportive roles have been less well investigated. Using a lymphocytic choriomeningitis virus (LCMV) Armstrong infection mouse model, we found that Treg cell-derived interleukin (IL)-15 is required for long-term maintenance of the KLRG1 + IL-7Rα - CD62L - terminal effector memory CD8 + T (tTEM) cell subset, but dispensable for the suppressive function of Treg cells themselves. In contrast, deletion of Il15 from other sources, including myeloid cells and muscles, did not affect the composition of the memory CD8 + T cell pool. Our findings identify Treg cells as an essential IL-15 source maintaining tTEM cells and suggest that Treg cells promote the diversity of immunological memory., (© 2022 The Authors. European Journal of Immunology published by Wiley-VCH GmbH.)

The incidence of aggressive B-cell lymphomas increases with age, but for elderly or frail patients not eligible for doxorubicin-containing treatment standard therapy remains to be defined. In this prospective, multicenter, phase-2 B-R-ENDA trial, we investigated the feasibility, toxicity, and efficacy of 8 cycles rituximab combined with 6 cycles bendamustine (BR) in elderly or frail aggressive B-cell lymphoma patients: 39 patients aged >80 years and 29 patients aged 61-80 years with elevated Cumulative Illness Rating Scalescore >6 were included. Progression-free survival (PFS) and overall survival (OS) at 2 years were 45% (95% confidence interval [CI], 28%-61%) and 46% (28%-63%) for the patients age >80, as well 32% (13%-51%) and 37% (17%-57%) for frail patients age 64-80, respectively. In a preplanned retrospective analysis, we found no significant differences in PFS and OS comparing the outcome of the 39 patients age >80 years with 40 patients aged 76-80 years treated with 6xR-CHOP (cyclophosphamide, doxorubicin, vincristine, prednisolone) and 2 x rituximab in the RICOVER-60 trial (DSHNHL 1999-1, NCT00052936, EU-20243), yet we detected lower rates of infections and treatment-related deaths in the BR-treated patients. We demonstrate that older and frail patients with aggressive B-cell lymphoma who are not able to receive standard CHOP-based therapy can benefit from anthracycline-free therapy as a feasible and effective therapeutic option., (Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the European Hematology Association.)

T cells become functionally exhausted in tumors, limiting T cell-based immunotherapies. Although several transcription factors regulating the exhausted T (T ex ) cell differentiation are known, comparatively little is known about the regulators of T ex cell survival. Here, we reported that the regulator of G protein signaling 16 (Rgs-16) suppressed T ex cell survival in tumors. By performing lineage tracing using reporter mice in which mCherry marked Rgs16-expressing cells, we identified that Rgs16 + CD8 + tumor-infiltrating lymphocytes (TILs) were terminally differentiated, expressed low levels of T cell factor 1 (Tcf1), and underwent apoptosis as early as 6 days after the onset of Rgs16 expression. Rgs16 deficiency inhibited CD8 + T cell apoptosis and promoted antitumor effector functions of CD8 + T cells. Furthermore, Rgs16 deficiency synergized with programmed cell death protein 1 (PD-1) blockade to enhance antitumor CD8 + T cell responses. Proteomics revealed that Rgs16 interacted with the scaffold protein IQGAP1, suppressed the recruitment of Ras and B-Raf, and inhibited Erk1 activation. Rgs16 deficiency enhanced antitumor CD8 + TIL survival in an Erk1-dependent manner. Loss of function of Erk1 decreased antitumor functions of Rgs16 -deficient CD8 + T cells. RGS16 mRNA expression levels in CD8 + TILs of patients with melanoma negatively correlated with genes associated with T cell stemness, such as SELL , TCF7 , and IL7R , and predicted low responses to PD-1 blockade. This study uncovers Rgs16 as an inhibitor of T ex cell survival in tumors and has implications for improving T cell-based immunotherapies.