The Timing and Abundance of IL-2Rβ (CD122) Expression Control Thymic iNKT Cell Generation and NKT1 Subset Differentiation

Single cell dynamics of tumor specificity vs bystander activity in CD8+ T cells define the diverse immune landscapes in colorectal cancer

CD8+ T cell activation via immune checkpoint blockade (ICB) is successful in microsatellite instable (MSI) colorectal cancer (CRC) patients. By comparison, the success of immunotherapy against microsatellite stable (MSS) CRC is limited. Little is known about the most critical features of CRC CD8+ T cells that together determine the diverse immune landscapes and contrasting ICB responses. Hence, we pursued a deep single cell mapping of CRC CD8+ T cells on transcriptomic and T cell receptor (TCR) repertoire levels in a diverse patient cohort, with additional surface proteome validation. This revealed that CRC CD8+ T cell dynamics are underscored by complex interactions between interferon-γ signaling, tumor reactivity, TCR repertoire, (predicted) TCR antigen-specificities, and environmental cues like gut microbiome or colon tissue-specific 'self-like' features. MSI CRC CD8+ T cells showed tumor-specific activation reminiscent of canonical 'T cell hot' tumors, whereas the MSS CRC CD8+ T cells exhibited tumor unspecific or bystander-like features. This was accompanied by inflammation reminiscent of 'pseudo-T cell hot' tumors. Consequently, MSI and MSS CRC CD8+ T cells showed overlapping phenotypic features that differed dramatically in their TCR antigen-specificities. Given their high discriminating potential for CD8+ T cell features/specificities, we used the single cell tumor-reactive signaling modules in CD8+ T cells to build a bulk tumor transcriptome classification for CRC patients. This "Immune Subtype Classification" (ISC) successfully distinguished various tumoral immune landscapes that showed prognostic value and predicted immunotherapy responses in CRC patients. Thus, we deliver a unique map of CRC CD8+ T cells that drives a novel tumor immune landscape classification, with relevance for immunotherapy decision-making.

NFAT1 and NFκB regulates expression of the common γ-chain cytokine receptor in activated T cells

INTRODUCTION

Cytokines of the common γ chain (γc) family are critical for the development, differentiation, and survival of T lineage cells. Cytokines play key roles in immunodeficiencies, autoimmune diseases, allergies, and cancer. Although γc is considered an assistant receptor to transmit cytokine signals and is an indispensable receptor in the immune system, its regulatory mechanism is not yet well understood.

OBJECTIVE

This study focused on the molecular mechanisms that γc expression in T cells is regulated under T cell receptor (TCR) stimulation.

METHODS

The γc expression in TCR-stimulated T cells was determined by flow cytometry, western blot and quantitative RT-PCR. The regulatory mechanism of γc expression in activated T cells was examined by promoter-luciferase assay and chromatin immunoprecipitation assays. NFAT1 and NFκB deficient cells generated using CRISPR-Cas9 and specific inhibitors were used to examine their role in regulation of γc expression. Specific binding motif was confirmed by γc promotor mutant cells generated using CRISPR-Cas9. IL-7TgγcTg mice were used to examine regulatory role of γc in cytokine signaling.

RESULTS

We found that activated T cells significantly upregulated γc expression, wherein NFAT1 and NFκB were key in transcriptional upregulation via T cell receptor stimulation. Also, we identified the functional binding site of the γc promoter and the synergistic effect of NFAT1 and NFκB in the regulation of γc expression. Increased γc expression inhibited IL-7 signaling and rescued lymphoproliferative disorder in an IL-7Tg animal model, providing novel insights into T cell homeostasis.

CONCLUSION

Our results indicate functional cooperation between NFAT1 and NFκB in upregulating γc expression in activated T cells. As γc expression also regulates γc cytokine responsiveness, our study suggests that γc expression should be considered as one of the regulators in γc cytokine signaling and the development of T cell immunotherapies. Video Abstract.

Proinflammatory IFNγ Is Produced by but Not Required for the Generation of Eomes+ Thymic Innate CD8 T Cells

Innate CD8 T cells are proinflammatory effector T cells that achieve functional maturation in the thymus prior to their export into and maturation in peripheral tissues. Innate CD8 T cells produce the Th1 cytokine IFNγ but depend on the Th2 cytokine IL-4 for their generation. Thus, innate CD8 T cells can permute the intrathymic cytokine milieu by consuming a Th2 cytokine but driving a Th1 cytokine response. The cellular source of IL-4 is the NKT2 subset of invariant NKT (iNKT) cells. Consequently, NKT2 deficiency results in the lack of innate CD8 T cells. Whether NKT2 is the only iNKT subset and whether IL-4 is the only cytokine required for innate CD8 T cell generation, however, remains unclear. Here, we employed a mouse model of NKT1 deficiency, which is achieved by overexpression of the cytokine receptor IL-2Rβ, and assessed the role of other iNKT subsets and cytokines in innate CD8 T cell differentiation. Because IL-2Rβ-transgenic mice failed to generate both NKT1 and innate CD8 T cells, we postulated an in vivo requirement for IFNγ-producing NKT1 cells for innate CD8 T cell development. In-depth analyses of IL-2Rβ-transgenic mice and IFNγ-deficient mice, however, demonstrated that neither NKT1 nor IFNγ was required to induce Eomes or to drive innate CD8 T cell generation. Instead, in vivo administration of recombinant IL-4 sufficed to restore the development of innate CD8 T cells in NKT1-deficient mice, affirming that intrathymic IL-4, and not IFNγ, is the limiting factor and key regulator of innate CD8 T cell generation in the thymus.

Impaired thymic iNKT cell differentiation at early precursor stage in murine haploidentical bone marrow transplantation with GvHD

Introduction

Early recovery of donor-derived invariant natural killer T (iNKT) cells are associated with reduced risk of graft-versus-host disease (GvHD) and overall survival. Patients with severe GvHD, however, had much slower iNKT cell reconstitution relative to conventional T cells.

Methods

To characterize the delay of iNKT cell reconstitution and explore its possible causes, we used a haploidentical bone marrow transplantation (haplo-BMT) mouse model with GvHD. We found the delayed recovery of thymic and peripheral iNKT cell numbers with markedly decreased thymic NKT1 subset in GvHD mice. The defective generation of thymic iNKT precursors with egress capability contributed to the reduced peripheral iNKT cells in GvHD mice. We further identified intermediate NK1.1- NKT1 precursor subpopulations under steady-state conditions and found that the differentiation of these subpopulations was impaired in the thymi of GvHD mice. Detailed characterization of iNKT precursors and thymic microenvironment showed a close association of elevated TCR/co-stimulatory signaling provided by double positive thymocytes and macrophages with defective down-regulation of proliferation, metabolism, and NKT2 signature in iNKT precursor cells. Correspondingly, NKT2 but not NKT1 differentiation was favored in GvHD mice.

Discussion

These data underline the important roles of TCR and co-stimulatory signaling in the differentiation of thymic iNKT subsets under transplantation conditions.

The cytokine receptor DR3 identifies and promotes the activation of thymic NKT17 cells

Invariant natural killer T (iNKT) cells correspond to a population of thymus-generated T cells with innate-like characteristics and effector functions. Among the various iNKT subsets, NKT17 is the only subset that produces the proinflammatory cytokine IL-17. But, how NKT17 cells acquire this ability and what would selectively trigger their activation remain incompletely understood. Here, we identified the cytokine receptor DR3 being specifically expressed on thymic NKT17 cells and mostly absent on other thymic iNKT subsets. Moreover, DR3 ligation promoted the in vivo activation of thymic NKT17 cells and provided costimulatory effects upon agonistic α-GalCer stimulation. Thus, we identified a specific surface marker for thymic NKT17 cells that triggers their activation and augments their effector functions both in vivo and in vitro. These findings provide new insights for deciphering the role and function of murine NKT17 cells and for understanding the development and activation mechanisms of iNKT cells in general.

CD138 expression is a molecular signature but not a developmental requirement for RORγt+ NKT17 cells

Invariant NKT (iNKT) cells are potent immunomodulatory cells that acquire effector function during their development in the thymus. IL-17-producing iNKT cells are commonly referred to as NKT17 cells, and they are unique among iNKT cells to express the heparan sulfate proteoglycan CD138 and the transcription factor RORγt. Whether and how CD138 and RORγt contribute to NKT17 cell differentiation, and whether there is an interplay between RORγt and CD138 expression to control iNKT lineage fate, remain mostly unknown. Here, we showed that CD138 expression was only associated with and not required for the differentiation and IL-17 production of NKT17 cells. Consequently, CD138-deficient mice still generated robust numbers of IL-17-producing RORγt+ NKT17 cells. Moreover, forced expression of RORγt significantly promoted the generation of thymic NKT17 cells, but did not induce CD138 expression on non-NKT17 cells. These results indicated that NKT17 cell generation and IL-17 production were driven by RORγt, employing mechanisms that were independent of CD138. Therefore, our study effectively dissociated CD138 expression from the RORγt-driven molecular pathway of NKT17 cell differentiation.