Canonical and non-canonical functions of NLRP3.

BACKGROUND: Since its discovery, NLRP3 is almost never separated from its major role in the protein complex it forms with ASC, NEK7 and Caspase-1, the inflammasome. This key component of the innate immune response mediates the secretion of proinflammatory cytokines IL-1ß and IL-18 involved in immune response to microbial infection and cellular damage. However, NLRP3 has also other functions that do not involve the inflammasome assembly nor the innate immune response. These non-canonical functions have been poorly studied. Nevertheless, NLRP3 is associated with different kind of diseases probably through its inflammasome dependent function as through its inflammasome independent functions. AIM OF THE REVIEW: The study and understanding of the canonical and non-canonical functions of NLRP3 can help to better understand its involvement in various pathologies. In parallel, the description of the mechanisms of action and regulation of its various functions, can allow the identification of new therapeutic strategies. KEY SCIENTIFIC CONCEPTS OF THE REVIEW: NLRP3 functions have mainly been studied in the context of the inflammasome, in myeloid cells and in totally deficient transgenic mice. However, for several year, the work of different teams has proven that NLRP3 is also expressed in other cell types where it has functions that are independent of the inflammasome. If these studies suggest that NLRP3 could play different roles in the cytoplasm or the nucleus of the cells, the mechanisms underlying NLRP3 non-canonical functions remain unclear. This is why we propose in this review an inventory of the canonical and non-canonical functions of NLRP3 and their impact in different pathologies.

Transcriptional signatures associated with persisting CD19 CAR-T cells in children with leukemia.

In the context of relapsed and refractory childhood pre-B cell acute lymphoblastic leukemia (R/R B-ALL), CD19-targeting chimeric antigen receptor (CAR)-T cells often induce durable remissions, which requires the persistence of CAR-T cells. In this study, we systematically analyzed CD19 CAR-T cells of 10 children with R/R B-ALL enrolled in the CARPALL trial via high-throughput single-cell gene expression and T cell receptor sequencing of infusion products and serial blood and bone marrow samples up to 5 years after infusion. We show that long-lived CAR-T cells developed a CD4/CD8 double-negative phenotype with an exhausted-like memory state and distinct transcriptional signature. This persistence signature was dominant among circulating CAR-T cells in all children with a long-lived treatment response for which sequencing data were sufficient (4/4, 100%). The signature was also present across T cell subsets and clonotypes, indicating that persisting CAR-T cells converge transcriptionally. This persistence signature was also detected in two adult patients with chronic lymphocytic leukemia with decade-long remissions who received a different CD19 CAR-T cell product. Examination of single T cell transcriptomes from a wide range of healthy and diseased tissues across children and adults indicated that the persistence signature may be specific to long-lived CAR-T cells. These findings raise the possibility that a universal transcriptional signature of clinically effective, persistent CD19 CAR-T cells exists.

Hematopoietic Prostaglandin D2 Synthase Controls Tfh/Th2 Communication and Limits Tfh Antitumor Effects.

T follicular helper (Tfh) cells are a subset of CD4+ T cells essential in immunity and have a role in helping B cells produce antibodies against pathogens. However, their role during cancer progression remains unknown. The mechanism of action of Tfh cells remains elusive because contradictory data have been reported on their protumor or antitumor responses in human and murine tumors. Like Tfh cells, Th2 cells are also involved in humoral immunity and are regularly associated with tumor progression and poor prognosis, mainly through their secretion of IL4. Here, we showed that Tfh cells expressed hematopoietic prostaglandin D2 (PGD2) synthase in a pSTAT1/pSTAT3-dependent manner. Tfh cells produced PGD2, which led to recruitment of Th2 cells via the PGD2 receptor chemoattractant receptor homologous molecule expressed on Th type 2 cells (CRTH2) and increased their effector functions. This cross-talk between Tfh and Th2 cells promoted IL4-dependent tumor growth. Correlation between Th2 cells, Tfh cells, and hematopoietic PGD2 synthase was observed in different human cancers and associated with outcome. This study provides evidence that Tfh/Th2 cross-talk through PGD2 limits the antitumor effects of Tfh cells and, therefore, could serve as a therapeutic target.

Modulation of CD4 T Cell Response According to Tumor Cytokine Microenvironment.

The advancement of knowledge on tumor biology over the past decades has demonstrated a close link between tumor cells and cells of the immune system. In this context, cytokines have a major role because they act as intermediaries in the communication into the tumor bed. Cytokines play an important role in the homeostasis of innate and adaptive immunity. In particular, they participate in the differentiation of CD4 T lymphocytes. These cells play essential functions in the anti-tumor immune response but can also be corrupted by tumors. The differentiation of naïve CD4 T cells depends on the cytokine environment in which they are activated. Additionally, at the tumor site, their activity can also be modulated according to the cytokines of the tumor microenvironment. Thus, polarized CD4 T lymphocytes can see their phenotype evolve, demonstrating functional plasticity. Knowledge of the impact of these cytokines on the functions of CD4 T cells is currently a source of innovation, for therapeutic purposes. In this review, we discuss the impact of the major cytokines present in tumors on CD4 T cells. In addition, we summarize the main therapeutic strategies that can modulate the CD4 response through their impact on cytokine production.

The Tumor Microenvironment Impairs Th1 IFNγ Secretion through Alternative Splicing Modifications of Irf1 Pre-mRNA.

It is clearly established that the immune system can affect cancer response to therapy. However, the influence of the tumor microenvironment (TME) on immune cells is not completely understood. In this respect, alternative splicing is increasingly described to affect the immune system. Here, we showed that the TME, via a TGFß-dependent mechanism, increased alternative splicing events and induced the expression of an alternative isoform of the IRF1 transcription factor (IRF1Δ7) in Th1 cells. We found that the SFPQ splicing factor (splicing factor, proline- and glutamine-rich) was responsible for the IRF1Δ7 production. We also showed, in both mice and humans, that the IRF1 alternative isoform altered the full-length IRF1 transcriptional activity on the Il12rb1 promoter, resulting in decreased IFNγ secretion in Th1 cells. Thus, the IRF1Δ7 isoform was increased in the TME, and inhibiting IRF1Δ7 expression could potentiate Th1 antitumor responses.

Follicular helper-T cells restore CD8+-dependent antitumor immunity and anti-PD-L1/PD-1 efficacy.

BACKGROUND: T follicular helper cells (Tfh) are essential to shape B cell response during germinal center formation. Tfh accumulation has been reported in various human cancers, with positive or negative prognostic roles. However, the mechanisms explaining the accumulation of Tfh and their role in cancer remain obscure. METHODS: In vitro differentiated and mouse cell sorted Tfh phenotype was evaluated by flow cytometry and quantitative PCR (qPCR). Antitumor effect of Tfh was evaluated by adoptive transfer in different tumor-bearing mice models. The involvement of immune cells, cytokines and chemokines was evaluated, using depleting antibodies. Chemokines and cytokines expression and production were evaluated by qPCR and ELISA. In human, the impact of immune cells and chemokines on survival was evaluated by analyzing transcriptomic data from public databases and from our own patient cohorts. RESULTS: In this study, we show that Tfh exert an antitumor immune effect in a CD8+-dependent manner. Tfh produce interleukin-21, which sustains proliferation, viability, cytokine production and cytotoxic functions of exhausted T cells. The presence of Tfh is required for efficacy of antiprogrammed cell death ligand-1 therapy. Tfh accumulate in the tumor bed and draining lymph nodes in different mouse cancer models. This recruitment is due to the capacity of transforming growth factor ß to drive Chemokine (C-X-C motif) Ligand 13 expression, a chemoattractant of Tfh, by intratumor CD8+ T cells. Accumulation of Tfh and exhausted CD8+ T cells predicts cancer outcome in various cancer types. In patients treated with anti-programmed cell death-1 mAb, accumulation of Tfh and CD8+ at the tumor site is associated with outcome. CONCLUSION: This study provides evidence that CD8+/Tfh crosstalk is important in shaping antitumor immune response generated by immunotherapy.