Therapeutic targeting of sphingosine-1-phosphate receptor 1 (S1PR1) in angioimmunoblastic T-cell lymphoma.

Abstract Angioimmunoblastic T-cell lymphoma (AITL) is an aggressive subtype of peripheral T-cell lymphoma (PTCL) derived from malignant transformation of T follicular helper (TFH) cells. AITL, which represents 20–30% of PTCLs, is associated with autoimmune features, poor response to conventional chemotherapy, and dismal prognosis. The molecular landscape of AITL is characterized by frequent genomic alterations in epigenetic regulators, including TET2, DNMT3A, and IDH2, as well as components of the T-cell receptor (TCR) signaling pathway. Among the latter, the RHOA G17V mutation has been recognized as a genetic hallmark uniquely associated with TFH-derived lymphomas. Previous work from our group demonstrated that the RHOA G17V mutation induces TFH specification and, in cooperation with the loss of Tet2, promotes lymphomagenesis. Recent data from our laboratory has shown that expression of RHOA G17V regulates the sphingosine-1-phosphate (S1P) receptor 1 (S1PR1), a key mediator of lymphocyte trafficking and immune activation. Expression of RHOA G17V in CD4⁺ T cells antagonizes S1PR1 internalization, leading to increased activation of S1PR1 downstream signaling. Interestingly, deletion of S1pr1 in CD4⁺ T cells in a murine Rhoa G17V conditional model partially rescues the thymic phenotype and peripheral systemic inflammation characteristic of RHOA G17V-expressing mice, suggesting a contribution of S1PR1 to the aberrant function of RHOA G17V. This, together with our observation of increased S1PR1 expression in human RHOA G17V⁺ AITL tumor samples, identifies S1PR1 deregulation as a potentially relevant effector of the oncogenic effects of RHOA G17V in TFH cells. S1P receptor inhibitors, such as fingolimod (FTY720) and next-generation, more selective modulators such as ozanimod, siponimod, and ponesimod, are FDA-approved for the treatment of multiple sclerosis and other autoimmune diseases. These agents function by inhibiting S1P receptors, thereby sequestering lymphocytes in lymphoid tissues and reducing pathogenic immune cell trafficking. Their established safety and immunomodulatory effects make them attractive candidates for repurposing as targeted therapies in AITL, where S1PR1 signaling seems to be implicated in disease pathogenesis. However, their mechanistic effects in T-cell lymphoma cells remain to be characterized. To dissect the effects of S1PR1 inhibition, we used fingolimod (a pan-S1PR modulator) and ozanimod (a more specific S1PR1 and S1PR5 modulator), in murine preclinical models of AITL in vitro. Both compounds significantly reduced viability and induced apoptosis in the murine AITL cell line. In parallel, migration assays with ex vivo primary murine lymphoma cells revealed potent inhibition of both spontaneous and S1P-induced migration. We performed RNAseq in a Tet2⁻/⁻ RHOA G17V-expressing murine lymphoma line treated with fingolimod or ozanimod for 24 h. GSEA analysis revealed robust downregulation of IL6-JAK-STAT3, TNFA-NFκB, and apoptosis pathways (FDR < 0.25), supporting the existence of a proinflammatory transcriptional program sustained by S1PR1 signaling. To functionally validate the contribution of STAT3 to this circuit, we treated cells with stattic, a selective inhibitor of STAT3 phosphorylation. Stattic partially recapitulated the anti-lymphoma effects of fingolimod, suppressing migration and inducing apoptosis in vitro. Importantly, in vivo treatment with either fingolimod or stattic led to reduced tumor burden and systemic dissemination and was associated with decreased STAT3 phosphorylation. These findings define an S1PR1–STAT3 inflammatory loop that promotes survival and dissemination in RHOA G17V-driven AITL and identify this axis as a therapeutically actionable vulnerability. In summary, our preliminary data establish a mechanistic link between oncogenic RHOA signaling and S1PR1-mediated membrane receptor signaling, highlighting a previously unrecognized pathway in AITL pathogenesis. The demonstration that clinically approved S1P receptor modulators suppress lymphoma growth and dissemination provides a strong rationale for repurposing these agents as targeted therapies for AITL, encouraging future translational studies and clinical investigation.