S1P in Tumor Microenvironment and Modulation of Anti-Tumor-Directed T-Cell Responses.

Adoptive cell therapy (ACT) using tumor-infiltrating lymphocytes (TILs) has achieved clinically and biologically relevant responses in patients with solid cancer. Clinical efficacy has been increasingly linked to a specific T-cell phenotype, particularly CD8+ TILs exhibiting a progenitor stem-cell-like profile (CD39- CD69-). This review explores the critical role of the sphingosine-1-phosphate (S1P) axis in orchestrating these responses. We detail the biological antagonism between the activation marker CD69 and S1P receptor 1 (S1PR1), where mutual exclusivity dictates thymic selection, if T-cells are retained in tissues or allowed to recirculate and maintain long-term immune surveillance. The S1PR1:S1P axis is further recognized as a critical regulator of mitochondrial fitness, sustaining the high energetic demands of precursor T-cells. We examine the "double-edged sword" nature of S1P in the tumor microenvironment (TME), where it can drive pro-tumorigenic processes like angiogenesis and vascular mimicry (VM), be hijacked by cancer cells to create immune-excluded environments, or S1P can increase T-cell fitness. We summarize the current landscape of clinical trials (as of January 2026) that target S1P production or signaling to modulate anti-tumor responses or use S1P as a biologically relevant marker of treatment outcome.