# Phase Separation Competent TIA1 Couples Glycolytic Shutdown to CD8+ T-Cell Activation and Shapes the Efficacy of Intravesical BCG in Bladder Cancer

## TL;DR

TIA1, a protein that forms droplets, links tumor metabolism to immune cell activity and may predict better outcomes in bladder cancer patients treated with BCG.

## Contribution

This study reveals a novel role for TIA1 in connecting tumor glycolysis to CD8+ T-cell activation via phase separation and mRNA regulation.

## Key findings

- High TIA1 expression in tumors correlates with better survival outcomes in bladder cancer patients.
- TIA1 reduces glycolysis and lactate production while enhancing CD8+ T-cell activation markers.
- BCG treatment effects depend on TIA1's phase separation ability, suggesting a new therapeutic axis for bladder cancer.

## Abstract

Many people with early-stage bladder cancer receive bladder instillations of the tuberculosis vaccine strain, Bacillus Calmette–Guérin (BCG), yet many patients relapse. One reason is that cancer cells switch to high-rate glycolysis and release acid (lactate), which makes the body’s killer immune cells tired and less able to fight. We studied TIA1, an RNA-binding protein that forms liquid-like droplets (LLPS). We asked whether this droplet-forming ability links tumor glycolysis to CD8+ T-cell activity and BCG benefit. We found that people whose tumors had higher TIA1 were more likely to have better survival outcomes. In cells and mouse models, droplet competent TIA1 lowered glycolysis, reduced lactate, and increased CD8+ T-cell activation markers. BCG tended to enhance this pattern, and the effect depended on TIA1’s low-complexity domain. In our models, increased TIA1 expression was associated with slower tumor growth. Meanwhile, TIA1 binds glycolysis-related RNAs (LDHA, PKM2, and HK2), suggesting an mRNA-linked mechanism. Clinically, measuring TIA1 in tumor tissue may help identify patients more likely to benefit from BCG; for those with low TIA1, future strategies could consider metabolic or immune co-modulation to personalize treatment.

Metabolic immune evasion is a major factor limiting the long-term efficacy of intravesical Bacillus Calmette–Guérin (BCG) therapy in non-muscle-invasive bladder cancer (NMIBC). TIA1 is a stress granule RNA-binding protein with liquid–liquid phase separation (LLPS) capacity. Its role in tumor metabolism and immunotherapy response has been unclear. Here, we demonstrated that high TIA1 expression was independently associated with favorable survival across multiple cohorts. Full-length TIA1 formed cytoplasmic condensates, repressed LDHA/PKM2/HK2, reduced lactate, and lowered extracellular acidification. A condensate-defective ΔLCD (deletion of the low-complexity domain) mutant was inactive. TIA1 showed physical association with these glycolytic mRNAs in human cells, consistent with mRNA-linked control. Condensate-competent TIA1 promoted CD8+ T-cell proliferation, increased CD69 and Granzyme-B, and reduced PD-1 in co-culture. TIMER (Tumor Immune Estimation Resource) and spatial-omics supported co-localization with tumoral CD8A. BCG induced this metabolic–immune signature in cell lines, murine models, and patient explants, but the effects were abolished by TIA1 knock-down. Conversely, TIA1 over-expression alone limited tumor growth and recapitulated BCG-mediated glycolytic restraint and T-cell activation. Together, these results support an LLPS-linked, mRNA-associated regulation of tumor glycolysis. BCG-driven glycolytic suppression and CD8+ T cell activation track with the condensate-forming capacity of TIA1. TIA1 emerges as a prognostic biomarker and a potential therapeutic axis to improve intravesical immunotherapy in NMIBC.