Abstract B115: Divergent T cell exhaustion dynamics in periphery versus tumor during neoadjuvant chemotherapy for pancreatic ductal adenocarcinoma

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer-related death in the United States, with a five-year survival rate of 13%. Neoadjuvant therapy (NAT) is thought to reshape anti-tumor immunity, but its effects on circulating T cell composition/exhaustion and how this relates to intratumoral exhaustion dynamics remain poorly defined. We hypothesized that NAT alters both circulating and intratumoral T cell exhaustion phenotype. PBMCs from 10 resectable or borderline resectable PDAC were collected pre- and post-NAT (n=5 FOLFIRINOX, n=5 Gemcitabine/nab-paclitaxel) and analyzed by spectral flow cytometry for CD4+/CD8+ T cells and Treg frequency. A tumor digest from an unrelated patient was analyzed fresh (day 0) and after ex vivo expansion (days 7, 14). CD4+ and CD8+ T cells were gated independently and each subjected to FlowSOM clustering on CD103, CTLA-4, PD-1, TIM-3, LAG-3, TCF1, CD39, TOX, and TIGIT. Frequencies were compared using paired Wilcoxon signed-rank or t-tests (PBMC) or descriptively (TIL). Generative AI (Claude, Anthropic) was used to assist with statistical analysis and data interpretation. NAT significantly shifted circulating T cell composition, where CD4+ T cells decreased as % of CD3+ T cells (62.0% to 55.0%, p=0.049) and CD8+ T cells reciprocally increased (29.8% to 36.2%, p=0.038); Tregs remained stable (2.59% to 2.48%, p=0.79). Per-cell CD8+ checkpoint receptor co-expression burden showed no group-level shift (bidirectional patient variation), though most CD8+ T cells expressed only 0-1 markers at both timepoints (74.9% vs 76.2%, pre-NAT vs post-NAT). By clustering, exhaustion phenotype was similarly stable: no CD4+ or CD8+ T cell cluster defined by checkpoint co-expression (PD-1, LAG-3, TIGIT, TIM-3, CD39) changed significantly (all p>0.09), including each lineage’s most exhausted subset. The exception was a CD103+ resident-memory-like CD8+ T cell subset lacking checkpoint co-expression, which decreased post-NAT (2.05% to 1.46% of CD8+ T cells, p=0.006). In contrast, the TIL sample showed transient exhaustion dynamics during expansion, with the dominant minimally exhausted CD8+ T cell population collapsing from 75.5% (day 0) to 8.5% (day 7) as exhausted phenotypes emerged, rebounding to 83.3% by day 14. CD4+ T cells followed a similar arc, but resolved into a different, previously minor phenotype (17.8% to 65.2%, day 0 to 14) rather than baseline. In the periphery, NAT drives a reciprocal CD4:CD8 T cell shift without a corresponding change in checkpoint-defined exhaustion phenotype, aside from a decline in a CD103+ CD8+ T cell subset. This suggests NAT's dominant peripheral effect is compositional/redistributive rather than exhaustion-inducing, and that the periphery may not capture the tumor's dynamic exhaustion surges observed during ex vivo expansion. These findings inform blood-based immune monitoring during NAT and TIL harvest timing for adoptive cell therapy, motivating a larger paired cohort. Umayal Sivagnanalingam, Renee R. Anderko, Charu Arora, Sebastiaan Ceuppens, Alessandro Paniccia, Kenneth K. Lee, Amer H. Zureikat, Tullia Bruno. Divergent T cell exhaustion dynamics in periphery versus tumor during neoadjuvant chemotherapy for pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Conference on Pancreatic Cancer: New Frontiers in Biology and Therapeutic Development; 2026 Sep 25-28; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(18_Suppl_2):Abstract nr B115.