Abstract B115: Divergent T cell exhaustion dynamics in periphery versus tumor during neoadjuvant chemotherapy for pancreatic ductal adenocarcinoma
Umayal Sivagnanalingam, Renee R. Anderko, Charu Arora, Sebastiaan Ceuppens, Alessandro Paniccia, Kenneth K. Lee, Amer H. Zureikat, Tullia BrunoAbstract
Background:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Citation Format:
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.