FOLFIRINOX Plus Nivolumab Promotes Irregular Intra-Tumoral Lymphoid Aggregates in Borderline Resectable Pancreatic Adenocarcinoma: A Phase 1 Trial

Combination therapies of chemotherapy and immune checkpoint inhibitors (ICIs) have failed to improve survival in pancreatic ductal adenocarcinoma (PDAC), except in rare MSI-H cases, despite their success in other solid tumors. Most prior studies have been conducted in advanced disease. Here, we present clinical, pathologic, and translational results from a phase 1b/2 investigator-initiated study evaluating neoadjuvant modified FOLFIRINOX (mFOLFIRINOX, mFFX) plus nivolumab in patients with borderline-resectable (BR) PDAC. Among 28 patients enrolled, 22 (79%) proceeded to surgery. Treatment was well tolerated with no significant delays or surgical complications, meeting the primary endpoint. Among patients who underwent surgical resection, median disease-free survival was 19.7 months, median progression-free survival was 26 months (95% CI: 14.7-34.3) and median overall survival was 38 months (95% CI: 27.9-not reached). The regimen demonstrated an acceptable safety profile, with all Grade 3-4 treatment-related adverse events due to chemotherapy and no Grade 3 immune related adverse events observed. Treatment effects were assessed using paired pre- and post-treatment samples and by comparing post-treatment tumors from the nivolumab cohort to historical BR mFFX-only controls. In paired analyses, intra-tumoral CD8 T cells and plasma cells increased together; in between-group comparisons, plasma cells were significantly higher in the nivolumab cohort, with a modest CD8 T cell increase. Immunohistochemistry revealed that plasma cell abundance correlated with dense intra-tumoral lymphoid aggregates (LA) lacking germinal center-like morphology, a pattern consistent with extrafollicular B cell differentiation. Single-cell spatial transcriptomics identified irregular lymphoid aggregates with high plasma cell to B cell ratios (PBRs) that were enriched for terminally exhausted CD8 T cells and de-enriched for progenitor exhausted CD8 T cells and central memory CD4 T cells. Together, these findings implicate intra-tumoral LA disorganization and skewed T cell subsets as complementary features associated with limited efficacy of PD-1-based chemoimmunotherapy in PDAC. (Clinicaltrials.gov identifier: NCT03970252).