Abstract 814: Lymphatic exudate is a novel source of tumor-associated immune cells.

Abstract Autologous tumor-infiltrating lymphocyte (TIL) therapy has demonstrated efficacy in multiple solid tumor types, but therapy requires surgery and extensive manufacturing. Lymphatic exudate (“lymph”) is routinely collected from surgical drains following tumor resection. Although usually discarded, we have shown that this novel proximal biofluid is rich in ctDNA and prognostic of recurrence in head and neck squamous carcinoma (HNSCC) patients. Here, we investigate lymph as a novel, accessible source of tumor-associated lymphocytes. Lymph was collected 24 hours post-surgery from 11 HPV- HNSCC and 14 bladder cancer (BLC) patients in K2EDTA blood collection tubes. Cells were isolated from lymph and immune populations were characterized by flow cytometry. Bulk T-cell receptor b (TCR-b) sequencing was performed on 17 patient sets with matched tumor (11 HNSCC, 6 BLC). Two BLC patients failed sequencing QC. TCR repertoires were compared between tumor and lymph and Simpsons clonality was used to assess clonal diversity. Lymph cells displayed high viability (>85%). Immune subpopulations are described in Table 1. Both CD4+ and CD8+ T cells were detected with variable CD4/CD8 ratios (1.05-4.9 [HNSCC] and 0.11-8.869 [BLC]). Bulk TCR-b analysis showed substantial clonal overlap between lymph and tumor (HNSCC mean 13.1% [0-33.1%] and BLC 9.1% [0.3-23.8%]), exceeding typical overlap described for peripheral blood. Lymph TCRs exhibited clonal expansion (Simpsons clonality means: HNSCC = 0.58% and BLC = 0.64%). Based on surgical drainage rates (median 1-3.5 mL/hour) and median number of CD3+ cells per mL, an estimated 4.8 x 106 - 1.68 x 107 T cells could be recovered daily from drains. Post-surgical lymph contains viable immune populations with substantial TCR overlap with tumor infiltrating lymphocytes. Lymph could enable the isolation of tumor-associated T cells without the challenges around metastasectomy. Lymph T cells may represent a novel, abundant, low cost, and easily accessible source for adoptive cell therapy. Citation Format: Seka Lazare, Michael A. Harmon, Ashley Tellis, Zachary Costliow, Zhuosheng Gu, Adam Benson, Samuel Espinoza, Abbey Crittenden, Megan Rivera, Michael Abern, Sunil Patel, Kamal Pohar, Gautum Agarwal, Rohann Correa, Wendy Winckler. Lymphatic exudate is a novel source of tumor-associated immune cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 814.