Background: Despite the excitement and approval of anti-PD1 therapy in first line setting of patients with aHNSCC, prognosis remains poor, with the majority experiencing disease progression after therapy. Consequently, novel strategies to improve treatment activity represent a critical and unmet need for this patient population. Cell therapies offer the advantage of a more personalized therapy for patients over standard immune checkpoint inhibitors. Historically, cell therapies have relied on bulk products that may not effectively select a tumor-reactive T cell population. TBio-4101 is produced by an industrialized manufacturing approach leveraging single-cell sorting of patient-specific neoepitope-reactive TIL with the potential to address immunologically ‘cold’ tumors. The TBio-4101 process specifically enriches polyclonal, polyfunctional, tumor-reactive T cells with an endogenous neoantigen-reactive T cell receptor repertoire that can target multiple tumor antigens. Non-tumor-reactive bystander T cells, which may negatively impact treatment efficacy via product dilution, and typically account for ≥90% of bulk TIL, are substantially reduced by this process. Inspired by the early academic clinically efficacious NCI selection and enrichment strategies (Tran et al 2014, 2016; Zacharakis et al, 2022), TBio-4101 is refined to better identify and potentially enrich to >70% tumor-reactive CD8+ and CD4+ T cells (median < 3% in bulk TIL). Methods: This is a Phase 1b, open-label, single-center study of TBio-4101 and pembrolizumab. Eligible patients are 18 to 75 years of age with aHNSCC. Prior to receiving pembrolizumab with or without chemotherapy as first line standard-of-care (SOC), these patients undergo tumor harvest for TILs followed by apheresis to collect monocytes. TILs are isolated from the tumor and expanded in vitro. Patient-specific neoepitopes are defined by whole exome and RNA sequencing of tumor versus germline to manufacture a peptide pool representing potential tumor-specific mutations. Monocytes isolated from apheresis are differentiated into dendritic cells, pulsed with the neoepitope peptides, and co-cultured with the TILs. Tumor-reactive T cells are specifically activated and selected based on upregulation of activation markers prior to expansion in culture. This process results in a patient-specific T cell product enriched for tumor-reactive T cells. Enrolled patients who progress on first line SOC therapy are preconditioned with 5 days of nonmyeloablative lymphodepletion followed by TBio-4101 infusion. Thereafter, patients receive ≤6 doses of IL-2 (600,000 IU/kg) every 8h, and pembrolizumab (200 mg) every 3 weeks until disease progression. The trial is currently open, with a target enrollment of 15 patients (NCT06236425). Clinical trial information: NCT06236425.