Introduction:

Clonal hematopoiesis of indeterminate potential (CHIP) has emerged as a biomarker of adverse outcomes across oncology and immunology, including inferior overall survival (OS) and increased risks of cardiovascular events, disease relapse, and therapy-related myeloid malignancies. Tumor-infiltrating lymphocyte (TIL) therapy is an emerging adoptive cellular immunotherapy for immune checkpoint inhibitor (ICI)- refractory melanoma, involving high-dose lymphodepletion (cyclophosphamide 120 mg/kg, fludarabine 125 mg/m²), followed by autologous TIL infusion and interleukin-2. TIL achieves ~30% objective response rate and improves progression-free survival (PFS) (Rohaan et al., NEJM 2022, Medina JCO 2025). Despite these advances, the impact of host hematopoietic factors such as CHIP on TIL manufacturing, efficacy, and toxicity remains poorly understood. Given CHIP's role in modulating inflammation and cellular infiltration within the solid tumor microenvironment, we undertook a pilot study to document its prevalence and clinical significance in patients undergoing TIL therapy.

Methods:

Peripheral blood were obtained from 49 patients with metastatic melanoma enrolled in investigator-initiated TIL trials at Moffitt Cancer Center (NCT01659151, NCT01701674). CHIP was defined as ≥1 pathogenic variant with variant allele frequency (VAF) ≥2%, identified via a 275-gene myeloid panel (Qiagen QiaSeq, 2000X average coverage). Clinical data, including blood counts and post-infusion hematologic recovery, were collected. TIL product characteristics, including total infused cells and T cell subset composition, were also assessed. Group comparisons were made using Fisher's exact and Wilcoxon rank-sum tests. Time-to-event outcomes were analyzed with Kaplan–Meier and log-rank tests.

Results: The median age of the cohort was 49.5 years (IQR 40–55), with 22 male and 16 female patients. Median follow-up was 36.5 months, during which 21 patients experienced disease progression, and 21 patients died. CHIP was detected in 6 of 49 patients (12%), with mutations in ASXL1 (n=3), KRAS (n=2), and DNMT3A (n=1). No significant differences in age (48.2 vs. 51 years), sex, race, ethnicity, BRAF mutation status, or presence of brain/liver metastases were observed between CHIP-positive and CHIP-negative groups. Patients with CHIP produced a lower median total TIL dose (~4.2 × 10¹⁰ cells vs. 6.4 × 10¹⁰) compared to those without CHIP though this difference was not statistically significant (p=0.11). No significant differences were seen in TIL product phenotype, including proportions of CD4⁺ (44.1% vs. 31.9%), CD8⁺ (50% vs. 63%), or stem cell memory (CD45RA⁺CCR7⁺CD62L⁺CD95⁺) T cells (15.8% vs. 13.2%).

Baseline platelet counts were lower in CHIP-positive patients (median 92 vs. 109 ×10⁹/L, p=0.25). Following TIL infusion, CHIP-positive patients demonstrated numerically slower hematologic recovery, with lower daily increases in absolute lymphocyte (0.39 vs. 0.74 ×10⁹/L/day), neutrophil (1.8 vs. 2.23 ×10⁹/L/day), and monocyte counts (0.36 vs. 0.22 ×10⁹/L/day). Eosinophil counts in CHIP-positive patients showed a slightly negative recovery slope (-0.0004 vs. +0.004 ×10⁹/L/day), suggesting a flat or declining trend in reconstitution. These differences did not reach statistical significance (all p > 0.05). Clinical response rates were similar (33% vs. 37.2, p>.05). While not statistically significant, OS was numerically shorter in CHIP-positive patients (median 10 vs. 19 months; log-rank p=0.37), whereas PFS was similar (13 vs. 10 months; p=0.57).

Conclusion:

This pilot study is the first to report the prevalence and clinical impact of CHIP in patients receiving TIL therapy. CHIP was detected in 12% of patients, likely reflecting the cohort's younger age and limited prior cytotoxic exposure. Our results suggest that CHIP may influence the tumor microenvironment or systemic inflammatory state in ways that impair TIL expansion during manufacturing. Although limited by sample size, CHIP-positive patients showed trends toward lower baseline platelet counts, delayed hematologic recovery, and shorter OS, suggesting impaired hematopoietic resilience following lymphodepleting chemotherapy. Future studies with sufficient power informed by our established CHIP prevalence are warranted to determine whether CHIP status can optimize lymphodepletion intensity or supportive care strategies in adoptive cell therapy.

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2025
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