Investigation of a potential protein biomarker signature that may predict clinical benefit of NT-I7 and pembrolizumab in patients with cold gastrointestinal tumors.

2563 Background: Microsatellite stable colorectal (MSS-CRC) and pancreatic cancer (PDAC) are immunologically cold tumors due to low immunogenicity and lack of genomic diversity. NT-I7, a long-acting IL-7, and pembrolizumab (pembro) show efficacy in these hard-to-treat indications. While a limited set of patients (pts) achieve objective response, frequency and duration of the disease control rate point to a larger subset obtaining clinical benefit. To identify novel predictive biomarkers, we analyzed baseline peripheral and biopsy samples from pts based on treatment duration. Methods: Open-label Phase 2a study in pts with relapsed/refractory checkpoint inhibitor-naïve MSS-CRC and PDAC; NT-I7 1200 µg/kg IM every 6 weeks (Q6W), pembro 200 mg IV Q3W. Subjects were grouped by treatment duration, measured in NT-I7 doses administered before treatment discontinuation for any cause: 1 dose was short (ST), 2-3 doses medium (MT) and ≥4 doses long (LT). Correlative studies included peripheral (proteomics, T cell receptor sequencing TCRseq, single cell RNA sequencing scRNAseq), and biopsy (genomics, transcriptomics, TCRseq). Results: As of 02OCT2023, 53 evaluable pts completed or discontinued treatment; 5 are still on follow up. ST group included 21 pts, MT 22 and LT 10 (including all 5 partial responders). Tumor biopsies were confirmed MSS with low tumor mutational burden (TMB). LT pts had similar age (59.0 53.0-71.5 vs 66.0 47.3-73.5; ST vs LT) and lower baseline tumor burden (81.0 mm vs 58.0 mm; ST vs LT, p = 0.022). Biopsy analysis showed LT pts had, at baseline, upregulated pathways related to immune activity despite confirmed cold tumor status. Baseline scRNAseq in peripheral blood showed that stem-like CD8 T cells (precursors of exhausted TPEX and stem-cell memory TSCM) had a differential activation pattern in LT pts; those pathways were enriched in memory effector subsets in ST pts. Preserved antigen-specific stemness may be needed for NT-I7 + pembro efficacy. Baseline concentrations of 3 proteins that can be produced by growing tumors were significantly increased in ST pts. Pts were classified based on elevated levels of these potential biomarkers: POSITIVE (≥2 biomarkers; 20 pts) and NEGATIVE (≤1 biomarker; 33 pts). Pts with NEGATIVE signature at baseline had significantly higher overall survival, regardless of ST, MT or LT status (13.2 vs 8.9 months, p = 0.030). Conclusions: Preserved tumor-specific TPEX activity may be required for NT-I7 + pembro activity based on its presence in LT pts, who remained on treatment the longest. According to this analysis, there are 3 potentially predictive protein biomarkers that may help identify a pt subset more likely to experience clinical benefits from the combination treatment of NT-I7 + pembro. Further verification of the predictive nature of this signature in independent cohorts is ongoing. Clinical trial information: NCT04332653 .