Abstract A045: Integrated tumor genomics and peripheral immune profiling identify complementary biomarkers of response to frontline pembrolizumab in extranodal NK/T-cell lymphoma

Abstract Introduction: Extranodal NK/T cell lymphoma (ENKTL) is a rare and aggressive lymphoma that requires better treatment options. Targeting PD1 has shown promising efficacy in the relapsed/refractory setting and has the potential to improve both efficacy and tolerability of front-line therapy. In a phase II investigator-initiated study conducted at MSKCC (Moskowitz et al., ASH 2024), single-agent pembrolizumab induced durable complete metabolic responses (CMR) in a subset of newly diagnosed patients, providing a unique opportunity to investigate biomarkers of sensitivity and primary resistance to PD-1 blockade. Methods: Our group recently completed a phase II trial evaluating lead in single-agent pembrolizumab in untreated ENKTL (Moskowitz et al., ASH 2024). To investigate biomarkers predictive of response or resistance to immune checkpoint blockade in ENKTL, we first analyzed tumor programmed death ligand 1 (PD-L1) structural variants (SVs) in pretreatment biopsies. PD-L1 (CD274) structural variants were evaluated using an MSK custom hybrid-capture assay covering the full locus, with deep sequencing of FFPE tumor DNA, computational detection by Destruct and GRIDSS, IGV confirmation, and healthy donor DNA as a negative control. We also analyzed 15 longitudinally collected peripheral blood samples from 6 patients using 5’ single-cell RNA, TCR, and surface epitope profiling (Single Cell Immune Profiling, 10x Genomics) to explore immune correlates of response and resistance. Results: PD-L1 SVs were identified in 4 patients, and all 4 achieved CMR (vs CMR in 4/15 without PD-L1 SV) supporting PD-L1 SV as a biomarker of marked sensitivity to PD-1 blockade. Responses in patients without PD-L1 SV, indicate that this alteration alone does not explain the full spectrum of pembrolizumab benefit. Peripheral immune profiling identified distinct T-cell states associated with clinical outcome. Response was associated with increased circulating naive T cells and PD-1+ CD8+ T cells with a self-renewing ‘progenitor-like’ exhausted T cell phenotype, whereas nonresponse was associated with enrichment of an inflammatory yet non-cytotoxic GZMK+ CD8+ T-cell subset. This subset is transcriptionally similar to GZMK+ CD8 T-cell states with inflammatory but limited cytotoxic potential that have been shown to accumulate in and drive autoimmune pathology. At the transcriptomic level, GZMK+ CD8+ T cells exhibited stress-associated programs, activation of the TP53 pathway, and impaired mitochondrial function, consistent with a dysfunctional effector state. Conclusion: Our findings support a biological model in which PD-L1 SV identifies a subset of ENKTL intrinsically sensitive to pembrolizumab, while peripheral immune profiling reveals distinct T-cell states associated with primary resistance. Integrating tumor genomics with single-cell immune profiling may improve patient selection for frontline PD-1 blockade and help identify mechanisms of resistance that could inform rational combination strategies for patients who fail anti-PD-1 therapy. Citation Format: Amira Marouf, Alison Moskowitz, William T Johnson, Sneha Mitra, Nivetha Ganesan, Andrew Mcpherson, Steven Horwitz, Santosha A. Vardhana. Integrated tumor genomics and peripheral immune profiling identify complementary biomarkers of response to frontline pembrolizumab in extranodal NK/T-cell lymphoma [abstract]. In: Proceedings of the Fifth AACR International Meeting on Advances in Malignant Lymphoma: From Discovery to Clinical Impact; 2026 Jun 24-27; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2026;7(3_Suppl):Abstract nr A045.