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 (3Suppl): Abstract nr A045.