Abstract 2440: Single-cell MRD profiling identifies CXCR4-high AML as a responder population to CXCR4 inhibition with Motixafortide

Abstract Background: The CXCL12-CXCR4 axis mediates bone marrow niche mediated protection of leukemic stem cells and contributes to chemoresistance. Motixafortide is a potent CXCR4 antagonist that disrupts leukemic cell retention in the microenvironment. We leveraged single-cell minimal residual disease (scMRD) profiling to quantify CXCR4 expression and clonal persistence after consolidation therapy within the BLAST trial (NCT02502968), aiming to define predictive biomarkers of Motixafortide response. Methods: Among 128 randomized AML patients in first complete remission (CR), 56 underwent bone marrow scMRD analysis using the Tapestri platform (Mission Bio) targeting 40 recurrent mutation hotspots and 19 surface markers including CXCR4. CXCR4 expression was quantified at single-cell resolution and dichotomized by cohort median. Clinical outcomes were correlated with treatment and scMRD metrics. Results: Although relapse-free survival (RFS) was not different between treatment arms in the ITT population (median RFS: 10.3 vs. 11.5 months, p=0.98), scMRD profiling uncovered a CXCR4 dependent treatment effect. In the placebo arm, high CXCR4 expression correlated with increased relapse risk (p=0.02). In contrast, in the Motixafortide arm, high CXCR4 expression was associated with reduced relapse (p=0.047). A multivariable Cox model confirmed a significant treatment by CXCR4 interaction (HRinteraction 0.032, 95% CI 0.004 to 0.269, p=0.0015), supporting CXCR4 as a predictive biomarker for Motixafortide benefit. scMRD revealed persistent clonal diversity, but conventional MRD positivity did not associate with outcome. Conclusion: While the BLAST trial showed no overall difference in RFS, single-cell MRD analysis revealed differential treatment effects according to CXCR4 expression. These findings suggest that CXCR4 may serve as a biomarker for response to Motixafortide and highlight the potential of single-cell profiling to inform patient stratification. Citation Format: Enise Ceran, Sonia Jaramillo-Segura, Anne Kahtrin Merbach, Christian Rohde, Robert Durruthy-Durruthy, Adam Sciambi, Marc Arribas-Layton, Michelle Lotze, Maxi Wass, Kathrin Rieger, Mathias Hänel, Regina Herbst, Christoph Röllig, Edgar Jost, Richard Schlenk, Katharina Götze, Marina Scheller, Marion Subklewe, Simone Kowoll, Jörg Steighardt, Bayram Edemir, Lutz P. Müller, Irit Glicko-Kabir, Abi Vainstein-Haras, Cora Gromann, Ella Sorani, Shaul Kadosh, Andreas Wienke, Claudia Baldus, Uwe Platzbecker, Hubert Serve, Martin Bornhäuser, Carsten Müller-Tidow. Single-cell MRD profiling identifies CXCR4-high AML as a responder population to CXCR4 inhibition with Motixafortide [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2440.