Longitudinal Localization of Leukemia Stem Cells Between Metaphysis and Central Marrow Governs Leukemic Stem Cell Behavior

Leukemic stem cells (LSCs) reside in protective bone marrow (BM) niches, evading chemotherapy and driving relapse. Disrupting LSC-niche represents a promising therapeutic strategy, yet effective approach remains elusive. Our study characterized longitudinal BM niches in support of LSC survival and proliferation, i.e. metaphysis vs. central marrow, compared to well-accepted endosteum vs. sinusoid niches. Quiescent LSCs mostly localize to metaphysis and show reduced stemness and aggressiveness when mobilized to the central marrow, the composition of both endosteum and sinusoid in the central marrow. Building on this, we developed an approach to restrict LSCs within the BM and induce LSC apoptosis by targeting DPP4 in AML cells. Genetic deletion of Dpp4 in AML cells alters CXCL12 gradient across three scales: 1) System-wide : A reversed CXCL12 gradient between the BM and peripheral blood confines AML cells within the BM, limiting their circulation. 2) BM level : Perturbation of the CXCL12 gradient between the metaphysis and central marrow mobilizes LSCs out of their protective metaphysis niche, leading to exhaustion in the sinusoidal region, despite the higher CXCL12 level in the sinusoidal region. 3) Microscale within the metaphysis : Loss of the CXCL12 gradient between N-cadherin ⁺ mesenchymal stromal cells and the surrounding matrix impairs LSC recruitment to N-cad ⁺ cells, further driving their exhaustion. These alterations stem from the CXCL12-DPP4-GPC3 axis. DPP4, highly expressed by AML cells, deactivates CXCL12, while GPC3, enriched in N-cad ⁺ cells, inhibits DPP4's enzymatic activity. This axis establishes a favorable CXCL12 gradient that attracts LSCs to N-cad ⁺ cell-rich niches in the metaphysis and facilitates their dissemination via circulation. These findings highlight the therapeutic potential of targeting CXCL12-DPP4-GPC3 axis to disrupt LSC niches and enhance AML treatment.