Allograft inflammatory factor -1 is essential for acute monocytic leukemia infiltration

Abstract Extramedullary infiltration (EMI) is a major cause of treatment failure and relapse in acute myeloid leukemia (AML), particularly in monocytic subtypes (FAB-M4/M5). However, the molecular mechanisms underlying EMI remain incompletely understood. Using public AML data (TARGET, TCGA, GSE1159, GSE6891 and scRNA-seq data), we found that among infiltration-related genes, allograft inflammatory factor-1 (AIF-1) was predominantly enriched within granulocyte/monocyte-like leukemic subpopulations, and exhibited specific elevation in acute monoblastic/monocytic leukemia (AMoL, FAB-M5) and acute myelomonocytic leukemia (AMML, FAB-M4) compared to other AML subtypes and healthy controls. Critically, High AIF-1 expression was significantly associated with poorer event-free survival (EFS) and overall survival (OS) in both pediatric (TARGET) and adult (TCGA) AML cohorts, underscoring its important prognostic relevance. To study the potential function of AIF-1 in AMoL, we performed AIF-1 knockdown (KD) in both monocytic and non-monocytic AML cell lines, and found growth inhibition only occurred in AMoL cell lines. Mechanistically, AIF-1 KD impaired self-renewal, migration, infiltration, and adhesion capacities of AMoL cells while promoting apoptosis, with minimal effects on cell cycle progression. In vivo, we found AIF-1 KD had dramatically suppressed the liver infiltration of leukemia cells, significantly increased leukemia latency and prolonged survival of THP-1 cell-derived xenograft model. Collectively, these findings demonstrate that AIF-1 is essential for AMoL cell survival and infiltrative capacity, positioning it as a critical driver of extramedullary dissemination in monocytic AML. To investigate the underlying mechanism of AIF-1 in AMoL development and infiltration, transcriptomic sequencing (RNA-seq) was performed and CCR2 (C-C chemokine receptor type 2) was identified as downstream target of AIF-1, as confirmed by flow cytometry and quantitative PCR. We also found AIF-1 KD in AML cell lines led to significant downregulation of MAPK pathway–related genes in our RNA-seq data, which validated by western blot. Furthermore, RS504393 (a CCR2 inhibitor) and Adezmapimod (a p38 MAPK inhibitor) were found to impair the migration and infiltration capacity of AMoL cells both in vitro and in vivo, indicate that the AIF1–CCR2–MAPK axis plays a pivotal role in mediating AMoL infiltration and that therapeutic targeting of CCR2 or MAPK may offer a promising strategy for the treatment of AMoL. Our study identifies AIF-1 as a critical driver of leukemic infiltration in AMoL via the CCR2–MAPK signaling axis. These findings reveal a novel mechanism underlying extramedullary dissemination in monocytic AML and suggest that targeting CCR2 or MAPK signaling may offer promising therapeutic strategies for EMI-associated AML.