Key Points
IGSF9 is induced by IFNγ and mediates extramedullary infiltration of AML cells.
Targeting IGSF9 with anti-IGSF9 or anti-IGSF9-DXd represents a promising therapeutic strategy for inhibiting AML progression.
Previously, we reported that targeting IGSF9 could enhance anti-tumor T-cell activity and sensitivity to anti-PD-1 immunotherapy, although the detailed mechanism remains unclear. In this study, we find that, similar to the regulation of PD-L1 expression, IFNγ also induces the expression of IGSF9 in acute myeloid leukemia (AML). The siRNA specifically targeting JAK1 and a STAT1 inhibitor blocking IFNγ signal pathway significantly inhibit the expression of IGSF9 and PD-L1. As a tumor-specific immune checkpoint molecule, IGSF9 plays a significant role in promoting tumor escape. The induction of both PD-L1 and IGSF9 by IFNγ in the tumor microenvironment explains why IGSF9 is highly expressed in tumors and tumor-infiltrating immune cells. This induction also underpins the strong synergistic effects when combining anti-IGSF9 and anti-PD-1 therapies. Additionally, IGSF9 also mediates the extramedullary infiltration of AML cells, which can be inhibited by depletion of IGSF9 or anti-IGSF9. The binding epitopes of anti-IGSF9 are located within the immunoglobulin G2 (IgG2) and fibronectin type-III-2(FnIII-2) domains of IGSF9. Based on these findings, we develop an antibody-drug conjugate (ADC) targeting IGSF9 (anti-IGSF9-linker-DXd). This ADC exhibits 99.7% purity, primarily exists in monomeric form, demonstrating excellent homogeneity (DAR=8-10) and specificity. Anti-IGSF9-linker-DXd effectively kills IGSF9-positive tumor cells and exhibits a potent bystander effect. In vivo, anti-IGSF9-linker-DXd almost completely eliminates early- and mid-stage tumors and significantly inhibits the progression of advanced tumors. In summary, our findings underscore the potential of IGSF9 as a novel therapeutic target for AML treatment, highlighting its role in disease progression and the efficacy of targeted therapies.
