IFN-gamma exposure of MOLM-13 cells enhances HLA gene expression

Challenges to developing immunotherapies for acute myeloid leukemia (AML) include the identification of suitable target antigens due to on-target-off-leukemia toxicity. CD70, expressed on AML bulk and leukemic stem cells with limited expression on healthy cells, has emerged as a promising target. This study evaluated CD70 as a target for NK-cell-based immunotherapy using a sugar-engineered antibody (SEA-CD70). Flow cytometry revealed CD70 expression ranging from 0.2% to 89.6% (median = 7.0%, n = 86) in primary AML cells across genetic subgroups; this expression remained stable at relapse (median = 3.9%, n = 14). SEA-CD70 showed potent, dose-dependent cytotoxicity against AML cell lines, primary cells and in an SCID mouse model, which correlated with CD70 expression levels. Notably, AML cells exposed to conditioned medium (CM) from activated T cells upregulated CD70. TNF-a was identified as the driver of CD70 upregulation, translating into enhanced antibody dependent cellular cytotoxicity (ADCC) against AML cells (cytotoxicity w/o TNF-a = 17.9% vs. with TNF-a = 34.3%, n = 13–15). Conversely, IFN-g exposure led to reduced ADCC (cytotoxicity w/o IFN-g = 17.9% vs. with IFN-g = 9.2%, n = 15), which is attributed to increased expression of NK inhibitory receptor ligands (HLA-ABC, HLA-E). Blocking of the corresponding inhibitory NK receptors (KIR/CD158b and NKG2A) partially reversed this effect. Similar findings were observed with a CD33-directed antibody, indicating a universal resistance mechanism against ADCC-based immunotherapy in AML. These findings suggest that IFN-g-dependent upregulation of HLA molecules contributes to resistance to NK-cell based therapy, warranting further biomarker studies from clinical trials.