Abstract 3269: Reappraisal of immunologic mechanisms of hypomethylating agents in treatment of high-risk myelodysplastic syndrome and acute myeloid leukemia
Authors: Hong Junshik , Min Suji , Park Jihyun , Fielder Carly M. , Hu Qianni , Yoon Sung-Soo , Kim Tae Kon 
Published: June 2023

Abstract
Hypomethylating agents (HMA) have been used for the treatment of high-risk myelodysplastic syndrome (HR-MDS) and acute myeloid leukemia (AML) of the elderly. In addition to direct cytotoxic effect of HMA on MDS/AML, HMA upregulates effector T-cell function by demethylating T-cell exhaustion-associated genes (Hazem, Cell 2017) and promoting effector T-cells trafficking to tumor microenvironment by Th1-type chemokines reactivation (Peng, Nature 2019). To elucidate dynamic changes of immune cells profile and gene expression after HMA treatment in MDS/AML, we conducted single cell RNA sequencing of three sequential bone marrow (BM) samples from one HR-MDS patient treated with azacitidine. In BM samples at diagnosis (‘diagnosis’), after 2 cycles of azacitidine (BM blasts increased from 6 to 11%; ‘progression’), and after 3 additional cycles of azacitidine (BM blasts decreased to 3.5% with trilineage hematopoiesis; ‘response’), cell clusters were identified according to immune cell types. The relative proportion of the NK-cell cluster showed the most significant increase up to response (1.3% at ‘diagnosis’, 4.3% at ‘progression’, and 11.8% at ‘response’). By contrast, the CD8 T-cells cluster showed modest increase of proportion at the 3 timepoints (2.7%, 3.9%, and 7%, respectively). Differentially Expressed Gene (DEG) analysis showed CXCR4 was overexpressed in the BM NK-cell cluster at the ‘response’ time point. To determine whether the NK cells can be trafficked to BM by HMA treatment in mouse MDS/AML models, mouse myeloid leukemia cells (C1498 cells) were transplanted into the tail vein of 6-to-8-week aged syngeneic C57/BL6 mice. C1498 bearing mice were intraperitoneally treated with HMA (decitabine) or vehicle for 5 consecutive days. While HMA inhibited in vivo AML proliferation, the quantity of NK cells (NK1.1+) was significantly increased in BM of HMA-treated mice than vehicle controls. In addition, CXCR4 expression in NK1.1+ cells from BM of HMA-treated mice were significantly up-regulated, compared with vehicle controls. The NK depletion in HMA-treated AML mice decreased anti-leukemic effect, suggesting that NK cells may be one of immune cell subsets responsible for HMA induced anti-leukemia effect. Taken together, recruitment of NK cells into MDS/AML BM through CXCR4 overexpression and anti-leukemic cytotoxicity exerted by NK cells can be one of the important immunologic mechanisms of HMA in MDS/AML. Treatment strategy of recruiting more NK cells BM by HMA and maximizing cytotoxicity of NK cells should be further investigated.
Citation Format: Junshik Hong, Suji Min, Jihyun Park, Carly M. Fielder, Qianni Hu, Sung-Soo Yoon, Tae Kon Kim. Reappraisal of immunologic mechanisms of hypomethylating agents in treatment of high-risk myelodysplastic syndrome and acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3269.