Immunotherapy has demonstrated promise as a treatment for acute myeloid leukemia (AML). However, there is still an urgent need to identify new molecules that inhibit the immune response to AML. Most prior research in this area has focused on protein-protein interaction interfaces. While carbohydrates also regulate immune recognition, the role of cell-surface glycans in driving AML immune evasion is comparatively understudied. The Siglecs, for example, are an important family of inhibitory, glycan-binding signaling receptors that have emerged as prime targets for cancer immunotherapy in recent years. In this study, we find that AML cells express ligands for the receptor Siglec-9 at high levels. Integrated CRISPR genomic screening and clinical bioinformatic analysis identified ST3GAL4 as a potential driver of Siglec-9 ligand expression in AML. Depletion of ST3GAL4 by CRISPR-Cas9 knockout (KO) dramatically reduced the expression of Siglec-9 ligands in AML cells. Mass spectrometry analysis of cell-surface glycosylation in ST3GAL4 KO cells revealed that Siglec-9 primarily binds N-linked sialoglycans on these cell types. Finally, we found that ST3GAL4 KO enhanced the sensitivity of AML cells to phagocytosis by Siglec-9-expressing macrophages. This work reveals a novel axis of immune evasion and implicates ST3GAL4 as a possible target for immunotherapy in AML.

免疫疗法已被证明有望治疗急性髓性白血病 （AML）。然而，仍然迫切需要确定抑制对 AML 的免疫反应的新分子。该领域的大多数先前研究都集中在蛋白质-蛋白质相互作用界面上。虽然碳水化合物也调节免疫识别，但细胞表面聚糖在驱动 AML 免疫逃避中的作用研究相对不足。例如，Siglecs 是抑制性聚糖结合信号受体的重要家族，近年来已成为癌症免疫治疗的主要靶点。在这项研究中，我们发现 AML 细胞高水平表达受体 Siglec-9 的配体。综合 CRISPR 基因组筛选和临床生物信息学分析确定ST3GAL4是 AML 中 Siglec-9 配体表达的潜在驱动因素。CRISPR-Cas9 敲除 （KO） 对 ST3GAL4 的消耗显著降低了 AML 细胞中 Siglec-9 配体的表达。ST3GAL4 KO 细胞中细胞表面糖基化的质谱分析显示，Siglec-9 主要结合这些细胞类型上的 N-连接唾液聚糖。最后，我们发现 ST3GAL4 KO 增强了 AML 细胞对表达 Siglec-9 的巨噬细胞吞噬作用的敏感性。这项工作揭示了一种新的免疫逃避轴，并暗示 ST3GAL4 是 AML 免疫治疗的可能靶点。