High expression of signal regulatory protein beta 2 marks a favourable prognostic AML subgroup and associates with increased sensitivity to phagocytosis

Abstract

Acute myeloid leukaemia is an aggressive hematologic malignancy that remains exceedingly difficult to treat despite recent advancements. High expression of CD47 on leukemic blasts interacts with the inhibitory receptor SIRP-alpha (SIRP-α) on innate immune cells, resulting in a strong "don't eat me" signal. Therefore, identifying AML patients who could benefit from immune-targeted therapies is crucial SIRP-β2 is predominantly expressed in myeloid cells and positively regulates innate anticancer immunity. Furthermore, endogenously expressed SIRP-β2 potentiates cancer cell trogocytosis by granulocytes. Here, we delineate the role of SIRP-β2 in AML. High expression of SIRP-β2 is independently associated with favorable overall survival (OS) and event free survival (EFS) independent of the ELN intermediate risk group. SIRP-β2 is more prevalent in the more committed FAB M4 and M5 subgroups. SIRP-β2 is also expressed on normal myeloid cells in patient samples, with higher expression on tumor-suppressive M1 macrophages than on adverse prognostic and tumor-supportive M2 macrophages. In line with this, co-culture of macrophages/neutrophils with ectopically expressed SIRP-β2 tumor cells results in an increased phagocytosis/trogocytosis treated with anti-CD47. These data indicate that AML patients with high SIRP-β2 AML expression could significantly benefit from innate immune-targeting therapies such as CD47 immune checkpoint inhibitor.

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