Blocking CD47 promotes antitumour immunity through CD103+ dendritic cell-NK cell axis in murine hepatocellular carcinoma model

Abstract

Background & aims: The CD47-signal regulatory protein α (SIRPα) axis inhibits dendritic cell (DC) phagocytosis and contributes to immune evasion. However, the behaviour of DCs and the potential crosstalk between DCs and natural killer (NK) cells in the hepatocellular carcinoma (HCC) microenvironment after CD47 blockade remain unclear.

Methods: The infiltration of CD103⁺ DCs and NK cells were analysed by immunohistochemistry and immunofluorescence in both human and murine HCC specimens. An orthotopic liver tumour model was used to evaluate the function of the CD103⁺ DC-NK cell axis after CD47 blockade in vivo in wild-type, Rag1^-/-, Batf3^-/-, and STING1^-/- mice. Phagocytosis assays were performed in CD103⁺ DC and HCC cell lines. CD103⁺ DC-derived cytokines were analysed by chemokine array. Spleen-derived NK cells in C57BL/6J mice were used to evaluate cytotoxic functions in vitro.

Results: Higher CD47 expression was associated with worse prognosis in patients with HCC. CD47 blockade enhanced antitumour efficacy by stimulating the CD103⁺ DC-NK cell axis. The hypoxic microenvironment promoted CD47 blockade-induced tumour DNA phagocytosis by CD103⁺ DCs. By releasing IL-12 and CXCL9, activated CD103⁺ DCs induced the recruitment of NK cells with upregulated expression of granzyme B, NKG2D, interferon-γ, and tumour necrosis factor-α and downregulated expression of NKG2A. The antitumour effects of CD47 blockade could be abolished by cyclic GMP-AMP synthase (cGAS)-STING pathway inhibition.

Conclusions: In addition to the classical DC-T cell axis, CD47 blockade significantly enhanced the ability of CD103⁺ DCs to take up tumour DNA, resulting in the stimulation of the cGAS-STING pathway, which promoted the infiltration and activation of NK cells in liver cancer.

Lay summary: Hypoxia (low oxygen levels) is prevalent in the hepatocellular carcinoma microenvironment and promotes the phagocytosis (ingestion and elimination) of tumour DNA by CD103⁺ dendritic cells (a type of immune cell). Blockade of the cell surface protein CD47 resulted in activation of CD103⁺ dendritic cells which led to the recruitment and activation of natural killer cells (a different immune cell). When activated, these cells exhibit an antitumour effect.

Keywords: CD103(+) dendritic cells; CD47; Hepatocellular carcinoma; Natural killer cells; STING.