Defining the spatial distribution of extracellular adenosine revealed a myeloid-dependent immunosuppressive microenvironment in pancreatic ductal adenocarcinoma

Abstract

The prognosis for patients with pancreatic ductal adenocarcinoma (PDAC) remains extremely poor. It has been suggested that the adenosine pathway contributes to the ability of PDAC to evade the immune system and its resistance to immunotherapies (Immuno-Oncology Therapy, IOT), by generating extracellular adenosine (eAdo). Using genetically engineered allograft models of PDAC in syngeneic mice with differential immune infiltration and response to IOT, we showed enrichment of the adenosine pathway in tumour-infiltrating immune cells (in particular, myeloid populations). Using MS-Imaging, we showed that extracellular adenosine distribution is heterogeneous in tumours, with high concentrations in hypoxic margins that surround necrotic areas, associated with a rich myeloid infiltration, demonstrated using Imaging Mass Cytometry (IMC). Pro-tumorigenic M2 macrophages express high levels of the Adora2a receptor; particularly in the IOT resistant model. Blocking the in vivo formation and function of eAdo (Adoi), using a combination of anti-CD73 antibody and an Adora2a inhibitor slowed tumour growth and reduced metastatic burden. In addition, blocking the adenosine pathway improved the efficacy of combinations of cytotoxic agents or immunotherapy. Finally, Adoi remodelled the tumour microenvironment (TME), as evidenced by reduced infiltration of M2 macrophages and Tregs. RNAseq analysis showed that genes related to immune modulation, hypoxia and tumour stroma were downregulated following Adoi and a specific adenosine signature derived from this is associated with a poorer prognosis in patients with PDAC. The formation of eAdo appears to promote the development of the immunosuppressive TME in PDAC, contributing to its resistance to conventional and novel therapies. Therefore, inhibition of the adenosine pathway may represent a strategy to modulate the stroma and improve therapy response in patients with PDAC.