A2AR-mediated inhibition of B cell maturation: a novel mechanism of immune suppression in cancer

High levels of extracellular adenosine, highly abundant in the tumor microenvironment, promote immune suppression mainly through the A2AR expressed by tumor-infiltrating immune cells. Here we show that plasma cells are the most negatively affected by adenosine among the immune cells present in the tumor microenvironment. Furthermore, both tonsillar and tumor-associated B cells, including germinal center (GC)-like B cells, plasma cells and plasma blasts (PCs and PBs, respectively, and collectively referred to as antibody-secreting cells (ASCs), express high levels of A2AR. Given the importance of tumor-infiltrating B and PCs in antitumor responses, we investigated how adenosine impairs their numbers and function. Triggering of A2AR inhibited B cell maturation into ASCs and immunoglobulin production in vitro, and impaired upregulation of PC genes upon stimulation. These effects were restored by inupadenant (EOS100850), a potent and highly selective small molecule A2AR antagonist. Spatial transcriptomics analysis of tumor biopsies from patients treated with inupadenant revealed that ASCs specifically increased in tertiary lymphoid structures. Altogether, these data demonstrate that A2AR plays a key role in adenosine-mediated inhibition of B cell maturation toward ASCs through a B cell-intrinsic mechanism, and that this effect is fully reverted by inupadenant.