Within a tumour, B cells can gather at the tumour edge, penetrate the tumour sites or form cellular structures. This suggests that B cells are not merely passive participants but may have an important role in the immune response, potentially affecting cancer progression and treatment outcomes. However, there has been limited characterization of the intratumoural B cell receptor (BCR) repertoire and their antigens, which could provide new insights into tumour–immune system interactions.

Recognizing the prominence of B cells in immunogenic tumours, Crescioli et al. characterized the differentiation and maturation of both tumour-resident and circulating B cells in patients with melanoma. The authors found that memory B cells, a subset of B cells that trigger a swift and augmented secondary immune response to an antigen, are enriched in patient tumours compared to the blood of the same patient. Moreover, the memory B cells display diverse combinations of variable (V), diversity (D) and joining (J) genes, suggesting they have been exposed to various antigens over time.