The immune receptor repertoire is a set of cellular receptors responsible for recognizing foreign antigens. Characterizing the immune receptor repertoire is critical to understanding mechanisms of human adaptive immunity and developing new approaches to cancer immunotherapy. In this issue, Song and colleagues utilize an advanced bioinformatics pipeline on large-scale samples to investigate the diversity of receptor repertoires in tumors and identify factors correlated with favorable outcomes. The result highlights the role of B cells in immunotherapy responses and suggests establishing B cells as biomarkers in future research. See related article by Song et al., p. 788 (3).