Fig. 1.

Functional properties of B cells in solid tumours. 1. B cells infiltrating various human cancers [41–48, 59] produce class-switched affinity-matured anti-tumour antibodies with protective effects [62–64]. 2. Human TIB cells produce cytokines enhancing type 1 cellular immunity [80]. 3. B cells concentrate low-dose antigens by membrane IgG-mediated antigen capture [83], and induce CD4⁺ and CD8⁺ T cell priming via antigen presentation [49, 78, 80] and cross-presentation [84–86], respectively. 4. Human B cells have been shown to secrete TRAIL, inducing in vitro tumour cell killing [96], as well as to produce Granzyme B after BCR and IL-21 receptor stimulation [97], but whether this activity results in anti-tumour effects or immune suppression is not known. 5. Human peripheral blood B cells promote the survival and proliferation of CTLs via CD70/CD27 interaction [38], but whether such mechanism is active also in tumour microenvironment is not known. 6. TIB cells acquire a regulatory phenotype and produce immunosuppressive cytokines and have been shown to suppress tumour immunity in mice [103–106]. 7. B cells produce CXCL13 and Lymphotoxin (LT), which induce the formation of tertiary lymphoid structures in mouse tumour models [118, 120], and under inflammatory conditions in humans [121]. Whether this also takes place in the human tumour microenvironment is not known. 8. TIB cells promote angiogenesis in a STAT3-dependent manner [108] or promote lymphangiogenesis [107] that facilitates tumour growth and dissemination, respectively, in mice. TIB-cell-derived LTα stimulates the recurrence of castration-resistant prostate tumours in mice [110, 111]. TIB-cell-derived BAFF might be involved in the promotion of human pancreatic cancer [113]