IgA+ B cells expressing programmed death ligand 1 (PD-L1) and interleukin 10 accumulate in the inflamed livers of humans and mice with non-alcoholic fatty liver disease where they promote the progression to hepatocellular carcinoma by limiting the local activation of PD-1-expressing CD8+ T cells. The role of adaptive immunity in early cancer development is controversial. Here we show that chronic inflammation and fibrosis in humans and mice with non-alcoholic fatty liver disease is accompanied by accumulation of liver-resident immunoglobulin-A-producing (IgA+) cells. These cells also express programmed death ligand 1 (PD-L1) and interleukin-10, and directly suppress liver cytotoxic CD8+ T lymphocytes, which prevent emergence of hepatocellular carcinoma and express a limited repertoire of T-cell receptors against tumour-associated antigens. Whereas CD8+ T-cell ablation accelerates hepatocellular carcinoma, genetic or pharmacological interference with IgA+ cell generation attenuates liver carcinogenesis and induces cytotoxic T-lymphocyte-mediated regression of established hepatocellular carcinoma. These findings establish the importance of inflammation-induced suppression of cytotoxic CD8+ T-lymphocyte activation as a tumour-promoting mechanism. Cancer progression beyond the early stages is thought to be caused in some cases by adaptive immunity, but its role remains controversial. In this study, Michael Karin and colleagues show that PD-L1-expressing IgA+ B cells accumulate in the inflamed livers of humans and mice with non-alcoholic fatty liver disease. The inflammation-induced IgA+ cells promote the progression to hepatocellular carcinoma by suppressing liver cytotoxic CD8+ T cells that prevent the emergence of this aggressive tumour.

IgA plasmocytes are shown to promote resistance to the immunogenic chemotherapeutic oxaliplatin in prostate cancer mouse models by inhibiting activation of cytotoxic T cells; immunosuppressive plasma cells, which are also found in human-therapy-resistant prostate cancer, are generated in response to TGFβ, and their functionality depends on PD-L1 expression and IL-10 secretion. Oxaliplatin, an immunogenic chemotherapeutic, is effective in aggressive prostate cancer, but as with most other known therapeutics, castration-resistant forms of the cancer become refractory to continued treatment. This study shows that IgA plasmocytes promote resistance to oxaliplatin in prostate cancer mouse models by inhibiting immunogenic tumour cell death and through activation of cytotoxic lymphocytes. Immunosuppressive plasma cells are generated in response to TGFβ, and their functionality depends on the expression of programmed death ligand 1 and interleukin 10. Elimination of these IgA plasmocytes, which also infiltrate human-therapy-resistant prostate cancer, allows cytotoxic-T-cell-dependent eradication of oxaliplatin-treated tumours. Cancer-associated genetic alterations induce expression of tumour antigens that can activate CD8+ cytotoxic T cells (CTLs), but the microenvironment of established tumours promotes immune tolerance through poorly understood mechanisms1,2. Recently developed therapeutics that overcome tolerogenic mechanisms activate tumour-directed CTLs and are effective in some human cancers1. Immune mechanisms also affect treatment outcome, and certain chemotherapeutic drugs stimulate cancer-specific immune responses by inducing immunogenic cell death and other effector mechanisms3,4. Our previous studies revealed that B cells recruited by the chemokine CXCL13 into prostate cancer tumours promote the progression of castrate-resistant prostate cancer by producing lymphotoxin, which activates an IκB kinase α (IKKα)-BMI1 module in prostate cancer stem cells5,6. Because castrate-resistant prostate cancer is refractory to most therapies, we examined B cell involvement in the acquisition of chemotherapy resistance. Here we focus on oxaliplatin, an immunogenic chemotherapeutic agent3,4 that is effective in aggressive prostate cancer7. We show that mouse B cells modulate the response to low-dose oxaliplatin, which promotes tumour-directed CTL activation by inducing immunogenic cell death. Three different mouse prostate cancer models were refractory to oxaliplatin unless genetically or pharmacologically depleted of B cells. The crucial immunosuppressive B cells are plasmocytes that express IgA, interleukin (IL)-10 and programmed death ligand 1 (PD-L1), the appearance of which depends on TGFβ receptor signalling. Elimination of these cells, which also infiltrate human-therapy-resistant prostate cancer, allows CTL-dependent eradication of oxaliplatin-treated tumours.