Activation of 4-1BB on liver myeloid cells triggers hepatitis via an interleukin-27 dependent pathway

Purpose: Agonist antibodies targeting the T cell co-stimulatory receptor 4-1BB (CD137) are among the most effective immunotherapeutic agents across pre-clinical cancer models. In the clinic, however, development of these agents has been hampered by dose-limiting liver toxicity. Lack of knowledge of the mechanisms underlying this toxicity has limited the potential to separate 4-1BB agonist driven tumor immunity from hepatotoxicity. Experimental Design: The capacity of 4-1BB agonist antibodies to induce liver toxicity was investigated in immunocompetent mice, with or without co-administration of checkpoint blockade, via 1) measurement of serum transaminase levels, 2) imaging of liver immune infiltrates, and 3) qualitative and quantitative assessment of liver myeloid and T cells via flow cytometry. Knockout mice were used to clarify the contribution of specific cell subsets, cytokines and chemokines. Results: We find that activation of 4-1BB on liver myeloid cells is essential to initiate hepatitis. Once activated, these cells produce interleukin-27 that is required for liver toxicity. CD8 T cells infiltrate the liver in response to this myeloid activation and mediate tissue damage, triggering transaminase elevation. FoxP3+ regulatory T cells limit liver damage, and their removal dramatically exacerbates 4-1BB agonist-induced hepatitis. Co-administration of CTLA-4 blockade ameliorates transaminase elevation, whereas PD-1 blockade exacerbates it. Loss of the chemokine receptor CCR2 blocks 4-1BB agonist hepatitis without diminishing tumor-specific immunity against B16 melanoma. Conclusions: 4-1BB agonist antibodies trigger hepatitis via activation and expansion of interleukin-27-producing liver Kupffer cells and monocytes. Co-administration of CTLA-4 and/or CCR2 blockade may minimize hepatitis, but yield equal or greater antitumor immunity.

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