Background/aims: Cancer therapy with agonist anti-CD137 mAbs has been shown to induce immune-mediated tumor rejections in mice, and equivalent agents of this kind are currently being tested in cancer patients. Previous reports indicated that CD137 stimulation induced polyclonal infiltrates of T lymphocytes in the liver. This study characterizes the liver infiltrates and the target dependency of the phenomena and addresses the question of whether tumors nested in the liver are a more favorable target for CD137-based immunotherapy.
Methods: Liver infiltrates were studied with conventional histology and multiple color flow cytometry of total liver leukocytes. CD137(-/-) mice, mice with a single rearrangement of the TCR (OT-1 mice) and Rag(-/-) mice were used to clarify molecular requirements. Mice implanted with MC38 colon carcinomas either subcutaneously or inside the liver were used for comparative studies under treatment with agonist anti-CD137 mAbs.
Results: CD137 treatment caused mononuclear inflammation in the portal spaces of the liver, which gave rise to moderate increases in transaminases without signs of cholestasis. Marked increases in the numbers of CD8+ T cells were observed, including CD8+ T lymphocytes co-expressing CD11c. Infiltrates were absent in CD137(-/-) mice and mitigated in mice harboring a single transgenic TCR on their CD8 T cells. Despite the tumor-independent accumulation of T cells in the liver, immunotherapeutic effects were not more prominent against tumors located in this organ.
Conclusions: Target-dependent effects of CD137 stimulation lead to liver infiltration with T cells, but lymphocyte enrichment in this organ does not privilege this site for immunotherapeutic effects against transplanted tumors.