An osteopontin/CD44 immune checkpoint controls CD8+ T cell activation and tumor immune evasion
John D. Klement, Amy V. Paschall, Priscilla S. Redd, Mohammed L. Ibrahim, Chunwan Lu, Dafeng Yang, Esteban Celis, Scott I. Abrams, Keiko Ozato, Kebin Liu
John D. Klement, Amy V. Paschall, Priscilla S. Redd, Mohammed L. Ibrahim, Chunwan Lu, Dafeng Yang, Esteban Celis, Scott I. Abrams, Keiko Ozato, Kebin Liu
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Research Article Immunology

An osteopontin/CD44 immune checkpoint controls CD8+ T cell activation and tumor immune evasion

Abstract

Despite breakthroughs in immune checkpoint inhibitor (ICI) immunotherapy, not all human cancers respond to ICI immunotherapy and a large fraction of patients with the responsive types of cancers do not respond to current ICI immunotherapy. This clinical conundrum suggests that additional immune checkpoints exist. We report here that interferon regulatory factor 8 (IRF8) deficiency led to impairment of cytotoxic T lymphocyte (CTL) activation and allograft tumor tolerance. However, analysis of chimera mice with competitive reconstitution of WT and IRF8-KO bone marrow cells as well as mice with IRF8 deficiency only in T cells indicated that IRF8 plays no intrinsic role in CTL activation. Instead, IRF8 functioned as a repressor of osteopontin (OPN), the physiological ligand for CD44 on T cells, in CD11b+Ly6CloLy6G+ myeloid cells and OPN acted as a potent T cell suppressor. IRF8 bound to the Spp1 promoter to repress OPN expression in colon epithelial cells, and colon carcinoma exhibited decreased IRF8 and increased OPN expression. The elevated expression of OPN in human colon carcinoma was correlated with decreased patient survival. Our data indicate that myeloid and tumor cell–expressed OPN acts as an immune checkpoint to suppress T cell activation and confer host tumor immune tolerance.

Authors

John D. Klement, Amy V. Paschall, Priscilla S. Redd, Mohammed L. Ibrahim, Chunwan Lu, Dafeng Yang, Esteban Celis, Scott I. Abrams, Keiko Ozato, Kebin Liu

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Figure 6

Mice with IRF8 deficiency only in T cells exhibit no deficiency in generation of antigen-specific CD8+ T cells and reject allograft tumor.

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Mice with IRF8 deficiency only in T cells exhibit no deficiency in gener...
(A) Blood cells were collected from WT (Lck-cre+/–Irf8+/+, n = 7) and IRF8-TKO (n = 4) mice. Cells were stained with CD8- and CD44-specific mAbs and analyzed by flow cytometry. The CD8+ and CD44hi cells were quantified. Column: mean; bar: SD. (B) Spleen cells were collected from WT (Lck-cre+/–Irf8+/+, n = 7) and IRF8-TKO (n = 4) stained with CD11b- and Gr1-specific mAbs, followed by intracellular staining with OPN-specific mAb. The CD11b+Gr1+ cells were then gated and analyzed for percentage of OPN+ cells (left panel) and OPN MFI (right panel). (C) WT (Lck-cre+/–Irf8+/+, n = 4) and IRF8-TKO (n = 3) mice vaccinated with OVA peptide, followed by a boost with OVA peptide 14 days later. Peripheral blood was collected 7 days after boost and stained with MHCII-, CD8-, and OVA tetramer–specific antibodies. MHCII-CD8+ cells were gated for OVA tetramer+ cells. Shown are representative plots of OVA-specific CD8+ T cells in WT and IRF8-TKO mice. (D) WT and IRF8-KO CD8+ OVA-specific T cells as shown in C were quantified. (E) 4T1 cells (1 × 104 cells/mouse) were injected into the mammary gland of BALB/c (n = 3) and IRF8-TKO (C57BL/6, n = 4) mice. Mice were sacrificed at day 26 and dissected for examination of tumor presence. Shown is a representative image of 4T1 tumor-bearing BALB/c and 4T1 tumor-challenged IRF8-TKO mice. The red arrow indicates location of the 4T1 tumor. Yellow area indicates lack of tumor in injected area. The right panel shows percentage of mice with tumor. (F) Tumor growth was monitored over time and the tumor growth kinetics is presented in the left panel. Each line represents the tumor growth kinetics of an individual mouse. The tumor size at day 31 after tumor injection is presented in the right panel.