Osteopontin Blockade Immunotherapy Increases Cytotoxic T Lymphocyte Lytic Activity and Suppresses Colon Tumor Progression.

John D Klement,Chunwan Lu,Priscilla S Redd,Dakota B Poschel,Alyssa D Merting,Dafeng Yang,Kebin Liu

doi:10.3390/cancers13051006

Abstract

Simple SummaryDespite the breakthrough in human cancer immunotherapy, colorectal cancer, except for the small subset of microsatellite instable colorectal cancer (MSI, ~4% total cases), is one of the few human cancers that does not respond to current immune checkpoint inhibitor (ICI) immunotherapy. CTLs are present in both MSI and microsatellite stable (MSS) human colon carcinoma, suggesting that PD-L1-independent mechanisms may exist and suppress CTL activation in the colon tumor microenvironment. We determined that osteopontin (OPN) inhibits tumor-specific cytotoxic T lymphocyte (CTL) lytic activity to promote colon tumor growth in vivo. Accordingly, OPN blockade immunotherapy using OPN neutralization monoclonal antibodies 100D3 and 103D6 suppressed colon tumor growth in vivo. Our findings indicate that 100D3 and 103D6 has the potential to be further developed for colorectal cancer immunotherapy. Human colorectal cancers are mostly microsatellite-stable with no response to anti-PD-1 blockade immunotherapy, necessitating the development of a new immunotherapy. Osteopontin (OPN) is elevated in human colorectal cancer and may function as an immune checkpoint. We aimed at elucidating the mechanism of action of OPN and determining the efficacy of OPN blockade immunotherapy in suppression of colon cancer. We report here that OPN is primarily expressed in tumor cells, myeloid cells, and innate lymphoid cells in human colorectal carcinoma. Spp1 knock out mice exhibit a high incidence and fast growth rate of carcinogen-induced tumors. Knocking out Spp1 in colon tumor cells increased tumor-specific CTL cytotoxicity in vitro and resulted in decreased tumor growth in vivo. The OPN protein level is elevated in the peripheral blood of tumor-bearing mice. We developed four OPN neutralization monoclonal antibodies based on their efficacy in blocking OPN inhibition of T cell activation. OPN clones 100D3 and 103D6 increased the efficacy of tumor-specific CTLs in killing colon tumor cells in vitro and suppressed colon tumor growth in tumor-bearing mice in vivo. Our data indicate that OPN blockade immunotherapy with 100D3 and 103D6 has great potential to be further developed for colorectal cancer immunotherapy and for rendering a colorectal cancer response to anti-PD-1 immunotherapy.

Highlights

Human colorectal cancer is a type of highly immunogenic tumor [1,2], but only the small subset of microsatellite instable (MSI) colorectal cancer, which accounts for only approximately 4% of human colorectal cancer cases, responds to anti-PD-1 immunotherapy [3].High tumor mutation burdens (TMB) may serve as neoantigens to generate tumor-reactive cytotoxic T lymphocytes (CTLs) in MSI colorectal cancer [3,4]
CTL infiltrates are present in both MSI and microsatellite stable (MSS) human colon carcinoma [5], suggesting that other immune checkpoints may compensate for PD-L1 function in suppression of tumor-infiltrating CTL effector function in human colorectal carcinoma [4]
Human colorectal cancers are mostly microsatellite-stable with no response to anti-PD1 immunotherapy, necessitating the development of a new immunotherapy

Summary

Introduction

Human colorectal cancer is a type of highly immunogenic tumor [1,2], but only the small subset of microsatellite instable (MSI) colorectal cancer, which accounts for only approximately 4% of human colorectal cancer cases, responds to anti-PD-1 immunotherapy [3].High tumor mutation burdens (TMB) may serve as neoantigens to generate tumor-reactive cytotoxic T lymphocytes (CTLs) in MSI colorectal cancer [3,4]. It has since been determined that OPN is often overexpressed in cells of the tumor microenvironment to promote tumor growth and progression in human cancer patients [7,8,9,10]. OPN may directly regulate tumor cell proliferation, migration through binding to CD44 or the integrin receptors on tumor cell surface [16,17,18,19]. Tumor-secreted OPN binds to αV β3 integrin and CD44 on fibroblasts to reprogram normal fibroblasts into tumor-promoting cancer-associated fibroblasts in mammary carcinoma [20]. Studies have determined that OPN regulates type-1 immunity to viral and bacterial infection through regulation of IL-12 and IL-10 expression in myeloid cells and T cells [23,24]. OPN-deficient mice exhibit altered invariant NKT (iNKT) cell maturation and function with downregulation of the iNKT cell receptor, reduced IL-4 production and decreased Fas ligand expression, leading to reduced Fas/FasL-dependent cytotoxicity against hepatocytes [25]

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