Research Article: In vitro and in vivo antivirus activity of an anti-programmed death-ligand 1 (PD-L1) rat-bovine chimeric antibody against bovine leukemia virus infection

Date Published: April 26, 2017

Publisher: Public Library of Science

Author(s): Asami Nishimori, Satoru Konnai, Tomohiro Okagawa, Naoya Maekawa, Ryoyo Ikebuchi, Shinya Goto, Yamato Sajiki, Yasuhiko Suzuki, Junko Kohara, Satoshi Ogasawara, Yukinari Kato, Shiro Murata, Kazuhiko Ohashi, Aftab A. Ansari.

http://doi.org/10.1371/journal.pone.0174916

Abstract

Programmed death-1 (PD-1), an immunoinhibitory receptor on T cells, is known to be involved in immune evasion through its binding to PD-ligand 1 (PD-L1) in many chronic diseases. We previously found that PD-L1 expression was upregulated in cattle infected with bovine leukemia virus (BLV) and that an antibody that blocked the PD-1/PD-L1 interaction reactivated T-cell function in vitro. Therefore, this study assessed its antivirus activities in vivo. First, we inoculated the anti-bovine PD-L1 rat monoclonal antibody 4G12 into a BLV-infected cow. However, this did not induce T-cell proliferation or reduction of BLV provirus loads during the test period, and only bound to circulating IgM+ B cells until one week post-inoculation. We hypothesized that this lack of in vivo effects was due to its lower stability in cattle and so established an anti-PD-L1 rat-bovine chimeric antibody (Boch4G12). Boch4G12 was able to bind specifically with bovine PD-L1, interrupt the PD-1/PD-L1 interaction, and activate the immune response in both healthy and BLV-infected cattle in vitro. Therefore, we experimentally infected a healthy calf with BLV and inoculated it intravenously with 1 mg/kg of Boch4G12 once it reached the aleukemic (AL) stage. Cultivation of peripheral blood mononuclear cells (PBMCs) isolated from the tested calf indicated that the proliferation of CD4+ T cells was increased by Boch4G12 inoculation, while BLV provirus loads were significantly reduced, clearly demonstrating that this treatment induced antivirus activities. Therefore, further studies using a large number of animals are required to support its efficacy for clinical application.

Partial Text

Programmed death-1 (PD-1) is an immunoinhibitory receptor that is expressed on activated T cells and B cells and induces immune suppression by binding to PD-ligand 1 (PD-L1) [1]. The PD-1/PD-L1 interaction normally works as a negative feedback system inhibiting excessive immune response, with PD-1 knockout mice developing autoimmune diseases such as lupus-like arthritis and glomerulonephritis [2]. However, this mechanism is often exploited by various chronic diseases to avoid immune elimination. For instance, the expression of PD-L1 has been reported in many human cancers, including melanoma, squamous cell carcinoma, urothelial carcinoma, and solid tumors in the lung, ovary, kidney, pancreas, stomach, and colon [3–9]. In addition, PD-1 upregulation has been demonstrated in tumor-infiltrating T lymphocytes [10]. Importantly, it has been shown that PD-L1 expression is strongly correlated with a progressive stage and worse prognosis, indicating a relationship with disease outcome [5–9].

In this study, we established Boch4G12, a chimeric antibody composed of the variable region from anti-bovine PD-L1 rat mAb (4G12) and the constant region from bovine IgG1. This antibody exhibited similar activities to the original antibody in terms of binding to bovine PD-L1 and interrupting the PD-1/PD-L1 interaction. The inhibition of T-cell function that is induced by PDL1/EGFP cells was restored using Boch4G12, indicating that this antibody has the potential to reactivate exhausted T cells through PD-L1 blockade. In addition, IFN-γ production was upregulated in PBMCs from BLV-infected cattle when cultured with Boch4G12. We previously demonstrated that PD-L1 on IgM+ B cells increases in line with the progression of BLV infection [28]. Thus, this observed increase in IFN-γ in the culture supernatant was probably caused by Boch4G12 preventing an interaction between PD-1 on T cells and PD-L1 on infected B cells, reactivating the ability of T cells to respond to the BLV antigen. Finally, a BLV-infected calf that was inoculated with Boch4G12 showed a proliferation of CD4+ T cells in response to the BLV antigen and a reduction in BLV provirus loads, suggesting that Boch4G12 has therapeutic potential for controlling BLV infection.

 

Source:

http://doi.org/10.1371/journal.pone.0174916

 

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