PD-L1 expression in equine malignant melanoma and functional effects of PD-L1 blockade.

Abstract

Programmed death-1 (PD-1) is an immunoinhibitory receptor expressed on lymphocytes. Interaction of PD-1 with its ligand PD-ligand 1 (PD-L1) delivers inhibitory signals and impairs proliferation, cytokine production, and cytotoxicity of T cells. In our previous studies, we have developed anti-bovine PD-L1 monoclonal antibodies (mAbs) and reported that the PD-1/PD-L1 pathway was closely associated with T-cell exhaustion and disease progression in bovine chronic infections and canine tumors. Furthermore, we found that blocking antibodies that target PD-1 and PD-L1 restore T-cell functions and could be used in immunotherapy in cattle and dogs. However, the immunological role of the PD-1/PD-L1 pathway for chronic equine diseases, including tumors, remains unclear. In this study, we identified cDNA sequences of equine PD-1 (EqPD-1) and PD-L1 (EqPD-L1) and investigated the role of anti-bovine PD-L1 mAbs against EqPD-L1 using in vitro assays. In addition, we evaluated the expression of PD-L1 in tumor tissues of equine malignant melanoma (EMM). The amino acid sequences of EqPD-1 and EqPD-L1 share a considerable identity and similarity with homologs from non-primate species. Two clones of the anti-bovine PD-L1 mAbs recognized EqPD-L1 in flow cytometry, and one of these cross-reactive mAbs blocked the binding of equine PD-1/PD-L1. Of note, immunohistochemistry confirmed the PD-L1 expression in EMM tumor tissues. A cultivation assay revealed that PD-L1 blockade enhanced the production of Th1 cytokines in equine immune cells. These findings showed that our anti-PD-L1 mAbs would be useful for analyzing the equine PD-1/PD-L1 pathway. Further research is warranted to discover the immunological role of PD-1/PD-L1 in chronic equine diseases and elucidate a future application in immunotherapy for horses.

• Authors: Otgontuya Ganbaatar, Satoru Konnai, Tomohiro Okagawa, Yutaro Nojima, Naoya Maekawa, Erina Minato, Atsushi Kobayashi, Ryo Ando, Nobuya Sasaki, Daisuke Miyakoshi, Osamu Ichii, Yukinari Kato, Yasuhiko Suzuki, Shiro Murata, Kazuhiko Ohashi
• Journal: PloS one (PLoS One) Vol. 15 Issue 11 Pg. e0234218 ( 2020) ISSN: 1932-6203 [Electronic] United States
• PMID: 33216754 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antibodies, Monoclonal
• B7-H1 Antigen

Topics

• Amino Acid Sequence
• Animals
• Antibodies, Monoclonal (pharmacology)
• B7-H1 Antigen (antagonists & inhibitors, immunology)
• Horses
• Immunotherapy (methods)
• Melanoma (drug therapy, metabolism, pathology, veterinary)
• Sequence Homology