Abstract 599: Identification of lymphocyte activation gene 3 binding peptides using phage displayed peptide libraries for cancer immunotherapy

Abstract

Abstract Treatment with immune checkpoint blockades against cytotoxic T lymphocyte associated protein-4, programmed cell death-1, and programmed death-ligand 1 is currently giving improved results to many cancer patients. Nevertheless, a significant proportion of cancer patients treated with immune checkpoint blockades are still largely unsatisfied with the benefits of these drugs. One of the reasons is that cancer cells also use other immune checkpoints such as lymphocyte activation gene-3 (LAG-3), T cell immunoreceptor with Ig and ITIM domains, and T-cell immunoglobulin and mucin-domain containing-3. LAG-3 negatively regulates activated T cells. In this study, we screened phage displayed-peptide libraries for peptides that selectively bind to LAG-3. After five rounds of screening, we selected a candidate peptide and named it LAG3Pep. LAG3Pep preferentially bound to human LAG-3-transfected HEK 293T cells over mock-transfected cells and phorbol myristate acetate/ionomycin/chloroquine-stimulated Jurkat T cells over unstimulated cells. LAG3Pep also bound to splenocytes isolated from tumor-bearing mice, suggesting the reactivity across human and mouse LAG-3. Pull-down of Jurkat T cell lysates using biotin-labeled LAG3Pep yielded a protein band of LAG-3. A competition by the pre-treatment of Jurkat T cells with a LAG-3-blocking antibody inhibited the cell binding of LAG3Pep. In addition, LAG3Pep inhibited the binding of LAG-3 protein to THP-1 cells expressing HLA-DR, a well-known LAG-3 ligand. Moreover, LAG3Pep recovered IL2 production by stimulated Jurkat T cells, which were suppressed by fibrinogen-like protein 1, another ligand of LAG-3, in the culture medium of HepG2 tumor cells. These results show that LAG3Pep selectively binds to LAG-3 and has a potential as a LAG-3 blocker for cancer immunotherapy. Citation Format: Seok-Min Lee, Byungheon Lee. Identification of lymphocyte activation gene 3 binding peptides using phage displayed peptide libraries for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 599.