Abstract B043: Identification of secreted PD-L1 variants as a decoy of PD-L1 blockade antibody mediating the therapeutic resistance

Immune checkpoint blockade therapy targeting PD-L1/PD-1 have been widely used and shown remarkable clinical response in various cancers. However, therapeutic resistance after initial response is increasingly observed and the detailed mechanisms of resistance have yet to be fully understood. Recently, several mechanisms including loss-of-function alteration in genes related to antigen presentation and interferon-receptor signaling have been suggested to induce the resistance to PD-1 blockade treatment, yet few studies have focused on anti-PD-L1 (aPD-L1) blockade therapy. In current study, we performed whole exome sequencing and RNA-sequencing analysis in two non-small cell lung cancer (NSCLC) patients who were refractory during aPD-L1 therapy. We have identified the mutations in RNA splicing related gene, TARDBP/TDP-43, which were uncovered as hot spot mutations in Amyotrophic lateral sclerosis (ALS), and found two unique secreted PD-L1 variants, which lacked the transmembrane domain by aberrant RNA splicing. These secreted PD-L1 variants were shown to be stable by pulse chase assay, and worked as “decoys” of aPD-L1 antibody in the HLA-matched coculture system of iPSC-derived CD8 T cells and cancer cells. Moreover, expression of secreted mPD-L1 variant in mouse MC38 cancer cells conferred the resistance to PD-L1 blockade therapy, and soluble PD-L1 were time dependently accumulated in plasma using the MC38 syngeneic mice model. To further investigate the presence of secreted PD-L1 splicing variants in patients, we additionally analyzed 15 specimen who were resistant to anti-PD-L1 treatment by RNA-seq. We revealed that approximately 20% of therapeutic resistant patients harbored secreted PD-L1 variants and several new mutations in JAK1/2, the key mediator of interferon-receptor signaling, were found in a part of patients as well. Furthermore, we also identified the presence of secreted PD-L1 variants in the surgical specimens of squamous NSCLC patients without prior chemotherapy, targeted therapy, and /or immune-checkpoint inhibitor therapy. Consistent to the data, the plasma level of soluble PD-L1 in patients with secreted PD-L1 variants were high than those without the variants. Collectively, our results elucidated a novel resistant mechanism of PD-L1 blockade antibody mediated by secreted PD-L1 variants. The presence of sPD-L1 splicing variants or the level of soluble PD-L1 in plasma or pleural effusion may work as a biomarker to predict a patient’s response to PD-L1 blockade therapy. Citation Format: Bo Gong, Kazuma Kiyotani, Seiji Sakata, Ken Takahashi, Seiji Nagano, Shun Kumehara, Satoko Baba, Benjamin Besse, Noriko Yanagitani, Luc Friboulet, Makoto Nishio, Kengo Takeuchi, Hiroshi Kawamoto, Naoya Fujita, Ryohei Katayama. Identification of secreted PD-L1 variants as a decoy of PD-L1 blockade antibody mediating the therapeutic resistance [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B043. doi:10.1158/1535-7163.TARG-19-B043