Targeting LRBA triggers CTLA4 degradation and antitumor immunity for cancer immunotherapy

The lipopolysaccharide-responsive beige-like anchor protein (LRBA) deficiency causes severe autoimmune diseases and cytotoxic T-lymphocyte-associated protein 4 (CTLA4) loss in humans. However, the impact of LRBA on antitumor immunity remains understudied. Here, we identified the role of LRBA in antitumor immunity and developed a novel immunotherapy for cancers. Interestingly, LRBA was negatively associated with antitumor immunity in human patients. Using high-throughput screening and subsequent structure-based hit optimization, we discovered a small molecule LC427 that bound directly to LRBA, and selectively interfered with the LRBA-CTLA4 interaction. This mechanistically unique LC427 facilitated the lysosomal degradation of CTLA4, and bolstered survival and functions of activated T cells. Importantly, orally administrated LC427 increased tumor-infiltrating CD8+ T cells and displayed effective antitumor activity in tumorbearing mouse models. Notably, LC427 did not induce typical irAEs observed with immune checkpoint inhibitors in colitis models. Our study demonstrates that targeting LRBA offers a novel and effective strategy with a favorable safety profile, highlighting the potential of LRBA-based immunomodulatory therapies in the treatment of cancers. MC38 cells (2×105) were implanted in C57BL/6 female mice. Mice were treated with LC427 or not. On day 14, tumors from mice treated with LC427 or not were harvested. Then, tumor tissues were cut into pieces, followed by enzymatic digestion using 0.5 mg/mL collagenase type IV (Roche) and 100U/mL DNase I (Aladdin, China) solution, and were incubated on a shaker (300 rpm) for 30 minutes at 37℃. The digested tissues were homogenized by passage through a 70 μm filter and centrifuged for 15 minutes at 4℃ and 400g. The dead cells were removed from single-cell pellets using the dead cell removal microbeads (Miltenyi, Germany) and CD45 positive cells were collected with CD45 MicroBeads (Miltenyi, Germany). The CD45 positive cells were analyzed using scRNA-seq.