SLIT2 treatment effect on transcription in bone marrow derived macrophages

Roundabout (ROBO) 1 and 2 are transmembrane receptors that bind secreted SLIT ligands through their extracellular domains (ECD), and signal through their cytoplasmic domains to modulate the cytoskeleton and regulate cell migration, adhesion, and proliferation. SLIT-ROBO signaling was discovered as a guidance cue for axons in the developing nervous system, but ROBO receptors are expressed by many additional cell types and more broadly regulate organ morphogenesis, as well as cancer and pathological ocular neovascularization. As pharmacological tools to prevent SLIT-ROBOR signaling are lacking, herein we developed human monoclonal antibodies (mAb ) against the ROBO1 and 2 ECD. One antibody that inhibited in vitro SLIT2 signaling through ROBO1/2 reduced ocular neovascularization in two pathological models in vivo. Single cell RNA sequencing revealed that antibody treatment affected several cell types relevant to angiogenesis, including endothelial cells, pericytes, and a heterogeneous population of myeloid cells. mAb treatment improved Blood-Retina Barrier integrity and prevented pathological pericyte activation. SLIT-ROBO signaling inhibition prevented pathological activation of myeloid cells, which was phenocopied by both myeloid cell specific ablation of Robo1 and 2 and by knockout of the downstream effector Pi3kγ. Anti-ROBO1/2 blocking antibodies may thus provide a new promising strategy to combat inflammation in blinding eye diseases.