An Engager Platform for In Vivo CAR T Cell Therapy, Gene Therapy, and Oncolytic Virotherapy

CAR T-cell therapy is shifting from complex, costly ex vivo protocols toward simpler, in vivo gene-delivery strategies. VSV-G-pseudotyped lentiviral vectors (LVVs) are widely used ex vivo because they efficiently transduce many cell types through the broadly expressed LDLR family (Rubinstein, 2013). However, this pantropism precludes in vivo application, where cell-type specificity is essential. Existing strategies that retarget LVVs by mutating VSV-G and incorporating T-cell-binding antibodies gave specificity but greatly reduced transduction efficiency. We developed a modular engager platform that redirects unmodified LVVs to specific cell types. Such engagers comprise a ligand or antibody that recognizes a cell-type-specific receptor, fused to the VSV-G-binding domains of LDLR. After receptor-mediated uptake, the reversible engager dissociates, releasing unmodified, fully potent LVV. Such reversible engagers provide a broadly applicable strategy for in vivo CAR T cell therapy, in vivo gene therapy, and oncolytic virotherapy. Engagers consisting of anti-CD3 scFv fused via a trimerizing peptide to the VSV-G-binding domains of LDLR mediated selective transduction of T cells within human PBMCs by BCMA-CAR-encoding LVV, achieving ex vivo-like transduction efficiencies without having to pre-activate the T cells. In an in vivo model, NSG mice bearing human OPM2 multiple myeloma xenografts received human PBMCs intraperitoneally, followed one week later by engager-coated BCMA-CAR-encoding LVV. Complete tumor clearance was observed within 21 days. Clinical trials for multiple myeloma are planned. This reversible engager technology is also being developed for cystic fibrosis gene therapy and for VSV-based oncolytic virotherapy.