CD47-targeted cancer immunogene therapy: secreted SIRPα-Fc fusion protein eradicates tumors by macrophage and NK cell activation

Abstract CD47 protects healthy cells from macrophage attack by binding to signal regulatory protein α (SIRPα), while its up-regulation in cancer prevents immune clearance. Systemic treatment with CD47 antibodies requires a weakened Fc-mediated effector function or lower CD47-binding affinity to prevent side effects. Our approach combines ‘the best of both worlds’, i.e. maximized CD47-binding and full Fc-mediated immune activity, by exploiting gene therapy for paracrine release. We developed a plasmid-vector encoding for the secreted fusion protein sCV1-hIgG1, comprising of highly efficient CD47-blocking moiety CV1 and Fc domain of human IgG1 with maximized immune activation. sCV1-hIgG1 exhibited potent bystander effect blocking CD47 on all cells via fusion protein secreted from only a fraction of cells or when transferring transfection-supernatant to untransfected cells. The CpG-free plasmid ensured sustained secretion of sCV1-hIgG1. In orthotopic human triple negative breast cancer in CB17-SCID mice, ex vivo transfection significantly delayed tumor growth and eradicated one-third of tumors. In intratumoral transfection experiments, CD47-blockage and increased migration of macrophages into the tumor was observed within 17h of a single injection. NK cell-mediated lysis of sCV1-hIgG1-expressing cells was demonstrated in vitro. Taken together, this approach also opens the opportunity to block, in principle, any immune checkpoints.