CD3-HAC

**CD3-HAC** is a recombinant bispecific fusion protein composed of a single-chain variable fragment (scFv) derived from an anti-CD3 antibody, fused to a high-affinity consensus (HAC) mutant PD-1 ectodomain that binds PD-L1 with high affinity. It is designed to simultaneously target CD3 on T cells and PD-L1 on tumor cells, thereby redirecting and activating T lymphocytes to kill PD-L1-positive cancer cells while blocking immune suppression mediated by PD-1/PD-L1 signaling. In preclinical studies, CD3-HAC showed strong tumor cell killing, enhanced lymphocyte activation, and reversal of T cell anergy/apoptosis induced by PD-1/PD-L1 axis. The drug has been investigated mainly for metastatic breast cancer, including triple-negative breast cancer, using mesenchymal stem cells (MSCs) loaded with adenoviral vectors for local delivery of CD3-HAC at tumor sites[2].