CD19 and neoplasm: Approximately 30% of T cell-engaging BsAbs are in clinical trials for treating hematological malignancies, and the specific targets are mainly well-known TAAs, such as CD19, CD20, CD33, CD38, CD123, and BCMA.110,119–123 The application of T cell engaging BsAbs in solid tumors faces more-challenging hurdles, such as poor T cell infiltration, a complex immunosuppressive TME, and the higher likelihood of on-target off-tumor toxicities, raising concerns for the safety and efficacy of T cell engaging BsAbs.