The present disclosure provides polypeptide heterodimers formed between two different single chain fusion polypeptides via natural heterodimerization of an immunoglobulin CH1 region and an immunoglobulin light chain constant region (CL). The polypeptide heterodimer comprises two or more binding domains that specifically bind one or more targets (e.g., a receptor). In addition, both chains of the heterodimer further comprise an Fc region portion. The present disclosure also provides nucleic acids, vectors, host cells and methods for making polypeptide heterodimers as well as methods for using such polypeptide heterodimers, such as in directing T cell activation, inhibiting solid malignancy growth, and treating autoimmune or inflammatory conditions.
