Provided are multispecific binding proteins and methods for using these multispecific binding proteins to modulate the activation state of immune cells, such as T-cells (e.g., cytotoxic T-cells). Also provided are methods of modulating an immune response (e.g., cell killing by cytotoxic T-cells) in a subject (e.g., a human subject). Also provided are nucleic acids, expression vectors and host cells encoding the multispecific binding proteins.
