BTN2A1/3A1-Fc-CD19scFv

Using a tumor cell-free assay, we demonstrated that a BTN2A1/3A1 heterodimeric fusion protein activated human Vγ9Vδ2 T cells, but only in the presence of costimulatory signal via CD28 or NK group 2 member D. Nonetheless, addition of a bispecific γδ T cell engager BTN2A1/3A1-Fc-CD19scFv alone enhanced granzyme B-mediated killing of human CD19 lymphoma cells when cocultured with Vγ9Vδ2 T cells, suggesting expression of costimulatory ligand(s) on tumor cells is sufficient to satisfy the "signal 2" requirement. These results highlight the parallels of signal 1 and signal 2 requirements in αβ and γδ T cell activation and demonstrate the utility of heterodimeric BTNs to promote targeted activation of γδ T cells.

In addition, the CD33-targeted GADLEN alone was able to specifically kill acute myeloid leukemia cells expressing CD33 and costimulatory ligands (e.g., CD80 and CD86) in a mechanism similar to the CD19-targeted GADLEN construct. These results highlight the ability of GADLENs in promoting targeted killing of tumor cells by providing the “active” heterodimeric BTN2A1 and BTN3A1 that is critical to enhance cytotoxic killing by Vγ9Vδ2 T cells. Furthermore, this study provides mechanistic insights into BTN-mediated activation of Vγ9Vδ2 T cells and offers proof of concept for using antigen-targeted butyrophilin heterodimeric fusion proteins for the treatment of cancer.