Bispecific killer engager for targeted depletion of PD-1 positive lymphocytes: A new avenue for autoimmune disease treatment

Bispecific killer cell engagers (BiKEs) are a powerful tool to incite the killing power of natural killer (NK) cells. Here, we posited that the BiKE technology could be utilized to deplete activated immune cells expressing programmed death-1 (PD-1⁺ cells), and hence treat autoimmune diseases since these cells drive the disorders. We designed and generated PD-1 BiKE that targets an activating NK cell receptor, CD16, and PD-1. PD-1 BiKE showed specific binding to PD-1⁺ cells and engaged CD16 simultaneously. PD-1 BiKE enhanced NK cell-mediated apoptosis and depletion of PD-1⁺ Raji cells, but not PD-1^- Raji cells. Further, PD-1 BiKE induced apoptosis of primary PD-1⁺ T lymphocytes that are highly relevant to autoimmune disease progression. The BiKE depleted 42% of primary T cells that were stimulated <i>in vitro</i>. Importantly, those ablated primary T cells were activated cells. Meanwhile, naive T cells were spared by the BiKE treatment, supporting the crucial selectivity of PD-1 BiKE-directed cell depletion. Lastly, PD-1 BiKE is more effective than a conventional depleting antibody in the depletion of PD-1⁺ cells. The current work supports PD-1 BiKE is a selective, potent, and safe tool to deplete PD-1⁺ cells.