Abstract
PD-1 immune checkpoint has been intensively investigated in pathogenesis and treatments for cancer and autoimmune diseases. Cells that express PD-1 (PD-1(+) cells) draw ever-increasing attention in cancer and autoimmune disease research although the role of PD-1(+) cells in the progression and treatments of these diseases remains largely ambiguous. One definite approach to elucidate their roles is to deplete these cells in disease settings and examine how the depletion impacts disease progression and treatments. To execute the depletion, we designed and generated the first depleting antibody (D-αPD-1) that specifically ablates PD-1(+) cells. D-αPD-1 has the same variable domains as an anti-mouse PD-1 blocking antibody (RMP1-14). The constant domains of D-αPD-1 were derived from mouse IgG2a heavy and κ-light chain, respectively. D-αPD-1 was verified to bind with mouse PD-1 as well as mouse FcγRIV, an immuno-activating Fc receptor. The cell depletion effect of D-αPD-1 was confirmed in vivo using a PD-1(+) cell transferring model. Since transferred PD-1(+) cells, EL4 cells, are tumorigenic and EL4 tumors are lethal to host mice, the depleting effect of D-αPD-1 was also manifested by an absolute survival among the antibody-treated mice while groups receiving control treatments had median survival time of merely approximately 30 days. Furthermore, we found that D-αPD-1 leads to elimination of PD-1(+) cells through antibody-dependent cell-mediate phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC) mechanisms. These results, altogether, confirmed the specificity and effectiveness of D-αPD-1. The results also highlighted that D-αPD-1 is a robust tool to study PD-1+ cells in cancer and autoimmune diseases and a potential therapeutic for these diseases.