A naive participant was a participant who did not use sutimlimab prior to enrollment. A switcher was a participant who used sutimlimab prior to enrollment. A naive participant was a responder if the platelet count was \>=50 × 10\^9/liter (L) at \>=50 percent (%) of scheduled visits, or for participants with baseline platelet count \<15 × 10\^9/L, a \>=20 × 10\^9/L increase in platelet count from baseline at \>=50% of scheduled visits, without receiving rescue immune thrombocytopenia (ITP) therapy. A switcher was a responder if the maintenance platelet count was \>=30 × 10\^9/L at \>=50% of scheduled visits, without receiving rescue ITP therapy.