SAR443809 prevents lysis of PNH patient RBCs by inhibiting the surface deposition of C3b. (A) Percent CD59^- cells (PNH RBCs) observed under various treatment conditions. The RBCs from a patient with PNH were tested for the presence of CD59 using flow cytometry and the percentage of CD59^- cells monitored as a function of various treatments (n = 1). (B) Percent hemolysis (calculated as a proportion of PNH RBCs, left Y-axis) and percent C3b deposition (observed on the surviving CD59^– cells, right Y-axis) observed under various treatment conditions. The RBCs from the patient with PNH were dual stained for C3b and CD59 on the cell surface using flow cytometry (n = 1). Percentage of Lysis and C3b deposition were calculated using Equation 1 and Equation 2 respectively. (C) Dose-dependent inhibition of acidified serum-mediated lysis of PNH RBCs by SARXX02. A dose titration of SARXX02 (●) and its antibody isotype control (○) were carried to assess the inhibition of acidified serum-mediated hemolysis of PNH RBCs. The extent of hemolysis was measured using the absorbance of hemoglobin released from the cells upon lysis and normalized to complete lysis as observed under hypotonic conditions. The data shown are an average of 2 independent experiments ± standard deviation.