BEAM-101 is an investigational cell therapy comprised of autologous CD34+ hematopoietic stem cells that are base edited to introduce A-to-G substitutions into the HBG1/2 gene promoters to disrupt BCL11A binding, leading to increased HbF production. The BEACON Phase 1/2 clinical trial is an open-label, single-arm, multicenter study evaluating the safety and efficacy of BEAM-101 in patients (pts) with sickle cell disease (SCD) and severe vaso-occlusive crisis (VOC).Biomarkers of red blood cell (RBC) health and function including cellular expression of HbF and HbS, flow adhesion of whole blood to vascular cell adhesion molecule 1 (FA-WB-VCAM) and P-selectin (FA-WB-PSel), real-time sickling kinetics, hemorheology, and RBC morphology were measured before and after BEAM-101 treatment to assess the degree of resolution of SCD pathophysiology with this therapy.Whole blood (WB) samples were collected from pts and double stained for HbF and HbS, followed by a duplex flow cytometry. For adhesion, WB samples were perfused through VCAM1- or PSel-coated microfluidic channels using pulsatile shear stress and images acquired and analyzed. Real-time sickling kinetics were captured using the dynamic sickling assay (DSA). Hemorheological assessments of blood such as oxygen affinity, deformability & RBC density were performed, as well as RBC count and cellular morphology.Preliminary data as of July 2, 2024 includes exploratory biomarker assessments for ≥2 of the following visits: screening, Month (M) 1, 2, 3, and 6 for up to 3 pts (P1, P2, P3).Duplex flow cytometry was performed at screening, M1, M2, and M6 (M6 for P1 only) for the first 3 pts and transfused cells were gated out in analysis. Total HbF+ cells in P1/2/3 increased from 34.1/20.8/48.5% at screening to >98% at M1 and >99% at M2; this further increased to 99.9% at M6 in P1. Total HbS+ cells in P1/2/3 decreased from 87.1/97.9/87.3% at screening to 34.6/26.2/19.1% at M2, respectively; this further decreased to 10.9% at M6 in P1. We observed >19 pg HbF/F-cell after treatment in all pts, above the protective threshold of 10pg to prevent sickling. Cells expressing HbS only for P1/2/3 were reduced to insignificant numbers after treatment from 65.9/79.1/51.4% at screening, to <2% at M1, and <0.4% at M2; this further reduced to 0.1% at M6 in P1.Adherent cells as assessed by FA-WB-VCAM in P1/2 were reduced from 616/689 at screening to 68/179 cells/mm2 at M3. Adherent cells in FA-WB-PSel in P1/2 were reduced from 52/118 at screening to 17.5/14 cells/mm2 at M3. Adhesion indices after BEAM-101 treatment for VCAM1 and P-selectin (predictive biomarkers for VOCs in SCD) were well below the critical SCD index of 408 and 46 cells/mm2, respectively. An increase in time under hypoxia for morphological point of sickling (mPoS), as well as a decrease in rate of sickling, maximum induced sickling and area under the curve (AUC) after BEAM-101 treatment were observed in P1/2 that were comparable to measurements observed in sickle cell trait (SCT) reference samples.In P1, p50 decreased from 30.9 at screening to 22.7 mm Hg at M6 [normal reference range (ref): 23-28.5 mm Hg] indicating higher oxygen affinity post-treatment; PoS decreased from 41.8 at screening to 16.5 mm Hg at M6 (HbSS ref: 17-85.4 mmHg) supporting mPoS observed in DSA; % dense RBC decreased from 7.3% at screening to 3.7% at M6 (HbSS ref: 2-21.5%).Abnormal morphology and sickle cells at screening resolved by M4/M6 in P1 and P2 along with an increase in RBC count.Based on available data on exploratory biomarkers in up to 3 pts, we demonstrate 98-99% of RBCs expressing HbF as early as M1, with near complete elimination of RBCs expressing solely HbS post-BEAM-101. Flow adhesion showed reduction in cell adhesion from higher levels pretreatment to significantly below the critical threshold by M3 post-BEAM-101 indicating improvement in blood health and predicting reduced risk for VOC.Reduced RBC sickling, comparable to SCT, was demonstrated post-BEAM-101 treatment. Oxygen affinity, RBC deformability and density showed improvements in hemorheological properties of blood post-BEAM-101. Finally, improvement in RBC cell number and resolution of abnormal RBC morphology were observed post-BEAM-101.In summary, the initial RBC functional biomarker data support base editing of the HBG1/2 promoters as a potentially transformative therapeutic modality for the treatment of SCD and will continue to be investigated in the ongoing BEACON study.