BeyondSpring Pharmaceuticals announced new data highlighting the mechanism of action of plinabulin in the prevention of chemotherapy-induced neutropenia (CIN) at the 63rd American Society of Hematology (ASH) Annual Meeting and Exposition, held virtually and in person in Atlanta, Georgia from December 11, 2021 to December 14, 2021. The data demonstrate that adding plinabulin to a myelosuppressive regimen rapidly reversed (within 24 hours) neutropenia and leukopenia in the PROTECTIVE-1 and -2 clinical studies by protecting progenitor stem cells in the bone marrow. This new data analysis from the PROTECTIVE-1 and 2 studies aimed to further evaluate plinabulin’s fast onset mechanism of action (MoA) and potential progenitor stem cell involvement in plinabulin’s fast onset MoA. The comparison was made between cancer patients receiving plinabulin 40 mg (n=228) or not receiving plinabulin (n=172), and with all patients receiving myelosuppressive chemotherapy (docetaxel with or without doxorubicin and cyclophosphamide). Plinabulin 40 mg was given 30 minutes after chemotherapy. Plinabulin rapidly (within 24 hours) reversed chemo-induced myelosuppression in both the PROTECTIVE-1 and 2 human studies. Plinabulin-mediated increases in cell numbers are dose-dependent and correlated among cells of the myeloid, lymphoid and erythroid lineages. Neutrophils (p<0.0001; increase by >3x10E9/L with plinabulin and decrease by >0.5x10E9/L without plinabulin); Monocytes (p=0.0023); Eosinophils (p=0.0775); Basophils (p<0.0001). The data suggest that plinabulin targets granulocyte-monocyte-progenitor (GMP) stem cells (N, M, B and E progenitor) as well as progenitor cells further upstream in the hematopoietic lineage.