A radiolabeled antibody targeting CD123+ leukemia stem cells – initial radioimmunotherapy studies in NOD/SCID mice engrafted with primary human AML

Radioimmunotherapy (RIT) with anti-CD123 monoclonal antibody CSL360 modified with nuclear translocation sequence (NLS) peptides and labeled with the Auger electron-emitter, 111In (111In-NLS-CSL360) was studied in the prevalent NOD/SCID mouse AML engraftment assay. Significant decreases in CD123+ leukemic cells and impairment of leukemic stem cell self-renewal were achieved with high doses of RIT. However, NOD/SCID mice were very radiosensitive to these doses. At low non-toxic treatment doses, 111In-NLS-CSL360 demonstrated a trend towards improved survival associated with decreased spleen/body weight ratio, an indicator of leukemia burden, and almost complete eradication of leukemia from the bone marrow in some mice.