The present invention provides methods for inhibiting
interleukin-3
receptor-expressing cells, and, in particular, inhibiting the growth of such cells by using a
diphtheria toxin-human
interleukin-3 conjugate (DT-IL3) that is toxic to cells expressing the
interleukin-3
receptor. In preferred embodiments, the DT-IL3 conjugate is a
fusion protein comprising amino acids 1-388 of
diphtheria toxin fused via
a peptide linker to full-length, human interleukin-3. In certain embodiments, the methods of the present invention relate to the administration of a DT-IL3 conjugate to inhibit the growth of
cancer cells and / or
cancer stem cells in humans, which cells express one or more subunits of the interleukin-3
receptor. Exemplary cells include
myeloid leukemia cancer stem cells. In other embodiments, the methods of the present invention relate to
ex vivo purging of
bone marrow or
peripheral blood to remove cells that express one or more subunits of the interleukin-3 receptor such that the purged
bone marrow or
peripheral blood is suitable, e.g., for autologous
stem cell transplantation to restore hematopoietic function.