CSF3 and Myelodysplasia: The possible biological explanation of leukopenia in children with HIV could be a decrease in the number of hematopoietic stem cells (HSCs) in the bone marrow, changes in marrow architecture include decreased cellularity and myelodysplasia as well as decreased levels of the factor that stimulates production of white blood cells in the bone marrow (granulocyte colony-stimulating factor (G-CSF)).