The present invention relates generally to the fields of immunology and molecular biology, and particularly to a method for treating hematopoietic disorders. The invention provides a method to treat a deficiency of one or more types of blood cells in a mammal, which includes administering an effective amount of TISF or of a compound that stimulates CD4+ cells like TISF does. In one embodiment, TISF that originates from a mammalian species is administered to a mammalian subject diagnosed as having a deficiency in one or more types of blood cells.