THE PRESENT INVENTION RELATES TO A NEW AND NONOBVIOUS METHOD OF PRODUCING THE C-TERMINAL HISTIDINE TAGGED TAT-HOXB4 FUSION PROTEIN (TAT-HOXB4H), PROVIDING UNEXPECTED BENEFITS OF INCREASED YIELD AND STABILITY TO ALLOW FOR IN VIVO ADMINISTRATION OF THIS PROTEIN, AND PHARMACEUTICAL COMPOSITION COMPRISING AN EFFECTIVE INGREDIENT, TAT-HOXB4H, HAVING STIMULATORY ACTIVITY ON THE PRODUCTION OF HEMATOPOIETIC CELLS. MORE SPECIFICALLY, RECOMBINANT TAT-HOXB4H PROTEIN ENHANCES ENGRAFTMENT OF BONE MARROW TRANSPLANTS, HEMATOPOIETIC RECONSTRUCTION, BONE MARROW RE-POPULATION AND NUMBER OF CIRCULATING STEM CELLS, PARTICULARLY AFTER CHEMOTHERAPY OR IRRADIATION.
