Method for chemoselection

A method of radiation-free hematopoietic stem cell (HSC) transplantation, the method comprising:

• (a) engrafting donor HSCs into a pre-conditioned mammalian subject, wherein hypoxanthine-guanine phosphoribosyltransferase (HPRT) is down regulated in the donor HSCs;
• and
• (b) immediately administering to the subject a purine base analog selected from 6-thioguanine (6TG), 6-mercaptopurine (6-MP), or azathiopurine (AZA) every two to four days for two to eight weeks;
• wherein the method is performed in the absence of pre-conditioning via radiation.

A method of treating symptoms of a disease or disorder in a mammalian subject, the method comprising:

• (a) administering a pre-conditioning treatment to the subject;
• (b) engrafting into the subject donor HSCs into a ¬pre-conditioned mammalian subject, wherein hypoxanthine-guanine phosphoribosyltransferase (HPRT) is down regulated in the donor HSCs;
• and
• (c) immediately administering to the subject a purine base analog selected from 6-thioguanine (6TG), 6-mercaptopurine (6-MP), or azathiopurine (AZA) every two to four days for two to eight weeks;
• wherein the method is performed in the absence of pre-conditioning via radiation.