Hematopoietic stem cell transplant (HSCT) is primarily indicated to treat malignancies and requires a conditioning of the subject's tissues (e.g., bone marrow tissue) prior to engraftment. HSCT indications and hemoglobinopathies include, for example, sickle cell anemia, beta thalassemias, Fanconi anemia, Wiskott-Aldrich syndrome, adenosine deaminase SCID (ADA SCID), metachromatic leukodystrophy and HIV/AIDS; the list of indications will continue to expand with improvement in gene editing technologies. In certain instances, 20% engraftment of transplanted cells may alleviate or cure the disease.
Current non-targeted conditioning methods, which include, for example, irradiation (e.g., total body irradiation or TBI) and DNA alkylating/modifying agents, are highly toxic to multiple organ systems, hematopoietic and non-hematopoietic cells and the hematopoietic microenvironment. These harsh conditioning regimens effectively kill the host subject's immune and niche cells and adversely affect multiple organ systems, frequently leading to life-threatening complications.
To fully realize the curative potential of HSCT, the development of mild-conditioning regimens that avoid undesirable toxicity is essential. Needed are novel, preferably non-myeloablative, compositions and methods that may be used to condition a subject's tissues (e.g., bone marrow tissues), while lessening undesirable toxicity and minimizing the incidence of serious adverse reactions. Also needed are novel therapies that can selectively ablate an endogenous hematopoietic stem cell population in a target tissue, while minimizing or eliminating the effects of such therapies on non-targeted cells and tissues, such as platelets, white blood cells and red blood cells. Also needed are assays and methods for identifying agents that can selectively deplete or ablate an endogenous hematopoietic stem cell population.