CD34 and precursor B-cell acute lymphoblastic leukemia: For example, mice with spontaneous human acute human B lymphoblastic leukemia (B-ALL) were created by transplanting human CD34+ hematopoietic stem cells (HSCs) after transduction with retroviral vectors carrying MLL-AF9 genes into immunodeficient mice, allowing the researchers to evaluate the underlying mechanisms of human B-ALL development (52).