An immature cell that can develop into all types of blood cells, including white blood cells, red blood cells, and platelets. Hematopoietic stem cells are found in the peripheral blood and the bone marrow. Also called blood stem cell. Hematopoietic progenitor cells (HPCs) or hematopoietic stem cells (HSCs) are cells present in blood and bone marrow. HPCs are capable of forming mature blood cells, such as red blood cells (the cells that carry oxygen), platelets (the cells that help stop bleeding) and white blood cells (the cells that fight infections). HPCs are used in the treatment of many malignant (e.g., leukemia, lymphoma) and non-malignant (e.g., sickle cell disease) diseases to replace or rebuild a patient's hematopoietic system. This type of treatment is called a bone marrow or stem cell transplant. HPCs also have been used in clinical trials with U.S. FDA oversight for the treatment of autoimmune diseases, genetic diseases and other indications.