HSCs - hematopoietic stem cells along with MSCs are the primary stem cell populations that make up the immune system. With the advancement of human aging, immune progenitors cells are circumvented by the threat of stem cell exhaustion, and myeloid bias. MSC biomarkers are understood well enough so that it's measurable how many stem cells are found in humans from infancy and childhood to adulthood and the elder years. How do populations of HSCs compare?