Fig. 1 |. Recipient conditioning and the composition of the haematopoietic stem cell compartment affect reconstitution.

a | Haematopoietic stem cells (HSCs) include lymphoid-biased HSC (Ly-HSC) and myeloid-biased HSC (My-HSC) subsets. The bone marrow of young animals has approximately equal numbers of Ly-HSCs and My-HSCs. Ly-HSC numbers are maintained with age, but the total number of My-HSCs increases so they become the predominant stem cell population in aged mice^43,44,46,47. Thus, when total HSCs from young mice are transplanted, the recipients receive similar numbers of Ly-HSCs and My-HSCs, whereas HSCs from old donors would have a majority of cells that are myeloid biased. When either young or old HSCs are transplanted into irradiated mice, they are transferred into an inflammatory environment that has been induced by irradiation. b | Recipient mice conditioned with 1,4-butanediol dimethanesulfonate (busulfan) have low levels of inflammation^21–24, thus allowing assessment of the lymphoid potential of young and old Ly-HSCs in a salutary environment and revealing no deficit in the lymphoid potential of Ly-HSCs⁴⁶. TNF, tumour necrosis factor.