Figure 2.

Hibernating HSCs maintain in vivo functional activity

(A) HSCs were cultured in hibernation conditions in either serum-supplemented or serum-free medium. Single fresh or day 7 hibernating LT-HSCs were transplanted into W41-CD45.1 recipients (fresh n = 69; serum-free n = 24; +serum n = 29). Secondary transplantations were undertaken in all mice with donor engraftment (>1%) at 16–24 weeks post-transplantation.

(B and C) Graphs show percent donor chimerism in the peripheral blood of primary (B) and secondary (C) recipient mice at 16–24 weeks post-transplantation. Recipients with chimerism >1% and at least 0.5% of GM, B, and T cells were considered to be repopulated. (Triangles represent mice where chimerism reached >1% at weeks 20–24 post-transplantation but had not done so by 16 weeks.)

(D) No significant difference was observed in the balance of mature cell outputs between freshly isolated and post-hibernation HSCs. Based on donor myeloid (M) to lymphoid (L) ratio at 16 weeks in primary recipients, the founder HSC was retrospectively assigned one of the following subtypes: α (alpha, M:L > 2), β (beta, M:L > 0.25 < 2), γ (gamma, M:L < 0.25), δ (delta, M:L < 0.25 and failure to contribute to myeloid lineage past 16 weeks) in accordance with Dykstra et al. (2007) (HSC n = 31/69; hibHSC (+serum) n = 12/29; hibHSC (serum-free) n = 15/24).