Figure 2. IL-2^−/− HSCs have increased proliferation and a competitive reconstitution disadvantage.

HSCs from 19-21 day old IL-2^WT or IL-2^−/− mice were analyzed (A-C). Representative flow plot of RBC-lysed BM stained for DAPI and Ki-67, gated on LSK HSCs, to determine proliferation stages (A). Frequencies of LSK HSCs in G₀, G₁, and S/G₂/M stages of cell cycle (B). Representative plot of BM stained for long-term HSCs (LT-HSCs) defined as LSK CD150⁺CD48⁻ (C). Schematic of LT-HSC competitive reconstitution strategy (D). LT-HSCs were FACS sorted from day 18-21 IL-2^WT or IL-2^−/− BM (CD45.2⁺CD45.1⁻) and age-matched CD45.2⁺CD45.1⁺ competitors. Cells were mixed at a 1:1 ratio with competitors and 400 total cells were injected via tail vein into lethally irradiated Rag^−/− recipient mice. Mice were harvested at 5 weeks post-transfer to assess competitive reconstitution in peripheral blood and spleen. Representative flow plots of competitive hematopoietic reconstitution from IL-2^WT LT-HSCs (E; upper) and IL-2^−/− LT-HSCs (E; lower) in peripheral blood. Percentage reconstitution relative to IL-2^WT LT-HSCs (F). Percentage of CD3⁺, CD19⁺ and GR1⁺CD11b⁺ cells within the CD45.2⁺CD45.1⁻ fraction (G). (A-C) Data are from 2 independent experiments with n=7-10 mice per group. (D-G) Data are from 3 independent experiments with IL-2^WT n=10; IL-2^−/− n=12. n.s. - not significant; * p < 0.05; *** p < 0.001; **** p < 0.0001 based on students t test.