Young environment does not support myeloid development. (A) Graphical representation of old into young (O→Y) vs old into old (O→O) transplantation. WBM cells (2-2.5 × 10⁶) from 17- to 18-month-old CD45.2 mice were transplanted into either 2-month-old (defined as O→Y) or 17- to 18-month-old (defined as O→O) CD45.1 mice. Lineage distribution of donor-derived cells of O→O vs O→Y transplants at 16 weeks (n = 10 O→Y, n = 8 O→O). (B) Graphical representation of young into young (Y→Y) vs young into old (Y→O) transplantation. WBM cells (2-2.5 × 10⁶) from 2-month-old CD45.2 mice were transplanted into either 2-month-old (defined as Y→Y) or 17- to 18-month-old (defined as Y→O) CD45.1 mice. Lineage distribution of donor-derived cells of Y→O vs Y→Y at 16 weeks (n = 4 Y→Y, n = 7 Y→O). (C) Graph represents lineage distribution of donor-derived cells of O→O vs O→Y transplants at 16 weeks excluding T cells (n = 10 O→Y, n = 8 O→O). (D) Graph represents lineage distribution of donor-derived cells of Y→O vs Y→Y transplants at 16 weeks excluding T cells (n = 4 Y→Y, n = 7 Y→O). Error bars represent SEM. Representative of 2 experiments.