The non-hematopoietic cell fraction of the bone marrow (BM) is classically identified as CD45^– Ter119^– CD31^– (herein referred to as triple-negative cells or TNCs). Although TNCs are believed to contain heterogeneous stromal cell populations, they remain poorly defined. Here we showed that the vast majority of TNCs (∼85%) have a hematopoietic rather than mesenchymal origin. Single cell RNA-sequencing revealed erythroid and lymphoid progenitor signatures among CD51^– TNCs. Ly6D⁺ CD44⁺ CD51^– TNCs phenotypically and functionally resembled CD45⁺ pro-B lymphoid cells, whereas Ly6D^– CD44⁺ CD51^– TNCs were enriched in previously unappreciated stromal-dependent erythroid progenitors hierarchically situated between preCFU-E and proerythroblasts. Upon adoptive transfer, CD44⁺ CD51^– TNCs contributed to repopulate the B-lymphoid and erythroid compartments. CD44⁺ CD51^– TNCs also expanded during phenylhydrazine-induced acute hemolysis or in a model of sickle cell anemia. These findings thus uncover physiologically relevant new classes of stromal-associated functional CD45^– hematopoietic progenitors.

骨髓（BM）的非造血细胞部分通常被称为CD45 ^– Ter119 ^– CD31 ^–（在此称为三阴性细胞或TNC）。尽管认为TNC包含异质基质细胞群，但定义仍然不明确。在这里，我们表明绝大多数TNC（约85％）具有造血起源而不是间充质起源。单细胞RNA测序显示CD51 ^– TNC中的类红细胞和淋巴样祖细胞签名。Ly6D ⁺ CD44 ⁺ CD51 ^– TNC在表型和功能上类似于CD45 ⁺ pro-B淋巴样细胞，而Ly6D ^– CD44 ⁺CD51 ^– TNC富含以前未认识到的基质依赖性红系祖细胞，这些祖细胞分层排列在preCFU-E和成红细胞之间。在过继转移中，CD44 ⁺ CD51 ^– TNC有助于重新填充B淋巴和红系区室。CD44 ⁺ CD51 ^– TNC在苯肼诱导的急性溶血或镰状细胞性贫血模型中也会扩增。这些发现因而基质细胞相关的功能的CD45揭开生理相关新的类^-造血祖细胞。