What we thought we knew about TNF—And what we now must re-learn

Tumor necrosis factor (TNF) was long cast as a hematopoiesis villain, driving bone marrow and hematopoietic stem cell (HSC) suppression. We now see that TNF's effects are cell type-, context-, and time-dependent. Rather than being simply "bad," TNF can prune progenitors while transiently reprogramming HSCs without sacrificing long-term regenerative capacity.