The earliest thymic progenitors for T cells possess myeloid lineage potential

In the current dominant model of haematopoiesis, T cells are thought to arise from lymphoid-restricted common lymphoid progenitors, and myeloid cells (including granulocytes and macrophages, found in bone marrow and spinal cord) from progenitors committed to the myeloid lineage. Two papers in this issue report evidence that contradicts this. Rather, they find a single type of progenitor in adult thymus with both T and myeloid potential. T cells are produced by an early population in the thymus that has lost the ability to produce B cells, but still produces macrophages and cells with T, NK (natural killer) and dendritic cell potential. These results support a model for haematopoiesis where the progenitor cell at the branch point of T and B cell lineages retains macrophage potential.