Immune cells protect the host from infection by pathogens. They include monocytes, which are large white blood cells that can differentiate into scavenger cells macrophages and dendritic cells in response to inflammatory signals. Monocytes are derived from blood stem cells in the bone marrow via an intermediate cell type, the progenitor cell, which is slightly more differentiated than stem cells. Previous research identified a common monocyte progenitor cell (cMoP) in mice that only develops into monocytes. Now, Tokyo Medical and Dental University(TMDU) has identified equivalent monocyte progenitors in humans. This expands what we know about the differentiation process of monocytes and opens up possible therapeutic applications targeting these cells.