Hematopoietic progenitor cells (HPCs) are cells that are capable of multiplying and producing additional blood cells of a particular lineage. The are often somewhat inaccurately called hematopoietic “stem cells” (HSCs), but true stem cells differ in that they are totipotent, meaning that they can develop into any of the blood cell lines (erythroid, myeloid, or megaloblastic), while progenitor cells are limited to a single cell line (one of the three above). Despite this, the terms “HPC transplant” or “HSC transplant” are commonly used interchangeably.