ISOLATION AND IDENTIFICATION OF 2 CD34-BLOOD( CELL SUBPOPULATIONS FROM NORMAL HUMAN PERIPHERAL)

Circulating CD34+ progenitors were separated from normal human periphe ral blood on the basis of size and density by counterflow centrifugal elutriation (CCE). The CD34+ cells, 0.15% of peripheral blood mononucl ear cells, were heterogeneous with respect to their elutriation charac teristics, mainly size and density. The least mature CD34+ cells, char acterized by lack of CD38 antigen, were predominantly found in the sma ll lymphoid cell fraction. In fractions containing larger and denser c ells (large lymphocytes, monocytes, and granulocytes), CD38 was increa singly expressed on the CD34+ cells, as were lineage commitment marker s CD10 (B lymphoid), CD33 (myeloid), CD13 (myelomonocytic) and CD71 (e rythroid) antigens. The smaller and less dense CD34+ cells expressed C D34 antigen brightly while the larger and denser CD34+ cells expressed it dimly. The smaller and less dense CD34+high cells failed to establ ish colony growth in short-term culture while the larger and denser CD 34+low cells gave rise to high counts of colony forming units-granuloc yte macrophage (CFU-GM). Physical separation on the basis of size and density by CCE differentiates between two main classes of steady-state CD34+ cells from normal human peripheral blood. The smaller and less dense CD34+high cells correspond to the earliest progenitors that expr ess differentiation markers poorly but CD34 antigen brightly, do not g ive rise to short-term colony growth in vitro, and thus represent indi rect evidence for pluripotent hematopoietic stem cells (PHSC). The lar ger and denser CD34+low cells are the more mature progenitor cells, al ready committed to myeloid, lymphoid or erythroid differentiation but only dimly expressing CD34 antigen, and these cells were responsible f or short-term colony growth in vitro.