Thy-1 (CDw90) and c-kit receptor (CD117) expression on CD34+ hematopoietic progenitor cells: A five dimensional flow cytometric study

Background and Objective. CD34⁺ hematopoietic progenitor cells (HPCs) constitute a heterogeneous population both in size and in immunological features. Lack of CD38, HLA-DR and lineage committed antigens as well as the co-expression of Thy-1 (CDw90) and c-kit receptor (CD117), are able to identify the so-called stem cells. A flow cytometric study was carried out to investigate the co-expression of Thy-1 and c-kit receptors, both members of Ig superfamily adhesion molecules, involved in cell to cell and cell to stroma interactions, on bone marrow (BM), mobilized peripheral blood (PB) and human umbilical cord blood (HUCB) CD34⁺ HPCs. Design and Methods. Lysed whole blood from 15 BM, 25 mobilized PB and 25 HUCB samples were used to perform a five-dimensional flow cytometric evaluation of both CDw90 and CD117 on CD34⁺ cells. Results. Few CD34⁺ cells co-expressed Thy-1 antigen in all three compartments (BM: 11.2±7.2%; PB: 6.2±3.6%; HUCB: 6±2.9%; BM vs PB + HPCs, particularly in HUCB (HUCB: 80.7±8.2%; BM: 72.3±13.1%; PB: 64.2±17%; HUCB vs BM +Thy-1⁺ and CD34⁺c-kit⁺ HPCs generally displayed HLA-DR antigen, as expression of early cell commitment. However, the most immature CD34⁺Thy- 1⁺HLA-DR^- (HUCB: 1± 0.6%; BM: 0.4±03%; PB: 0.7±0.5%; HUCB vs BM +c-kit⁺HLA-DR^- HPCs (HUCB: 6.5±4.4%; BM: 6.3±4.8%; PB: 2.2±1.8%; HUCB vs BM ns; BM vs PB +Thy-1⁺c-kit⁺ cells was found in BM (6.9±4.1%) followed by leukapheretic samples (4.4%±2.7) and then by HUCB (3.7±1.2%; BM vs PB ns; BM vs HUCB + HPCs found in the three hemopoietic compartments evaluated can lead to new knowledge about the mobilization kinetics in which the Ig superfamily adhesion molecules are involved.