Monoclonal antibody 1.6.1 against human MPL receptor allows HSC enrichment of CB and BM CD34+CD38− populations

Thrombopoietin (TPO) and its receptor Mpl (CD110) play a crucial role in the regulation of hematopoietic stem cells (HSCs). Functional study of Mpl-expressing HSCs has, however, been hampered by the lack of efficient monoclonal antibodies, explaining the very few data available on Mpl+ HSCs during human embryonic development and after birth. Investigating the main monoclonal antibodies used so far to sort CD110+ cells from cord blood (CB) and adult bone marrow (BM), we found that only the recent monoclonal antibody 1.6.1 engineered by Immunex Corporation was specific. Using in vitro functional assays, we found that this antibody can be used to sort a CD34+CD38−CD110+ population enriched in hematopoietic progenitor stem cells, both in CB and in adult BM. In vivo injection into NSG mice further indicated that the CB CD34+CD38−CD110+ population is highly enriched in HSCs compared with both CD34+CD38−CD110− and CD34+CD38− populations. Together our results validate MAb1.6.1 as an important tool, which has so far been lacking, in the HSC field.