Expression of CD10 and CD7 Defines Distinct In Vivo Lymphoid Reconstituting Capacity within Human Cord Blood CD34+CD38-Cells.
Authors: Yoshida Shuro , Ishikawa Fumihiko , Shultz Leonard D. , Saito Noriyuki , Fukata Mitsuhiro , Shimoda Kazuya , Akashi Koichi , Harada Mine 
Published: October 2019

Abstract
Human cord blood (CB) CD34+ cells are known to contain both long-term hematopoietic stem cells (LT-HSCs) and lineage-restricted progenitor cells. In the past, in vitro studies suggested that CD10, CD7 or CD127 (IL7Ra) could be candidate surface markers that could enrich lymphoid-restricted progenitor cells in human CB CD34+ cells (Galy A, 1995, Immunity; Hao QL, 2001, Blood; Haddad R, 2004, Blood). However, in vivo repopulating capacity of these lymphoid progenitors has not been identified due to the lack of optimal xenogeneic transplantation system supporting development of human T cells in mice. We aim to identify progenitor activity of human CB CD34+ cells expressing CD10/CD7 by using newborn NOD-scid/IL2rgKO transplant assay that can fully support the development of human B, T, and NK cells in vivo (Ishikawa F, 2005, Blood). Although LT-HSCs exist exclusively in Lin-CD34+CD38- cells, not in Lin-CD34+CD38+ cells, CD10 and CD7 expressing cells are present in Lin-CD34+CD38- cells as well as in Lin-CD34+CD38+ cells (CD10+CD7+ cells, CD10+CD7- cells, CD10-CD7+ cells, CD10-CD7- cells accounted for 4.7+/−2.7%, 10.5+/−1.9%, 7.6+/−4.4%, and 77.1+/−5.2% in Lin-CD34+CD38- CB cells, respectively). We transplanted 500–6000 purified cells from each fraction into newborn NOD-scid/IL2rgKO mice, and analyzed the differentiative capacity. CD34+CD38-CD10-CD7- cells engrafted long-term (4–6 months) in recipient mice efficiently (%hCD45+ cells in PB: 30–70%, n=5), and gave rise to all types of human lymphoid and myeloid progeny that included granulocytes, platelets, erythroid cells, B cells, T cells, and NK cells. Successful secondary reconstitution by human CD34+ cells recovered from primary recipient bone marrow suggested that self-renewing HSCs are highly enriched in CD34+CD38–CD10–CD7- cells. CD10–CD7+ cells were present more frequently in CD34+CD38+ cells rather than in CD34+CD38- cells. Transplantation of more than 5000 CD34+CD38+CD10–CD7+ cells, however, resulted in less than 0.5% human cell engraftment in the recipients. Within CD34+CD38–CD10+ cells, the expression of CD7 clearly distinguished the distinct progenitor capacity. At 8 weeks post-transplantation, more than 70% of total human CD45+ cells were T cells in the CD10+CD7+ recipients, whereas less than 30% of engrafted human CD45+ cells were T cells in the CD10+CD7– recipients. In the CD10+CD7- recipients, instead, more CD19+ B cells and HLA–DR+CD33+ cells were present in the peripheral blood, the bone marrow and the spleen. Both CD34+CD38–CD10+CD7+ and CD34+CD38–CD10+CD7- cells highly repopulate recipient thymus, suggesting that these progenitors are possible thymic immigrants. Taken together, human stem and progenitor activity can be distinguished by the expressions of CD7 and CD10 within Lin-CD34+CD38- human CB cells. Xenotransplant model using NOD-scid/IL2rgKO newborns enable us to clarify the heterogeneity of Lin-CD34+CD38- cells in CB by analyzing the in vivo lymphoid reconstitution capacity.