Flow cytometric assessment of lymphocyte subsets, lymphoid progenitors, and hematopoietic stem cells in allogeneic stem cell grafts

Abstract

Currently, bone marrow (BM), cord blood (CB), and G-CSF-mobilized peripheral blood progenitor cells (PBPCs) are the most commonly used sources for allogeneic stem cell transplantation (SCT). The aim of this study was to assess the yields and distribution of lymphocyte subsets, lymphocyte progenitors and hematopoietic stem cells (HSC) in each type of allograft by three-color flow cytometry. The yields of CD34(+)CD38(-) HSCs did not differ significantly between BM grafts (2.80 +/- 0.74 x 10(6)) and leukapheresis products (LPs) (1.82 +/- 0.64 x 10(6)), and were lowest in CB grafts (0.21 +/- 0.05 x 10(6)). For most lymphocyte subsets yields were lowest in CB grafts and significantly higher in LPs than in BM grafts. BM grafts, however, contained the highest yields of CD34(+)CD19(+)CD20(-) B cell progenitors and CD19(+)CD20(-) B cells. The relative frequencies of the naive CD45RA(+)CD45RO(-) phenotype among CD4(+) and CD8(high) T cells were highest in CB grafts (P < or = 0.001), and higher in LPs than in BM grafts (P < or = 0.02). The latter finding was in accordance with a preferential G-CSF mobilization of naive T cells relative to the total lymphocyte population (P < or = 0.014). CD3(+)CD8(low) and CD3(+)CD8(low)CD4(-) subsets, which facilitate engraftment in murine transplantation models, demonstrated a tendency towards lower frequencies among T cells in CB grafts and LPs compared to BM grafts. This observation coincided with a significantly reduced mobilization of subsets potentially enriched for facilitating cells as compared to the total lymphocyte population (P < or = 0.036). The CD34(+) compartment of CB grafts contained a significantly higher percentage (12.1%) of CD34(+)CD7(+)CD3(-) T cell progenitors than those of BM grafts (5.1%) and LPs (3.6%). In addition, CB lymphocytes contained the highest fraction of CD3(-)CD16/56(+) NK cells (P < or = 0.013) and almost no CD3(+)CD16/56(+) NKT cells (P < 0.001) compared to adult cell sources. In summary, LPs, CB allografts and BM allografts differ widely with respect to the cellular composition of their lymphocyte compartments, which is partially affected by a varying mobilization efficiency of G-CSF for distinct lymphocyte subsets.