Expression of a Surface Antigen (MA6) by Peripheral Blood CD34⁺Cells Is Correlated with Improved Platelet Engraftment and May Explain Delayed Platelet Engraftment Following Cord Blood Transplantation

Abstract

CD34 + cell dose provides a measure of hematopoietic tissue that predicts the rate of engraftment upon transplant. It is positively correlated with multiple measures of hematopoietic recovery, including platelet engraftment. Here we identify a subpopulation of CD34 + cells that coexpress a surface antigen-MA6, which is more positively correlated with platelet engraftment in a clinical setting than CD34 + alone. The specific identity and function of MA6 remain to be determined, however, it is expressed by primitive megakaryocyte (MK) progenitors, but is lost with differentiation and is not expressed by platelets. Commitment of CD34 + MA6 + cells to the MK lineage was confirmed by in vitro assays and their significance in hematopoietic transplantation explored by flow cytometric analysis of cryopreserved samples of granulocyte colony stimulating factor-mobilized peripheral blood progenitor cell (PBPC) products along with a retrospective analysis of platelet engraftment data. Platelet engraftment by day 21 was predicted by receipt of ‡ 6 · 10 6 CD34 + cells/kg or ‡ 0.3 · 10 6 CD34 + MA6 + cells/kg. Subsequent analysis of cord blood (CB) CD34 + cells revealed < 0.2% coexpressed MA6 + , compared to 8% of PBPC CD34 + cells. This low proportion of CD34 + MA6 + cells may be responsible, at least in part, for the delayed platelet engraftment associated with CB transplantation. However, platelet engraftment is markedly improved in recipients of ex vivo-expanded CB. This may be a consequence of an increased proportion of CD34 + MA6 + cells present in the ex vivo-expanded product and also suggests that optimizing ex vivo culture conditions to generate CD34 + MA6 + cells might further improve platelet engraftment in CB recipients.

Short‐Term exposure of umbilical cord blood CD34+ cells to human platelet lysate and cytokines enhances engraftment

“…Our results revealed that the treatment had no significant effect on the percentage of CD34-expressing cells suggesting that the treatment preserves the CD34+ phenotype of HSPC, an important index of hematopoietic recovery. 19 However, treatment also showed a significant increase in the CD34 MFI which was likely the result of cell enlargement that occurs during the S phase of the cell cycle as shown in Figure 1C. Furthermore, evaluation of the clonogenic ability of primed CD34+ cells using the MethoCult assay, indicated that our treatment did not negatively affect the clonogenic capacity of HSPC, thus supporting the potential use of this approach on this latter cell type.…”

“…It is positively correlated with multiple measures of hematopoietic recovery, including platelet engraftment. 19 Our results show that a 24-hour exposure of HSPC to increasing concentrations of either hPL or cytokines, or to hPL combined with cytokines (hPL + cytokines), does not affect the number of cells expressing CD34 ( Figure 1A). However, we found a significantly increased mean fluorescence intensity (MFI) of CD34, which represents the density of the antigen expression on the cell surface, on cells primed with 36 mg/mL of hPL + cytokines (>3-fold; Figure 1B), compared to cells primed with either hPL or cytokines alone, or to untreated cells.…”

“…29,30 CD34+ cells, either untreated (control) or primed, were transplanted both IV or directly into the bone marrow (IBM) of NSG mice and 2-month post-transplantation, the number of human CD45+ cells in PB, showed no difference for all the tested groups. Four months following the transplantation, the number of human platelets (an index of hematopoietic recovery 19 ) was found: (a) similar to control CD34+ cells transplanted both IBM or IV suggesting as reported by others that IBM injection by itself does not significantly improve the engraftment ( Figure 3C) which could be the result of rapid drainage into the central venous circulation and cellular extravasation into surrounding muscle and soft tissues as reported by Pantin et al 31 ; (b) to be significantly higher in mice that received primed CD34+ cells (>5-fold) through IBM injection only, suggesting that our treatment in association with IBM injection efficiently improves human platelet count and consequently HSPC engraftment through a mechanism that involves retention of HSPCs into the bone marrow rather than their migration. This increased retention hypothesis is supported by the fact that in the bone marrow of mice that received primed CD34+ cells through IBM injection, a higher level human engraftment was observed when compared to their control ( Figure 3C,D).…”

Arachidonic acid and Docosahexanoic acid enhance platelet formation from human apheresis-derived CD34+ cells

“…Many investigators worldwide are trying to achieve this goal but with limited success. [36][37][38][39][40] This is because the process of megakaryocyte and platelet formation is very complex and the mechanism is not yet completely understood. Two main approaches for in vitro MK production are genetic manipulations or altering media components.…”

How to Improve Cord Blood Engraftment?

“…Migliaccio et al ( 11 ) have compared TNC with colony-forming unit (CFU) numbers and have shown TNC to be inferior to CFU in determining neutrophil and platelet recovery speed following UCBT. Recently, Simmons et al have identified a CD34 + cell subpopulation that co-expresses an antigen (-MA6) ( 12 ). This antigen expression predicted platelet engraftment better than CD34 + cell counts.…”