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

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

BACKGROUND

Intra bone marrow (IBM) injection has been proposed as a strategy to bypass homing inefficiencies associated with intravenous (IV) hematopoietic progenitor stem cell (HSPC) transplantation and thus increases the number of HSPC that engraft. Despite physical delivery into the bone marrow cavity, many donor cells are rapidly redistributed by vascular perfusion. Thus, the objective of our study was to evaluate the ability of human platelet lysates (hPL) to improve HSPC retention into the bone marrow and consequently to improve engraftment.

STUDY DESIGN AND METHODS

HSPC were isolated from human umbilical cord blood. HSPC were seeded in the wells of a 24-well microplate and exposed to increasing concentrations of hPL with or without cytokines for 24 hours. Following priming, HSPC cells chemotaxis to rhSDF-1 was determined in vitro and engraftment in NSG mice was evaluated.

RESULTS

Priming of cord blood CD34+ cells to a combination of hPL and cytokines resulted in a significant increase (up to 3-fold) in the expression of the CD34 antigen on HSPC. This effect was closely correlated to a significantly increased (up to 7-fold) migration toward a rhSDF-1 concentration gradient. In addition, IBM injection of CD34+ cells previously primed with hPL+cytokines into NSG mice showed significantly increased engraftment as measured by human platelet numbers, human CD45 and human CD34+ cells for unprimed and primed cells, respectively.

CONCLUSION

The use of hPL + cytokines as a short-term priming treatment for UCB could be an advantageous strategy to improve clinical outcomes following IBM injection.

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

An Aberration in megakaryopoiesis and thrombopoiesis, 2 important processes that maintain hemostasis, leads to thrombocytopenia. Though platelet transfusions are used to treat this condition, blood banks frequently face a shortage of platelets. Therefore, methods to generate platelets on a large scale are strongly desirable. However, to generate megakaryocytes (MKs) and platelets (PLTs) in numbers sufficient for clinical application, it is essential to understand the mechanism of platelet production and explore efficient strategies accordingly. We have earlier reported that the N-6 and N-3 poly-unsaturated fatty acids (PUFAs), Arachidonic acid (AA)/Docosahexanoic acid (DHA) have beneficial effect on the generation of MKs and PLTs from umbilical cord blood derived CD34⁺ cells. Here we tested if a similar effect is observed with peripheral blood derived CD34⁺ cells, which are more commonly used in transplantation settings. We found a significant enhancement in cell numbers, surface marker expression, cellular ploidy and expression of cytoskeletal components during PLT biogenesis in cultures exposed to media containing AA/DHA than control cultures that were not exposed to these PUFAs. The test cells engrafted more efficiently in NOD/SCID mice than control cells. AA/DHA appears to have enhanced MK/PLT generation through upregulation of the NOTCH and AKT pathways. Our data show that PUFAs could be valuable additives in the culture system for large scale production of platelets for clinical applications.

How to Improve Cord Blood Engraftment?

Various factors make cord blood (CB) a significant source of hematopoietic stem cells (HSCs), including ease of procurement and lack of donor attrition, with the ability to process and store the donor cells long term. Importantly, high proliferative potential of the immature HSCs allows one log less use of cells compared to bone marrow or peripheral blood stem cells. As total nucleated cell (TNC) and CD34(+) cell content of CB grafts are correlated to engraftment rate and speed, strategies to expand HSC and homing have been developed. This chapter will focus only on modalities such as intrabone administration, fucosylation, CD26 inhibition, prostaglandin E2 derivative or complement 3 exposure, and SDF-1/CXCR4/CXCL-12 pathway interventions that have been experimented successfully. Furthermore, increasing evidence in line with better recognition of CB progenitors that are involved in engraftment and homing will also be addressed.