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Prolonged ex vivo culture of cord blood CD34+ cells facilitates myeloid and megakaryocytic engraftment in the non‐obese diabetic severe combined immunodeficient mouse model

A clinical goal for ex vivo expansion of cord blood (CB) CD34+ cells is to shorten the period of neutropenia and thrombocytopenia following myeloablative therapy and transplantation. Prolongation of cytokine expansion leads to the production of greater numbers of cells, and should have an impact on neutrophil and platelet recovery. Furthermore, expansion of CD34+ cells should support the continued production of neutrophils and platelets in the 6‐week period following transplantation. We tested these hypotheses by characterization of the kinetics (human CD45+ cells in the blood) and phenotype (CD45, CD34, CD61, CD33, CD19 and CD3) of human engraftment in the non‐obese diabetic severe combined immunodeficient mouse (NOD–SCID) following 7 or 14 d of ex vivo expansion of CB CD34+ cells. Mice transplanted with 14 d cells showed greater percentages of human CD45+ cells in the blood, bone marrow and spleen than mice transplanted with unexpanded cells or 7 d cells. Prolonging cytokine exposure of CD34+ cells and transplantation with increasing numbers of input cells facilitated the production of absolute numbers of CD34+, CD33+, CD61+ and CD19+ cells in vivo. Furthermore, analysis of SCID engrafting potential showed that prolongation of culture duration facilitates in vivo expansion of CD45+, CD34+ and CD19+ cells after transplantation. It is anticipated that prolonged (2 weeks) ex vivo culture of CB will have a beneficial clinical effect.