Stable engraftment after megadose blood stem cell transplantation across the HLA barrier -: The case for natural killer cells as craft-facilitating cells

Background The case of a patient with chronic myelogenous leukemia who underwent transplantation with highly purified CD34(+) peripheral blood stem cells from his two-antigen-mismatched mother is reported. No graft-versus-host disease has been observed so far and stable engraftment has been documented until day 100. Methods. Weekly analysis of chimerism in different cellular subsets was performed using a quantitative polymerase chain reaction assay for nine short tandem repeat markers in leukocytes sorted by fluorescence-activated cell sorting. Results. No donor CD4(+) or CD8(+) T cells have been detected up to 3 months after transplantation, whereas a rapid increase of donor CD56(+) natural killer (NK) cells was observed in parallel with circulating donor CD34(+) progenitors and myeloid cells. Conclusions. Because the graft contained virtually no T and NK cells, we believe the rapid in vivo generation of NK cells supported stable engraftment across the HLA barrier. The differentiation of CD34(+) progenitors into NK cells might be a distinct feature of megadose stem cell transplants.