Israel Medical Association Journal

In recent years, umbilical cord blood has emerged as an alternative source of hematopoietic progenitors (CD34+) for allogeneic stem cell transplantation, mainly in patients who lack an human leukocyte antigen-matched marrow donor. Since 1998, about 2,500 patients have received UCB[1] transplants for a variety of malignant and non-malignant diseases. The vast majority of recipients were children with an average weight of 20 kg, however more than 500 UCB transplantations have already been performed in adults. The “naive” nature of UCB lymphocytes may explain the lower incidence and severity of graft versus host disease encountered in UCBT[2] compared to the allogeneic transplant setting. Furthermore, UCB is rich in primitive CD16^-CD56⁺⁺ natural killer cells, which possess significant proliferative and cytotoxic capacities and can be expanded using interleukin-12 or 15, so as to mount a substantial graft versus leukemia effect. The major disadvantage of UCB is the low yield of stem cells, resulting in higher graft failure rates and slower time to engraftment compared to bone marrow transplantation. A rational approach thus involves ex vivo expansion of UCB-derived hematopoietic precursors.

Background: Experimental and clinical protocols are being developed for the cryopreservation of human hematopoietic progenitor cells. However, the effect of these procedures on the potential for HPC[1] to repopulate bone marrow is unknown.

Objectives: To examine the effect of cryopreservation on the ability of fetal human liver HPC, which include CD34+ cells and long-term culture-initiating cells, to repopulate immunodeficient non-obese diabetic/severe combined immunodeficiency mouse bone marrow.

Methods: Groups of sublethally irradiated NOD[2]/SCID[3] mice were injected intravenously with cryopreserved or freshly isolated fetal human liver HPC.

Results: Seven weeks after transplantation, flow cytometric analysis of bone marrow samples showed that mice that received the transplanted cells (either cryopreserved or freshly isolated) demonstrated both lymphoid and myeloid differentiation as well as the retention of a significant fraction of CD34+ cells. Conclusions: Cryopreserved fetal human liver-derived HPC appear to be capable of initiating human cell engraftment in NOD/SCID mouse bone marrow and open the possibility of using cryopreserved fetal human liver HPC for gene manipulation, gene transfusion therapy, and transplantation purposes.

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[1] HPC = hematopoietic progenitor cells

[2] NOD = non-obese diabetic

[3] SCID = severe combined immunodeficiency

Background: The etiology of bone marrow failure, a prominent feature of paroxysmal nocturnal hemoglobulinuria, is presently unknown.

Objectives: To evaluate the possible influence of cellular immune mechanisms in the bone marrow failure of PNH.

Methods: We studied marrow erythroid colony formation in a patient with paroxysmal nocturnal hemoglobinuria without hypoplastic/aplastic marrow complications.

Results: In vitro assays revealed a pronounced inhibition of primitive erythroid (BFU-E) progenitor cell growth by marrow T lymphocytes. Removal of T cells prior to culture resulted in a 4.5-fold enhancement of BFU-E numbers. Reevaluation of in vitro erythropoiesis during steroid administration indicated a persistent, albeit less prominent, T cell inhibitory effect.

Conclusion: Our findings provide the first direct evidence for a cellular immune inhibitory phenomenon accompanying PNH.

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PNH= paroxysmal nocturnal hemoglobinuria