Umbilical cord blood transplantation : clinical outcome, chimerism development, and in vitro expansion of T-cells for clinical use

• Umbilical cord blood (UCB) is an alternative graft source in allogeneic hematopoietic stem cell transplantation (HSCT). The unique advantages with UCB as a stem cell source are found in the permissibility for human leukocyte antigen (HLA)-mismatch, rapid availability, and comparatively risk-free graft collection. Important drawbacks to UCBT are delayed engraftment, poor immune reconstitution and the lack of donor cells for post-transplant therapy. In this thesis we aimed to: 1) evaluate clinical outcome and chimerism development after UCBT, and 2) develop treatment alternatives to donor lymphocyte infusions (DLI) for UCBT recipients. In scientific paper I, we performed a retrospective single-center analysis of chimerism development and clinical outcome in 50 single and double UCBTs (DCBTs) in children and adults with hematological malignancies and non-malignant diseases. Complete donor chimerism was found to be associated with total body irradiation. A negative correlation was seen between 5-year survival and age, acute graft-versus-host disease (GVHD) grades III-IV, and mesenchymal stem cell (MSC) treatment. In scientific paper II, we focused on chimerism development in seven patients undergoing DCBT. Two patients developed longterm mixed donor–donor chimerism (MDC) in all cell lineages, at 25 and 35 months after DCBT. The work in scientific paper III was performed to study the immunological phenotype and function of these patients with MDC. We found that there were differences between the engrafted units: one unit had more naïve, less functional T-cells and more NKcells. When the patients with MDC were compared with patients with single UCB unit chimerism, they had a more naïve T-cell profile. The results also indicated that inter-unit matching of the HLA-C genes and high-dose anti-thymocyte globulin (ATG) might influence MDC development after DCBT. We have expanded T-cells from clinical cord blood grafts with anti-CD3+/CD28+ beads and interleukin (IL)-2 for possible use as alternative DLI. In scientific paper IV we studied the effect of adding IL-7, and found that it conferred a greater proliferation rate, higher CD4+/CD8+ ratio, and less central memory T-cells. We also noticed a higher percentage of polyfunctional T-cells with IL-7. The cultured UCB DLI has been used clinically in four patients with mixed chimerism (MC), minimal residual disease (MRD) and graft failure without certain adverse effects. The results were presented in scientific paper V. In the patient treated due to MRD, the malignant cell clone was undetectable at treatment and for 3 months after infusion. In one patient with MC, the percentage of recipient cells decreased in temporal association to the treatment. These events indicate possible treatment benefits, but without certain causal association to UCB DLI treatment. In summary, we found that MSC treatment was negatively correlated to survival in our UCBT recipients. High-dose ATG and HLA-C match might predispose for MDC. Cultured UCB DLI products are feasible to produce, and have been used in patients with no certain adverse effects, but with possible benefits.

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