Stem Cell Transplantation from HLA-Identical Siblings Versus Alternative Donors in β-Thalassemia Diseases.

Background: Allogeneic hematopoietic stem cell transplantation (SCT) has been established as a curative therapy for β-thalassemia major which is prevalent among Thais. Donors are usually patients’ siblings but the chance to find an optimal HLA-identical is just about 30%. Thus clinical trial using alternative donors such as partially-mismatched related donors or matched unrelated donors could be a good choice.

Methods: To study the efficacy and results, we retrospectively review our experience with β-thalassemia pediatric patients undergoing transplantation from July 1999 to July 2006.

Results: There were 43 patients categorized into HLA-identical siblings group (n=26, 13 male and 13 female) and alternative donors group (n=17, 14 male and 3 female). Median age and weight were 7.2 years (1.2–14.8 years), 19.8 kg (9.8–34 kg) and 7.7 years (1.4–14.8 years), 21.5 kg (11–33 kg), respectively. Amongst 26 matched siblings there were 17 bone marrow (BM), 4 peripheral blood stem cell (PBSC), and 5 cord blood (CB) donors. Of the alternative group stem cells derived from 12 matched unrelated, 2 two-antigen mismatched sibling CB, 2 one-antigen mismatched unrelated CB, and 1 one-allele mismatched unrelated BM donors. Myeloablative conditioning regimen consisted of busulfan (oral or intravenous) and cyclophosphamide for matched siblings SCT. Anti-thymocyte globulin was added for alternative donors SCT. Fludarabine was also used in addition for unrelated donors SCT. Graft-vs-host disease (GvHD) prophylaxis consisted of cyclosporine plus methotrexate except for unrelated SCT that tacrolimus plus methotrexate were used instead. Median numbers of infused CD34+ cells of the matched siblings group were 11.1x10⁶/kg (3.7–35.4) in BMT (n=17), 9.3x10⁶/kg (7.1–12.8) in PBSCT (n=4), and 0.94x10⁵/kg (0.2–5.3) in CBT (n=5), compared to 5.5x10⁶/kg (1.5–18.1) in BMT (n=10), 11.1x10⁶/kg (11–17.2) in PBSCT (n=3), and 2.1x10⁵/kg (1.5–3) in CBT (n=4) of the alternative group. Median times to neutrophil and platelet engraftments in each groups were 15 and 33 days, compared to 17 and 41 days, respectively. 39 successful donor engraftments were achieved from 38 HLA-matched (25 related and 13 unrelated) donors and from 1 mismatched unrelated CB unit. The remaining 1 of the matched related group and 3 of the alternative group did not engrafted, all but one case subsequently resumed autologous recovery. Acute GvHD occurred in 4 matched-sibling and 5 unrelated SCT recipients. After immunosuppressive therapy the lesions were completely resolved in all but two patients, one who suffered from severe grade IV intestinal GvHD and another who later developed extensive chronic GvHD which required treatment longer than 4 years. There were 4 mortalities only in the alternative group: 3 patients died post-engraftment due to severe fatal GvHD (n=1), cerebral aspergillosis (n=1), severe veno-occlusive disease with liver failure (n=1; Pesaro class 3); and one died from neutropenic sepsis 3-week after 4/6 matched related CBT. Median follow-up time for surviving patients was 53.5 months (2–84 months). Overall and disease-free survival in HLA-matched SCT (n=38) recipients were 94.7% (n=36) and 92.1% (n=35), compared to in HLA-mismatched (n=5) 60% (n=3) and 20% (n=1), respectively.

Conclusions: SCT for β-thalassemia major using HLA-matched donors, either related or unrelated, had superior results than HLA-mismatched. In situation of unavailable matched sibling donors, the search for an appropriate complete HLA-matched unrelated volunteer donor using high resolution DNA typing is essential for favorable outcomes.