A 12-year-old boy with myelodysplastic syndrome underwent a double transplantation of hematopoietic progenitor cells from his haploidentical brother. After conditioning with busulfan, cyclophosphamide, and Vepesid, the first bone marrow transplantation was performed using 3.53 x 10(6)/kg of CD34+ cells. Initial engraftment was followed by graft rejection. The second conditioning consisted of melphalan and anti-thymocyte globulin. The boy was then transplanted with 5.15 x 10(6)/kg of CD34+ cells, harvested from bone marrow (BM) and peripheral blood. Graft versus host disease (GvHD) prophylaxis consisted of cyclosporine A + short methotrexate. Hematological recovery was rapid and stable. Acute GvHD 1 degree (skin) resolved after 2 weeks of steroid treatment. A relapse occurred on day +140. At that time NK cells decreased from 20 to 7% with the lowest CD4+/CD8+ ratio, 0.07. Just after relapse, the percentage of cytokine-induced killer cells (CIK-CD3+CD56+) dropped from 3.34 to 0.1%. CsA treatment was stopped and the patient received T cell (CD3+ cells) add-back four times on days +146, +199, +234, and +262 in doses of 0.5 x 10(5), 1.0 x 10(5), 2.0 x 10(5), and 4.0 x 10(5)/kg, respectively. No acute GvHD occurred. Additionally, bone marrow biopsy before the second add-back showed complete remission. Analysis of lymphocyte subsets before the fourth add-back showed the highest values of CD4+, NK, and CIK cells and also the highest CD4+/CD8+ ratio.