Haploidentical Stem Cell Transplantation in Children: A Comparison between Positive Selection of Stem Cells and Depletion of T- and B-Cells.

Profound depletion of T- and B-cells is a fundamental prerequisite for haploidentical 1–3 loci mismatched stem cell transplantation. Here, we compare hematopoietic engraftment and occurrence of GvHD after positive selection procedures (with anti-CD34 coated or anti-CD133 coated beads, n=64 patients) and after a direct depletion procedure with anti-CD3/anti-CD19 coated microbeads (n=12) in children with leukemias (ALL, AML, CML), lymphomas and nonmalignant diseases. Median purity of stem cells was comparable after CD34+ selection and CD133+ selection, whereas stem cells were only slightly enriched after CD3+/CD19+ depletion (97.5%, 93.4% and 1.02%). Indirect depletion of T-cells by positive selection methods resulted in 10 000 residual CD3+ cells/kg (7000–30 000). Patients with grafts depleted with anti-CD3/anti-CD19 coated microbeads, received 32 000 (7000–160 000) residual T-cells/kg. Those grafts comprised also remarkable amounts of effector cells such as NK-cells (median number: 86 × 10⁶/kg), dendritic cells and monocytes/granulocytes (median number: 700 × 10⁶/kg) with antileukemic activity in vitro. Primary engraftment occurred in 83% of patients with positive selected stem cells. After reconditioning, sustained engraftment was achieved in 98%. In patients with CD3+/CD19+ depleted grafts, primary engraftment was observed in 92% (11/12) and sustained engraftment (after reconditioning) in 100% (12/12). GvHD grade II occurred in 6% (positive selection) and 25% (CD3/CD19 depletion). Only one patient had severe GvHD grade III-IV (CD34+). T-cell recovery was significantly faster in patients with CD3/CD19 depleted grafts. In the group with positive selected grafts, 5 year EFS for patients with ALL CR1-3, myeloic leukemias and nonmalignant diseases was 45%, 22% and 60%, respectively. CD3+/CD19+ depleted grafts were given to patients with refractory disease (AML/MDS, ALL) or with high risk of graft failure. 4/10 patients with leukemias and 2/2 patients with SAA/PNH are disease free (median follow-up: 8 months). Conclusions: Haploidentical transplantation with standard CD34+ or CD133+ selected grafts provides stable long term survival rates. CD3+/CD19+ depletion resulted in better and more reliable engraftment but produced slightly more GvHD than positive selection methods. Our preliminary results indicate, that CD3/CD19 selected grafts may be advantageous regarding engraftment and immunoreconstitution. Since effector cell with potential antileukemic activity are cotransfused, such grafts may be suited in particular for patients with insufficient remission.