Low Transplant Related Toxicity and Mortality after Transplantation of CD3/CD19 Depleted Haploidentical Stem Cells with Reduced Intensity Conditioning in Children.

Transplantation of haploidentical, positive selected grafts with TBI or Bu based conditioning regimens can result in significant toxicity and TRM. New graft manipulation methods and a melphalan based intensity reduced regimen decreased these complications. We present our results with a direct depletion procedure using antiCD3/antiCD19 coated magnetic microbeads. Melphalan (2×70mg/m²), fludarabine (4×40mg/m²), thiotepa (10mg/kg) and OKT3 (0.1mg/kg) was used as preparative regimen in 27 pediatric patients. All patients underwent intensive pretreatment according to current study protocols; 11/27 already received previous autologous or allogeneic transplantations (median time between 1^st and 2^nd trp: 2.3 years). Diagnoses were: AML/MDS (n=9), ALL (n=5), relapsed neuroblastoma/Ewing-/rhabdomyosarcoma (n=11), SAA (n=2); remission status: CR2=6, CR3=3, NR/PR=16. Donors were full haplotype mismatched parents. The grafts comprised a median number of 14×10⁶/kg stem cells and 139×10⁶/kg NK-cells with 55×10³/kg residual CD3+ cells and 24×10³/kg CD20+ cells. Primary engraftment occurred in 85%. After TLI based reconditioning and second haploidentical stem cell donation, final engraftment was achieved in 100%. Median time to reach >500 neutrophiles/μl and independence from platelet substitution was 10 (9–12) and 8 (6–188) days respectively. GvHD grade 0–1 occurred in 63%. 30% and 7% had grade II and III, respectively. Chronic GvHD was observed in 3 patients. Transplant related mortality (TRM) occurred only in 1/27 patients (4%) with a median follow up of 0.8 years (3 months-3.0 years). In general, the regimen was well tolerated without severe side effects. The profile of toxic side effects according to NCI-CTC grading system was: gastrointestinal: diarrhea grade 0–2 (n=25), grade 3 (n=2); stomatits grade 3–4 (n=27); skin: grade 0–2 (n=27); pulmonary: hypoxia grade 0 (n=24), grade 3 (n=3); pneumonitis (n=1); cardiac: lethal myocardiopathy (n=1), none (n=26); hepatic: GOT/GPT or bilirubin elevation grade 0–2 (n=19), grade 3 (n=4), grade 4 (n=4), VOD: none; renal: creatinine grade 0–2 (n=27); neurological: none; infection: grade 0–2 (n=17), grade 3 (n=7), grade 4 (n=3), EBV-LPD: none. Overall survival at 1 year was 47% for the whole group and 40% for patients with solid tumors. Causes of death were myocardiopathy (n=1) and relapse (n=13). Pretransplant disease status was predictive: 1 year EFS in patients with leukemias in CR and SAA was 83%, whereas all patients with active disease relapsed (median time to relapse: 0.3 years).

Conclusions: transplantation of CD3/CD19 depleted haploidentical stem cells with our melphalan based reduced intensity regimen resulted in a fast recovery of neutrophiles and platelets. Engraftment rates similar to that of patients with standard conditioning regimens and positive selected grafts were achieved, possibly due to graft facilitating effects of cotransfused NK-cells. The regimen helped to minimize side effects and TRM. No lethal infections occurred despite delayed T cell recovery. Thus, our approach forms the basis for haploidentical transplantation with low toxicity even in intensively pretreated patients(including previous transplantations). However, relapse remains an unsolved problem in patients with active disease. In those patients, further therapeutic elements have to be evaluated, like additional cytoreductive drugs immediately before transplantation as well as posttransplant immunotherapy.