Dose Reduced Conditioning and CD3/CD19 Depletion for Haploidentical Allogeneic Hematopoietic Cell Transplantation in Adults: Fast Engraftment and Low Toxicity.

Haploidentical hematopoietic cell transplantation (HHCT) has been made feasible with the use of megadoses of CD34+ peripheral blood stem cells. Despite this progress, HHCT is still complicated by high treatment related toxicity, slow engraftment and immune reconstitution. A new regimen using graft CD3/CD19 depletion with anti-CD3- and anti-CD19-coated microbeads on a CliniMACS device and dose reduced conditioning may allow HHCT with lower toxicity and faster engraftment. CD3/CD19 depleted grafts not only contain CD34+ stem cells but also CD34 negative progenitors, natural killer-, dendritic- and graft-facilitating-cells. As dose reduced conditioning fludarabine (150–200 mg/m²), thiotepa (10 mg/kg), melphalan (120 mg/m²) and OKT-3 (5 mg/day, day -5 to +14) without posttransplant immunosuppression was used. So far 9 consecutive adult patients have been transplanted with this regimen. Median age of the patients was 37 (range, 27–58) years and the diagnoses were AML (n=3), ALL (n=3), NHL (n=2) and multiple myeloma (n=1). All patients were high risk with relapse after preceding hematopoietic cell transplantation. The CD3/CD19 depleted haploidentical grafts contained a median of 8 x 10E6 (range, 5.2–17x10E6) CD34+ cells/kg, 6x10E7 (range, 0.02–8.6 x10E7) CD56+ cells/kg and 2x10E4 (range, 0.006–8.2x10E4) CD3+ T-cells/kg. 8 of 9 patients had a donor-recipient KIR-mismatch. The conditioning regimen was well tolerated with maximum acute toxicity being grade 2–3 mucositis and nausea. In 4/9 patients reversible peripheral neuropathy grade 2–3 occurred, combined with multifocal leucencephalopathy in one patient. Subsequently the dose of fludarabine was reduced to 150 mg/m². Engraftment was rapid with median time to neutrophils >500/μL of 13 (range, 10–17) days, platelets >20000/μL of 11 (range, 8–14) days and full donor chimerism after two weeks in all patients. All evaluable patients had fast immune reconstitution with T-cells >100/μL by day +100. Five cases of grade 2 skin GVHD rapidly responded to steroids. Three patients with controlled fungal pneumonia at time of transplant had resolution of infiltrates with neutrophil reconstitution and antifungal therapy. Treatment related mortality in the first 100 days was low with one death due to idiopathic pneumonia syndrome. Three patients died after day 100, one each due to relapse, systemic adenoviral infection and CMV infection. Overall survival is 5/9 patients with a median follow-up of 406 days (range, 44–661). In conclusion, this regimen seems to be promising in adult high risk patients lacking a suitable donor and a prospective phase I/II study is ongoing.