Safety and Efficacy of Tcralpha/Beta and CD19 Depleted Haploidentical Stem Cell Transplantation Following Reduced Intensity Conditioning in Children: Results of a Prospective Multicenter Phase I/II Clinical Trial

We report one year follow-up data on safety and efficacy from the first prospective, multi-center, open-label, single-arm phase I/II clinical trial of TCRalpha/beta and CD19-depleted haploidentical stem cells grafts which were generated with the CliniMACS ^plus System (Miltenyi Biotec, Germany) and transplanted after reduced-intensity conditioning in pediatric patients with various malignant and non-malignant diseases (www.clinicaltrialsregister.org; 2011-005562-38). 30 patients were enrolled in the pediatric cohort of the trial and received single agent MMF as short-term GVHD prophylaxis (40mg/kg/day for 30 days). The grafts were manufactured in 4 GMP sites. The kinetics of immune cell reconstitution were measured in two core labs using standardized phenotypic analyses and the MACSQuant flow cytometer (Miltenyi Biotec, Germany). We previously reported the outcome of the first 100 days. This report covers a median follow-up of 367 days.

Results: Thirty patients from six hospitals were treated (13 female, 17 male; median age 7 years, range 1 - 17 years). 10 patients had ALL, 8 AML, 6 solid tumors (soft tissue sarcomas and neuroblastomas), 3 MDS/MPS, and 1 each with lysosomal storage disorder, SCID, and Wiskott Aldrich syndrome. Disease status in acute leukemias/MDS were: CR1 (n=4), relapsed/refractory (n=17). 5/6 patients with solid tumors had relapsed metastatic disease. The conditioning regimen consisted of 15 or 30 mg ATG (Fresenius/Grafalon) or 7 Gy total nodal irradiation, 160 mg/m² fludarabine, 10 mg/kg thiotepa, and 140 mg/m² melphalan. The median numbers of CD34+ cells, TCRab+ cells and CD20+ cells infused per kg bw were 14.6 x 10⁶ (range, 4 - 54.9), 14 x 10³ (range, 0.62 - 40.6) and 0.55 x 10⁵ (range, 0.04 - 1.85), respectively. Main cellular components of the graft were NK and TCRgd+ cells (median 6.67 x 10⁷ and 1.58 x 10⁷ cells per kg bw, respectively) with consistently high log depletions of TCRab+ and CD19+ cells: 4.75 and 3.44, respectively.

None of the 30 recipients developed severe acute GVHD grades III - IV. The vast majority of patients (97%) experienced no or only grade I acute GVHD despite minimal GVHD prophylaxis after transplantation. One patient had acute GVHD grade II. Chronic GVHD was observed in two out of 23 patients (9%): one with skin and one with gut/liver involvement. In both cases GVHD was extensive.

Twenty-four patients were evaluable for assessment of immune reconstitution until 1 year or discontinuation. Figure 1 shows fast and stable reconstitution of T, B and NK cells. TCRab+ T cells continued to increase during the observation period up to a median value of 741 cells/µL (range, 245 - 3132), whereas TCRgd+ T cells remained stable after reaching a plateau around day 20.

ADV reactivation in 16 patients contributed most to infectious complications following transplantation. Of these 6 patients developed ADV disease. Within the first year after transplantation 3 patients died of overwhelming of ADV infection. One EBV reactivation was observed but recovered completely. 8 patients experienced CMV reactivation after transplantation. 7 of 8 patients recovered. Another 2 patients had CMV reactivation prior to transplant, but recovered shortly after engraftment. No CMV disease was observed within the first year. 6 patients had bacterial sepsis but recovered. In one patient CMV reactivation continued until death due to sepsis after graft failure.

At a median of 367 days (range, 14 - 809) among the 30 recipients, 16 are alive at time of last follow-up, 8 died of relapse, 3 died of ADV infection, 1 died of sepsis after graft failure and 1 died of ARDS. 1 patient is lost to follow-up. Of the 8 patients who died of relapsed disease, 4 had active disease at time of transplant, 2 were in remission and 2 had disease status not evaluable. Cumulative incidences of relapse and NRM were 27% and 16% at one year, respectively. Kaplan-Meyer estimates of overall survival and DFS were 64% and 60% at one year, respectively.

Conclusion: The CliniMACS TCRab+ / CD19+ depletion system yielded a large number of CD34+ cells, NK cells and TCRgd+ cells, that could be infused safely into pediatric patients with minimal risk of severe acute and chronic GVHD. The immune reconstitution was rapid. Coupled with a reduced-intensity regimen, the overall TRM was low. However, further efforts have to be made to avoid ADV associated infections.

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