Results of a Prospective, Multicenter, Phase I/II Clinical Study in Pediatric and Adult Patients Using TCR Alpha/Beta and CD19 Depleted Haploidentical Hematopoietic Stem Cell Grafts Following Reduced-Intensity Conditioning

Abstract:

Here we report for the first time on long term follow-up data of a cohort of 60 patients who received TCRαβ and CD19 depleted peripheral blood stem cell grafts from haploidentical family donors within a prospective, multi-center, single-arm, phase I/II clinical study (EudraCT No.: 2011-005562-38).

As planned, 30 pediatric and 30 adult patients were enrolled in this trial: All patients received a reduced-intensity conditioning regimen consisting of fludarabine (160 mg/m²), thiotepa (10 mg/kg), melphalan (140 mg/m²) and either antithymocyte globulin (Grafalon, 15 or 30 mg/kg, N=53) or 7 Gy total nodal irradiation (N=7). MMF (40 mg/kg/day) was administered as single-agent GVHD prophylaxis until Day 30.

Results:

Sixty patients with a median age of 18.5 years (range 1-63) were treated. Twenty-five patients had AML, 17 ALL, 6 MDS/MPS and 1 each had multiple myeloma and acute undifferentiated leukemia. Six patients had solid tumors (soft tissue sarcomas and neuroblastomas) and 4 non-malignant disorders (SCID, Wiskott-Aldrich syndrome, lysosomal storage disorder and sickle cell anemia). Of the 56 patients with malignant disease, 33 were transplanted in complete (CR), 11 in partial (PR) and 12 in non-remission (NR). Twenty of the 56 patients with malignant diseases received a 2^nd or 3^rd transplantation within this protocol.

In total, 88 depletion procedures were performed with the CliniMACS ^plus System (Miltenyi Biotec, Germany) at 7 GMP laboratories and resulted in a median T and B cell log depletion of 4.7 (range 3.6-5.3) and 3.4 (range: 2.3-4.5), respectively. The median number of infused CD34⁺ cells and TCRαβ T cells was 12.4 × 10⁶ /kg BW (range 4.0 - 54.9) and 1.4× 10⁴ /kg BW (range 0.06-6.4), respectively.

Engraftment was rapid with a median of 13 (range 9-41) and 15 (11-38) days to reach ANC >500 cell/µl and PLT > 20,000 cells/µl. Nine patients rejected the graft. Eight of them were successfully re-transplanted and 1 patient died. One patient received stem cell boosts from the original donor due to poor graft function.

On day 100, peripheral T cell chimerism was completely donor-type in 44 of 47 evaluable patients, and mixed in 3.

None of the patients developed grade III/IV aGVHD and only 6 patients (10%) had grade II aGVHD. Of 47 evaluable patients 4 had severe cGVHD (9%), and 6 (13%) and 5 (11%) had moderate and mild cGVHD, respectively.

CMV reactivation was seen in 25 (42%) mainly adult patients, and only 1 (2%) patient developed disease. Twenty-one (35%) patients had ADV reactivation and 7 children and 1 adult (13%) developed disease. Only 1 case of EBV disease (encephalitis) occurred (2%).

A median of 221 (range 8-1230) CD3⁺ cells/µl was reached on day 100. The median numbers of CD3/CD4⁺ and CD3/CD8⁺ cells at 1 year post transplant were 316 (range 1-1173) and 308 (range 0-2203) /µl.

As of July 15 2018, 57 patients have completed the 2 year follow-up, died or discontinued the study resulting in a median follow-up of 706 days (range 18-800). 37 patients (62%) are alive and 23 (38%) died. Relapse was the major cause of death (N=12) followed by ADV infection (N=3), ARDS (N=3) and 1 case each of cardiac arrest, multi organ failure, sepsis due to graft failure and demyelinating neuropathy. Cause of death was not reported in 1 patient. Eight of the 20 patients who received the 2^nd or 3^rd transplantation are alive; 1 discontinued the study prematurely. Of the 23 patients transplanted in PR or NR, 13 are alive.

The Kaplan-Meier estimated probabilities of overall survival, disease-free survival (DFS) were 62% and 53%, respectively. Cumulative incidences of relapse and NRM at 2 years were 34% and 20%, respectively. For those patients with leukemia receiving a first SCT in CR, the overall survival, DFS and relapse rate were 75%, 64% and 20%, respectively.

Conclusion:

The transplantation of TCRαβ and CD19 depleted haploidentical hematopoietic stem cell grafts was safe and feasible. Decentralized production using the CliniMACS System was feasible and reliably resulted in grafts containing sufficient numbers of stem cells with only minimal numbers of co-infused TCRαβ T cells. None of the patients developed grade III-IV aGVHD and incidence of cGVHD was acceptable. Given the heterogeneous patient cohort with respect to age, disease, remission status and number of previous transplants, the outcome of patients after 2 years follow-up is promising.

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