Transplantation Of TcRαβ/CD19 Depleted Stem Cells From Haploidentical Donors In Children: Current Results
Authors: Lang Peter , Feuchtinger Tobias , Teltschik Heiko-Manuel , Schumm Michael , Schlegel Patrick , Pfeiffer Matthias , Ebinger Martin , Schwarze Carl-Philipp , Handgretinger Rupert 
Published: October 2019

Abstract

T-cell depletion of the graft is an effective method to prevent or completely avoid Graft-versus-Host Disease (GvHD) in haploidentical stem cell transplantation. In order to increase the T-cell depletion efficacy while maintaining the anti-tumor and anti-infectious properties of the graft, we have investigated a new T-cell depletion method which removes αβ+ T-lymphocytes via a biotinylated anti-TcRαβ antibody followed by an anti-biotin antibody conjugated to magnetic microbeads while retaining γδ+ T-lymphocytes, Natural killer (NK) cells and other cells in the graft. In addition, CD19+ B-lymphocytes were concomitantly depleted for the prevention of posttransplant EBV-associated lymphoproliferative disease. The CliniMACS system was used for manipulation of peripheral stem cell grafts from full haplotype mismatched family donors in 35 patients.

Results
The overall depletion of αβ+ T-cells was highly effective with 4.6 log (range 3.8–5.0). Patients received a median number of only 14 x 103/kg residual αβ+ T-cells. Recovery of CD34+ stem cells was 72%, and the median number of infused CD34+ stem cells was 12 x 106/kg (range 5-38 x 106/kg). Additionally, the patients received 2 types of potential antileukemic effector cells: 107 x 106/kg (range 35 -192 x 106/kg) CD56+ NK-cells and 11 x 106/kg (range 5–30 x 106/kg) γδ+ T-lymphocytes.

Diagnoses were
ALL (n=20), AML/MDS/JMML (n=9), nonmalignant diseases (n=4), solid tumors (n=2); disease status: CR2-CR6 (n=17), active disease (n=18). 23 patients received a second or third SCT (65%). A toxicity reduced conditioning regimen (fludarabin 40mg/m² or clofarabin 50mg/m² (day -8 to d -5), thiotepa 10mg/kg (d -4), melphalan 70mg/m² (d -3 and d -2) was used. The anti CD3 specific OKT3 antibody was used as rejection prophylaxis from day -8 to day -1 without affecting cotransfused effector cells because of its short half-life period in the first 7 patients. However, due to its restricted availability, the substance was substituted since 2011 by a reduced ATG-F dose (15mg/kg) given at start of the conditioning regimen in order not to impair NK and γδ+ T-cells of the grafts (1 mg/kg d -12, 4 mg/kg d -11, 5 mg/kg d -10 and -9; n=28 patients). Short course MMF (until day +30) was given in 25 patients. Graft rejection occurred in 14% of the patients. However, after reconditioning and second stem cell donation, final engraftment was achieved in all patients. The median time to reach neutrophil and platelet recovery in patients with primary engraftment was 10 and 11 days respectively. All patients showed a rapid immune reconstitution with 250 (OKT3 conditioning) and 273 (ATG conditioning) CD3+ T-cells/µl, 30 (OKT3) and 47 (ATG) CD3+4+/µl and 300 (OKT3) and 382 (ATG) CD56+ NK-cells/µl at day +30 posttransplant. γδ+ T-cells started to expand faster than αβ+ T-cells in the early post-transplant period (156 vs. 82 cells/µl at day +30) whereas at day +90, αβ+ T-cells were predominant (170 vs. 134 cells/µl). Acute GvHD grade 0-I occurred in 25 patients (71%); 6 patients had GvHD II (17%), 3 patients had GvHD III (9%) and one patients experienced GvHD grade IV (3%). 3 patients experienced chronic GvHD (8%). Incidence of acute GvHD was not influenced by the number of residual T cells or by the type of serotherapy. 1 year EFS for patients with acute leukemias was 66% (any CR) and 14% (active disease).TRM at 1 year was 20%.

Conclusions
These data indicate that transplantation of TcR αβ+/CD19 depleted cells from a haploidentical donor results in sustained engraftment, remarkably fast immune reconstitution and low incidence of both acute and chronic GvHD. OKT3 could be substituted by ATG without negative effects. The anti-leukemic efficacy of this approach in comparison to other methods of T-cell depletion needs to be evaluated with a longer patient follow-up.

Disclosures:
No relevant conflicts of interest to declare.