Improved T Cell Recovery After Transplantation of CD3/CD19 depleted Haploidentical Stem Cell Grafts in Pediatric Patients.

Abstract 4652

Profound depletion of T and B cells is a fundamental prerequisite for haploidentical transplantation and allows to minimize GvHD despite HLA incompatibility. However, posttransplant recovery of donor derived T cells is delayed after various graft manipulation procedures and may result in severe infections. Methods to improve this recovery are of great importance. Here we present immune reconstitution data in patients who received CD3/CD19 depleted stem cells in combination with melphalan based or standard conditioning regimens.

32 patients with ALL (n=14), AML/MDS (n=17), CML (n=1) were included. T and B cells were directly depleted using antiCD3/antiCD19 coated magnetic microbeads and the CliniMACS^TM device.

The patients received either TBI or Bu i.v. and OKT3 (n=9) or a reduced intensity conditioning (“RIC”: Mel 140mg/m², Flud 160mg/m², TT 10mg/kg, OKT3, n= 23).

Absolute numbers of lymphocyte subsets per microliter on day 90 were compared within these both groups and with a historical control group (patients with leukemias who received CD34 selected grafts and TBI or Bu based standard conditioning regimen in combination with ATG, n=28).

CD3+4+, CD3+8+ and total numbers of CD3+ of patients after CD3/CD19 depletion were significantly higher in the RIC-group than in the TBI/Bu-group (mean numbers: 85.83 vs. 38.84; 133.46 vs. 19.69; 270.27 vs. 63.99; p<0.05, unpaired t-test).

Comparison with the whole CD34 historical group showed a faster recovery of CD3+4+ in patients with CD3/19 depletion and RIC (104.26 vs. 54.22; p= 0,034) but no significant difference in CD3+8+ and CD3+. Furthermore, subgroups of the CD34 historical population were compared: patients with CD3/19 depletion and RIC had a significantly faster recovery of CD3+4+, CD3+8+ and CD3+ than CD34 patients with TBI (104.26vs. 25.48; 133.46vs. 43.17; 270.27 vs. 65.86; p<0.05) but had no advantage over CD34 patients with non-TBI conditioning.

Conclusions: the type of graft manipulation appeared to have an influence on the speed of CD4+ recovery (CD3/19 depletion > CD34 selection). Moreover, the use of TBI had a clear negative impact on all T cell subsets: patients with TBI had a slower recovery than patients with non-TBI conditioning, independent from graft manipulation procedures and probably due to thymic damage. Thus, the use of RIC-protocols in combination with CD3/CD19 depletion may help to speed up the immune recovery after haploidentical transplantation. Further studies are warranted to evaluate the risk of relapse.