CD8-Depleted Donor Lymphocyte Infusions Can Boost Immune Reconstitution after Haploidentical Stem Cell Transplantation Following Reduced-Intensity Conditioning Regimen.

Haploidentical stem cell transplantation (SCT) can be used in relapsed haematological malignancies for patients lacking a matched sibling or unrelated donor. Major barriers of this strategy are the poor immune reconstitution and the high risk of relapse. Here, we report results of a phase I–II trial evaluating early add-backs of CD8-depleted donor lymphocytes (DLIs) (from 1x10^4 up to 1x10^5 cells/kg starting at day+45 up to day +105 at monthly intervals) after a reduced intensity conditioning (RIC) regimen [thiotepa (10 mg/kg), fludarabine (120 mg/sqm), cyclophosphamide (60 mg/kg) and TBI (2 Gy)]. Ex-vivo and in-vivo TCD were carried out by CD34+ cell selection using the CliniMACS device and alemtuzumab (15mg/m2, day-2), respectively. Twenty-one patients [n= 10 NHL (n=5 CLL, n=5 high-grade NHL), n=7 HL, n=1 MM, n=1 ALL, n=2 AML] were transplanted with advanced disease: 16 (76%) failed a previous autograft and 13 (62%) had refractory disease. A median of 10.4x10^6/Kg CD34+, 1x10^4/kg CD3+, 10x10^4/kg CD19+, 0.9 x10^4/kg NK+ were infused. All patients engrafted with full donor chimerism from day +90. At a median follow-up of 12 months (range, 4–41 months), 12 of 21 pts are alive (7 CR, 2 PR and 3 PD) and 9 died [n=3 infection with GVHD (+610, +187, +253), n=6 disease]. The estimated 2-year overall survival was 49%: pts transplanted in remission had better outcome (83% versus 31%, p=0.13). The estimated 2-year cumulative incidence of TRM and relapse were 27% and 58%, respectively. CMV reactivation and hospital readmissions for opportunistic infections occurred in 76% and 57% of patients, respectively. For CD8 depletion of donor leukaphereses, a new depletion protocol using clinical grade CD8 microbeads (Miltenyi) was applied. This procedure is efficient to reduce the content of CD8 T cells by 3 logs while the median cell recovery of CD3+, CD4+, CD56+/CD3+, CD 20+ was 60%, 86%, 54%, 72%, respectively. Before DLIs, only 2 of 21 patients (10%) developed acute GVHD (no grade III–IV). A total of 36 CD8-depleted DLIs were administered to 17 pts without any acute toxicity. Following DLIs, 6 pts (35%) developed acute GVHD (grade II) and 5 (30%) chronic GVHD (n=2 limited, n=3 extensive). Overall, the incidence of acute GVHD is higher (50% vs 22%, p=0.33) in pts receving larger numbers of donor cells (10–15x10^4/kg versus 3–5x10^4/kg CD8-depleted DLIs). The median values of CD4+/uL, CD8+/uL and NK+ were 100, 280 and 680 at 4 months and 220, 200, 500 at 6 months after SCT in patients receiving CD8-depleted DLIs. Measurable TREC/ucg DNA (mean value 316; mean value donors 3740) and polyclonal T cell repertoire, evaluated by spectratyping, were observed at 9 months in patients younger than 40 years and/or without GVHD. Our results suggest that:

1. haploidentical SCT with RIC regimen provides high engraftment rate

2. T-cell addback allows the achievement of more than 100/uL CD4+ at 4 months after SCT in the majority of patients

3. Survival rate is promising in patients who had transplantation in remission suggesting that this strategy should be evaluated earlier in high risk haematological diseases.