Haploidentical Stem Cell Transplantation After Negative Depletion Of T Cells Expressing The αβ Chain Of The T-Cell Receptor (TCR) For Adults With Hematological Malignancies

Introduction For many years, T cell depletion (TCD) of hematopoietic stem cells (HSCs) has been based on either positive or negative selection of mobilised peripheral blood cells (PBPCs). After CD34+ cell selection, the T cell repertoire is very narrow since the number of T lymphocytes in the graft has to be particularly low to prevent GvHD and ATG in the conditioning exerts an additional in vivo T cell depletion. Thus the immune recovery is slow and patients tend to remain susceptible to opportunistic infections for several months after HSCT. To hasten and improve post-transplant immune reconstitution broad repertoire various strategies of adoptive donor T cell immunotherapy (e.g. engineering with a suicide gene; depleting alloreactivity by means of photodynamic purging or through the use of freshly purified regulatory T cells) have been investigated over the past years. More recently, selective elimination of αβ+ T cells has been performed to achieve a 4,5–5 log TCD and to retain in the graft NK, dendritic cells, monocytes and γδT lymphocytes. Under this approach, a rapid immunological reconstitution and very promising outcome have been reported in pediatric patients. With the aims of confirming these results even in adults, we have recently launched this programme and here we report our preliminar clinical data. Methods Thirteen patients, median age 40 years (range 19-65), with AML (n=9), ALL (n=2), HL (n=1) or Rhabdomyosarcoma (n=1) entered the study. All but two patients, who were in first remission, were in advanced-stage disease at transplant with five patients in chemoresistant relapse. Conditioning consisted of ATG 1,5 mg/kg from day -13 to day -10, Treosulfan 12gr/sqm from -9 to –7, Fludarabine 30mg/sqm from -6 to -2 and Thiotepa 5mg/Kg on days -5 and -4. Ten μg/kg G-CSF was used to mobilize PBPCs from one-haplotype mismatched donors (4 mothers, 4 brothers, 2 sisters, 1 son, 1 daughter and 1 cousin). Mobilized mononuclear cells were incubated with a biotinylated anti-TcRαβ antibody and subsequently with an antibiotin antibody conjugated to magnetic microbeads (Miltenyi Biotec, Germany). Under a strong magnetic field, TcRαβ T lymphocytes were retained, whereas all nonmagnetized cells were recovered. Short sirolimus (1mg/day x3 weeks) was used as additional GVHD prophylaxis in 3 cases whose grafts contained more than 2x105/kg αβ+Tcells. Results Grafts contained a median of 12,3x106/kg CD34+ cells(range7-19), 6 x106 CD3+Tcells/kg (range 2,3-13)with 10,4x104/kg αβ+T cells (range 1,38-62) and 5,8x106 γδ+Tcells/kg (range2,1-12,6), 6x104B cells/kg (range 0,2–32) and 34x108 CD56+NKcells/kg (range10-91). All but one patient, who required a second graft from the same donor to boost hematopoietic reconstitution, achieved a full donor sustained engraftment. Median time to reach 500 neutrophils and 50,000 platelets was 13 (range 9-18) and 11 days (range 9-13), respectively. Four patients had skin grade I/II aGVHD. No patients has so far developed chronic GvHD. Median CD4+ cell counts at 30, 60, 90 and 120 days since the transplant were 33, 122, 190 and 251 n/mL, respectively. CMV reactivation occurred in only 2 cases (in one, CMV serology was unfavourable: CMV-negative donor/CMV-positive recipient). Overall, 3 patients have so far died (2 non-hematologic causes and 1 early relapse). Ten survive disease-free at a median follow-up of 104 days (range 30-178). Conclusions The infusion of αβ/CD19-depleted grafts was safe and effective also in adult setting, resulting into rapid donor hematopoietic engraftment and early expansion of donor-derived γδT lymphocytes, without life-threatening infectious complications. Disclosures: No relevant conflicts of interest to declare.