HLA-Haploidentical Hematopoietic Cell Transplantation after TCR-Αβ and CD45RA+ Depletion Following Reduced Intensity Conditioning in Adults and Children with Hematological Malignancies- Two-Year Follow-up of Multicenter Study in Singapore
Authors: Poon Li Mei , Linn Yeh Ching , Tan Poh Lin , LIM Ziyi , Vellayappan Balamurugan , Bhattacharyya Rajat , Tan Ah Moy , Tan Lip Kun , Soh Teck Guan , Diong Colin Phipps , Leung Wing H. , Koh Liang Piu 
Published: November 2019

Background: Haploidentical hematopoietic cell transplantation (HCT) provides an alternative option for patients without HLA-matched donor. GVHD, engraftment failure, and infectious complications continue to be the main causes of non-relapse mortality (NRM). We hypothesized that selective depletion of TCRαβ+ and CD45RA+ naïve T cells subset will permit hematopoietic engraftment, while effectively reducing GVHD, and provide improved donor immune reconstitution through adoptive transfer of donor's mature NK cells, γδ T cells and CD45RO+ memory T cells.
Methods: Mobilized PBSC product were divided into two fractions in 9:1 ratio, and depleted using CliniMACS device after labeling with TCRαβ and CD45RA reagents (Miltenyi Biotec, Bergish-Gladbach, Germany), respectively. The conditioning regimen consisted of fludarabine 160 mg/m2 divided daily over 4 days, thiotepa 10 mg/kg divided twice daily for 1 day and melphalan 70-140 mg/m2 for 1 day, in combination with total lymphoid irradiation 6 Gy (n=23), or 7.5 Gy (n=12) over 3 equal fractions, or total body irradiation of 2 Gy (n=2). Short term GVHD prophylaxis for 30 days was given to 1 patient using MMF, 25 patients using tacrolimus and 2 patients using sirolimus.
Results: We transplanted 37 patients, including 32 adults (median age 47 years, range 20 - 69) and 5 children (median age 13 years, range 7-15 years) with high risk AML (n=17), ALL (n=11), MDS (n=5), myeloma (n=1), mast cell leukemia (n=1), acute undifferentiated leukemia (n=1) or NK/T lymphoma (n=1). The patients were infused with TCRαβ and CD45RA depleted graft containing a median of 8.65 x 106 (range, 3.54 - 20.78) CD34+ cells/kg, 0.00 x 104 (range 0 - 0.97) CD45RA+CD3+ cells/kg, and 2.4 x 106 (range, 0.15 - 11.67) CD45RO+CD3+ cells/kg. The TCRαβ depleted graft fraction contained a median of 0.19 x 104 (range 0 - 8.53) TCRαβ+ cells/kg, and 8.76 x 106 (range 1.73 - 30.00) TCRγδ+ cells/kg. Only 1 patient experienced primary graft failure. All others had engraftment of ANC > 500 cells/µL at a median of 10 day (range, 8 - 22) and PLT > 20,000 cells/µL at a median of 12 day (range, 7 - 19). There was no secondary graft failure. Four patients with high titers of donor-specific HLA antibodies (DSA) engrafted successfully after effective desensitisation with plasma exchange, rituximab and immunoglobulin.
Fourteen patients (38%) developed acute GVHD of grade II-IV (Gd II n=9 ; Gd III n=4 ; Gd IV n=1 ). Only one patient experienced chronic GVHD, giving 2 year cumulative incidence (CI) of chronic GVHD of 3.9 %.
Day 180 CI of NRM and relapse were 22.7 % (95% 10.5-37.7%) and 12.0 % (95% CI 3.7-25.7%), respectively. NRM was attributed to aGVHD in 3 of the 13 deaths. Viral reactivation included CMV (n=13), HHV6 (n=4), EBV (n=3) and adenovirus (n=4), with no fatal viral infection occurred within 180 days. Seven patients died of infection, including 3 patients who had fatal blood stream infection (bacteria n=2; fusarium n=1) within 180 days. With a median follow up of 436 days (range 20- 916 days) in surviving patients, the 6 month and 2 year overall survival (OS) were 77.2% (95% CI 59.4-87.9%) and 57.7 % (95% CI 37.6-73.4%), respectively (Figure 1). The 2-year OS for patients with intermediate risk and high/very high risk disease risk index (DRI) were 60% and 24%, respectively (p=0.07) (Figure 2).
Conclusions: Our preliminary results suggest that RIC haplo-HCT with TCRαβ and CD45RA+ depleted grafts allows successful allograft in high-risk patients lacking a suitable matched donor, including patients with high level of donor-specific HLA antibodies. Acute GVHD was generally abortive, leading to chronic GVHD in <5% of the patients. Fatal viral infection was not observed. Further efforts are needed to lower the risk of death due to bacterial infection, and also relapse in patients with high risk DRI, such as antibiotic prophylaxis or repeated doses of memory-cell DLI.

Disclosures
Leung: Miltenyi Biotec: Employment.