Allogeneic hematopoietic cell transplant for bone marrow failure or myelodysplastic syndrome in dyskeratosis congenita/telomere biology disorders: Single-center single-arm open-label trial of reduced intensity conditioning without radiation.

BACKGROUND:Dyskeratosis congenita/Telomere biology disorders (DC/TBD) often manifest as bone marrow failure (BMF) or myelodysplastic syndrome (MDS). Allogeneic hematopoietic cell transplant (alloHCT) rescues hematologic complications, but radiation and alkylator-based conditioning regimens cause diffuse whole-body toxicity and may expedite DC/TBD-specific non-hematopoietic complications. Optimization of conditioning intensity in DC/TBD to allow for donor hematopoietic cell engraftment with the least amount of toxicity remains a critical goal of the alloHCT field. OBJECTIVES/STUDY DESIGN:We report prospectively collected standard alloHCT outcomes from a single-center single-arm open-label clinical trial of bone marrow or peripheral blood stem cell alloHCT for DC/TBD-associated BMF or MDS. Conditioning was reduced intensity (RIC) including alemtuzumab 1mg/kg, fludarabine 200 mg/m2, and cyclophosphamide 50 mg/kg. A previous single-arm open-label phase II clinical trial for the same patient population conducted at the same center, differing only by inclusion of 200 centigray of total body irradiation (TBI), served as a control cohort. RESULTS:The Non-TBI cohort included 10 patients (ages 1.7-65.9 years, median follow-up of 3.9 years) compared to the control TBI cohort which included 12 patients (ages 2.2-52.2 years, median follow-up of 10.5 years). Baseline characteristics differed only in total CD34+ cells received, with a median of 5.6 (Non-TBI) compared to 2.6 (TBI) x 106/kg (p=0.02; no difference in total nucleated cells). The cumulative incidence of day +100 grade II-IV acute and 4-year chronic graft-versus-host disease (GvHD) were low at 0 and 10% (Non-TBI) and 8 and 17% (TBI), respectively (acute, p=0.36; chronic, p=0.72). Primary graft failure was absent. Secondary non-neutropenic graft failure occurred in one (Non-TBI cohort). The Non-TBI cohort demonstrated delayed achievement of full donor chimerism but superior lymphocyte recovery. There was no difference in 4-year overall survival at 80% (Non-TBI) and 75% (TBI; p=0.78). MDS as an indication for alloHCT was uncommon, but overall associated with poor outcomes. There were 3 MDS patients in the Non-TBI cohort: 1 relapsed and died at day+387; 1 relapsed at day+500 and is alive 5.5 years later following salvage with a 2nd alloHCT; 1 relapsed at day+1093 and is alive at day +100 after a 2nd alloHCT. There was 1 MDS patient in the TBI cohort who achieved 100% donor myeloid engraftment without relapse but died at day+827 from a bacterial infection in the setting of immune mediated cytopenia. CONCLUSION:Elimination of TBI from the RIC regimen for DC/TBD was not associated with significant changes in rates of graft failure, GvHD, and overall survival, but was associated with delayed achievement of full donor chimerism and improved lymphocyte reconstitution. For DC/TBD-associated BMF, TBI appears to be dispensable. Optimal approaches to DC/TBD-associated MDS remain unclear. Larger cohorts are needed to better assess the unique contribution of TBI and donor CD34+ cell dose. Longer follow-up is required to assess differences in DC/TBD complications and late effects.