Haploidentical Stem Cell Transplantation for Children with High-Risk Leukemia In Chile: Report of the First 15 Cases.

Abstract 4581

The Chilean population is ethnically diverse, and more than 50% of the children referred for hematopoietic stem cell transplantation lack a suitable donor. To expand the donor pool we assessed the feasibility, tolerance, and efficacy of using a parental haploidentical (HI) donor and a reduced-intensity conditioning regimen for patients with high-risk leukemia; this study was preceded by 2 years of technology transfer from St. Jude Children's Research Hospital. Between March 2006 and November 2009 fifteen patients (median age, 9.6 years) received T cell-depleted grafts at Calvo Mackenna Hospital, from peripheral stem cells mobilized with G-CSF from parental donors. N° aphaeresis/patient = one; 6/15 products required a second depletion, final Log of depletion= 3, 11 (5, 05-1, 64). Median cell doses were CD34+: 9.5 × 10⁶ cells/kg (range, 2.13 – 20.0), CD3+: 1.0 ×10⁵cells/kg (0.11 – 1.59), and CD56+: 67, 9 × 10⁶cells/kg (7, 6–131, 8). 14/15 patients engrafted one1^ry primary engraftment failure and in 2 cases a 2^ry engraftment failure (CMV and Toxoplasmosis treatment). Eight remain alive and clinically well at a median follow up of 12.4 months post-transplant (7.2 – 52.2). Four patients died after bone marrow relapse, while only one died of transplant-related causes. Virus reactivation was the main post-transplant complication: 9/15 had positive CMV PCR but none had CMV disease. One patient developed acute GvHD > grade II and one had chronic GvHD. In this setting, HI transplantation offers a rational option for children who lack suitable stem cell donors. This information is especially relevant for populations that are poorly represented in international donor registries. On the other hand HISCT with RIC with ATG and TNI permits a good OS and EFS in this especially high risk population low TRM. This approach is associated with low incidence of GvHD and high viral reactivation incidence but no lethal infection even without CD3+ lymphocyte recovery due probably to pre-emptive treatment and fast NK cell recovery.