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<p>Most children who may benefit from stem cell transplantation lack matched related donors. Alternative donor transplantations with unrelated (URD) or partially matched related donors (PMRD) carry increased risks of graft-versus-host-disease (GVHD) and mortality compared to matched related donor transplants. We hypothesized a strategy of partial CD3/CD19-depletion for URD or PMRD peripheral stem cell transplantation (PSCT) would attenuate risks of GVHD and mortality. We enrolled 84 pediatric patients with hematologic malignancies at the Children's Hospital of Philadelphia and the Children's Hospital of Wisconsin between April 2005 and February 2015 (NCT00579124: https://clinicaltrials.gov/ct2/show/NCT00579124; NCT01071226: https://clinicaltrials.gov/ct2/show/NCT01071226). Two (2.4%) experienced primary graft failure. Relapse occurred in 23 patients (27.4%; cumulative incidence 26.3%), and 17 patients (20.2%) experienced non-relapse mortality (NRM). Grade III-IV acute GVHD was observed in 18 patients (21.4%), and chronic GVHD was observed and graded as limited in 24 (35.3%) and extensive in 8 (11.7%). Three-year OS was 61.8% (95% CI 50.2 -71.4%) and EFS 52.0% (95% CI 40.3 - 62.4%). Age ≥15 years was associated with decreased OS (p=0.05) and EFS (p=0.05). Relapse was more common in children in second complete remission (p=0.03). Partially CD3-depleted alternative donor PSCT NRM, OS, and EFS compare favorably with previously published studies of T cell-replete PSCT. Historically, T cell-replete PSCTs have had a high ratio of extensive compared to limited chronic GVHD, which may explain the comparatively low relapse and NRM rates in our study despite similar overall rates of chronic GVHD. Partial T cell-depletion may expand donor options for children with malignant transplant indications lacking matched related donors by mitigating but not eliminating chronic GVHD.</p>