Background Post-transplant cyclophosphamide (Pt-Cy) was a breakthrough in achieving immune tolerance after HSCT. Nevertheless, time to engraftment, GvHD, GvL effect, toxicity, and immune reconstitution are not yet optimal and can be improved. Evidence suggests that post-transplant bendamustine (Pt-Ben) can decrease GvHD and preserve GvL effect. Here we compare two GvHD prophylaxis platforms related to engraftment, GvHD, viral infections, lymphocyte recovery, and one-year non-relapse mortality (1y-NRM) in pediatric HSCT. Methods On Sept/2016 we introduced Pt-Ben to our standard Pt-Cy 50mg/kg/dose; days +3 and +4/Sirolimus aGvHD prophylaxis. The new protocol included Pt-Cy 50mg/kg/dose; day +3, Pt-Ben 200mg/m2/dose; day +4, and CSA starting on day +5. In both cohorts, we used low-dose methotrexate (MTX) in a subgroup of patients. We started G-CSF at day +10, and used rATG mainly for RIC transplants. We preferred PBSC as the cell source for donors >10 years of age. We compared Pt-Cy/Ben/csa cohort (39 cases; Sept/2016-June/2018) with Pt-Cy/sirolimus historical cohort (63 cases; Jan/2013-Aug/2016). We included all patients receiving one of the two protocols, except for Fanconi anemia patients (6 cases). We use non-parametric statistics to compare the median time of cell recovery. We used cumulative hazards to estimate 1y-NRM. We carried-out Cox's multivariate regression models (clustered by number of transplants/subject) to adjust hazard ratios (HR) by the following covariates: recipients age, sex, diagnosis, CMV status, MTX, ATG, TBI, conditioning intensity, infused CD34+ and total nucleated cells, haploidentical graft, donors age, and sex. Results Table 1 presents recipients, graft and donors characteristics by group. Table 2 shows frequencies of GvHD, viral infections, the median time to engraftment, and +30-day lymphocyte recovery. Acute GvHD II-IV was more frequent in the Pt-Cy/Ben/csa group, but III-IV was the same in both groups. The frequency of hemorrhagic cystitis was about half in the Pt-Cy/Ben/csa group compared to the other. Median time to blood cell recovery was faster in the Pt-Cy/Ben/csa group, particularly of platelet counts (11 vs. 20 days; P Conclusions GvHD prophylaxis with Pt-Cy/Ben/csa decreased by 3-times 1y-NRM, proved superior to Pt-Cy/sirolimus in engraftment and NK cell 30-day recovery. Although the historical cohort comparison is not absent of various biases, the association was robust after adjusting for many potential confounders. We consider that this novel strategy deserves further research in larger and better-designed studies.