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Measurable residual disease (MRD) is a powerful prognostic factor in acute myeloid leukemia (AML). However, pre-treatment molecular predictors of immunophenotypic MRD clearance remain unclear. We analyzed a dataset of 211 patients with pre-treatment next-generation sequencing who received induction chemotherapy and had MRD assessed by serial immunophenotypic monitoring after induction, subsequent therapy, and allogeneic stem cell transplant (allo-SCT). Induction chemotherapy led to MRD- remission, MRD+ remission, and persistent disease in 35%, 27%, and 38% of patients, respectively. With subsequent therapy, 34% of patients with MRD+ and 26% of patients with persistent disease converted to MRD-. Mutations in CEBPA, NRAS, KRAS, and NPM1 predicted high rates of MRD- remission, while mutations in TP53, SF3B1, ASXL1, and RUNX1 and karyotypic abnormalities including inv (3), monosomy 5 or 7 predicted low rates of MRD- remission. Patients with fewer individual clones were more likely to achieve MRD- remission. Among 132 patients who underwent allo-SCT, outcomes were favorable whether patients achieved early MRD- after induction or later MRD- after subsequent therapy prior to allo-SCT. As MRD conversion with chemotherapy prior to allo-SCT is rarely achieved in patients with specific baseline mutational patterns and high clone numbers, upfront inclusion of these patients into clinical trials should be considered.

Adenovirus infection is a significant complication in paediatric AlloSCT recipients with a mortality rate for disseminated adenovirus that may exceed 80%. We sought to determine the incidence, risk factors, and associated outcomes of adenovirus infection in 123 consecutive paediatric AlloSCT recipients. Adenovirus was diagnosed by antigen detection or viral culture, and was defined by isolation of virus with presence of correlating clinical symptoms. The probability of developing adenovirus infection was 12.3% (CI(95) 6.0-18.6). There were no statistically significant differences in probability of adenovirus infection in univariate analysis of risk factors including donor source, use of ATG/Alemtuzumab, ≥ Grade II GVHD, among others (age, diagnosis, conditioning regimen). Probability of overall survival for patients that experienced adenovirus infection was 15.4% vs. 50% for those without adenovirus (P = 0.0286). In multivariate analysis, the most important risk factor for an increased risk of death was adenovirus infection [HR 3.15 (CI(95) 1.6-6.18) P = 0.0009]. In this series of paediatric AlloSCT recipients, the development of adenovirus infection was the leading multivariate predictor of treatment-related mortality. Enhanced surveillance with adenovirus PCR and identification of the risk factors associated with poor outcomes from adenovirus infection may identify patients that may benefit from pre-emptive therapeutic interventions including adenovirus-specific cellular immunotherapies.

Immune reconstitution appears to be delayed following myeloablative conditioning (MAC) and umbilical cord blood transplantation (UCBT) in paediatric recipients. Although reduced toxicity conditioning (RTC) versus MAC prior to allogeneic stem cell transplantation is associated with decreased transplant-related mortality, the effects of RTC versus MAC prior to UCBT on immune reconstitution and risk of graft-versus-host disease (GVHD) are unknown. In 88 consecutive paediatric recipients of UCBT, we assessed immune cell recovery and immunoglobulin reconstitution at days +100, 180 and 365 and analysed risk factors associated with acute and chronic GVHD. Immune cell subset recovery, immunoglobulin reconstitution, and the incidence of opportunistic infections did not differ significantly between MAC versus RTC groups. In a Cox model, MAC versus RTC recipients had significantly higher risk of grade II-IV acute GVHD [Hazard Ratio (HR) 6·1, P = 0·002] as did recipients of 4/6 vs. 5-6/6 HLA-matched UCBT (HR 3·1, P = 0·03), who also had significantly increased risk of chronic GVHD (HR 18·5, P = 0·04). In multivariate analyses, MAC versus RTC was furthermore associated with significantly increased transplant-related (Odds Ratio 26·8, P = 0·008) and overall mortality (HR = 4·1, P = 0·0001). The use of adoptive cellular immunotherapy to accelerate immune reconstitution and prevent and treat opportunistic infections and malignant relapse following UCBT warrants further investigation.