Fludarabine exposure predicts outcome after CD19 CAR T-cell therapy in children and young adults with acute leukemia.

The addition of fludarabine to cyclophosphamide as a lymphodepleting regimen prior to CD19 chimeric antigen receptor (CAR) T-cell therapy significantly improved outcomes in patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL). Fludarabine exposure, previously shown to be highly variable when dosing is based on body surface area (BSA), is a predictor for survival in allogeneic hematopoietic cell transplantation (allo-HCT). Hence, we hypothesized that an optimal exposure of fludarabine might be of clinical importance in CD19 CAR T-cell treatment. We examined the effect of cumulative fludarabine exposure during lymphodepletion, defined as concentration-time curve (AUC), on clinical outcome and lymphocyte kinetics. A retrospective analysis was conducted with data from 26 patients receiving tisagenlecleucel for r/r B-ALL. Exposure of fludarabine was shown to be a predictor for leukemia-free survival (LFS), B-cell aplasia, and CD19-positive relapse following CAR T-cell infusion. Minimal event probability was observed at a cumulative fludarabine AUCT0-∞ ≥14 mg*h/L, and underexposure was defined as an AUCT0-∞ <14 mg*h/L. In the underexposed group, the median LFS was 1.8 months, and the occurrence of CD19-positive relapse within 1 year was 100%, which was higher compared with the group with an AUCT0-∞ ≥14 mg*h/L (12.9 months; P < .001; and 27.4%; P = .0001, respectively). Furthermore, the duration of B-cell aplasia within 6 months was shorter in the underexposed group (77.3% vs 37.3%; P = .009). These results suggest that optimizing fludarabine exposure may have a relevant impact on LFS following CAR T-cell therapy, which needs to be validated in a prospective clinical trial.

Implementation of paediatric precision oncology into clinical practice: The Individualized Therapies for Children with cancer program 'iTHER'.

iTHER is a Dutch prospective national precision oncology program aiming to define tumour molecular profiles in children and adolescents with primary very high-risk, relapsed, or refractory paediatric tumours. Between April 2017 and April 2021, 302 samples from 253 patients were included. Comprehensive molecular profiling including low-coverage whole genome sequencing (lcWGS), whole exome sequencing (WES), RNA sequencing (RNA-seq), Affymetrix, and/or 850k methylation profiling was successfully performed for 226 samples with at least 20% tumour content. Germline pathogenic variants were identified in 16% of patients (35/219), of which 22 variants were judged causative for a cancer predisposition syndrome. At least one somatic alteration was detected in 204 (90.3%), and 185 (81.9%) were considered druggable, with clinical priority very high (6.1%), high (21.3%), moderate (26.0%), intermediate (36.1%), and borderline (10.5%) priority. iTHER led to revision or refinement of diagnosis in 8 patients (3.5%). Temporal heterogeneity was observed in paired samples of 15 patients, indicating the value of sequential analyses. Of 137 patients with follow-up beyond twelve months, 21 molecularly matched treatments were applied in 19 patients (13.9%), with clinical benefit in few. Most relevant barriers to not applying targeted therapies included poor performance status, as well as limited access to drugs within clinical trial. iTHER demonstrates the feasibility of comprehensive molecular profiling across all ages, tumour types and stages in paediatric cancers, informing of diagnostic, prognostic, and targetable alterations as well as reportable germline variants. Therefore, WES and RNA-seq is nowadays standard clinical care at the Princess Máxima Center for all children with cancer, including patients at primary diagnosis. Improved access to innovative treatments within biology-driven combination trials is required to ultimately improve survival.

Secondary antifungal prophylaxis in paediatric allogeneic haematopoietic stem cell recipients.

OBJECTIVES: Presumed or proven invasive pulmonary aspergillosis (IPA) is an important cause of infectious morbidity in patients with acute leukaemia. Although prior IPA is not a contraindication for subsequent allogeneic haematopoietic stem cell transplantation (HSCT), its management during granulocytopenia and immunosuppression remains challenging. PATIENTS AND METHODS: In the absence of an evidence-based approach, 11 adolescents (11-18 years) with acute leukaemia and a history of antecedent possible (4) or probable (7) IPA received liposomal amphotericin B (LAMB; 1 mg/kg once a day) from the start of the conditioning regimen until engraftment and ability to take oral medication, followed by oral voriconazole (200 mg twice a day) until the end of the at-risk period. Nine patients had a good partial response (>50% reduction in pulmonary infiltrates) and two had a complete response prior to HSCT. RESULTS: The median duration of intravenous treatment with LAMB was 30 days (range, 19-36), followed by a median of 152 days (range, 19-210) of oral voriconazole. LAMB was discontinued early in one patient and voriconazole was transiently or permanently discontinued due to adverse events/new contraindications in two and two patients, respectively. At +180 days post-transplant, eight patients were alive, six with complete, and one each with near complete and ongoing resolution of pulmonary infiltrates; all but one were in continuing haematological remission. Three patients had succumbed either to recurrent leukaemia (two) or refractory graft failure (one); whereas one of these patients had maintained a complete response, two died with secondary possible (one) or probable (one) IPA. Both patients had discontinued voriconazole early and developed IPA in lung areas involved during the primary episode. CONCLUSIONS: This prospective paediatric series supports the notion that secondary antifungal prophylaxis for possible or probable IPA can be safely achieved in allogeneic HSCT. In the absence of chronic graft-versus-host disease, breakthrough infection appeared to be associated with recurrent leukaemia/graft failure and shorter duration of post-engraftment prophylaxis.

Malignant stem cells in childhood acute lymphoblastic leukemia: the stem cell concept revisited.

We have recently shown that in childhood acute lymphoblastic leukemia (ALL) blasts at different stages of immunophenotypic maturation possess stem cell properties. Here, we discuss our results in the context of previous investigations of ALL stem cells and recent studies highlighting specific limitations of the xenotransplantation models for human hematopoietic cells. Leukemia-propagating stem cells in ALL may be more frequent than previously thought!