ABSTRACT:We evaluated long-term outcomes of 288 children with refractory-Langerhans cell histiocytosis (R-LCH) from 26 countries, who were prescribed off-label MAPK inhibitors (MAPKis) according to clinical indications. MAPKi indications included 148 R-risk-organ-positive (R-RO+), 67 R-risk-organ-negative (R-RO-), 13 lung destruction (lung), 9 sclerosing cholangitis (SC), 49 neurodegeneration (ND), and 2 diabetes insipidus (DI) cases. Median ages at diagnosis and MAPKi onset were 1.3 and 2.3 years, respectively, with median follow-up of 3.7 years (1166 person-years). Agents mostly prescribed as monotherapies were 184 prescriptions of vemurafenib, 115 of dabrafenib, 3 of encorafenib, 42 of cobimetinib, 45 of trametinib, and/or 1 prescription of binimetinib; followed 51 times by various chemotherapies or hematopoietic stem-cell transplantation, or 28 times by combined anti-BRAF-anti-MEK. Short-term responses (<8 weeks) ranged from 98% (R-RO+ and R-RO-), to 30% (lung) to none (ND, DI, and SC); although long-term lung and ND responses could be observed. Skin rash was the most frequent adverse event (∼55%), and 7 others included 1 case of cardiomyopathy and 6 of retinitis. Five developed MAPKi-unrelated tumors and 9 patients died. Five-year survival was 98%. After 113 patients with R-LCH discontinued MAPKi, 69 experienced disease reactivation. None of the various empirical maintenance therapies were able to prevent secondary reactivation. Among the 143 assessable patients without ND-LCH at MAPKi onset, 60 developed ND (45%, 5-year risk). MAPKis appeared to be safe and effective in children with R-RO+/RO-LCH, whereas other indications' responses were less frequent or occurred later. Further studies are needed to find effective maintenance-therapy approaches, particularly to prevent frequently observed secondary ND.

Allogeneic hematopoietic stem cell transplantation (HSCT) is an established therapy for many inborn errors of immunity (IEI). The indications for HSCT have expanded over the last decade. The study aimed to collect and analyze the data on HSCT activity in IEI in Russia. The data were collected from the Russian Primary Immunodeficiency Registry and complemented with information from five Russian pediatric transplant centers. Patients diagnosed with IEI by the age of 18 years and who received allogeneic HSCT by the end of 2020 were included. From 1997 to 2020, 454 patients with IEI received 514 allogeneic HSCT. The median number of HSCTs per year has risen from 3 in 1997–2009 to 60 in 2015-2020. The most common groups of IEI were immunodeficiency affecting cellular and humoral immunity (26

Langerhans cell histiocytosis (LCH) is a disorder with a variety of clinical signs. The most severe forms affect risk organs (RO). The established role of the BRAF V600E mutation in LCH led to a targeted approach. However, targeted therapy cannot cure the disease, and cessation leads to quick relapses. Here, we combined cytosine-arabinoside (Ara-C) and 2'-chlorodeoxyadenosine (2-CdA) with targeted therapy to achieve stable remission. Nineteen children were enrolled in the study: 13 were RO-positive (RO+) and 6 RO-negative (RO-). Five patients received the therapy upfront, whereas the other 14 received it as a second or third line. The protocol starts with 28 days of vemurafenib (20 mg/kg), which is followed by 3 courses of Ara-C and 2-CdA (100 mg/m2 every 12 h, 6 mg/m2 per day, days 1-5) with concomitant vemurafenib therapy. After that, vemurafenib therapy was stopped, and 3 courses of mono 2-CdA followed. All patients rapidly responded to vemurafenib: the median disease activity score decreased from 13 to 2 points in the RO+ group and from 4.5 to 0 points in the RO- group on day 28. All patients except 1 received complete protocol treatment, and 15 of them did not have disease progression. The 2-year reactivation/progression-free survival (RFS) for RO+ was 76.9% with a median follow-up of 21 months and 83.3% with a median follow-up of 29 months for RO-. Overall survival is 100%. Importantly, 1 patient experienced secondary myelodysplastic syndrome after 14 months from vemurafenib cessation. Our study demonstrates that combined vemurafenib plus 2-CdA and Ara-C is effective in a cohort of children with LCH, and the toxicity is manageable. This trial is registered at www.clinicaltrials.gov as NCT03585686.

Background: Secondary immunodeficiency in recipients after allogeneic hematopoietic stem cell transplantation (allo-HSCT) in the pediatric practice is often accompanied by bacterial and viral infections of the gastrointestinal tract (GIT), resistant to conventional therapy. Fecal microbiota transplantation (FMT) promotes intestinal recolonization and eradication of gastrointestinal symptoms. Clinical case description: A 2.5-year-old patient underwent allo-HSCT from a haploidentical related donor (father) as a part of the treatment of acute myeloid leukemia. A month after the last procedure, diarrhea (up to 10 times a day) and abdominal pain appeared. The astrovirus RNA and Clostridium difficile toxin A were detected in the feces. The FMT was prescribed. After two FMT procedures, the intestinal syndrome leveled out, and the tests for the astrovirus RNA and clostridial toxins were negative. The content of cholic and, in particular, deoxycholic acids, as well as their conjugates with glycine and taurine, in the feces increased; the acetic acid content increased with a simultaneous decrease in the level of propionic acid, which indicates the restoration of the intestinal microbiota’s functional potential. Conclusion: FMT contributes to the restoration of the normal intestinal microflora, the elimination of clostridial toxins, enteroinvasive E. coli and astrovirus infection in allo-HSCT recipients, as evidenced by the indicators of the intestinal microbiota activity, and can be used in allo-HSCT recipients with infections refractory to conventional therapy.

We report incidence and deep molecular characteristics of lineage switch in 182 pediatric patients affected by B-cell precursor acute lymphoblastic leukemia (BCP-ALL), who were treated with blinatumomab. We documented six cases of lineage switch that occurred after or during blinatumomab exposure. Therefore, lineage conversion was found in 17.4% of all resistance cases (4/27) and 3.2% of relapses (2/63). Half of patients switched completely from BCP-ALL to CD19-negative acute myeloid leukemia, others retained CD19-positive B-blasts and acquired an additional CD19-negative blast population: myeloid or unclassifiable. Five patients had KMT2A gene rearrangements; one had TCF3::ZNF384 translocation. The presented cases showed consistency of gene rearrangements and fusion transcripts across initially diagnosed leukemia and lineage switch. In two of six patients, the clonal architecture assessed by IG/TR gene rearrangements was stable, while in others, loss of clones or gain of new clones was noted. KMT2A-r patients demonstrated very few additional mutations, while in the TCF3::ZNF384 case, lineage switch was accompanied by a large set of additional mutations. The immunophenotype of an existing leukemia sometimes changes via different mechanisms and with different additional molecular changes. Careful investigation of all BM compartments together with all molecular –minimal residual disease studies can lead to reliable identification of lineage switch.