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Hematopoietic stem cell transplantation (HSCT) is a curative therapy for an increasing number of nonmalignant indications. Its use is restricted by severe transplant-related complications, including CMV infection; despite various prophylactic and therapeutic strategies, CMV reactivation has remarkable morbidity and mortality. The analysis included 94 children with nonmalignant disorder who underwent allogeneic HSCT in the Department of Pediatric Hematology, Oncology, and Bone Marrow Transplantation in Wrocław during years 2016–2020. Twenty-seven (29%) children presented with CMV infection, including ten (10/27; 37%) with high level CMV viremia (10,000 copies/mL). Six patients experienced subsequent CMV reactivation. The first-line ganciclovir-based (GCV) treatment was insufficient in 40% (11/27) of children. Overall survival (OS) was significantly lower in children with high CMV viremia compared to those with low levels/no CMV [1yrOS High CMV = 0.80 (95% CI 0.41–0.95) vs. 1yrOS others = 0.96 (95% CI 0.89–0.99)]. Similarly, patients with resistant and recurrent infections had greater risk of death. CMV reactivation at any level relevantly prolonged the hospital stay. CMV reactivation with high viremia load and resistant/recurrent CMV infections lead to a significant decrease in OS in children with nonmalignant disorders treated with HSCT. Our data proves there is an urgent need to introduce an effective anti-CMV prophylaxis in this cohort of patients. [ABSTRACT FROM AUTHOR]

It is estimated that millions of birds globally die due to collisions with glass surfaces. In order to reduce this mortality, it is essential to provide an objective assessment of the effectiveness of bird-friendly preventive methods. Several types of opaque films and stickers are available nowadays and can be highly effective in protecting birds from fatal collisions. However, by being visible to the human eye, they can affect the users' quality of view from within protected spaces. Products that take advantage of the birds' ability to see ultraviolet light seem to offset these impediments. This study determines if UV-reflective BirdShades film prevents birds from collisions with glass in natural environmental conditions. We monitored eight glass bus stops, where we had previously recorded high numbers of birds collisions. On four of them, we applied UV film, and the other four bus stops were used as control. A generalized additive mixed model showed a significant interaction between time (before vs. after) and film UV treatment (control vs. treated). Before the treatment, the number of collisions tended to be higher at treated bus shelters than control. However, this significantly changed after the treatment, suggesting that UV film reduces bird glass collision rate over 5-fold. Our study is the first worldwide that tested UV film on glass shelters and supports a conclusion that the UV film efficiently reduces the risk of bird collision. [ABSTRACT FROM AUTHOR]

Respiratory viral infections are known causes of mortality after allogeneic hematopoietic stem cell transplantation (HSCT). Here, we report a unique case of a child with viral pneumonia caused by coinfection with human metapneumovirus (MPV), respiratory syncytial virus (RSV), and SARS‐CoV‐2 after HSCT. A 9‐year‐old girl with acute lymphoblastic leukemia underwent allogeneic HSCT from a matched, unrelated donor. During the post‐transplant period, in profound leukopenia (below 10 leukocytes/µL), she was diagnosed with SARS‐CoV‐2, MPV, and RSV pneumonia and was treated with ribavirin and chloroquine. Before leukocyte recovery, the girl became asymptomatic, and SARS‐CoV‐2 and RSV clearance was achieved. The shedding of SARS‐CoV‐2 stopped before immune system recovery, and one may hypothesize that the lack of an inflammatory response might have been a contributing factor to the mild clinical course. Post‐transplant care in HSCT recipients with COVID‐19 infection is feasible in regular transplant units, provided the patient does not present with respiratory failure. Early and repeated testing for SARS‐CoV‐2 in post‐transplant patients with concomitant infection mitigation strategies should be considered in children after HSCT who develop fever, respiratory symptoms, and perhaps gastrointestinal symptoms to control the spread of COVID‐19 both in patients and in healthcare workers in hospital environments. Training of staff and the availability of personal protective equipment are crucial for containing SARS‐CoV‐2 infection. [ABSTRACT FROM AUTHOR]

Collisions with glass or glass-covered objects are an important source of bird mortality worldwide. In this study, we investigate bird-glass collision pattern with the help of novel method using marks left by birds on glass surfaces. We surveyed 85 glass bus shelters every 12 days over a year to evaluate which parts of glass surfaces have the highest risk of collision. Among 178 bird-glass collisions recorded only 3% took place within 10 cm from glass edge, although this glass band (i.e. 0–10 cm from edge) covers over 30% of the whole glass area, on average. More inner parts of glass (10–70 cm from glass edge) had collision frequency slightly higher than expected by their coverage or proportional to their coverage. Different collisions recorded at one glass seemed independent suggesting no spatial aggregations within single glass. This study is the first to demonstrate the non-random risk of bird collision in relation to position on the glass surface and may suggest that there is no need to implement mitigating measures, like visible markers placed on the glass, closer than 10 cm from the glass edge. [ABSTRACT FROM AUTHOR]

Allo‐HSCT is associated with life‐threatening complications. Therefore, a considerable number of patients require admission to a PICU. We evaluated the incidence and outcome of PICU admissions after allo‐HSCT in children, along with the potential factors influencing PICU survival. A retrospective chart review of 668 children who underwent first allo‐HSCT in the Department of Pediatric Hematology/Oncology and BMT in Wrocław during years 2005‐2017, particularly focusing on patients admitted to the PICU within 1‐year post‐HSCT. Fifty‐eight (8.7%) patients required 64 admissions to the PICU. Twenty‐four (41.5%) were discharged, and 34 (58.6%) patients died. Among the discharged patients, 6‐month survival was 66.7%. Compared with survivors, death cases were more likely to have required MV (31/34; 91.2% vs. 16/24; 66.7% P =.049), received more aggressive cardiac support (17/34; 50% vs. 2/24; 8.3% P =.002), and had a lower ANC on the last day of their PICU stay (P =.004). Five patients were successfully treated with NIV and survived longer than 6 months post‐discharge. The intensity of cardiac support and ANC on the last day of PICU treatment was independent factors influencing PICU survival. Children admitted to the PICU after allo‐HSCT have a high mortality rate. Mainly those who needed a more aggressive approach and had a lower ANC on the last day of treatment had a greater risk of death. While requiring MV is associated with decreased PICU survival, early implementation of NIV might be considered. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this nationwide study was to evaluate the characteristics of bacterial infections (BI), invasive fungal disease (IFD), and viral infections (VI) in pediatric patients with PID after allogeneic hematopoietic stem cell transplantation (allo‐HSCT). Patients and methods: In total, 114 HSCT recipients were enrolled into the study. At least one infectious complication (IC) was diagnosed in 60 (52.6%) patients aged 0.1‐17.7 years, that is, 59.5% with SCID and 49.4% with non‐SCID. Results: Among 60 HSCT recipients diagnosed with at least one IC, 188 episodes of infectious complications (EIC) were recorded, that is, 46.8% of BI, 41.5% of VI, and 11.7% of proven/probable IFD. According to PID and HSCT donor type, the incidence of EIC was comparable (P =.679). The localization of infections differed significantly due to PID type (P =.002). After each HSCT donor type, the most common site of infection was GI. Overall, BI caused by Gram‐positive strains (59.1%) were prevalent, especially Staphylococcaceae. The multidrug‐resistant (MDR) pathogens were diagnosed in 52.3%, especially ESBL + Enterobacteriaceae. The profile of VI was comparable for SCID and non‐SCID patients (P =.839). The incidence of IFD was comparable for each PID and HSCT donor type. Survival after infection was 91.5% and was comparable for PID and HSCT donor type. Conclusions: The rate of patients diagnosed with IC among pediatric PID‐HSCT recipients did not depend on PID type, but rather on HSCT donor type. The localization of IC depended on PID and HSCT donor type. Within bacterial infections, predominated Gram‐positive strains and the MDR pathogens were responsible for more than half of EIC. [ABSTRACT FROM AUTHOR]

Background. Hepatic veno-occlusive disease (VOD) is a life-threatening complication following hematopoietic stem cell transplantation (HSCT) and associated with a high mortality rate. Therefore, accurate and immediate diagnosis is crucial for implementing appropriate treatment. Objectives. In our single-center retrospective study, we assessed the accuracy of the Modified Seattle Criteria in children and adolescents undergoing HSCT, and compared them to the diagnostic criteria recently established by the European Society for Blood and Marrow Transplantation (EBMT). Material and methods. Retrospective analysis of medical records of 951 HSCT procedures performed in 850 children and young adults in the years 2001-2015 in the Department of Pediatric Hematology, Oncology and Bone Marrow Transplantation of Wroclaw Medical University Supraregional Center of Pediatric Oncology "Cape of Hope" in Wrocław, Poland. Results. Among the 850 children, 48 were diagnosed with VOD according to the Modified Seattle Criteria (5.05%). Thirteen patients (27%) developed VOD later than within 20 days after transplantation, as required in the diagnostic criteria. Five of the 6 patients who died from VOD were diagnosed with late-onset VOD. Using the categories of symptoms described in the Modified Seattle Criteria, hepatomegaly and weight gain were the most common symptoms in the analyzed cohort (81.25% and 68.75%). Fourteen patients (29%) never demonstrated elevated plasma bilirubin level (>2 mg/dL), as suggested in the Modified Seattle Criteria. Twenty-nine patients (64%) had increased platelet consumption requiring daily transfusions. Only 5 patients with decreased plasma antithrombin III (ATIII) activity level (<80%) on the day of HSCT developed VOD despite supplementation of ATIII. Conclusions. The Modified Seattle Criteria seemed to not meet the special needs of the pediatric population. The new diagnostic criteria proposed by the EBMT appear to be more adequately tailored to the pediatric population and may significantly change the conception of VOD in the future. The surprisingly low incidence of VOD in our cohort may suggest a beneficial role of monitoring and early supplementation of ATIII. [ABSTRACT FROM AUTHOR]

Background. Acute graft-versus-host disease (aGvHD) is a potentially fatal complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Identifying its risk factors would enable the proper prophylaxis and management, which may significantly improve the general outcome of children treated with HSCT. Objectives. The aim of this single-center, retrospective cohort study was to assess the potential risk factors for grades II-IV of aGvHD in children after the 1st allo-HSCT from an unrelated donor (UD), performed as a result of an underlying malignant disease. Material and methods. From among patients who received HSCT in our center in the years 2004-2015, 237 were included in the study cohort. All the patients received standard aGvHD prophylaxis consisting of cyclosporine (CsA) and a short course of methotrexate (MTX). Various clinical and epidemiological features, the transplant proceedings, graft composition, conditioning regimens, as well as the duration and coherence of aGvHD prophylaxis were analyzed as potential risk factors for aGvHD. Results. The incidence of II-IV aGvHD in the study cohort was 58.6%. The median time of the diagnosis of aGvHD was 18 days post-HSCT. In the multivariate analysis, risk factors significantly associated with grades II-IV of aGvHD were: myeloablative conditioning regimen containing total body irradiation (TBI-MAC) (RR (relative risk): 1.69; p = 0.03), premature termination of CsA administration due to its toxicity (RR: 1.99; p = 0.0003) and HSCT performed before the year 2009 (RR: 1.97; p = 0.0001). Donor and recipient age, donor-recipient sex mismatch, stem cell source, risk of disease, and amount of infused CD34+ cells seem to be insignificant as risk factors for aGvHD. The overall survival (OS) of patients with aGvHD was noticeably worse that in those who were aGvHD-free: 60.8% vs 74.1% (p = 0.08). Conclusions. The conditioning regimen and the proper aGvHD prophylaxis, including continuous CsA administration, have a major impact on aGvHD occurrence. According to our results, the termination of CsA therapy should be carefully considered, and avoided if possible. [ABSTRACT FROM AUTHOR]

Background. Unmanipulated haploidentical stem cell transplantation (haploSCT) with post-transplant cyclophosphamide is an option for patients with advanced hematologic malignancies. It offers a platform both for non-major histocompatibility complex-restricted alloimmunity due to killer-like immunoglobulin receptor (KIR)-mediated mechanisms of natural killer lymphocyte regulation and for classical T-cell mediated antileukemic effects. Objectives. The devastating long-term sequelae after total body irradiation (TBI) in children are encouraging omission of irradiation techniques in pediatric stem cell transplantations (SCT). Material and methods. Five children, 4 with acute leukemia and 1 with hemophagocytic lymphohistiocytosis, aged from 1 to 10 years, underwent haploSCT with post-transplantation cyclophosphamide. In all children, the conditioning regimen consisted of chemotherapy without TBI. The graft material was bone marrow (BM) in 4 cases and peripheral blood stem cells in 1 case. Three out of 5 leukemic patients showed better KIR haplotype associated with augmented alloreactivity. Results. Engraftment with complete donor chimerism was achieved in 4 patients, and 1 recipient died before leukocyte recovery. Three patients developed skin acute graft-versus-host-disease (aGvHD), 1 gut aGvHD and 1 liver aGvHD. In 2 recipients, chronic graft-versus-host-disease (cGvHD) was observed (1 limited and 1 extensive). The 4 engrafted patients were alive and in complete remission 3, 9, 32, and 36 months after transplantation. A T-cell count of 200 cells/uL was reached 90 days after haploSCT in all patients. Conclusions. HaploSCT with TBI-free protocols can be a viable option for heavily pretreated patients with advanced malignancies. [ABSTRACT FROM AUTHOR]

The article presents the discussion on CAR-T cell therapy being a groundbreaking treatment launching a new era in the treatment of hematological malignancies penetrating tissues, self-activate, amplify, eliminating neoplastic cells, and act long-term.

Krabbe disease (KD) is a lysosomal storage disorder, caused by a deficiency of galactocerebrosidase (GALC) or a mutation in the prosaposin gene, which leads to psychosine accumulation. Consequently, demyelination and degradation of the nervous system occur. Newborns with early infantile Krabbe disease usually present with poor feeding, irritability, hypertonicity, deafness and visual impairment. They usually die, unless transplanted with hematopoietic stem cells (HSC) during the 1st month of life. Patients with late form KD have heterogeneous symptoms, like ataxia or spastic paresis followed by slow progression. Therapeutic options are limited and hematopoietic stem cell transplantation (HSCT) remains the only life-saving method. In this report, we describe the first HSCT in late-infantile Krabbe disease in Poland. The post-transplant period was complicated by graft versus host disease (GvHD), veno-occlusive disease (VOD), mucositis and impairment of renal function. The 5-year follow-up was uneventful, confirming clinical efficacy of the HSCT. [ABSTRACT FROM AUTHOR]

Bark stripping behaviour of bears, which may significantly reduce the value of timber, has been reported mostly from North America and Japan, but in recent decades also from Europe. We surveyed forest plots in the Bieszczady Mountains of southeast Poland and recorded bark stripping by brown bears. We distinguished two types of tree damage by brown bears - damage to single (since no other damaged trees were found in their vicinity) and groups of trees (when five or more damaged trees were found in a small area). We found that all wound parameters, but especially the wound area and the proportion of the trunk with missing bark, were greater on single damaged trees. Comparison of damaged and control tree plots (1000m²) revealed that bears foraged in stands where silver firs (Abies alba Mill.) with larger circumferences were present. Moreover, in stands where damage occurred, bears tended to strip large trees. The preference ratio index clearly showed that bears mostly preferred to forage on firs with circumferences in the 120-180 cm range, even though a wide spectrum of tree circumferences were available. Our results suggest that the brown bear should not be viewed as a pest species in commercial tree stands in Poland. The trees preferred by bears for foraging are large enough for timber production. To minimize economical losses, forestry personnel should regularly monitor tree stands that consist of trees of dimensions preferred by bears. [ABSTRACT FROM AUTHOR]

Background. Management of febrile neutropenia in pediatric patients is challenging. Chest X-ray and CT scan help to identify infective foci; however, exposure to radiation is a risk factor for development of secondary cancer. For this reason, attention is paid to reducing radiation exposure. Objectives. The aim of the study was to define the role of LDCT examination in the early detection of pulmonary lesions in children during oncology or autoimmune treatment complicated by neutropenia-related fever. Additionally, we focused on the possibility to optimize image quality in low-dose protocols. Material and methods. The study included 138 pediatric patients (mean age 8.08 years) with fever of 38.2°C or higher with an absolute neutrophil count of 10 mm with or without surrounding GGO or cavitations was sensitive at 77% and specific at 65% for fungal infection insert after neutrophil count: < 500/pL who underwent chest X-ray and LDCT in the maximal interval of 24 h. CT findings were compared with initial and final diagnosis as well as with clinical information. Results. LDCT detected pulmonary abnormalities in 116 patients (84.06%) showing ground-glass opacities (GGO) (n = 79), nodules (n = 60) and air-space consolidations (n = 58). Radiologists correctly diagnosed infective lesions in 94 out of 116 patients (81.03%). The presence of random or pleural-based nodules. Diagnosis of pyogenic infection based on the presence of air-space consolidation, pleural effusion, GGO or centrilobular nodules showed a sensitivity of 78% and specificity of 67%, whereas patchy or diffuse GGO, interstitial thickening and/or air-space consolidation showed a high sensitivity of 81% and specificity of 68% for Pneumocystis jirovecii pneumonia. Conclusions. LDCT is an excellent modality in the diagnostic algorithm in patients with febrile neutropenia. It allows early detection and detailed characterization of pulmonary abnormalities. Using contrast, unenhanced CT examinations can further reduce radiation dose and diminish the number of complications without a negative influence on the diagnostic process. [ABSTRACT FROM AUTHOR]

Severe aplastic anemia (SAA) is a bone marrow failure syndrome that can be treated with hematopoietic cell transplantation (HCT) or immunosuppressive (IS) therapy. A retrospective cohort of 56 children with SAA undergoing transplantation with fludarabine–cyclophosphamide–ATG-based conditioning (FluCyATG) was analyzed. The endpoints were overall survival (OS), event-free survival (EFS), cumulative incidence (CI) of graft versus host disease (GVHD) and CI of viral replication. Engraftment was achieved in 53/56 patients, and four patients died (two due to fungal infection, and two of neuroinfection). The median time to neutrophil engraftment was 14 days and to platelet engraftment was 16 days, and median donor chimerism was above 98%. The overall incidence of acute GVHD was 41.5%, and that of grade III-IV acute GVHD was 14.3%. Chronic GVHD was diagnosed in 14.2% of children. The probability of 2-year GVHD-free survival was 76.1%. In the univariate analysis, a higher dose of cyclophosphamide and previous IS therapy were significant risk factors for worse overall survival. Episodes of viral replication occurred in 33/56 (58.9%) patients, but did not influence OS. The main advantages of FluCyATG include early engraftment with a very high level of donor chimerism, high overall survival and a low risk of viral replication after HCT. [ABSTRACT FROM AUTHOR]

Background: The objective of the study was to analyze the profile of infections in children with BMF following alloHCT. Methods: Data of 169 consecutive children with inherited and acquired BMF treated with alloHCT between 2012 and 2017 in Polish pediatric transplant departments were analyzed in registry‐based retrospective study, with respect to the type of infection, and clinical outcome. Results: At least 1 infection was diagnosed in 107/169 patients (60.4%). In total, 182 infections were diagnosed. The most common were VI (96; 52.7%), followed by BI (71; 39.0%), and FI (15; 8.2%), P < .001. The most common etiological factors of VI were as follows: CMV (38.5%), EBV (22.9%), and BK virus (24%); while of BI were as follows: Staphylococcus spp. (17; 23.9%), Enterococcus faecium (10; 14.1%), and Klebsiella pneumoniae (9; 12.7%). No difference was found between the occurrence of infections with respect to donor type, graft source, and conditioning type. GvHD had no impact on the incidence of VI, BI, and FI. Fifteen FI were diagnosed in 12 patients, of which 14 FI were diagnosed in children transplanted for FA. Of total 107 children, 9 died (8.4%), of which 4 (3.7%) due to infections: bacterial sepsis (2) and invasive FI (2). Conclusion: Infections in children with BMF following alloHCT remain an important cause of morbidity. Children with FA had high incidence of FI. In our analysis, aGvHD had no impact on the occurrence on infections, although the study was not strong enough to prove such a difference. [ABSTRACT FROM AUTHOR]

The optimal bridging therapy before CAR-T cell infusion in pediatric relapsed or refractory B-cell precursor acute lymphoblastic leukemia (r/r BCP-ALL) still remains an open question. The administration of blinatumomab prior to CAR-T therapy is controversial since a potential loss of CD19+ target cells may negatively impact the activation, persistence, and, as a consequence, the efficacy of subsequently used CAR-T cells. Here, we report a single-center experience in seven children with chemorefractory BCP-ALL treated with blinatumomab before CAR-T cell therapy either to reduce disease burden before apheresis (six patients) or as a bridging therapy (two patients). All patients responded to blinatumomab except one. At the time of CAR-T cell infusion, all patients were in cytological complete remission (CR). Four patients had low positive PCR-MRD, and the remaining three were MRD-negative. All patients remained in CR at day +28 after CAR-T infusion, and six out of seven patients were MRD-negative. With a median follow-up of 497 days, four patients remain in CR and MRD-negative. Three children relapsed with CD19 negative disease: two of them died, and one, who previously did not respond to blinatumomab, was successfully rescued by stem cell transplant. To conclude, blinatumomab can effectively lower disease burden with fewer side effects than standard chemotherapeutics. Therefore, it may be a valid option for patients with high-disease burden prior to CAR-T cell therapy without clear evidence of compromising efficacy; however, further investigations are necessary.

Introduction: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a treatment method for a wide range of malignant and non-malignant diseases. Infants constitute a distinct patient group, especially due to their organ immaturity and differences in drug metabolism. The present paper aims to analyse the short- and long-term outcomes after allo-HSCT in infants., Material and Methods: In the study period, 67 patients under 12 months of age underwent allo-HSCT. This study is a retrospective analysis of patient medical records, in the form of paper and electronic documentation., Results: The probability of 5-year OS was 69% and 72% in patients with malignant and non-malignant diseases, respectively. The allo-HSCT from a matched donor was associated with improved OS in comparison to haploidentical donor (0.8 vs. 0.58%, p = 0.0425). The overall incidence of acute graft-vs.-host disease (aGVHD) was 59.3%, and grade III-IV aGVHD was diagnosed in 23% of patients. The 100-day non-relapse mortality (NRM) in the study cohort was 17.9%, while the 5-year NRM was 26.9%. Among the causes of NRM, infections occurred in 83.3% of patients, and aGVHD in 16.3% of individuals. Twenty-two children (32.8%) required hospitalization in the pediatric intensive care unit (PICU). The median length of PICU hospitalization was 6 days (range 1 to 12 days). Late sequelae diagnosed during post-transplant surveillance included ocular disorders in 26.8% of patients, cardiac complications in 4.4%, as well as endocrinopathy with short stature (<3rd percentile) in 37.2% and overt hypothyroidism in 35.4%. In the long-term perspective, 83.3% of survivors were able to attend a regular school., Conclusions: Improvements in unrelated donor availability, and better supportive care resulted in better outcomes. Management of infant allo-HSCT recipients requires the formation of multi-disciplinary specialist teams. In addition, the role of parental empowerment must be acknowledged; for example, in speech therapy and rehabilitation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Miśkiewicz-Bujna, Miśkiewicz-Migoń, Szmit, Przystupski, Rosa, Król, Kałwak, Ussowicz and Gorczyńska.)

We report a child with Fanconi anemia who, after hematopoietic stem cell transplantation (HSCT) complicated by acute graft-versus-host disease (GVHD), underwent orthotopic liver transplantation (OLT). Approximately 1 month after OLT, the presence of third-party genetic material from the liver donor was noted and in the next few weeks, the chimerism assessment revealed 100% liver donor leukocytes in the peripheral blood. The rapidly progressing GVHD with gut involvement resulted in patient's death 6 months after OLT. The liver can act as a clinically significant source of hematopoietic stem cells, and the liver donor's young age must be emphasized as potentially predisposing to this phenomenon. Transfer of OLT hematopoietic stem cells may not have clinical significance unless the patient is not immunocompetent or develops liver-transplantation associated GVHD, that can result in lymphocyte mediated elimination of original hematopoiesis. Patients with preexisting immunity disorder (such as primary or secondary immunodeficiency) might require intensified immunosuppressive therapy in peritransplant period as a prevention of liver-transplantation associated GVHD. Close monitoring of hematopoietic chimerism after OLT is warranted in patients at risk, because cytopenia or OLT hematopoiesis can reflect subclinical GVHD and further studies are necessary to elucidate this phenomenon., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Jarmoliński, Rosa, Rybka, Ryczan-Krawczyk, Gajek, Bogunia-Kubik, Klaudel-Dreszler, Czubkowski, Kaliciński, Teisseyre, Stefanowicz, Gorczyńska, Kałwak and Ussowicz.)

Adoptive immunotherapy with interleukin-2 (IL-2) may control minimal residual disease (MRD) and prevent relapse after autologous hematopoietic cell transplantation (AHCT). The objective of this study was to determine the immunologic effects of intermediate doses of intravenous (i.v.) IL-2 after AHCT in children with poor-prognosis solid tumors. Eleven patients received a median five cycles consisting of escalating doses of IL-2 i.v. for 5 days after a median time interval of 94 days post-AHCT. The phenotype of lymphocyte subsets was investigated before and after each cycle, and parallel determination of natural killer (NK) cell activity was performed. Immunotherapy induced a significant increase in total lymphocyte count (TLC), T, NK, and, to some extent, B cells. Among NK cells, CD56+ bright cells expanded more than CD56+ dim cells. High expansion of CD56+ cells with CD94 inhibitory receptor was observed, whereas no difference was recorded in the number of CD3+ CD56+ and CD8+ CD57+ cells. NK activity stabilized after the first cycle of IL-2 and remained elevated during the study period. Cycles of IL-2 immunotherapy induced repeated significant expansion of T cells and NK cells, mostly of the immature CD56+ bright phenotype. Despite enhanced NK activity, relapses occurred frequently, which might have been due to increased CD94 activation and a poor response from the cytotoxic NK T cells and CD8+ CD57+ T cells.