Adolescent gender dysphoria management: position paper from the Italian Academy of Pediatrics, the Italian Society of Pediatrics, the Italian Society for Pediatric Endocrinology and Diabetes, the Italian Society of Adolescent Medicine and the Italian Society of Child and Adolescent Neuropsychiatry.

BACKGROUND: In response to the imperative need for standardized support for adolescent Gender Dysphoria (GD), the Italian Academy of Pediatrics, in collaboration with the Italian Society of Pediatrics, the Italian Society for Pediatric Endocrinology and Diabetes, Italian Society of Adolescent Medicine and Italian Society of Child and Adolescent Neuropsychiatry is drafting a position paper. The purpose of this paper is to convey the author's opinion on the topic, offering foundational information on potential aspects of gender-affirming care and emphasizing the care and protection of children and adolescents with GD. MAIN BODY: Recognizing that adolescents may choose interventions based on their unique needs and goals and understanding that every individual within this group has a distinct trajectory, it is crucial to ensure that each one is welcomed and supported. The approach to managing individuals with GD is a multi-stage process involving a multidisciplinary team throughout all phases. Decisions regarding treatment should be reached collaboratively by healthcare professionals and the family, while considering the unique needs and circumstances of the individual and be guided by scientific evidence rather than biases or ideologies. Politicians and high court judges should address discrimination based on gender identity in legislation and support service development that aligns with the needs of young people. It is essential to establish accredited multidisciplinary centers equipped with the requisite skills and experience to effectively manage adolescents with GD, thereby ensuring the delivery of high-quality care. CONCLUSION: Maintaining an evidence-based approach is essential to safeguard the well-being of transgender and gender diverse adolescents.

Disseminated Mycobacterial Infection With Reactive Polyarthritis (Poncet's Disease) During Immune-suppressive Treatment Including Ustekinumab for Pediatric Crohn's Disease.

BACKGROUND: The incidence of pediatric inflammatory bowel disease is increasing. tumor necrosis factor alpha inhibitors medicines improved the prognosis of affected subjects. Nonetheless, a proportion of patients do not respond or lose response to treatment. Newer biologics, like ustekinumab, have been approved for adults. The pediatric off-label use of these drugs is increasing, despite limited safety evidence. We report a case of disseminated mycobacterial infection (MI) presenting with reactive polyarthritis (Poncet's disease, PD) in a girl with Crohn's disease receiving various immunosuppressants, including ustekinumab. CASE REPORT: A 12-year-old girl with Crohn's disease was admitted for acute-onset migratory polyarthritis of large and small joints and opioid-resistant pain. She had recently received adalimumab and methotrexate and was currently under treatment with ustekinumab. She was vaccinated with Bacillus Calmette-Guérin and screened for tuberculosis before starting immunosuppressants. Interferon-gamma release assay, Mantoux test and chest computed tomography scan were negative. Disseminated MI with PD was diagnosed following positive cultures for Mycobacterium tuberculosis complex in blood and intestinal biopsies (with negative in synovial fluid and gastric aspirate). Whole-exome sequencing did not identify any genetic susceptibility to MI. Antituberculosis treatment eradicated MI. CONCLUSIONS: Children with inflammatory bowel disease receiving combination immunosuppressive treatments including tumor necrosis factor alpha inhibitors and anti-IL-12/23 agents are at higher risk for MI. Disseminated MI should be considered and ruled out in these patients when presenting with pulmonary, extrapulmonary or unusual clinical manifestations, like PD. The collection of multiple specimens (including intestinal biopsies) for mycobacterial culture is recommended when mycobacterial disease is suspected.

Nurturing the next generation of pediatric physician scientists: the Padova Physician Scientist Research Training for pediatric residents.

Less than 2% of physicians complete a research training (PhD) after the residency with a declining trend in those pursuing a clinical scientist pathway in pediatrics. The exposure to research methodology during the clinical training may play a role in engaging the next generations of pediatric physician scientist. Herein, we describe the experience of the Padova Physician Scientist Research Training (PPSRT) of the pediatric residency program at the University of Padova. The PPSRT was addressed to residents attending PGY2 to PGY4 of the pediatric program and consisted of two cores: a general one including in person or virtual lectures about research methodology in pediatrics including design of a clinical trial, writing of a scientific paper and statistical methods, and a subspecialties core for the discussion of research challenges in each area and the scientific writing activities. The perceived barriers to a research training and an evaluation of the program were assessed by an anonymized questionnaire. Sixty-four out 150 residents registered for the research training with 62/64 completing the two cores. The major perceived barrier to research during clinical training was the absence of protected time (89%) followed by the lack of specific funds (37%). The group activities lead to the publication of 24 papers.    Conclusion: This is the first experience in the Italian pediatric training of a dedicated research program within the frame of postgraduate medical education. Our report highlights the need for protected time to promote research interest and nurture a new generation of physician scientists. What is Known: • Training to medical research is not part of residency program. • The declining trend of physician scientists might be reverted by early exposure to research methodology and challenges during residency. What is New: • An early exposure to research training during pediatric residency increases the research engagement of pediatric residents. • The lack of protected time for research is perceived as the major barrier to research training during residency.

Present and future are getting confused: are we equipped to face the technological revolution?

BACKGROUND: This is a commentary reporting the outcome of a workshop promoted by the Department of Woman's and Child's Health of the University of Padua (Italy) focused on the emerging issue of what seems to be the increasing agemone role of technology. MAIN BODY: Over the centuries, technology has always been at the service of science, with theoretical insights anticipating experimental proofs. Over the last decades, however, the situation has radically changed, due to several factors. Technology seems to be playing an agemone role. The present and notably the future generation of scientists have major challenges to face. They have to deal with the forces generated by the infosphera; to dominate the technology and to maintain the capacity of generating inquisitive, creative, ethical and spiritual thoughts capable of addressing new scientific hypotheses and projects directed to the individual and collective good. However, in this scenario, what seems more relevant is to focus all our efforts in preparing ourselves, first, and then the new generations to face these challenges. From this point of view, the academic institutions and the scientific societies, have a major responsibility to deal with. CONCLUSIONS: The academic ecosystem traditionally used to educate the new generation of professionals as well as, and most importantly, the cultural, the professional pathways presently used to form them need to be extensively revised. The time is running short and the stakes are high. The debate is open.

Vaccination practices in pediatric transplantation: A survey among member centers of the European reference network TransplantChild.

BACKGROUND: There is considerable variation in vaccination practices between pediatric transplant centers. This study aims to evaluate active immunization attitudes and practices among ERN-TransplantChild centers and identify potential areas of improvement that could be addressed by shared evidence-based protocols. METHODS: A cross-sectional questionnaire of attitudes and practices toward immunization of pediatric SOT and HSCT candidates and recipients was sent to a representative member of multidisciplinary teams from 27 European centers belonging to the ERN-TransplantChild. RESULTS: A total of 28/62 SOT programs and 6/12 HSCT programs across 21 European centers participated. A quarter of centers did not have an on-site protocol for the immunizations. At the time of transplantation, pediatric candidates were fully immunized (80%-100%) in 57% and 33% of the SOT and HSCT programs. Variations in the time between vaccine administration and admission to the waiting list were reported between the centers, with 2 weeks for inactivated vaccines and variable time (2-4 weeks) for live-attenuated vaccines (LAVs). Almost all sites recommended immunization in the post-transplant period, with a time window of 4-8 months for the inactivated vaccines and 16-24 months for MMR and Varicella vaccines. Only five sites administer LAVs after transplantation, with seroconversion evaluated in 80% of cases. CONCLUSIONS: The immunization coverage of European pediatric transplant recipients is still inconsistent and far from adequate. This survey is a starting point for developing shared evidence-based immunization protocols for safe vaccination among pediatric transplant centers and generating new research studies.

Efficacy and safety of ketamine for neonatal refractory status epilepticus: case report and systematic review.

Background: Evidence-based data on treatment of neonatal status epilepticus (SE) are scarce. We aimed to collect data on the efficacy and safety of ketamine for the treatment of neonatal SE and to assess its possible role in the treatment of neonatal SE. Methods: We described a novel case and conducted a systematic literature review on neonatal SE treated with ketamine. The search was carried out in Pubmed, Cochrane, Clinical Trial Gov, Scopus and Web of Science. Results: Seven published cases of neonatal SE treated with ketamine were identified and analyzed together with our novel case. Seizures typically presented during the first 24 h of life (6/8). Seizures were resistant to a mean of five antiseizure medications. Ketamine, a NMDA receptor antagonist, appeared to be safe and effective in all neonates treated. Neurologic sequelae including hypotonia and spasticity were reported for 4/5 of the surviving children (5/8). 3/5 of them were seizure free at 1-17 months of life. Discussion: Neonatal brain is more susceptible to seizures due to a shift towards increased excitation because of a paradoxical excitatory effect of GABA, a greater density of NMDA receptors and higher extracellular concentrations of glutamate. Status epilepticus and neonatal encephalopathy could further enhance these mechanisms, providing a rationale for the use of ketamine in this setting. Conclusions: Ketamine in the treatment of neonatal SE showed a promising efficacy and safety profile. However, further in-depth studies and clinical trials on larger populations are needed.

Deep Medullary Vein Thrombosis in Newborns: A Systematic Literature Review.

BACKGROUND: Deep medullary vein (DMV) thrombosis is a rare cause of brain damage in both preterm and full-term neonates. In this study, we aimed to collect data on clinical and radiological presentation, treatment, and outcome of neonatal DMV thrombosis. METHODS: Systematic literature review on neonatal DMV thrombosis was carried out in PubMed, ClinicalTrial.gov, Scopus, and Web of Science up to December 2022. RESULTS: Seventy-five published cases of DMV thrombosis were identified and analysed (preterm newborns were 46%). Neonatal distress, respiratory resuscitation, or need for inotropes were present in 34/75 (45%) of patients. Signs and symptoms at presentation included seizures (38/75, 48%), apnoea (27/75, 36%), lethargy or irritability (26/75, 35%). At magnetic resonance imaging (MRI), fan-shaped linear T2 hypointense lesions were documented in all cases. All had ischaemic injuries, most often involving the frontal (62/74, 84%) and parietal lobes (56/74, 76%). Signs of haemorrhagic infarction were present in 53/54 (98%). Antithrombotic treatment was not mentioned in any of the studies included. Although mortality was low (2/75, 2.6%), a large proportion of patients developed neurological sequelae (intellectual disability in 19/51 [37%] and epilepsy in 9/51 [18%] cases). CONCLUSIONS: DMV thrombosis is rarely identified in the literature, even if it is possibly under-recognized or under-reported. Presentation in neonatal age is with seizures and non-specific systemic signs/symptoms that often cause diagnostic delay, despite the pathognomonic MRI picture. The high rate of morbidity, which determines significant social and health costs, requires further in-depth studies aimed at earlier diagnosis and evidence-based prevention and therapeutic strategies.

A pilot study on sports activities in pediatric palliative care: just do it.

BACKGROUND: There has been a growing interest in studying the value of physical exercise in children with disabilities or chronic health conditions because of evidence of improvement in quality of life, social acceptance, and physical functioning. However, only scant evidence exists for routine sports activities in children requiring pediatric palliative care (PPC), and in most cases, such evidence has been collected in oncological patients. The Pediatric Hospice of Padua is the referral center for PPC in the Veneto region (northern Italy). Starting from the experience of this PPC center, this pilot study aims to describe the personal experience of children and young people who practice physical activity and their caregivers' perspectives, focusing particularly on the emotional and social impact of exercise and sports practice. METHODS: Patients involved in at least one regular and structured sports activity were included in the pilot analysis. Two different ICF-CY (International Classification of Functioning, Disability and Health-Children and Youth Version) scales ("Body Function" and "Activity and Participation") were filled out to assess the children's global functional competence. Two online ad hoc questionnaires were created and administered to children, when able to respond, and caregivers. RESULTS: A total of 9% of patients reported being involved in a sports activity. All children who played sports did not have indications of cognitive retardation. The most practiced sport was swimming. The use of standardized methods such as ICF-CY shown that severe motor impairments do not limit sports accessibility. Questionnaires result suggest that sports are a positive experience for both children needing PPC and their parents. Children encourage other children to do sports and can find the positive side even in difficulties. CONCLUSION: Since PPC is encouraged as early as the diagnosis of incurable pathologies, the inclusion of sports activities in the context of a PPC plan should be considered from the perspective of improving quality of life.

Neonatal Arterial Ischemic Stroke Secondary to Carotid Artery Dissection: A Case Report and Systematic Literature Review.

BACKGROUND: Carotid artery (CA) dissection is a rare etiology of neonatal arterial ischemic stroke (NAIS). METHODS: We describe one novel case and conduct a systematic literature review on NAIS attributed to CA dissection, to collect data on its clinical-radiological presentation, treatment, and outcome. RESULTS: Eight published cases of NAIS attributed to CA dissection were identified and analyzed with our case. All patients (nine of nine) were born at term, and eight of nine experienced instrumental/traumatic delivery or urgent Caesarean section. None had fetal problems during pregnancy or thrombophilia. Signs and symptoms at presentation (between days of life 0 and 6) included seizures (eight of nine), respiratory distress or irregular breathing (five of nine), hyporeactivity, decreased consciousness or irritability (four of nine), and focal neurological signs (two of nine). At magnetic resonance imaging (MRI), stroke was unilateral in seven of nine and extensive in five of nine. CA dissection was documented by neuroimaging or at postmortem studies (seven of nine), and hypothesized by the treating physicians based on delivery and neuroradiology characteristics (in the remaining two of nine). Antithrombotic treatment was used in two of nine. According to available follow-up, one of eight died at age seven days, seven of eight had neurological/epileptic sequelae, and CA recanalization occurred in three of four. CONCLUSIONS: NAIS attributed to CA dissection is rarely identified in the literature, often preceded by traumatic/instrumental delivery, presenting with seizures and systemic signs/symptoms, and often characterized by extensive MRI lesions and neurological sequelae. Definite evidence and recommendations on antithrombotic treatment are lacking.

Pediatric Preventive Care in Middle-High Resource Countries-The Padova Chart for Health in Children.

Importance: The Padova Chart for Health in Children (PCHC) aims to gather the evidence of healthcare promotion and protection for chidren and adolescents (i.e., aged <18 y) into a single document in order to guide families, healthcare providers and social actors on healthy choices. No more than 2% of Europeans and North Americans aged <30 y have a healthy lifestyle. This, together with metabolic and brain plasticity during childhood, creates the ideal opportunity to implement preventive strategies. Guided interventions promoting healthy lifestyle in children and families therefore have a key role in abating the unprecedented pandemic of non-communicable diseases (NCDs) in adulthood. Observations: The PCHC is divided into four sections: nutrition, cardiovascular health, respiratory health, and mental and social health. Each section is structured in an ALICE approach (assessment, lobbying, intervention, call-for-action, evaluation): assessment of necessity, describing relevance to healthcare; lobbying to identify those who can effect the proposed interventions; interventions involving family, school and peers; a call-for-action to define priorities among the proposed interventions; and objective evaluation measures that can be applied on a population basis. Conclusions and Relevance: Interventions promoting health in childhood require joint action from multiple institutional, local and family representatives, with the shared goal of promoting health across the entire age group. These lifestyle interventions have the potential to change the lifetime risk trajectory for NCDs.

Pediatric Palliative Care in Oncology: Basic Principles.

About 4 million children with an oncological disease worldwide require pediatric palliative care (PPC) due to the nature of their condition. PPC is not limited to end-of-life care; it is a general approach continuing over the entire disease trajectory, regardless of whether the patient receives any oncological treatment. This review addresses the value of integrating PPC in treating children with cancer, focusing on the basic principles of PPC and its application in pediatric oncology. Moreover, models for PPC implementation in oncology, end-of-life care, and advanced care planning are discussed.

The Intervention Areas of the Psychologist in Pediatric Palliative Care: A Retrospective Analysis.

Infants, children and adolescents with life-limiting and life-threatening disease need long-term care that may change according to disease's natural history. With the primary goal of quality of life, the psychologist of pediatric palliative care (PPC) network deals with a large variety of issues. Little consideration has been given to the variety of intervention areas of psychology in PPC that concern the whole life span of the patient and family. The PPC network is composed by a multidisciplinary team of palliative care specialists that intervenes at home, in the hospital and in every place where the patient is living. The network coordinates different public health services to respond to clinical, psychosocial and spiritual needs. In these scenarios, the psychological need is not a single event but a moment inserted in the complexity of the child's needs. This retrospective monocentric project consists of an analysis of characteristics of psychological interventions in our PPC service. The time frame taken into consideration is 2019-2020, analyzing the clinical records of 186 patients of Pediatric Palliative Care and Pain Service of Veneto Region (Italy). The areas that emerged in the analysis show how the intervention of the psychologist in PPC does not concern only end-of-life, but a series of topics that are significant for the family to guarantee psycho-social wellbeing oriented toward the best quality of life. In conclusion, these different topics highlight the complexity of the child and family experience. This variety must be taken into consideration, the psychologist must increase holistic support with a dedicated skills curriculum.

Protective SARS-CoV-2 Antibody Response in Children With Inflammatory Bowel Disease.

BACKGROUND: To date, there's no evidence of an increased risk of SARS-CoV-2 infection or more severe COVID-19 in patients with inflammatory bowel disease (IBD). However, whether COVID-19 alters the clinical course of IBD or whether IBD treatment affects the immunological response to SARS-CoV-2 is still under investigation, especially in children. AIM: To assess the serological response to SARS-CoV-2 in children with IBD, and to evaluate the impact of COVID-19 on the clinical course of IBD. MATERIAL AND METHODS: This prospective study enrolled children (0-18 years) followed-up at the University Hospital of Padova for IBD, who acquired a confirmed SARS-CoV-2 infection between 02.2020 and 02.2021. The anti-SARS-CoV-2 S-RBD IgG titer was evaluated at 3 months after infection and compared to that of a control group of healthy children matched for age, sex, and COVID-19 severity. RESULTS: Twelve children with IBD (M = 5; median age 14 years) contracted COVID-19 during the study period. 11/12 patients were under immunomodulatory treatment (4/12 steroids; 6/12 azathioprine; 3/12 anti-TNFs; 2 vedolizumab; 1 ustekinumab). SARS-CoV-2 infection remained asymptomatic in 4/12 children and caused mild COVID-19 in the remaining 8. Mean anti-SARS-CoV-2 IgG S-RBD titer was similar between IBD patients and controls (27.3 ± 43.8 vs. 36.8 ± 35.3 kAU/L, p = ns). No children experienced IBD flares nor required gastroenterological support during the infection period. DISCUSSION: Children with IBD can mount a protective humoral response against SARS-CoV-2, which is comparable to that of their healthy peers regardless of ongoing immunomodulatory treatment. This study also supports the favorable course of PIBD during COVID-19 and vice-versa.

Case Report: Intestinal Nodular Lymphoid Hyperplasia as First Manifestation of Activated PI3Kδ Syndrome Due to a Novel PIK3CD Variant.

Nodular lymphoid hyperplasia (NLH) is a lymphoproliferative disease caused by non-clonal expansion of lymphoid cells in the gut mucosa. Little is known about the pathogenesis of NLH, which is often disregarded as an insignificant or para-physiologic phenomenon. We present the case of a girl with isolated diffuse NLH (extending from the stomach to the rectum) caused by activated PI3Kδ syndrome (APDS) due to the novel p.Glu525Gly variant in PIK3CD. The gain-of-function effect of the variant was confirmed by demonstration of over activation of the Akt/mTOR pathway in the patient's cells. APDS diagnosis led to treatment with sirolimus, which resulted in the complete remission of NLH and in the prevention of extra intestinal complications. In conclusion, we identify APDS as a novel cause of isolated NLH and suggest that patients with severe pan-enteric NLH should be screened for this disorder that may not be apparent on first-line immunological testing.

IFIH1 loss-of-function variants contribute to very early-onset inflammatory bowel disease.

Genetic defects of innate immunity impairing intestinal bacterial sensing are linked to the development of Inflammatory Bowel Disease (IBD). Although much evidence supports a role of the intestinal virome in gut homeostasis, most studies focus on intestinal viral composition rather than on host intestinal viral sensitivity. To demonstrate the association between the development of Very Early Onset IBD (VEOIBD) and variants in the IFIH1 gene which encodes MDA5, a key cytosolic sensor for viral nucleic acids. Whole exome sequencing (WES) was performed in two independent cohorts of children with VEOIBD enrolled in Italy (n = 18) and USA (n = 24). Luciferase reporter assays were employed to assess MDA5 activity. An enrichment analysis was performed on IFIH1 comparing 42 VEOIBD probands with 1527 unrelated individuals without gastrointestinal or immunological issues. We identified rare, likely loss-of-function (LoF), IFIH1 variants in eight patients with VEOIBD from a combined cohort of 42 children. One subject, carrying a homozygous truncating variant resulting in complete LoF, experienced neonatal-onset, pan-gastrointestinal, IBD-like enteropathy plus multiple infectious episodes. The remaining seven subjects, affected by VEOIBD without immunodeficiency, were carriers of one LoF variant in IFIH1. Among these, two patients also carried a second hypomorphic variant, with partial function apparent when MDA5 was weakly stimulated. Furthermore, IFIH1 variants were significantly enriched in children with VEOIBD as compared to controls (p = 0.007). Complete and partial MDA5 deficiency is associated with VEOIBD with variable penetrance and expressivity, suggesting a role for impaired intestinal viral sensing in IBD pathogenesis.

Novel CARMIL2 loss-of-function variants are associated with pediatric inflammatory bowel disease.

CARMIL2 is required for CD28-mediated co-stimulation of NF-κB signaling in T cells and its deficiency has been associated with primary immunodeficiency and, recently, very early onset inflammatory bowel disease (IBD). Here we describe the identification of novel biallelic CARMIL2 variants in three patients presenting with pediatric-onset IBD and in one with autoimmune polyendocrine syndrome (APS). None manifested overt clinical signs of immunodeficiency before their diagnosis. The first patient presented with very early onset IBD. His brother was found homozygous for the same CARMIL2 null variant and diagnosed with APS. Two other IBD patients were found homozygous for a nonsense and a missense CARMIL2 variant, respectively, and they both experienced a complicated postoperative course marked by severe infections. Immunostaining of bowel biopsies showed reduced CARMIL2 expression in all the three patients with IBD. Western blot and immunofluorescence of transfected cells revealed an altered expression pattern of the missense variant. Our work expands the genotypic and phenotypic spectrum of CARMIL2 deficiency, which can present with either IBD or APS, aside from classic immunodeficiency manifestations. CARMIL2 should be included in the diagnostic work-up of patients with suspected monogenic IBD.

Do we always need to treat patients with spinal muscular atrophy? A personal view and experience.

BACKGROUND: We report the clinical outcomes observed in our patients with SMA type 1 or 2 receiving nusinersen, and we comment on the ethical implications of this treatment, in line with our results and those reported by Audic et al. in their analysis published in the Orphanet Journal of Rare Diseases. METHODS: We analyzed records of all children with a genetically diagnosed SMA and clinically confirmed diagnosis of SMA Type 1 or 2 to whom nusinersen was offered. Follow-up lasted 30 months. RESULTS: Among the 17 children with SMA type 1, 6 interrupted treatment with nusinersen due to adverse events or lack of efficacy. Of the remaining 11 patients, 9 are responding to therapy, though multidisciplinary complex care is still required. All those children started nusinersen at a very early age. Eighteen patients with SMA type 2 received nusinersen; five required treatment interruption. The other 13 patients are still on nusinersen therapy, and 6 are responders. Among the seven non-responders, only two met the inclusion criteria of the pivotal trial. CONCLUSIONS: Our analysis further supports the findings reported in the study by Audic et al. We believe that a wider use of nusinersen in clinical practice would require a comprehensive assessment of its actual benefits weighed against the discomfort caused to patients, as well as the identification of the patients who may obtain the best benefits from this treatment.

Intratracheal administration of mesenchymal stem cell-derived extracellular vesicles reduces lung injuries in a chronic rat model of bronchopulmonary dysplasia.

Early therapeutic effect of intratracheally (IT)-administered extracellular vesicles secreted by mesenchymal stem cells (MSC-EVs) has been demonstrated in a rat model of bronchopulmonary dysplasia (BPD) involving hyperoxia exposure in the first 2 postnatal weeks. The aim of this study was to evaluate the protective effects of IT-administered MSC-EVs in the long term. EVs were produced from MSCs following GMP standards. At birth, rats were distributed in three groups: (a) animals raised in ambient air for 6 weeks (n = 10); and animals exposed to 60% hyperoxia for 2 weeks and to room air for additional 4 weeks and treated with (b) IT-administered saline solution (n = 10), or (c) MSC-EVs (n = 10) on postnatal days 3, 7, 10, and 21. Hyperoxia exposure produced significant decreases in total number of alveoli, total surface area of alveolar air spaces, and proliferation index, together with increases in mean alveolar volume, mean linear intercept and fibrosis percentage; all these morphometric changes were prevented by MSC-EVs treatment. The medial thickness index for <100 µm vessels was higher for hyperoxia-exposed/sham-treated than for normoxia-exposed rats; MSC-EV treatment significantly reduced this index. There were no significant differences in interstitial/alveolar and perivascular F4/8-positive and CD86-positive macrophages. Conversely, hyperoxia exposure reduced CD163-positive macrophages both in interstitial/alveolar and perivascular populations and MSC-EV prevented these hyperoxia-induced reductions. These findings further support that IT-administered EVs could be an effective approach to prevent/treat BPD, ameliorating the impaired alveolarization and pulmonary artery remodeling also in a long-term model. M2 macrophage polarization could play a role through anti-inflammatory and proliferative mechanisms.