The Inborn Errors of Immunity-Virtual Consultation System Platform in Service for the Italian Primary Immunodeficiency Network: Results from the Validation Phase.

PURPOSE: Inborn errors of immunity (IEI) represent a heterogeneous group of rare genetically determined diseases. In some cases, patients present with complex or atypical phenotypes, not fulfilling the accepted diagnostic criteria for IEI and, thus, at high risk of misdiagnosis or diagnostic delay. This study aimed to validate a platform that, through the opinion of immunologist experts, improves the diagnostic process and the level of care of patients with atypical/complex IEI. METHODS: Here, we describe the functioning of the IEI-Virtual Consultation System (VCS), an innovative platform created by the Italian Immunodeficiency Network (IPINet). RESULTS: In the validation phase, from January 2020 to June 2021, 68 cases were entered on the IEI-VCS platform. A final diagnosis was achieved in 35/68 cases (51%, 95% CI 38.7 to 64.2). In 22 out of 35 solved cases, the diagnosis was confirmed by genetic analysis. In 3/35 cases, a diagnosis of secondary immunodeficiency was made. In the remaining 10 cases, an unequivocal clinical and immunological diagnosis was obtained, even though not substantiated by genetic analysis. CONCLUSION: From our preliminary study, the VCS represents an innovative and useful system to improve the diagnostic process of patients with complex unsolved IEI disorders, with benefits both in terms of reduction of time of diagnosis and access to the required therapies. These results may help the functioning of other international platforms for the management of complex cases.

Patients with STAT1 Gain-of-function Mutations Display Increased Apoptosis which is Reversed by the JAK Inhibitor Ruxolitinib.

INTRODUCTION: The signal transducer and activator of transcription (STAT1) gain-of-function (GOF) syndrome accounts for most cases of chronic mucocutaneous candidiasis but is characterized by a broader clinical phenotype that may include bacterial, viral, or invasive fungal infections, autoimmunity, autoinflammatory manifestations, vascular complications, or malignancies. The severity of lymphopenia may vary and influence the infectious morbidity. METHODS: In our cohort of seven STAT1-GOF patients, we investigated the mechanisms that may determine T lymphopenia, we characterized the interferon gene signature (IGS) and analyzed the effect of ruxolitinib in reverting the immune dysregulation. RESULTS: STAT1-GOF patients exhibited increased T lymphocyte apoptosis that was significantly augmented in both resting conditions and following stimulation with mitogens and IFNα, as evaluated by flow cytometry by Annexin V/ Propidium iodide assay. The JAK inhibitor ruxolitinib significantly reduced the IFNα-induced hyperphosphorylation of STAT1 and reverted the stimulation-induced T-cell apoptosis, in vitro. In two adult STAT1-GOF patients, the JAKinib treatment ameliorated chronic mucocutaneous candidiasis and lymphopenia. Most STAT1-GOF patients, particularly those who had autoimmunity, presented increased IGS that significantly decreased in the two patients during ruxolitinib treatment. CONCLUSION: In STAT1-GOF patients, T lymphocyte apoptosis is increased, and T lymphopenia may determine higher risk of severe infections. The JAKinib target therapy should be evaluated to treat severe chronic candidiasis and lymphopenia, and to downregulate the IFNs in patients with autoinflammatory or autoimmune manifestations.

Clinical and transcriptomic characteristics of a novel SMARCD2 mutation that disrupts neutrophil maturation and function.

We report a novel case of SMARCD2 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily D, member 2) mutation successfully treated with hematopoietic stem cell transplantation. The female patient presented delayed cord separation, chronic diarrhea, skin abscesses, skeletal dysmorphisms, and neutropenia with specific granule deficiency. Analysis of the transcriptomic profile of peripheral blood sorted mature and immature SMARCD2 neutrophils showed defective maturation process that associated with altered expression of genes related to specific, azurophilic, and gelatinase granules, such as LTF, CRISP3, PTX3, and CHI3L1. These abnormalities account for the prevalence of immature neutrophils in the peripheral blood, impaired function, and deregulated inflammatory responses.

Increased use of high-flow nasal cannulas after the pandemic in bronchiolitis: a more severe disease or a changed physician's attitude?

After the SARS-CoV-2 pandemic, we noticed a marked increase in high-flow nasal cannula use for bronchiolitis. This study aims to report the percentage of children treated with high-flow nasal cannula (HFNC) in various seasons. The secondary outcomes were admissions for bronchiolitis, virological results, hospital burden, and NICU/PICU need. We conducted a retrospective study in four Italian hospitals, examining the medical records of all infants (< 12 months) hospitalized for bronchiolitis in the last four winter seasons (1 September-31 March 2018-2022). In the 2021-2022 winter season, 66% of admitted children received HFNC versus 23%, 38%, and 35% in the previous 3 years. A total of 876 patients were hospitalized in the study periods. In 2021-2022, 300 infants were hospitalized for bronchiolitis, 22 in 2020-2021, 259 in 2019-2020, and 295 in 2018-2019. The percentage of patients needing intensive care varied from 28.7% to 18%, 22%, and 15% in each of the four considered periods (p < 0.05). Seventy-seven percent of children received oxygen in the 2021-2022 winter; vs 50%, 63%, and 55% (p < 0.01) in the previous 3 years. NIV/CPAP was used in 23%, 9%, 16%, and 12%, respectively. In 2021-2020, 2% of patients were intubated; 0 in 2020-2021, 3% in 2019-2020, and 1% in 2018-2019. CONCLUSION: This study shows a marked increase in respiratory support and intensive care admissions this last winter. While these severity indexes were all driven by medical choices, more reliable indexes such as intubation rate and length of stay did not change. Therefore, we suggest that there is a more aggressive treatment attitude rather than a more severe disease. WHAT IS KNOWN: • COVID-19 pandemic deeply impacted bronchiolitis epidemiology, reducing hospitalizations to onetenth. In the 2021-2022 winter, bronchiolitis resurged to pre-pandemic numbers in Europe. WHAT IS NEW: • Bronchiolitis hospitalization rose much faster in the 2021-2022 winter period, peaking at a higher level. Respiratory supports and high-flow nasal cannula increased significantly compared to the pre-pandemic era.

Consensus of the Italian Primary Immunodeficiency Network on transition management from pediatric to adult care in patients affected with childhood-onset inborn errors of immunity.

Medical advances have dramatically improved the long-term prognosis of children and adolescents with inborn errors of immunity (IEIs). Transfer of the medical care of individuals with pediatric IEIs to adult facilities is also a complex task because of the large number of distinct disorders, which requires involvement of patients and both pediatric and adult care providers. To date, there is no consensus on the optimal pathway of the transitional care process and no specific data are available in the literature regarding patients with IEIs. We aimed to develop a consensus statement on the transition process to adult health care services for patients with IEIs. Physicians from major Italian Primary Immunodeficiency Network centers formulated and answered questions after examining the currently published literature on the transition from childhood to adulthood. The authors voted on each recommendation. The most frequent IEIs sharing common main clinical problems requiring full attention during the transitional phase were categorized into different groups of clinically related disorders. For each group of clinically related disorders, physicians from major Italian Primary Immunodeficiency Network institutions focused on selected clinical issues representing the clinical hallmark during early adulthood.

Diagnostic approach of hypogammaglobulinemia in infancy.

Primary B-cell immunodeficiency is the most frequent immune defect in infancy. Selective absence of serum and secretory immunoglobulin IgA is the most common, with rates ranging from 1/333 persons to 1/16 000, among different races. By contrast, it has been estimated that hypo/agammaglobulinemia occurs with a frequency of 1/50 000 persons. Patients with antibody deficiency are usually recognized because they have recurrent infections with encapsulated bacteria or a history of failure to respond adequately to antibiotic treatment. However, some individuals, mainly those affected by IgA deficiency (SIgAD) or transient hypogammaglobulinemia of infancy , may have few or no infections.

Impaired natural killer cell functions in patients with signal transducer and activator of transcription 1 (STAT1) gain-of-function mutations.

BACKGROUND: Gain-of-function (GOF) mutations affecting the coiled-coil domain or the DNA-binding domain of signal transducer and activator of transcription 1 (STAT1) cause chronic mucocutaneous candidiasis disease. This condition is characterized by fungal and bacterial infections caused by impaired generation of TH17 cells; meanwhile, some patients with chronic mucocutaneous candidiasis disease might also have viral or intracellular pathogen infections. OBJECTIVE: We sought to investigate the effect of STAT1 GOF mutations on the functioning of natural killer (NK) cells. METHODS: Because STAT1 is involved in the signaling response to several cytokines, we studied NK cell functional activities and STAT1 signaling in 8 patients with STAT1 GOF mutations. RESULTS: Functional analysis of NK cells shows a significant impairment of cytolytic and degranulation activities in patients with STAT1 GOF mutations. Moreover, NK cells from these patients display lower production of IFN-γ in response to IL-15 and reduced proliferation after stimulation with IL-2 or IL-15, suggesting that STAT5 signaling is affected. In addition, signaling studies demonstrate that the increased phosphorylation of STAT1 in response to IFN-α is associated with detectable activation of STAT1 and increased STAT1 binding to the interferon-induced protein with tetratricopeptide repeats 1 (IFIT1) promoter in response to IL-15, whereas STAT5 phosphorylation and DNA binding to IL-2 receptor α (IL2RA) are reduced or not affected in response to the same cytokine. CONCLUSION: These observations suggest that persistent activation of STAT1 might affect NK cell proliferation and functional activities.

Signal transducer and activator of transcription gain-of-function primary immunodeficiency/immunodysregulation disorders.

PURPOSE OF REVIEW: To describe primary immunodeficiencies caused by gain-of-function (GOF) mutations of signal transducer and activator of transcription (STAT) genes, a group of genetically determined disorders characterized by susceptibility to infections and, in many cases, autoimmune manifestations. RECENT FINDINGS: GOF mutations affecting STAT1 result in increased STAT tyrosine phosphorylation and secondarily increased response to STAT1-signaling cytokines, such as interferons. In contrast, STAT3 hyperactivity is not usually related to hyperphosphorylation but rather to increased STAT3-mediated transcriptional activity. In both cases, heterozygous STAT1 and STAT3 GOF mutations trigger a distinct set of genes in target cells that lead to abnormal functioning of antimicrobial response and/or autoimmunity and result in autosomal dominant diseases. SUMMARY: Clinical manifestations of patients with STAT1 GOF are characterized by mucocutaneous candidiasis and recurrent lower tract respiratory infections. In addition, many patients have thyroiditis, type 1 diabetes mellitus, autoimmune cytopenias, cancer or aneurysms. Patients with germline STAT3 GOF mutations have an increased frequency of early-onset multiorgan autoimmunity (i.e. autoimmune enteropathy, type 1 diabetes mellitus, autoimmune interstitial lung disease and autoimmune cytopenias), lymphoproliferation, short stature and, less frequently, severe recurrent infections. Treatment options range from antimicrobial therapy, intravenous or subcutaneous immunoglobulin and immunosuppressive drugs. Some patients with STAT1 GOF disorder have undergone hematopoietic stem cell transplantation, although these have been difficult because of the underlying proinflammatory milieu from the mutation.

Clinical heterogeneity of dominant chronic mucocutaneous candidiasis disease: presenting as treatment-resistant candidiasis and chronic lung disease.

In gain-of-function STAT1 mutations, chronic mucocutaneous candidiasis disease (CMCD) represents the phenotypic manifestation of a complex immunodeficiency characterized by clinical and immunological heterogeneity. We aimed to study clinical manifestations, long-term complications, molecular basis, and immune profile of patients with dominant CMCD. We identified nine patients with heterozygous mutations in STAT1, including novel amino acid substitutions (L283M, L351F, L400V). High risk of azole-resistance was observed, particularly when intermittent regimens of antifungal treatment or use of suboptimal dosage occurs. We report a case of Cryptococcosis and various bacterial and viral infections. Risk of developing bronchiectasis in early childhood or gradually evolving to chronic lung disease in adolescent or adult ages emerges. Lymphopenia is variable, likely progressing by adulthood. We conclude that continuous antifungal prophylaxis associated to drug monitoring might prevent resistance to treatment; prompt diagnosis and therapy of lung disease might control long-term progression; careful monitoring of lymphopenia-related infections might improve prognosis.

Increased bronchiolitis burden and severity after the pandemic: a national multicentric study.

BACKGROUND: The coronavirus 2019 (COVID-19) related containment measures led to the disruption of all virus distribution. Bronchiolitis-related hospitalizations shrank during 2020-2021, rebounding to pre-pandemic numbers the following year. This study aims to describe the trend in bronchiolitis-related hospitalization this year, focusing on severity and viral epidemiology. METHODS: We conducted a retrospective investigation collecting clinical records data from all infants hospitalized for bronchiolitis during winter (1st September-31th March) from September 2018 to March 2023 in six Italian hospitals. No trial registration was necessary according to authorization no.9/2014 of the Italian law. RESULTS: Nine hundred fifty-three infants were hospitalized for bronchiolitis this last winter, 563 in 2021-2022, 34 in 2020-2021, 395 in 2019-2020 and 483 in 2018-2019. The mean length of stay was significantly longer this year compared to all previous years (mean 7.2 ± 6 days in 2022-2023), compared to 5.7 ± 4 in 2021-2022, 5.3 ± 4 in 2020-2021, 6.4 ± 5 in 2019-2020 and 5.5 ± 4 in 2018-2019 (p < 0.001), respectively. More patients required mechanical ventilation this winter 38 (4%), compared to 6 (1%) in 2021-2022, 0 in 2020-2021, 11 (2%) in 2019-2020 and 6 (1%) in 2018-2019 (p < 0.05), respectively. High-flow nasal cannula and non-invasive respiratory supports were statistically more common last winter (p = 0.001 or less). RSV prevalence and distribution did not differ this winter, but coinfections were more prevalent 307 (42%), 138 (31%) in 2021-2022, 1 (33%) in 2020-2021, 68 (23%) in 2019-2020, 61 (28%) in 2018-2019 (p = 0.001). CONCLUSIONS: This study shows a growth of nearly 70% in hospitalisations for bronchiolitis, and an increase in invasive respiratory support and coinfections, suggesting a more severe disease course this winter compared to the last five years.

Reduced probability of improving viro-immunological state in subjects with vertical transmission of HIV reaching adult age: A multicenter retrospective cohort study.

INTRODUCTION: Young adults with vertical transmission (VT) of human immunodeficiency virus (HIV) represent a fragile population. This study evaluates factors associated with viro-immunological outcome of these patients. METHODS: We performed a multicenter study including HIV-infected subjects with VT ≥ 18 years old from six Italian clinics. Subjects were observed from birth to death, lost to follow-up, or last visit until December 31, 2019. Condition of "optimal viro-immunological status" (OS) was defined as the simultaneous presence of HIV ribonucleic acid (RNA) < 50 copies/mL, CD4+ > 500 cells/mm3 , and CD4+/CD8+ ratio ≥ 1. RESULTS: A total of 126 subjects were enrolled. At 18 years of age, 52/126 (44.4%) had HIV-RNA > 50 copies/mL, 47/126 (38.2%) had CD4+ < 500/mm3 , and 78/126 (67.2%) had CD4+/CD8+ < 1; 28 subjects (23.7%) presented in the condition of OS. Having a CD4+/CD8+ ratio ≥ 1 at 18 years of age was related with an increased probability of shift from suboptimal viro-immunological status (SOS) to OS (HR: 7.7, 95% confidence interval [CI]: 4.23-14.04), and a reduced risk of shift from the OS to the SOS (HR: 0.49, 95% CI: 0.26-0.92). Acquired immunodeficiency syndrome (AIDS) diagnosis significantly reduced the probability of shift from a viro-immunological SOS to OS (HR: 0.09, 95% CI: 0.03-0.30). Subjects who had not achieved an OS at 18 years of age had an increased risk of discontinuation of combination antiretroviral therapy (cART, p = .019). CONCLUSIONS: Only a small proportion of subjects with VT of HIV reached the adult age with "OS". Transition to the adult care with a compromised viro-immunological condition represents a negative driver for future optimal infection control, with a higher risk of discontinuation of cART and a reduced probability to improve the immunological status later in the years.

Reduced G protein signaling despite impaired internalization and ß-arrestin recruitment in patients carrying a CXCR4Leu317fsX3 mutation causing WHIM syndrome.

WHIM syndrome is an inherited immune disorder caused by an autosomal dominant heterozygous mutation in CXCR4. The disease is characterized by neutropenia/leukopenia (secondary to retention of mature neutrophils in bone marrow), recurrent bacterial infections, treatment-refractory warts, and hypogammaglobulinemia. All mutations reported in WHIM patients lead to the truncations in the C-terminal domain of CXCR4, R334X being the most frequent. This defect prevents receptor internalization and enhances both calcium mobilization and ERK phosphorylation, resulting in increased chemotaxis in response to the unique ligand CXCL12. Here, we describe 3 patients presenting neutropenia and myelokathexis, but normal lymphocyte count and immunoglobulin levels, carrying what we believe to be a novel Leu317fsX3 mutation in CXCR4, leading to a complete truncation of its intracellular tail. The analysis of the L317fsX3 mutation in cells derived from patients and in vitro cellular models reveals unique signaling features in comparison with R334X mutation. The L317fsX3 mutation impairs CXCR4 downregulation and ß-arrestin recruitment in response to CXCL12 and reduces other signaling events - including ERK1/2 phosphorylation, calcium mobilization, and chemotaxis - all processes that are typically enhanced in cells carrying the R334X mutation. Our findings suggest that, overall, the L317fsX3 mutation may be causative of a form of WHIM syndrome not associated with an augmented CXCR4 response to CXCL12.

Longitudinal Characterization of Immune Response in a Cohort of Children Hospitalized with Multisystem Inflammatory Syndrome.

BACKGROUND: Multisystem Inflammatory Syndrome in Children (MIS-C) is a severe complication of SARS-CoV-2 infection caused by hyperactivation of the immune system. METHODS: this is a retrospective analysis of clinical data, biochemical parameters, and immune cell subsets in 40 MIS-C patients from hospital admission to outpatient long-term follow-up. RESULTS: MIS-C patients had elevated inflammatory markers, associated with T- and NK-cell lymphopenia, a profound depletion of dendritic cells, and altered monocyte phenotype at disease onset, while the subacute phase of the disease was characterized by a significant increase in T- and B-cell counts and a rapid decline in activated T cells and terminally differentiated B cells. Most of the immunological parameters returned to values close to the normal range during the remission phase (20-60 days after hospital admission). Nevertheless, we observed a significantly reduced ratio between recently generated and more differentiated CD8+ T- and B-cell subsets, which partially settled at longer-term follow-up determinations. CONCLUSIONS: The characterization of lymphocyte distribution in different phases of MIS-C may help to understand the course of diseases that are associated with dysregulated immune responses and to calibrate prompt and targeted treatments.

Long term longitudinal follow-up of an AD-HIES cohort: the impact of early diagnosis and enrollment to IPINet centers on the natural history of Job's syndrome.

Job's syndrome, or autosomal dominant hyperimmunoglobulin E syndrome (AD-HIES, STAT3-Dominant Negative), is a rare inborn error of immunity (IEI) with multi-organ involvement and long-life post-infective damage. Longitudinal registries are of primary importance in improving our knowledge of the natural history and management of these rare disorders. This study aimed to describe the natural history of 30 Italian patients with AD-HIES recorded in the Italian network for primary immunodeficiency (IPINet) registry. This study shows the incidence of manifestations present at the time of diagnosis versus those that arose during follow up at a referral center for IEI. The mean time of diagnostic delay was 13.7 years, while the age of disease onset was < 12 months in 66.7% of patients. Respiratory complications, namely bronchiectasis and pneumatoceles, were present at diagnosis in 46.7% and 43.3% of patients, respectively. Antimicrobial prophylaxis resulted in a decrease in the incidence of pneumonia from 76.7% to 46.7%. At the time of diagnosis, skin involvement was present in 93.3% of the patients, including eczema (80.8%) and abscesses (66.7%). At the time of follow-up, under therapy, the prevalence of complications decreased: eczema and skin abscesses reduced to 63.3% and 56.7%, respectively. Antifungal prophylaxis decreased the incidence of mucocutaneous candidiasis from 70% to 56.7%. During the SARS-CoV-2 pandemic, seven patients developed COVID-19. Survival analyses showed that 27 out of 30 patients survived, while three patients died at ages of 28, 39, and 46 years as a consequence of lung bleeding, lymphoma, and sepsis, respectively. Analysis of a cumulative follow-up period of 278.7 patient-years showed that early diagnosis, adequate management at expertise centers for IEI, prophylactic antibiotics, and antifungal therapy improve outcomes and can positively influence the life expectancy of patients.

Tetralogy of fallot is an uncommon manifestation of warts, hypogammaglobulinemia, infections, and myelokathexis syndrome.

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is a rare immunodeficiency disorder. We report three patients with WHIM syndrome who are affected by Tetralogy of Fallot (TOF). This observation suggests a possible increased risk of TOF in WHIM syndrome and that birth presentation of TOF and neutropenia should lead to suspect WHIM syndrome.

Pathogenesis of Autoimmune Cytopenias in Inborn Errors of Immunity Revealing Novel Therapeutic Targets.

Autoimmune diseases are usually associated with environmental triggers and genetic predisposition. However, a few number of autoimmune diseases has a monogenic cause, mostly in children. These diseases may be the expression, isolated or associated with other symptoms, of an underlying inborn error of immunity (IEI). Autoimmune cytopenias (AICs), including immune thrombocytopenic purpura (ITP), autoimmune hemolytic anemia (AIHA), autoimmune neutropenia (AN), and Evans' syndrome (ES) are common presentations of immunological diseases in the pediatric age, with at least 65% of cases of ES genetically determined. Autoimmune cytopenias in IEI have often a more severe, chronic, and relapsing course. Treatment refractoriness also characterizes autoimmune cytopenia with a monogenic cause, such as IEI. The mechanisms underlying autoimmune cytopenias in IEI include cellular or humoral autoimmunity, immune dysregulation in cases of hemophagocytosis or lymphoproliferation with or without splenic sequestration, bone marrow failure, myelodysplasia, or secondary myelosuppression. Genetic characterization of autoimmune cytopenias is of fundamental importance as an early diagnosis improves the outcome and allows the setting up of a targeted therapy, such as CTLA-4 IgG fusion protein (Abatacept), small molecule inhibitors (JAK-inhibitors), or gene therapy. Currently, gene therapy represents one of the most attractive targeted therapeutic approaches to treat selected inborn errors of immunity. Even in the absence of specific targeted therapies, however, whole exome genetic testing (WES) for children with chronic multilineage cytopenias should be considered as an early diagnostic tool for disease diagnosis and genetic counseling.

Gut-dependent inflammation and alterations of the intestinal microbiota in individuals with perinatal HIV exposure and different HIV serostatus.

OBJECTIVE: HIV-exposed infected (HEI) and uninfected (HEU) children represent the two possible outcomes of maternal HIV infection. Modifications of the intestinal microbiome have been linked to clinical vulnerability in both settings, yet whether HEI and HEU differ in terms of gut impairment and peripheral inflammation/activation is unknown. DESIGN: We performed a cross-sectional, pilot study on fecal and plasma microbiome as well as plasma markers of gut damage, microbial translocation, inflammation and immune activation in HIV-infected and uninfected children born from an HIV-infected mother. METHODS: Fecal and plasma microbiome were determined by means of 16S rDNA amplification with subsequent qPCR quantification. Plasma markers were quantified via ELISA. RESULTS: Forty-seven HEI and 33 HEU children were consecutively enrolled. The two groups displayed differences in fecal beta-diversity and relative abundance, yet similar microbiome profiles in plasma as well as comparable gut damage and microbial translocation. In contrast, monocyte activation (sCD14) and systemic inflammation (IL-6) were significantly higher in HEI than HEU. CONCLUSION: In the setting of perinatal HIV infection, enduring immune activation and inflammation do not appear to be linked to alterations within the gut. Given that markers of activation and inflammation are independent predictors of HIV disease progression, future studies are needed to understand the underlying mechanisms of such processes and elaborate adjuvant therapies to reduce the clinical risk in individuals with perinatal HIV infection.

When a Nontuberculous Mycobacterial Infection Reveals an Error of Immunity: A Single Center's Experience.

We present an algorithm that may be applied in case of a diagnosis of pediatric nontuberculous mycobacterial disease to identify the patients who may require an immunologic assessment to discover a possible underlying immune system defect predisposing to their nontuberculous mycobacterial infections.

Intrapartum use of zidovudine in a large cohort of pregnant women living with HIV in Italy.

BACKGROUND: Intravenous administration of zidovudine (ZDV) during labour is a key step for vertical HIV transmission (VT) prevention, but there is no evidence of benefit when maternal HIV-RNA at delivery is <50 copies/mL. The aim of this study is evaluating the appropriateness of intrapartum ZDV use in Italy. METHODS: Observational study including mother-infant pairs with perinatal HIV exposure during 2002-2019, enrolled in the Italian Register for HIV Infection in Children. Univariable and multivariable logistic regression were used to evaluate factors associated with VT. RESULTS: A total of 3,861 infants, born from 3,791 pregnancies were included. The frequency of ZDV use was 79.9%, 92.1%, 93.7% and 92.8% when HIV-RNA was not available, ≥400 copies, between 50 and 399 copies, and <50 copies/mL. Thirty-three out of 3861 (0.85%) infants were subsequently diagnosed with HIV, 25/3861 (0.6%) of them born to mothers receiving intrapartum ZDV, and 31 (93.9%) to mothers with HIV-RNA ≥50 copies/mL or not available. In women with HIV-RNA < 50 copies/mL, ART discontinuation during pregnancy was the strongest risk factor for VT (odds ratio, OR, 23.1, 95%CI 2.4-219.3), while a higher gestational age (OR 0.6, 95%CI 0.4-0.8) and PEP administration to the newborn (aOR 0.004, 95%CI <0.0001-0.4) were protective factors. Intrapartum ZDV administration did not influence the final outcome in this group. CONCLUSIONS: In ART era, more transmission events may occur in utero, limiting value of intrapartum ZDV, particularly for women with suppressed HIV-RNA load. More attention to the HIV-RNA testing of mothers before delivery may avoid unnecessary ZDV use.