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Background: Mouse models that recapitulate key features of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection are important tools for understanding complex interactions between host genetics, immune responses, and SARS-CoV-2 pathogenesis. Little is known about how predominantly cellular (Th1 type) versus humoral (Th2 type) immune responses influence SARS-CoV-2 dynamics, including infectivity and disease course., Methods: We generated knock-in (KI) mice expressing human ACE2 (hACE2) and/or human TMPRSS2 (hTMPRSS2) on Th1-biased (C57BL/6; B6) and Th2-biased (BALB/c) genetic backgrounds. Mice were infected intranasally with SARS-CoV-2 Delta (B.1.617.2) or Omicron BA.1 (B.1.1.529) variants, followed by assessment of disease course, respiratory tract infection, lung histopathology, and humoral and cellular immune responses., Findings: In both B6 and BALB/c mice, hACE2 expression was required for infection of the lungs with Delta, but not Omicron BA.1. Disease severity was greater in Omicron BA.1-infected hTMPRSS2-KI and double-KI BALB/c mice compared with B6 mice, and in Delta-infected double-KI B6 and BALB/c mice compared with hACE2-KI mice. hACE2-KI B6 mice developed more severe lung pathology and more robust SARS-CoV-2-specific splenic CD8 T cell responses compared with hACE2-KI BALB/c mice. There were no notable differences between the two genetic backgrounds in plasma cell, germinal center B cell, or antibody responses to SARS-CoV-2., Interpretation: SARS-CoV-2 Delta and Omicron BA.1 infection, disease course, and CD8 T cell response are influenced by the host genetic background. These humanized mice hold promise as important tools for investigating the mechanisms underlying the heterogeneity of SARS-CoV-2-induced pathogenesis and immune response., Funding: This work was funded by NIH U19 AI142790-02S1, the GHR Foundation, the Arvin Gottleib Foundation, and the Overton family (to SS and EOS); Prebys Foundation (to SS); NIH R44 AI157900 (to KJ); and by an American Association of Immunologists Career Reentry Fellowship (FASB)., Competing Interests: Declaration of interests CC, NS, and KJ were employees of Synbal, Inc. DOC is employed by and holds stock in TransViragen Inc., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: The Critical Care Societies Collaborative included not ordering diagnostic tests at regular intervals as one of their Choosing Wisely initiatives. A reduction in unnecessary chest radiographs (CXRs) can help reduce exposure to radiation and eliminate health care waste. We aimed to reduce daily screening CXRs in a pediatric ICU (PICU) by 20% from baseline within 4 months of implementation of CXR criteria., Methods: All intubated patients in the PICU were included in this quality improvement project. Patients with tracheostomies were excluded. We developed criteria delineating which patients were most likely to benefit from a daily screening CXR, and these criteria were discussed for each patient on rounds. Patients on extracorporeal membrane oxygenation, on high-frequency oscillatory ventilation, or on high support on conventional mechanical ventilation were included as needing a daily screening CXR. We tracked the percentage of intubated subjects receiving a screening CXR as an outcome measure. Unplanned extubations and the number of non-screening CXRs per intubated subject were followed as balancing measures., Results: The percentage of intubated subjects receiving a daily screening CXR was reduced from 79% to 31%. There was no increase in frequency of unplanned extubations or number of non-screening CXRs. With an estimated subject charge of roughly $270 and hospital cost of $54 per CXR, this project led to an estimated $300,000 in patient charge savings and $60,000 in hospital cost savings., Conclusions: Adopting criteria to delineate which patients are most likely to benefit from screening CXRs can lead to a reduction in the percentage of intubated patients receiving screening CXRs without appearing to increase harm., Competing Interests: The authors have disclosed no conflicts of interest., (Copyright © 2023 by Daedalus Enterprises.)

Therapeutic antibodies are an important tool in the arsenal against coronavirus infection. However, most antibodies developed early in the pandemic have lost most or all efficacy against newly emergent strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), particularly those of the Omicron lineage. Here, we report the identification of a panel of vaccinee-derived antibodies that have broad-spectrum neutralization activity. Structural and biochemical characterization of the three broadest-spectrum antibodies reveal complementary footprints and differing requirements for avidity to overcome variant-associated mutations in their binding footprints. In the K18 mouse model of infection, these three antibodies exhibit protective efficacy against BA.1 and BA.2 infection. This study highlights the resilience and vulnerabilities of SARS-CoV-2 antibodies and provides road maps for further development of broad-spectrum therapeutics., Competing Interests: Declaration of interests K.M.H, S.S.H., and E.O.S. have a patent pending for the antibodies described in this study., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Although severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) initially infects the respiratory tract, it also directly or indirectly affects other organs, including the brain. However, little is known about the relative neurotropism of SARS-CoV-2 variants of concern (VOCs), including Omicron (B.1.1.529), which emerged in November 2021 and has remained the dominant pathogenic lineage since then. To address this gap, we examined the relative ability of Omicron, Beta (B.1.351), and Delta (B.1.617.2) to infect the brain in the context of a functional human immune system by using human angiotensin-converting enzyme 2 (hACE2) knock-in triple-immunodeficient NGC mice with or without reconstitution with human CD34 + stem cells. Intranasal inoculation of huCD34 + -hACE2-NCG mice with Beta and Delta resulted in productive infection of the nasal cavity, lungs, and brain on day 3 post-infection, but Omicron was surprisingly unique in its failure to infect either the nasal tissue or brain. Moreover, the same infection pattern was observed in hACE2-NCG mice, indicating that antiviral immunity was not responsible for the lack of Omicron neurotropism. In independent experiments, we demonstrate that nasal inoculation with Beta or with D614G, an ancestral SARS-CoV-2 with undetectable replication in huCD34 + -hACE2-NCG mice, resulted in a robust response by human innate immune cells, T cells, and B cells, confirming that exposure to SARS-CoV-2, even without detectable infection, is sufficient to induce an antiviral immune response. Collectively, these results suggest that modeling of the neurologic and immunologic sequelae of SARS-CoV-2 infection requires careful selection of the appropriate SARS-CoV-2 strain in the context of a specific mouse model., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Objective: To determine whether dogs can be trained to utilize olfaction to differentiate between saliva samples from dogs with cancer and those from healthy control dogs., Sample: Canine patient saliva samples were collected (October 2020 to July 2022) from 139 dogs diagnosed with malignant tumors and from 161 healthy dogs (control samples) for use during training and testing of the dog detection team. Samples from canine patients were collected prior to treatment with radiation therapy or chemotherapy., Procedures: Six pet dogs (mean ± SD age, 5.4 ± 1.9 years) were trained for odor discrimination between healthy control and malignant tumor samples. Training of the dogs, using a reward-based positive reinforcement method, took place 1 to 3 times per week for a period of 6 months (January to June 2022). After training was complete, a subset of samples not utilized during the training sessions were selected for use during odor discrimination testing of the dog team., Results: The trained dogs could accurately distinguish between samples from cancer patients versus control dogs with a mean sensitivity of 90% and mean specificity of 98%, and with mean positive and negative predictive values of 95%., Clinical Relevance: This study serves as preliminary evidence that dogs can be trained to detect differences in scent between saliva samples from cancer and normal patients. Further studies should expand upon these results with a larger sample, varied tumor types, use of non-cancer diseases as controls, and exploration of this technique in feline patients.

Background: Adult critical care and radiographical societies have recommended changing practice from routine screening radiographs to on-demand chest radiographs (CXRs) for stable mechanically ventilated adult patients. There are no similar recommendations for patients in the pediatric ICU. Reducing the frequency with which unneeded CXRs are obtained can decrease radiation exposure and reduce waste, a substantial contributor to rising health care costs. We aimed to reduce unneeded daily screening CXRs in a pediatric cardiovascular ICU (CICU) by 20% in 6 months., Methods: Criteria delineating which subjects in the CICU required daily screening CXRs were created and added to the daily rounding sheet for discussion for each subject. The primary goal of this study was to reduce CXRs in mechanically ventilated subjects as our previous practice had been to order daily CXRs. Respiratory therapists increased the frequency of evaluating and documenting endotracheal tube positioning prior to the initiation of this project. The outcome measure was the percentage subjects who received a daily screening CXR. The ratio of daily screening CXRs to the number of total CXRs ordered and unplanned extubations were followed as balancing measures., Results: The number of subjects who received a daily screening CXR decreased from a baseline of 67% to 44% over the course of this project. There was no change in the ratio of daily screening CXRs to the number of total CXRs ordered or an increase in unplanned extubations. With an estimated cost of $268 per CXR, a reduction of 33% in routine screening CXRs saves an estimated $250,000 annually., Conclusions: A decrease in daily screening CXRs can be sustained through the development of specific criteria to determine which patients need screening radiographs. This can be achieved without an increase in CXRs obtained at other times throughout the day or an increase in unplanned extubations. This eliminates unneeded health care expenditures, improves resource allocation for radiology technicians, and decreases disruptive interventions for patients., Competing Interests: The authors have disclosed no conflicts of interest., (Copyright © 2023 by Daedalus Enterprises.)

Background: This study was conducted to determine the association between fluid balance metrics and mortality and other postoperative outcomes after neonatal cardiac operation in a contemporary multicenter cohort., Methods: This was an observational cohort study across 22 hospitals in neonates (≤30 days) undergoing cardiac operation. We explored overall percentage fluid overload, postoperative day 1 percentage fluid overload, peak percentage fluid overload, and time to first negative daily fluid balance. The primary outcome was in-hospital mortality. Secondary outcomes included postoperative duration of mechanical ventilation and intensive care unit (ICU) and hospital length of stay. Multivariable logistic or negative binomial regression was used to determine independent associations between fluid overload variables and each outcome., Results: The cohort included 2223 patients. In-hospital mortality was 3.9% (n = 87). Overall median peak percentage fluid overload was 4.9% (interquartile range, 0.4%-10.5%). Peak percentage fluid overload and postoperative day 1 percentage fluid overload were not associated with primary or secondary outcomes. Hospital resource utilization increased on each successive day of not achieving a first negative daily fluid balance and was characterized by longer duration of mechanical ventilation (incidence rate ratio, 1.11; 95% CI, 1.08-1.14), ICU length of stay (incidence rate ratio, 1.08; 95% CI, 1.03-1.12), and hospital length of stay (incidence rate ratio, 1.09; 95% CI, 1.05-1.13)., Conclusions: Time to first negative daily fluid balance, but not percentage fluid overload, is associated with improved postoperative outcomes in neonates after cardiac operation. Specific treatments to achieve an early negative fluid balance may decrease postoperative care durations., (Copyright © 2022 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Monoclonal antibodies (mAbs) are emerging as safe and effective therapeutics against SARS-CoV-2. However, variant strains of SARS-CoV-2 have evolved, with early studies showing that some mAbs may not sustain their efficacy in the face of escape mutants. Also, from the onset of the COVID-19 pandemic, concern has been raised about the potential for Fcγ receptor-mediated antibody-dependent enhancement (ADE) of infection. In this study, plaque reduction neutralization assays demonstrated that mAb 1741-LALA neutralizes SARS-CoV-2 strains B.1.351, D614 and D614G. MAbs S1D2-hIgG1 and S1D2-LALA mutant (STI-1499-LALA) did not neutralize B.1.351, but did neutralize SARS-CoV-2 strains D614 and D614G. LALA mutations did not result in substantial differences in neutralizing abilities between clones S1D2-hIgG1 vs STI-1499-LALA. S1D2-hIgG1, STI-1499-LALA, and convalescent plasma showed minimal ability to induce ADE in human blood monocyte-derived macrophages. Further, no differences in pharmacokinetic clearance of S1D2-hIgG1 vs STI-1499-LALA were observed in mice expressing human FcRn. These findings confirm that SARS-CoV-2 has already escaped some mAbs, and identify a mAb candidate that may neutralize multiple SARS-CoV-2 variants. They also suggest that risk of ADE in macrophages may be low with SARS-CoV-2 D614, and LALA Fc change impacts neither viral neutralization nor Ab clearance., (Copyright © 2021. Published by Elsevier B.V.)

Follicular CXCR5+ PD-1+ CD8 T cells (CD8 Tfc) arise in multiple models of systemic autoimmunity yet their functional contribution to disease remains in debate. Here we define the follicular localization and functional interactions of CD8 Tfc with B cells during autoimmune disease. The absence of functional T regulatory cells in autoimmunity allows for CD8 Tfc development that then expands with lymphoproliferation. CD8 Tfc are identifiable within the lymph nodes and spleen during systemic autoimmunity, but not during tissue-restricted autoimmune disease. Autoimmune CD8 Tfc cells are polyfunctional, producing helper cytokines IL-21, IL-4, and IFNγ while maintaining cytolytic proteins CD107a, granzyme B, and TNF. During autoimmune disease, IL-2-KO CD8 T cells infiltrate the B cell follicle and germinal center, including the dark zone, and in vitro induce activation-induced cytidine deaminase in naïve B cells via IL-4 secretion. CD8 Tfc represent a unique CD8 T cell population with a diverse effector cytokine repertoire that can contribute to pathogenic autoimmune B cell response., (Copyright © 2021. Published by Elsevier Ltd.)

Background: We sought to evaluate the institutional use of inhaled nitric oxide (INO) and to create a pathway to reduce waste using the Institute for Healthcare Improvement's model for improvement. Our aim was to reduce the use of INO by 20% within 8 months., Methods: This was a prospective, respiratory therapist-driven, quality improvement project. We implemented a hospital-wide INO utilization protocol that was developed by neonatology, pediatric critical care, cardiac critical care, and respiratory therapy. INO use and respiratory therapist input for protocol failures were derived from the electronic medical record and were used to generate improvement opportunities. Monthly total hospital use of INO (in hours) was used as the primary outcome measure. Median hourly use per subject (evaluated in groups of 7 subjects) was used as a secondary outcome measure. New sildenafil dosing was tabulated for pre- and post-INO weaning protocol intervention as a balancing measure. Subjects included all patients in the hospital who were given INO therapy during the specified timeframe., Results: Hospital-wide total hours were reduced from 1,515 h/month to 930 h/month. This hospital-wide reduction of 39% equates to a cost-avoidance of approximately $912,000 per year based on 2018 costs of INO of $130 per hour. Median hours of INO per subject decreased from 88 h to 50 h. Sildenafil was started in 18 of 98 subjects (18%) in the pre-intervention period and in 12 of 109 subjects (11%) in the post-intervention period ( P = .27)., Conclusions: A hospital-wide, multi-professional initiative led to a reduction in unnecessary INO use, resulting in decreased subject exposure and associated cost avoidance., Competing Interests: The authors have disclosed no conflicts of interest., (Copyright © 2021 by Daedalus Enterprises.)

IL-2Rα, in part, comprises the high affinity receptor for IL-2, a cytokine important in immune proliferation, activation, and regulation. IL-2Rα deficient mice (IL-2Rα-KO) develop systemic autoimmune disease and die from severe anemia between 18 and 80 days of age. These mice develop kinetically distinct autoimmune progression, with approximately a quarter dying by 21 days of age and half dying after 30 days. This research aims to define immune parameters and cytokine signaling that distinguish cohorts of IL-2Rα-KO mice that develop early- versus late-stage autoimmune disease. To investigate these differences, we evaluated complete blood counts (CBC), antibody binding of RBCs, T cell numbers and activation, hematopoietic progenitor changes, and signaling kinetics, during autoimmune hemolytic anemia (AIHA) and bone marrow failure. We identified several alterations that, when combined, correlate to disease kinetics. Early onset disease correlates with anti-RBC antibodies, lower hematocrit, and reduced IL-7 signaling. CD8 regulatory T cells (Tregs) have enhanced apoptosis in early disease. Further, early and late end stage disease, while largely similar, had several differences suggesting distinct mechanisms drive autoimmune disease kinetics. Therefore, IL-2Rα-KO disease pathology rates, driven by T cell signaling, promote effector T cell activation and expansion and Treg dysfunction.

Pre-existing immunity to dengue virus (DENV) can either protect against or exacerbate, a phenomenon known as antibody dependent enhancement (ADE), a secondary DENV infection. DENV, as an escalating health problem worldwide, has increased the urgency to understand the precise parameters shaping the anti-DENV antibody (Ab) and T cell responses, thereby tipping the balance towards protection versus pathogenesis. Herein, we present the current state of knowledge of about the interplay between the Ab and T cell responses that dictate the outcome of DENV infection and discuss how this newfound knowledge is reshaping strategies for developing safe and effective DENV vaccines., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Counting intraepithelial lymphocytes (IELs) is a key part of the assessment of duodenal biopsies. Immunohistochemistry (IHC) for CD3 can aid identification of lymphocytes in this context, but it is not evident that counts on hematoxylin and eosin (H&E) and CD3 are comparable. This study aimed to compare the IEL counts in duodenal biopsies using H&E stains and CD3 IHC, and to examine the interobserver variability. Thirty-five paired H&E and CD3 sections were reviewed by 6 pathologists who counted the number of IELs per 100 enterocytes. The counts were categorized into groups: normal (<25 lymphocytes), mildly raised (25-40 lymphocytes), and markedly raised (>40 lymphocytes). CD3 IHC was associated with significantly higher IEL counts than H&E. Four cases with normal H&E counts had raised counts with CD3. There was moderate agreement between observers for both H&E and CD3. Lack of concordance between CD3 and H&E IEL counts suggests that counts derived from the 2 methods may not be comparable to each other and should not be considered equivalent. There was no significant improvement in interobserver variability with CD3 IHC.

The underlying mechanisms by which prior immunity to dengue virus (DENV) affords cross-protection against the related flavivirus Zika virus (ZIKV) are poorly understood. Here, we examine the ability of DENV/ZIKV-cross-reactive CD4 + T cells to protect against versus exacerbate ZIKV infection by using a histocompatibility leukocyte antigen (HLA)-DRB1 ∗ 0101 transgenic, interferon α/β receptor-deficient mouse model that supports robust DENV and ZIKV replication. By mapping the HLA-DRB1 ∗ 0101-restricted T cell response, we identify DENV/ZIKV-cross-reactive CD4 + T cell epitopes that stimulate interferon gamma (IFNγ) and/or tumor necrosis factor (TNF) production. Vaccination of naive HLA-DRB1 ∗ 0101 transgenic mice with these peptides induces a CD4 + T cell response sufficient to reduce tissue viral burden following ZIKV infection. Notably, this protective response requires IFNγ and/or TNF secretion but not anti-ZIKV immunoglobulin G (IgG) production. Thus, DENV/ZIKV-cross-reactive CD4 + T cells producing canonical Th1 cytokines can suppress ZIKV replication in an antibody-independent manner. These results may have important implications for increasing the efficacy and safety of DENV/ZIKV vaccines and for developing pan-flavivirus vaccines., Competing Interests: Declaration of Interests The La Jolla Institute for Immunology has a pending USA patent application, 16/537,447, covering methods and compositions utilizing the epitopes described in this manuscript for the treatment and prevention of flaviviruses, with S.S. listed as the inventor., (Published by Elsevier Inc.)

CD8 T cells are infrequently considered part of germinal center reactions. Yet, a distinct CXCR5+ CD8 T cell subset identified within the B cell follicle and germinal center in situations of chronic antigen has recently been defined. CXCR5+ CD8 T cells maintain transcriptional and phenotypic features consistent with the CD8 T cell nomenclature of a non-exhausted, effector memory population. CD8 T cell localization to the B cell follicle suggests a functional profile similar to CD4 T follicular helper cells that are licensed to promote B cell responses. The functional mechanisms defined under different immune settings, while largely similar, differentially control disease pathogenesis. CXCR5+ CD8 T cells control viral load during infection, and also promote antibody-mediated autoimmune disease progression. The existence of this novel CXCR5+ CD8 T cell subset in human and murine models of disease may provide a paradigm shift in our understanding of germinal center reactions.

Objectives: Thrombosis is a cause of morbidity in 4-15% of children who undergo pediatric cardiac surgery. Data on how to prevent this complication are sorely needed. We aimed to identify risk factors for thrombosis following pediatric cardiac surgery and determine if use of low molecular weight heparin prophylaxis is associated with a reduction in thrombosis risk., Design: Retrospective cohort study., Setting: Tertiary pediatric cardiovascular ICU., Patients: Patients who underwent cardiac surgery between June 2014 and December 2015., Interventions: None., Measurements and Main Results: Data from patients with venous or arterial thrombosis confirmed by radiologic studies were matched two-to-one to controls based on age, Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery mortality category, and gender. Thrombosis was detected in 33 patients (6.2%): 25 patients (76%) had venous thromboses, five patients (15%) had arterial thromboses, and three patients (9%) had both. Median time to thrombosis detection was 13 days (25-75%; 7-31 d). On multivariate analysis, which included adjustment for postoperative disease severity, fresh frozen plasma exposure was independently associated with thrombosis (odds ratio, 3.7; 95% CI, 1.4-9.4). Twenty-eight patients (85%) had central venous catheter-related thromboses. Low molecular weight heparin prophylaxis use in this subset of patients was not statistically different from controls (50% vs 45%, respectively; p = 0.47). On multivariable analysis, fresh frozen plasma exposure was also independently associated with central venous catheter-related thrombosis (odds ratio, 3.6; 95% CI, 1.2-10.6)., Conclusions: The occurrence of thrombosis after pediatric cardiac surgery at our institution was 6.2%, similar to what has been reported in other studies, despite frequent use of low molecular weight heparin. Further study is needed to determine the role of low molecular weight heparin for thromboprophylaxis and the relationship between fresh frozen plasma and thrombosis risk in children who undergo cardiac surgery.

T cell exhaustion is a state of hyporesponsiveness that develops during many chronic infections and cancer. Neutralization of inhibitory receptors, or "checkpoint blockade," can reverse T cell exhaustion and lead to beneficial prognoses in experimental and clinical settings. Whether checkpoint blockade can resolve lethal acute infections is less understood but may be beneficial in vaccination protocols that fail to elicit sterilizing immunity. Since a fully protective vaccine for any human parasite has yet to be developed, we explored the efficacy of checkpoint inhibitors in a mouse model of Toxoplasma gondii reinfection. Mice chronically infected with an avirulent type III strain survive reinfection with the type I RH strain but not the MAS, GUY-DOS, and GT1 parasite strains. We report here that mouse susceptibility to secondary infection correlates with the initial parasite burden and that protection against the RH strain is dependent on CD8 but not CD4 T cells in this model. When given a lethal secondary infection, CD8 and CD4 T cells upregulate several coinhibitory receptors, including PD-1, TIM-3, 4-1bb, and CTLA-4. Moreover, the gamma interferon (IFN-γ) response of CD8 but not CD4 T cells is significantly reduced during secondary infection with virulent strains, suggesting that checkpoint blockade may reduce disease severity. However, single and combination therapies targeting TIM-3, CTLA-4, and/or PD-L1 failed to reverse susceptibility to secondary infection. These results suggest that additional host responses, which are refractory to checkpoint blockade, are likely required for immunity to this pathogen., (Copyright © 2018 American Society for Microbiology.)

CD8 T cells can play both a protective and pathogenic role in inflammation and autoimmune development. Recent studies have highlighted the ability of CD8 T cells to function as T follicular helper (Tfh) cells in the germinal center in the context of infection. However, whether this phenomenon occurs in autoimmunity and contributes to autoimmune pathogenesis is largely unexplored. In this study, we show that CD8 T cells acquire a CD4 Tfh profile in the absence of functional regulatory T cells in both the IL-2-deficient and scurfy mouse models. Depletion of CD8 T cells mitigates autoimmune pathogenesis in IL-2-deficient mice. CD8 T cells express the B cell follicle-localizing chemokine receptor CXCR5, a principal Tfh transcription factor Bcl6, and the Tfh effector cytokine IL-21. CD8 T cells localize to the B cell follicle, express B cell costimulatory proteins, and promote B cell differentiation and Ab isotype class switching. These data reveal a novel contribution of autoreactive CD8 T cells to autoimmune disease, in part, through CD4 follicular-like differentiation and functionality., (Copyright © 2018 by The American Association of Immunologists, Inc.)

Objective: To describe the utility of high frequency jet ventilation (HFJV) as a rescue therapy in patients with respiratory failure secondary to respiratory syncytial virus (RSV) that was refractory to conventional mechanical ventilation (CMV)., Design: Descriptive study by retrospective review., Setting: Pediatric intensive care unit at a tertiary care children's hospital., Patients: Infants on mechanical ventilation for respiratory failure due to RSV., Interventions: Use of HFJV., Main Results: Eleven patients were placed on HFJV. There was sustained improvement in ventilation on HFJV with a mean decrease in PCO2 of 9 mmHg at 24 h and 11 mmHg at 72 h. There were no significant changes in oxygenation by oxygenation index. No patients required extracorporeal support or suffered pneumothorax, pneumomediastinum, or subcutaneous emphysema. Ten out of 11 (91%) patients survived to discharge from the hospital., Conclusion: High frequency jet ventilation may represent an alternative therapy for RSV-induced respiratory failure that is refractory to CMV.