Innate Immune Responses and Gut Microbiomes Distinguish HIV-Exposed from HIV-Unexposed Children in a Population-Specific Manner.

In both high- and low-income countries, HIV-negative children born to HIV-positive mothers (HIV exposed, uninfected [HEU]) are more susceptible to severe infection than HIV-unexposed, uninfected (HUU) children, with altered innate immunity hypothesized to be a cause. Both the gut microbiome and systemic innate immunity differ across biogeographically distinct settings, and the two are known to influence each other. And although the gut microbiome is influenced by HIV infection and may contribute to altered immunity, the biogeography of immune-microbiome correlations among HEU children have not been investigated. To address this, we compared the innate response and the stool microbiome of 2-y-old HEU and HUU children from Belgium, Canada, and South Africa to test the hypothesis that region-specific immune alterations directly correlate to differences in their stool microbiomes. We did not detect a universal immune or microbiome signature underlying differences between HEU versus HUU that was applicable to all children. But as hypothesized, population-specific differences in stool microbiomes were readily detected and included reduced abundances of short-chain fatty acid-producing bacteria in Canadian HEU children. Furthermore, we did not identify innate immune-microbiome associations that distinguished HEU from HUU children in any population. These findings suggest that maternal HIV infection is independently associated with differences in both innate immunity and the stool microbiome in a biogeographical population-specific way.

Single-cell analysis of innate cytokine responses to pattern recognition receptor stimulation in children across four continents.

Innate immunity instructs adaptive immunity, and suppression of innate immunity is associated with an increased risk for infection. We showed previously that whole-blood cellular components from a cohort of South African children secreted significantly lower levels of most cytokines following stimulation of pattern recognition receptors compared with whole blood from cohorts of Ecuadorian, Belgian, or Canadian children. To begin dissecting the responsible molecular mechanisms, we set out to identify the relevant cellular source of these differences. Across the four cohorts represented in our study, we identified significant variation in the cellular composition of whole blood; however, a significant reduction in the intracellular cytokine production on the single-cell level was only detected in South African children's monocytes, conventional dendritic cells, and plasmacytoid dendritic cells. We also uncovered a marked reduction in polyfunctionality for each of these cellular compartments in South African children compared with children from the other continents. Together, our data identify differences in cell composition, as well as profoundly lower functional responses of innate cells, in our cohort of South African children. A possible link between altered innate immunity and increased risk for infection or lower response to vaccines in South African infants needs to be explored.

Functional genetic variation in NFKBIA and susceptibility to childhood asthma, bronchiolitis, and bronchopulmonary dysplasia.

Respiratory diseases are the most frequent chronic illnesses in babies and children. Although a vigorous innate immune system is critical for maintaining lung health, a balanced response is essential to minimize damaging inflammation. We investigated the functional and clinical impact of human genetic variants in the promoter of NFKBIA, which encodes IκBα, the major negative regulator of NF-κB. In this study, we quantified the functional impact of NFKBIA promoter polymorphisms (rs3138053, rs2233406, and rs2233409) on promoter-driven protein expression, allele-specific and total NFKBIA mRNA expression, IκBα protein expression, and TLR responsiveness; mapped innate immune regulatory networks active during respiratory syncytial virus infection, asthma, and bronchopulmonary dysplasia; and genotyped and analyzed independent cohorts of children with respiratory syncytial virus infection, asthma, and bronchopulmonary dysplasia. Genetic variants in the promoter of NFKBIA influenced NFKBIA gene expression, IκBα protein expression, and TLR-mediated inflammatory responses. Using a systems biology approach, we demonstrated that NFKBIA/IκBα is a central hub in transcriptional responses of prevalent childhood lung diseases, including respiratory syncytial virus infection, asthma, and bronchopulmonary dysplasia. Finally, by examining independent pediatric lung disease cohorts, we established that this immunologically relevant genetic variation in the promoter of NFKBIA is associated with differential susceptibility to severe bronchiolitis following infection with respiratory syncytial virus, airway hyperresponsiveness, and severe bronchopulmonary dysplasia. These data highlight the importance of negative innate immune regulators, such as NFKBIA, in pediatric lung disease and begin to unravel common aspects in the genetic predisposition to bronchopulmonary dysplasia, bronchiolitis, and childhood asthma.

Pattern recognition receptor-mediated cytokine response in infants across 4 continents.

BACKGROUND: Susceptibility to infection as well as response to vaccination varies among populations. To date, the underlying mechanisms responsible for these clinical observations have not been fully delineated. Because innate immunity instructs adaptive immunity, we hypothesized that differences between populations in innate immune responses may represent a mechanistic link to variation in susceptibility to infection or response to vaccination. OBJECTIVE: Determine whether differences in innate immune responses exist among infants from different continents of the world. METHODS: We determined the innate cytokine response following pattern recognition receptor (PRR) stimulation of whole blood from 2-year-old infants across 4 continents (Africa, North America, South America, and Europe). RESULTS: We found that despite the many possible genetic and environmental exposure differences in infants across 4 continents, innate cytokine responses were similar for infants from North America, South America, and Europe. However, cells from South African infants secreted significantly lower levels of cytokines than did cells from infants from the 3 other sites, and did so following stimulation of extracellular and endosomal but not cytosolic PRRs. CONCLUSIONS: Substantial differences in innate cytokine responses to PRR stimulation exist among different populations of infants that could not have been predicted. Delineating the underlying mechanism(s) for these differences will not only aid in improving vaccine-mediated protection but possibly also provide clues for the susceptibility to infection in different regions of the world.

Humanized TLR4/MD-2 mice reveal LPS recognition differentially impacts susceptibility to Yersinia pestis and Salmonella enterica.

Although lipopolysaccharide (LPS) stimulation through the Toll-like receptor (TLR)-4/MD-2 receptor complex activates host defense against Gram-negative bacterial pathogens, how species-specific differences in LPS recognition impact host defense remains undefined. Herein, we establish how temperature dependent shifts in the lipid A of Yersinia pestis LPS that differentially impact recognition by mouse versus human TLR4/MD-2 dictate infection susceptibility. When grown at 37°C, Y. pestis LPS is hypo-acylated and less stimulatory to human compared with murine TLR4/MD-2. By contrast, when grown at reduced temperatures, Y. pestis LPS is more acylated, and stimulates cells equally via human and mouse TLR4/MD-2. To investigate how these temperature dependent shifts in LPS impact infection susceptibility, transgenic mice expressing human rather than mouse TLR4/MD-2 were generated. We found the increased susceptibility to Y. pestis for "humanized" TLR4/MD-2 mice directly paralleled blunted inflammatory cytokine production in response to stimulation with purified LPS. By contrast, for other Gram-negative pathogens with highly acylated lipid A including Salmonella enterica or Escherichia coli, infection susceptibility and the response after stimulation with LPS were indistinguishable between mice expressing human or mouse TLR4/MD-2. Thus, Y. pestis exploits temperature-dependent shifts in LPS acylation to selectively evade recognition by human TLR4/MD-2 uncovered with "humanized" TLR4/MD-2 transgenic mice.

Benefits and risks of off-label olanzapine use for symptom management in cancer patients-a case report.

BACKGROUND: Cancer patients often experience symptoms such as anorexia, anxiety and insomnia, which can impact their quality of life. Randomized placebo-controlled trials support prophylactic use of olanzapine for the prevention of nausea and vomiting due to moderate and high-emetic risk chemotherapy. In the setting of palliative care, olanzapine is increasingly utilized as an off-label treatment of symptoms including anorexia-cachexia, anxiety, and insomnia. The following case reports will highlight the potential benefits and risks of off-label olanzapine use for symptom management in cancer patients. CASE DESCRIPTION: Patient 1 is a female in her 70s with stage IV infiltrating ductal carcinoma of the right breast was having trouble tolerating treatment with letrozole, palbociclib, and denosumab due to uncontrolled nausea resulting in weight loss. Her nausea was refractory to multiple anti-emetics. Low dose olanzapine (2.5 mg) prevented nausea and allowed her to tolerate treatment. Patient 2 is a male in his 50s with renal cell carcinoma, who was receiving treatment with cabozantinib, presented with uncontrolled pain improved with opioid rotation from oxycodone to morphine. He was also experiencing uncontrolled anxiety despite treatment with alprazolam. Alprazolam was weaned and replaced with olanzapine resulting in improvement of his symptoms. Patient 3 is a male in his 60s with pancreatic adenocarcinoma who presented with muscle weakness and fatigue resulting in discontinuation of gemcitabine plus cisplatin. He also had symptoms of depression, poor appetite, and sleep problems. He was prescribed short course of dexamethasone 4 mg by mouth twice daily and olanzapine 5 mg by mouth nightly to improve symptoms. One week after, he presented with confusion and workup revealed hyperammonia which was treated with lactulose, which led to the return of baseline mentation. CONCLUSIONS: Olanzapine antagonizes multiple receptors and has potential to treat a host of symptoms including nausea, anorexia, anxiety, and insomnia, but healthcare providers should be mindful of potential risks and unclear benefits for off-label indications. More research and funding are needed evaluating off-label use of olanzapine for palliation of symptoms in cancer patients who are often frail and susceptible to adverse events.

Neonatal innate TLR-mediated responses are distinct from those of adults.

The human neonate and infant are unduly susceptible to infection with a wide variety of microbes. This susceptibility is thought to reflect differences from adults in innate and adaptive immunity, but the nature of these differences is incompletely characterized. The innate immune response directs the subsequent adaptive immune response after integrating information from TLRs and other environmental sensors. We set out to provide a comprehensive analysis defining differences in response to TLR ligation between human neonates and adults. In response to most TLR ligands, neonatal innate immune cells, including monocytes and conventional and plasmacytoid dendritic cells produced less IL-12p70 and IFN-alpha (and consequently induced less IFN-gamma), moderately less TNF-alpha, but as much or even more IL-1beta, IL-6, IL-23, and IL-10 than adult cells. At the single-cell level, neonatal innate cells generally were less capable of producing multiple cytokines simultaneously, i.e., were less polyfunctional. Overall, our data suggest a robust if not enhanced capacity of the neonate vs the adult white-blood cell TLR-mediated response to support Th17- and Th2-type immunity, which promotes defense against extracellular pathogens, but a reduced capacity to support Th1-type responses, which promote defense against intracellular pathogens.

Correlation analysis of intracellular and secreted cytokines via the generalized integrated mean fluorescence intensity.

The immune response in humans is usually assessed using immunogenicity assays to provide biomarkers as correlates of protection (CoP). Flow cytometry is the assay of choice to measure intracellular cytokine staining (ICS) of cell-mediated immune (CMI) biomarkers. For CMI analysis, the integrated mean fluorescence intensity (iMFI) was introduced as a metric to represent the total functional CMI response as a CoP. iMFI is computed by multiplying the relative frequency (percent positive) of cells expressing a particular cytokine with the MFI of that population, and correlates better with protection in challenge models than either the percentage or the MFI of the cytokine-positive population. While determination of the iMFI as a CoP can readily be accomplished in animal models that allow challenge/protection experiments, this is not feasible in humans for ethical reasons. As a first step toward extending the iMFI concept to humans, we investigated the correlation of the iMFI derived from a human innate immune response ICS assay with functional cytokine release into the culture supernatant, as innate cytokines need to be released to have a functional impact. Next, we developed a quantitatively more correlative mathematical approach for calculating the functional response of cytokine-producing cells by incorporating the assignment of different weights to the magnitude (frequency of cytokine-positive cells) and the quality (the MFI) of the observed innate immune response. We refer to this model as generalized iMFI.

Identification of B cells through negative gating-An example of the MIFlowCyt standard applied.

Polychromatic flow cytometric analysis takes advantage of the increasing number of available fluorophores to positively identify and simultaneously assess multiple parameters in the same cell (1). Additional parameters may be analyzed through negative identification (i.e., through exclusion of particular stains or antibodies employed). In this report, we tested whether such negative-gating strategy would identify human B lymphocytes in innate immune phenotyping studies. To this end, B cells were identified as the negatively-stained subpopulation from the CD123 vs. CD11c plot of the CD14(neg-low), MHC II(high) human peripheral blood mononuclear cells. To test the specificity of this negative gating approach, we confirmed that negatively gated B cells indeed expressed CD19, the bona fide marker for human B cells. However, a small number of unidentified cells were contained in the negatively-gated B cells. Furthermore, a small percentage cells expressing markers used to identify monocytes and myeloid dendritic cells (mDC) coexpressed CD19. This identifies such negative B-cell gating approach as potentially problematic. When applied to the analysis of Toll-like receptors (TLR) stimulation experiments, we were however able to interpret the results, as B-cells respond to TLR stimulation in a qualitative different pattern as compared to monocytes and DC. This report is presented in a manner that is fully compliant with the Minimum Information about a Flow Cytometry Experiment (MIFlowCyt) standard, which was recently adopted by the International Society for Advancement of Cytometry (ISAC) (2) and incorporated in the publishing policies of Cytometry and other journals. We demonstrate how a MIFlowCyt-compliant report can be prepared with minimal effort, and yet provide the reader with a much clearer picture of the portrayed FCM experiment and data.

Smad10 is required for formation of the frog nervous system.

Before the nervous system establishes its complex array of cell types and connections, multipotent cells are instructed to adopt a neural fate and an anterior-posterior pattern is established. In this report, we show that Smad10, a member of the Smad family of intracellular transducers of TGFbeta signaling, is required for formation of the nervous system. In addition, two types of molecules proposed as key to neural induction and patterning, bone morphogenetic protein (BMP) antagonists and fibroblast growth factor (FGF), require Smad10 for these activities. These data suggest that Smad10 may be a central mediator of the development of the frog nervous system.

Elevated inflammatory mediators in adults with oculorespiratory syndrome following influenza immunization: a public health agency of Canada/Canadian Institutes of Health Research Influenza Research Network Study.

Oculorespiratory syndrome (ORS) is an infrequent adverse event following influenza vaccination. Its clinical presentation suggests that ORS is an immune-mediated phenomenon, but studies of symptomatic individuals have been few. This study measured cytokine levels in peripheral blood samples following influenza vaccination in those with and without current ORS symptoms. Canadian adults receiving the 2010-2011 seasonal influenza vaccine were recruited and asked to promptly report any adverse effects. ORS symptoms occurring 4 to 48 h after vaccination were identified using previously published criteria. Two blood samples were collected from each subject to measure blood plasma cytokine and hemagglutination inhibition antibody (HAI) titers; visit 1 occurred during the acute disease phase or 4 to 72 h after vaccination for controls, and visit 2 occurred another 21 days postimmunization. Nine ORS cases and 35 controls were enrolled. The median age of ORS cases was 49 years, and 89% were female. Most cases had multiple symptoms, but none required medical care. HAI titers before and after vaccination were similar for the cases and controls. Blood plasma cytokine concentrations did not differ between the ORS cases and controls for most cytokines measured (interleukin 4 [IL-4], IL-5, IL-10, IL-13, IL-1α, IL-8, tumor necrosis factor alpha [TNF-α], gamma interferon [IFN-γ], and IL-17A). However, ORS cases had higher levels of IL-10 and IL-3 than the controls at visits 1 and 2, even after all symptoms had subsided. Persistent higher levels of IL-10 and IL-3 in ORS cases suggest that host factors may have predisposed these individuals to develop ORS following influenza vaccination. Further investigations are warranted, as they might identify subjects who are at risk for ORS prior to vaccination.

Evaluation of 2009 pandemic H1N1 influenza vaccination in adults with lymphoid malignancies receiving chemotherapy or following autologous stem cell transplant.

This is a randomized trial evaluating the safety and immunogenicity of one or two doses of 2009 pandemic H1N1 influenza vaccination in adults with lymphoid malignancies. Adults with a lymphoid malignancy receiving active systemic therapy, or within a year after autologous stem cell transplant, received one dose of AS03-adjuvanted A/California/7/2009 (H1N1) vaccine, and were randomized 21 days later to a second dose or no further vaccination. The primary outcomes were seroprotection and seroconversion rates by hemagglutination inhibition 21 and 42 days after initial vaccination. Twenty-two patients received one dose, and 20 patients received a second dose. Seroconversion rates at day 21 were 30% (one dose) and 5% (two doses), and subsequently 30% for both groups at day 42. Seroprotection rates at day 21 were 40% (one dose) and 15% (two doses), and subsequently 35% (one dose) and 40% (two doses) at day 42. Differences in serologic endpoints were not statistically significant between both study arms at day 42. Patients with low levels of B-cells (CD19-positive) had low seroconversion rates on days 21 (odds ratio [OR] 0.74, 95% confidence interval [CI] 0.59-0.93, p = 0.043) and 42 (OR 0.12, 95% CI 0.01-1.07, p = 0.058). Only three of the 14 patients who received rituximab achieved seroprotective titers by day 42. Patients with lymphoid malignancies did not achieve rates of seroconversion or seroprotection seen in healthy subjects despite a second dose and the use of an adjuvant. Notwithstanding suboptimal immunogenicity, seasonal and pandemic influenza vaccination should continue to be recommended.

Recurrent subacute post-viral onset of ataxia associated with a PRF1 mutation.

Inflammation is an important contributor to pediatric and adult neurodegeneration. Understanding the genetic determinants of neuroinflammation provides valuable insight into disease mechanism. We characterize a disorder of recurrent immune-mediated neurodegeneration. We report two sisters who presented with neurodegeneration triggered by infections. The proband, a previously healthy girl, presented at 22.5 months with ataxia and dysarthria following mild gastroenteritis. MRI at onset showed a symmetric signal abnormality of the cerebellar and peritrigonal white matter. Following a progressive course of partial remissions and relapses, she died at 5 years of age. Her older sister had a similar course following varicella infection, she died within 13 months. Both sisters had unremarkable routine laboratory testing, with exception of a transient mild cytopenia in the proband 19 months after presentation. Exome sequencing identified a biallelic perforin1 mutation (PRF1; p.R225W) previously associated with familial hemophagocytic lymphohistiocytosis (FHL). In contrast to FHL, these girls did not have hematopathology or cytokine overproduction. However, 3 years after disease onset, the proband had markedly deficient interleukin-1 beta (IL-1ß) production. These observations extend the spectrum of disease associated with perforin mutations to immune-mediated neurodegeneration triggered by infection and possibly due to primary immunodeficiency.

Age of recipient and number of doses differentially impact human B and T cell immune memory responses to HPV vaccination.

Vaccination is one of the most effective medical interventions. However, optimization of existing as well as design of new vaccines is still mostly conducted empirically; a rational approach to vaccine design is largely prohibited by the lack of insight into the relevant mechanisms underlying immune-mediated protection. To delineate the impact of variables on immune memory formation following vaccination, we took advantage of a trial assessing the role of the age of the recipient and the number of administered doses of the quadrivalent HPV vaccine in a well-characterized longitudinal cohort of girls and young women. We found that age of the recipient and the number of doses administered differentially impact the development of B and T cell memory. Specifically, age of the recipient significantly impacted generation of HPV 18-specific B cell memory, while the number of vaccine doses displayed a significant effect on the development of HPV-specific T cell memory. Our data indicate that rational design of vaccines has to be tailored according to the desired induction of B and/or T cell memory.

Ontogeny of Toll-like receptor mediated cytokine responses of South African infants throughout the first year of life.

The first year of life represents a time of marked susceptibility to infections; this is particularly true for regions in sub-Saharan Africa. As innate immunity directs the adaptive immune response, the observed increased risk for infection as well as a suboptimal response to vaccination in early life may be due to less effective innate immune function. In this study, we followed a longitudinal cohort of infants born and raised in South Africa over the first year of life, employing the most comprehensive analysis of innate immune response to stimulation published to date. Our findings reveal rapid changes in innate immune development over the first year of life. This is the first report depicting dramatic differences in innate immune ontogeny between different populations in the world, with important implications for global vaccination strategies.

Variables to be controlled in the assessment of blood innate immune responses to Toll-like receptor stimulation.

Variability in TLR function influences susceptibility to infectious as well as immune-mediated diseases. Given the outbred nature of humans, identifying functional Toll-like receptor variability and its role in clinical disease requires such analysis to be conducted in large, often multi-centered cohorts. Yet the technically complex measurements involved in innate immune analysis benefit from centralized processing of samples. Centralization requires shipping of samples or prolonged storage, possibly even cryopreservation. Deviation from standard operating procedures (SOP) for sample procurement, storage and processing may alter the final innate immune read out. We here set out to define the impact of variables most likely to be encountered during large, multi-site studies: (i) the source of the sample, (ii) time between sample procurement to processing, and (iii) processing of fresh vs. cryopreserved samples. We found that all of these variables exert a profound impact on the final innate response to TLR stimulation. Specific innate responses appeared to be affected in response to specific TLR stimuli by a particular variable under study, proving it impossible to provide global generalizations. Based on our studies and other published work on this topic, we propose a minimal list of variables that have to be met for samples to be comparable within and across studies: a) timing between procurement and processing cannot vary by more than 10%; b) all samples have to be stored the same; and c) the source of samples needs to be the same. In summary, for innate immune analysis scrupulous adherence to standard operating procedures is paramount.

Facilitating the analysis of immunological data with visual analytic techniques.

Visual analytics (VA) has emerged as a new way to analyze large dataset through interactive visual display. We demonstrated the utility and the flexibility of a VA approach in the analysis of biological datasets. Examples of these datasets in immunology include flow cytometry, Luminex data, and genotyping (e.g., single nucleotide polymorphism) data. Contrary to the traditional information visualization approach, VA restores the analysis power in the hands of analyst by allowing the analyst to engage in real-time data exploration process. We selected the VA software called Tableau after evaluating several VA tools. Two types of analysis tasks analysis within and between datasets were demonstrated in the video presentation using an approach called paired analysis. Paired analysis, as defined in VA, is an analysis approach in which a VA tool expert works side-by-side with a domain expert during the analysis. The domain expert is the one who understands the significance of the data, and asks the questions that the collected data might address. The tool expert then creates visualizations to help find patterns in the data that might answer these questions. The short lag-time between the hypothesis generation and the rapid visual display of the data is the main advantage of a VA approach.

A single immunization near birth elicits immediate and lifelong protective immunity.

Most existing vaccines do not induce protective immunity immediately following birth, nor do they retain protective efficacy in the latter years of life without booster doses. Using a mouse model, we present evidence that a live-replicating vaccine administered only once shortly after birth was able to induce both immediate and lifelong protection. Newborn mice immunized with a safe, highly attenuated strain of Listeria monocytogenes (Lm) were already protected by day 7 post-vaccination when challenged with a virulent strain of Lm. Furthermore, all mice remained fully protected for 2 years after only a single immunization. Vaccine-specific T cell immune responses were still detectable 2 years later, indicating long-lived immune memory even in neonatal vaccine recipients. Analysis of memory precursor subsets, specific for antigens homologous to Lm or a model vaccine (Ova), demonstrated remarkable similarity between adult and neonatal vaccine recipient effector and central memory CD8 T cell development. The magnitude of expansion of antigen specific memory T cells post-infectious challenge correlated with protection in both groups. This is the first direct evidence that vaccination--even in the absence of a booster dose--is capable of inducing immediate and lifelong protective immune memory regardless of age at the time of initial vaccination.

Ontogeny of Toll-like receptor mediated cytokine responses of human blood mononuclear cells.

Newborns and young infants suffer increased infectious morbidity and mortality as compared to older children and adults. Morbidity and mortality due to infection are highest during the first weeks of life, decreasing over several years. Furthermore, most vaccines are not administered around birth, but over the first few years of life. A more complete understanding of the ontogeny of the immune system over the first years of life is thus urgently needed. Here, we applied the most comprehensive analysis focused on the innate immune response following TLR stimulation over the first 2 years of life in the largest such longitudinal cohort studied to-date (35 subjects). We found that innate TLR responses (i) known to support Th17 adaptive immune responses (IL-23, IL-6) peaked around birth and declined over the following 2 years only to increase again by adulthood; (ii) potentially supporting antiviral defense (IFN-α) reached adult level function by 1 year of age; (iii) known to support Th1 type immunity (IL-12p70, IFN-γ) slowly rose from a low at birth but remained far below adult responses even at 2 years of age; (iv) inducing IL-10 production steadily declined from a high around birth to adult levels by 1 or 2 years of age, and; (v) leading to production of TNF-α or IL-1ß varied by stimuli. Our data contradict the notion of a linear progression from an 'immature' neonatal to a 'mature' adult pattern, but instead indicate the existence of qualitative and quantitative age-specific changes in innate immune reactivity in response to TLR stimulation.

Neonatal immunization with Listeria monocytogenes induces T cells with an adult-like avidity, sensitivity, and TCR-Vbeta repertoire, and does not adversely impact the response to boosting.

Listeria monocytogenes (Lm) holds promise as a neonatal vaccine vehicle. Here we show that Lm immunized neonatal mice reached maximal Ag-specific CD8(+) T cell expansion after only a single immunization, while adults required two doses. Ag-specific CD4(+) T cell expansion in both age groups required a boost to reach its peak. Neither functional avidity, sensitivity, nor the TCR-Vbeta repertoire of the Ag-specific T cells differed between mice immunized as neonates or adults. Lastly, neonatal immunization did not decrease protection or preclude a booster response. Overall, our data provide further evidence in support of immunization at birth as a feasible public health strategy to combat early life infections.