Analysis of Cell-Mediated Immune Responses in Support of Dengue Vaccine Development Efforts

Dengue vaccine development has made significant strides, but a better understanding of how vaccine-induced immune responses correlate with vaccine efficacy can greatly accelerate development, testing, and deployment as well as ameliorate potential risks and safety concerns. Advances in basic immunology knowledge and techniques have already improved our understanding of cell-mediated immunity of natural dengue virus infection and vaccination. We conclude that the evidence base is adequate to argue for inclusion of assessments of cell-mediated immunity as part of clinical trials of dengue vaccines, although further research to identify useful correlates of protective immunity is needed

Stress and Predation Impacts on North American Quail Translocations

Translocations have been used in attempts to bolster or restore native quail populations for \u3e150 years, often with little success. However, with some northeastern United States quail populations undetectable or extirpated, and others across the United States on the extreme decline, translocation as a tool for quail population restoration is becoming increasingly popular. Two factors contributing to translocation failure are physiological stress and predation. Chronic stress associated with translocations can result in weight loss, reduced immune system function, suppressed reproduction, and an altered fight-or-flight response. These stress-induced responses increase vulnerability to predation, the primary cause of quail mortality. Here, we review the relationship between quail translocations, stress, and predation, and recommend future research and best practices to mitigate the impacts of stress and predation on translocated quail. To improve future translocation outcomes, more research is needed on stress mitigation throughout the translocation process (capture, handling, transport, and release). While capture and handling are unavoidably stressful, there is greater potential to reduce stress levels during holding and transport. Recent validation of fecal corticosterone metabolites as a non-invasive method to quantify stress in quail offers a useful tool for testing stress reduction protocols. Preliminary experimental results regarding nutritional supplements and stress levels are inconclusive, but enrichment during temporary holding and access to travel rations may help improve survival in long-distance (\u3e800 km) translocations. We also recommend predator control at release sites, particularly for raccoons (Procyon lotor) and other mesomammals

Defining epitope coverage requirements for T cell-based HIV vaccines: Theoretical considerations and practical applications

<p>Abstract</p> <p>Background</p> <p>HIV vaccine development must address the genetic diversity and plasticity of the virus that permits the presentation of diverse genetic forms to the immune system and subsequent escape from immune pressure. Assessment of potential HIV strain coverage by candidate T cell-based vaccines (whether natural sequence or computationally optimized products) is now a critical component in interpreting candidate vaccine suitability.</p> <p>Methods</p> <p>We have utilized an N-mer identity algorithm to represent T cell epitopes and explore potential coverage of the global HIV pandemic using natural sequences derived from candidate HIV vaccines. Breadth (the number of T cell epitopes generated) and depth (the variant coverage within a T cell epitope) analyses have been incorporated into the model to explore vaccine coverage requirements in terms of the number of discrete T cell epitopes generated.</p> <p>Results</p> <p>We show that when multiple epitope generation by a vaccine product is considered a far more nuanced appraisal of the potential HIV strain coverage of the vaccine product emerges. By considering epitope breadth and depth several important observations were made: (1) epitope breadth requirements to reach particular levels of vaccine coverage, even for natural sequence-based vaccine products is not necessarily an intractable problem for the immune system; (2) increasing the valency (number of T cell epitope variants present) of vaccine products dramatically decreases the epitope requirements to reach particular coverage levels for any epidemic; (3) considering multiple-hit models (more than one exact epitope match with an incoming HIV strain) places a significantly higher requirement upon epitope breadth in order to reach a given level of coverage, to the point where low valency natural sequence based products would not practically be able to generate sufficient epitopes.</p> <p>Conclusions</p> <p>When HIV vaccine sequences are compared against datasets of potential incoming viruses important metrics such as the minimum epitope count required to reach a desired level of coverage can be easily calculated. We propose that such analyses can be applied early in the planning stages and during the execution phase of a vaccine trial to explore theoretical and empirical suitability of a vaccine product to a particular epidemic setting.</p

Dengue virus downregulates TNFR1- and TLR3-stimulated NF-kB activation by targeting RIPK1

Dengue virus (DENV) infection is the most prevalent arthropod-borne virus disease and is endemic in more than 100 countries. Several DENV proteins have been shown to target crucial human host proteins to evade innate immune responses and establish a productive infection. Here we report that the DENV NS3 protein targets RIPK1 (Receptor Interacting Protein Kinase I), a central mediator of inflammation and cell death, and decreases intracellular RIPK1 levels during DENV infection. The interaction of NS3 with RIPK1 results in the inhibition of NF-κB activation in response to TNFR or TLR3 stimulation. Also, we observed that the effects of NS3 on RIPK1 were independent of NS3 protease activity. Our data demonstrate a novel mechanism by which DENV suppresses normal cellular functions to evade host innate immune response

CTL epitope distribution patterns in the Gag and Nef proteins of HIV-1 from subtype A infected subjects in Kenya: Use of multiple peptide sets increases the detectable breadth of the CTL response

BACKGROUND: Subtype A is a major strain in the HIV-1 pandemic in eastern Europe, central Asia and in certain regions of east Africa, notably in rural Kenya. While considerable effort has been focused upon mapping and defining immunodominant CTL epitopes in HIV-1 subtype B and subtype C infections, few epitope mapping studies have focused upon subtype A. RESULTS: We have used the IFN-γ ELIspot assay and overlapping peptide pools to show that the pattern of CTL recognition of the Gag and Nef proteins in subtype A infection is similar to that seen in subtypes B and C. The p17 and p24 proteins of Gag and the central conserved region of Nef were targeted by CTL from HIV-1-infected Kenyans. Several epitope/HLA associations commonly seen in subtype B and C infection were also observed in subtype A infections. Notably, an immunodominant HLA-C restricted epitope (Gag 296–304; YL9) was observed, with 8/9 HLA-C(W)0304 subjects responding to this epitope. Screening the cohort with peptide sets representing subtypes A, C and D (the three most prevalent HIV-1 subtypes in east Africa), revealed that peptide sets based upon an homologous subtype (either isolate or consensus) only marginally improved the capacity to detect CTL responses. While the different peptide sets detected a similar number of responses (particularly in the Gag protein), each set was capable of detecting unique responses not identified with the other peptide sets. CONCLUSION: Hence, screening with multiple peptide sets representing different sequences, and by extension different epitope variants, can increase the detectable breadth of the HIV-1-specific CTL response. Interpreting the true extent of cross-reactivity may be hampered by the use of 15-mer peptides at a single concentration and a lack of knowledge of the sequence that primed any given CTL response. Therefore, reagent choice and knowledge of the exact sequences that prime CTL responses will be important factors in experimentally defining cross-reactive CTL responses and their role in HIV-1 disease pathogenesis and validating vaccines aimed at generating broadly cross-reactive CTL responses

Iatrogenic Spinal Cord Injury Resulting From Cervical Spine Surgery.

STUDY DESIGN: Retrospective cohort study of prospectively collected data. OBJECTIVE: To examine the incidence of iatrogenic spinal cord injury following elective cervical spine surgery. METHODS: A retrospective multicenter case series study involving 21 high-volume surgical centers from the AOSpine North America Clinical Research Network was conducted. Medical records for 17 625 patients who received cervical spine surgery (levels from C2 to C7) between January 1, 2005, and December 31, 2011, were reviewed to identify occurrence of iatrogenic spinal cord injury. RESULTS: In total, 3 cases of iatrogenic spinal cord injury following cervical spine surgery were identified. Institutional incidence rates ranged from 0.0% to 0.24%. Of the 3 patients with quadriplegia, one underwent anterior-only surgery with 2-level cervical corpectomy, one underwent anterior surgery with corpectomy in addition to posterior surgery, and one underwent posterior decompression and fusion surgery alone. One patient had complete neurologic recovery, one partially recovered, and one did not recover motor function. CONCLUSION: Iatrogenic spinal cord injury following cervical spine surgery is a rare and devastating adverse event. No standard protocol exists that can guarantee prevention of this complication, and there is a lack of consensus regarding evaluation and treatment when it does occur. Emergent imaging with magnetic resonance imaging or computed tomography myelography to evaluate for compressive etiology or malpositioned instrumentation and avoidance of hypotension should be performed in cases of intraoperative and postoperative spinal cord injury

Longitudinal Analysis of Dengue Virus–Specific Memory T Cell Responses and Their Association With Clinical Outcome in Subsequent DENV Infection

Memory T cells resulting from primary dengue virus (DENV) infection are hypothesized to influence the clinical outcome of subsequent DENV infection. However, the few studies involving prospectively collected blood samples have found weak and inconsistent associations with outcome and variable temporal trends in DENV-specific memory T cell responses between subjects. This study used both ex-vivo and cultured ELISPOT assays to further evaluate the associations between DENV serotype-cross-reactive memory T cells and severity of secondary infection. Using ex-vivo ELISPOT assays, frequencies of memory T cells secreting IFN-γ in response to DENV structural and non-structural peptide pools were low in PBMC from multiple time points prior to symptomatic secondary DENV infection and showed a variable response to infection. There were no differences in responses between subjects who were not hospitalized (NH, n=6) and those who were hospitalized with dengue hemorrhagic fever (hDHF, n=4). In contrast, responses in cultured ELISPOT assays were more reliably detectable prior to secondary infection and showed more consistent increases after infection. Responses in cultured ELISPOT assays were higher in individuals with hDHF (n=8) compared to NH (n=9) individuals before the secondary infection, with no difference between these groups after infection. These data demonstrate an association of pre-existing DENV-specific memory responses with the severity of illness in subsequent DENV infection, and suggest that frequencies of DENV-reactive T cells measured after short-term culture may be of particular importance for assessing the risk for more severe dengue disease

Longitudinal Analysis of Memory B and T Cell Responses to Dengue Virus in a 5-Year Prospective Cohort Study in Thailand

Prior exposure to dengue virus (DENV) has a profound impact on the outcome of infection, which varies according to the interval between infections. Antibodies secreted by B cells and cytokines secreted by T cells are thought to contribute both to protective immunity against DENV and the pathogenesis of dengue disease. We analyzed peripheral blood mononuclear cells (PBMC) collected from Thai children over a 5-year prospective cohort study to define the dynamics of DENV-specific memory B and T cell responses and the impact of symptomatic or subclinical DENV infections. To measure B cell responses, PBMC were stimulated with IL-2 plus R848 and culture supernatants were tested for DENV-binding antibodies by ELISA. To measure T cell responses, PBMC were stimulated in dual-color ELISPOT assays with overlapping peptide pools of structural and non-structural proteins from the four DENV types. B cell responses were low to one or more DENV types prior to symptomatic infection and increased with reactivity to all four types after infection. Subjects who had a subclinical infection or who did not experience a DENV infection during the study period showed strong memory B cell responses to all four DENV types. T cell responses to DENV peptides demonstrated a cytokine hierarchy of IFN-γ \u3e IL-2 \u3e IFN-γ/IL-2. T cell responses were low or absent prior to secondary infections. The trends in T cell responses to DENV peptides over 3 year post-infection were highly variable, but subjects who had experienced a secondary DENV1 infection showed higher cytokine responses compared to subjects who had experienced a secondary DENV2 or subclinical infection. The longitudinal nature of our study demonstrates persistent memory B cell responses over years and a lasting but variable impact of secondary DENV infection on DENV-specific T cell responses

Cell-Mediated Immunity Generated in Response to a Purified Inactivated Vaccine for Dengue Virus Type 1

Dengue is the most prevalent arboviral disease afflicting humans, and a vaccine appears to be the most rational means of control. Dengue vaccine development is in a critical phase, with the first vaccine licensed in some countries where dengue is endemic but demonstrating insufficient efficacy in immunologically naive populations. Since virus-neutralizing antibodies do not invariably correlate with vaccine efficacy, other markers that may predict protection, including cell-mediated immunity, are urgently needed. Previously, the Walter Reed Army Institute of Research developed a monovalent purified inactivated virus (PIV) vaccine candidate against dengue virus serotype 1 (DENV-1) adjuvanted with alum. The PIV vaccine was safe and immunogenic in a phase I dose escalation trial in healthy, flavivirus-naive adults in the United States. From that trial, peripheral blood mononuclear cells obtained at various time points pre- and postvaccination were used to measure DENV-1-specific T cell responses. After vaccination, a predominant CD4+ T cell-mediated response to peptide pools covering the DENV-1 structural proteins was observed. Over half (13/20) of the subjects produced interleukin-2 (IL-2) in response to DENV peptides, and the majority (17/20) demonstrated peptide-specific CD4+ T cell proliferation. In addition, analysis of postvaccination cell culture supernatants demonstrated an increased rate of production of cytokines, including gamma interferon (IFN-γ), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF). Overall, the vaccine was found to have elicited DENV-specific CD4+ T cell responses as measured by enzyme-linked immunosorbent spot (ELISpot), intracellular cytokine staining (ICS), lymphocyte proliferation, and cytokine production assays. Thus, together with antibody readouts, the use of a multifaceted measurement of cell-mediated immune responses after vaccination is a useful strategy for more comprehensively characterizing immunity generated by dengue vaccines

Monomeric IgA Antagonizes IgG-Mediated Enhancement of DENV Infection

Dengue virus (DENV) is a prevalent human pathogen, infecting approximately 400 million individuals per year and causing symptomatic disease in approximately 100 million. A distinct feature of dengue is the increased risk for severe disease in some individuals with preexisting DENV-specific immunity. One proposed mechanism for this phenomenon is antibody-dependent enhancement (ADE), in which poorly-neutralizing IgG antibodies from a prior infection opsonize DENV to increase infection of Fc gamma receptor-bearing cells. While IgM and IgG are the most commonly studied DENV-reactive antibody isotypes, our group and others have described the induction of DENV-specific serum IgA responses during dengue. We hypothesized that monomeric IgA would be able to neutralize DENV without the possibility of ADE. To test this, we synthesized IgG and IgA versions of two different DENV-reactive monoclonal antibodies. We demonstrate that isotype-switching does not affect the antigen binding and neutralization properties of the two mAbs. We show that DENV-reactive IgG, but not IgA, mediates ADE in Fc gamma receptor-positive K562 cells. Furthermore, we show that IgA potently antagonizes the ADE activity of IgG. These results suggest that levels of DENV-reactive IgA induced by DENV infection might regulate the overall IgG mediated ADE activity of DENV-immune plasma in vivo, and may serve as a predictor of disease risk