Janet C. Lindow

A Single Dose of Any of Four Different Live Attenuated Tetravalent Dengue Vaccines Is Safe and Immunogenic in Flavivirus-naive Adults: A Randomized, Double-blind Clinical Trial

BACKGROUND Dengue virus (DENV) causes hundreds of millions of infections annually. Four dengue serotypes exist, and previous infection with one serotype increases the likelihood of severe disease with a second, heterotypic DENV infection. METHODS In a randomized, placebo-controlled study, the safety and immunogenicity of 4 different admixtures of a live attenuated tetravalent (LATV) dengue vaccine were evaluated in 113 flavivirus-naive adults. Serum neutralizing antibody levels to all 4 dengue viruses were measured on days 0, 28, 42, and 180. RESULTS A single dose of each LATV admixture induced a trivalent or better neutralizing antibody response in 75%-90% of vaccinees. There was no significant difference in the incidence of adverse events between vaccinees and placebo-recipients other than rash. A trivalent or better response correlated with rash and with non-black race (P < .0001). Black race was significantly associated with a reduced incidence of vaccine viremia. CONCLUSIONS TV003 induced a trivalent or greater antibody response in 90% of flavivirus-naive vaccinees and is a promising candidate for the prevention of dengue. Race was identified as a factor influencing the infectivity of the LATV viruses, reflecting observations of the effect of race on disease severity in natural dengue infection.

The Human CD8+ T Cell Responses Induced by a Live Attenuated Tetravalent Dengue Vaccine Are Directed against Highly Conserved Epitopes

ABSTRACT The incidence of infection with any of the four dengue virus serotypes (DENV1 to -4) has increased dramatically in the last few decades, and the lack of a treatment or vaccine has contributed to significant morbidity and mortality worldwide. A recent comprehensive analysis of the human T cell response against wild-type DENV suggested an human lymphocyte antigen (HLA)-linked protective role for CD8+ T cells. We have collected one-unit blood donations from study participants receiving the monovalent or tetravalent live attenuated DENV vaccine (DLAV), developed by the U.S. National Institutes of Health. Peripheral blood mononuclear cells from these donors were screened in gamma interferon enzyme-linked immunosorbent spot assays with pools of predicted, HLA-matched, class I binding peptides covering the entire DENV proteome. Here, we characterize for the first time CD8+ T cell responses after live attenuated dengue vaccination and show that CD8+ T cell responses in vaccinees were readily detectable and comparable to natural dengue infection. Interestingly, whereas broad responses to structural and nonstructural (NS) proteins were observed after monovalent vaccination, T cell responses following tetravalent vaccination were, dramatically, focused toward the highly conserved NS proteins. Epitopes were highly conserved in a vast variety of field isolates and able to elicit multifunctional T cell responses. Detailed knowledge of the T cell response will contribute to the identification of robust correlates of protection in natural immunity and following vaccination against DENV. IMPORTANCE The development of effective vaccination strategies against dengue virus (DENV) infection and clinically significant disease is a task of high global public health value and significance, while also being a challenge of significant complexity. A recent efficacy trial of the most advanced dengue vaccine candidate, demonstrated only partial protection against all four DENV serotypes, despite three subsequent immunizations and detection of measurable neutralizing antibodies to each serotype in most subjects. These results challenge the hypothesis that seroconversion is the only reliable correlate of protection. Here, we show that CD8+ T cell responses in vaccinees were readily detectable and comparable to natural dengue virus infection. Detailed knowledge of the T cell response may further contribute to the identification of robust correlates of protection in natural immunity and vaccination against DENV.

Vaccination of volunteers with low-dose, live-attenuated, dengue viruses leads to serotype-specific immunologic and virologic profiles.

There are currently no vaccines or therapeutics to prevent dengue disease which ranges in severity from asymptomatic infections to life-threatening illness. The National Institute of Allergy and Infectious Diseases (NIAID) Division of Intramural Research has developed live, attenuated vaccines to each of the four dengue serotypes (DENV-1-DENV-4). Two doses (10PFU and 1000PFU) of three monovalent vaccines were tested in human clinical trials to compare safety and immunogenicity profiles. DEN4Δ30 had been tested previously at multiple doses. The three dengue vaccine candidates tested (DEN1Δ30, DEN2/4Δ30, and DEN3Δ30/31) were very infectious, each with a human infectious dose 50%≤ 10PFU. Further, infectivity rates ranged from 90 to 100% regardless of dose, excepting DEN2/4Δ30 which dropped from 100% at the 1000PFU dose to 60% at the 10PFU dose. Mean geometric peak antibody titers did not differ significantly between doses for DEN1Δ30 (92 ± 19 vs. 214 ± 97, p=0.08); however, significant differences were observed between the 10PFU and 1000PFU doses for DEN2/4Δ30, 19 ± 9 vs. 102 ± 25 (p=0.001), and DEN3Δ30/31, 119 ± 135 vs. 50 ± 50 (p=0.046). No differences in the incidences of rash, neutropenia, or viremia were observed between doses for any vaccines, though the mean peak titer of viremia for DEN1Δ30 was higher at the 1000PFU dose (0.5 ± 0 vs. 1.1 ± 0.1, p=0.007). These data demonstrate that a target dose of 1000PFU for inclusion of each dengue serotype into a tetravalent vaccine is likely to be safe and generate a balanced immune response for all serotypes.

In a randomized, double-blinded, placebo-controlled trial, the single oral dose typhoid vaccine, M01ZH09, is safe and immunogenic at doses up to 1.7 × 1010 colony-forming units

M01ZH09, S. Typhi (Ty2 Delta aroC Delta ssaV) ZH9, is a single oral dose typhoid vaccine with independently attenuating deletions. A phase II randomized, double-blind, placebo-controlled, dose-escalating trial evaluated the safety and immunogenicity of M01ZH09 to 1.7 x 10(10) colony-forming units (CFU). 187 Healthy adults received vaccine or placebo in four cohorts. Serologic responses and IgA ELISPOT were measured. At all doses, the vaccine was well tolerated and without bacteremias. One subject had a transient low-grade fever. 62.2-86.1% of subjects seroconverted S. Typhi-specific LPS IgG and 83.3-97.4% IgA; 92.1% had a positive S. Typhi LPS ELISPOT. M01ZH09 is safe and immunogenic up to 1.7 x 10(10)CFU. Efficacy testing of this single-dose oral typhoid vaccine is needed.

Antibodies in Action: Role of Human Opsonins in Killing Salmonella enterica Serovar Typhi

ABSTRACT Although vaccines have been available for over a century, a correlate of protection for typhoid fever has yet to be identified. Antibodies are produced in response to typhoid infection and vaccination and are generally used as the gold standard for determining vaccine immunogenicity, even though their role in clearance of Salmonella enterica serovar Typhi infections is poorly defined. Here, we describe the first functional characterization of S. Typhi-specific antibodies following vaccination with a new vaccine, M01ZH09 (Ty2 ΔaroC ΔssaV). We determined that postvaccination sera increased the uptake of wild-type S. Typhi by human macrophages up to 2.3-fold relative to prevaccination (day 0) or placebo samples. These results were recapitulated using immunoglobulins purified from postvaccination serum, demonstrating that antibodies were largely responsible for increases in uptake. Imaging verified that macrophages internalized 2- to 9.5-fold more S. Typhi when the bacteria were opsonized with postvaccination sera than when the bacteria were opsonized with day 0 or placebo sera. Once inside macrophages, the survival of S. Typhi was reduced as much as 50% when opsonized with postvaccination sera relative to day 0 or placebo serum samples. Lastly, bactericidal assays indicated that antibodies generated postvaccination were recognized by complement factors and assisted in killing S. Typhi: mean postvaccination bactericidal antibody titers were higher at all time points than placebo and day 0 titers. These data clearly demonstrate that there are at least two mechanisms by which antibodies facilitate killing of S. Typhi. Future work could lead to improved immunogenicity tests associated with vaccine efficacy and the identification of correlates of protection against typhoid fever.

Primary Vaccination with Low Dose Live Dengue 1 Virus Generates a Proinflammatory, Multifunctional T Cell Response in Humans

The four dengue virus serotypes (DENV-1–DENV-4) have a large impact on global health, causing 50–100 million cases of dengue fever annually. Herein, we describe the first kinetic T cell response to a low-dose DENV-1 vaccination study (10 PFU) in humans. Using flow cytometry, we found that proinflammatory cytokines, IFNγ, TNFα, and IL-2, were generated by DENV-1-specific CD4+ cells 21 days post-DENV-1 exposure, and their production continued through the latest time-point, day 42 (p<0.0001 for all cytokines). No statistically significant changes were observed at any time-points for IL-10 (p = 0.19), a regulatory cytokine, indicating that the response to DENV-1 was primarily proinflammatory in nature. We also observed little T cell cross-reactivity to the other 3 DENV serotypes. The percentage of multifunctional T cells (T cells making ≥2 cytokines simultaneously) increased with time post-DENV-1 exposure (p<0.0001). The presence of multifunctional T cells together with neutralizing antibody data suggest that the immune response generated to the vaccine may be protective. This work provides an initial framework for defining primary T cell responses to each DENV serotype and will enhance the evaluation of a tetravalent DENV vaccine.

Deficient Serum Mannose-Binding Lectin Levels and MBL2 Polymorphisms Increase the Risk of Single and Recurrent Cryptosporidium Infections in Young Children

Mannose-binding lectin (MBL) is an evolutionarily conserved protein that functions in human innate immunity by binding to microbial surfaces and promoting opsonophagocytosis. MBL has been shown to bind to Cryptosporidium sporozoites, and earlier work has suggested that the protective role of MBL may be most important in childhood. We evaluated the association between polymorphisms in the MBL gene (MBL2), serum MBL deficiency, and infection with Cryptosporidium, Entamoeba histolytica, and Giardia intestinalis in children. A large, prospective cohort of Bangladeshi preschool children was followed up for >3 years. Clinical outcomes, serum MBL levels, and MBL2 polymorphisms and haplotypes were determined. Statistically significant associations with E. histolytica and G. intestinalis were not found. Serum MBL deficiency, polymorphisms in the -221 promoter region, and the YO/XA MBL2 haplotype were strongly associated with Cryptosporidium infections, particularly recurrent infection. Children with multiple infections with Cryptosporidium were more likely to be MBL deficient (odds ratio [OR], 10.45), carry the -221 promoter variant (OR, 4.02), and have the YO/XA haplotype (OR, 4.91). We have identified a potentially important component of the human innate immune response to Cryptosporidum infection. Further work is needed to evaluate the mechanism of protection of MBL in Cryptosporidium infection.

Cathelicidin Insufficiency in Patients with Fatal Leptospirosis

Leptospirosis causes significant morbidity and mortality worldwide; however, the role of the host immune response in disease progression and high case fatality (>10–50%) is poorly understood. We conducted a multi-parameter investigation of patients with acute leptospirosis to identify mechanisms associated with case fatality. Whole blood transcriptional profiling of 16 hospitalized Brazilian patients with acute leptospirosis (13 survivors, 3 deceased) revealed fatal cases had lower expression of the antimicrobial peptide, cathelicidin, and chemokines, but more abundant pro-inflammatory cytokine receptors. In contrast, survivors generated strong adaptive immune signatures, including transcripts relevant to antigen presentation and immunoglobulin production. In an independent cohort (23 survivors, 22 deceased), fatal cases had higher bacterial loads (P = 0.0004) and lower anti-Leptospira antibody titers (P = 0.02) at the time of hospitalization, independent of the duration of illness. Low serum cathelicidin and RANTES levels during acute illness were independent risk factors for higher bacterial loads (P = 0.005) and death (P = 0.04), respectively. To investigate the mechanism of cathelicidin in patients surviving acute disease, we administered LL-37, the active peptide of cathelicidin, in a hamster model of lethal leptospirosis and found it significantly decreased bacterial loads and increased survival. Our findings indicate that the host immune response plays a central role in severe leptospirosis disease progression. While drawn from a limited study size, significant conclusions include that poor clinical outcomes are associated with high systemic bacterial loads, and a decreased antibody response. Furthermore, our data identified a key role for the antimicrobial peptide, cathelicidin, in mounting an effective bactericidal response against the pathogen, which represents a valuable new therapeutic approach for leptospirosis.

Proteomic features predict seroreactivity against leptospiral antigens in leptospirosis patients.

With increasing efficiency, accuracy, and speed we can access complete genome sequences from thousands of infectious microorganisms; however, the ability to predict antigenic targets of the immune system based on amino acid sequence alone is still needed. Here we use a Leptospira interrogans microarray expressing 91% (3359) of all leptospiral predicted ORFs (3667) and make an empirical accounting of all antibody reactive antigens recognized in sera from naturally infected humans; 191 antigens elicited an IgM or IgG response, representing 5% of the whole proteome. We classified the reactive antigens into 26 annotated COGs (clusters of orthologous groups), 26 JCVI Mainrole annotations, and 11 computationally predicted proteomic features. Altogether, 14 significantly enriched categories were identified, which are associated with immune recognition including mass spectrometry evidence of in vitro expression and in vivo mRNA up-regulation. Together, this group of 14 enriched categories accounts for just 25% of the leptospiral proteome but contains 50% of the immunoreactive antigens. These findings are consistent with our previous studies of other Gram-negative bacteria. This genome-wide approach provides an empirical basis to predict and classify antibody reactive antigens based on structural, physical–chemical, and functional proteomic features and a framework for understanding the breadth and specificity of the immune response to L. interrogans.

Efficient Detection of Pathogenic Leptospires Using 16S Ribosomal RNA.

Pathogenic Leptospira species cause a prevalent yet neglected zoonotic disease with mild to life-threatening complications in a variety of susceptible animals and humans. Diagnosis of leptospirosis, which primarily relies on antiquated serotyping methods, is particularly challenging due to presentation of non-specific symptoms shared by other febrile illnesses, often leading to misdiagnosis. Initiation of antimicrobial therapy during early infection to prevent more serious complications of disseminated infection is often not performed because of a lack of efficient diagnostic tests. Here we report that specific regions of leptospiral 16S ribosomal RNA molecules constitute a novel and efficient diagnostic target for PCR-based detection of pathogenic Leptospira serovars. Our diagnostic test using spiked human blood was at least 100-fold more sensitive than corresponding leptospiral DNA-based quantitative PCR assays, targeting the same 16S nucleotide sequence in the RNA and DNA molecules. The sensitivity and specificity of our RNA assay against laboratory-confirmed human leptospirosis clinical samples were 64% and 100%, respectively, which was superior then an established parallel DNA detection assay. Remarkably, we discovered that 16S transcripts remain appreciably stable ex vivo, including untreated and stored human blood samples, further highlighting their use for clinical detection of L. interrogans. Together, these studies underscore a novel utility of RNA targets, specifically 16S rRNA, for development of PCR-based modalities for diagnosis of human leptospirosis, and also may serve as paradigm for detection of additional bacterial pathogens for which early diagnosis is warranted.