Catherine J. Larsson

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.

Robust and Balanced Immune Responses to All 4 Dengue Virus Serotypes Following Administration of a Single Dose of a Live Attenuated Tetravalent Dengue Vaccine to Healthy, Flavivirus-Naive Adults

BACKGROUND The 4 serotypes of dengue virus, DENV-1-4, are the leading cause of arboviral disease globally. The ideal dengue vaccine would provide protection against all serotypes after a single dose. METHODS Two randomized, placebo-controlled trials were performed with 168 flavivirus-naive adults to demonstrate the safety and immunogenicity of a live attenuated tetravalent dengue vaccine (TV003), compared with those of a second tetravalent vaccine with an enhanced DENV-2 component (TV005), and to evaluate the benefit of a booster dose at 6 months. Safety data, viremia, and neutralizing antibody titers were evaluated. RESULTS A single dose of TV005 elicited a tetravalent response in 90% of vaccinees by 3 months after vaccination and a trivalent response in 98%. Compared with TV003, the higher-dose DENV-2 component increased the observed frequency of immunogenicity to DENV-2 in the TV005 trial. Both the first and second doses were well tolerated. Neither vaccine viremia, rash, nor a significant antibody boost were observed following a second dose. CONCLUSIONS A single subcutaneous dose of TV005 dengue vaccine is safe and induces a tetravalent antibody response at an unprecedented frequency among vaccinees. A second dose has limited benefit and appears to be unnecessary. Studies to confirm these findings and assess vaccine efficacy will now move to populations in regions where DENV transmission is endemic. CLINICAL TRIALS REGISTRATION NCT01072786 and NCT01436422.

The live attenuated dengue vaccine TV003 elicits complete protection against dengue in a human challenge model

A controlled dengue human challenge model may determine whether to evaluate candidate dengue vaccines in large efficacy trials. Dengue model rises to the challenge Human efficacy testing remains a major hurdle in bringing new vaccine candidates to the clinic. In the absence of accepted correlates of protection, rounds of safety trials must be performed before efficacy can be tested in a large population in an endemic area. Kirkpatrick et al. have developed a controlled dengue human challenge model to assess the protective efficacy of the most clinically advanced dengue vaccine candidate. They found that TV003, a live attenuated dengue vaccine that induces antibodies to all four dengue virus serotypes, protected against infection of an attenuated virus in 21 recipients when compared with 20 nonvaccinated controls. This model may serve as an early check for dengue vaccine candidates, limiting the risk of conducting large unsuccessful trials. A dengue human challenge model can be an important tool to identify candidate dengue vaccines that should be further evaluated in large efficacy trials in endemic areas. Dengue is responsible for about 390 million infections annually. Protective efficacy results for the most advanced dengue vaccine candidate (CYD) were disappointing despite its ability to induce neutralizing antibodies against all four dengue virus (DENV) serotypes. TV003 is a live attenuated tetravalent DENV vaccine currently in phase 2 evaluation. To better assess the protective efficacy of TV003, a randomized double-blind, placebo-controlled trial in which recipients of TV003 or placebo were challenged 6 months later with a DENV-2 strain, rDEN2Δ30, was conducted. The primary endpoint of the trial was protection against dengue infection, defined as rDEN2Δ30 viremia. Secondary endpoints were protection against rash and neutropenia. All 21 recipients of TV003 who were challenged with rDEN2Δ30 were protected from infection with rDEN2Δ30. None developed viremia, rash, or neutropenia after challenge. In contrast, 100% of the 20 placebo recipients who were challenged with rDEN2Δ30 developed viremia, 80% developed rash, and 20% developed neutropenia. TV003 induced complete protection against challenge with rDEN2Δ30 administered 6 months after vaccination. TV003 will be further evaluated in dengue-endemic areas. The controlled dengue human challenge model can accelerate vaccine development by evaluating the protection afforded by the vaccine, thereby eliminating poor candidates from further consideration before the initiation of large efficacy trials.

The Novel Oral Typhoid Vaccine M01ZH09 Is Well Tolerated and Highly Immunogenic in 2 Vaccine Presentations

BACKGROUND M01ZH09 (Salmonella enterica serovar Typhi [Ty2 aroC(-) ssaV(-)] ZH9) is a live oral-dose typhoid vaccine candidate. M01ZH09 was rationally modified with 2 independently attenuating mutations, including a novel mutation in Salmonella pathogenicity island (SPI)-2. We demonstrate that M01ZH09, in a single oral dose, is well tolerated and prompts broad immune responses, regardless of whether prevaccination with a bicarbonate buffer is given. METHODS Thirty-two healthy adult subjects were randomized and given 5x109 cfu of M01ZH09, with (presentation 1) or without (presentation 2) prevaccination with a bicarbonate buffer. Immunogenicity data included Salmonella Typhi lipopolysaccharide (LPS)-specific immunoglobulin (Ig) A antibody-secreting cells (enzyme-linked immunospot [ELISPOT] assay), IgG serologic responses to Salmonella Typhi LPS, lymphocyte proliferation, and interferon (IFN)- gamma production. RESULTS The vaccine was well tolerated; adverse events after vaccination were mild. No fever or prolonged vaccine shedding occurred. Immunogenicity data demonstrated that 88% and 93% of subjects who received presentation 1 and presentation 2, respectively, had a positive response by ELISPOT assay; 81% of subjects in both groups underwent IgG seroconversion on day 14. Both groups had similar cellular immune responses to presentation 1 and presentation 2; lymphocyte proliferation to Salmonella Typhi flagellin occurred in 63% and 67% of subjects, respectively, and 69% and 73% of subjects, respectively, had an increase in IFN- gamma production. CONCLUSION The oral typhoid vaccine M01ZH09 is well tolerated and highly immunogenic in a single oral dose, with and without prevaccination with a bicarbonate buffer. Field studies to demonstrate protective efficacy are planned.

Serum Mannose-Binding Lectin Deficiency Is Associated with Cryptosporidiosis in Young Haitian Children

BACKGROUND Mannose-binding lectin (MBL) is a component of the innate immune response and binds microbial surfaces through carbohydrate recognition domains. MBL deficiency may contribute to susceptibility to a variety of infectious diseases, particularly in young children. MBL binds to the Cryptosporidium sporozoite and may be important in resistance to cryptosporidiosis. METHODS We studied the association of serum MBL levels and cryptosporidiosis in a case-control study of young Haitian children with cryptosporidiosis versus children who were control subjects. RESULTS Ninety-nine children were enrolled, as follows: 49 children with cryptosporidiosis, 41 healthy controls, and 9 children with diarrhea from other causes. Case children were more malnourished than controls, and 49% had persistent or chronic diarrhea. At enrollment, mean serum MBL levels were markedly lower in children with cryptosporidiosis (P = .002), as was the number of children with an MBL deficiency of < or = 70 ng/mL (P = .005). In multivariate analysis, the association of cryptosporidiosis and MBL deficiency persisted (P = .002; adjusted odds ratio, 22.4), as did the association of cryptosporidiosis with general malnutrition. The subset of children with cryptosporidiosis and MBL deficiency were more likely to be male (P = .025). CONCLUSIONS MBL may be an important component of innate immune protection against Cryptosporidium infection in young children. Additional studies are necessary to determine whether MBL intestinal losses, deficient epithelial expression, and/or genetic polymorphisms in the MBL gene contribute to MBL deficiency in cryptosporidiosis and other enteric infections in young children.

Campylobacter jejuni Strain CG8421: A Refined Model for the Study of Campylobacteriosis and Evaluation of Campylobacter Vaccines in Human Subjects

BACKGROUND A robust human challenge model for Campylobacter jejuni is an important tool for the evaluation of candidate vaccines. The previously established model conveys a potential risk of Guillain-Barré syndrome attributable to lipooligosaccharide ganglioside mimicry. This work establishes a new C. jejuni human challenge model that uses a strain (CG8421) without ganglioside mimicry and that applies Campylobacter-specific cellular immunity screening to achieve high attack rates at lower inoculum doses. METHODS Healthy Campylobacter-naive adults participated in an open-label challenge trial. Participants were dosed with C. jejuni CG8421 and followed as inpatients. Pattern of illness, bacterial shedding, and immunologic responses were determined. RESULTS Following screening, 23 subjects received 1 X 10(6) or 1 X 10(5) colony-forming units of C. jejuni, with attack rates (percentage of patients who became ill) of 100% (1 X 10(6) colony-forming units) or 93% (1 X 10(5) colony-forming units). Every subject shed CG8421; the median time to diarrhea onset was 72.3 h (interquartile range, 53.9-99.9 h). Symptoms included abdominal cramps (74%), nausea (65%), and fever (39%). No major safety concerns occurred, including bacteremia, hypotension, or postinfectious sequelae. Unexpectedly, recrudescent infection occurred in 2 subjects (1 subject without Campylobacter-specific adaptive immune responses and 1 with azithromycin resistance acquired in vivo); both infections cleared after receipt of additional antibiotics. Cumulative Campylobacter-specific immune responses were as follows: serologic response occurred in 87% (immunoglobulin [Ig] A) and 48% (IgG) of subjects, in vitro interferon-gamma production occurred in 91% of subjects, and 96% of subjects had IgA antibody-secreting cells and fecal IgA detected. CONCLUSIONS The C. jejuni CG8421 challenge model provides a safe and effective tool, without the risk of Guillain-Barré syndrome. The model demonstrates high attack rates after lower doses of challenge inoculum, provides further understanding of immunologic responses, and permits future investigation of candidate Campylobacter vaccines.

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.

Childhood Cryptosporidiosis Is Associated with a Persistent Systemic Inflammatory Response

Cryptosporidiosis in young children prompts local inflammation in the intestinal tract. We studied a cohort of young children with cryptosporidiosis to determine whether systemic inflammatory responses occur and, if so, to evaluate whether inflammation persists after infection. Cryptosporidiosis was associated with increased levels of interleukin-8 and tumor necrosis factor- alpha systemically, which persisted at 6 months after enrollment. The level of intestinal tumor necrosis factor- alpha was elevated at enrollment, but elevated levels did not persist. Worsening of malnutrition, particularly stunting, was observed after infection. The association of cryptosporidiosis, inflammation, and stunting in children with cryptosporidiosis warrants further evaluation.

A 12-Month–Interval Dosing Study in Adults Indicates That a Single Dose of the National Institute of Allergy and Infectious Diseases Tetravalent Dengue Vaccine Induces a Robust Neutralizing Antibody Response

UNLABELLED The ideal dengue vaccine will provide protection against all serotypes of dengue virus and will be economical and uncomplicated in its administration. To determine the ability of a single dose of the live attenuated tetravalent dengue vaccine TV003 to induce a suitable neutralizing antibody response, a placebo-controlled clinical trial was performed in 48 healthy adults who received 2 doses of vaccine or placebo administered 12 months apart. Evaluation of safety, vaccine viremia, and neutralizing antibody response after each dose indicated that the first dose of vaccine was capable of preventing infection with the second dose, thus indicating that multiple doses are unnecessary. CLINICAL TRIALS REGISTRATION NCT01782300.

Lack of Homologous Protection against Campylobacter jejuni CG8421 in a Human Challenge Model

BACKGROUND Campylobacter jejuni is a common cause of diarrhea and is associated with serious postinfectious sequelae. Although symptomatic and asymptomatic infections are recognized, protective immunity is not well understood. Previous data suggests that interferon γ (IFN-γ) may be associated with protection. To better define the clinical and immunologic development of protective immunity to C. jejuni, we assessed the ability of an initial infection to prevent clinical illness after a second experimental infection. METHODS Subjects with no clinical or immunologic evidence of prior infection with C. jejuni received an initial challenge with C. jejuni CG8421 with rechallenge 3 months later. The primary endpoint was campylobacteriosis, as defined by diarrhea and/or systemic signs. Close inpatient monitoring was performed. Serum immunoglobulin A (IgA) and immunoglobulin G (IgG), fecal IgA, IgA antibody-secreting cells (ASCs), and IFN-γ production were evaluated. All subjects were treated with antibiotics and were clinically well at discharge. RESULTS Fifteen subjects underwent a primary infection with C. jejuni CG8421; 14 (93.3%) experienced campylobacteriosis. Eight subjects received the second challenge, and all experienced campylobacteriosis with similar severity. Immune responses after primary infection included serum IgA, IgG, ASC, and IFN-γ production. Responses were less robust after secondary infection. CONCLUSIONS In naive healthy adults, a single infection with CG8421 did not protect against campylobacteriosis. Although protection has been demonstrated with other strains and after continuous environmental exposure, our work highlights the importance of prior immunity, repeated exposures, and strain differences in protective immunity to C. jejuni. CLINICAL TRIALS REGISTRATION NCT01048112.