Identification of minimal human MHC-restricted CD8+ T-cell epitopes within the Plasmodium falciparum circumsporozoite protein (CSP).

BACKGROUND: Plasmodium falciparum circumsporozoite protein (CSP) is a leading malaria vaccine candidate antigen, known to elicit protective antibody responses in humans (RTS,S vaccine). Recently, a DNA prime / adenovirus (Ad) vector boost vaccine encoding CSP and a second P. falciparum antigen, apical membrane antigen-1, also elicited sterile protection, but in this case associated with interferon gamma ELISpot and CD8+ T cell but not antibody responses. The finding that CSP delivered by an appropriate vaccine platform likely elicits protective cell-mediated immunity provided a rationale for identifying class I-restricted epitopes within this leading vaccine candidate antigen. METHODS: Limited samples of peripheral blood mononuclear cells from clinical trials of the Ad vaccine were used to identify CD8+ T cell epitopes within pools of overlapping 15mer peptides spanning portions of CSP that stimulated recall responses. Computerized algorithms (NetMHC) predicted 17 minimal class I-restricted 9-10mer epitopes within fifteen 15mers positive in ELISpot assay using PBMC from 10 HLA-matched study subjects. Four additional epitopes were subsequently predicted using NetMHC, matched to other study subjects without initial 15mer ELISpot screening. Nine of the putative epitopes were synthesized and tested by ELISpot assay, and six of these nine were further tested for CD8+ T cell responses by ELISpot CD4+ and CD8+ T cell-depletion and flow cytometry assays for evidence of CD8+ T cell dependence. RESULTS: Each of the nine putative epitopes, all sequence-conserved, recalled responses from HLA-matched CSP-immunized research subjects. Four shorter sequences contained within these sequences were identified using NetMHC predictions and may have contributed to recall responses. Five (9-10mer) epitopes were confirmed to be targets of CD8+ T cell responses using ELISpot depletion and ICS assays. Two 9mers among these nine epitopes were each restricted by two HLA supertypes (A01/B07; A01A24/A24) and one 9mer was restricted by three HLA supertypes (A01A24/A24/B27) indicating that some CSP class I-restricted epitopes, like DR epitopes, may be HLA-promiscuous. CONCLUSIONS: This study identified nine and confirmed five novel class I epitopes restricted by six HLA supertypes, suggesting that an adenovirus-vectored CSP vaccine would be immunogenic and potentially protective in genetically diverse populations.

A three-antigen Plasmodium falciparum DNA prime-Adenovirus boost malaria vaccine regimen is superior to a two-antigen regimen and protects against controlled human malaria infection in healthy malaria-naïve adults.

BACKGROUND: A DNA-prime/human adenovirus serotype 5 (HuAd5) boost vaccine encoding Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP) and Pf apical membrane antigen-1 (PfAMA1), elicited protection in 4/15 (27%) of subjects against controlled human malaria infection (CHMI) that was statistically associated with CD8+ T cell responses. Subjects with high level pre-existing immunity to HuAd5 were not protected, suggesting an adverse effect on vaccine efficacy (VE). We replaced HuAd5 with chimpanzee adenovirus 63 (ChAd63), and repeated the study, assessing both the two-antigen (CSP, AMA1 = CA) vaccine, and a novel three-antigen (CSP, AMA1, ME-TRAP = CAT) vaccine that included a third pre-erythrocytic stage antigen [malaria multiple epitopes (ME) fused to the Pf thrombospondin-related adhesive protein (TRAP)] to potentially enhance protection. METHODOLOGY: This was an open label, randomized Phase 1 trial, assessing safety, tolerability, and VE against CHMI in healthy, malaria naïve adults. Forty subjects (20 each group) were to receive three monthly CA or CAT DNA priming immunizations, followed by corresponding ChAd63 boost four months later. Four weeks after the boost, immunized subjects and 12 infectivity controls underwent CHMI by mosquito bite using the Pf3D7 strain. VE was assessed by determining the differences in time to parasitemia as detected by thick blood smears up to 28-days post CHMI and utilizing the log rank test, and by calculating the risk ratio of each treatment group and subtracting from 1, with significance calculated by the Cochran-Mantel-Haenszel method. RESULTS: In both groups, systemic adverse events (AEs) were significantly higher after the ChAd63 boost than DNA immunizations. Eleven of 12 infectivity controls developed parasitemia (mean 11.7 days). In the CA group, 15 of 16 (93.8%) immunized subjects developed parasitemia (mean 12.0 days). In the CAT group, 11 of 16 (63.8%) immunized subjects developed parasitemia (mean 13.0 days), indicating significant protection by log rank test compared to infectivity controls (p = 0.0406) and the CA group (p = 0.0229). VE (1 minus the risk ratio) in the CAT group was 25% compared to -2% in the CA group. The CA and CAT vaccines induced robust humoral (ELISA antibodies against CSP, AMA1 and TRAP, and IFA responses against sporozoites and Pf3D7 blood stages), and cellular responses (IFN-γ FluoroSpot responses to CSP, AMA1 and TRAP) that were not associated with protection. CONCLUSIONS: This study demonstrated that the ChAd63 CAT vaccine exhibited significant protective efficacy, and confirmed protection was afforded by adding a third antigen (T) to a two-antigen (CA) formulation to achieve increased VE. Although the ChAd63-CAT vaccine was associated with increased frequencies of systemic AEs compared to the CA vaccine and, historically, compared to the HuAd5 vectored malaria vaccine encoding CSP and AMA1, they were transient and associated with increased vector dosing.

Identification and localization of minimal MHC-restricted CD8+ T cell epitopes within the Plasmodium falciparum AMA1 protein.

BACKGROUND: Plasmodium falciparum apical membrane antigen-1 (AMA1) is a leading malaria vaccine candidate antigen that is expressed by sporozoite, liver and blood stage parasites. Since CD8+ T cell responses have been implicated in protection against pre-erythrocytic stage malaria, this study was designed to identify MHC class I-restricted epitopes within AMA1. METHODS: A recombinant adenovirus serotype 5 vector expressing P. falciparum AMA1 was highly immunogenic when administered to healthy, malaria-naive adult volunteers as determined by IFN-γ ELISpot responses to peptide pools containing overlapping 15-mer peptides spanning full-length AMA1. Computerized algorithms (NetMHC software) were used to predict minimal MHC-restricted 8-10-mer epitope sequences within AMA1 15-mer peptides active in ELISpot. A subset of epitopes was synthesized and tested for induction of CD8+ T cell IFN-γ responses by ELISpot depletion and ICS assays. A 3-dimensional model combining Domains I + II of P. falciparum AMA1 and Domain III of P. vivax AMA1 was used to map these epitopes. RESULTS: Fourteen 8-10-mer epitopes were predicted to bind to HLA supertypes A01 (3 epitopes), A02 (4 epitopes), B08 (2 epitopes) and B44 (5 epitopes). Nine of the 14 predicted epitopes were recognized in ELISpot or ELISpot and ICS assays by one or more volunteers. Depletion of T cell subsets confirmed that these epitopes were CD8+ T cell-dependent. A mixture of the 14 minimal epitopes was capable of recalling CD8+ T cell IFN-γ responses from PBMC of immunized volunteers. Thirteen of the 14 predicted epitopes were polymorphic and the majority localized to the more conserved front surface of the AMA1 model structure. CONCLUSIONS: This study predicted 14 and confirmed nine MHC class I-restricted CD8+ T cell epitopes on AMA1 recognized in the context of seven HLA alleles. These HLA alleles belong to four HLA supertypes that have a phenotypic frequency between 23% - 100% in different human populations.

IMRAS-A clinical trial of mosquito-bite immunization with live, radiation-attenuated P. falciparum sporozoites: Impact of immunization parameters on protective efficacy and generation of a repository of immunologic reagents.

BACKGROUND: Immunization with radiation-attenuated sporozoites (RAS) by mosquito bite provides >90% sterile protection against Plasmodium falciparum (Pf) malaria in humans. RAS invade hepatocytes but do not replicate. CD8+ T cells recognizing parasite-derived peptides on the surface of infected hepatocytes are likely the primary protective mechanism. We conducted a randomized clinical trial of RAS immunization to assess safety, to achieve 50% vaccine efficacy (VE) against controlled human malaria infection (CHMI), and to generate reagents from protected and non-protected subjects for future identification of protective immune mechanisms and antigens. METHODS: Two cohorts (Cohort 1 and Cohort 2) of healthy, malaria-naïve, non-pregnant adults age 18-50 received five monthly immunizations with infected (true-immunized, n = 21) or non-infected (mock-immunized, n = 5) mosquito bites and underwent homologous CHMI at 3 weeks. Immunization parameters were selected for 50% protection based on prior clinical data. Leukapheresis was done to collect plasma and peripheral blood mononuclear cells. RESULTS: Adverse event rates were similar in true- and mock-immunized subjects. Two true- and two mock-immunized subjects developed large local reactions likely caused by mosquito salivary gland antigens. In Cohort 1, 11 subjects received 810-1235 infected bites; 6/11 (55%) were protected against CHMI vs. 0/3 mock-immunized and 0/6 infectivity controls (VE 55%). In Cohort 2, 10 subjects received 839-1131 infected bites with a higher first dose and a reduced fifth dose; 9/10 (90%) were protected vs. 0/2 mock-immunized and 0/6 controls (VE 90%). Three/3 (100%) protected subjects administered three booster immunizations were protected against repeat CHMI vs. 0/6 controls (VE 100%). Cohort 2 uniquely showed a significant rise in IFN-γ responses after the third and fifth immunizations and higher antibody responses to CSP. CONCLUSIONS: PfRAS were generally safe and well tolerated. Cohort 2 had a higher first dose, reduced final dose, higher antibody responses to CSP and significant rise of IFN-γ responses after the third and fifth immunizations. Whether any of these factors contributed to increased protection in Cohort 2 requires further investigation. A cryobank of sera and cells from protected and non-protected individuals was generated for future immunological studies and antigen discovery. TRIAL REGISTRATION: ClinicalTrials.gov NCT01994525.

Finishing what was started: an analysis of theater research conducted from 2010 to 2012.

The Joint Combat Casualty Research Team (JC2RT) is part of the human research protection regulatory system implemented in 2005 to oversee the conduct of research in a deployed military combatant command. In 2010, SharePoint, a web-based tool, was established to track study documents. This study conducted by JC2RT no. 13 describes characteristics of research studies under the purview of the JC2RT from 2010 through 2012. Of the 83 research studies reviewed, 34% were completed, 32% were not completed, and 34% were still in progress. Target sample sizes ranged from 12 to 70,000, with 96% of the research studying U.S. military members. The design of 61% of the studies was prospective, 20% surveys, and 14% retrospective reviews. Approximately one-half of the studies were conducted at single sites. Eighty-four percent of the studies that finished an institutional review board (IRB) were completed, whereas a large number of studies never made it to IRB approval. Even after studies have gone through the rigorous process of scientific review and IRB approval some continue to struggle for years to be completed in the theater of operations. The JC2RT is committed to helping facilitate the ethical conduct of research during war.

Controlled Human Malaria Infection (CHMI) differentially affects cell-mediated and antibody responses to CSP and AMA1 induced by adenovirus vaccines with and without DNA-priming.

We have previously shown that a DNA-prime followed by an adenovirus-5 boost vaccine containing CSP and AMA1 (DNA/Ad) successfully protected 4 of 15 subjects to controlled human malaria infection (CHMI). However, the adenovirus-5 vaccine alone (AdCA) failed to induce protection despite eliciting cellular responses that were often higher than those induced by DNA/Ad. Here we determined the effect of CHMI on pre-CHMI cellular and antibody responses against CSP and AMA1 expressed as fold-changes in activities. Generally, in the DNA/Ad trial, CHMI caused pre-CHMI ELISpot IFN-γ and CD8+ T cell IFN-γ responses of the protected subjects to fall but among non-protected subjects, CHMI caused rises of pre-CHMI ELISpot IFN-γ but falls of CD8+ T cell IFN-γ responses. In contrast in the AdCA trial, CHMI caused both pre-CHMI ELISpot IFN-γ and CD8+ T cell IFN-γ responses of the AdCA subjects to fall. We suggest that the falls in activities are due to migration of peripheral CD8+ T cells to the liver in response to developing liver stage parasites, and this fall, in the DNA/Ad trial, is masked in ELISpot responses of the non-protected subjects by rises in other immune cell types. In addition, CHMI caused falls in antibody activities of protected subjects, but rises in non-protected subjects in both trials to CSP, and dramatically in the AdCA trial to AMA1, reaching 380 µg/ml that is probably due to boosting by transient blood stage infection before chloroquine treatment. Taken together, these results further define differences in cellular responses between DNA/Ad and AdCA trials, and suggest that natural transmission may boost responses induced by these malaria vaccines especially when protection is not achieved.

Diverse HIV-1 subtypes and clinical, laboratory and behavioral factors in a recently infected US military cohort.

OBJECTIVE: To describe the demographics, risk behaviors, and HIV-1 subtypes in a large cohort of recently HIV-infected military personnel. DESIGN: Descriptive, cross-sectional study. METHODS: US military personnel with recent HIV seroconversion from six medical referral centers were enrolled with a self-administered questionnaire, CD4 cell counts, syphilis and hepatitis B serologies, plasma viral RNA levels, and HIV-1 subtype nucleic acid sequencing. RESULTS: Between February 1997 and May 2000, 520 patients were enrolled. Most [488 (94.3%)] were infected with HIV-1 subtype B. The most prevalent non-B subtype was a circulating recombinant form (CRF01_AE) [17 (61%)]; however, two pure subtypes (C and D), as well as CRF02_AG, CRF09_cpx and a BE recombinant were identified. The likely area of HIV-1 acquisition was the United States for 70% of the volunteers. At least three non-B subtype infections (two subtype C, one subtype CRF01_AE) were apparently acquired domestically. Risk behaviors and comorbid sexually transmitted diseases were reported during the seroconversion period. Volunteers with non-B subtype HIV infection were more likely to report heterosexual contacts [92% vs. 39%; odds ratio (OR), 10.0], including contacts with commercial sex workers (41% vs. 13%; OR, 4.9). The Roche Amplicor version 1.0 assay was less sensitive for non-B subtype infections than the Roche Amplicor version 1.5 assay. CONCLUSION: There is a high prevalence and diversity of non-B HIV subtypes in this large cohort. Efficient diagnosis of acute primary HIV-1 infection was identified as a goal for prevention programs. Modifiable risk behaviors and target populations for intervention were identified.

Long-term efficacy of routine access to antiretroviral-resistance testing in HIV type 1-infected patients: results of the clinical efficacy of resistance testing trial.

The long-term efficacy of making resistance testing routinely available to clinicians has not been established. We conducted a clinical trial at 6 US military hospitals in which volunteers infected with human immunodeficiency virus type-1 were randomized to have routine access to phenotype resistance testing (PT arm), access to genotype resistance testing (GT arm), or no access to either test (VB arm). The primary outcome measure was time to persistent treatment failure despite change(s) in antiretroviral therapy (ART) regimen. Overall, routine access to resistance testing did not significantly increase the time to end point. Time to end point was significantly prolonged in the PT arm for subjects with a history of treatment with > or =4 different ART regimens or a history of treatment with nonnucleoside reverse-transcriptase inhibitors before the study, compared with that in the VB arm. These results suggest that routine access to resistance testing can improve long-term virologic outcomes in HIV-infected patients who are treatment experienced but may not impact outcome in patients who are naive to or have had limited experience with ART.

Disseminated vaccine-strain varicella as initial presentation of the acquired immunodeficiency syndrome: a case report and review of the literature.

Varicella-zoster virus (VZV) infections have declined in many industrialized countries due to vaccination with the attenuated Oka strain virus. Rare cases of severe, disseminated vaccine-strain VZV infection have occurred in the immunocompromised, although rarely in HIV-infected persons. We describe a man with previously-undiagnosed human immunodeficiency virus (HIV) infection who received VZV vaccination and subsequently presented to a combat hospital in Afghanistan with disseminated varicella, respiratory failure, and sepsis. The patient recovered with ventilator and hemodynamic support, intravenous acyclovir, and empiric antibiotic therapy. DNA sequencing detected Oka strain virus from patient blood specimens. Although safe in most populations, the VZV vaccine may cause life-threatening disease in immunocompromised patients. Improved detection of HIV infection may be useful in preventing such cases.

Sterile immunity to malaria after DNA prime/adenovirus boost immunization is associated with effector memory CD8+T cells targeting AMA1 class I epitopes.

BACKGROUND: Fifteen volunteers were immunized with three doses of plasmid DNA encoding P. falciparum circumsporozoite protein (CSP) and apical membrane antigen-1 (AMA1) and boosted with human adenovirus-5 (Ad) expressing the same antigens (DNA/Ad). Four volunteers (27%) demonstrated sterile immunity to controlled human malaria infection and, overall, protection was statistically significantly associated with ELISpot and CD8+ T cell IFN-γ activities to AMA1 but not CSP. DNA priming was required for protection, as 18 additional subjects immunized with Ad alone (AdCA) did not develop sterile protection. METHODOLOGY/PRINCIPAL FINDINGS: We sought to identify correlates of protection, recognizing that DNA-priming may induce different responses than AdCA alone. Among protected volunteers, two and three had higher ELISpot and CD8+ T cell IFN-γ responses to CSP and AMA1, respectively, than non-protected volunteers. Unexpectedly, non-protected volunteers in the AdCA trial showed ELISpot and CD8+ T cell IFN-γ responses to AMA1 equal to or higher than the protected volunteers. T cell functionality assessed by intracellular cytokine staining for IFN-γ, TNF-α and IL-2 likewise did not distinguish protected from non-protected volunteers across both trials. However, three of the four protected volunteers showed higher effector to central memory CD8+ T cell ratios to AMA1, and one of these to CSP, than non-protected volunteers for both antigens. These responses were focused on discrete regions of CSP and AMA1. Class I epitopes restricted by A*03 or B*58 supertypes within these regions of AMA1 strongly recalled responses in three of four protected volunteers. We hypothesize that vaccine-induced effector memory CD8+ T cells recognizing a single class I epitope can confer sterile immunity to P. falciparum in humans. CONCLUSIONS/SIGNIFICANCE: We suggest that better understanding of which epitopes within malaria antigens can confer sterile immunity and design of vaccine approaches that elicit responses to these epitopes will increase the potency of next generation gene-based vaccines.

A systematic review of safety data reporting in clinical trials of vaccines against malaria, tuberculosis, and human immunodeficiency virus.

INTRODUCTION: Malaria, tuberculosis (TB) and human immunodeficiency virus (HIV) are diseases with devastating effects on global public health, especially in the developing world. Clinical trials of candidate vaccines for these diseases are being conducted at an accelerating rate, and require accurate and consistent methods for safety data collection and reporting. We performed a systematic review of publications describing the safety results from clinical trials of malaria, TB and HIV vaccines, to ascertain the nature and consistency of safety data collection and reporting. METHODS: The target for the review was pre-licensure trials for malaria, TB and HIV vaccines published in English from 2000 to 2009. Search strategies were customized for each of the databases utilized (MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews and the Database of Reviews and Effects). Data extracted included age of trial participants, vaccine platform, route and method of vaccine administration, duration of participant follow-up, reporting of laboratory abnormalities, and the type, case definitions, severity, reporting methods and internal reporting consistency of adverse events. RESULTS: Of 2278 publications screened, 124 were eligible for inclusion (malaria: 66, TB: 9, HIV: 49). Safety data reporting was found to be highly variable among publications and often incomplete: overall, 269 overlapping terms were used to describe specific adverse events. 17% of publications did not mention fever. Descriptions of severity or degree of relatedness to immunization of adverse events were frequently omitted. 26% (32/124) of publications failed to report data on serious adverse events. CONCLUSIONS: The review demonstrated lack of standardized safety data reporting in trials for vaccines against malaria, TB and HIV. Standardization of safety data collection and reporting should be encouraged to improve data quality and comparability. LIMITATIONS: The search strategy missed studies published in languages other than English and excluded studies reporting on vaccine trials for diseases besides malaria, TB and HIV.

Evolution of biomedical research during combat operations.

BACKGROUND: The implementation of a human research protection program in Afghanistan and the mobilization of the combat casualty research team have made it possible to design and efficiently conduct multifaceted, multisite, and prospective research studies in a combat environment. Still, to conduct research in such an environment, several unique challenges must be overcome. METHODS: This article describes the development and conduct of three ongoing trauma-related biomedical research studies in Afghanistan, highlighting the challenges and lessons learned within the context of these studies. RESULTS: Key challenges include the process of developing and getting approval for in-theater research protocols, the informed consent process, and logistics of conducting a biomedical research study in an austere environment. Despite these challenges, important lessons learned that can contribute to the success of a protocol include the need for clear operating procedures, judicious selection for which data points must be collected in-theater, and the importance anticipating the "fog and friction" of war. CONCLUSION: As we continue the journey toward more sophisticated research capabilities in combat, this article will help inform the design and conduct of future research performed in a theater of war. Conducting biomedical research in a combat zone is an important but difficult element of military medicine.

First-in-human evaluation of genetically attenuated Plasmodium falciparum sporozoites administered by bite of Anopheles mosquitoes to adult volunteers.

BACKGROUND: Immunization with genetically engineered, attenuated malaria parasites (GAP) that arrest during liver infection confers sterile protection in mouse malaria models. A first generation Plasmodium falciparum GAP (Pf p52(-)/p36(-) GAP) was previously generated by deletion of two pre-erythrocytic stage-expressed genes (P52 and P36) in the NF54 strain. METHODS: A first-in-human, proof-of-concept, safety and immunogenicity clinical trial in six human volunteers was conducted. Exposure consisted of delivery of Pf p52(-)/p36(-) GAP sporozoites via infected Anopheles mosquito bite with a five-bite/volunteer exposure followed by an approximately 200-bite exposure/volunteer one month later. RESULTS: The exposures were well tolerated with mild to moderate local and systemic reactions. All volunteers remained blood stage negative after low dose exposure. Five volunteers remained blood stage negative after high dose exposure. One volunteer developed peripheral parasitemia twelve days after high dose exposure. Together the findings indicate that Pf p52(-)/p36(-) GAP was severely but not completely attenuated. All six volunteers developed antibodies to CSP. Furthermore, IFN-γ responses to whole sporozoites and multiple antigens were elicited in 5 of 6 volunteers, with both CD4 and CD8 cell cytokine production detected. CONCLUSION: Severe attenuation and favorable immune responses following administration of a first generation Pf p52(-)/p36(-) GAP suggests that further development of live-attenuated strains using genetic engineering should be pursued.

Human adenovirus 5-vectored Plasmodium falciparum NMRC-M3V-Ad-PfCA vaccine encoding CSP and AMA1 is safe, well-tolerated and immunogenic but does not protect against controlled human malaria infection.

BACKGROUND: In a prior study, a DNA prime / adenovirus boost vaccine (DNA/Ad) expressing P. falciparum circumsporozoite protein (CSP) and apical membrane antigen-1 (AMA1) (NMRC-M3V-D/Ad-PfCA Vaccine) induced 27% protection against controlled human malaria infection (CHMI). To investigate the contribution of DNA priming, we tested the efficacy of adenovirus vaccine alone (NMRC-M3V-Ad-PfCA ) in a Phase 1 clinical trial. METHODOLOGY/PRINCIPAL FINDINGS: The regimen was a single intramuscular injection with two non-replicating human serotype 5 adenovectors encoding CSP and AMA1, respectively. One x 10 (10) particle units of each construct were combined prior to administration. The regimen was safe and well-tolerated. Four weeks later, 18 study subjects received P. falciparum CHMI administered by mosquito bite. None were fully protected although one showed delayed onset of parasitemia. Antibody responses were low, with geometric mean CSP ELISA titer of 381 (range<50-1626) and AMA1 ELISA of 4.95 µg/mL (range 0.2-38). Summed ex vivo IFN-γ ELISpot responses to overlapping peptides were robust, with geometric mean spot forming cells/million peripheral blood mononuclear cells [sfc/m] for CSP of 273 (range 38-2550) and for AMA1 of 1303 (range 435-4594). CD4+ and CD8+ T cell IFN-γ responses to CSP were positive by flow cytometry in 25% and 56% of the research subjects, respectively, and to AMA1 in 94% and 100%, respectively. SIGNIFICANCE: In contrast to DNA/Ad, Ad alone did not protect against CHMI despite inducing broad, cell-mediated immunity, indicating that DNA priming is required for protection by the adenovirus-vectored vaccine. ClinicalTrials.gov Identifier: NCT00392015.

DNA prime/Adenovirus boost malaria vaccine encoding P. falciparum CSP and AMA1 induces sterile protection associated with cell-mediated immunity.

BACKGROUND: Gene-based vaccination using prime/boost regimens protects animals and humans against malaria, inducing cell-mediated responses that in animal models target liver stage malaria parasites. We tested a DNA prime/adenovirus boost malaria vaccine in a Phase 1 clinical trial with controlled human malaria infection. METHODOLOGY/PRINCIPAL FINDINGS: The vaccine regimen was three monthly doses of two DNA plasmids (DNA) followed four months later by a single boost with two non-replicating human serotype 5 adenovirus vectors (Ad). The constructs encoded genes expressing P. falciparum circumsporozoite protein (CSP) and apical membrane antigen-1 (AMA1). The regimen was safe and well-tolerated, with mostly mild adverse events that occurred at the site of injection. Only one AE (diarrhea), possibly related to immunization, was severe (Grade 3), preventing daily activities. Four weeks after the Ad boost, 15 study subjects were challenged with P. falciparum sporozoites by mosquito bite, and four (27%) were sterilely protected. Antibody responses by ELISA rose after Ad boost but were low (CSP geometric mean titer 210, range 44-817; AMA1 geometric mean micrograms/milliliter 11.9, range 1.5-102) and were not associated with protection. Ex vivo IFN-γ ELISpot responses after Ad boost were modest (CSP geometric mean spot forming cells/million peripheral blood mononuclear cells 86, range 13-408; AMA1 348, range 88-1270) and were highest in three protected subjects. ELISpot responses to AMA1 were significantly associated with protection (p = 0.019). Flow cytometry identified predominant IFN-γ mono-secreting CD8+ T cell responses in three protected subjects. No subjects with high pre-existing anti-Ad5 neutralizing antibodies were protected but the association was not statistically significant. SIGNIFICANCE: The DNA/Ad regimen provided the highest sterile immunity achieved against malaria following immunization with a gene-based subunit vaccine (27%). Protection was associated with cell-mediated immunity to AMA1, with CSP probably contributing. Substituting a low seroprevalence vector for Ad5 and supplementing CSP/AMA1 with additional antigens may improve protection. TRIAL REGISTRATION: ClinicalTrials.govNCT00870987.

Evaluation of a prototype dengue-1 DNA vaccine in a Phase 1 clinical trial.

Candidate dengue DNA vaccine constructs for each dengue serotype were developed by incorporating pre-membrane and envelope genes into a plasmid vector. A Phase 1 clinical trial was performed using the dengue virus serotype-1 (DENV-1) vaccine construct (D1ME(100)). The study was an open-label, dose-escalation, safety and immunogenicity trial involving 22 healthy flavivirus-naïve adults assigned to one of two groups. Each group received three intramuscular injections (0, 1, and 5 months) of either a high dose (5.0mg, n=12) or a low dose (1.0mg, n=10) DNA vaccine using the needle-free Biojector(®) 2000. The most commonly reported solicited signs and symptoms were local mild pain or tenderness (10/22, 45%), local mild swelling (6/22, 27%), muscle pain (6/22, 27%) and fatigue (6/22, 27%). Five subjects (41.6%) in the high dose group and none in the low dose group developed detectable anti-dengue neutralizing antibodies. T-cell IFN gamma responses were detected in 50% (4/8) and 83.3% (10/12) of subjects in the low and high dose groups, respectively. The safety profile of the DENV-1 DNA vaccine is acceptable at both doses administered in the study. These results demonstrate a favorable reactogenicity and safety profile of the first in human evaluation of a DENV-1 DNA vaccine.

Adenovirus 5-vectored P. falciparum vaccine expressing CSP and AMA1. Part A: safety and immunogenicity in seronegative adults.

BACKGROUND: Models of immunity to malaria indicate the importance of CD8+ T cell responses for targeting intrahepatic stages and antibodies for targeting sporozoite and blood stages. We designed a multistage adenovirus 5 (Ad5)-vectored Plasmodium falciparum malaria vaccine, aiming to induce both types of responses in humans, that was tested for safety and immunogenicity in a Phase 1 dose escalation trial in Ad5-seronegative volunteers. METHODOLOGY/PRINCIPAL FINDINGS: The NMRC-M3V-Ad-PfCA vaccine combines two adenovectors encoding circumsporozoite protein (CSP) and apical membrane antigen-1 (AMA1). Group 1 (n = 6) healthy volunteers received one intramuscular injection of 2×10∧10 particle units (1×10∧10 each construct) and Group 2 (n = 6) a five-fold higher dose. Transient, mild to moderate adverse events were more pronounced with the higher dose. ELISpot responses to CSP and AMA1 peaked at 1 month, were higher in the low dose (geomean CSP = 422, AMA1 = 862 spot forming cells/million) than in the high dose (CSP = 154, p = 0.049, AMA1 = 423, p = 0.045) group and were still positive at 12 months in a number of volunteers. ELISpot depletion assays identified dependence on CD4+ or on both CD4+ and CD8+ T cells, with few responses dependent only on CD8+ T cells. Intracellular cytokine staining detected stronger CD8+ than CD4+ T cell IFN-γ responses (CSP p = 0.0001, AMA1 p = 0.003), but similar frequencies of multifunctional CD4+ and CD8+ T cells secreting two or more of IFN-γ, TNF-α or IL-2. Median fluorescence intensities were 7-10 fold higher in triple than single secreting cells. Antibody responses were low but trended higher in the high dose group and did not inhibit growth of cultured P. falciparum blood stage parasites. SIGNIFICANCE: As found in other trials, adenovectored vaccines appeared safe and well-tolerated at doses up to 1×10∧11 particle units. This is the first demonstration in humans of a malaria vaccine eliciting strong CD8+ T cell IFN-γ responses. TRIAL REGISTRATION: ClinicalTrials.govNCT00392015.

Adenovirus-5-vectored P. falciparum vaccine expressing CSP and AMA1. Part B: safety, immunogenicity and protective efficacy of the CSP component.

BACKGROUND: A protective malaria vaccine will likely need to elicit both cell-mediated and antibody responses. As adenovirus vaccine vectors induce both these responses in humans, a Phase 1/2a clinical trial was conducted to evaluate the efficacy of an adenovirus serotype 5-vectored malaria vaccine against sporozoite challenge. METHODOLOGY/PRINCIPAL FINDINGS: NMRC-MV-Ad-PfC is an adenovirus vector encoding the Plasmodium falciparum 3D7 circumsporozoite protein (CSP). It is one component of a two-component vaccine NMRC-M3V-Ad-PfCA consisting of one adenovector encoding CSP and one encoding apical membrane antigen-1 (AMA1) that was evaluated for safety and immunogenicity in an earlier study (see companion paper, Sedegah et al). Fourteen Ad5 seropositive or negative adults received two doses of NMRC-MV-Ad-PfC sixteen weeks apart, at 1 x 1010 particle units per dose. The vaccine was safe and well tolerated. All volunteers developed positive ELISpot responses by 28 days after the first immunization (geometric mean 272 spot forming cells/million[sfc/m]) that declined during the following 16 weeks and increased after the second dose to levels that in most cases were less than the initial peak (geometric mean 119 sfc/m). CD8+ predominated over CD4+ responses, as in the first clinical trial. Antibody responses were poor and like ELISpot responses increased after the second immunization but did not exceed the initial peak. Pre-existing neutralizing antibodies (NAb) to Ad5 did not affect the immunogenicity of the first dose, but the fold increase in NAb induced by the first dose was significantly associated with poorer antibody responses after the second dose, while ELISpot responses remained unaffected. When challenged by the bite of P. falciparum-infected mosquitoes, two of 11 volunteers showed a delay in the time to patency compared to infectivity controls, but no volunteers were sterilely protected. SIGNIFICANCE: The NMRC-MV-Ad-PfC vaccine expressing CSP was safe and well tolerated given as two doses, but did not provide sterile protection. TRIAL REGISTRATION: ClinicalTrials.gov NCT00392015.

Rickettsia parkeri infection after tick bite, Virginia.

We describe a man with a febrile illness and an eschar that developed at the site of a tick bite. Rickettsia parkeri was detected and isolated from the eschar. This report represents the second documented case of R. parkeri rickettsiosis in a US serviceman in eastern Virginia.