Clinical and Vaccine Immunology最新文献

Current pneumococcal vaccines are composed of bacterial polysaccharides as antigens, plain or conjugated to carrier proteins. While efficacious against vaccine serotypes, epidemiologic data show an increasing incidence of infections caused by nonvaccine serotypes of Streptococcus pneumoniae The use of pneumococcal surface protein A (PspA) as a carrier protein in a conjugate vaccine could help prevent serotype replacement by increasing vaccine coverage and reducing selective pressure of S. pneumoniae serotypes. PspA is present in all pneumococcal strains, is highly immunogenic, and is known to induce protective antibodies. Based on its sequence, PspA has been classified into three families and six clades. A PspA fragment derived from family 2, clade 4 (PspA4Pro), was shown to generate antibodies with a broad range of cross-reactivity, across clades and families. Here, PspA4Pro was modified and conjugated to capsular polysaccharide serotype 14 (PS14). We investigated the impact of conjugation on the immune response induced to PspA4Pro and PS14. Mice immunized with the PS14-mPspA4Pro conjugate produced higher titers of anti-PS14 antibodies than the animals that received coadministered antigens. The conjugate induced antibodies with opsonophagocytic activity against PS14-carrying strains, as well as against a panel of strains bearing PspAs from five clades (encompassing families 1 and 2) bearing a non-PS14 serotype. Furthermore, mice immunized with PS14-mPspA4Pro were protected against nasal colonization with a nonrelated S. pneumoniae strain bearing PspA from clade 1, serotype 6B. These results demonstrate that the cross-reactivity mediated by PspA4Pro is retained following conjugation, supporting the use of PspA4 as a carrier protein in order to enhance pneumococcal vaccine coverage and encourage its further investigation as a candidate in future vaccine designs.

MenB-FHbp is a meningococcal serogroup B vaccine with two factor H binding protein (FHbp) antigens from subfamilies A and B. For licensure, efficacy was inferred from serum bactericidal antibody (SBA) responses to four reference strains. Only limited information is available on the breadth or duration of protective SBA responses to genetically diverse disease-causing strains. Seventeen health care or laboratory workers were immunized with two (n = 2) or three (n = 15) doses of MenB-FHbp at 0, 2, and 6 months. SBA levels were measured against 14 serogroup B case isolates, including 6 from U.S. college outbreaks and 2 from Quebec during hyperendemic disease. Compared with preimmunization titers, the proportion of subjects with ≥4-fold increases in SBA titer 1 month after 2 doses of vaccine ranged from 35% to 94% for six isolates with FHbp subfamily A and from 24% to 76% for eight isolates with subfamily B FHbp. The respective proportions with ≥4-fold titer increases at 1 month after dose 3 were 73% to 100% and 67% to 100%. At that time point, the proportion of subjects with titers of ≥1:4 (presumed sufficient for short-term protection) ranged from 93% to 100% for all 14 isolates. By 9 to 11 months after dose 3, 50% or fewer of the subjects with follow-up sera had protective titers of ≥1:4 for 4 of 9 isolates tested. Three doses of MenB-FHbp elicited short-term protective SBA responses to diverse disease-causing serogroup B strains. For some strains, serum titers declined to <1:4 by 9 to 11 months, which raises concerns about the duration of broad, long-term protection. (This study has been registered at ClinicalTrials.gov under registration no. NCT02569632.).

Invasive nontyphoidal Salmonella (iNTS) infections are commonly associated with Plasmodium falciparum infections, but the immunologic basis for this linkage is poorly understood. We hypothesized that P. falciparum infection compromises the humoral and cellular immunity of the host to NTS, which increases the susceptibility of the host to iNTS infection. We prospectively recruited children aged between 6 and 60 months at a Community Health Centre in Blantyre, Malawi, and allocated them to the following groups; febrile with uncomplicated malaria, febrile malaria negative, and nonfebrile malaria negative. Levels of Salmonella enterica serovar Typhimurium-specific serum bactericidal activity (SBA) and whole-blood bactericidal activity (WBBA), complement C3 deposition, and neutrophil respiratory burst activity (NRBA) were measured. Levels of SBA with respect to S Typhimurium were reduced in febrile P. falciparum-infected children (median, -0.20 log10 [interquartile range {IQR}, -1.85, 0.32]) compared to nonfebrile malaria-negative children (median, -1.42 log10 [IQR, -2.0, -0.47], P = 0.052). In relation to SBA, C3 deposition on S Typhimurium was significantly reduced in febrile P. falciparum-infected children (median, 7.5% [IQR, 4.1, 15.0]) compared to nonfebrile malaria-negative children (median, 29% [IQR, 11.8, 48.0], P = 0.048). WBBA with respect to S Typhimurium was significantly reduced in febrile P. falciparum-infected children (median, 0.25 log10 [IQR, -0.73, 1.13], P = 0.0001) compared to nonfebrile malaria-negative children (median, -1.0 log10 [IQR, -1.68, -0.16]). In relation to WBBA, S Typhimurium-specific NRBA was reduced in febrile P. falciparum-infected children (median, 8.8% [IQR, 3.7, 20], P = 0.0001) compared to nonfebrile malaria-negative children (median, 40.5% [IQR, 33, 65.8]). P. falciparum infection impairs humoral and cellular immunity to S Typhimurium in children during malaria episodes, which may explain the increased risk of iNTS observed in children from settings of malaria endemicity. The mechanisms underlying humoral immunity impairment are incompletely understood and should be explored further.

Since the middle of the 20th century, vaccines have made a significant public health impact by controlling infectious diseases globally. Although long-term protection has been achieved with some vaccines, immunity wanes over time with others, resulting in outbreaks or epidemics of infectious diseases. Long-term protection against infectious agents that have a complex life cycle and antigenic variation remains a key challenge. Novel strategies to characterize the short- and long-term immune responses to vaccines and to induce immune responses that mimic natural infection have recently emerged. New technologies and approaches in vaccinology, such as adjuvants, delivery systems, and antigen formulations, have the potential to elicit more durable protection and fewer adverse reactions; together with in vitro systems, these technologies have the capacity to model and accelerate vaccine development. The National Institute of Allergy and Infectious Diseases (NIAID) held a workshop on 19 September 2016 that focused on waning immunity to selected vaccines (for Bordetella pertussis, Salmonella enterica serovar Typhi, Neisseria meningitidis, influenza, mumps, and malaria), with an emphasis on identifying knowledge gaps, future research needs, and how this information can inform development of more effective vaccines for infectious diseases.

Virus-like particles (VLPs) are noninfectious multiprotein structures that are engineered to self-assemble from viral structural proteins. Here, we developed a novel VLP-based vaccine platform utilizing VLPs from the chikungunya virus. We identified two regions within the envelope protein, a structural component of chikungunya, where foreign antigens can be inserted without compromising VLP structure. Our VLP displays 480 copious copies of an inserted antigen on the VLP surface in a highly symmetric manner and is thus capable of inducing strong immune responses against any inserted antigen. Furthermore, by mimicking the structure of the immature form of the virus, we altered our VLP's in vivo dynamics and enhanced its immunogenicity. We used the circumsporozoite protein (CSP) of the Plasmodium falciparum malaria parasite as an antigen and demonstrated that our VLP-based vaccine elicits strong immune responses against CSP in animals. The sera from immunized monkeys protected mice from malaria infection. Likewise, mice vaccinated with P. yoelii CSP-containing VLPs were protected from an infectious sporozoite challenge. Hence, our uniquely engineered VLP platform can serve as a blueprint for the development of vaccines against other pathogens and diseases.

Naturally acquired antibodies to Plasmodium falciparum schizont egress antigen 1 (PfSEA-1A) are associated with protection against severe malaria in children. Vaccination of mice with SEA-1A from Plasmodium berghei (PbSEA-1A) decreases parasitemia and prolongs survival following P. berghei ANKA challenge. To enhance the immunogenicity of PfSEA-1A, we identified five linear B-cell epitopes using peptide microarrays probed with antisera from nonhuman primates vaccinated with recombinant PfSEA-1A (rPfSEA-1A). We evaluated the relationship between epitope-specific antibody levels and protection from parasitemia in a longitudinal treatment-reinfection cohort in western Kenya. Antibodies to three epitopes were associated with 16 to 17% decreased parasitemia over an 18-week high transmission season. We are currently designing immunogens to enhance antibody responses to these three epitopes.

The distinction between bacterial and viral causes of infections of the respiratory tract is a major but important clinical challenge. We investigated the diagnostic performance of human neutrophil lipocalin (HNL) in respiratory tract infections compared to those of C-reactive protein (CRP) and procalcitonin (PCT). Patients were recruited from the emergency department and from a primary care unit (n = 162). The clinical diagnosis with regard to bacterial or viral cause of infection was complemented with objective microbiological/serological testing. HNL was measured in whole blood after preactivation with the neutrophil activator formyl-methionine-leucine-phenylalanine (fMLP) (B-HNL), and CRP and PCT were measured in plasma. Head-to-head comparisons of the three biomarkers showed that B-HNL was a superior diagnostic means to distinguish between causes of infections, with areas under the concentration-time curve (AUCs) of receiver operating characteristic (ROC) analysis for HNL of 0.91 (95% confidence interval [CI], 0.83 to 0.96) and 0.92 (95% CI, 0.82 to 0.97) for all respiratory infections and for upper respiratory infections, respectively, compared to 0.72 (95% CI, 0.63 to 0.80) and 0.68 (95% CI, 0.56 to 0.79) for CRP, respectively (P = 0.001). In relation to major clinical symptoms of respiratory tract infections (cough, sore throat, stuffy nose, and signs of sinusitis), AUCs varied between 0.88 and 0.93 in those patients with likely etiology (i.e., etiology is likely determined) of infection, compared to 0.63 and 0.71 for CRP, respectively, and nonsignificant AUCs for PCT. The diagnostic performance of B-HNL is superior to that of plasma CRP (P-CRP) and plasma PCT (P-PCT) in respiratory tract infections, and the activity specifically reflects bacterial challenge in the body. The rapid and accurate analysis of HNL by point-of-care technologies should be a major advancement in the diagnosis and management of respiratory infections with respect to antibiotic treatment.

From experimental models and the analyses of patients, it is well documented that antigen-specific T cells are critical for protection against Leishmania infection. Effective vaccines require both targeting to the pathogen and an immune stimulant to induce maturation of appropriate immune responses. While a great number of antigens have been examined as vaccine candidates against various Leishmania species, few have advanced to human or canine clinical trials. With emphasis on antigen expression, in this minireview we discuss some of the vaccine platforms that are currently being explored for the development of Leishmania vaccines. It is clear that the vaccine platform of choice can have a significant impact upon the level of protection induced by particular antigens, and we provide and highlight some examples for which the vaccine system used has impacted the protective efficacy imparted.

Johne's disease, a chronic gastrointestinal inflammatory disease caused by Mycobacterium avium subspecies paratuberculosis, is endemic in dairy cattle and other ruminants worldwide and remains a challenge to diagnose using traditional serological methods. Given the close phylogenetic relationship between M. avium subsp. paratuberculosis and the human pathogen Mycobacterium tuberculosis, here, we applied a whole-proteome M. tuberculosis protein array to identify seroreactive and diagnostic M. avium subsp. paratuberculosis antigens. A genome-scale pairwise analysis of amino acid identity levels between orthologous proteins in M. avium subsp. paratuberculosis and M. tuberculosis showed an average of 62% identity, with more than half the orthologous proteins sharing >75% identity. Analysis of the M. tuberculosis protein array probed with sera from M. avium subsp. paratuberculosis-infected cattle showed antibody binding to 729 M. tuberculosis proteins, with 58% of them having ≥70% identity to M. avium subsp. paratuberculosis orthologs. The results showed that only 4 of the top 40 seroreactive M. tuberculosis antigens were orthologs of previously reported M. avium subsp. paratuberculosis antigens, revealing the existence of a large number of previously unrecognized candidate diagnostic antigens. Enzyme-linked immunosorbent assay (ELISA) testing of 20 M. avium subsp. paratuberculosis recombinant proteins, representing reactive and nonreactive M. tuberculosis orthologs, further confirmed that the M. tuberculosis array has utility as a screening tool for identifying candidate antigens for Johne's disease diagnostics. Additional ELISA testing of field serum samples collected from dairy herds around the United States revealed that MAP2942c had the strongest seroreactivity with Johne's disease-positive samples. Collectively, our studies have considerably expanded the number of candidate M. avium subsp. paratuberculosis proteins with potential utility in the next generation of rationally designed Johne's disease diagnostic assays.