Long-term Humoral Immune Responses Research Articles

Long-lasting adaptive immune memory specific to SARS-CoV-2 in convalescent coronavirus disease 2019 stable people with HIV.

While the course of natural immunization specific to SARS-CoV-2 has been described among convalescent coronavirus disease 2019 (COVID-19) people without HIV (PWOH), a thorough evaluation of long-term serological and functional T- and B-cell immune memory among people with HIV (PWH) has not been reported. Eleven stable PWH developing mild ( n = 5) and severe ( n = 6) COVID-19 and 39 matched PWOH individuals with mild (MILD) ( n = 20) and severe (SEV) ( n = 19) COVID-19 infection were assessed and compared at 3 and 6 months after infection for SARS-CoV-2-specific serology, polyfunctional cytokine (interferon-γ [IFN-γ], interleukin 2 [IL-2], IFN-γ/IL-2, IL-21) producing T-cell frequencies against four main immunogenic antigens and for circulating SARS-CoV-2-specific immunoglobulin G (IgG)-producing memory B-cell (mBc). In all time points, all SARS-COV-2-specific adaptive immune responses were highly driven by the clinical severity of COVID-19 infection, irrespective of HIV disease. Notably, while a higher proportion of mild PWH showed a higher decay on serological detection between the two time points as compared to PWOH, persistently detectable IgG-producing mBc were still detectable in most patients (4/4 (100%) for SEV PWH, 4/5 (80%) for MILD PWH, 10/13 (76.92%) for SEV PWOH and 15/18 (83.33%) for MILD PWOH). Likewise, SARS-CoV-2-specific IFN-γ-producing T-cell frequencies were detected in both PWH and PWOH, although significantly more pronounced among severe COVID-19 (6/6 (100%) for SEV PWH, 3/5 (60%) for MILD PWH, 18/19 (94.74%) for SEV PWOH and 14/19 (73.68%) for MILD PWOH). PWH develop a comparable short and long-term natural functional cellular and humoral immune response than PWOH convalescent patients, which are highly influenced by the clinical severity of the COVID-19 infection.

Adjuvant-free cellulose nanofiber vaccine induces permanent humoral immune response in mouse

Vaccines have become one of the most effective strategies to deal with various infectious diseases and chronic noninfectious diseases, such as SARS virus, Novel Coronavirus, cancer, etc. However, recent studies have found that the neutralizing antibody titers induced by vaccines would drop to half level or even lower after vaccination. In this study, we designed a novel small-sized positively charged nanofiber-1 (PEI-CNF-1) as a vaccine carrier, which can induce a high long-term humoral immune response by controlled release of antigen. Further studies showed that PEI-CNF-1 could significantly induce the release of immune response factor IL-1β and bone marrow-derived cell (BMDC) maturation. Moreover, compare to other cellulose nanofibers (CNFs), PEI-CNF-1 combined antigen (ovalbumin, OVA) induced and maintained the highest and longest antibody titers after vaccination. Interestingly, the antibody titers have no significant difference between at 21 and 90 d. Mechanically, we found that PEI-NCF-1 not only could control the slow-release of antigen, but also could be more easily swallowed by macrophages and metabolized by the bodies, thus presenting antigen more effectively. In conclusion, we believe that PEI-CNF-1 have a very high application prospect in inducing long-term humoral immune response, so as to achieve efficient prevention effect to epidemic viruses.

MO888: Long-Term Humoral Immune Response Following Full SARS-COV-2 MRNA Vaccination and Booster Dose in Haemodialysis Patients

Abstract BACKGROUND AND AIMS COVID-19 is associated with an increased mortality in maintenance haemodialysis patients. Considering the baseline immunosuppressed status of this population, humoral immune responses to SARS-CoV-2 vaccination remain to be studied. There is no information regarding sustained immune response in this population after a third booster dose following complete m-RNA vaccination. The aim of our study was to describe the humoral immune response in haemodialysis patients following a complete SARS-CoV-2 vaccine schedule and a third booster dose, and explore the factors associated with a sustained immune response. METHOD We conducted a retrospective study in which we included haemodialysis patients with or without (naïve) previous COVID-19 infection. Patients received the following vaccination schedule: two initial doses of m-RNA vaccine with a 4-week interval (complete immunization) followed by a third booster dose at least 4 months after the second initial dose. IgG anti-SARS-CoV-2 spike antibody titles were measured before the first initial vaccine dose and then monthly up to 3 months after the booster dose. We excluded patients without baseline serological samples and those who did not receive the full vaccination schedule. RESULTS The study included 182 haemodialysis patients with a mean age of 68.5 ± 14.5 years, 63.2% were males and 14.3% were under immunosuppression, 67.7% were responders to HBV vaccine and 18.1% had been infected with SARS-CoV-2 prior to vaccination. After the first two vaccine doses, 96.5% developed immediate humoral immune response, and 91.5% remained with positive anti-SARS-CoV-2 spike antibodies after 4 months from complete vaccination. Median antiSARS-CoV-2 spike antibody titles were significantly higher in patients with previous COVID-19 infection and HBV vaccine responders, both immediately (40 000 AU/mL versus 2926 AU/mL, P < 0.001 and 4885 versus 2056 AU/mL, P = 0.003, respectively) and after 4 months from complete vaccination (27 741 versus 663 AU/mL, P < 0.001 and 1356 versus 341 AU/mL, P = 0.001). In the 4 months between complete initial vaccination and the third booster dose, the mean monthly decrease in antiSARS-CoV-2 spike antibody titles was of 31.8% (±18.9) and was significantly lower in patients with prior COVID-19 infection compared with naïve patients (17.2% versus 34.8%, P < 0.001). After the third booster dose, 98.2% of patients showed positive anti-SARS-CoV-2 S antibodies, and this proportion remained stable in the following 3 months. Nevertheless, median anti-SARS-CoV-2 spike antibody titles remained higher in patients with prior COVID-19 both immediately and after 3 months. However, we observed a more sustained humoral response after the booster dose, with a lower mean monthly decrease in antibody titles compared with the initial vaccine schedule (31.8% to 22.6%, P < 0.001). This finding was reciprocated in all groups, regardless of prior serological COVID-19 status, HBV vaccine response, age or sex. Multivariate logistic regression for the risk of a >25% monthly decrease in antibodies showed that prior infection with COVID-19 was a protective factor both after the complete initial vaccination {OR: 0.23, [95% confidence interval (95% CI) 0.06–0.87]} as well as after the third dose (OR: 0.23, 95% CI 0.06–0.81). CONCLUSION Vaccination with m-RNA anti-SARS-CoV-2 is effective in eliciting an immediate humoral response in haemodialysis patients, with a progressive reduction in immune response after 4 months particularly in COVID-19 naive patients. A third booster dose enhances the immune response with significantly higher antibody levels and more sustained humoral immune after 3 months in haemodialysis patients.

MO836: Patients Receiving Haemodialysis Maintain Sars-Cov-2 Immunity Comparable With Healthy Individuals: A Prospective Cohort Study

Abstract BACKGROUND AND AIMS Patients with end-stage kidney disease receiving maintenance haemodialysis (HD) are at increased risk for mortality after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) compared with the general population. However, it is currently unknown whether the long-term SARS-CoV-2 humoral and cellular immune responses in patients receiving HD are comparable to individuals with normal kidney function. We aimed to investigate the 6-month kinetics of SARS-CoV-2 IgG antibody and specific T-cell levels in patients receiving HD compared with those in healthy individuals. METHOD The prospective cohort study included 24 patients treated with maintenance HD and 27 healthy controls with confirmed history of coronavirus disease (COVID-19). Nobody of them received vaccination before and during the study period. In all participants, the levels of specific IgG were quantified at three timepoints: 10, 18 and 26 weeks from disease onset. In a subgroup of patients, specific CD4+ and CD8+ T-lymphocyte responses were evaluated using IGRA test. RESULTS The incidence of COVID-19-related symptoms did not differ between the groups, except for the loss of smell, which occurred much more frequently among healthy subjects (70% versus 30.4% in HD group, P = 0.01). The seropositivity rate declined in healthy subjects over time and was 85% and 70.4% at weeks 18 and 26, respectively. All HD patients remained seropositive over the study period. Seropositivity rate at week 26 was greater among patients receiving HD: RR = 1.4 [95% confidence interval (95% CI): 1.17–1.94] (reciprocal of RR = 0.7, 95% CI: 0.52–0.86), P = 0.0064. In both groups, IgG levels decreased from week 10 to week 26, but antibodies vanished more rapidly in controls than in HD group (ANOVA P = 0.0012)—Figure 1. The magnitude of T-cell response was significantly lower in controls than in HD patients at weeks 10 (P = 0.019) and 26 (P = 0.0098) after COVID-19 diagnosis, but not at week 18—Figure 2. CONCLUSION Compared with healthy adults, patients receiving HD maintain significant long-term humoral and cellular immune responses following natural COVID-19. SARS-CoV-2 IgG antibodies did not decline more rapidly in patients receiving HD than in healthy controls over 6-months period.

Long-term SARS-CoV-2-specific and cross-reactive cellular immune responses correlate with humoral responses, disease severity, and symptomatology.

BackgroundCellular immune memory responses post coronavirus disease 2019 (COVID‐19) have been difficult to assess due to the risks of contaminating the immune response readout with memory responses stemming from previous exposure to endemic coronaviruses. The work herein presents a large‐scale long‐term follow‐up study investigating the correlation between symptomology and cellular immune responses four to five months post seroconversion based on a unique severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2)‐specific peptide pool that contains no overlapping peptides with endemic human coronaviruses.MethodsPeptide stimulated memory T cell responses were assessed with dual interferon‐gamma (IFNγ) and interleukin (IL)‐2 Fluorospot. Serological analyses were performed using a multiplex antigen bead array.ResultsOur work demonstrates that long‐term SARS‐CoV‐2‐specific memory T cell responses feature dual IFNγ and IL‐2 responses, whereas cross‐reactive memory T cell responses primarily generate IFNγ in response to SARS‐CoV‐2 peptide stimulation. T cell responses correlated to long‐term humoral immune responses. Disease severity as well as specific COVID‐19 symptoms correlated with the magnitude of the SARS‐CoV‐2‐specific memory T cell response four to five months post seroconversion.ConclusionUsing a large cohort and a SARS‐CoV‐2‐specific peptide pool we were able to substantiate that initial disease severity and symptoms correlate with the magnitude of the SARS‐CoV‐2‐specific memory T cell responses.

Poly (lactic-co-glycolic acid) nanoparticle-based vaccines delivery systems as a novel adjuvant for H9N2 antigen enhance immune responses

Poly (lactic-co-glycolic acid) (PLGA) nanoparticle used as vaccine adjuvants have been widely investigated due to their safety, antigen slow-release ability, and good adjuvants activity. In this study, immunopotentiator Alhagi honey polysaccharide encapsulated PLGA nanoparticles (AHPP) and assembled pickering emulsion with AHPP as shell and squalene as core (PPAS) were prepared. Characterization of AHPP and PPAS were investigated. H9N2 absorbed nanoparticles formulations were immunized to chicken, then the magnitude and kinetics of antibody and cellular immune responses were assessed. Our results showed that PPAS had rough strawberry-like surfaces, a large number of antigens could be absorbed on their surfaces through simple mixing. Adjuvant activity of PPAS showed that, PPAS/H9N2 can induce long-lasting and high HI titers, high thymus, spleen, and bursa of fabricius organ index. Moreover, chicken immunized with PPAS/H9N2 showed a mixed high differentiation of CD4+ and CD8a+ T cell, and strong Th1 and Th2-type cytokines mRNA expression. Thus, these findings demonstrated that PPAS could induce a strong and long-term cellular and humoral immune response, and has the potential to serve as an effective vaccine delivery adjuvant system for H9N2 antigen.

Full efficacy and long-term immunogenicity induced by the SARS-CoV-2 vaccine candidate MVA-CoV2-S in mice

Two doses of the MVA-CoV2-S vaccine candidate expressing the SARS-CoV-2 spike (S) protein protected K18-hACE2 transgenic mice from a lethal dose of SARS-CoV-2. This vaccination regimen prevented virus replication in the lungs, reduced lung pathology, and diminished levels of pro-inflammatory cytokines. High titers of IgG antibodies against S and receptor-binding domain (RBD) proteins and of neutralizing antibodies were induced against parental virus and variants of concern, markers that correlated with protection. Similar SARS-CoV-2-specific antibody responses were observed at prechallenge and postchallenge in the two-dose regimen, while the single-dose treatment does not avoid vaccine breakthrough infection. All vaccinated animals survived infection and were also protected to SARS-CoV-2 reinfection. Furthermore, two MVA-CoV2-S doses induced long-term memory S-specific humoral and cellular immune responses in C57BL/6 mice, 6 months after immunization. The efficacy and immunological benefits of the MVA-CoV2-S vaccine candidate against COVID-19 supports its consideration for human clinical trials.

Alhagi honey polysaccharides encapsulated into PLGA nanoparticle-based pickering emulsion as a novel adjuvant to induce strong and long-lasting immune responses

Alhagi honey polysaccharides, extracted from a perennial plant Alhagi pseudalhagi syn, possessed many biological activities such as immune enhancement, anti-tumor effect, and antioxygenation. In this study, we used Alhagi honey polysaccharide encapsulated (poly lactic-co-glycolic acid) (PLGA) nanoparticles to prepare an assembled particles-oil pickering emulsion: PPAS and PEI-PPAS. We investigated the characterization of two pickering emulsions, and the possible mechanism to enhance immune responses. The results showed that PPAS and PEI-PPAS both could load high adsorption of OVA and had ability to sustained controlled release OVA. In vivo experiment, PEI-PPAS/OVA enhanced the levels of IgG and cytokines. Meanwhile, it could effectively target dendritic cells (DCs), promoted the cellular uptake of OVA then activated DCs in lymph nodes. And this effect of PEI-PPAS might be induced through the MHC II and MHC I pathway in DCs. Thus, these findings demonstrated that PEI-PPAS could induce a strong and long-term cellular and humoral immune response, and have potential to applied to vaccine adjuvant delivery system.

Robust and durable serological response following pediatric SARS-CoV-2 infection

The quality and persistence of children’s humoral immune response following SARS-CoV-2 infection remains largely unknown but will be crucial to guide pediatric SARS-CoV-2 vaccination programs. Here, we examine 548 children and 717 adults within 328 households with at least one member with a previous laboratory-confirmed SARS-CoV-2 infection. We assess serological response at 3–4 months and 11–12 months after infection using a bead-based multiplex immunoassay for 23 human coronavirus antigens including SARS-CoV-2 and its Variants of Concern (VOC) and endemic human coronaviruses (HCoVs), and additionally by three commercial SARS-CoV-2 antibody assays. Neutralization against wild type SARS-CoV-2 and the Delta VOC are analysed in a pseudotyped virus assay. Children, compared to adults, are five times more likely to be asymptomatic, and have higher specific antibody levels which persist longer (96.2% versus 82.9% still seropositive 11–12 months post infection). Of note, symptomatic and asymptomatic infections induce similar humoral responses in all age groups. SARS-CoV-2 infection occurs independent of HCoV serostatus. Neutralization responses of children and adults are similar, although neutralization is reduced for both against the Delta VOC. Overall, the long-term humoral immune response to SARS-CoV-2 infection in children is of longer duration than in adults even after asymptomatic infection.

Long-Term Humoral Immune Response against SARS-CoV-2 after Natural Infection and Subsequent Vaccination According to WHO International Binding Antibody Units (BAU/mL).

The new WHO reference standard allows for the definition of serum antibodies against various SARS-CoV-2 antigens in terms of binding antibody units (BAU/mL) and thus to compare the results of different ELISA systems. In this study, the concentration of antibodies (ABs) against both the S- and the N-protein of SARS-CoV-2 as well as serum neutralization activity were evaluated in three patients after a mild course of COVID-19. Serum samples were collected frequently during a period of over one year. Furthermore, in two individuals, the effects of an additional vaccination with a mRNA vaccine containing the S1-RBD sequence on these antibodies were examined. After natural infection, the antibodies (IgA, IgG) against the S1-protein remained elevated above the established cut-off to positivity (S-IgA 60 BAU/mL and S-IgG 50 BAU/mL, respectively) for over a year in all patients, while this was not the case for ABs against the N-protein (cut-off N-IgG 40 BAU/mL, N-IgA 256 BAU/mL). Sera from all patients retained the ability to neutralize SARS-CoV-2 for more than a year. Vaccination resulted in a rapid boost of antibodies to S1-protein but, as expected, not to the N-protein. Most likely, the wide use of the WHO reference preparation will be very useful in determining the individual immune status of patients after an infection with SARS-CoV-2 or after vaccination.

Long-term analysis of antibodies elicited by SPUTNIK V: A prospective cohort study in Tucumán, Argentina

BackgroundGam-COVID-Vac (SPUTNIK V) has been granted emergency use authorization in 70 nations and has been administered to millions worldwide. However, there are very few peer-reviewed studies describing its effects. Independent reports regarding safety and effectiveness could accelerate the final approval by the WHO. We aimed to study the long-term humoral immune response in naïve and previously infected volunteers who received SPUTNIK V.MethodsHumoral immune responses, assayed by anti-SARS-CoV-2-spike-RBD IgG ELISA and neutralization assays, were measured in 602 healthcare workers at 0, 14, 28, 60 and 180 days after receiving SPUTNIK V between December 2020 and July 2021 in Tucumán, Argentina.FindingsSeroconversion was detected in 97% of individuals after 28 days post-vaccination (dpv) (N = 405). Anti-RBD titers began to decrease after 60 dpv (N = 328), but remained detectable in 94% at 90 dpv (N = 224). At 180 dpv, anti-RDB titers persisted in 31% (N = 146). Previous infection triggered an increased immune response to the first dose and increased neutralization activity against variants of concern (VOC). Second doses in previously infected individuals further increased titers, even 90 dpv (N = 75). Basal antibody titers had more influence on post-vaccination anti-RBD responses than the time elapsed between diagnosis and vaccination (N = 274).InterpretationData presented herein provides essential knowledge regarding the kinetics of antibodies induced by SPUTNIK V up to six months after immunization, and suggests that when considering one-dose vaccination policies for individuals with previous SARS-CoV-2 infection, serological studies to determine basal titers may be important, independent of when diagnosis occurred.FundingTucumán Public Health System (SIPROSA), Argentinean National Research Council (CONICET), National University of Tucumán (UNT).

Intranasal delivery of plasmids expressing bovine herpesvirus 1 gB/gC/gD proteins by polyethyleneimine magnetic beads activates long-term immune responses in mice

BackgroundDNA vaccine is one of the research hotspots in veterinary vaccine development. Several advantages, such as cost-effectiveness, ease of design and production, good biocompatibility of plasmid DNA, attractive biosafety, and DNA stability, are found in DNA vaccines.MethodsIn this study, the plasmids expressing bovine herpesvirus 1 (BoHV-1) gB, gC, and gD proteins were mixed at the same mass ratio and adsorbed polyethyleneimine (PEI) magnetic beads with a diameter of 50 nm. Further, the plasmid and PEI magnetic bead polymers were packaged into double carboxyl polyethylene glycol (PEG) 600 to use as a DNA vaccine. The prepared DNA vaccine was employed to vaccinate mice via the intranasal route. The immune responses were evaluated in mice after vaccination.ResultsThe expression of viral proteins could be largely detected in the lung and rarely in the spleen of mice subjected to a vaccination. The examination of biochemical indicators, anal temperature, and histology indicated that the DNA vaccine was safe in vivo. However, short-time toxicity was observed. The total antibody detected with ELISA in vaccinated mice showed a higher level than PBS, DNA, PEI + DNA, and PBS groups. The antibody level was significantly elevated at the 15th week and started to decrease since the 17th week. The neutralizing antibody titer was significantly higher in DNA vaccine than naked DNA vaccinated animals. The total IgA level was much greater in the DNA vaccine group compared to other component vaccinated groups. The examination of cellular cytokines and the percentage of CD4/CD8 indicated that the prepared DNA vaccine induced a strong cellular immunity.ConclusionThe mixed application of plasmids expressing BoHV-1 gB/gC/gD proteins by nano-carrier through intranasal route could effectively activate long-term humoral, cellular, and mucosal immune responses at high levels in mice. These data indicate PEI magnetic beads combining with PEG600 are an efficient vector for plasmid DNA to deliver intranasally as a DNA vaccine candidate.

Long-Term Humoral Immune Response in Persons with Asymptomatic or Mild SARS-CoV-2 Infection, Vietnam.

Antibody response against nucleocapsid and spike proteins of SARS-CoV-2 in 11 persons with mild or asymptomatic infection rapidly increased after infection. At weeks 18–30 after diagnosis, all remained seropositive but spike protein–targeting antibody titers declined. These data may be useful for vaccine development.

Live attenuated coronavirus vaccines deficient in N7-Methyltransferase activity induce both humoral and cellular immune responses in mice

Coronaviruses (CoVs) can infect a variety of hosts, including humans, livestock and companion animals, and pose a serious threat to human health and the economy. The current COVID-19 pandemic, which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has killed millions of people. Unfortunately, effective treatments for CoVs infection are still lacking, suggesting the importance of coronavirus vaccines. Our previous work showed that CoV nonstuctural protein 14 (nsp14) functions as (guanine-N7)-methyltransferase (N7-MTase), which is involved in RNA cap formation. Moreover, we found that N7-MTase is well conserved among different CoVs and is a universal target for developing antivirals against CoVs. Here, we show that N7-MTase of CoVs can be an ideal target for designing live attenuated vaccines. Using murine hepatitis virus strain A59 (MHV-A59), a representative and well-studied model of coronaviruses, we constructed N7-MTase-deficient recombinant MHV D330A and Y414A. These two mutants are highly attenuated in mice and exhibit similar replication efficiency to the wild type (WT) virus in a cell culture. Furthermore, a single dose immunization of D330A or Y414A can induce long-term humoral immune responses and robust CD4+ and CD8+ T cell responses, which can provide full protection against the challenge of a lethal-dose of MHV-A59. Collectively, this study provides an ideal strategy to design live attenuated vaccines for coronavirus by abolishing viral RNA N7-MTase activity. This approach may apply to other RNA viruses that encode their own conservative viral N7-methyltransferase.

Antibody kinetics and exposure to Toxoplasma gondii in cats: a seroepidemiological study

Domestic cats are the most important definitive hosts for Toxoplasma gondii, the agent of an important global zoonosis. Serial sera from cats orally inoculated either withT. gondii tissue cysts (n = 3) or sporulated oocysts (n = 3) and from 65 client-owned cats, plus sera from 1,757 client-owned cats presented to veterinarians in Switzerland were analysed for an antibody response to T. gondii by ELISA. Risk factors for seropositivity and prevalence were estimated with a generalised linear and beta regression model. The first model examined the association of an OD405 value as the dependent variable, with gender, age, and outside access as possible independent variables. In the second model, we first analysed the data assuming a bimodal distribution representing two overlapping distributions of OD405 values from positive and negative cats, enabling the assignment of a probability of true infection status to each cat. Mean probabilities of true infection status across groups represent an estimate of true prevalence. These probabilities were then regressed against age, gender and outside access. Antibody kinetics in cats orally inoculated with tissue cysts, shedding oocysts, did not differ significantly from those of cats inoculated with sporulated oocysts without detectable oocyst excretion, suggesting extraintestinal parasite invasion and exposure to tachyzoites in both situations at an early stage of infection. Analysis of serial serum samples suggested a persisting long-term humoral immune response. Of the client-owned cats, 42.4% (95% confidence interval (CI): 40.1–44.6) had a positive true infection status. This was higher (56.3% (95% CI: 53.2–59.6)) in cats with outside access than in those without (22.1% (95% CI: 18.9–25.4)). In the first model, the factors age (P < 0.0001), gender (male: P = 0.046), and outside access (P < 0.0001) were independently associated with significantly higher OD405 values. In the second model, the probability of having a positive true infection status increased with age (P < 0.0001), was higher with outside access (P < 0.0001) and in outdoor male cats (P = 0.0006).

Short- and long-term humoral immune response against Yersinia pestis in plague patients, Madagascar

BackgroundPlague, a fatal disease caused by the bacillus, Yersinia pestis, still affects resources-limited countries. Information on antibody response to plague infection in human is scarce. Anti-F1 Ig G are among the known protective antibodies against Y. pestis infection. As a vaccine preventable disease, knowledge on antibody response is valuable for the development of an effective vaccine to reduce infection rate among exposed population in plague-endemic regions. In this study, we aim to describe short and long-term humoral immune responses against Y. pestis in plague-confirmed patients from Madagascar, the most affected country in the world.MethodsBubonic (BP) and pneumonic plague (PP) patients were recruited from plague- endemic foci in the central highlands of Madagascar between 2005 and 2017. For short-term follow-up, 6 suspected patients were enrolled and prospectively investigated for kinetics of the anti-F1 IgG response, whereas the persistence of antibodies was retrospectively studied in 71 confirmed convalescent patients, using an ELISA which was validated for the detection of plague in human blood samples in Madagascar.ResultsSimilarly to previous findings, anti-F1 IgG rose quickly during the first week after disease onset and increased up to day 30. In the long-term study, 56% of confirmed cases remained seropositive, amongst which 60 and 40% could be considered as high- and low-antibody responders, respectively. Antibodies persisted for several years and up to 14.8 years for one individual. Antibody titers decreased over time but there was no correlation between titer and time elapsed between the disease onset and serum sampling. In addition, the seroprevalence rate was not significantly different between gender (P = 0.65) nor age (P = 0.096).ConclusionOur study highlighted that the circulating antibody response to F1 antigen, which is specific to Y. pestis, may be attributable to individual immune responsiveness. The finding that a circulating anti-F1 antibody titer could persist for more than a decade in both BP and PP recovered patients, suggests its probable involvement in patients’ protection. However, complementary studies including analyses of the cellular immune response to Y. pestis are required for the better understanding of long-lasting protection and development of a potential vaccine against plague.

Rational Design of PLGA Nanoparticle Vaccine Delivery Systems To Improve Immune Responses.

Nanoparticle-based vaccine delivery systems have been extensively used to promote and induce immune responses to protein antigens. The properties of the nanoparticles, such as size, surface charge, and antigen loading mode, have been proved to significantly influence the adjuvant effect and immunoreactivity of nanoparticle-based vaccine delivery systems. The purpose of the study was to investigate how the surface charge and antigen loading mode of nanoparticles impact the immune responses. In this study, three ovalbumin (OVA)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles with different surface charges and antigen loading modes were developed. The three nanoparticles were designed as antigen encapsulated with negatively charged (Angelica sinensis polysaccharide (ASP)-PLGA/OVA), antigen encapsulated with polyethylenimine (PEI)-coated (ASP-PLGA/OVA-PEI), and antigen adsorbed on PEI-coated (ASP-PLGA-PEI-OVA) nanoparticles. The Angelica sinensis polysaccharide (ASP) was used as the immunopotentiator and encapsulated into three nanoparticles. The results demonstrated that both PEI-coated (positively charged) nanoparticles promoted the antigen escape from the endosome, which led to the cytoplasmic antigen delivery to generate cross presentation, compared to negatively charged nanoparticles. In addition, PEI-coated nanoparticles activated the DCs in lymph nodes 5 days after the primary vaccination. In vivo experiments demonstrated that both antigen-encapsulated nanoparticles induced more potent and long-term antigen-specific antibody responses, compared to that of antigen-adsorbed nanoparticles. Thus, the PEI-coated and antigen-encapsulated nanoparticles (ASP-PLGA/OVA-PEI) as a vaccine adjuvant delivery system have the potential to induce strong and long-term humoral and cellular immune responses.

The acquisition of long-lived memory B cell responses to merozoite surface protein-8 in individuals with Plasmodium vivax infection

BackgroundThe ability of a malaria antigen to induce effective, long-lasting immune responses is important for the development of a protective malaria vaccine. Plasmodium vivax merozoite surface protein-8 (PvMSP8) has been shown to be immunogenic in natural P. vivax infections and produces both cell-mediated and antibody-mediated immunity. Thus, PvMSP8 has been proposed as a vaccine candidate following fusion with other merozoite antigens in blood stage vaccine design. Here, the long-term responses of antibodies and memory B cells (MBCs) specific to PvMSP8 in individuals were monitored in a longitudinal cohort study.MethodsBoth cross-sectional surveys and cohort studies were utilized to explore the persistence of antibody and MBC responses to PvMSP8. Antibody titers were detected in individuals with acute disease and those who recovered from an infection for 4 years. The dominant peptide epitope of PvMSP8 recognized by naturally acquired antibodies was examined to observe the durability of the post-infection antibody response. PvMSP8-specific MBCs were also in subjects 4 years post-infection using an enzyme-linked immunospot assay.ResultsThe prevalence of antibodies to PvMSP8 was high during and after infection. The antibody levels in individual responders were monitored for up to 12 months post-infection and showed that most patients maintained their seropositive response. Interestingly, the anti-PvMSP8 antibody responses stably persisted in some patients who had recovered from an infection for 4 years. Positive PvMSP8-specific MBCs were also detected at 4 years post-infection. However, analysis in these individuals showed no correlation with the presence or titer of circulating antibody.ConclusionPvMSP8 had the ability to induce a long-term humoral immune response. The antibodies and MBCs specific for this antigen developed and persisted in subjects who acquired a natural P. vivax infection. Inclusion of the PvMSP8 antigen in blood stage vaccine design should be considered.

Incorporation of CD40 ligand or granulocyte-macrophage colony stimulating factor into Hantaan virus (HTNV) virus-like particles significantly enhances the long-term immunity potency against HTNV infection.

Hantavirus infections cause severe haemorrhagic fever with renal syndrome (HFRS) in humans and are associated with high fatality rates. In 2017, numerous outbreaks were reported in China and Germany. This represents a significant public-healthcare issue with no effective HFRS vaccines that offer a long-term immune response. In this study, we investigated the long-term humoral and cellular immune responses and protective immunity of Hantaan virus (HTNV) granulocyte-macrophage colony stimulating factor (GM-CSF) and CD40 ligand (CD40L) virus-like particles (VLPs) in mice. GM-CSF and CD40L VLPs were constructed via co-transfection of pCI-S and pCI-M-CD40L, and pCI-S and pCI-M-GM-CSF, into dihydrofolatereductase (dhfr)-deficient Chinese hamster ovary cells, respectively. Mice were immunized with HTNV VLPs 2 weeks apart. The animals were challenged 6 months after immunization. Specific and neutralizing antibodies were assessed by ELISA; IFN-γ was measured by enzyme-linked immunospot (ELISpot) assay and effectiveness by cytotoxic T lymphocyte (CTL) cytotoxicity assays. Nucleic acid loads of HTNV were tested by quantitative real-time PCR and viral antigen was detected via indirect ELISA. Pathological alterations were detected via haematoxylin-eosin staining. GM-CSF and CD40L VLPs provided stable, long-term protection with a high titre of neutralizing antibody in mice 6 months after immunization. Furthermore, VLPs increased HTNV-specific cellular immune responses via higher expression of IFN-γ and CTL responses. HTNV challenge assay results showed long-term protection against HFRS. No significant pathological alteration was observed in the organs of mice after immunization. This is, to the best of our knowledge, the first report demonstrating the long-term potency of HTNV VLP vaccines against HTNV infection and offers new insights into HTNV vaccine development.

Longitudinal cohort study of serum antibody responses towards Giardia lamblia variant-specific surface proteins in a non-endemic area

Introduction/AimsThe long-term humoral immune response after a natural giardiasis infection is not well understood. The aim of this study was to evaluate longitudinal serum IgA and IgG/M responses towards conserved regions of two Giardia variant-specific surface proteins (VSP) and whether these responses differ between Giardia assemblages and durations of infection. MethodsWe recruited thirty Giardia-positive patients, mainly returning travellers, and eighteen healthy adults presumed to be Giardia unexposed. Blood samples were collected before treatment, and at 6 weeks, 6 months and 12 months after the infection cleared. We used a multiplex bead-based flow cytometry immunoassay to measure Giardia specific IgA and IgG/M responses targeting two recombinant antigens from G. lamblia VSP proteins 3 and 5 (VSP3 and VSP5). ResultsSerum levels of anti-VSP5 and anti-VSP3 IgA decreased rapidly to low levels after treatment but continued to be substantially higher than that of presumed unexposed controls even after 6 and 12 months. The IgG/M response decreased more gradually but remained significantly higher than presumed unexposed controls at all time points, except for anti-VSP3 at 12 months. There were no significant difference in responses for infections with assemblage A and assemblage B Giardia lamblia. Chronic infections (>8 weeks) were associated with a significantly lower anti-VSP5 IgG/M response. ConclusionThis study describes the kinetics of the humoral immune response against two Giardia VSP proteins over one year, and the considerable cross reactivity between the two human infective Giardia assemblages. Persons with chronic Giardia infection seem to have lower levels of VSP antibodies.