Plasmodium falciparum-specific memory B-cell and antibody responses are associated with immunity in children living in an endemic area of Kenya

Identifying the mechanism of naturally acquired immunity against Plasmodium falciparum malaria could contribute to the design of effective malaria vaccines. Using a recently developed multiplexed FluoroSpot assay, we assessed cross-sectional pre-existing memory B-cells (MBCs) and antibody responses against six well known P. falciparum antigens (MSP-119, MSP-2 (3D7), MSP-2 (FC27), MSP-3, AMA-1 and CSP) and measured their associations with previous infections and time to clinical malaria in the ensuing malaria season in Kenyan children. These children were under active weekly surveillance for malaria as part of a long-term longitudinal malaria immunology cohort study, where they are recruited from birth. After performing Cox regression analysis, we found that children with a breadth of three or more antigen-specific MBC or antibody responses at the baseline had a reduced risk for malaria in the ensuing P. falciparum transmission season. Specifically, MBC responses against AMA-1, MSP-2 (3D7) and MSP-3, as well as antibody responses to MSP-2 (3D7) and MSP-3 were prospectively associated with a reduced risk for malaria. The magnitude or breadth of MBC responses were however not correlated with the cumulative number of malaria episodes since birth. We conclude that increased breadth for merozoite antigen-specific MBC and antibody responses is associated with protection against malaria

Memory B-cell responses against merozoite antigens after acute Plasmodium falciparum malaria, assessed over one year using a novel multiplexed fluorospot assay

Memory B cells (MBCs) are believed to be important for the maintenance of immunity to malaria, and these cells need to be explored in the context of different parasite antigens and their breadth and kinetics after natural infections. However, frequencies of antigen-specific MBCs are low in peripheral blood, limiting the number of antigens that can be studied, especially when small blood volumes are available. Here, we developed a multiplexed reversed B-cell FluoroSpot assay capable of simultaneously detecting MBCs specific for the four Plasmodium falciparum blood-stage antigens, MSP-119, MSP-2, MSP-3 and AMA-1. We used the assay to study the kinetics of the MBC response after an acute episode of malaria and up to one year following treatment in travelers returning to Sweden from sub-Saharan Africa. We show that the FluoroSpot assay can detect MBCs to all four merozoite antigens in the same well, and that the breadth and kinetics varied between individuals. We further found that individuals experiencing a primary infection could mount and maintain parasite-specific MBCs to a similar extent as previously exposed adults, already after a single infection. We conclude that the multiplexed B-cell FluoroSpot is a powerful tool for assessing antigen-specific MBC responses to several antigens simultaneously, and that the kinetics of MBC responses against merozoite surface antigens differ over the course of one year. These findings contribute to the understanding of acquisition and maintenance of immune responses to malaria

Lancet Infect Dis

Background Long-term protection and herd immunity induced by existing pertussis vaccines are imperfect, and a need therefore exists to develop new pertussis vaccines. This study aimed to investigate the safety, colonisation, and immunogenicity of the new, live attenuated pertussis vaccine, BPZE1, when given intranasally. Methods This phase 1b, double-blind, randomised, placebo-controlled, dose-escalation study was done at the phase 1 unit, Karolinska Trial Alliance, Karolinska University Hospital, Stockholm, Sweden. Healthy adults (18–32 years) were screened and included sequentially into three groups of increasing BPZE1 dose strength (107 colony-forming units [CFU], 108 CFU, and 109 CFU), and were randomly assigned (3:1 within each group) to receive vaccine or placebo. Vaccine and placebo were administered in phosphate-buffered saline contained 5% saccharose as 0·4 mL in each nostril. The primary outcome was solicited and unsolicited adverse events between day 0 and day 28. The analysis included all randomised participants who received a vaccine dose. Colonisation with BPZE1 was determined by repeatedly culturing nasopharyngeal aspirates at day 4, day 7, day 11, day 14, day 21, and day 28 after vaccination. Immunogenicity, as serum IgG and IgA responses were assessed at day 0, day 7, day 14, day 21, day 28, 6 months, and 12 months after vaccination. This trial is registered at Clinicaltrials.gov, NCT02453048. Findings Between Sept 1, 2015, and Feb 3, 2016, 120 participants were assessed for eligibility, 48 of whom were enrolled and randomly assigned (3:1) to receive vaccine or placebo, with 12 participants each in a low-dose, medium-dose, and high-dose vaccine group. Adverse events between day 0 and day 28 were reported by one (8%, 95% CI 0–39) of 12 participants in both the placebo and low-dose groups, and two (17%; 2–48) of 12 participants in both the medium-dose and high-dose groups, including cough of grade 2 or more, oropharyngeal pain, and rhinorrhoea and nasal congestion. During this time, none of the participants experienced any spasmodic cough, difficulties in breathing, or adverse events following immunisation concerning vital signs. The tested doses of BPZE1 or placebo were well tolerated, with no apparent difference in solicited or unsolicited adverse events following immunisation between groups. Colonisation at least once after vaccination was observed in 29 (81%; 68–93) of 36 vaccinated participants. The tested vaccine doses were immunogenic, with increases in serum IgG and IgA titres against the four B pertussis antigens from baseline to 12 months. Interpretation The tested vaccine was safe, induced a high colonisation rate in an adult population, and was immunogenic at all doses. These findings justify further clinical development of BPZE1 to ultimately be used as a priming vaccine for neonates or a booster vaccine for adolescents and adults, or both

Optimisation of ex vivo memory B cell expansion/differentiation for interrogation of rare peripheral memory B cell subset responses [version 2; peer review: 2 approved]

Background: Human memory B cells play a vital role in the long-term protection of the host from pathogenic re-challenge. In recent years the importance of a number of different memory B cell subsets that can be formed in response to vaccination or infection has started to become clear. To study memory B cell responses, cells can be cultured ex vivo, allowing for an increase in cell number and activation of these quiescent cells, providing sufficient quantities of each memory subset to enable full investigation of functionality. However, despite numerous papers being published demonstrating bulk memory B cell culture, we could find no literature on optimised conditions for the study of memory B cell subsets, such as IgM+ memory B cells. Methods: Following a literature review, we carried out a large screen of memory B cell expansion conditions to identify the combination that induced the highest levels of memory B cell expansion. We subsequently used a novel Design of Experiments approach to finely tune the optimal memory B cell expansion and differentiation conditions for human memory B cell subsets. Finally, we characterised the resultant memory B cell subpopulations by IgH sequencing and flow cytometry. Results: The application of specific optimised conditions induce multiple rounds of memory B cell proliferation equally across Ig isotypes, differentiation of memory B cells to antibody secreting cells, and importantly do not alter the Ig genotype of the stimulated cells. Conclusions: Overall, our data identify a memory B cell culture system that offers a robust platform for investigating the functionality of rare memory B cell subsets to infection and/or vaccination