Specific Memory B-cells Research Articles

The Divergent Effect of Different Infant Vaccination Schedules of the 13-Valent Pneumococcal Conjugate Vaccine on Serotype-Specific Immunological Memory.

Pneumococcal vaccination schedules are traditionally assessed based on the antibody response. The Memory B Cell (MBC) response has been less studied, despite its role in the magnitude and longevity of protection. We compared the immune response to different vaccination schedules with the 13-valent Pneumococcal Conjugate Vaccine (PCV13) and investigated the relationship between MBCs and the antibody response. Total and pneumococcal serotype (PS)-specific MBCs, their subsets and PS-specific IgG antibodies induced by a 3 + 0 (group A), 2 + 1 (group B) or 3 + 1 (group C) schedule in healthy infants were studied before and 1 month after the last PCV13. The relatively immature IgM+IgD+ MBC subset was the predominant subset in all groups but was larger in group A compared to group B and group C, indicating that age might be a significant parameter of the composition of the MBC pool. PS-specific MBCs at baseline were higher in group A, but they increased significantly only in the groups receiving the booster schedules (groups B and C). PS-specific IgM-only MBCs at baseline positively corelated with the antibody response and the PS-specific swIg MBCs post-immunization. Our findings illustrate the importance of a booster dose for the enrichment of PS-specific immunological memory. IgM-only MBCs and swIg MBCs may serve as additional correlates of vaccine-induced protection.

Primary SARS-CoV-2 variant of concern infections elicit broad antibody Fc-mediated effector functions and memory B cell responses.

Neutralization of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by human sera is a strong correlate of protection against symptomatic and severe Coronavirus Disease 2019 (COVID-19). The emergence of antigenically distinct SARS-CoV-2 variants of concern (VOCs) and the relatively rapid waning of serum antibody titers, however, raises questions about the sustainability of serum protection. In addition to serum neutralization, other antibody functionalities and the memory B cell (MBC) response are suggested to help maintaining this protection. In this study, we investigate the breadth of spike (S) protein-specific serum antibodies that mediate effector functions by interacting with Fc-gamma receptor IIa (FcγRIIa) and FcγRIIIa, and of the receptor binding domain (RBD)-specific MBCs, following a primary SARS-CoV-2 infection with the D614G, Alpha, Beta, Gamma, Delta, Omicron BA.1 or BA.2 variant. Irrespectively of the variant causing the infection, the breadth of S protein-specific serum antibodies that interact with FcγRIIa and FcγRIIIa and the RBD-specific MBC responses exceeded the breadth of serum neutralization, although the Alpha-induced B cell response seemed more strain-specific. Between VOC groups, both quantitative and qualitative differences in the immune responses were observed, suggesting differences in immunogenicity. Overall, this study contributes to the understanding of protective humoral and B cell responses in the light of emerging antigenically distinct VOCs, and highlights the need to study the immune system beyond serum neutralization to gain a better understanding of the protection against emerging variants.

Frequency of B-Cell Subpopulations in Low Responders in Comparison with High Responders to Hepatitis B Vaccine Among Health Care Workers.

Vaccination is the most effective way to prevent Hepatitis B (HB) infection. The goal of vaccination is to induce immunological memory. Hence, determining the frequency of memory B-cell (MBC) subsets is an important indicator of vaccine efficacy. This study aimed to evaluate the frequency of different B-cell subpopulations and the expression of PD-1 on B-cell subsets in low responders (LR) and high responders (HR) to HB vaccine. According to our findings, the expression level of PD-1 was significantly higher on atypical MBC (atMBC) than that of naive B cell and classical MBC (cMBC) in LR and HR groups. Moreover, cMBCs had a significant higher PD-1 expression than naive B cells in LR group. No significant differences were found in the frequency of various B-cell subpopulations and the expression level of PD-1 on B-cell subsets between LR and HR groups. We observed a negative correlation between age and HBsAb titer and a positive correlation between age and PD-1 expression level on cMBC in LR group. It can be concluded that inadequate specific memory B-cell response, rather than total memory B-cell deficiency, may be implicated in low responsive rate to HB vaccine in healthy individuals.

MRNA-based SARS-CoV-2 Comirnaty vaccine elicits weak and short specific memory B cell response in individuals with no previous infection.

The dynamics of the memory B cell (MBC) repertoire after SARS-CoV-2 vaccination is crucial for assessing long-term immunity. We compare spike-specific MBC responses between SARS-CoV-2 unexposed and recovered individuals, and their impact on breakthrough infections during follow-up. Spike-specific MBC and T cells were quantified at inclusion and after two doses of mRNA vaccine in a longitudinal cohort of 85 naïve and 64 recovered participants (47 with positive serology and 17 with negative serology after infection). At inclusion, there was minimal spike-specific MBC in naïve SARS-CoV-2 individuals. After the second vaccine dose, MBCs were significantly boosted in naïve individuals, but reached a significantly lower level than that observed even in unvaccinated SARS-CoV-2 convalescents (p<0.001). Furthermore, while the secondary memory B cell (MBC) population consisted of 100%, 33%, and 76% IgG+, IgM+, and IgA+ expressing cells, respectively, in the unexposed group, the MBC response showed a significant decrease across all isotypes. Similarly, although secondary specific IgG+, IgM+, and IgA+-MBC isotypes were found in 100%, 39%, and 76% of the unexposed participants, respectively, the magnitude of the MBC levels was significantly lower for all the isotypes compared to convalescents. Interestingly, convalescents without an initial serological response had a lower MBC response, like what found in unexposed subjects. There was an inverse correlation between specific MBCs (r=-0.307; p=0.027), especially for isotype IgA+ (r=-0.279, p=0.045), and the time since the second vaccination dose. Furthermore, during a median follow-up of 434 days (IQR, 339-495), 49 out of 149 individuals (33%) became infected, 29 in naïve and 20 in convalescent individuals, showing a significant correlation between spike-specific MBC magnitude after vaccination and the time for SARS-CoV-2 infection, especially for IgA+/IgG+ MBC isotypes. MBCs were primed by mRNA-based vaccination in most cases, but SARS-CoV-2 naïve individuals had a blunted specific MBC response, and this was associated with a shorter time to breakthrough SARS-CoV-2 infection.

Tracking B Cell Memory to SARS-CoV-2 Using Rare Cell Analysis System.

Rapid mutations within SARS-CoV-2 are driving immune escape, highlighting the need for in-depth and routine analysis of memory B cells (MBCs) to complement the important but limited information from neutralizing antibody (nAb) studies. In this study, we collected plasma samples and peripheral blood mononuclear cells (PBMCs) from 35 subjects and studied the nAb titers and the number of antigen-specific memory B cells at designated time points before and after vaccination. We developed an assay to use the MiSelect R II System with a single-use microfluidic chip to directly detect the number of spike-receptor-binding domain (RBD)-specific MBCs in PBMCs. Our results show that the number of spike-RBD-specific MBCs detected by the MiSelect R II System is highly correlated with the level of nAbs secreted by stimulated PBMCs, even 6 months after vaccination when nAbs were generally not present in plasma. We also found antigen-specific cells recognizing Omicron spike-RBD were present in PBMCs from booster vaccination of subjects, but with a high variability in the number of B cells. The MiSelect R II System provided a direct, automated, and quantitative method to isolate and analyze subsets of rare cells for tracking cellular immunity in the context of a rapidly mutating virus.

Impact of Previous Common Human Coronavirus Exposure on SARS-CoV-2-Specific T-Cell and Memory B-Cell Response after mRNA-Based Vaccination

T-cell responses against SARS-CoV-2 are observed in unexposed individuals, attributed to previous common human coronavirus (HCoV) infections. We evaluated the evolution of this T-cell cross-reactive response and the specific memory B-cells (MBCs) after the SARS-CoV-2 mRNA-based vaccination and its impact on incident SARS-CoV-2 infections. This was a longitudinal study of 149 healthcare workers (HCWs) that included 85 unexposed individuals that were subdivided according to previous T-cell cross-reactivity, who were compared to 64 convalescent HCWs. Changes in specific T-cell response and memory B-cell (MBC) levels were compared at baseline and after two doses of the SARS-CoV-2 mRNA-based vaccine. A cross-reactive T-cell response was found in 59% of unexposed individuals before vaccination. Antibodies against HKU1 positively correlated with OC43 and 229E antibodies. Spike-specific MBCs was scarce in unexposed HCWs regardless of the presence of baseline T-cell cross-reactivity. After vaccination, 92% and 96% of unexposed HCWs with cross-reactive T-cells had CD4+ and CD8+ T-cell responses to the spike protein, respectively. Similar results to that were found in convalescents (83% and 92%, respectively). Contrarily, higher than that which was observed in unexposed individuals without T-cell cross-reactivity showed lower CD4+ and CD8+ T-cell responses (73% in both cases, p = 0.03). Nevertheless, previous cross-reactive T-cell response was not associated with higher levels of MBCs after vaccination in unexposed HCWs. During a follow-up of 434 days (IQR, 339-495) after vaccination, 49 HCWs (33%) became infected, with a significant positive correlation between spike-specific MBC levels and isotypes IgG+ and IgA+ after vaccination and a longer time to get infected. Interestingly, T-cell cross-reactivity did not reduce the time to vaccine breakthrough infections. While pre-existing T-cell cross-reactivity enhances the T-cell response after vaccination, it does not increase SARS-CoV-2-specific MBC levels in the absence of previous infection. Overall, the level of specific MBCs determines the time to breakthrough infections, regardless of the presence of T-cell cross-reactivity.

High activation levels maintained in receptor-binding domain-specific memory B cells in people with severe coronavirus disease 2019.

The long-term health consequences of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are still being understood. The molecular and phenotypic properties of SARS-CoV-2 antigen-specific T cells suggest a dysfunctional profile that persists in convalescence in those who were severely ill. By contrast, the antigen-specific memory B-cell (MBC) population has not yet been analyzed to the same degree, but phenotypic analysis suggests differences following recovery from mild or severe coronavirus disease 2019 (COVID-19). Here, we performed single-cell molecular analysis of the SARS-CoV-2 receptor-binding domain (RBD)-specific MBC population in three patients after severe COVID-19 and four patients after mild/moderate COVID-19. We analyzed the transcriptomic and B-cell receptor repertoire profiles at ~2 months and ~4 months after symptom onset. Transcriptomic analysis revealed a higher level of tumor necrosis factor-alpha (TNF-α) signaling via nuclear factor-kappa B in the severe group, involving CD80, FOS, CD83 and TNFAIP3 genes that was maintained over time. We demonstrated the presence of two distinct activated MBCs subsets based on expression of CD80hi TNFAIP3hi and CD11chi CD95hi at the transcriptome level. Both groups revealed an increase in somatic hypermutation over time, indicating progressive evolution of humoral memory. This study revealed distinct molecular signatures of long-term RBD-specific MBCs in convalescence, indicating that the longevity of these cells may differ depending on acute COVID-19 severity.

Impact of SARS-CoV-2-specific memory B cells on the immune response after mRNA-based Comirnaty vaccine in seronegative health care workers.

PurposeTo analyze the impact of SARS-COV-2-specific memory B cells (MBC) on the immune response after two doses of mRNA-based Comirnaty COVID-19 vaccine in seronegative health care workers. This study is seeking a rationale for boosting vaccines.MethodsLongitudinal study including 31 seronegative health care workers with undetectable specific MBCs (IgG−MBC− group), 24 seronegative with detectable specific MBCs (IgG−MBC+ group), and 24 seropositive with detectable specific MBCs (IgG+MBC+ group). The level of antibodies that inhibit ACE2-RBD interaction, and anti-Spike IgG, IgA, and IgM antibodies was quantified by ELISA. In addition, specific memory B and T cells were quantified by flow cytometry.ResultsThe level of specific MBCs, and isotypes, in the IgG−MBC− group was lower compared to that found in IgG−MBC+ (p = 0.0001) and IgG+MBC+ (p < 0.0001) groups, respectively. ACE2-RBD neutralizing antibodies and anti-S IgG antibodies were at lower levels in the IgG−MBC−group after the vaccine. Specific MBCs directly correlated with specific CD4+ T cells (although not significant, p = 0.065), while no correlation was found with specific CD8+ T cells (p = 0.156) after the vaccine. In parallel, ACE2-RBD neutralizing antibodies only positively correlated with specific CD4+ T cells (p = 0.034).ConclusionIgG−MBC− individuals showed the worst humoral and cellular responses, both in frequency and magnitude, after vaccination. Individuals whose antibodies wane and become undetectable after a given period of time post vaccination and show no specific MBCs are less protected and hence are good candidates for boosting vaccine. On the other hand, seronegative individuals with specific MBC showed faster and higher responses compared to the IgG−MBC− group.

Updated International Society of Geriatric Oncology COVID-19 working group recommendations on COVID-19 vaccination among older adults with cancer

Updated International Society of Geriatric Oncology COVID-19 working group recommendations on COVID-19 vaccination among older adults with cancer

P313 Within, 6 months from COVID-19 BNT162b2 vaccine patients with Inflammatory Bowel Diseases treated with Anti-TNFα have significantly lower serologic responses

BackgroundWhile vaccines against COVID-19 are effective in healthy individuals, we reported significantly lower serologic responses to BNT162b2 in patients with inflammatory bowel diseases (IBD) treated with anti-tumor necrosis factor (TNF) α agents. As this was apparent already, 4 weeks post vaccination, vaccine longevity is concerning. Aim: to assess long-term serologic responses to BNT162b2 in patients with IBD stratified according to medical treatment.MethodsA prospective, observational multi-center Israeli study. Patients with IBD (anti-TNFα treated versus non-anti-TNFα treated) and healthy controls (HC) were followed from before the, 1st BNT162b2 dose until, 6 months after vaccination. COVID-19 spike (S) and nucleocapsid (N) antibodies (Abs) concentrations were analyzed by ELISA, followed by neutralization studies. Specific anti-receptor binding domain (RBD) memory B-cells response, serologic responses against variants of concern (VOCs), Beta, Gamma and Delta, immunoglobulin levels and lymphocyte cell subsets were evaluated as well. Safety was assessed using questionnaires, clinical and laboratory data.ResultsOf, 193 subjects, 130 had IBD (45 and, 85 in the anti-TNFα and non-anti-TNFα groups, respectively), 63 HC. Serologic response assessed, 176 (median) days (IQR, 166–186) and compared to, 4 weeks after, 1st dose significantly declined in all three groups, but was lowest in the anti-TNFα group:, 6 months anti-S Abs titer geometric means:, 193 (95%CI:, 128–292), 703 (520–951), and, 1253 (1023–1534) in anti-TNFα, non- anti-TNFα and HC groups, respectively, p<0.001, Figure, 1. This was further supported by neutralization and inhibition studies. Importantly, significantly decreased memory B-cell response towards RBD was detected only in the anti-TNFα group, with the most significant reduction in response to Beta VOC (p<0.0008 and p<0.0001, vs. non-anti-TNFα and HC, respectively). Older age was an additional predictor of lower serologic response. Immunoglobulin levels and lymphocyte cell subsets were comparable between the study groups. Infection rate reflected by anti-N Abs was ~1% in all groups. Safety was comparable in all groups.ConclusionThe, 6-months serologic response to BNT162b2 vaccine, evaluated prospectively, decreased in all subjects, most prominently in patients with IBD treated with anti-TNFα. Importantly, the latter also had the sharpest decline in serologies, the lowest functional activity and lowest RBD specific memory B-cells. Older age is an additional predictor of decreased serologic response. Altogether, waning of COVID-19 serologic and functional response over, 6 months, specifically in patients with IBD treated with anti-TNFα, supports the need for an early third vaccine dose.

Main B-cell epitopes of PvAMA-1 and PvMSP-9 are targeted by naturally acquired antibodies and epitope-specific memory cells in acute and convalescent phases of vivax malaria.

Although antibodies are considered critical for malaria protection, little is known about the mechanisms/factors that maintain humoral immunity, especially regarding the induction and maintenance of memory B cells over time. In Brazilian endemic areas, this is the first time that the profile of antibody responses and the occurrence of antigen-specific memory B cells (MBC) against P vivax were investigated during acute malaria and up to six months after parasite clearance. For this, we selected two peptides, PvAMA-1(S290-K307) and PvMSP-9(E795-A808) , which represent the apical membrane antigen-1 and merozoite surface protein-9 of P vivax, respectively. Both peptides were previously described as containing linear B-cell epitopes. Our findings were as follows: 1-both peptides were recognized by IgG antibodies at a high frequency (between 24% and 81%) in all study groups; 2-in the absence of infection, the IgG levels remained stable throughout 6months of follow-up; and 3-PvAMA-1(S290-K307) and PvMSP-9(E795-A808) -specific MBCs were detected in all individual groups in the absence of reinfection throughout the follow-up period, suggesting long-lived MBC. However, no positive association was observed between malaria-specific antibody levels and frequency of MBCs over time. Taken together, these results suggest that peptides can be, in the future, an alternative strategy to polypeptidic vaccine formulation.

The persistence of naturally acquired antibodies and memory B cells specific to rhoptry proteins of Plasmodium vivax in patients from areas of low malaria transmission

BackgroundRhoptries are the large, paired, secretory organelles located at the apical tip of the malaria merozoite that are considered important for parasite invasion processes. Plasmodium vivax rhoptry proteins have been shown to induce humoral immunity during natural infections. Therefore, these proteins may be potential novel vaccine candidates. However, there is a lack of data on the duration of antibody and memory B cell (MBC) responses. Here, the longitudinal analysis of antibody and MBC responses to the P. vivax rhoptry proteins PvRALP1-Ecto and PvRhopH2 were monitored and analysed in individuals to determine their persistence.MethodsThirty-nine samples from P. vivax-infected subjects (age 18–60 years) were recruited to explore the frequency and persistence of antibody and MBC responses against rhoptry proteins (PvRALP1-Ecto and PvRhopH2) using both cross-sectional and longitudinal cohort study designs. Antibody levels were determined by ELISA during clinical malaria, and at 3, 9 and 12 months post-infection. The frequency of MBC sub-sets and presence of rhoptry-specific MBCs in subjects 18 months after treatment were detected by flow cytometry and ELISPOT assay.ResultsThe seroprevalence of antibodies against PvRALP1-Ecto and PvRhopH2 proteins was found to be high during acute infection, with IgG1, IgG2 and IgG3 sub-classes predominant. However, these anti-rhoptry responses were short-lived and significantly decreased at 9 months post-infection. To relate the durability of these antibody responses to MBC persistence at post-infection, 18-month post-infection peripheral blood mononuclear cells (PBMCs) samples were taken to detect rhoptry-specific MBCs and frequency of MBC sub-sets, and correlate with antibody responses. These late post-infection samples revealed that rhoptry-specific MBCs were present in about 70% of total subjects. However, the persistence of specific MBCs was not correlated with antibody responses as the majority of malaria subjects who were positive for PvRALP1-Ecto- or PvRhopH2-specific MBCs were seronegative for the rhoptry antigens. The frequencies of classical MBCs were increased after infection, whereas those of activated and atypical MBCs were decreased, indicating that MBC responses could switch from activated or atypical MBCs to classical MBCs after parasite clearance, and were maintained in blood circulating at post-infection.ConclusionThe study showed that rhoptry antigens induced the development and persistence of MBC responses in P. vivax-infected subjects who lived in a region of low malaria transmission, which were not related to the longevity of antibody responses.

Approaches to Interrogating the Human Memory B-Cell and Memory-Derived Antibody Repertoire Following Dengue Virus Infection.

Memory B-cells (MBCs) are potential antibody secreting immune cells that differentiate and mature following host exposure to a pathogen. Following differentiation, MBCs remain in peripheral circulation after recovery and are poised to secrete antigen-specific antibodies if and when they are re-exposed to their cognate antigen. Consequently, MBCs form the founder population and provide one of the first lines of pathogen-specific defense against reinfection. The role MBCs play is complicated for viruses that are heterologous, such as dengue virus (DENV), which exist as antigenically different serotypes. On second infection with a different serotype, MBCs from initial dengue infection rapidly proliferate and secrete antibodies: many of these MBC derived antibodies will be cross-reactive and weakly neutralizing, while some antibodies may recognize epitopes conserved across serotypes and have the capacity to broadly neutralize 2 or more serotypes. It is also possible that a new population of MBCs and antibodies specific for the second virus serotype need to arise for long-term broader immunity to develop. Methods to interrogate and track memory B cell responses are important for evaluating both natural immunity and vaccine response. However, the low abundance of MBCs for any specific pathogen makes it challenging to interrogate frequency, specificity, and breadth for the pathogen of interest. This review discusses current approaches that have been used to interrogate the memory B cell immune response against viral pathogens in general and DENV specifically. Including strengths, limitations, and future directions. Single-cell approaches could help uncover the DENV specific MBC antibody repertoire, and improved methods for isolating DENV specific monoclonal antibodies from human peripheral blood cells would allow for a functional analysis of the anti-DENV repertoire.

Epigenetic priming underpins enhanced memory B cell differentiation

Abstract Immunological memory is a hallmark of the adaptive immune response. Memory B cells (MBC) have increased affinity, expression of costimulatory molecules, and capacity to proliferate and differentiate than their naïve counterparts; however, the epigenetic mechanisms that control enhanced MBC functions are currently unknown. Using a murine model of influenza infection, nucleoprotein (NP)-specific MBC and follicular naïve B cells (nB) were isolated and the chromatin accessibility and transcriptional landscape determined by ATAC and RNA-seq, respectively. MBC displayed distinct gene expression profiles from nB, including an upregulation of plasma cell (PC) signature genes and significant overall increases in total mRNA content. Furthermore, MBC display an open and primed chromatin conformation in gene regulatory regions that map to transcription factors controlling either PC (Prdm1 and Irf4), germinal center (Aicda), or MBC (Zbtb32) fates. These data reveal additional novel MBC-specific transcription factor networks and describe an epigenetic “antigen experience” signature that correlates with enhanced MBC function. To confirm the importance of these molecular changes, naïve and memory mice were challenged with a heterosubtypic influenza infection or isolated and cultured with CD40L, IL-4, and IL-5. In vivo, MBC form germinal centers earlier and to a higher frequency than nB. MBC also form significantly more NP+IgG+ PCs by flow cytometry and ELISPOT, corroborating the open chromatin signature. Ex vivo, MBCs upregulated primed transcription factors earlier than nB, validating the enhanced formation of CD138+ PCs. These data describe an epigenetic basis for enhanced the differentiation capacity and function of MBC.

The impact of pre-existing B-cell memory in the response to Influenza vaccination

Abstract Influenza is a highly contagious viral respiratory disease with more than 200 thousand cases reported in the US last season (2017/18). Annual vaccination is recommended by the World Health Organization with the goal to reduce influenza severity and limit transmission. However, currently available split inactivated influenza vaccines can only elicit protection up to ~60% in well-matched-strain years. Furthermore, vaccine effectiveness frequently varies between different influenza subtypes within a single influenza season for unclear reasons. Immunological imprinting from early-life influenza infection can prominently shape the immune response to subsequent infections. Here, the impact of pre-existing B-cell memory in the response to quadrivalent influenza vaccine was assessed. Blood samples were collected from healthy subjects (18 to 85 years old) prior to vaccination and 21–28 days after vaccination with quadrivalent influenza vaccine. Samples were assessed for changes in serological antibodies to the hemagglutinin protein (HA) by ELISA and by hemagglutination-inhibition (HAI) assays against the four strains in the vaccine. The number of antigen specific memory B-cells (Bmem) were quantified by flow cytometry and the polyclonal Bmemresponse was assessed against the HA of the four vaccine strains. Influenza vaccination greatly induces the HA-specific Bmem-cell pool and, despite no differences in antigenicity between the four vaccine components, most individuals are biased towards one of the influenza A or Influenza B vaccine strains. Overall, this study unveils a new mechanism behind the differences in vaccine effectiveness against different influenza subtypes.

Bivalent oral cholera vaccination induces a memory B cell response to the V. cholerae O1-polysaccharide antigen in Haitian adults

The bivalent killed whole-cell oral cholera vaccine (BivWC) is being increasingly used to prevent cholera. The presence of O-antigen-specific memory B cells (MBC) has been associated with protective immunity against cholera, yet MBC responses have not been evaluated after BivWC vaccination. To address this knowledge gap, we measured V. cholerae O1-antigen MBC responses following BivWC vaccination. Adults in St. Marc, Haiti, received 2 doses of the BivWC vaccine, Shanchol, two weeks apart. Participants were invited to return at days 7, 21, 44, 90, 180 and 360 after the initial vaccination. Serum antibody and MBC responses were assessed at each time-point before and following vaccination. We observed that vaccination with BivWC resulted in significant O-antigen specific MBC responses to both Ogawa and Inaba serotypes that were detected by day 21 and remained significantly elevated over baseline for up to 12 months following vaccination. The BivWC oral cholera vaccine induces durable MBC responses to the V. cholerae O1-antigen. This suggests that long-term protection observed following vaccination with BivWC could be mediated or maintained by MBC responses.

Lipopolysaccharide-specific memory B cell responses to an attenuated live cholera vaccine are associated with protection against Vibrio cholerae infection

BackgroundThe single-dose live attenuated vaccine CVD 103-HgR protects against experimental Vibrio cholerae infection in cholera-naïve adults for at least 6 months after vaccination. While vaccine-induced vibriocidal seroconversion is associated with protection, vibriocidal titers decline rapidly from their peak 1–2 weeks after vaccination. Although vaccine-induced memory B cells (MBCs) might mediate sustained protection in individuals without detectable circulating antibodies, it is unknown whether oral cholera vaccination induces a MBC response. MethodsIn a study that enrolled North American adults, we measured lipopolysaccharide (LPS)- and cholera toxin (CtxB)-specific MBC responses to PXVX0200 (derived from the CVD 103-HgR strain) and assessed stool volumes following experimental Vibrio cholerae infection. We then evaluated the association between vaccine-induced MBC responses and protection against cholera. ResultsThere was a significant increase in % CT-specific IgG, % LPS-specific IgG, and % LPS-specific IgA MBCs which persisted 180 days after vaccination as well as a significant association between vaccine-induced increase in % LPS-specific IgA MBCs and lower post-challenge stool volume (r = −0.56, p < 0.001). DiscussionOral cholera vaccination induces antigen-specific MBC responses, and the anamnestic LPS-specific responses may contribute to long-term protection and provide correlates of the duration of vaccine-induced protection.Clinical trials registration: NCT01895855.

Abstract 594: Antibodies targeting LAG-3, TIM-3, KIR cloned from healthy human donors

Abstract The immunosurveillance/immunoediting theory postulates that tumor growth is repressed in healthy individuals through the activation of adaptive and innate immune mechanisms. The clinical success of antibodies that target inhibitory checkpoint pathways of the immune system (i.e. CTLA-4, PD-1) has provided compelling evidence in support of this theory and raises the question of whether antibodies targeting these, or other inhibitory immune cell modulators (ICM), are present in apparently healthy individuals. The present studies were designed to answer this question by probing the circulating memory B-cell compartment that represents a historic record of an individual's lifelong adaptive immune response. Methods: Blood from donors, with no known cancer history, was screened for the presence of anti-ICM binding memory B-cells targeting LAG-3, TIM-3, B7-H3, KIR, and VISTA, using Trellis's established CellSpotTM technology that can detect the presence of antigen specific memory B-cells at a frequency of 0.1 per 100,000 memory B-cells. Results: Circulating memory B-cells targeting ICM's were present in all apparently healthy individuals tested (20 total). There was substantial variation as to which ICM's were recognized within each individual across this sample population. Antibodies cloned from these rare B-cells were of IgG class and exhibited low to sub-nM affinity toward the specific ICM. These high affinity antibodies bound their respective antigens on activated T-cells and were able to augment immune stimulatory cytokine release in cellular assays. Data from ongoing studies will be presented. Conclusion: These studies demonstrate that apparently healthy individuals produce high affinity, pharmacologically active anti-ICM antibodies. Thus, healthy individuals represent a previously unrecognized source of antibodies that have undergone natural selection and hold particular promise as potential therapeutic agents for the treatment of cancer. Citation Format: Angeles Estelles, Robert Stephenson, Keyi Liu, Evelene Lomongsod, Da Ngyen, Jianzhong Zhzng, Yifan Yang, Manfred Heideker, Lawrence Kauvar, Stefan Ryser, Mikhail L. Gishizky. Antibodies targeting LAG-3, TIM-3, KIR cloned from healthy human donors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 594.

Higher numbers of memory B-cells and Th2-cytokine skewing in high responders to hepatitis B vaccination

In the present study, differences in hepatitis B surface antigen (HBsAg)-specific memory B-cell responses between low and high responders to hepatitis B vaccine (HepB), based on levels of antibodies against HBsAg (anti-HBs), were determined. In addition, HBsAg specific T-cell responses between high (anti-HBs level >20,000IU/L) and low (anti-HBs level <1500IU/L) responders were compared.Numbers of HBsAg-specific B-cells, plasma immunoglobulin G (Ig) levels, and T-cell cytokine concentrations were measured in low and high responders directly before and one month after the second booster vaccination. In advance, an Enzyme-linked Immunosorbent Spot (ELISpot) Assay was optimized for the determination of HBsAg-specific B-cell responses.The number of HBsAg-specific B-cells was significantly higher (p<0.01) in the high responder group compared to the low responder group after a booster vaccination with HepB. In addition, the plasma IgG levels and numbers of HBsAg-specific B-cells were significantly correlated (RS=0.66, p<0.01). The HBsAg-specific Th1 cell response showed the same values in the low and high responder group and did not change by the booster vaccination with HepB. However, a significant correlation (RS=0.6975, p=0.007) between the IL-13 levels and the plasma IgG levels post-booster was found. Subsequently, the IL-13 level in the high-responder group post-booster was significantly higher compared to the low-responder group.Since activation of the B-cell response after vaccination is induced by Th2 cells and IL-13 is produced by these cells, we conclude that the difference in HBsAg-specific Th2 cells is involved in determining the differences in anti-HBs level and memory B-cell numbers between low and high responders.

Profiling the Autoantibody Repertoire of Acquired Thrombotic Thrombocytopenic Purpura (aTTP) Patients By Single Cell Sorting and Deep Sequencing of Splenic B-Cells

Introduction: Antibodies are the primary effector molecules in the humoral immune system. To create a diversity of receptors-antibodies B-cells undergo V(D)J gene recombination and somatic hypermutation. This allows the recognition of most of pathogens but also sometimes of self-antigen, which can lead to autoimmune diseases. Autoantibodies (Abs) neutralizing and/or accelerating the clearance of ADAMTS13 are present in nearly all acquired thrombotic thrombocytopenic purpura (aTTP) patients with severe ADAMTS13 activity (<5%). As increasing evidence points at the spleen as a major reservoir for antigen specific memory B-cells, we investigated the splenic B-cell repertoire. We sequenced heavy and corresponding light chains from single antigen-specific memory B-cells and deep sequenced global antibody repertoire among different B-cell populations. Combining both, the single antigen-specific repertoire and the general global repertoire from the same patients specimens allows an investigation of the V(D)J gene usage and abundance of specific V(D)J junction in the B-cell populations within one patient and also among different patients. Analysis of the repertoire enables better understanding of the humoral autoimmune response.Methods: Specimens were analyzed from 8 aTTP patients who were splenectomized due to a refractory course of the autoimmune disease. Splenic mononuclear cells were sorted by flow-cytometry into naïve and transitional (CD27-, IgD+), unswitched memory (CD27+, IgD+) and switched memory (CD27+, IgD-) as well as (CD27+, CD20-/CD19-, CD38+) plasma cells. The frequencies of highly positive anti-ADAMTS13 B-cells in each B-cell population were calculated. Library consisting of antibody cDNA from each B-cell population was deep sequenced on MiSeq Ilumina. Prime analysis were performed in CLC Genomics Workbench. High quality sequences were submitted to IMGT/high V-QUEST web-based analysis tool to determine for V(D)J genes alignments, and V(D)J junction (antigen binding region) and mutations analysis. The IMGT output was parsed into MySQL database for further analysis. In addition, from 4 patients anti-ADAMTS13 specific IgG bearing cells were individually sorted. Gene transcripts of single cells were reverse-transcribed followed by nested PCR of IgG heavy/light chains. V(D)J pairings were visualized with Circos software. In MySQL we compared single cell antigen specific sequence with global repertoire.Results: Anti-ADAMTS13 specific B-cells were detected in the spleen of all patients (average 0.01% of total B-cell population). Deep sequencing of the total B-cell repertoire revealed ~3 million productive sequences, from which ~2 million were unique. Splenic anti-ADAMTS13 specific B-cells of four aTTP patients revealed 80 antibodies with unique V(D)J junction. Among those most frequently used V-genes were IGHV1-69 and IGHV3-30 (15% and 12% respectively) in global repertoire 1.5% of antibodies were encoded with IGHV1-69 gene within respective population. The average identity to germline was lower in ADMTST13 specific B-cells (92% compare to 96%). Four V(D)J junctions were convergent in at least 2 patients (identical amino acid sequence).Conclusion: Anti-ADAMTS13 specific B-cells were found in all aTTP patients in different B-cell populations. We observed enrichment of some variable gene segments when comparing the specific anti-ADAMTS13 to the total splenic repertoire (mainly IGHV1-69). Finding convergent V(D)J junction is very promising and also confirms previous finding of our group where similar V(D)J junction were found among two patients. Currently we clone selected single sorted monoclonal Abs (Schaller et al, Blood 2014;124(23):3469-79). Functional testing will allow the selection of the inhibitory Abs to be used as tools to develop anti-idiotypic specific therapies for aTTP patients. DisclosuresNo relevant conflicts of interest to declare.