The extent of affinity maturation differs between the memory and antibody-forming cell compartments in the primary immune response.

Immunization with protein-containing antigens results in two types of antigen-specific B cell: antibody forming cells (AFCs) producing antibody of progressively higher affinity and memory lymphocytes capable of producing high affinity antibody upon re-exposure to antigen. The issue of the inter-relationship between affinity maturation of memory B cells and AFCs was addressed through analysis of single, antigen-specific B cells from the memory and AFC compartments during the primary response to a model antigen. Only 65% of splenic memory B cells were found capable of producing high affinity antibody, meaning that low affinity cells persist into this compartment. In contrast, by 28 days after immunization all AFCs produced high affinity antibody. We identified a unique, persistent sub-population of bone marrow AFCs containing few somatic mutations, suggesting they arose early in the response, yet highly enriched for an identical affinity-enhancing amino acid exchange, suggesting strong selection. Our results imply that affinity maturation of a primary immune response occurs by the early selective differentiation of high affinity variants into AFCs which subsequently persist in the bone marrow. In contrast, the memory B-cell population contains few, if any, cells from the early response and is less stringently selected.     

Generation of B cell memory and affinity maturation. Induction with Th1 and Th2 T cell clones.

We used an adoptive transfer system and CD4+ T cell clones with defined lymphokine profiles to examine the role of CD4+ T cells and the types of lymphokines involved in the development of B cell memory and affinity maturation. Keyhole limpet hemocyanin (KLH)-specific CD4+ Th2 clones (which produce IL-4 and IL-5 but not IL-2 or IFN-gamma) were capable of inducing B cell memory and affinity maturation, after transfer into nude mice or after transfer with unprimed B cells into irradiated recipients and immunization with TNP-KLH. In addition, KLH-specific Th1 clones, which produce IL-2 and IFN-gamma but not IL-4 or IL-5, were also effective in inducing B cell memory and high affinity anti-TNP-specific antibody. The induction of affinity maturation by Th1 clones occurred in the absence of IL-4, as anti-IL-4 mAb had no effect on the affinity of the response whereas anti-IFN-gamma mAb completely blocked the response. Th1 clones induced predominantly IgG2a and IgG3 antibody, although Th2 clones induced predominantly IgG1 and IgE antibody. We thus demonstrated that some Th1 as well as some Th2 clones can function in vivo to induce Ig synthesis. These results also suggest that a single type of T cell with a restricted lymphokine profile can induce both the terminal differentiation of B cells into antibody secreting cells as well as induce B cell memory and affinity maturation. Moreover, these results suggest that B cell memory and affinity maturation can occur either in the presence of Th2 clones secreting IL-4 but not IFN-gamma, or alternatively in the presence of Th1 clones secreting IFN-gamma but not IL-4.     

Induction of antigen-specific antibody responses in primed and unprimed B cells. Functional heterogeneity among Th1 and Th2 T cell clones

CD4+ T cells have been recently divided into two subsets. The functions of these subsets are thought to be distinct: one subset (Th1) is responsible for delayed type hypersensitivity responses and another (Th2) is primarily responsible for induction of antibody synthesis. To more precisely define the roles of both subsets in humoral immune responses, we examined the ability of a panel of nominal antigen specific Th1 and Th2 clones to induce anti-TNP specific antibody synthesis in TNP-primed or unprimed B cells. Four of nine Th1 clones induced little or no antibody synthesis with TNP-primed B cells. However, five other Th1 clones were very effective at inducing IgG anti-TNP plaque-forming cell (PFC) responses in primed B cells. One of these Th1 clones was analysed in detail and found to also provide helper function for unprimed B cells. Cognate B-T cell interaction was required for induction of both primary and secondary responses with this clone, indicating that a Th1 clone could function as a "classical" Th cell. The seven IL-4 producing Th2 clones examined were also heterogeneous in their ability to induce antibody secretion by TNP-primed B cells. Although four of the Th2 clones induced IgG and IgM anti-TNP PFC responses, two Th2 clones induced only IgM and no IgG antibody, and another clone failed to induce any anti-TNP PFC. All Th2 clones failed to induce any anti-TNP PFC. All Th2 clones produced high levels of IL-4, but "helper" Th2 clones produced significantly greater amounts of IL-5 than "non-helper" Th2 clones. These studies indicate that some IL-2- and some IL-4-producing T cell clones can induce TNP-specific antibody in cell clones can induce TNP-specific antibody in primed and unprimed B cells, and that Th1 and Th2 clones are heterogeneous in their ability to induce Ig synthesis. Therefore, although T cell clones can be classified as Th1 or Th2 types according to patterns of IL-2, IFN-gamma, or IL-4 synthesis, the functional capacity to induce antibody synthesis cannot be predicted solely by their ability to secrete these lymphokines.     

Neo-Lymphoid Aggregates in the Adult Liver Can Initiate Potent Cell-Mediated Immunity

Subcutaneous immunization delivers antigen (Ag) to local Ag-presenting cells that subsequently migrate into draining lymph nodes (LNs). There, they initiate the activation and expansion of lymphocytes specific for their cognate Ag. In mammals, the structural environment of secondary lymphoid tissues (SLTs) is considered essential for the initiation of adaptive immunity. Nevertheless, cold-blooded vertebrates can initiate potent systemic immune responses even though they lack conventional SLTs. The emergence of lymph nodes provided mammals with drastically improved affinity maturation of B cells. Here, we combine the use of different strains of alymphoplastic mice and T cell migration mutants with an experimental paradigm in which the site of Ag delivery is distant from the site of priming and inflammation. We demonstrate that in mammals, SLTs serve primarily B cell priming and affinity maturation, whereas the induction of T cell-driven immune responses can occur outside of SLTs. We found that mice lacking conventional SLTs generate productive systemic CD4- as well as CD8-mediated responses, even under conditions in which draining LNs are considered compulsory for the initiation of adaptive immunity. We describe an alternative pathway for the induction of cell-mediated immunity (CMI), in which Ag-presenting cells sample Ag and migrate into the liver where they induce neo-lymphoid aggregates. These structures are insufficient to support antibody affinity maturation and class switching, but provide a novel surrogate environment for the initiation of CMI.     

The agonists of TLR4 and 9 are sufficient to activate memory B cells to differentiate into plasma cells in vitro but not in vivo

Memory B cells can persist for a lifetime and be reactivated to yield high affinity, isotype switched plasma cells. The generation of memory B cells by Ag immunization requires adjuvants that generally contain TLR agonists. However, requirements for memory B cell activation and the role of TLRs in this activation are not well understood. In this study, we analyzed the response of memory B cells from immunized mice to TLR9 and 4 agonists CpG oligodeoxynucleotides (ODN) and LPS. Mouse memory B cells express both TLR9 and 4, and respond to both CpG ODN and LPS in vitro by differentiating into high affinity IgG secreting plasma cells. In contrast, neither CpG ODN nor LPS alone is sufficient to activate memory B cells in vivo. Ag is required for the clonal expansion of Ag-specific memory B cells, the differentiation of memory B cells to high affinity IgG secreting plasma cells, and the recall of high affinity Ab responses. The Ag-specific B cells that have not yet undergone isotype switching showed a relatively higher expression of TLR4 than memory B cells, which was reflected in a heightened response to LPS, but in both cases yielded mostly low affinity IgM secreting plasma cells. Thus, although memory B cells are sensitive to TLR agonists in vitro, TLR agonists alone appear to have little affect on B cell memory in vivo.     

AID Activity in B Cells Strongly Correlates with Polyclonal Antibody Affinity Maturation in-vivo Following Pandemic 2009-H1N1 Vaccination in Humans

The role of Activation-Induced Cytidine Deaminase (AID) in somatic hypermutation and polyclonal antibody affinity maturation has not been shown for polyclonal responses in humans. We investigated whether AID induction in human B cells following H1N1pdm09 vaccination correlated with in-vivo antibody affinity maturation against hemagglutinin domains in plasma of young and elderly individuals. AID was measured by qPCR in B cells from individuals of different ages immunized with the H1N1pdm09 influenza vaccine. Polyclonal antibody affinity in human plasma for the HA1 and HA2 domains of the H1N1pdm09 hemagglutinin was measured by antibody-antigen complex dissociation rates using real time kinetics in Surface Plasmon Resonance. Results show an age-related decrease in AID induction in B cells following H1N1pdm09 vaccination. Levels of AID mRNA before vaccination and fold-increase of AID mRNA expression after H1N1pdm09 vaccination directly correlated with increase in polyclonal antibody affinity to the HA1 globular domain (but not to the conserved HA2 stalk). In the younger population, significant affinity maturation to the HA1 globular domain was observed, which associated with initial levels of AID and fold-increase in AID after vaccination. In some older individuals (>65 yr), higher affinity to the HA1 domain was observed before vaccination and H1N1pdm09 vaccination resulted in minimal change in antibody affinity, which correlated with low AID induction in this age group. These findings demonstrate for the first time a strong correlation between AID induction and in-vivo antibody affinity maturation in humans. The ability to generate high affinity antibodies could have significant impact on the elucidation of age-specific antibody responses following vaccination and eventual clinical efficacy and disease outcome.     

Aberrant maturational characteristics of the immune responses of NZB mice to autologous and heterologous erythrocyte antigens

The maturational characteristics of the humoral immune responses of C3H and NZB mice to autologous and heterologous erythrocyte antigens were investigated. Clonal selection of antibody-secreting B lymphocytes was examined at the plaque-forming cell level of analysis of changes in mean antibody affinity and the heterogeneity of binding affinities. The primary immune response of C3H mice to SRBC exhibited a progressive temporal increase in mean relative antibody affinity and a concomitant restriction in the heterogeneity of binding affinities consistent with clonal selection and restriction of B lymphocytes to high affinity antibody-secreting cells. By contrast, the anti-SRBC immune response of NZB mice displayed aberrant maturational characteristics with a progressive decrease in mean relative antibody affinity but also clonal restriction with selection of clones of cells secreting low affinity antibodies. The spontaneous autoimmune responses of NZB mice to autologous erythrocyte surface autoantigens X and HB were different from the response to heterologous erythrocytes in that there was neither a progressive change in mean relative binding affinity nor evidence of progressive clonal restriction. Although the precise mechanisms responsible for the aberrant selection and derepression of B lymphocyte clones in NZB mice have not been identified, the very nature of the aberration suggests the existence of one or more defects which may be intrinsic to the B lymphocytes of NZB mice.     

An Engineered Non-Toxic Superantigen Increases Cross Presentation of Hepatitis B Virus Nucleocapsids by Human Dendritic Cells

Virus like particles (VLPs) are potent immunogens capable of priming strong protective antibody responses due to their repetitive structural arrangement and affinity for specific B cell receptors. By contrast, T cell responses to VLPs can be weak due to inefficient uptake and processing by antigen presenting cells. We report here a novel strategy for increasing the T cell reactivity of a VLP, the nucleocapsid of hepatitis B virus, through covalent coupling of M1, an engineered form of the Streptococcal superantigen SMEZ2, that binds MHC II with high affinity but lacks its T cell mitogenic capability. M1:HBcAg conjugates bound to dendritic cells and were efficiently endocytosed into late endosomes. Human dendritic cells pulsed with M1:HBcAgs stimulated HBV-specific CD8⁺ T cells more effectively than cells pulsed with native capsids indicating that the modified VLP was more effectively cross presented by APCs. Coupling of M1 was also able to induce significantly greater reactivity of human CD4⁺ T cells specific for a common T-helper epitope. These studies indicate the potential of recombinant superantigens to act as flexible molecular adjuvants that can be incorporated into various subunit vaccine platforms leading to enhanced T cell reactivity in humans.     

Ontogeny of B-lymphocyte function: XII. Evidence that the ability to generate memory cells precedes the ability to produce antibody-secreting cells

Using a cell transfer system it was shown that lymphoid cells of B.C-9 mice mature to be able to generate a primary response of high magnitude and high affinity to dinitrophenylated γ-globulin at about 4 weeks of age. Irradiated mice reconstituted with lymphoid cells from B.C-9 or C57BL/6 donors younger than 4 weeks of age fail to produce high-affinity plaque-forming cells and their serum antibody responses were of low magnitude. Nevertheless such recipients give adult-like, high-affinity, high-magnitude secondary responses when assayed at both the plaque-forming cell and serum antibody levels. The antibody produced by the reconstituted mice, in both the primary and secondary responses, was shown to be of donor cell origin in transfers between allotype congenic pairs. Thus, naive, immature lymphoid cells, although not capable of giving rise to high-affinity antibody-secreting cells in a primary response, are capable of giving rise to high-affinity memory B cells which in turn can give an adult-like, high-affinity secondary response following boosting.     

Prostaglandin E2 production is enhanced in mice genetically selected to produce high affinity antibody responses

Spleen cells from mice selectively bred to produce high affinity antibody responses to protein antigens (HI) had reduced responses to both T and B cell mitogens when compared to those from mice selectively bred to produce low affinity (LO) responses. The reduced response by spleen cells from HI mice was partially reversed by the addition of indomethacin in vitro. Spleen adherent cells from HI mice had increased production of prostaglandin E2 when compared to those from LO mice. In addition, spleen adherent cells from mice which fail to show affinity maturation not only produced lower amounts of PGE2 than those from HI mice but also a decreased proportion of spleen cells adhered to plastic in these mice. To test the possibility that the increased PGE2 production in HI mice was responsible for the production of high affinity antibodies, indomethacin was administered in vivo and resulted in a significant reduction in antibody affinity. The possibility that PGE2 production may control the balance between the TH1 and TH2 cells of Mosmann and Coffman is discussed.     

IL-4 requirements for the generation of secondary in vivo IgE responses.

IL-4 has been shown to induce B lymphocytes to switch from the expression of membrane IgM to the expression of membrane IgE and to be required for the generation of primary polyclonal and secondary Ag-specific IgE responses in mice. To further define the role of IL-4 in the generation of memory IgE responses, we investigated the ability of a combination of anti-IL-4 and anti-IL-4R mAb to block the generation of secondary IgE responses induced by: 1) a second infection with the nematode parasites Nippostrongylus brasiliensis or Heligmosomoides polygyrus; or 2) injection of anti-IgD antibody-primed mice with anti-IgE antibody. The latter stimulus was designed to induce intrinsic membrane IgE-expressing B cells to differentiate into IgE-secreting cells. Although the IgE responses induced by a second nematode infection were completely inhibited by the combination of anti-IL-4 and anti-IL-4R mAb, anti-IgE antibody-induced IgE responses in anti-IgD primed mice were not inhibited by these antibodies to a large degree. Additional experiments demonstrated that the anti-IgE antibody-induced memory IgE response was dependent on CD4+ T cells but did not involve the low affinity B cell Fc epsilon RII. Taken together, these observations provide evidence that IL-4 is required for virgin B lymphocytes to develop into IgE-expressing cells, but is not required for B cells that express intrinsic membrane IgE to differentiate into IgE-secreting cells in a T-dependent response. Furthermore, these data suggest that secondary IgE responses in the parasite models that we have studied develop from B cells that had not previously switched to the expression of IgE.     

Streptococcal serotype carbohydrate represents a novel class of type 2 antigen which is T-independent

Our studies reported here, fully characterize two unique type 2 antigens trinitrophenol (TNP)-M1 serotype carbohydrates (TNP-M1 g and TNP-M1 c) derived from streptococci, which fail to induce antibody responses in xid or neonatal mouse splenic cultures. These antigens generate brisk responses in normal spleen and Peyer's patch cell cultures of xid mice, all of which suggest that responses are elicited in the Lyb-3+, 5+ B subpopulation. The antibody responses to TNP-M1 g (and TNP-M1 c) are not dependent upon T cells. Furthermore, TNP-M1 carbohydrates induce anti-TNP plaque-forming (PFC) responses in cultures of small, resting splenic B cell populations without an added T cell requirement. Thus two categories of type 2 antigens are distinguished, one which requires T cells or derived factors, e.g., TNP-Ficoll, and a second TNP-carbohydrate antigen TNP-M1 that does not. Studies of the mitogenic and polyclonal B cell activation properties of M1 carbohydrates indicated that B cell proliferation is induced in both xid (Lyb-3-, 5-) and normal (Lyb-3-, 5- and Lyb-3+, 5+) splenic B cell subpopulations, but that differentiation to IgM synthesis fails to occur in the Lyb-3-, 5- B cell subpopulation. Thus M1 carbohydrates are unique probes that allow the selective induction of proliferation and differentiation of mature B cells that are presumably Lyb-3+, 5+. Because the M1 serotype carbohydrates induce polyclonal IgM synthesis and antigen-specific responses in only the mature B cell population in the absence of T cells, whereas TNP-Ficoll and other type 2 antigens require T cells or their derived factors, the Lyb-3+, 5+ B cell subpopulation may consist of a T cell-dependent and a T cell-independent compartment for responses to different carbohydrate type 2 antigens.     

Feedback by early and late primary antisera on the primary and secondary adoptive immune responses of mice to burro erythrocytes

Experiments on antibody feedback inhibition of the immune response have confirmed that control is more effective against a primary response than against a secondary response. The cells producing antibodies in primary and secondary responses are different both in terms of number of IgFC and amount of antibody produced by individual IgFC (plaque size). Late primary anti-burro RBC sera (greater than 200 days), despite low titers, are, on a volume for volume basis, feedback inhibitors at least as good as early (8-12 days) primary antisera on primary responses but are more effective in suppressing secondary responses (B memory cells). Late primary antisera, due to the process of affinity maturation, have a high affinity for antigen. The suppressive effect of early and late antisera is equally removable by absorption with burro erythrocytes: a result which it is thought, decreases the likelihood of feedback by anti-idiotype being involved in the observed suppression. It is suggested that feedback antibody acts (a) in competition with receptors, inter alia removing antigen into immunologically irrelevant pathways, (b) by a process involving the linking of antigen to Fc receptors, and (c) as a blocking antibody coating B cells (Bm) or APC which are already binding epitopes, thus preventing their cooperation with specific helper or other accessory cells.     

HIV-1 gp120 vaccine induces affinity maturation in both new and persistent antibody clonal lineages

Most antibodies that broadly neutralize HIV-1 are highly somatically mutated in antibody clonal lineages that persist over time. Here, we describe the analysis of human antibodies induced during an HIV-1 vaccine trial (GSK PRO HIV-002) that used the clade B envelope (Env) gp120 of clone W6.1D (gp120_W6.1D). Using dual-color antigen-specific sorting, we isolated Env-specific human monoclonal antibodies (MAbs) and studied the clonal persistence of antibodies in the setting of HIV-1 Env vaccination. We found evidence of V_H somatic mutation induced by the vaccine but only to a modest level (3.8% ± 0.5%; range 0 to 8.2%). Analysis of 34 HIV-1-reactive MAbs recovered over four immunizations revealed evidence of both sequential recruitment of naïve B cells and restimulation of previously recruited memory B cells. These recombinant antibodies recapitulated the anti-HIV-1 activity of participant serum including pseudovirus neutralization and antibody-dependent cell-mediated cytotoxicity (ADCC). One antibody (3491) demonstrated a change in specificity following somatic mutation with binding of the inferred unmutated ancestor to a linear C2 peptide while the mutated antibody reacted only with a conformational epitope in gp120 Env. Thus, gp120_W6.1D was strongly immunogenic but over four immunizations induced levels of affinity maturation below that of broadly neutralizing MAbs. Improved vaccination strategies will be needed to drive persistent stimulation of antibody clonal lineages to induce affinity maturation that results in highly mutated HIV-1 Env-reactive antibodies.     

GPR174-CCL21调控体液免疫应答的两性差异

体液免疫应答具有明显的两性差异。通常女性产生的针对外来病原体或者自身抗原的抗体水平相比男性更高,因此女性比男性更容易清除病原体的感染,但女性也比男性更容易患自身免疫疾病。长效且高亲和力的体液免疫应答依赖由B细胞形成的生发中心(germinal center, GC)反应,然而B细胞形成GC的能力是否存在两性差异从而直接导致体液免疫应答的两性差异尚不清楚。该研究提出了一套在分子和细胞水平上解释体液免疫应答两性差异的新机制,即雄激素可以增强B细胞表达的GPR174在接收到CCL21信号后与Gαi蛋白的结合水平,由此促进雄性B细胞更多地迁移在滤泡外周,而不能更多地迁移至滤泡中心形成GC及抗体应答,从而直接介导体液免疫应答的两性差异。该研究为解决在增强保护性疫苗抗体应答水平以及治疗自身免疫疾病时遇到的B细胞介导的两性差异问题提供了新的见解。     

The affinity threshold for antigenic triggering differs for tolerance susceptible immature precursors vs mature primary B cells

The specificity of antibody responses is dependent on the extent to which a given antigen selectively stimulates cells from within a diverse B cell repertoire. Previous studies have shown that the triggering of B cells by T cell-dependent antigens is a highly discriminatory process, and that tolerance induction of immature B cells by antigen is equally discriminatory. This symmetry in the requirements for stimulation and tolerance induction could provide a basis for the capacity of antibody responses to discriminate among foreign antigens and yet minimize self recognition. The extent to which this potential for discriminate recognition is applicable to the mature immune system remains controversial, because B cells reactive to self antigens have been identified and, in addition, several investigators have identified heteroclitic immune responses, such as the response to NP of Ighb mice, wherein antibodies are found with higher affinities for analogues of the immunogen than for the immunogen itself. To further investigate the capacity of B cells to discriminate among closely related antigenic determinants, we analyzed the fine specificity and idiotypic distribution of monoclonal antibodies derived from both splenic B cells and immature sIg- bone marrow B cell precursors stimulated in fragment culture with NP-Hy and its structural analogues NIP-Hy and NNP-Hy. The results indicate that the majority of responsive B cells discriminate among these haptenic determinants; however, lambda-bearing B cells responsive to the NP and NIP determinants represent a highly overlapping set of clonotypes. Comparison of the responses to NP-Hy and NIP-Hy of splenic vs sIg- precursors of this clonotype family suggests that the T cell-dependent stimulation of both mature and immature B cells by antigen is highly affinity dependent. Significantly, the affinity thresholds for both stimulation and tolerance induction of immature B cells appears to be higher than that required for the stimulation of mature splenic B cells. Such a disparity in the requisites for triggering mature vs immature B cells could readily account for the presence of low-affinity self-reactive B cells in the mature B cell pools of normal individuals.     

疟原虫抗原B表位NKND在鼠伤寒沙门氏菌鞭毛蛋白中的表达

疟原虫抗原B表位NKND是由本课题组首先报道的一个新的疟疾抗原表位．它是存在于多种不同疟原虫分离株中的保守序列．以减毒沙门氏菌为载体制备口服活疫苗,方法简单,使用方便,其鞭毛蛋白有较强的免疫原性,有利于激发人体的细胞和体液免疫．人工合成8肽的实验中[2]发现NKNDD可增强NKND对相应抗体的亲和力．将人工合成的NKNDD寡核苷酸片段插入鼠伤寒沙门氏菌鞭毛蛋白表达体系中,经Western杂交鉴定,表达出具有多拷贝NKNDD表位的重组鞭毛蛋白．     

Immunocompetence of chimeric rabbits. III. Serial passage and persistence of B-lymphocyte memory

In a model consisting of noninbred rabbits matched for major histocompatibility antigens and mismatched for immunoglobulin allotypes, using cell donors and recipients unrelated to each other, B-cell memory has been demonstrated to persist through three successive transfers for a period approaching 2 years. Memory cells from the original donor are shown to dominate specific antibody responses of the primary and secondary recipients. Vigorous antibody responses by donor-derived cells are obtained even when antigenic stimulation is delayed by several months. The data suggest that B memory cells may be particularly efficient in the colonization of recipients, and the potential significance of these findings for adoptive immunization of human bone marrow recipients is discussed.     

In vitro parasite antigen-induced antibody responses in human helminth infections

Helminth parasites characteristically induce vigorous antibody responses in human infections, but the immunoregulatory mechanisms determining the level of these responses are not at all understood. To investigate these mechanisms, peripheral blood mononuclear cells were obtained from 10 patients with parasitic helminth infections (three with schistosomiasis, three with onchocerciasis, and four with loiasis), along with six normal controls. These cells were then cultured in vitro and the capacity of the cells to respond to a specific parasite antigenic stimulus was examined by measuring the amount of parasite-specific antibody produced. Parasite antigen alone, without exogenous mitogen, induced an IgG anti-parasite antibody response in vitro. Optimal responses were obtained at extremely low antigen concentrations--concentrations at which little if any polyclonal immunoglobulin production occurred. Additionally, the in vitro induction of parasite-specific antibody was antigen dose-dependent, requiring much lower antigen concentrations than those necessary to induce lymphocyte blastogenesis. Antibody production was shown to require the cooperative interaction of B and T cells. These studies demonstrate that in vitro responses to antigens from naturally acquired parasitic infections, like those in individuals postimmunization, can be utilized to dissect the cellular and humoral factors that regulate antibody production to naturally acquired human pathogens.     

Induction of Plasmodium falciparum-specific CD4+ T cells and memory B cells in Gabonese children vaccinated with RTS,S/AS01(E) and RTS,S/AS02(D)

The recombinant circumsporozoite protein (CS) based vaccine, RTS,S, confers protection against Plasmodium falciparum infection in controlled challenge trials and in field studies. The RTS,S recombinant antigen has been formulated with two adjuvant systems, AS01 and AS02, which have both been shown to induce strong specific antibody responses and CD4 T cell responses in adults. As infants and young children are particularly susceptible to malaria infection and constitute the main target population for a malaria vaccine, we have evaluated the induction of adaptive immune responses in young children living in malaria endemic regions following vaccination with RTS,S/AS01(E) and RTS,S/AS02(D). Our data show that a CS-specific memory B cell response is induced one month after the second and third vaccine dose and that CS-specific antibodies and memory B cells persist up to 12 months after the last vaccine injection. Both formulations also induced low but significant amounts of CS-specific IL-2(+) CD4(+) T cells one month after the second and third vaccine dose, upon short-term in vitro stimulation of whole blood cells with peptides covering the entire CS derived sequence in RTS,S. These results provide evidence that both RTS,S/AS01(E) and RTS,S/AS02(D) induced adaptive immune responses including antibodies, circulating memory B cells and CD4(+) T cells directed against P. falciparum CS protein. TRIAL REGISTRATION: ClinicalTrials.gov NCT00307021.