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M Plebanski

Publications and source records attributed to M Plebanski.

34 records · Page 2Linked to original sources
PubMed1998

Protection from Plasmodium berghei infection by priming and boosting T cells to a single class I-restricted epitope with recombinant carriers suitable for human use.

The desirability of inducing cytotoxic T cell responses to defined epitopes in humans has led to the development of a variety of recombinant delivery systems. Recombinant protein particles derived from a yeast retrotransposon (Ty) and the modified Ankara vaccinia (MVA) virus can deliver large epitope strings or even whole proteins. Both have previously been administered safely in humans. Immunization with recombinant Ty and MVA containing a single Plasmodium berghei class I-binding epitope provided 95% sterile protection against malaria in mice. The sequence of immunization, Ty followed by MVA, was critical to elicit high levels of IFN-gamma-producing cells and protection. The reciprocal sequence (MVA/TY) or homologous boosting was not protective. Both constructs (Ty and MVA) contain the H-2Kd-restricted pb9 CTL epitope from the circumsporozoite protein of P. berghei among a string of 8-15 human P. falciparum-derived CTL epitopes restricted through 7 common HLA alleles as well as widely recognized CD4 T cell epitopes. Thus, the novel recombinant Ty/MVA prime/boost combination with these constructs provides a safe alternative for evaluation for human vaccination against P. falciparum malaria.

Animals↗
PubMed1997

Genetic analysis of host-parasite coevolution in human malaria.

Recent twin studies of clinical malaria and immune responses to malaria antigens have underscored the importance of both major histocompatability complex (MHC) and non-MHC genes in determining variable susceptibility and immune responsiveness. By using a combination of whole genome genetic linkage studies of families and candidate genes analysis, non-MHC genes are being mapped and identified. Human leucocyte antigen (HLA) genotype was found to affect susceptibility to severe malaria in a large study of West African children. T lymphocytes that may mediate such resistance have been identified and their target antigens and epitopes characterized. Some of these epitopes show substantial polymorphism, which appears to result from immune selection pressure. Natural variant epitopes have been found to escape T-cell recognition in cytolytic and other T-cell assays. More recently a novel immune escape mechanism has been described in viral infections, altered peptide ligand antagonism, whereby variants of a T-cell epitope can downregulate or ablate a T cell response to the index peptide. The likely implications of such immune escape mechanisms for the population structure of malaria parasites, for HLA associations with malaria infection and disease, and for the design of new malaria vaccines, are discussed. The evolutionary consequences of such molecular interactions can be assessed by using mathematical models that capture the dynamic of variable host and parasite molecules. Combined genetic, immunological and mathematical analysis of host and parasite variants in natural populations can identify some mechanisms driving host-parasite coevolution.

Amino Acid Sequence↗
PubMed1997

Precursor frequency analysis of cytotoxic T lymphocytes to pre-erythrocytic antigens of Plasmodium falciparum in West Africa.

Some individuals living in malaria-endemic areas have CTL to Plasmodium falciparum liver stage Ags. We have quantified these CTL responses using limiting dilution analysis studies on the peripheral blood cells of naturally exposed Gambian donors. CTL precursor frequencies were determined to a wide range of epitopes derived from different liver stage Ags (liver stage protein 1, circumsporozoite protein, thrombospondin-related anonymous protein, and sporozoite threonine/asparagine-rich protein) restricted through common HLA alleles present in this population (HLA-A2.1, -A2.2, -B7, -B8, -B35, and B53). Precursor frequencies were between 17 and 98/million PBMC and correlated with the levels of specific lysis in parallel bulk cultures. The quantitative nature of limiting dilution assay analysis revealed varying degrees of immunodominance in the CTL responses to different epitopes within single proteins (thrombospondin related anonymous protein: tr42, tr43, tr26, tr29, and tr39; circumsporozoite protein: cp6, cp26, and cp29) and within individual donors. The temporal stability of some of these CTL responses was determined over a 4-yr period. This is the first quantitative study of CTL specific for any plasmodial species or nonviral pathogen in humans and provides a basis for a multiepitope approach to malaria vaccination.

Adult↗
PubMed1997

Immune evasion in malaria: altered peptide ligands of the circumsporozoite protein.

T cells are central to immunity in malaria. CD4+ helper T cells favour the generation of high-affinity antibodies that are effective against blood stages and they are necessary to establish immunological memory. The intrahepatic stage of infection can be eliminated by specific CD8+ cytotoxic T cells (CTL). Cytokines secreted by CD4+ T cells may also contribute to liver stage immunity. Evolution has selected varied mechanisms in pathogens to avoid recognition by T cells. T cells recognize foreign epitopes as complexes with host major histocompatibility (MHC) molecules. Thus, a simple form of evasion is to mutate amino acid residues which allow binding to an MHC allele. Recently, more sophisticated forms of polymorphic evasion have been described. In altered peptide ligand (APL) antagonism, the concurrent presentation of particular closely related epitope variants can prevent memory T cell effector functions such as cytotoxicity, lymphokine production and proliferation. In immune interference, the effect of the concurrent presentation of such related epitope variants can go a step further and prevent the induction of memory T cells from naive precursors. The analysis of immune responses to a protein of P. falciparum, the circumsporozoite protein (CSP), indicates that the malaria parasite may utilize these evasion strategies.

Animals↗
PubMed1997

A protein particle vaccine containing multiple malaria epitopes.

Ty virus-like particles consist of a single protein species that can be produced in yeast. Recombinant Ty-VLPs carrying a string of up to 15 defined cytotoxic T lymphocyte (CTL) epitopes from Plasmodium species prime protective CTL responses in mice following a single administration without adjuvant. Effective processing of epitopes from the string was demonstrated in vitro and in vivo and was not affected by flanking sequences.

Amino Acid Sequence↗
PubMed1996

Comparison of numerous delivery systems for the induction of cytotoxic T lymphocytes by immunization.

A variety of vaccine delivery systems including peptides with various adjuvants, recombinant particles, live recombinant viruses and bacteria and plasmid DNA were tested for their ability to induce CD8+ cytotoxic T lymphocytes (CTL) against a well-defined epitope (amino acids 252-260) from the circumsporozoite (CS) protein of Plasmodium berghei. We compared routes of immunization that would be applicable for the administration of a malaria vaccine in humans. The majority of these vaccines did not induce high CTL responses in the spleens of immunized mice. However, both a yeast-derived Ty virus-like particle expressing the optimal nine-amino acid epitope SYIPSAEKI from the CS protein (CSP-VLP) and a lipid-tailed peptide of this same sequence induced high levels of the major histocompatibility complex (MHC) class I-restricted CTL with one and three subcutaneous immunizations, respectively. Moreover, these CTL were able to recognize naturally processed antigen expressed by a recombinant vaccinia virus. The levels of CTL induced by CSP-VLP could be augmented by co-immunization with certain cytokines. Target cells pulsed with CSP-VLP were recognized and lysed, showing that the particles were effectively processed and presented through MHC class I presentation pathway. The levels of CTL induced using CSP-VLP and lipopeptides are comparable to those observed after immunization with multiple doses of irradiated sporozoites.

Amino Acid Sequence↗
PubMed1995

Identification and characterization of three members of the human SR family of pre-mRNA splicing factors.

SR proteins have a characteristic C-terminal Ser/Arg-rich repeat (RS domain) of variable length and constitute a family of highly conserved nuclear phosphoproteins that can function as both essential and alternative pre-mRNA splicing factors. We have cloned a cDNA encoding a novel human SR protein designated SRp30c, which has an unusually short RS domain. We also cloned cDNAs encoding the human homologues of Drosophila SRp55/B52 and rat SRp40/HRS. Recombinant proteins expressed from these cDNAs are active in constitutive splicing, as shown by their ability to complement a HeLa cell S100 extract deficient in SR proteins. Additional cDNA clones reflect extensive alternative splicing of SRp40 and SRp55 pre-mRNAs. The predicted protein isoforms lack the C-terminal RS domain and might be involved in feedback regulatory loops. The ability of human SRp30c, SRp40 and SRp55 to modulate alternative splicing in vivo was compared with that of other SR proteins using a transient contransfection assay. The overexpression of individual SR proteins in HeLa cells affected the choice of alternative 5' splice sites of adenovirus E1A and/or human beta-thalassemia reporters. The resulting splicing patterns were characteristic for each SR protein. Consistent with the postulated importance of SR proteins in alternative splicing in vivo, we demonstrate complex changes in the levels of mRNAs encoding the above SR proteins upon T cell activation, concomitant with changes in the expression of alternatively spliced isoforms of CD44 and CD45.

Alternative Splicing↗
PubMed1995

Identification of conserved antigenic components for a cytotoxic T lymphocyte-inducing vaccine against malaria.

Several cellular and humoral mechanisms probably play a role in natural immunity to Plasmodium falciparum malaria, but the development of an effective vaccine has been impeded by uncertainty as to which antigens are targeted by protective immune responses. Experimental models of malaria have shown that cytotoxic T lymphocytes (CTL) which kill parasite-infected hepatocytes can provide complete protective immunity against certain species of Plasmodium in mice, and studies in The Gambia have provided indirect evidence that CTL play a protective role against P falciparum in humans. By using an HLA-based approach, termed reverse immunogenetics, we have previously identified peptide epitopes for CTL in liver-stage antigen-1 and the circumsporozoite protein of P falciparum. We have extended this work to identify CTL epitopes for HLA class I antigens that are found in most individuals from Caucasian and African populations. Most of these epitopes are in conserved regions of P falciparum. CTL peptide epitopes were found in a further two antigens, thrombospondin-related anonymous protein and sporozoite threonine and asparagine rich protein, indicating that a subunit vaccine designed to induce a protective CTL response may need to include parts of several parasite antigens. However, CTL levels in both children with malaria and in semi-immune adults from an endemic area were low suggesting that boosting these low levels by immunisation might provide substantial or even complete protection against infection and disease.

Adult↗
PubMed1995

Induction of peptide-specific primary cytotoxic T lymphocyte responses from human peripheral blood.

Various protocols were developed and compared for eliciting specific cytotoxic T lymphocyte (CTL) cell lines from the unselected human peripheral blood mononuclear cells of naive donors. Interleukin-7 and CD4+ T cells primed in vitro by keyhole limpet hemocyanin were shown to act together in the generation of these responses. Primary responses were consistently induced with a variety of different HLA class I-binding malarial peptides. Primary CTL responses could be induced from unselected CD8+ and from CD45RA+CD8+ T cells. The CTL lines derived from these naive donors were CD8+ and demonstrated a high level of HLA class I-restricted killing for > 3 months after priming in vitro. They were also able to recognize and kill targets infected with a recombinant vaccinia virus containing the full-length antigen. In addition, this same protocol enhanced up to fourfold the levels of secondary CTL responses induced. The optimal method presented for naive cytotoxic T cell stimulation is simple, rapid and generally applicable and should provide a useful tool for both basic research and human therapy.

CD8-Positive T-Lymphocytes↗
PubMed1994

Human leukocyte antigens and natural selection by malaria.

The extraordinary polymorphism of human leukocyte antigens (HLA) poses a question as to how this remarkable diversity arose and is maintained. The explanation that infectious pathogens are largely responsible is theoretically attractive but clear and consistent associations between HLA alleles and major infectious diseases have rarely been identified. Large case-control studies of HLA types in African children with severe malaria indicate that HLA associations with this parasitic infection do exist and it is becoming possible to investigate the underlying mechanisms by identification of peptide epitopes in parasite antigens. Such analysis reveals how the magnitude and detectability of HLA associations may be influenced by numerous genetic and environmental factors. These complex interactions will give rise to variation over time and space in the selective pressures exerted by infectious diseases and this fluctuation may, in itself, contribute to the maintenance of HLA polymorphism.

Biological Evolution↗
PubMed1994

In vitro primary responses of human T cells to soluble protein antigens.

The optimum culture conditions to support in vitro proliferative responses to conventional soluble protein antigens by human CD4+ T cells from healthy non-immunised donors have been determined. These responses were blocked by anti-HLA-DR monoclonal antibodies (mAbs) and were strictly dependent on the presence of antigen-presenting cells (APCs). Primary responses showed a reproducible pattern of proliferation kinetics which distinguished them from secondary in vitro T cells reactions. T cells specific for the sensitising antigen were recovered from primary cultures.

Adjuvants, Immunologic↗
PubMed1992

Dependency on interleukin-1 of primary human in vitro T cell responses to soluble antigens.

The role of interleukin (IL)-1 in antigen-specific activation of naive human T cells has been examined. Primary human T cell proliferative responses to the soluble antigen keyhole limpet hemocyanin (KLH) were decreased by neutralizing antisera to IL-1 alpha (25 +/- 7% standard error) and IL-1 beta (56 +/- 6% standard error). Inhibition by both antisera in a primary culture was usually additive. Recombinant IL-1 alpha and recombinant IL-1 beta could both re-establish responses in cultures blocked by neutralizing anti-IL-1 beta. Interestingly, the susceptibility of KLH-stimulated T cell responses to inhibition by neutralizing anti-IL-1 sera decreased with time in culture. This observation suggested that T cell responses may become less IL-1 dependent as T cells become activated or primed. In support of this notion, secondary T cell responses to purified protein derivative from Mycobacterium tuberculosis (PPD) were markedly less affected by the addition of comparable amounts of the neutralizing anti-IL-1 sera. These results demonstrate that IL-1 is one of the main co-stimulators for primary T cell activation and suggest a different requirement for IL-1 in the activation of naive compared to memory human T cells.

Cells, Cultured↗
PubMed1992

Primary and secondary human in vitro T-cell responses to soluble antigens are mediated by subsets bearing different CD45 isoforms.

A culture system has been developed which consistently supports in vitro proliferative responses to conventional soluble antigens by human CD4+ T cells from non-immunized donors. T cells exposed to an antigen in primary cultures could be restimulated in vitro in an antigen-specific manner to give secondary responses with greater magnitudes and a more rapid onset than the initial reaction. To characterize further the responding T-cell population in primary compared with secondary reactions, T cells were depleted of CD45RA+ or CD45RO+ cells and stimulated with recall and non-recall antigens. It was found that the soluble non-recall antigen keyhole limpet haemocyanin did not stimulate CD45RO+ T cells, yet induced strong proliferative responses from CD45RA+ T cells. Conversely, it was confirmed that human CD45RO+ T cells respond to the recall antigen-purified protein derivative from Mycobacterium tuberculosis. Cell mixing experiments indicated that CD45RO+ T cells are unlikely to have any suppressive effect on the reactivity of CD45RA+ cells to non-recall antigens. These data provide new support for the hypothesis that CD45RA+ represents the naive and CD45RO+ the memory phenotype of human CD4+ T cells.

Antigens↗
PubMedDate not supplied

Identification of frequently recognized dimorphic T-cell epitopes in plasmodium falciparum merozoite surface protein-1 in West and East Africans: lack of correlation of immune recognition and allelic prevalence.

The merozoite surface protein-1 (MSP1) is the most studied malaria blood-stage vaccine candidate. Lymphokines such as interferon gamma (IFN-gamma) and interleukin 4 (IL-4) may mediate blood-stage specific protection. Here we identify Plasmodiumfalciparum MSP1 T-cell epitopes capable of rapid induction of IFN-gamma and/or IL-4 from peripheral blood mononuclear cells of East and West African donors. Both allelic forms of these novel MSP1 T-cell epitopes were stimulatory. An unusually high numbers of Gambian responders (> 80%) to these epitopes were observed, suggesting that MSPI reactivity may have been underestimated previously in this population. Surprisingly, IFN-gamma responses to allelic T-cell epitopes failed to correlate with differential antigenic exposure in The Gambia compared to Kenya. These results suggest an unexpected level of immunoregulation of IFN-gamma response with variable allelic T-cell reactivity independent of the level of antigenic exposure. Further analysis of the mechanisms determining this response pattern may be required if vaccines are to overcome this allelic reactivity bias in malaria-exposed populations.

Adolescent↗
PubMedDate not supplied

Malaria parasite interactions with the human host.

The interaction between the malaria parasite and the human host involves a number of interactions that result in the parasite evading the human immune system. Since the stages of the malaria lifecycle are complex, this allows the use of various immune evasion strategies by the malaria parasite and has major implications in the development of a vaccine for malaria endemic areas. The present review highlights key host:parasite interactions. Plasmodia puts selection pressure on human gene frequencies, and studies into host genetic factors such as the Duffy blood group and sickle cell anaemia offer insight into the host- parasite relationship. In addition, parasite interactions with the different effector arms of the immune system can result in altered peptide ligand (APL) antagonism which alters the immune response from a pro- to an anti-inflammatory T cell response. Recent insights into the interaction between professional antigen presenting cells, dendritic cells (DCs), and malaria parasites is discussed in detail.

Animals↗