Biomedical subjects

Lorena E Brown

Publications and source records attributed to Lorena E Brown.

14 recordsLinked to original sources

PubMed2006

Pandemic vaccines: promises and pitfalls.

Prototype vaccines against influenza A/H5N1 may be poorly immunogenic, and two or more doses may be required to induce levels of neutralising antibody that are deemed to be protective. The actual levels of antibody required to protect against a highly pathogenic virus that potentially can spread beyond the large airways is unknown. The global capacity for vaccine manufacture in eggs or tissue culture is considerable, but the number of doses that can theoretically be produced in a pandemic context will only be sufficient for a small fraction of the world's population, even less if a high antigen content is required. The safety of new pandemic vaccines should be addressed in an internationally coordinated way. Steps are underway through the Therapeutic Goods Administration to evaluate mock-up vaccines now, so that the time to registration of a new product can be minimised. It will be 3-6 months into the pandemic before an effective vaccine becomes available, so other control measures will be important in the early stages of a pandemic. The primary goal of a pandemic influenza vaccine must be to prevent death, and not necessarily to prevent infection.

Australia↗

PubMed2006

Lipid-containing mimetics of natural triggers of innate immunity as CTL-inducing influenza vaccines.

Anti-viral CD8(+) T cell responses can be induced using synthetic lipopeptides and a range of different lipid moieties have been examined in a variety of model systems and in man for this purpose. Nevertheless, only limited data exist on comparative efficacy of different lipopeptides in a single model of protection so that the optimal composition for vaccination purposes remains unknown. In this study, we examined different lipid structures from bacterial or non-bacterial sources coupled to peptides representing influenza viral epitopes recognized by CD8(+) and CD4(+) T cells. These were assessed in the context of intra-nasal (i.n.) immunization in the absence of added adjuvant. The strongest immunogens were those containing bacterially derived lipids that induced dendritic cell (DC) maturation via Toll-like receptor 2 (TLR2) binding. The number of DCs induced to mature in vitro was directly associated with the strength of the CD8(+) T cell-mediated viral clearing responses in primed mice. Mice immunized with the TLR2-binding lipopeptides showed greatly enhanced numbers of specific IFN-gamma-secreting CD8(+) T cells at the site of infection after i.n. exposure to virus, which resulted in enhanced protection of the pneumonic lung. Importantly, lipopeptide-pulsed DCs were able to induce the appropriate T cells, indicating that the self-adjuvanting effects could occur in the absence of free lipopeptide interacting with additional TLR2-bearing cells in vivo. This study defines a hierarchy of lipopeptide constructs that can program DC to prime memory CD8(+) T cells that on recall function to clear influenza virus from the infected lung.

Amino Acid Sequence↗

PubMed2006

Intranasal lipopeptide primes lung-resident memory CD8+ T cells for long-term pulmonary protection against influenza.

The longevity of the influenza virus-specific CD8+ T cell response following intranasal delivery of a synthetic lipopeptide was investigated and the characteristics and location of the cells associated with viral clearance examined. The lipopeptide, incorporating an epitope for CD8+ T cells and another for CD4+ T cells with the lipid moiety S-[2,3-bis(palmitoyloxy)propyl]cysteine (Pam2Cys) attached, induced potent and long-lived pulmonary protection. Both the lipopeptide and its largely unprotective non-lipidated counterpart elicited comparable numbers of CD8+ T cells in the spleen, which was the main location of the memory pool. However, the lipopeptide, unlike the non-lipidated peptide, also induced a substantial memory population that remained in the lungs and was rapidly activated upon viral challenge months later. These lipopeptide-induced lung-resident CD8+ T cells were also very similar in number and IFN-gamma-secreting potential to those induced by prior exposure to the virus itself and are likely mediators of initial viral clearance prior to recruitment from the expanding lymph node T cell pool. Significant clearing responses were demonstrated as late as 9 months post-lipopeptide vaccination. This study shows that CD8+ T cells primed by the lipopeptide are not only long-lived but can take up residence in the lung where they are important early mediators of pulmonary protection.

Administration, Intranasal↗

PubMed2005

Targeting CD45RB alters T cell migration and delays viral clearance.

CD45 is a receptor tyrosine phosphatase essential for TCR signaling. One isoform, CD45RB, is down-regulated in memory cells and targeting CD45RB with a specific antibody has been shown to inhibit graft rejection. Its role in immunity to infection, however, has not been tested. Here, we report the effect of anti-CD45RB antibody treatment on the induction of anti-influenza CD8+ T cells and viral clearance. Anti-CD45RB-treated mice had delayed pulmonary viral clearance compared with untreated mice whose infection was completely cleared by day 8 post-infection. In anti-CD45RB-treated mice, the total CD4+ and CD8+ T cell numbers in both the lungs and mediastinal nodes were substantially reduced at days 5 and 8; this effect was less marked for the spleen. CD8+ T cells specific for influenza virus were also reduced compared with the control group in all three organs at day 8. By day 11, when both treated and control groups showed no virus remaining in the lungs, specific CD8+ T cell numbers were at similar low levels. Homing to lymph nodes and lung of dye-labeled T cells was greatly inhibited (by >80%) by anti-CD45RB treatment. This reduced homing corresponded with reduced CD62L and beta1-integrin expression in both uninfected and infected mice. Since CD62L plays a critical role in homing lymphocytes to lymph nodes, and high levels of CD62L and alpha4beta1-integrin are expressed by lymphocytes that home to bronchus-associated lymphoid tissue, we suggest that reduced expression of these molecules is a key explanation for the delay in immune responses.

Animals↗

PubMed2005

ISCOM-based vaccines: the second decade.

The immunostimulating complex or 'iscom' was first described 20 years ago as an antigen delivery system with powerful immunostimulating activity. Iscoms are cage-like structures, typically 40 nm in diameter, that are comprised of antigen, cholesterol, phospholipid and saponin. ISCOM-based vaccines have been shown to promote both antibody and cellular immune responses in a variety of experimental animal models. This review focuses on the evaluation of ISCOM-based vaccines in animals over the past 10 years, as well as examining the progress that has been achieved in the development of human vaccines based on ISCOM adjuvant technology.

Animals↗

PubMed2005

Lipid-based self-adjuvanting vaccines.

Lipopeptides incorporating epitopes for CD4+ T cells and either CD8+ T cells or B cells have proven to be immunogenic in animal models and in humans and are well tolerated in these species. This form of vaccine candidate has great benefits over competing technology in terms of providing a totally synthetic and pure product that is effective when administered in the absence of any adjuvant, and is immunogenic when delivered by a variety of routes, including application to mucosal surfaces. The immune response can be focused on critical epitopes of the pathogen or tumour antigen to provide clearing immunity, and responses can also be invoked that modulate hormone activity. This review will cover examples of lipopeptides of different design and their efficacy in different systems as well as challenges for the future. Our recent understanding of how the lipid component confers the "self-adjuvanting" property on these immunogens by targeting the cell at the heart of immune response induction, the dendritic cell, will also be discussed.

Adjuvants, Immunologic↗

PubMed2004

A totally synthetic vaccine of generic structure that targets Toll-like receptor 2 on dendritic cells and promotes antibody or cytotoxic T cell responses.

A simple generic peptide-based vaccine structure that targets Toll-like receptor 2-expressing dendritic cells and causes their activation is described. The vaccines are totally synthetic, serve as their own adjuvant, and are composed of (i) a single helper T cell epitope, (ii) a target epitope that is either recognized by CD8+ T cells or B cells, and (iii) a Toll-like receptor 2-targeting lipid moiety, S-[2,3-bis(palmitoyloxy)propyl]cysteine, that is situated between the peptide epitopes to form a branched configuration. The different CD8+ T cell epitopes examined were from (i) influenza virus, (ii) the intracellular bacterium Listeria monocytogenes, and (iii) ovalbumin as a model tumor antigen. Vaccines containing a B cell epitope from gastrin or luteinizing hormone-releasing hormone as a B cell epitope were also examined for their ability to elicit antibody against the parent hormones. Each of the vaccines was capable of inducing either CD8+ T cell or antibody-mediated immune responses. The lipidated vaccines, but not the nonlipidated vaccines, were able to mediate protection against viral or bacterial infection and mediate prophylactic and therapeutic anticancer activity. The two hormone-based vaccines induced high antibody titers, which in the case of luteinizing hormone-releasing hormone resulted in abrogation of reproductive function. These results highlight the utility of simple, totally synthetic, epitope-based vaccines.

Amino Acid Sequence↗

PubMed2004

Responses against complex antigens in various models of CD4 T-cell deficiency: surprises from an anti-CD4 antibody transgenic mouse.

The most common models of CD4 T-cell deficiency are mice exogenously injected with anti-CD4 antibody (Ab), CD4 knockout (CD4-/-) and major histocompatibility complex (MHC) class II knockout (class II-/-) mice. We recently described the anti-CD4 Ab transgenic mouse (GK) as an improved CD4 cell-deficient model. This review compares this new GK mouse model with the widely available class II-/- and CD4-/- mice, when exposed to complex antigens (foreign grafts and during bacterial or viral infection). We highlight here the cytometric and functional differences (including Ab isotype, viral or bacterial clearance, and graft survival) among these CD4 cell-deficient models. For example, whereas grafts are generally rejected in class II-/- and CD4-/- mice as quickly as in wild-type mice, they survive longer in GK mice. Also, CD4-/- mice produce IgG against both simple model and complex antigens, but class II-/- and GK mice produce small amounts of IgG2a against complex antigens but not simple model antigens. These differences harbinger the caveats in the use of these various mice.

Animals↗

PubMed2003

Single-cell perforin and granzyme expression reveals the anatomical localization of effector CD8+ T cells in influenza virus-infected mice.

Influenza virus infection activates cytolytic T lymphocytes (CTL) that contribute to viral clearance by releasing perforin and granzymes from cytoplasmic granules. Virus-specific, perforin-dependent CD8(+) CTL were detected in freshly isolated cells from the mouse lung parenchyma but not from the mediastinal lymph nodes (MLN), where they are primed, or from the spleen during primary influenza virus infection. To determine whether this difference was due to the low frequency or incomplete maturation of effector CTL in MLN, we measured expression of perforin, granzymes A, B, and C, and IFN-gamma mRNAs in CD8(+) populations and single cells immediately after isolation from virus-infected mice. Quantitative PCR revealed significant expression of perforin, granzyme A, granzyme B, and IFN-gamma in activated CD8(+) cells from MLN, spleen, and lung parenchyma. Granzyme C expression was not detected. Individual activated or nucleoprotein peptide/class I tetramer-binding CD8(+) cells from the three tissues expressed diverse combinations of perforin, granzyme, and IFN-gamma mRNAs. Although cells from lung expressed granzymes A and B at higher frequency, each of the tissues contained cells that coexpressed perforin with granzymes A and/or B. The main difference between MLN and lung was the elevated frequency of activated CD8(+) T cells in the lung, rather than their perforin/granzyme expression profile. The data suggest that some CTL mature into perforin/granzyme-expressing effector cells in MLN but reach detectable frequencies only when they accumulate in the infected lung.

Animals↗

PubMed2003

Immune responses in hepatitis C virus infection: the role of dendritic cells.

Cellular immune responses are critical for the clearance of hepatitis C virus. Persistent infection results from a narrow and weak cellular immune response, in direct contrast to the broad, strong response associated with viral clearance in acute infection. The presence of dendritic cells in the liver facilitates presentation of viral antigens to both CD4+ and CD8+ T cell populations. Exploiting the potent antigen presentation capability of dendritic cells for immunotherapy of chronic hepatitis C is attractive; however, infection or transfection of segments or the entire hepatitis C virus genome appears to impair the allostimulation capacity of dendritic cells. If dendritic cell immunotherapy for hepatitis C virus infection is to become a reality, the mechanism behind the defective allostimulatory capacity needs to be deciphered.

Dendritic Cells↗

PubMed2003

Maturation of dendritic cells with lipopeptides that represent vaccine candidates for hepatitis C virus.

The ability of antigens to elicit immune responses depends upon their initial recognition, uptake, processing and presentation by dendritic cells. This fact has been recognized by many workers and dendritic cells are now regarded as natural 'adjuvants' in the business of vaccine design. One way of persuading dendritic cells to become interested in foreign material is to decorate it with lipid moieties found in bacteria. This approach has been used in the context of synthetic peptide-based immunogens and depending on the nature of the epitopes included, can provide highly immunogenic structures capable of eliciting antibody or cytotoxic T cell responses. In this paper we describe the results of experiments in which the stimulatory effects of peptide-based vaccine candidates on human dendritic cells are examined. Our findings indicate that lipidated structures comprising vaccine target sequences of viral origin coupled to the synthetic lipid groups of bacteria are able to induce the maturation of dendritic cells, as measured by the expression of cell surface MHC class II molecules.

Cell Differentiation↗

PubMed2002

Highly immunogenic and totally synthetic lipopeptides as self-adjuvanting immunocontraceptive vaccines.

In this study, we describe the synthesis of various lipopeptides based on the sequence of luteinizing hormone-releasing hormone (LHRH) and report on their abilities to induce Abs against this "self" hormone when inoculated into mice in the absence of additional adjuvant. The peptides consisted of a colinear CD4(+) T helper cell epitope from the L chain of influenza virus hemagglutinin and LHRH, which has B cell epitopes but no T cell epitopes present in its sequence. Lipids were attached either at the N terminus or between the T cell epitope and LHRH, in the approximate center of the peptide. The lipopeptide constructs displayed different solubilities and immunological properties that depended not only on the lipid content but also on the position of attachment of the lipids. Some of these constructs were highly immunogenic, inducing high titers of Ab, which were capable of efficiently sterilizing female mice when administered in saline by s.c. or intranasal routes. The most effective vaccines were highly soluble, contained the dipalmitoyl-S-glyceryl cysteine moiety, and had this lipid attached at the center of the molecule. The relative ability of the lipopeptides to induce an Ab response in the absence of external adjuvant was reflected by their ability to up-regulate the surface expression of MHC class II molecules on immature dendritic cells. These results demonstrate that the composition and position within peptide vaccines of self-adjuvanting lipid groups can influence the ability to induce the maturation of dendritic cells and, in turn, the magnitude of the resulting Ab response.

Adjuvants, Immunologic↗

PubMed2002

Identification of antigenically active tryptic fragments of apical membrane antigen-1 (AMA1) of Plasmodium chabaudi malaria: strategies for assembly of immunologically active peptides.

Apical membrane antigen-1 (AMA1) is a prime vaccine candidate for inclusion in a vaccine against malaria. It is known that the disulphide bond stabilised conformation of this antigen is important for eliciting a protective antibody response, however little is known about the epitopes within this molecule that are targeted by the immune response. We have used a peptide approach for the identification and characterisation of such regions. In this study, the in vitro refolded, recombinant ectodomain of AMA1 from the D strain of Plasmodium chabaudi adami, was digested with trypsin and individual peptide fragments examined for antigenic activity. We found that a tryptic fragment, which was derived from a loop-like structure within the putative domain I of the intact AMA1 molecule, was highly reactive with antibodies from the sera of hyperimmune mice. Two different synthetic peptide constructs incorporating this antigenically active fragment were assembled. The first consisted of two separate peptide chains which were linked through a disulphide bond formed using chemo-selective chemistry. A larger 45-mer loop peptide, generated by the oxidation of two cysteine residues close to the N- and C-termini of the 45-mer, represented the complete loop structure and incorporated the tryptic fragment. Each peptide construct was also able to elicit production of high titres of antibodies in mice and furthermore, the 45-residue loop peptide elicited antibodies capable of binding to AMA1 with titres comparable to those present in a mouse which had recovered from multiple exposures to P. chabaudi adami parasites. Passive immunisation with anti-loop antibodies did not suppress the development of parasitaemia in mice challenged with P. chabaudi adami suggesting that although highly immunogenic, the peptides represented inadequate or inappropriate epitopes for vaccination purposes.

Amino Acid Sequence↗

PubMed2002

Induction of long-term memory CD8(+) T cells for recall of viral clearing responses against influenza virus.

Induction of cytotoxic T-cell-mediated virus-clearing responses by influenza virus T cell determinant-containing peptide immunogens was examined. The most potent synthetic immunogens for eliciting pulmonary viral-clearing responses contained peptides representing determinants for CD4 and CD8 T cells (TH and CTL peptides, respectively) together with two or four palmitic acid (Pal) groups. Inoculated in adjuvant, these Pal2- or Pal4-CTL-TH lipopeptides and the nonlipidated CTL peptide induced equivalent levels of cytolytic activity in the primary effector phase of the response. The ability to recall lytic responses, however, diminished much more rapidly in CTL peptide-primed than in lipopeptide-primed mice. By 15 months postpriming, the recalled lytic activity in lipopeptide-inoculated mice remained potent, but the response induced by the CTL peptide was weak. Enumeration of specific gamma interferon-secreting CD8 T cells revealed that a greater number of these T cells had entered or remained in the memory pool in lipopeptide-primed mice, arguing for a quantitative rather than qualitative enhancement of the response on recall. Addition of either the lipid or the TH peptide to the CTL peptide was not sufficient to provide these long-lived antiviral responses, but inclusion of both components augmented the response. CD4 T cells elicited by the lipopeptides did not influence the rate of viral clearance upon challenge and most likely had a role in induction or maintenance of the memory response. It therefore appears that the lipopeptide immunogens, although not significantly superior at inducing primary effector CD8 T cells, elicit a much more effective memory population, the recall of which may account for their superiority in inducing pulmonary protection after viral challenge.

Animals↗