ADJUVANT RESEARCH

Dr Ed Lavelle

Dr Ed Lavelle
Lecturer in Immunology
Phone: +353-1-8962488
Fax: +353-1- 6772400
Email: lavellee@tcd.ie
Location: Room 4.30, Biomedical Sciences Institute

Research Interests

Mechanisms of action of vaccine adjuvants and delivery systems
Vaccines represent the most significant scientific contribution to global public health over the past two hundred years. Adjuvants and delivery systems are essential to enhance immune responses induced by vaccines since in many cases the protective antigens are not strongly immunogenic when administered alone. Adjuvants are substances that when co-administered with vaccines can enhance the vaccine-specific immune response. Most vaccines are administered in the presence of alum, a generic name for aluminium salts. This substance has been used effectively for decades but its more of action is not well understood. In the case of live attenuated vaccines, the “adjuvants” are intrinsic to the microbe, comprising factors such as bacterial LPS, flagellae or unmethylated CpG motifs within the DNA sequence or viral nucleic acids. The explosion in knowledge concerning innate immunity in recent years has facilitated a more mechanistic approach to adjuvant research since it is now clear that a principal mode of adjuvant action is via the induction of innate immune responses.
Dendritic cells are the pivotal cell in the induction of primary T cell responses against pathogens and vaccines. Thus I have a particular interest in the instruction of T cell responses by adjuvant-modulated dendritic cells. This work encompasses fundamental aspects of leukocyte biology but has wide application in the fields of vaccination and immunotherapy. The modes of action of a majority of pathogen-derived and other immunomodulatory molecules that are used both experimentally and clinically are incompletely understood. For example, widely used adjuvants such as alum and chitosan that are regarded as ‘inert’ delivery systems induce polarised Th2 type T cell responses but the mechanisms underlying this induction are unclear. In the light of emerging evidence that Th2 induction does not merely reflect a default pathway but results from specific interaction of ligands on antigen presenting cells (APCs) with CD4 T cells, the responses induced by these systems are likely to result from specific interactions with receptors on APCs and lymphocytes. Chitosan can modulate dendritic cell activation and thus represents an immunomodulator in addition to its role as a delivery system. This is a significant finding that supports the clinical use of chitosan in vaccines particularly as the molecule was been widely tested and found to be safe. Similarly the strong effects of biodegradable microparticles on humoral and cellular immunity is likely to involve specific effects on antigen presenting cells including enhanced antigen presentation.

In addition to studies on inert delivery systems, my research also focuses on bacterial toxins as adjuvants. We have demonstrated that bacterial toxins including cholera toxin and Escherichia.coli heat-labile enterotoxin can induce antigen-specific Tr1 type regulatory T cells in addition to Th2 and/or Th1 cells via the selective modulation of dendritic cell activation. These novel studies indicate that strong Th1 and Th2 polarizing adjuvants also induce a population of regulatory T cells which is likely to be an adaptation to control potent T cell responses. The specific interactions between APC and T cells that lead to Tr1 cell differentiation are not fully elucidated but roles for IL-10, down-regulation of the co-stimulatory molecule CD40 and inhibition of NF-kB activity have been proposed. My work has demonstrated that cAMP-inducing bacterial A-B toxins enhance IL-10 production, inhibit CD40 expression and reduce NF-kB activity and this may partly account for their ability to induce Tr1 cells. However, our recent (unpublished) data indicate that non-cAMP inducing derivatives of these molecules that do not exert these effects can also induce Tr1 type cells indicating a role for other toxin activities in T cell differentiation. Furthermore, the demonstration over recent years that many adjuvants represent ‘pathogen-derived molecular patterns’ (PAMPS) that interact specifically with pattern recognition receptors (PRR) on host cells provides a new, rational basis for adjuvant design. While ganglioside receptors are not regarded as classic PRR, the interaction of CT and LT with these receptors is central to their ability to enter cells and exert their modulatory functions.

Cell signalling events triggered by adjuvants
To underpin studies on the immune responses induced by adjuvants and the maturation of dendritic cells, my research is concentrating on cell signalling pathways induced by these molecules. We have shown that the cAMP-inducing bacteria bacterial toxins cholera toxin and E. coli heat-labile enterotoxin can inhibit NF-kB activation in dendritic cells. While IkB degradation and NF-kB translocation are not affected, NF-kB transactivation is strongly inhibited. In addition to this inhibitory effect on NF-kB, these toxins are strong activators of cAMP-response element-binding protein (CREB) transcriptional activity. I have established a collaboration with Dr Cormac Taylor at the Conway Institute in UCD to establish the potential suppressive role of CREB on the induction of DC inflammatory responses by PAMPS. We have shown that the DC2.4 dendritic cell line can be transfected and used to study NF-kB and CREB transcriptional activity. Using this system the role of CREB in the inhibition of inflammatory responses is being studied as is the ability of bacterial A-B toxins to exploit this pathway. Our studies indicate that inhibition of protein kinase A (PKA) activity using specific inhibitors enhances the inflammatory responses of DC to PAMPS suggesting that PKA may be an endogenous repressor of DC inflammatory responses.

Plant lectins as a novel class of vaccine adjuvants
Lectins are sugar-binding proteins and are expressed by most plants. These molecules have many remarkable properties including stability in the presence of proteases, specific binding to epithelial cells and in some cases strong immunogenicity. The stability and receptor binding properties of plant lectins make them excellent candidates for the targeting of drugs and vaccines to the gastrointestinal tract. Screening of a large panel of lectins as immunogens and adjuvants revealed that mistletoe lectins I, II and III were unique in their strong effects on the mucosal immune system. These molecules are among the most potent mucosal adjuvants yet identified but are highly toxic so may not be used in their native form. Studies are underway to produce the binding (B) subunit of the lectins in recombinant form to determine if these retain the immunostimulatory properties of the holotoxins. Furthermore, a programme of site directed mutagenesis is being used to inactivate the enzymatic activity of the A chain in order to generate mutants which will be characterised for adjuvant activity. The aim of these studies is to generate novel non-toxic mucosal adjuvants for subunit vaccines.

Research Personnel

Post Doctoral Fellow:
Dr Edel McNeela
Dr Karen Misstear
Dr Marie Yang
Dr Corinna Brereton

Research Students:
Eimear Lambe
Graham Tynan
Andres Mori
Ewa Oleszycka
Darren Ruane
Christopher Davitt
Clair Helen Hearnden

Visiting Scientist
Sergio Arancibia

Financial Support

SFI
Enterprise Ireland
Meningitis Research Foundation
Irish Medical Charities Group
Sigmoid Biotechnologies Ltd.

Collaborators

Dr Derek O’Hagan, Chiron Corporation, Emeryville, USA.
Prof Kingston Mills, School of Biochemistry and Immunology, TCD.
Dr Andrew Bowie, School of Biochemistry and Immunology, TCD.
Prof Uwe Pfuller, Institut für Phytochemie, Fakultät für Biowissenschaften, Private Universität Witten/Herdecke, gGmbH, Witten, Germany.
Prof Tomas Girbes, Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Universidad de Valladolid, Valladolid, Spain.
Dr Aoife Boyd, Department of Microbiology, NUI Galway
Dr Neil Williams, Univeristy of Bristol, U.K.
Dr George Grant, Rowett Research Institute, Aberdeen, U.K.
Prof Dolores Cahill, CHIP, RCSI, Dublin.

Recent Publications by the Adjuvant Research Group