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European Biopharmaceutical Review

Natural and Synthetic Additives

Vincent W Bramwell and Yvonne Perrie at the University of Aston discuss adjuvants and delivery systems, and find them a useful resource for vaccine delivery

The field of vaccine research is comprised of highly multidisciplinary and diverse aspects of investigation. For example, the consideration of mechanisms of adjuvant activity may involve analysis of complex immunological characteristics, whilst formulation and delivery may be highly pharmaceutical in essence.

Historically, there has been a tendency for these disparate aspects to be taken somewhat in isolation. However, more recently, there finally seems to be an increasing rationale for the full evaluation and delineation of these facets and characteristics. For a long time immunologists have ignored the fortuitous and covert particulate nature of many good adjuvant and antigen combinations. This is now changing, however, and novel adjuvant research may be accompanied by some examination of pharmaceutical characteristics along with the presiding immunological analysis. It is increasingly common to see extensive pharmaceutical analysis accompanied by detailed immunological investigations. These changes are in part driven by the recent increase in understanding of mechanisms of adjuvant activity, largely facilitated by the description of highly specific innate immune recognition (by toll-like receptors (TLR) for example) of components usually associated with the presence of invading bacteria or virus.

The widening potential applications for vaccine technology in cancer, allergy and other areas (1,2), as well as the specific requirements for vaccines against chronic viral and bacterial pathogens (in therapeutic as well as prophylactic mode) implies that a diversity of adjuvants are probably required in order to fulfil discrete immunological requirements for these new generation vaccines (3).

PARTICULATE DELIVERY SYSTEMS

Interest in synthetic particulate delivery systems for protein subunit vaccines (liposomes or polymer microspheres, for example) is derived from their increased safety in comparison to live vaccines and, in common with other types of adjuvants, the need for better immunological activity against purified protein or peptide vaccine epitopes. When considering the mechanism of adjuvant action of particulate delivery systems, it may be especially important to consider the geographical concepts of antigen distribution. The induction of immune reactivity is thought to depend upon antigen reaching, and being available in lymphoid organs in a dose and time dependent manner. It is thought that antigen that does not reach lymphoid organs is ignored by immune cells (4). It has also been suggested that antigen kinetics, load and distribution are different for pathogens and model antigens, and that this also contributes to the effective immune responses initiated against pathogens in comparison to soluble antigen (5).

Facilitation of effective antigen delivery to draining lymph nodes is, therefore, potentially a highly desirable facet of candidate vaccine particulate delivery systems. It is likely that biodistribution, including any depot effect, and antigen kinetics, mediated by incorporation into a delivery system, play a highly important role in the mechanisms of adjuvant activity of particulate delivery systems. Partly, this role may be assisted by effective uptake of many particulate systems by antigen presenting cells (APC). The extent and diversity of formulation materials and methods employed experimentally for these systems is truly enormous, and even the longest reviews cannot encompass more than the tip of the proverbial iceberg (3).

However, some of the most promising and interesting formulations include carriers that utilise chitosan as an absorption enhancing agent for mucosal delivery, immunostimulating complexes or ISCOMs (6), virus-like particles and virosomes, as well as cationic lipid vesicles prepared from (for example) dimethyl dioctadecyl ammonium (DDA) chloride or DC-cholesterol. This is in addition to liposomes and biodegradable polymer micro and nanosphere formulations. Figure 1 shows examples of particulate delivery systems in vaccine design, along with the major mechanisms of adjuvant activity postulated for these delivery systems.


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Dr Vincent W Bramwell began his studies with the Open University in 1991, studying Environment, Science Foundation before going on to studying Applied and Human Biology at Aston University in Birmingham obtaining a BSc and being awarded the Mini-Moore Prize. Following a short break, he began a PhD in ‘Particulate Delivery Systems in Vaccine Design’, again at Aston University and finishing this in 2004 at the University of London, School of Pharmacy, for Professor H Oya Alpar. Vincent then took up post-doctoral research, joining the group of Yvonne Perrie in the Medicines Research Unit at Aston University in 2004, working as part of Yvonne’s TB-VAC collaborative project. He has co-authored 18 publications covering vaccines, adjuvants and vaccine delivery systems.

Dr Yvonne Perrie is a Senior Lecturer in Pharmaceutics/Drug Delivery within the Medicines Research Unit, Aston University. Her research is focused on the strategic development of particulate-based delivery systems for the delivery of vaccines, biopharmaceuticals and nucleic acid-based therapies. Prior to her appointment at Aston University, Yvonne spent several years developing liposome-based systems in the laboratories of Professor Gregory Gregoriadis at the University of London.

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Dr Vincent W Bramwell
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Dr Yvonne Perrie
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