Vaccine 19 (2001) 4153–4161 Potentiation by a novel alkaloid glycoside adjuvant of a protective cytotoxic T cell immune response specific for a preerythrocytic malaria vaccine candidate antigen Karen G Heal a , Nadeem A. Sheikh b , Michael R. Hollingdale a , W. John W. Morrow b , Andrew W. Taylor-Robinson a a School of Biology, Uniersity of Leeds, Clarendon Way, Leeds LS29JT, UK b Department of Immunology, St. Bartholomew’s and The Royal London School of Medicine and Dentistry, Turner Street, London EC1A 7BE, UK Received 6 November 2000; received in revised form 19 April 2001; accepted 23 April 2001 Abstract We have recently demonstrated that the novel glycoalkaloid tomatine, derived from leaves of the wild tomato Lycopersicon pimpinellifolium, can act as a powerful adjuvant for the elicitation of antigen-specific CD8 + T cell responses. Here, we have extended our previous investigation with the model antigen ovalbumin to an established malaria infection system in mice and evaluated the cellular immune response to a major preerythrocytic stage malaria vaccine candidate antigen when administered with tomatine. The defined MHC H-2k d class I-binding 9-mer peptide (amino acids 252 – 260) from Plasmodium berghei circumsporozoite (CS) protein was prepared with tomatine to form a molecular aggregate formulation and this used to immunise BALB/c (H-2k d ) mice. Antigen-specific IFN- secretion and cytotoxic T lymphocyte activity in vitro were both significantly enhanced compared to responses detected from similarly stimulated splenocytes from naive and tomatine-saline-immunised control mice. Moreover, when challenged with P. berghei sporozoites, mice immunised with the CS 9-mer-tomatine preparation had a significantly delayed onset of erythrocytic infection compared to controls. The data presented validate the use of tomatine to potentiate a cellular immune response to antigenic stimulus by testing in an important biologically relevant system. Specifically, the processing of the P. berghei CS 9-mer as an exogenous antigen and its presentation via MHC class I molecules to CD8 + T cells led to an immune response that is an in vitro correlate of protection against preerythrocytic malaria. This was confirmed by the protective capacity of the 9-mer-tomatine combination upon in vivo immunisation. These findings merit further work to optimise the use of tomatine as an adjuvant in malaria vaccine development. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Alkaloid glycoside; Peptide delivery; Malaria; Circumsporozoite protein www.elsevier.com/locate/vaccine 1. Introduction Adjuvants are immunogenic compounds that, when combined with an antigen, potentiate an antigen-spe- cific immune response. Adjuvants may not only boost the response of an immunologically weak antigen but also influence the type of immune response elicited [1]. In the past, the main focus of adjuvant research has been to assess the ability of compounds to elicit hu- moral immunity, with cellular immune responses largely neglected. Alum, the only adjuvant licensed for human use, is poor at stimulating cell-mediated immu- nity and so is not suitable for use with all antigens [2]. Cellular immune responses generated by T cells of both CD4 + and CD8 + subsets can generally be classified as either type 1 or 2 as determined by the distinct cytokine profile of the antigen-specific T cells which produce them [3]. Type 1 responses are charac- terised by IL-2 and IFN-, mediate macrophage activa- tion and antibody-dependent cellular cytotoxicity, and promote production of IgG2a opsonising and comple- ment-fixing antibodies. Type 2 responses feature IL-4, IL-5, IL-10 and IL-13, and provide help for B cell maturation and production of IgG1 and IgE. Hence, in both mice and humans, T cells secreting type 1 and 2 * Corresponding author. Tel.: +44-113-2332893; fax: +44-113- 2332882. E-mail address: bgyawtr@leeds.ac.uk (A.W. Taylor-Robinson). 0264-410X/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S0264-410X(01)00166-9