ASian Pacific Journal of Allergy and Immunology (1991) 9 : 25-30 Comparison of the Immune Response against Polio Peptides Covalently-Surface-Linked to and Internally-Entrapped in Liposomes Lloyd Tan 1, Volkmar Weisslg 2 and Gregory Gregorladls 3 Synthetic antigens have been very useful in the study of various immunological phenomena, including the chemical basis of antigenicity and the genetic control of the immune response. 1 It has been demonstrated that synthetic peptides can elicit antibodies with the capacity to in- activate the respective viruses and to protect against a viral challenge. 2 However, synthetic oligo pep- tides are non- or only weakly immu- nogenic and are presently used experi- mentally as haptens coupled to carrier proteins, often in admixture with Freund's adjuvant. Liposomes have been shown to have the potential of being versatile and non-toxic immuno- logical adjuvants for a wide range of natural bacterial and viral pro- ducts. 3.4 The presentation of syn- thetic virus subunit peptides associated with liposomes may represent a novel and clinically acceptable way of enhancing their immunogenicity. In this paper, the adjuvanticity of Iiposomes on the polio virus pep- tides type 3-VP2 (designated WI) and type 2- VP2 (W2) is described. A comparison is made between two different modes of presentation of the peptides:- internally entrapped and surface-linked. Entrapped pep- tides may avoid conformational SUMMARY The adjuvantlclty of IIposomes on two different modes of presen· tation of polio virus subunit peptldes was demonstrated by incorporating the poorly Immunogenic synthetic polio peptldes, W1 and W2, Into the Intemal space of and covalently·llnked to the surface of dehydratlon'rehydration vesicles (DRV). It was found that for both peptldes, llposome association in either mode boosted the primary and secondary IgG 1 responses against 5 p.g peptide as compared to controls in which free peptide was administered. Surface' linkage of peptldes (both W1 and W2) exhibited an InltlaUy more rapid rise In antibody levels, as compared to internal entrapment of the peptldes, but elicited no observable secondary response. How- ever, although encapsulated W1 showed a milder primary response when compared to the surface-linked formulation, It later elicited a strong secondary response. These results suggested that It may be advantageous to admlnlsterllposomal virus subunit vaccines In both surface-linked and Internally entrapped formulations to achieve adequate Initial antibody levels followed by an anamnestic response_ (Abbreviations: MLV, multilamellar vesicles; SUV, small unllamellar vesicles; DRV, dehydration-rehydration vesicles; PC, phosphatldylchollne; DSPC, distearoyl phos· phatldylchollne; Chol, cholesterol; ELISA, enzyme-linked Immunosorbent assay.) changes induced by coupling proce- dures and gives rise to immunological memory (for WI) whilst linking peptides to the surface of liposomes results in more efficient antigen pre- sentation in the primary response without the disadvantage of intro- ducing an immunogenic carrier protein. MATERIALS AND METHODS Preparation of small unilamenar vesicle (SUV) Jiposomes Multilamellar vesicles (ML V) were prepared from equimolar egg phosphatidylcholine (PC) (Lipoid) and cholesterol as described. 5 Briefly, 32 ",moles egg PC were mixed with 32 cholesterol (British Drug From the 1Department of Pharmacology, Faculty of Medicine, National University of Singapore, Kent Ridge (0511), Singapore, 21nstitute of Biochemistry, Martin·Luther University, Haile/Saale. PSF 184 Halle, Germany and 3The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1 N 1AX, U.K. Correspondence: Dr. Lloyd Tan.