Enhancement of in vivo and in vitro T cell response against measles virus haemagglutinin after its incorporation into liposomes: effect of the phospholipid composition Florence Garnier*, Fr6d6rique Forquet*, Patrick Bertolino* and Denis Gerlier** Artificial phospholipid bilayer vesicles were tested for their capacity to enhance the priming and the restimulation of mouse T cells against the haemagglutinin (H) glycoprotein of the measles virus in vivo and in vitro. H glycoprotein was purified and incorporated into liposomes made of cholesterol, dicetylphosphate and dilauroylphosphatidylcholine (DLPC) or distearoylphosphatidylcholine (DSPC). H in DLPC or DSPC-liposomes was found to be a potent in vivo stimulator of lymph node T cells harvested from mice immunized with measles virus, whereas H glycoprotein in free form did not elicit any proliferative T cell response. When used to immunize naive mice, only H in DSPC-liposomes was able to prime T cells as evidenced by the capacity of lymph node cells to proliferate in the presence of H in liposomes or measles virus as secondary stimulating agents in vitro. H-specific T cell clones derived from animals immunized with H in DSPC-liposomes were able to recognize H glycoprotein both in free form and incorporated into liposomes in the presence of naive spleen cells as APC. However, compared with the liposome forms, 20-fold more H protein in free form was required to elicit a T cell clone response at a similar level. This liposome immune enhancing effect on the T cell clone recognition of H glycoprotein was also observed when peritoneal exudate cells were used as APC. These data demonstrate that the insertion of a membrane-derived antigen into artificial membranes may be a prerequisite for the priming and stimulation of specific T cells both in vivo and in vitro. In addition, the nature of the phospholipid used to build the liposomes appears to be a critical parameter. Keywords: T cell response; liposome; haemagglutinin; measles virus INTRODUCTION The use of artificial phospholipid bilayer vesicles (liposomes) as antigen carriers has been demonstrated to enhance the antibody response in vivo against a large variety of antigens (see Ref. 1 for review) including diphtheria toxoid 2, bovine serum albumin s, histo- compatibility antigens 4, tumour associated cell surface antigen 5, and human immunodeficiency virus glyco- protein 6. The phospholipid composition of the liposomes used as antigen carrier strongly influences their immuno- enhancing capabilities and for example phospholipids of low transition temperature may be preferable to enhance the immune response against a water soluble antigen (see Ref. 1 for review). Pharmacological studies on the *INSERM U218, Centre Leon Berard, 69373 Lyon Cedex 08, France. *lmmunobiologie Moleculaire, CNRS-UMR 49, ENS Lyon, 46 Allee d'ltalie, 69364 Lyon Cedex 07, France. *To whom correspondence should be addressed. (Received 10 July 1990; accepted 15 October 1990) 0264-410x/91/050340436 © 1991 Butterworth-Heinemann Ltd 340 Vaccine, Vol. 9, May 1991 fate of liposomes in vivo have clearly demonstrated that they are cleared almost exclusively by phagocyte cells of the reticulo-endothelial system 1. Indeed, the liposome adjuvant effect is likely to be mediated by macrophages able to phagocytose particles and to act as antigen presenting cells. This central role of macrophages in the liposome adjuvant effect has been reported in vivo 7'8. Therefore, it is thought that the mechanism by which the liposomes enhance the immune response is both to act as an antigen bag with efficient delivery to Antigen Presenting Cells (APC) and to favour a depot effect when the macrophage uptake is delayed 3. The high amount of antigen that can be delivered by one vesicle to a single APC might enhance the generation of complexes associating molecules Major Histocompatibility Com- plex (MHC) and antigen-derived peptides by overcoming the competition with peptides derived from self protein 9. The resulting enhanced expression of these MHC-peptide complexes'at the cell surface will thus favour the capacity of APC to stimulate T cells. Although some recent experiments performed in vitro are favouring these