INTERLEUKIN-15 ACTS AS AN IMMUNOLOGICAL CO-ADJUVANT FOR LIPOSOMAL ANTIGEN IN-VIVO

The recently discovered interleukin-15 (IL-15) is known to bind to the receptor of interleukin-2 (IL-2) and to share several of the latter's immunological properties. In the present study, the first to our know ledge on IL-15 behaviour in vivo, we examined the possibility that IL- 15 also shares the ability of IL-2 to enhance the immunological adjuva nt property of liposomes by acting as a co-adjuvant. The cytokine and a model antigen (tetanus toroid) were either co-entrapped by the dehyd ration rehydration method into, or covalently co-linked by diazotizati on to the surface of the same liposomes, or entrapped in different lip osome populations. Intramuscular immunization of CD-1 mice with a vari ety of IL-15 and toroid formulations revealed that IL-15 augments anti -toroid IgG (IgG(1,) IgG(2,) IgG(2b)) responses well above (up to ten- fold) those achieved with liposomal toroid alone (or with a mixture of free IL-15 and toroid) when the cytokine and the antigen are associat ed with the same vesicles but not when in different vesicle population s that were mixed before injection. Higher responses were observed for all three subclasses studied only with liposomes where IL-15 and anti gen were accommodated on their surface. (C) 1997 Elsevier Science B.V.