THE IMMUNOLOGICAL CO-ADJUVANT ACTION OF LIPOSOMAL INTERLEUKIN-2 - THEROLE OF MODE OF LOCALIZATION OF THE CYTOKINE AND ANTIGEN IN THE VESICLES

In experiments designed to study the co-adjuvant action of interleukin -2, a model antigen (tetanus toroid) was passively entrapped in, or co valently coupled to multilamellar liposomes in the presence or absence of interleukin-2 (IL-2). When present, IL-2 was either co-entrapped w ith the toroid, entrapped alone in liposomes with toroid coupled to th eir surface, or coupled to the surface of liposomes with entrapped tor oid. The role of spatial localization of IL-2 within the liposomal str ucture (vis a vis that of the toroid) was studied in terms of its immu noadjuvant action in vivo, Male CD-1 mice were injected intramuscularl y twice with a variety of toxoid-containing liposomal preparations in the absence or presence of IL-2 incorporated in the same liposomes as above, In some experiments mice were immunized with liposomal toroid m ixed with separately entrapped IL-2. Results show that IL-2 augments s ignificantly secondary immune responses (IgG(1), IgG(a), IgG(2b) subcl asses) against the liposomal toroid (up to 15-fold compared with the l iposomal toroid alone), regardless of cytokine and antigen mode of acc ommodation in the liposomal structure but only when both are present i n the same vesicles. It is suggested that liposomal IL-2 may prove use ful as a co-adjuvant for vaccines which are weak or ineffective.