Liposomes as sustained release system for human interferon-gamma: biopharmaceutical aspects

Interferon-gamma (IFNgamma) has proven to be a promising adjuvant in vaccines against cancer and infectious diseases. However, due to its rapid biodegradation and clearance, its efficacy is severely reduced. Liposomal association might prolong the residence time of IFNgamma, but no efforts have been made to optimize the biopharmaceutical characteristics of liposomal IFNgamma for its application in therapy or as vaccine immunoadjuvant. In the present study, various liposomal formulations of recombinant human IFNgamma (hIFNgamma), differing in lipid composition, were prepared via the film hydration method and characterized in vitro regarding association efficiency and bioactivity, and in vivo regarding cytokine release kinetics after subcutaneous (s.c.) administration into mice. Human IFNgamma can be formulated in large, multilamellar liposomes with high association efficiency (>80%) and preservation of bioactivity. A critical parameter is the inclusion of negatively charged phospholipids to obtain a high liposome association efficiency, which is dominated by electrostatic interactions. The fraction of externally adsorbed protein compared to the total associated protein can be minimized from 74+/-9% to 8+/-3% by increasing the ionic strength of the dispersion medium. After injection of free (125)I-hIFNgamma, the radiolabel was detectable up to 48 h at the injection site. Liposomal encapsulation of (125)I-hIFNgamma increased the local area under the curve 4-fold, and the presence of the radiolabeled hIFNgamma at the injection site was prolonged to 7 days. The release kinetics and overall residence time of the cytokine at the s.c. administration site was influenced by depletion of the externally adsorbed IFNgamma, reducing the initial burst release. Increasing the rigidity of the liposome bilayer also resulted in a more pronounced reduction of the burst release and a 19-fold increase in the residence time of the protein at the s.c. administration site, compared to the free cytokine. As adjuvanticity of liposomal IFNgamma may strongly depend on the release kinetics of cytokines in vivo, the findings in this paper may contribute to a rational design of liposomal-cytokine adjuvants in vaccines against cancer and infectious diseases.

Initial events in infectious salmon anemia virus infection: evidence for the requirement of a low-pH step

We have investigated the initial steps in the interaction between infectious salmon anemia virus (ISAV) and cultured cells from Atlantic salmon (SHK-1 cell line). Using radioactively or fluorescently labelled viral particles we have studied the binding and fusion kinetics and the effect of pH on binding, uptake, and fusion of ISAV to SHK-1 cells and liposomes. As pH in the medium was reduced from 7.5 to 4.5, the association of virus to the cells was nearly doubled. The same effect of pH was observed when fusion between ISAV and liposomes was analyzed. In addition, the binding of ISAV to intact SHK-1 cells and to cell membrane proteins blotted onto filters was neuraminidase sensitive. However, the increased binding induced by low pH was not neuraminidase sensitive, probably reflecting activation of a fusion peptide at low pH. By using confocal fluorescence microscopy, the increased fusion of fluorescently labelled ISAV with the plasma membrane due to low pH could be demonstrated. When vacuolar pH in the cells was raised during inoculation with chloroquine or ammonium chloride, both electron and confocal microscopy showed accumulation of ISAV in endosomes and lysosomes. Production of infectious virus could be increased by lowering the extracellular pH during infection. Furthermore, chloroquine present during virus inoculation also caused a reduction in the synthesis of viral proteins in ISAV-infected cells as well as in the production of infective virus. These results indicate that ISAV binds to sialic acid residues on the cell surface and that the fusion between virus and cell membrane takes place in the acid environment of endosomes. This provides further evidence for a high degree of similarity between ISAV and influenza virus and extends the basis for the classification of this virus as a member of the Orthomyxoviridae family.