Immunoadjuvant activity of interferon-γ-liposomes co-administered with influenza vaccines

In an attempt to potentiate the relatively low immunogenicity of the currently used influenza vaccines, especially in high-risk groups, monovalent and divalent subunit vaccine preparations were co-administered with free or liposome-associated murine interferon γ (mIFNγ) as an adjuvant. Recombinant murine IFNγ was entrapped (50-70% efficiency) in two types of large multilamellar vesicles: mIFNγ-LIP A-'conventional' liposomes, and mIFNγ-LIP B- 'surface-depleted' liposomes, in which 60 and 8% of the associated cytokine was located at the external liposome membrane, respectively. Subunit preparations containing the viral surface proteins hemagglutinin and neuraminidase (HN) were injected once, i.p. (0.5 μg each), into BALB/c mice, alone and combined with free or liposomal mIFNγ (mIFNγ-LIP, 0.5 or 3.0 μg). Sera were tested 3-16 weeks post-vaccination by hemagglutination inhibition (HI), and by ELISA for IgG1 and IgG2a antibodies (Abs). In addition, protective immunity against intranasal viral infection was assayed at 11 and 17 weeks post-vaccination. The results showed that: (a) Vaccination with HN alone produces very low HI and IgG titers and does not afford any protection. (b) Although co-administration with free mIFNγ (particularly using 3.0 μg) markedly enhances HI titer as well as the IgG1 and IgG2a levels, protection is negligible (0-33%). (c) In most cases, mIFNγ-LIP is significantly more potent than free mIFNγ (2-40-fold increase in Ab titer), and the low dose (0.5 μg) is generally more efficient than the high dose. Up to 83% of the mice co-vaccinated with mIFNγ-LIP were protected against viral challenge. (d) Both the IgG2a level and the HI titer appear to be crucial for protection. (e) Although the two liposomal preparations differ in their cytokine release profile in vivo and in their bioactivity in vitro, their adjuvant activity is comparable.