Amended recombinant cells (ARCs™) expressing bovine IFN-γ: An economical and highly effective adjuvant system

Interferon-gamma (IFN-γ) has potent immune stimulatory activity, but purifying recombinant protein is expensive, soluble cytokine delivery is inefficient, and high doses of IFN-γ cause adverse systemic effects. We've shown, however, that chemically fixed, amended recombinant Pseudomonas fluorescens cells (ARCs), expressing soluble bovine IFN-γ (BGI/ARCs), provide an effective production and delivery vehicle for highly active cytokine. In this report we investigate the immune enhancing activity of BGI/ARCs in the presence or absence of two other adjuvants which enhance cell recruitment and protein uptake. Adjuvant activity and immune-mediated protection was evaluated using recombinant, truncated glycoprotein-D (tgD) and a bovine herpesvirus-1 (BHV-1) disease challenge. Our initial dose-titration study showed that100 μg of recombinant IFN-γ in BGI/ARCs significantly increased both IgG1 and IgG2 tgD-specific antibody titres and IgG1/IgG2 ratios were significantly reduced with as little as 1.0 μg IFN-γ. Vaccine formulation studies, using 20 μg tgD/vaccine dose and 100 μg IFN-γ delivered in BGI/ARCs, formulated in phosphate buffered saline (PBS), induced significantly increased antibody responses, following both primary and secondary immunization, and immune-mediated protection following a BHV-1 respiratory infection. Co-formulating BGI/ARCs with either an oil and water emulsion (Emulsigen®) or a polyphosphazene polymer (PCPP) did not significantly enhance tgD-specific antibody titres or disease protection when compared with BGI/ARCs alone. Surprisingly, co-delivering a single dose of BGI/ARCs with tgD protein in PBS had optimal adjuvant activity and the dose of IFN-γ delivered was four-fold less than the dose previously shown to induce adverse systemic responses.