The Immunogenicity of Subunit Vaccines for Respiratory Syncytial Virus after Co-formulation with Aluminum Hydroxide Adjuvant and Recombinant Interleukin-12

The effects of recombinant interleukin-12 (rIL-12) on immune responses generated by subunit vaccines for respiratory syncytial virus (RSV) were evaluated in BALB/c mice. Parenteral co-administration of rIL-12 with F/AIOH or F/PBS resulted in accelerated clearance of infectious virus from the lungs 4 days after challenge. The immune responses elicited by 0.03 μg of F protein plus 10 ng of rIL-12 adsorbed to AIOH were more efficacious than those induced by 3 μg of F protein co-formulated with 1,000 ng of rIL-12 in PBS alone. Adsorption to AlOH prolonged the presence of rIL-12 in the sera. The resultant systemic humoral immune responses after vaccination with F/AIOH or G/AIOH were dependent on the dose of rIL-12 and characterized by heightened serum immunoglobulin G_2a (IgG_2a) antibody titers. Co-administration of rIL-12 with F/AIOH was also associated with diminished protein-specific IgE titers, elevated neutralizing antibody titers, and interferon-γ and (IFN-γ) in the sera, and enhanced antigen-dependent killer cell activity in the lungs after challenge. For maximum benefit, the data suggested that rIL-12 must be co-administered with F/AIOH. Collectively, the results indicated that rIL-12 directed immune responses toward a type 1 phenotype. However, examination of pulmonary inflammatory cells after challenge suggested that the type 1 phenotype was not absolute. Co-formulation with rIL-12 did not diminish pulmonary eosinophilia upon challenge of naive mice primed with F/AIOH, G/AIOH, or FI-RSV, and CD4⁺ T cells were expanded relative to the CD8⁺ T-cell compartment. These results are important for the future design of subunit vaccines against RSV.