Adjuvanticity of plasmid DNA encoding cytokines fused to immunoglobulin Fc domains.

PURPOSE Plasmid DNAs encoding cytokines enhance immune responses to vaccination in models of infectious diseases and cancer. We compared DNA adjuvants for their ability to enhance immunity against a poorly immunogenic self-antigen expressed by cancer. EXPERIMENTAL DESIGN DNAs encoding cytokines that affect T cells [interleukin (IL)-2, IL-12, IL-15, IL-18, IL-21, and the chemokine CCL21] and antigen-presenting cells [granulocyte macrophage colony-stimulating factor (GM-CSF)] were compared in mouse models as adjuvants to enhance CD8+ T-cell responses and tumor immunity. A DNA vaccine against a self-antigen, gp100, expressed by melanoma was used in combination with DNA encoding cytokines and cytokines fused to the Fc domain of mouse IgG1 (Ig). RESULTS We found that (a) cytokine DNAs generally increased CD8+ T-cell responses against gp100; (b) ligation to Fc domains further enhanced T-cell responses; (c) adjuvant effects were sensitive to timing of DNA injection; (d) the most efficacious individual adjuvants for improving tumor-free survival were IL-12/Ig, IL-15/Ig, IL-21/Ig, GM-CSF/Ig, and CCL21; and (e) combinations of IL-2/Ig+IL-12/Ig, IL-2/Ig+IL-15/Ig, IL-12/Ig+IL-15/Ig, and IL-12/Ig+IL-21/Ig were most active; and (f) increased adjuvanticity of cytokine/Ig fusion DNAs was not related to higher tissue levels or greater stability. CONCLUSIONS These observations support the potential of cytokine DNA adjuvants for immunization against self-antigens expressed by cancer, the importance of timing, and the enhancement of immune responses by Fc domains through mechanisms unrelated to increased half-life.