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Improved efficiency and delivery of IL-15 DNA in combination with IL-15 receptor alpha DNA in mice and macaques as vaccine adjuvants and for immunotherapy deliver a potent growth signal for NK and T cells
Presented by George Pavlakis, United States.
Bergamaschi C.1, Jalah R.1, Rosati M.1, Valentin A.1, Kulkarni V.1, Alicea C.1, Patel V.1, Zhang G.-M.1, Felber B.1, Pavlakis G.1
1National Cancer Institute at Frederick, Center for Cancer Research, Frederick, United States
Aim: To generate DNA vectors expressing high levels of human IL-15 or IL-15 Receptor alpha (IL-15Ra). To study the in vivo biological activity as vaccine adjuvants and immune-based therapies, when expressed in combination.
Methods: Optimized plasmids for IL-15 and IL-15Ra (RNA/codon optimization; improvement of IL-15 secretion) were examined in vitro and in vivo (mice, rhesus macaques) and showed dramatic increase in gene expression. Hydrodynamic DNA delivery in mice led to very high plasma levels. Mice were sacrificed after 3 to 21 days and IL-15 was measured in muscle or plasma by ELISA. The phenotype of different lymphocyte subsets in spleen, liver, lung and GALT was analyzed by multiparameter flow cytometry.
Results: Coexpression of the optimized IL-15 and IL-15Ra greatly increased the levels of IL-15 in vivo, and resulted in ~1000-fold increase compared to the wild type IL-15 alone. These data show that the complex IL-15/IL-15Ra increases the half-life of the cytokine in vivo, as we have also shown in vitro. The high concentration of systemic IL-15 was biologically active as demonstrated by the increased frequency of NK cells in liver and lung, and the dramatic increase of T lymphocytes with properties of effector memory cells in lung, liver and spleen. Analysis of GALT demonstrated a significant increase of CD4 T cells in lamina propria and Peyer’s patches. Rhesus macaques injected with these vectors express high levels of plasma IL-15, demonstrating the ability of these vectors to achieve high levels of expression in vivo.
Conclusion: Coexpression of optimized IL15 and IL15Ra plasmids results in the mutual stabilization of the proteins in vitro and in vivo. The high level of expression of the optimized vectors and their enhanced activity suggest their use as adjuvants in DNA-based vaccines and in immunotherapy protocols against cancer.
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