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318 Determination by DNA-Delivered HIV Antigens of the Induction of Humoral or Cellular Immunity and Modulation by Genetic Adjuvants
A. Moore*, W. Kong, B. Chakrabarti, and G. J. Nabel
NIAID, NIH, Bethesda, MD, USA and Oxford Univ., UK
Background: In the context of designing an efficacious DNA-based strategy for the development of an HIV vaccine, we investigated the shift in immune responses to 2 HIV-1 antigens, Env and Nef, delivered by nucleic acid immunization, when mice are coinjected with DNA encoding cytokine and hematopoietic factors.
Methods: Mice were intramuscularly immunized with a plasmid expressing Env or Nef with or without DNA expressing IL-2, IL-12, IL-15, Flt3 ligand (FL), and GM-CSF. Serum samples taken after the second and third immunization were analyzed for antigen-specific IgG titers by ELISA and Western blot. Cytokine secretion by in vitro stimulated spleen cells from immunized mice was assessed by ELISA 2 weeks after the final immunization. Induction of CTL activity was assessed by a 51Cr release assay.
Results: The immune responses following DNA immunization differed for these 2 HIV gene products. Immunization with a Nef-expressing plasmid generated a strong humoral response and antigen-specific IFN-gamma production. In contrast, immunization with the Env-expressing vector stimulated CTL activity but did not induce substantial antibody production. Coadministration of cytokine genes altered the immune responses induced by the DNA expressing antigen. IL-12 induced the most significant increase in IFN-gamma and IgG responses to Nef, however GM-CSF induced the most significant increase in gp160-specific IFN-gamma production and CTL responses. A dual approach of expanding innate immunity by administering the FL gene in conjunction with a cytokine which enhances adaptive T-cell responses was found to be a potent mechanism of creating a sensitive immune response, which was activated by a low dose of antigen.
Conclusions: This study highlights the role that the expressed antigen plays in inducing a predominantly CTL or humoral immune response and it demonstrates the potential of cytokine gene delivery strategies to facilitate development of immunotherapies and DNA vaccines.
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