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300 Highly Attenuated Shigella Is Superior to Attenuated Salmonella for Mucosal DNA Vaccination against HIV
W. Vecino*1, P. Morin1, W. Jacobs, Jr.1,2, and G. Fennelly1
1Albert Einstein Coll. of Med. and 2Howard Hughes Med. Inst., Bronx, NY, USA
Background: Mucosal sites are important portals for HIV entry following sexual exposure. Attenuated bacteria are being developed as inexpensive vehicles for mucosal DNA vaccination. We previously demonstrated that transiently (<72 h) persistent DELTAasd S. flexneri strain 15D harboring DNA vaccines induces antigen-specific CTLs following intranasal (I.N.) immunization in mice. To determine which of several attenuated bacteria (strain 15D, Salmonella typhi strain Ty21a or DELTAaroD Salmonella typhimurium strain SL7207) harboring DNA vaccine plasmids induces the highest frequency of T cells against HIV, HIV-specific IFN-gamma-secreting T cells were measured after I.N. immunization in mice.
Methods: The persistence of Ty21a and SL7207 in Balb/c mice was determined by calculating the viable CFU/lung at various intervals after I.N. instillation of 107 CFU. To compare the frequency of antigen-specific T cells after 3 I.N. doses of 106 CFU of 15D, Ty21a, or SL7207 harboring syngp120 or pcDNA3-nefSIVmac25, gp120- or nef-specific responses among splenocytes were measured by IFN-gamma ELISPOT. To compare the ability of parenteral DNA vaccination to engender nef-specific T cells, a group of mice was given 100 mug of purified pcDNA3-nefSIVmac25 intramuscularly (I.M.). One-way ANOVA and Student’s t tests for unpaired samples were performed to compare differences between groups.
Results: Ty21a persisted in mouse lungs for <72 hours and SL7202 up to 20 days following I.N. instillation. The frequency of IFN-gamma-secreting splenocytes was significantly higher in 15D-syngp120-immunized mice than in either SL7207- or Ty21a-syngp120-immunized mice (p < 0.001). CD8+ depletion of splenocytes reduced the frequency of gp120-specific IFN-gamma-secreting cells by >80%. Remarkably, the frequencies of nef-specific IFN-gamma-producing T cells were comparable (p < 0.3) in 15D- pcDNA3-nefSIVmac25 and I.M. pcDNA3-nefSIVmac25-immunized mice.
Conclusions: Nonpersistent DELTAasd Shigella flexneri-DNA vaccination induces antigen-specific T cells among splenocytes as efficiently as parenteral DNA vaccination, and more efficiently than immunization with longer persisting attenuated S. typhimurium-DNA vaccines. These data support the evaluation of oral DELTAasd Shigella-DNA vaccination in rhesus macaques against an oral SIV challenge.
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