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Direct inoculation of DNA, in the form of purified bacterial plasmids that are unable to replicate in mammalian cells but are able to direct cell synthesis of foreign proteins, is being explored as an approach to vaccine development. Here, a highly attenuated Shigella vector invaded mammalian cells and delivered such plasmids into the cytoplasm of cells, and subsequent production of functional foreign protein was measured. Because this Shigella vector was designed to deliver DNA to colonic mucosa, the method is a potential basis for oral and other mucosal DNA immunization and gene therapy strategies.

Development of a vaccine against pulmonary tuberculosis (TB) may require immunization strategies that induce a high frequency of antigen-specific CD4 and CD8 T cells in the lung. The nonhuman primate (NHP) model is essential for testing such approaches because it has predictive value for how vaccines elicit responses in humans. Here, we used an aerosol (AE) vaccination strategy to administer AERAS-402, a replication-defective recombinant adenovirus (rAd) type 35 expressing Mycobacterium tuberculosis (M.tb) antigens Ag85A, Ag85B, and TB10.4, in bacille Calmette-Guerin (BCG)-primed or unprimed rhesus macaques. Immunization with BCG generated low purified protein derivative (PPD)-specific CD4 T cell responses in blood and bronchoalveolar lavage (BAL). In contrast, aerosolized AERAS-402 alone or following BCG induced potent and stable Ag85A/b-specific CD4 and CD8 effector T cells in BAL that largely produced IFN-γ, as well as TNF and IL-2. Such responses induced by BCG, AERAS-402, or both failed to confer overall protection following challenge with 275 CFU of M.tb Erdman, although vaccine-induced responses associated with reduced pathology were observed in some animals. Anamnestic T cell responses to Ag85A/b were not detected in blood of immunized animals after challenge. Overall, our data suggest that a high M.tb challenge dose may be a critical factor in limiting vaccine efficacy in this model. However, the ability of AE rAd immunization to generate potent cellular immunity in the lung by AE rAd immunization suggests that using different or more immunogens, alternative rAd serotypes with enhanced immunogenicity, and a physiological challenge dose may achieve protection against M.tb.

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BackgroundBCG vaccination, combined with adenoviral-delivered boosts, represents a reasonable strategy to augment, broaden and prolong immune protection against tuberculosis (TB). We tested BCG (SSI1331) (in 6 animals, delivered intradermally) and a recombinant (rBCG) AFRO-1 expressing perfringolysin (in 6 animals) followed by two boosts (delivered intramuscullary) with non-replicating adenovirus 35 (rAd35) expressing a fusion protein composed of Ag85A, Ag85B and TB10.4, for the capacity to induce antigen-specific cellular immune responses in rhesus macaques (Macaca mulatta). Control animals received diluent (3 animals).Methods and FindingsCellular immune responses were analyzed longitudinally (12 blood draws for each animal) using intracellular cytokine staining (TNF-alpha, IL-2 and IFN-gamma), T cell proliferation was measured in CD4+, CD8alpha/beta+, and CD8alpha/alpha+ T cell subsets and IFN-gamma production was tested in 7 day PBMC cultures (whole blood cell assay, WBA) using Ag85A, Ag85B, TB10.4 recombinant proteins, PPD or BCG as stimuli. Animals primed with AFRO-1 showed i) increased Ag85B-specific IFN-gamma production in the WBA assay (median >400 pg/ml for 6 animals) one week after the first boost with adenoviral-delivered TB-antigens as compared to animals primed with BCG (<200 pg/ml), ii) stronger T cell proliferation in the CD8alpha/alpha+ T cell subset (proliferative index 17%) as compared to BCG-primed animals (proliferative index 5% in CD8alpha/alpha+ T cells). Polyfunctional T cells, defined by IFN-gamma, TNF-alpha and IL-2 production were detected in 2/6 animals primed with AFRO-1 directed against Ag85A/b and TB10.4; 4/6 animals primed with BCG showed a Ag85A/b responses, yet only a single animal exhibited Ag85A/b and TB10.4 reactivity.ConclusionAFRO-1 induces qualitatively and quantitatively different cellular immune responses as compared with BCG in rhesus macaques. Increased IFN-gamma-responses and antigen-specific T cell proliferation in the CD8alpha/alpha+ T cell subset represents a valuable marker for vaccine-take in BCG-based TB vaccine trials