Effectiveness of intragastric immunization with protein and oligodeoxynucleotides containing a CpG motif for inducing a gastrointestinal mucosal immune response in mice

Membrane-anchored CCL20 augments HIV Env-specific mucosal immune responses

Background

Induction of broad immune responses at mucosal site remains a primary goal for most vaccines against mucosal pathogens. Abundance of evidence indicates that the co-delivery of mucosal adjuvants, including cytokines, is necessary to induce effective mucosal immunity. In the present study, we set out to evaluate the role of a chemokine, CCL20, as an effective mucosal adjuvant for HIV vaccine.

Methods

To evaluate the role of CCL20 as a potent adjuvant for HIV vaccine, we examined its effects on antigen-specific antibody responses, level of antibody-secreting cells, cytokine production and intestinal homing of plasma cells in vaccine immunized mice.

Results

CCL20-incorporated VLP administered by mucosal route (intranasal (n = 10, p = 0.0085) or intravaginal (n = 10, p = 0.0091)) showed much higher potency in inducing Env-specific IgA antibody response than those administered by intramuscular route (n = 10). For intranasal administration, the HIV Env-specific IFN-γ(751 pg/ml), IL-4 (566 pg/ml), IL-5 (811 pg/ml) production and IgA-secreting plasma cells (62 IgA-secreting plasma cells/10⁶ cells) in mucosal lamina propria were significantly augmented in CCL20-incorporated VLP immunized mice as compared to those immunized with Env only VLPs (p = 0.0332, 0.0398, 0.033, 0.0302 for IFN-γ, IL-4, IL-5, and IgA-secreting plasma cells, respectively).

Further, anti-CCL20 mAb partially suppressed homing of Env-specific IgA ASCs into small intestine in mice immunized with CCL20-incorporated VLP by intranasal (62 decreased to 16 IgA- secreting plasma cells/10⁶ cells, p = 0.0341) or intravaginal (52 decreased to 13 IgA- secreting plasma cells/10⁶ cells, p = 0.0332) routes.

Conclusion

Our data indicated that the VLP-incorporated CCL20 can enhance HIV Env-specific immune responses in mice, especially those occurring in the mucosal sites. We also found that i.m. prime followed by mucosal boost is critical and required for CCL20 to exert its full function as an effective mucosal adjuvant. Therefore, co-incorporation of CCL20 into Env VLPs when combined with mucosal administration could represent a novel and promising HIV vaccine candidate.

Synthetic oligodeoxynucleotides induce gastritis in mice

To investigate whether DNA directly induces gastritis and/or peptic ulcer, we injected synthetic DNA including CpG motif (CpG-DNA) to mouse stomach. BALB/c mice were injected with either saline, acetic acid (AA), CpG-DNA, or Control-DNA. Mice were sacrificed, and sections of the stomachs were stained with hematoxylin and eosin. The lesions were histopathologically scored from 0 to 4 based on the extent of the inflammation. Populations of neutrophils and mononuclear cells infiltrated to the lesion were calculated. IFN-y mRNA expression at the injection site was analyzed by RT-PCR. The number of CpG motifs included in the complete genomes of H. pylori HP26695 and J99, Escherichia coli O157, and Salmonella Typhi was determined by genomic analysis of these bacteria. Intragastric injection with CpG-DNA induced gastritis, and statistical analysis of histological scores revealed a significant difference between saline vs CpG-DNA (p = 0.037). The population of mononuclear cells infiltrated to the lesions was significantly higher in mice injected with CpG-DNA than that injected with AA (p = 0.0061). IFN-gamma mRNA expression was detected in the CpG-DNA group. While H. pylori includes multiple CpG motifs in its genome, it has fewer than the other pathogenic gram-negative bacilli. We conclude that synthetic DNA including CpG motif directly causes gastritis in mice and induces IFN-gamma production in the stomach. Bacterial DNA including CpG motif is known to stimulate innate immunity and to cause inflammation. Thus, H. pylori genomic DNA may be one of the virulent factors involved in H. pylori infection.