Mucosal Luminal Manipulation of T Cell Geography Switches on Protective Efficacy by Otherwise Ineffective Parenteral Genetic Immunization

Abstract

Genetic immunization holds great promise for future vaccination against mucosal infectious diseases. However, parenteral genetic immunization is ineffective in control of mucosal intracellular infections, and the underlying mechanisms have remained unclear. By using a model of parenteral i.m. genetic immunization and pulmonary tuberculosis (TB), we have investigated the mechanisms that determine the failure and success of parenteral genetic immunization. We found that lack of protection from pulmonary Mycobacterium tuberculosis (M.tb) challenge by i.m. immunization with a recombinant adenovirus-vectored tuberculosis vaccine was linked to the absence of M.tb Ag-specific T cells within the airway lumen before M.tb challenge despite potent T cell activation in the systemic compartments. Furthermore, pulmonary mycobacterial challenge failed to recruit CD8 T cells into the airway lumen of i.m. immunized mice. Such defect in T cell recruitment, intra-airway CTL, and immune protection was restored by creating acute inflammation in the airway with inflammatory agonists such as virus. However, the Ag-specific T cells recruited as such were not retained in the airway lumen, resulting in a loss of protection. In comparison, airway exposure to low doses of soluble M.tb Ags not only recruited but retained Ag-specific CD8 T cells in the airway lumen over time that provided robust protection against M.tb challenge. Thus, our study reveals that mucosal protection by parenteral immunization is critically determined by T cell geography, i.e., whether Ag-specific T cells are within or outside of the mucosal lumen and presents a feasible solution to empower parenteral immunization strategies against mucosal infectious diseases.

Pulmonary Mycobacterial Granuloma

“…For intracellular cytokine staining, single cell suspensions from airway lumen and granuloma were cultured and stained as previously described. 29 Briefly, cells were cultured for 24 hours with or without mycobacterial antigens [M.tb-Culture Filtrate (CF) and crude BCG], Golgi Plug (5 g/mL brefeldin A; BD Bioscience, Burlington, ON, Canada) was added 18 hours after stimulation. After culture, cells were washed and blocked with CD16/CD32 for 15 minutes on ice and stained with cell surface Abs.…”

Importance of T-cell location rekindled: implication for tuberculosis vaccination strategies

“…Experimental studies using genetic or genetically modified cellbased TB vaccines have provided compelling evidence that a robust level of anti-TB protection in the lung is always correlated with the presence of antigen-specific T cells within the airway lumen [24][25][26][27]. And if such T cells are only present in the lung interstitium, spleen and circulation, even when in large quantities, the vaccinated host is poorly protected from pulmonary M. tuberculosis challenge.…”

“…Indeed, in most instances of parenteral vaccination, the magnitude of lung interstitial T-cell responses often mirrors that of the spleen [24][25][26][27]. However, the lung can be divided into two compartments: the airway lumen and lung interstitium.…”

“…While the results from aforementioned studies promote the notion of respiratory mucosal TB immunization, they provide an important immunologic clue to developing much needed novel strategies for improving the protective efficacy of parenteral immunization [17,24,[27][28][29][30]. Such new strategies will aim to mobilize the systemically located antigen-specific T cells activated by parenteral immunization into the airway lumen and subsequently sustain them.…”

“…Thus, the lack of airway luminal T cells may explain why parenteral immunization with plasmid DNA, virus-vectored or cell-based TB vaccine is poorly protective [10,15,17,24,26,27]. By contrast, a single respiratory mucosal inoculation of virus-vectored or cell-based TB vaccine induces a strong presence of antigen-specific memory T cells within the airway lumen and provides robust protection from pulmonary M. tuberculosis challenge [24][25][26][27]. The maintenance of, and protection by, airway luminal CD8 T cells can be independent of systemic T-cell recruitment [Jeyanathan M et al, Unpublished Data].…”