Allergic asthma is a chronic inflammatory disease of the lower airways resulting, in many cases, from dysregulated Th2 CD4+ T-cell responses to inhaled environmental allergens. Allergic sensitisation, defined as the induction of Th2 mediated allergen-specific responses for the clinical disease, is a key risk factor for asthma. Although current therapies are relatively safe and effective at controlling symptoms they do not alter the chronic course of disease. Additionally, there are complications associated with chronic use of pharmacologic disease modifiers. Current allergen-specific immunotherapy aims to reintroduce immune-regulation, in an immune environment where regulation has failed. We propose an alternative approach to ‘turn off’ the ‘reservoir’ of pathogenic allergen-sensitised effector and memory T cells in established allergic asthma. Previously, it has been shown that antigen targeted genetically to be expressed in resting dendritic cells (DC) inactivates naïve, memory and effector CD4+ and CD8+ T cells and this could provide a therapeutic approach.
In this study, I will investigate, using the model allergen ovalbumin (OVA), whether genetically-targeting antigen to DC can prevent allergic sensitisation and allergen-induced airway inflammation. In addition, the project will determine whether antigen-encoding bone marrow cell (BM) transfer under non-myeloablative conditions terminates the established allergic airway disease. I also develop a robust murine model of airway inflammation elicited by the major ryegrass pollen allergen Lol p 1 in which therapeutic strategies could be tested. In addition, I produce a lentivirus vector encoding Lol p 1 which can be used to test therapeutic strategies in conjunction with the model developed.
Transgenic (Tg) mice genetically-engineered to express OVA in DC under control of the CD11c promoter (11c.OVA mice) were sensitised with OVA323-339/alum intraperitoneally and intranasally challenged with OVA. When splenocytes and mediastinal lymph nodes (MLNs) of OVA323-339-sensitised and OVA challenged mice were restimulated in vitro with OVA323-339 peptide, IL-4, IL-5, IL-13 levels were significantly decreased in OVA-expressing 11c.OVA transgenic relative to control mice. Also little or no inflammatory cell infiltrate was present in bronchoalveolar lavage fluid (BALF) in OVA-expressing mice after sensitisation and i.n. challenge. Next, using non-myeloablative conditions, OVA-encoding or non-Tg BM was transferred to OVA323-339/alum-sensitised and OVA-intranasally challenged BALB/c mice. Production of IL-4, IL-5 and IL-13 by OVA323-339 restimulated spleen cells and MLN cells was dramatically reduced in recipients of OVA-encoding, but not non-Tg, BM. Eosinophil content in BALF and histological evidence of mucus hypersecretion were also reduced indicating reversal of pathogenic processes associated with dysregulated T-cell responses.
For Lol p 1, BALB/c mice were sensitised with crude ryegrass pollen extract (containing Lol p 1)/alum intraperitoneally. When splenocytes of the sensitised mice were restimulated in vitro with ryegrass pollen extract, IL-4, IL-5, IL-13 levels were significantly increased in sensitised vs sham-sensitised mice. Ryegrass pollen extract/alum-sensitised BALB/c mice also showed significant airway inflammation when challenged intranasally with Lol p 1 compared to mice challenged with PBS.
Significantly, when fused with the transmembrane portion of the human transferrin receptor the plant allergen Lol p 1 was successfully expressed and targeted to the membrane of mammalian cells. When lentiviral vectors encoding Lol p 1 under control of a truncated DC-specific (11c960) promoter were generated and tested these effectively transduced hematopoietic progenitor cells based on reported gene expression. This indicated that lentiviral vectors encoding a plant allergen targeted to DC could be could be successfully engineered.
From the findings of my studies I conclude that expression of OVA in DC prevents allergic priming and consequently respiratory immune responses to respiratory antigen challenge. Allergen-encoding BM transfer under non-myeloablative conditions terminates established allergic T-cell responses and reduces allergen-induced airway inflammation. Lol p 1 is a good model for clinically relevant allergic responses and the lentiviral approach could provide a potential robust method for the induction of tolerance to terminate allergen-induced airway inflammation.