Investigation of the Immunomodulatory Properties of a Novel Allergen Variant That Targets Human Dendritics Cells

The allergen variant H22-Fel d 1 targets cat allergen to the high affinity IgG receptor FcγRI on DCs. This molecule was developed as a possible treatment for cat-allergic patients. The objective of this dissertation was to investigate the immunomodulatory properties of H22-Fel d 1 using an in vitro human-based system. H22-Fel d 1 induced a semi-mature phenotype in monocyte-derived dendritic cells (moDCs), characterized by enhanced production of Th1-associated cytokines with no change in expression of costimulatory molecules. Furthermore, H22-Fel d 1-primed moDCs induced a selective increase in Th2 and IL-10-expressing regulatory T cell types pointing to qualitative changes in the T cell cytokine repertoire. Importantly, this effect was restricted to cat-allergic subjects. Blockade of IL-10 selectively enhanced the Th2 component of the T cell response to H22-Fel d 1, suggesting that this arm of the response was regulated by IL-10. The clinical efficacy of H22-Fel d 1 will likely depend on its capacity to induce a protective T cell cytokine repertoire in a "pro-allergic" cytokine milieu in vivo. Therefore, we investigated whether the Th2- promoting cytokine, thymic stromal lymphopoietin (TSLP), which acts directly on DCs and is expressed in the skin and lungs of patients with allergic disease, mitigates the immunomodulatory capacity of H22-Fel d 1. Surprisingly, TSLP was a weak inducer of Th2 responses in vitro when, irrespective of atopic status; however, when moDCs were co-primed with TSLP and H22-Fel d 1 Th2 responses were amplified in a synergistic manner in highly atopic subjects. This effect was OX40 ligand-independent and not associated with secretion of the iii Th2-attracting chemokine, CCL17, pointing to an unconventional TSLPmediated pathway. Expression of TSLP receptor was markedly enhanced on atopic moDCs after priming with H22-Fel d 1 through a pathway regulated by PI3K and PKC. Moreover, inhibition of these molecules selectively abolished TSLP-mediated Th2 responses triggered by H22-Fel d 1. Discovery of a novel pathway linking FcγRI to TSLP receptor upregulation and consequent TSLPmediated effects questions the validity of allergen vaccines which engage surface receptors on DCs, but serendipitously identifies DC signaling components which could serve as new therapeutic targets for Th2-driven diseases.

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