A chimeric human-cat Fcγ-Fel d1 fusion protein inhibits systemic, pulmonary, and cutaneous allergic reactivity to intratracheal challenge in mice sensitized to Fel d1, the major cat allergen

Co-aggregation of FcεRI with FcγRIIb can block FcεRI-mediated reactivity and Fc gamma:allergen chimeric proteins, by co-crosslinking FcγRIIb to allergen-specific IgE bound to the FcεRI can block allergen-specific reactivity. We evaluated whether a human cat chimeric fusion protein (GFD) composed of part of the human Ig G1 Fc fused to the major cat allergen (Fel d1) would function as allergen immunotherapy while not inducing acute allergic reactivity in mice sensitized to Fel d1. Injection of GFD 6 h prior to Fel d1 challenge acutely blocked systemic and skin reactivity to Fel d1 challenge while mice given subcutaneous immunotherapy with GFD at days 37, 38, and 39 showed inhibition of systemic, lung, and cutaneous reactivity to Fel d1 2 weeks later. GFD immunotherapy did not induce systemic reactivity. Overall, the Fcγ-Fel d1 chimeric fusion protein blocked Fel d1-induced IgE-mediated reactivity but did not induce in vivo mediator release on its own; suggesting that this approach using allergen combined with Fc gamma1 so as to achieve inhibitory signaling may provide an enhanced form of allergen immunotherapy.