Protective Efficacy of Lectin-Fc(IgG) Fusion Proteins In Vitro and in a Pulmonary Aspergillosis In Vivo Model

Abstract

Aspergillosis cases by Aspergillus fumigatus have increased, along with fungal resistance to antifungals, urging the development of new therapies. Passive immunization targeting common fungal antigens, such as chitin and β-glucans, are promising and would eliminate the need of species-level diagnosis, thereby expediting the therapeutic intervention. However, these polysaccharides are poorly immunogenic. To overcome this drawback, we developed the lectin-Fc(IgG) fusion proteins, Dectin1-Fc(IgG2a), Dectin1-Fc(IgG2b) and wheat germ agglutinin (WGA)-Fc(IgG2a), based on their affinity to β-1,3-glucan and chitooligomers, respectively. The WGA-Fc(IgG2a) previously demonstrated antifungal activity against Histoplasma capsulatum, Cryptococcus neoformans and Candida albicans. In the present work, we evaluated the antifungal properties of these lectin-Fc(s) against A. fumigatus. Lectin-Fc(IgG)(s) bound in a dose-dependent manner to germinating conidia and this binding increased upon conidia germination. Both lectin-Fc(IgG)(s) displayed in vitro antifungal effects, such as inhibition of conidia germination, a reduced length of germ tubes and a diminished biofilm formation. Lectin-Fc(IgG)(s) also enhanced complement deposition on conidia and macrophage effector functions, such as increased phagocytosis and killing of fungi. Finally, administration of the Dectin-1-Fc(IgG2b) and WGA-Fc(IgG2a) protected mice infected with A. fumigatus, with a 20% survival and a doubled life-span of the infected mice, which was correlated to a fungal burden reduction in lungs and brains of treated animals. These results confirm the potential of lectin-Fc(IgGs)(s) as a broad-spectrum antifungal therapeutic.

Neuroimmune Responses in a New Experimental Animal Model of Cerebral Aspergillosis

“…Some studies have employed the neutrophil depleting antibody 1A8 with an intravenous challenge, or intravenous challenge without any immunosuppression ( 40 – 42 ). We found only a single study that employed a relevant cyclophosphamide-cortisone acetate immunosuppression model and administered A. fumigatus intratracheally, which resulted in 100% mortality by day 5 ( 43 ). Although live organism was detected in the lung in 100% of these mice, only 50% had detectable A. fumigatus in the brain ( 43 ).…”

“…We found only a single study that employed a relevant cyclophosphamide-cortisone acetate immunosuppression model and administered A. fumigatus intratracheally, which resulted in 100% mortality by day 5 ( 43 ). Although live organism was detected in the lung in 100% of these mice, only 50% had detectable A. fumigatus in the brain ( 43 ).…”

Monoclonal Antibodies and Invasive Aspergillosis: Diagnostic and Therapeutic Perspectives

“…Subsequently, surviving conidia start to swell and release surface hydrophobin and melanin, exposing PAMPs that interact with pattern recognition receptors (PRRs) on pulmonary epithelial cells. Conidial wall β (1-3)-glucan is recognized by dectin-1 and initiates engulfment by epithelia [ 30 ]. This internalization process is promoted by the interaction of conidial calcineurin A (Cal A) and integrin α5β1 [ 31 ] and the activation of cellular molecules [ 32 , 33 , 34 ].…”

Fc‐conjugated C‐type lectin receptors: Tools for understanding host–pathogen interactions

“…A.f conidia into mice significantly decreases the immune response (CXCL1/KC, TNF-alpha, CCL3/MIP-1, IL-6, and GM-CSF) and results in much higher fungal burdens (Steele et al, 2005). Secondly, the exposed β-glucan bound by a mIgG Fc portion fused to Dectin-1 targets the microbe for enhanced clearance via Fc binding receptors, this decreased fungal burden and enhanced survival of the infected mice (Mattila et al, 2008;Rodriguez-de la Noval et al, 2020). The aspergillus GAG layer masks the β-glucan layer as can be observed with the Δuge3 mutant, lacking GalNAc, has increased binding to FcDectin-1 on both swollen conidia and hyphae, and the mutant is less virulent due to the increased detection of the exposed β-glucan by the immune system (Gravelat et al, 2013).…”

“…A murine Fc domain fused to Dectin-1 protects mice against P. carinii infection due to enhanced host recognition and killing of the pathogen by the heightened FcγR-based recognition (Rapaka et al, 2007) and similarly for Aspergillus, growth clearance and survival were all altered when treated with FcDectin-1 (Mattila et al, 2008;Rodriguez-de la Noval et al, 2020). Diagnostic uses include screening for urine and blood stream pathogens by ELISA: an Fc fusion of the serum protein mannose-binding lectin bound to a broad range of bacteria, fungi, viral antigens, and parasites (Seiler et al, 2019).…”