MPE8 and 54G10 were reported to neutralize both HRSV and HMPV in vitro [35,36]. HMPV titers in the lung. Overall, this study identifies several human mAbs with virus-specific therapeutic potential and a unique mAb with inhibitory activities against both HRSV and HMPV. Keywords: HMPV, HRSV, therapeutic antibodies 1. Introduction The human metapneumovirus (HMPV) and the human respiratory virus (HRSV) are two ubiquitous respiratory viruses belonging to the family. Both viruses circulate within the human population worldwide (reviewed in [1,2]). Seroprevalence studies in European countries, Japan and the USA have indicated that more than 90% of children aged between 5 and 10 were previously infected with HMPV [3,4,5,6]. Similarly, studies in Europe, Kenya and India have indicated that HRSV seropositivity was above 95% in children of the same age range [6,7,8]. The HRSV and HMPV infections lead to similar symptoms, ranging from fever and coughing to wheezing, hypoxia, pneumonia and even death, in rare cases [4,9]. The HRSV and HMPV infections are more severe in immunocompromised individuals, including the elderly and younger children. Indeed, premature children and children with pre-existing conditions such as chronic heart or lung disease are especially vulnerable to these viruses [1,2]. The health and economic burden related to these viruses is illustrated by the facts that HRSV and HMPV are estimated to account for 28C57 % and 3C6%, respectively, of hospitalizations for acute respiratory tract infections in young children in Canada, France and China [9,10,11]. Furthermore, studies from Finland, South Africa and the USA suggest that HRSV and HMPV account for 15C30% and 4C12% of consultations for young children with upper or lower respiratory tract infections [12,13,14,15,16]. To date, there is no approved vaccine against HRSV or HMPV. There is also no licensed therapeutic drug against HMPV or HRSV. Palivizumab, a humanized monoclonal antibody (mAb), is Acetyl-Calpastatin (184-210) (human) used prophylactically in high-risk children including premature infants and children with pre-existing comorbidities such as chronic lung disease, bronchopulmonary dysplasia and congenital heart disease [17]. However, the efficacy of Palivizumab for preventing hospitalization is partial and estimated at 50% [18]. New therapeutics are therefore being developed against HRSV. Among them, two therapeutic antibodies including Nirsevimab and MK-1654 are currently in clinical phases of development [19,20]. In contrast, existing therapeutics against HMPV are still in the pre-clinical phases of development [21]. It is worth noting that although aerosol administration of ribavirin, a nucleotide analog, could be effective against HRSV and HMPV, the high cost of ribavirin and its documented side effects have prevented its widespread use [22]. Due to the limited therapeutic options for HRSV and HMPV infections, the development of novel treatments is required. Both HRSV Rabbit polyclonal to AAMP and HMPV encode for a fusion (F) and a glycoprotein (G) that are important for viral entry. The G protein is highly divergent among HRSV and HMPV subtypes (groups A and B), while the F protein is highly Acetyl-Calpastatin (184-210) (human) conserved [23,24,25]. As a result, the F protein of both viruses is the most attractive target for the generation of therapeutic mAbs against HRSV and HMPV. This study documented the isolation, using flow cytometry-based cell sorting, of therapeutic mAbs against HRSV and HMPV from healthy human donors. The capacity of the plant-based expression platform from Medicago to effectively express the isolated mAbs was also assessed and the binding affinity and neutralization capacity of the resulting mAbs were evaluated in vitro by enzyme-linked immunosorbent assay (ELISA) and micro-neutralization, respectively. Finally, the ability of the selected mAbs to reduce lung viral loads was evaluated in murine Acetyl-Calpastatin (184-210) (human) models of HRSV and HMPV. 2. Materials and Methods 2.1. Human Samples Blood samples from healthy human donors were obtained from the University Institute of Cardiology and Respirology of Quebec (IUCPQ). Signed informed consent was obtained from every study participant. Ethical approval (#2018-2982) for the conduct of this study was obtained from the ethics committee of the Universit Laval-CHU de Quebec. 2.2. HMPV and HRSV Fusion Protein Production The HMPV WT F, RSV WT F and RSV PreF genes were amplified and cloned in vector pcDNA 3.1+ (ThermoFisher Scientific, Burlington, Acetyl-Calpastatin (184-210) (human) ON, Canada, cat#V790-20). Acetyl-Calpastatin (184-210) (human) The HMPV and HRSV F proteins originated from the C-85473 and A2 strains,.