Abstract
Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause developmental disorders following congenital infection and life-threatening complications among transplant patients. Potent neutralizing monoclonal antibodies (MAbs) are promising drug candidates against HCMV infection. HCMV can infect a broad range of cell types. Therefore, single neutralizing antibodies targeting one HCMV glycoprotein often lack either potency or broad cell-type coverage. We previously characterized two human-derived HCMV neutralizing MAbs. One was the broadly neutralizing MAb 3-25, which targets the antigenic domain 2 of glycoprotein B (gB). The other was the highly potent MAb 2-18, which specifically recognizes the gH/gL/pUL128/130/131 complex (pentamer). To combine the strengths of gB- and pentamer-targeting MAbs, we developed an IgG-single-chain variable fragment (scFv) bispecific antibody by fusing the 2-18 scFv to the heavy-chain C terminus of MAb 3-25. The resulting bispecific antibody showed high-affinity binding to both gB and pentamer. Functionally, the bispecific antibody demonstrated a combined neutralization breadth and potency of the parental MAbs in multiple cell lines and inhibited postinfection viral spreading. Furthermore, the bispecific antibody was easily produced in CHO cells at a yield above 1 g/liter and showed a single-dose pharmacokinetic profile comparable to that of parental MAb 3-25 in rhesus macaques. Importantly, the bispecific antibody retained broadly and potent neutralizing activity after 21 days in circulation. Taken together, our research provides a proof-of-concept study for developing bispecific neutralizing antibody therapies against HCMV infection.
Highlights
Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause developmental disorders following congenital infection and life-threatening complications among transplant patients
The variable light-chain (VL) fragment and variable heavy-chain (VH) fragments of monoclonal antibodies (MAbs) 3-25 or 2-18 were joined with a (G4S)3 linker and fused at the N terminal of human CH1-Fc, which results in two proteins termed 2-18 scFv-Fc and 3-25 scFv-Fc, respectively (Fig. 1A and B)
CytoGam, which contains pooled immunoglobulin derived from adult human plasma with high-titer HCMV antibody, has been successfully used in combination with antiviral chemotherapies for prophylaxis of HCMV diseases in transplant recipients [39,40,41]
Summary
Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause developmental disorders following congenital infection and life-threatening complications among transplant patients. Antibodies targeting gB and gH have a broad but moderate HCMV neutralizing potency in most cell types, including epithelial cells, endothelial cells, and fibroblasts. Pentamer-specific antibodies are extremely potent neutralizers in epithelial and endothelial cells but fail to inhibit HCMV infection of fibroblasts [26, 27]. A combination of monoclonal antibodies (MAbs) targeting different HCMV glycoproteins can potentially provide a broader protection range and decrease the risk of developing viral resistance [29]. We sought to combine the strengths of broad cell-type coverage by MAb 3-25 and the extremely high potency by MAb 2-18 To this end, we developed and evaluated a MAb 3-25- and MAb 2-18-based tetravalent IgG–single-chain variable fragment (scFv) bispecific HCMV neutralizing antibody as a drug candidate for HCMV infection
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