Characterization of a monoclonal antibody to a novel glycan-dependent epitope in the V1/V2 domain of the HIV-1 envelope protein, gp120

Analysis of the avian coronavirus spike protein reveals heterogeneity in the glycans present

Infectious bronchitis virus (IBV) is an economically important coronavirus, causing damaging losses to the poultry industry worldwide as the causative agent of infectious bronchitis. The coronavirus spike (S) glycoprotein is a large type I membrane protein protruding from the surface of the virion, which facilitates attachment and entry into host cells. The IBV S protein is cleaved into two subunits, S1 and S2, the latter of which has been identified as a determinant of cellular tropism. Recent studies expressing coronavirus S proteins in mammalian and insect cells have identified a high level of glycosylation on the protein’s surface. Here we used IBV propagated in embryonated hens’ eggs to explore the glycan profile of viruses derived from infection in cells of the natural host, chickens. We identified multiple glycan types on the surface of the protein and found a strain-specific dependence on complex glycans for recognition of the S2 subunit by a monoclonal antibody in vitro, with no effect on viral replication following the chemical inhibition of complex glycosylation. Virus neutralization by monoclonal or polyclonal antibodies was not affected. Following analysis of predicted glycosylation sites for the S protein of four IBV strains, we confirmed glycosylation at 18 sites by mass spectrometry for the pathogenic laboratory strain M41-CK. Further characterization revealed heterogeneity among the glycans present at six of these sites, indicating a difference in the glycan profile of individual S proteins on the IBV virion. These results demonstrate a non-specific role for complex glycans in IBV replication, with an indication of an involvement in antibody recognition but not neutralisation.

Production of a recombinant monoclonal antibody to Herpes Simplex Virus glycoprotein D for immunoaffinity purification of tagged proteins

We have developed a stable Chinese Hamster Ovary (CHO) cell line for the production of a recombinant monoclonal antibody (mAb) to a short protein sequence derived from the N-terminus of human herpes simplex virus type 1 glycoprotein D (HSV-1 gD). The antibody (designated r34.1) provides a useful tool for the immunoaffinity purification of HSV-1 gD tagged proteins, and provides a generic purification system by which various proteins and peptides can be purified. Recombinant 34.1 was assembled using cDNA derived from a HSV-1 gD specific murine hybridoma engineered to encode a full-length IgG molecule. Antibody expression cassettes were transfected into CHO-S cells, and a stable cell-line expressing up to 500 mg/L of antibody, isolated. Affinity purified r34.1 exhibited nanomolar affinity for its cognate ligand, and is stable throughout multiple cycles of immunoaffinity purification involving ligand binding at neutral pH, followed by acid elution. The HSV-1 gD tag expression and purification strategy has been used to enhance the secretion and purification of several vaccine immunogens including HIV envelope protein rgp120s, but the protocol has potential for generic application.

Development of a Stable MGAT1- CHO Cell Line to Produce Clade C gp120 With Improved Binding to Broadly Neutralizing Antibodies

The high rate of new HIV infections, particularly in Sub-Saharan Africa, emphasizes the need for a safe and effective vaccine to prevent acquired immunodeficiency syndrome (AIDS). To date, the only HIV vaccine trial that has exhibited protective efficacy in humans was the RV144 study completed in Thailand. The finding that protection correlated with antibodies to gp120 suggested that increasing the quality or magnitude of the antibody response that recognize gp120 might improve the modest yet significant protection (31.2%) achieved with this immunization regimen. However, the large-scale production of rgp120 suitable for clinical trials has been challenging due, in part, to low productivity and difficulties in purification. Moreover, the antigens that are currently available were produced largely by the same technology used in the early 1990s and fail to incorporate unique carbohydrates presented on HIV virions required for the binding of several major families of broadly neutralizing antibodies (bNAbs). Here we describe the development of a high-yielding CHO cell line expressing rgp120 from a clade C isolate (TZ97008), representative of the predominant circulating HIV subtype in Southern Africa and Southeast Asia. This cell line, produced using robotic selection, expresses high levels (1.2 g/L) of the TZ97008 rgp120 antigen that incorporates oligomannose glycans required for binding to multiple glycan dependent bNAbs. The resulting rgp120 displays a lower degree of net charge and glycoform heterogeneity as compared to rgp120s produced in normal CHO cells. This homogeneity in net charge facilitates purification by filtration and ion exchange chromatography methods, eliminating the need for expensive custom-made lectin, or immunoaffinity columns. The results described herein document the availability of a novel cell line for the large-scale production of clade C gp120 for clinical trials. Finally, the strategy used to produce a TZ97008 gp120 in the MGAT⁻ CHO cell line can be applied to the production of other candidate HIV vaccines.

Immunogenicity and malaria transmission reducing potency of Pfs48/45 and Pfs25 encoded by DNA vaccines administered by intramuscular electroporation

Pfs48/45 and Pfs25 are leading candidates for the development of Plasmodium falciparum transmission blocking vaccines (TBV). Expression of Pfs48/45 in the erythrocytic sexual stages and presentation to the immune system during infection in the human host also makes it ideal for natural boosting. However, it has been challenging to produce a fully folded, functionally active Pfs48/45, using various protein expression platforms. In this study, we demonstrate that full-length Pfs48/45 encoded by DNA plasmids is able to induce significant transmission reducing immune responses. DNA plasmids encoding Pfs48/45 based on native (WT), codon optimized (SYN), or codon optimized and mutated (MUT1 and MUT2), to prevent any asparagine (N)-linked glycosylation were compared with or without intramuscular electroporation (EP). EP significantly enhanced antibody titers and transmission blocking activity elicited by immunization with SYN Pfs48/45 DNA vaccine. Mosquito membrane feeding assays also revealed improved functional immunogenicity of SYN Pfs48/45 (N-glycosylation sites intact) as compared to MUT1 or MUT2 Pfs48/45 DNA plasmids (all N-glycosylation sites mutated). Boosting with recombinant Pfs48/45 protein after immunization with each of the different DNA vaccines resulted in significant boosting of antibody response and improved transmission reducing capabilities of all four DNA vaccines. Finally, immunization with a combination of DNA plasmids (SYN Pfs48/45 and SYN Pfs25) also provides support for the possibility of combining antigens targeting different life cycle stages in the parasite during transmission through mosquitoes.