Andrew DiChiara | Senior Scientist II
AbbVie

Festival of Biologics Day 2 @ 17:10

Innovative strategies for neutralizing viral entry and application to future pandemics

The 2019 SARS-CoV-2 virus caused a global pandemic, killing more than 7 million people over the course of more than four years. The scientific community responded quickly to the declaration of a global pandemic, identifying panels of neutralizing antibodies as treatment options, but most of the monoclonal or co-formulated antibody treatments failed to maintain longitudinal efficacy as the virus continued to evolve. To better prepare a response to the threat of future pandemics, we contemplated the lessons learned from this pandemic and investigated several alternative methods of neutralizing coronaviruses’ entry by targeting a highly conserved region of the Spike protein.

The Spike protein is a SARS-CoV-2 membrane protein, composed of two domains, S1 and S2, with S1 located at the apex of the S2 stem. Upon binding to its receptor, ACE2, through the receptor binding domain (RBD), the S1 domain sheds from the S2 domain, releasing S2 to undergo drastic conformational changes that enable binding and fusion with the host cell membrane. Clinical stage antibodies predominantly targeted Spike’s RBD domain as a mechanism of neutralizing receptor binding and thereby curbing infection. The RBD, however, is a mutational hot spot for the coronavirus, making therapeutic antibody development a significant challenge, constantly chasing a moving target.

In contrast, the heptad-repeat 2 (HR2) domains in the S2 region are highly conserved across all identified variants as well as multiple species of sarbecoviruses, posing an attractive target for future pandemic preparedness. The HR2 domain is a three-helix bundle that undergoes drastic reorganization after S1 is shed from S2, enabling fusion of the viral membrane with the host cell membrane. We generated a panel of antibodies that bound to the HR2 region with high affinity but showed low neutralization potency in our in vitro pseudoviral assays. Identification of high affinity antibodies to this highly conserved region, however, presents an opportunity to investigate new and creative ways to prevent viral entry.

We identified two strategies that significantly improved in vitro pseudoviral neutralization potency of the lead HR2 binding antibody. In the first, we fused a deglycosylation enzyme to the anti-HR2 antibody, aimed at removing the glycan shield of the Spike protein. In vitro experiments demonstrate the ability of this fusion molecule to successfully deglycosylate discrete glycans on the surface of the bound Spike protein, and shows improved neutralization potency over the unmodified parental antibody. In the second strategy, we generated a triparatopic molecule targeting all three HR2 domains in a single Spike trimer simultaneously, aimed at preventing the drastic conformational changes that the HR2 domains undergo in the context of an infection.

We’ve demonstrated by SEC-MALS that the triparatopic molecule we generated binds in a one-to-one ratio with recombinant Spike trimer and subsequently have shown an improvement in pseudoviral neutralization potency over bi- and mono-valent binders. Overall, our data suggests that new molecule formats that target steps in the mechanism of viral infection other than initial receptor recognition can deliver potent neutralization that should be remembered for future pandemic preparedness efforts.

Andrew DiChiara, Senior Scientist II, AbbVie

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Andrew DiChiara / Innovative strategies for neutralizing viral entry and application to future pandemics

Andrew DiChiara, Senior Scientist II,
AbbVie

Andrew received his B.S. in Chemistry from Boston College in 2008, and his Ph.D. in Biological Chemistry from Massachusetts Institute of Technology in 2012. Since completing his thesis work, he has been part of the Biotherapeutics and Genetic Medicine department at AbbVie in Worcester, MA. Focusing ...

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