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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has been responsible for a global pandemic. Monoclonal antibodies (mAbs) have been used as antiviral therapeutics; however, these therapeutics have been limited in efficacy by viral sequence variability in emerging variants of concern (VOCs) and in deployment by the need for high doses. In this study, we leveraged the multi-specific, multi-affinity antibody (Multabody, MB) platform, derived from the human apoferritin protomer, to enable the multimerization of antibody fragments. MBs were shown to be highly potent, neutralizing SARS-CoV-2 at lower concentrations than their corresponding mAb counterparts. In mice infected with SARS-CoV-2, a tri-specific MB targeting three regions within the SARS-CoV-2 receptor binding domain was protective at a 30-fold lower dose than a cocktail of the corresponding mAbs. Furthermore, we showed in vitro that mono-specific MBs potently neutralize SARS-CoV-2 VOCs by leveraging augmented avidity, even when corresponding mAbs lose their ability to neutralize potently, and that tri-specific MBs expanded the neutralization breadth beyond SARS-CoV-2 to other sarbecoviruses. Our work demonstrates how avidity and multi-specificity combined can be leveraged to confer protection and resilience against viral diversity that exceeds that of traditional monoclonal antibody therapies. Editor's summary: Monoclonal antibodies targeting SARS-CoV-2 have become an essential component in the treatment toolbox. However, as new variants have emerged, these antibodies can lose their potency, sometimes drastically. To avoid this, Burn Aschner et al. generated SARS-CoV-2–specific multimerized antibodies, called Multabodies, that leverage improved avidity and multiple specificities to better target SARS-CoV-2. The Multabodies potently neutralized SARS-CoV-2 variants and other sarbecoviruses in vitro and conferred protection against SARS-CoV-2 in vivo when administered at low concentration. Together, these data highlight the potential clinical benefit of the Multabody platform as a therapeutic for SARS-CoV-2. –Courtney Malo [ABSTRACT FROM AUTHOR]

Deep mining of B cell repertoires of HIV-1-infected individuals has resulted in the isolation of dozens of HIV-1 broadly neutralizing antibodies (bNAbs). Yet, it remains uncertain whether any such bNAbs alone are sufficiently broad and potent to deploy therapeutically. Here, we engineered HIV-1 bNAbs for their combination on a single multispecific and avid molecule via direct genetic fusion of their Fab fragments to the human apoferritin light chain. The resulting molecule demonstrated a remarkable median IC50 value of 0.0009 µg/mL and 100% neutralization coverage of a broad HIV-1 pseudovirus panel (118 isolates) at a 4 µg/mL cutoff--a 32-fold enhancement in viral neutralization potency compared to a mixture of the corresponding HIV-1 bNAbs. Importantly, Fc incorporation on the molecule and engineering to modulate Fc receptor binding resulted in IgG-like bioavailability in vivo. This robust plug-and-play antibody design is relevant against indications where multispecificity and avidity are leveraged simultaneously to mediate optimal biological activity. [ABSTRACT FROM AUTHOR]

SARS-CoV-2, the virus responsible for COVID-19, has caused a global pandemic. Antibodies can be powerful biotherapeutics to fight viral infections. Here, we use the human apoferritin protomer as a modular subunit to drive oligomerization of antibody fragments and transform antibodies targeting SARS-CoV-2 into exceptionally potent neutralizers. Using this platform, half-maximal inhibitory concentration (IC50) values as low as 9 × 10−14 M are achieved as a result of up to 10,000-fold potency enhancements compared to corresponding IgGs. Combination of three different antibody specificities and the fragment crystallizable (Fc) domain on a single multivalent molecule conferred the ability to overcome viral sequence variability together with outstanding potency and IgG-like bioavailability. The MULTi-specific, multi-Affinity antiBODY (Multabody or MB) platform thus uniquely leverages binding avidity together with multi-specificity to deliver ultrapotent and broad neutralizers against SARS-CoV-2. The modularity of the platform also makes it relevant for rapid evaluation against other infectious diseases of global health importance. Neutralizing antibodies are a promising therapeutic for SARS-CoV-2. Here, the authors combine three different antibody specificities and an Fc domain on a single multivalent molecule, resulting in high neutralization activity despite viral sequence variability. [ABSTRACT FROM AUTHOR]

Subunit vaccines typically require co-administration with an adjuvant to elicit protective immunity, adding development hurdles that can impede rapid pandemic responses. To circumvent the need for adjuvant in a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) subunit vaccine, we engineer a thermostable immunotargeting vaccine (ITV) that leverages the pan-HLA-DR monoclonal antibody 44H10 to deliver the viral spike protein receptor-binding domain (RBD) to antigen-presenting cells. X-ray crystallography shows that 44H10 binds to a conserved epitope on HLA-DR, providing the basis for its broad HLA-DR reactivity. Adjuvant-free ITV immunization in rabbits and ferrets induces robust anti-RBD antibody responses that neutralize SARS-CoV-2 variants of concern and protect recipients from SARS-CoV-2 challenge. We demonstrate that the modular nature of the ITV scaffold with respect to helper T cell epitopes and diverse RBD antigens facilitates broad sarbecovirus neutralization. Our findings support anti-HLA-DR immunotargeting as an effective means to induce strong antibody responses to subunit antigens without requiring an adjuvant. [Display omitted] • Modular ITV design consists of SARS-CoV-2 spike RBD fused to a pan-MHC class II mAb • Structure of conserved epitope on HLA-DR offers molecular basis of broad reactivity • Adjuvant-free ITV immunization elicits broad neutralizing Ab responses in rabbits • Adjuvant-free ITV immunization protects ferrets from SARS-CoV-2 challenge Kassardjian et al. engineer and characterize a modular vaccine scaffold for the delivery of antigen to MHC class II on antigen-presenting cells. This protein vaccine induces broad sarbecovirus neutralizing antibody responses and protects from SARS-CoV-2 viral challenge independently of adjuvant co-administration. [ABSTRACT FROM AUTHOR]

Current coronavirus (CoV) vaccines primarily target immunodominant epitopes in the S1 subunit, which are poorly conserved and susceptible to escape mutations, thus threatening vaccine efficacy. Here, we use structure-guided protein engineering to remove the S1 subunit from the Middle East respiratory syndrome (MERS)-CoV spike (S) glycoprotein and develop stabilized stem (SS) antigens. Vaccination with MERS SS elicits cross-reactive β-CoV antibody responses and protects mice against lethal MERS-CoV challenge. High-throughput screening of antibody-secreting cells from MERS SS-immunized mice led to the discovery of a panel of cross-reactive monoclonal antibodies. Among them, antibody IgG22 binds with high affinity to both MERS-CoV and severe acute respiratory syndrome (SARS)-CoV-2 S proteins, and a combination of electron microscopy and crystal structures localizes the epitope to a conserved coiled-coil region in the S2 subunit. Passive transfer of IgG22 protects mice against both MERS-CoV and SARS-CoV-2 challenge. Collectively, these results provide a proof of principle for cross-reactive CoV antibodies and inform the development of pan-CoV vaccines and therapeutic antibodies. [Display omitted] • Structure-guided design generates MERS-CoV spike stabilized stem (SS) antigens • Cross-reactive CoV-spike-stem-specific monoclonal antibodies • Structures of the Fab22-spike complexes reveal a conserved, protective epitope • Passive transfer of IgG22 protects mice against MERS-CoV and SARS-CoV-2 challenge Hsieh et al. generate MERS-CoV spike stabilized stem (SS) antigens using a structure-guided approach. Mice immunized with MERS SS are protected against MERS-CoV challenge and used for isolation of cross-reactive monoclonal antibodies, including IgG22, which protects mice against MERS-CoV and SARS-CoV-2 challenges. Structures of Fab22-spike complexes reveal a conserved epitope. [ABSTRACT FROM AUTHOR]