Omicron sub-lineage BA.5 infection results in attenuated pathology in hACE2 transgenic mice

Pathogenesis and virulence of coronavirus disease: Comparative pathology of animal models for COVID-19

Animal models that can replicate clinical and pathologic features of severe human coronavirus infections have been instrumental in the development of novel vaccines and therapeutics. The goal of this review is to summarize our current understanding of the pathogenesis of coronavirus disease 2019 (COVID-19) and the pathologic features that can be observed in several currently available animal models. Knowledge gained from studying these animal models of SARS-CoV-2 infection can help inform appropriate model selection for disease modelling as well as for vaccine and therapeutic developments.

Delivery of SARS-CoV-2 spike and membrane genes in a single Baculoviral vector enhance the immune breadth against SARS-CoV-2 variants of concern

Although the coronavirus pandemic has ended, new variants of concern (VOCs) continue to emerge. Therefore, novel vaccines targeting VOCs are highly warranted. We initially constructed three recombinant baculovirus-vectored vaccines (AcHERV-COVID19S) carrying the spike genes of the SARS-CoV-2 prototype, Delta, and Omicron BA.1 variants. However, the SARS-CoV-2 spike gene alone could not provide protection against multiple VOCs. To develop a universal vaccine, we constructed a recombinant baculovirus-vectored vaccine (AcHERV-COVID19 OmiM) by introducing the M gene, which is conserved among VOCs, as a secondary cellular immune antigen in addition to the S gene. AcHERV-COVID19 OmiM could provide higher protection against SARS-CoV-2 variants (prototype, Delta, BA.5 and XBB.1) compared with that of AcHERV-COVID19S. The membrane protein of SARS-CoV-2 synergizes with the S gene, thereby enhancing both humoral and cellular immunity against VOCs. Although AcHERV-COVID19 OmiM may not provide sterile protection against new variants, it may help reduce symptoms and curb viral transmission.

SARS-CoV-2 infection induces thymic atrophy mediated by IFN-γ in hACE2 transgenic mice

Pathogenic infections cause thymic atrophy, perturb thymic T-cell development, and alter immunological response. Previous studies reported dysregulated T-cell function and lymphopenia in coronavirus disease-19 (COVID-19). However, immunopathological changes in the thymus associated with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection have not been elucidated. Here, we report that SARS-CoV-2 infects thymocytes, and induces CD4+CD8+ (double positive; DP) T-cell apoptosis leading to thymic atrophy and loss of peripheral TCR repertoire in K18-hACE2 transgenic mice. Infected thymus led to increased CD44+CD25- T-cells, indicating an early arrest in the T-cell maturation pathway. Thymic atrophy was notably higher in male hACE2-Tg mice than in females and involved an upregulated de-novo synthesis pathway of thymic glucocorticoid. Further, IFN-γ was crucial for thymic atrophy, as anti-IFN-γ -antibody neutralization blunted thymic involution. Therapeutic use of Remdesivir also rescued thymic atrophy. While the Omicron variant and its sub-lineage BA.5 variant caused marginal thymic atrophy, the delta variant of SARS-CoV-2 exhibited severe thymic atrophy characterized by severely depleted DP T-cells. Recently characterized broadly SARS-CoV-2 neutralizing monoclonal antibody P4A2 was able to rescue thymic atrophy and restore the thymic maturation pathway of T-cells. Together, we report SARS-CoV-2-associated thymic atrophy resulting from impaired T-cell maturation pathway which may contribute to dyregulated T cell response during COVID-19.

Functional and structural investigation of a broadly neutralizing SARS-CoV-2 antibody

Since its emergence, SARS-CoV-2 has been continuously evolving, hampering the effectiveness of current vaccines against COVID-19. mAbs can be used to treat patients at risk of severe COVID-19. Thus, the development of broadly protective mAbs and an understanding of the underlying protective mechanisms are of great importance. Here, we isolated mAbs from donors with breakthrough infection with Omicron subvariants using a single-B cell screening platform. We identified a mAb, O5C2, which possesses broad-spectrum neutralization and antibody-dependent cell-mediated cytotoxic activities against SARS-CoV-2 variants, including EG.5.1. Single-particle analysis by cryo-electron microscopy revealed that O5C2 targeted an unusually large epitope within the receptor-binding domain of spike protein that overlapped with the angiotensin-converting enzyme 2 binding interface. Furthermore, O5C2 effectively protected against BA.5 Omicron infection in vivo by mediating changes in transcriptomes enriched in genes involved in apoptosis and interferon responses. Our findings provide insights into the development of pan-protective mAbs against SARS-CoV-2.

Potent neutralization by a receptor binding domain monoclonal antibody with broad specificity for SARS-CoV-2 JN.1 and other variants

SARS-CoV-2 continues to be a public health burden, driven in-part by its continued antigenic diversification and resulting emergence of new variants. While increasing herd immunity, current vaccines, and therapeutics have improved outcomes for some; prophylactic and treatment interventions that are not compromised by viral evolution of the Spike protein are still needed. Using a rationally designed SARS-CoV-2 Receptor Binding Domain (RBD) - ACE2 fusion protein and differential selection process with native Omicron RBD protein, we developed a recombinant human monoclonal antibody (hmAb) from a convalescent individual following SARS-CoV-2 Omicron infection. The resulting hmAb, 1301B7 potently neutralized a wide range of SARS-CoV-2 variants including the original Wuhan and more recent Omicron JN.1 strain, as well as SARS-CoV. Structure determination of the SARS-CoV-2 EG5.1 Spike/1301B7 Fab complex by cryo-electron microscopy at 3.1Å resolution demonstrates 1301B7 contacts the ACE2 binding site of RBD exclusively through its VH1-69 heavy chain, making contacts using CDRs1-3, as well as framework region 3 (FR3). Broad specificity is achieved through 1301B7 binding to many conserved residues of Omicron variants including Y501 and H505. Consistent with its extensive binding epitope, 1301B7 is able to potently diminish viral burden in the upper and lower respiratory tract and protect mice from challenge with Omicron XBB1.5 and Omicron JN.1 viruses. These results suggest 1301B7 has broad potential to prevent or treat clinical SARS-CoV-2 infections and to guide development of RBD-based universal SARS-CoV-2 prophylactic vaccines and therapeutic approaches.

Divergent trajectory of replication and intrinsic pathogenicity of SARS-CoV-2 Omicron post-BA.2/5 subvariants in the upper and lower respiratory tract

BACKGROUND

Earlier Omicron subvariants including BA.1, BA.2, and BA.5 emerged in waves, with a subvariant replacing the previous one every few months. More recently, the post-BA.2/5 subvariants have acquired convergent substitutions in spike that facilitated their escape from humoral immunity and gained ACE2 binding capacity. However, the intrinsic pathogenicity and replication fitness of the evaluated post-BA.2/5 subvariants are not fully understood.

METHODS

We systemically investigated the replication fitness and intrinsic pathogenicity of representative post-BA.2/5 subvariants (BL.1, BQ.1, BQ.1.1, XBB.1, CH.1.1, and XBB.1.5) in weanling (3-4 weeks), adult (8-10 weeks), and aged (10-12 months) mice. In addition, to better model Omicron replication in the human nasal epithelium, we further investigated the replication capacity of the post-BA.2/5 subvariants in human primary nasal epithelial cells.

FINDINGS

We found that the evaluated post-BA.2/5 subvariants are consistently attenuated in mouse lungs but not in nasal turbinates when compared with their ancestral subvariants BA.2/5. Further investigations in primary human nasal epithelial cells revealed a gained replication fitness of XBB.1 and XBB.1.5 when compared to BA.2 and BA.5.2.

INTERPRETATION

Our study revealed that the post-BA.2/5 subvariants are attenuated in lungs while increased in replication fitness in the nasal epithelium, indicating rapid adaptation of the circulating Omicron subvariants in the human populations.

FUNDING

The full list of funding can be found at the Acknowledgements section.