Determinants and Mechanisms of the Low Fusogenicity and Endosomal Entry of Omicron Subvariants (preprint)

The rapid spread and strong immune evasion of the SARS-CoV-2 Omicron subvariants has raised serious concerns for the global COVID-19 pandemic. These new variants exhibit reduced fusogenicity and increased endosomal entry pathway utilization compared to the ancestral D614G variant, the underlying mechanisms of which remain elusive. Here we show that the C-terminal S1 mutations of the BA.1.1 subvariant, H655Y and T547K, critically govern the low fusogenicity of Omicron. Notably, H655Y also dictates the enhanced endosome entry pathway utilization. Mechanistically, T547K and H655Y likely stabilize the spike trimer conformation, as shown by increased molecular interactions in structural modeling as well as reduced S1 shedding. Importantly, the H655Y mutation also determines the low fusogenicity and high dependence on the endosomal entry pathway of other Omicron subvariants, including BA.2, BA.2.12.1, BA.4/5 and BA.2.75. These results uncover mechanisms governing Omicron subvariant entry and provide insights into altered Omicron tissue tropism and pathogenesis.

Prime-pull immunization of mice with a BcfA-adjuvanted vaccine elicits mucosal immunity and prevents SARS CoV-2 infection and pathology (preprint)

Vaccines against SARS-CoV-2 that induce mucosal immunity capable of preventing infection and disease remain urgently needed. We show that intramuscular priming of mice with an alum and BcfA-adjuvanted Spike subunit vaccine, followed by a BcfA-adjuvanted mucosal booster, generated Th17 polarized tissue resident CD4+ T cells, and mucosal and serum antibodies. The serum antibodies efficiently neutralized SARS-CoV-2 and its Delta variant, suggesting cross-protection against a recent variant of concern (VOC). Immunization with this heterologous vaccine prevented weight loss following challenge with mouse-adapted SARS-CoV-2 and reduced viral replication in the nose and lungs. Histopathology showed a strong leukocyte and polymorphonuclear (PMN) cell infiltrate without epithelial damage in mice immunized with BcfA-containing vaccines. In contrast, viral load was not reduced in the upper respiratory tract of IL-17 knockout mice immunized with the same formulation, suggesting that the Th17 polarized T cell responses are critical for protection. We show that vaccines adjuvanted with alum and BcfA, delivered through a heterologous prime-pull regimen, protect against SARS-CoV-2 infection without causing enhanced respiratory disease.

Suppression of de novo antibody responses against SARS-CoV2 and the Omicron variant after mRNA vaccination and booster in patients with B cell malignancies undergoing active treatment, but maintenance of pre-existing antibody levels against endemic viruses. (preprint)

The impact of SARS-CoV2 vaccination in cancer patients remains incompletely understood given the heterogeneity of cancer and cancer therapies. We assessed vaccine-induced antibody response to the SARS-CoV2 Omicron (B.1.1.529) variant in 57 patients with B cell malignancies with and without active B cell-targeted therapy. Ancestral- and Omicron- reactive antibody levels were determined by ELISA and neutralization assays. In over one third of vaccinated patients at the pre-booster timepoint, there were no ELISA-detectable antibodies against either the ancestral strain or Omicron variant. The lack of vaccine-induced antibodies was predominantly in patients receiving active therapy such as anti-CD20 monoclonal antibody (mAb) or Bruton's tyrosine kinase inhibitors (BTKi). While booster immunization was able to induce detectable antibodies in a small fraction of seronegative patients, the benefit was disproportionately evident in patients not on active therapy. Importantly, in patients with post-booster ELISA-detectable antibodies, there was a positive correlation of antibody levels against the ancestral strain and Omicron variant. Booster immunization increased overall antibody levels, including neutralizing antibody titers against the ancestral strain and Omicron variant; however, predominantly in patients without active therapy. Furthermore, ancestral strain neutralizing antibody titers were about 5-fold higher in comparison with those to Omicron, suggesting that even with booster administration, there may be reduced protection against the Omicron variant. Interestingly, in almost all patients regardless of active therapy, including those unable to generate detectable antibodies against SARS-CoV2 spike, we observed comparable levels of EBV, influenza, and common cold coronavirus reactive antibodies demonstrating that B cell-targeting therapies primarily impair de novo but not pre-existing antibody levels. These findings suggest that patients with B cell malignancies on active therapy may be at disproportionately higher risk to new versus endemic viral infection and suggest utility for vaccination prior to B cell-targeted therapy.

mRNA Booster Vaccines Elicit Strong Protection Against SARS-CoV-2 Omicron Variant in Cancer Patients (preprint)

Following its emergence in late November of 2020, the SARS-CoV-2 Omicron (B.1.1.529) variant has caused major global public health concerns. We recently demonstrated that in healthy adults the Omicron variant exhibits strong resistance to immunity induced by two doses of the mRNA vaccines, but a booster mRNA vaccine dose can provide strong protection against Omicron. However, it is currently unknown how well these mRNA vaccine boosters protect immunocompromised groups, including cancer patients, from the Omicron variant. Here we show that (1) neutralizing antibody (nAb) titers against the Delta and Omicron variants in cancer patients after two-dose mRNA vaccines are 4.2-fold and 21.3-fold lower, respectively, compared to the ancestral D614G, and (2) nAb titers against the Delta and Omicron variants in boosted cancer patients are 3.6-fold and 5.1-fold lower, respectively, compared to D614G. Our findings highlight the effectiveness and need for booster vaccination strategies in immunocompromised groups including cancer patients to protect from the Omicron variant.

Loss of Neutralizing Antibody Response to mRNA Vaccination against SARS-CoV-2 Variants: Differing Kinetics and Strong Boosting by Breakthrough Infection (preprint)

The waning efficacy of SARS-CoV-2 vaccines combined with the continued emergence of variants resistant to vaccine-induced immunity has reignited debate over the need for booster vaccines. To address this, we examined the neutralizing antibody (nAb) response against four major SARS-CoV-2 variants--D614G, Alpha (B.1.1.7), Beta (B.1.351), and Delta (B.1.617.2)--in health care workers (HCWs) at pre-vaccination, post-first and post-second mRNA vaccine dose, and six months post-second mRNA vaccine dose. Neutralizing antibody titers against all variants, especially the Delta variant, declined dramatically from four weeks to six months post-second mRNA vaccine dose. Notably, SARS-CoV-2 infection enhanced vaccine durability, and mRNA-1273 vaccinated HCWs also exhibited ~2-fold higher nAb titers than BNT162b2 vaccinated HCWs. Together these results demonstrate possible waning of protection from infection against SARS-CoV-2 Delta variant based on decreased nAb titers, dependent on COVID-19 status and the mRNA vaccine received.

Impaired Neutralizing Antibody Response to COVID-19 mRNA Vaccines in Cancer Patients (preprint)

There is currently a critical need to determine the efficacy of SARS-CoV-2 vaccination for immunocompromised patients. In this study, we determined the neutralizing antibody response in 160 cancer patients diagnosed with chronic lymphocytic leukemia (CLL), lung cancer, breast cancer, and various non-Hodgkins lymphomas (NHL), after they received two doses of mRNA vaccines. Serum from 46 mRNA vaccinated health care workers (HCWs) served as healthy controls. We discovered that (1) cancer patients exhibited reduced neutralizing antibody titer (NT50) compared to HCWs; (2) CLL and NHL patients exhibited the lowest NT50 levels, with 50-60% of them below the detection limit; (3) mean NT50 levels in patients with CLL and NHL was [~]2.6 fold lower than those with solid tumors; and (4) cancer patients who received anti-B cell therapy exhibited significantly reduced NT50 levels. Our results demonstrate an urgent need for novel immunization strategies for cancer patients against SARS-CoV-2, particularly those with hematological cancers and those on anti-B cell therapies.

Lung-selective Cas13d-based nanotherapy inhibits lethal SARS-CoV-2 infection by targeting host protease Ctsl (preprint)

SUMMARY The COVID-19 pandemic persists as a global health crisis for which curative treatment has been elusive. Development of effective and safe anti-SARS-CoV-2 therapies remains an urgent need. SARS-CoV-2 entry into cells requires specific host proteases including TMPRSS2 and Cathepsin L (Ctsl) 1–3 , but there has been no reported success in inhibiting host proteases for treatment of SARS-CoV-2 pathogenesis in vivo . Here we have developed a lung Ctsl mRNA-targeted, CRISPR/Cas13d-based nanoparticle therapy to curb fatal SARS-CoV-2 infection in a mouse model. We show that this nanotherapy can decrease lung Ctsl expression in normal mice efficiently, specifically, and safely. Importantly, this lung-selective Ctsl -targeted nanotherapy significantly extended the survival of lethally SARS-CoV-2 infected mice by decreasing lung virus burden, reducing expression of pro-inflammatory cytokines/chemokines, and diminishing the severity of pulmonary interstitial inflammation. Additional in vitro analyses demonstrated that Cas13d-mediated Ctsl knockdown inhibited infection mediated by the spike protein of SARS-CoV-1, SARS-CoV-2, and more importantly, the authentic SARS-CoV-2 B.1.617.2 Delta variant, regardless of TMPRSS2 expression status. Our results demonstrate the efficacy and safety of a lung-selective, Ctsl -targeted nanotherapy against infection by SARS-CoV-2 and likely other emerging coronaviruses, forming a basis for investigation of this approach in clinical trials.

Immunological Insights Into the Therapeutic Roles of CD24Fc Against Severe COVID-19 (preprint)

BACKGROUNDSARS-CoV-2 causes COVID-19 through direct lysis of infected lung epithelial cells, which releases damage-associated molecular patterns (DAMPs) and induces a pro-inflammatory cytokine milieu causing systemic inflammation. Anti-viral and anti-inflammatory agents have shown limited therapeutic efficacy. Soluble CD24 (CD24Fc) is able to blunt the broad inflammatory response induced by DAMPs in multiple models. A recent randomized phase III trial evaluating the impact of CD24Fc in patients with severe COVID-19 demonstrated encouraging clinical efficacy. METHODSWe studied peripheral blood samples obtained from patients enrolled at a single institution in the SAC-COVID trial (NCT04317040) collected before and after treatment with CD24Fc or placebo. We performed high dimensional spectral flow cytometry analysis of peripheral blood mononuclear cells and measured the levels of a broad array of cytokines and chemokines. A systems analytical approach was used to discern the impact of CD24Fc treatment on immune homeostasis in patients with COVID-19. FINDINGSTwenty-two patients were enrolled, and the clinical characteristics from the CD24Fc vs. placebo groups were matched. Using high-content spectral flow cytometry and network-level analysis, we found systemic hyper-activation of multiple cellular compartments in the placebo group, including CD8+ T cells, CD4+ T cells, and CD56+ NK cells. By contrast, CD24Fc-treated patients demonstrated blunted systemic inflammation, with a return to homeostasis in both NK and T cells within days without compromising the ability of patients to mount an effective anti-Spike protein antibody response. A single dose of CD24Fc significantly attenuated induction of the systemic cytokine response, including expression of IL-10 and IL-15, and diminished the coexpression and network connectivity among extensive circulating inflammatory cytokines, the parameters associated with COVID-19 disease severity. INTERPRETATIONOur data demonstrates that CD24Fc treatment rapidly down-modulates systemic inflammation and restores immune homeostasis in SARS-CoV-2-infected individuals, supporting further development of CD24Fc as a novel therapeutic against severe COVID-19. FUNDINGNIH

NSUN2-mediated m5C methylation of IRF3 mRNA negatively regulates type I interferon responses (preprint)

5-Methylcytosine (m 5 C) is a widespread post-transcriptional RNA modification and is reported to be involved in manifold cellular responses and biological processes through regulating RNA metabolism. However, its regulatory role in antiviral innate immunity has not yet been elucidated. Here, we report that NSUN2, a typical m 5 C methyltransferase, can negatively regulate type I interferon responses during viral infection. NSUN2 specifically mediates m 5 C methylation of IRF3 mRNA and accelerates its degradation, resulting in low levels of IRF3 and downstream IFN-β production. Knockout or knockdown of NSUN2 could enhance type I interferon responses and downstream ISG expression after viral infection in vitro . And in vivo , the antiviral innate responses is more dramatically enhanced in Nsun2 +/− mice than in Nsun2 +/+ mice. Four highly m 5 C methylated cytosines in IRF3 mRNA were identified, and their mutation could enhance the cellular IRF3 mRNA levels. Moreover, infection with Sendai virus (SeV), vesicular stomatitis virus (VSV), herpes simplex virus 1 (HSV-1), Zika virus (ZIKV), or especially SARS-CoV-2 resulted in a reduction in endogenous levels of NSUN2. Together, our findings reveal that NSUN2 serves as a negative regulator of interferon response by accelerating the fast turnover of IRF3 mRNA, while endogenous NSUN2 levels decrease after viral infection to boost antiviral responses for the effective elimination of viruses. Our results suggest a paradigm of innate antiviral immune responses ingeniously involving NSUN2-mediated m 5 C modification.

SARS-CoV-2 Spreads through Cell-to-Cell Transmission (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible coronavirus responsible for the global COVID-19 pandemic. Herein we provide evidence that SARS-CoV-2 spreads through cell-cell contact in cultures, mediated by the spike glycoprotein. SARS-CoV-2 spike is more efficient in facilitating cell-to-cell transmission than SARS-CoV spike, which reflects, in part, their differential cell-cell fusion activity. Interestingly, treatment of cocultured cells with endosomal entry inhibitors impairs cell-to-cell transmission, implicating endosomal membrane fusion as an underlying mechanism. Compared with cell-free infection, cell-to-cell transmission of SARS-CoV-2 is refractory to inhibition by neutralizing antibody or convalescent sera of COVID-19 patients. While ACE2 enhances cell-to-cell transmission, we find that it is not absolutely required. Notably, despite differences in cell-free infectivity, the variants of concern (VOC) B.1.1.7 and B.1.351 have similar cell-to-cell transmission capability. Moreover, B.1.351 is more resistant to neutralization by vaccinee sera in cell-free infection, whereas B.1.1.7 is more resistant to inhibition by vaccine sera in cell-to-cell transmission. Overall, our study reveals critical features of SARS-CoV-2 spike-mediated cell-to-cell transmission, with important implications for a better understanding of SARS-CoV-2 spread and pathogenesis.

Neutralizing antibody against SARS-CoV-2 spike in COVID-19 patients, health care workers and convalescent plasma donors: a cohort study using a rapid and sensitive high-throughput neutralization assay (preprint)

Rapid and specific antibody testing is crucial for improved understanding, control, and treatment of COVID-19 pathogenesis. Herein, we describe and apply a rapid, sensitive, and accurate virus neutralization assay for SARS-CoV-2 antibodies. The new assay is based on an HIV-1 lentiviral vector that contains a secreted intron Gaussia luciferase or secreted Nano-luciferase reporter cassette, pseudotyped with the SARS-CoV-2 spike (S) glycoprotein, and is validated with a plaque reduction assay using an authentic, infectious SARS-CoV-2 strain. The new assay was used to evaluate SARS-CoV-2 antibodies in serum from individuals with a broad range of COVID-19 symptoms, including intensive care unit (ICU) patients, health care workers (HCWs), and convalescent plasma donors. The highest neutralizing antibody titers were observed among ICU patients, followed by general hospitalized patients, HCWs and convalescent plasma donors. Our study highlights a wide phenotypic variation in human antibody responses against SARS-CoV-2, and demonstrates the efficacy of a novel lentivirus pseudotype assay for high-throughput serological surveys of neutralizing antibody titers in large cohorts.