Early induction of anti-Spike binding antibodies and T cells confer protection against COVID-19 in children during an Omicron wave (preprint)

For improved safety, children are vaccinated with a lower dose and extended interval for mRNA COVID-19 vaccines; however, whether there is protection before dose 2 is unknown. We recruited 113 children receiving BNT162b2 primary vaccination during an Omicron wave. After dose 1, 96% had detectable anti-Spike(S) IgG and 100% had S-reactive T cells; those with both had a lower risk of symptomatic infection compared to those with undetectable anti-S IgG [RR 0.19 (95% CI; 0.06, 0.59)]. This suggests that dosing can be extended without risk of insufficient early protection.

Immune gene expression analysis indicates the potential of a self-amplifying Covid-19 mRNA vaccine (preprint)

Remarkable potency has been demonstrated for mRNA vaccines in reducing the global burden of the ongoing COVID-19 pandemic. This vaccine platform has been extended to encode an alphavirus replicase that self-amplifies the full length mRNA and SARS-CoV-2 spike (S) transgene (self-amplifying mRNA or sa mRNA). However, early phase clinical trials of sa-mRNA COVID-19 vaccine candidates have questioned the potential of this platform to develop potent vaccines. We examined the immune gene response to a candidate sa-mRNA vaccine against COVID-19, and compared our findings to the host response to other forms of vaccines. In blood samples from healthy volunteers that participated in a phase I/II clinical trial, greater induction of transcripts involved in Toll-like receptor (TLR) signalling, antigen presentation and complement activation at 1 day post-vaccination was associated with higher anti-S antibody titers. Conversely, transcripts involved in T-cell maturation at day 7 post-vaccination informed the magnitude of eventual anti-S T-cell responses. The transcriptomic signature for ARCT-021 vaccination strongly correlated with live viral vector vaccines, adjuvanted vaccines and BNT162b2. Correlation with live attenuated vaccines was weaker. Our findings suggest the potential for sa-mRNA to be further developed to be among the most potent forms of vaccines in our arsenal to prevent infectious diseases.

A phase 1/2 randomized, double-blinded, placebo controlled ascending dose trial to assess the safety, tolerability and immunogenicity of ARCT-021 in healthy adults (preprint)

BackgroundThe pandemic of coronavirus disease-19 (Covid-19) continues to afflict the lives and livelihoods of many as global demand for vaccine supply remains unmet. MethodsPhase 1 of this trial (N=42) assessed the safety, tolerability and immunogenicity of ascending levels of one-dose ARCT-021, a self-amplifying mRNA vaccine against Covid-19. Phase 2 (N=64) tested two-doses of ARCT-021 given 28 days apart. Both young and older adults were enrolled. The primary safety outcomes were local and systemic solicited adverse events (AEs) reported immediately and up to 7 days post-inoculation and unsolicited events reported up to 56 days after inoculation. Secondary and exploratory outcomes were antibody and T cell responses to vaccination, respectively. ResultsARCT-021 was well tolerated up to one 7.5 g dose and two 5.0 g doses. Local solicited AEs, namely injection-site pain and tenderness, as well as systemic solicited AEs, such as fatigue, headache and myalgia, were more common in ARCT-021 than placebo recipients, and in younger than older adults. Seroconversion rate for anti-S IgG was 100% in all cohorts except for the 1 g one-dose in younger adults and the 7.5 g one-dose in older adults, which were each 80%. Neutralizing antibody titers increased with increasing dose although the responses following 5.0 g and 7.5 g ARCT-021 were similar. Anti-S IgG titers overlapped with those in Covid-19 convalescent plasma. ARCT-021 also elicited T-cell responses against the S glycoprotein. ConclusionTaken collectively, the favorable safety and immunogenicity profiles support further clinical development of ARCT-021.

Early T Cell and Binding Antibody Responses are Associated with COVID-19 RNA Vaccine Efficacy Onset (preprint)

RNA vaccines against Covid-19 have demonstrated ~95% efficacy in Phase III clinical trials. Although complete vaccination consisted of two-doses, the onset of protection for both licensed RNA vaccines was observed as early as 12 days after a single dose. The adaptive immune response that coincides with this onset of protection could represent the necessary elements of immunity against Covid-19. Herein, we tracked the early adaptive immune responses after Covid-19 RNA vaccination, in a cohort of 20 healthcare workers. Our findings suggest that early T cell and binding antibody responses, rather than either receptor-blocking or virus neutralizing activity, induced early protection against Covid-19.Funding: This study was partially funded through a generousdonation from The Hourglass to support Covid-19 research in ViREMiCS. SK receives salary support from the Transition Award, RdA receives funding from the Open Research Fund Young Investigator Award, JGL and EEO receive salary support from the Clinician Scientist Award, and AB receives salary support from the Singapore Translational Research Award, all administered by the National Medical Research Council of Singapore.Conflict of Interest: Duke-NUS Medical School is in partnership with Arcturus Therapeutics to develop a self-replicating RNA vaccine against Covid-19, with EEO as the principal investigator. No monetary or personal benefits are derived from this partnership.Ethical Approval: This study was approved by the SingHealth Centralized Institutional Review Board (CIRB/F2021/2014). Healthcare workers (HCWs) from the Singapore Health Services institutions whowere eligible for Covid-19 vaccination were invited to participate in this study, and written informed consent was obtained.

The discovery of gene mutations making SARS-CoV-2 well adapted for humans: host-genome similarity analysis of 2594 genomes from China, the USA and Europe (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive-sense single-stranded virus approximately 30 kb in length, causes the ongoing novel coronavirus disease-2019 (COVID-19). Studies confirmed significant genome differences between SARS-CoV-2 and SARS-CoV, suggesting that the distinctions in pathogenicity might be related to genomic diversity. However, the relationship between genomic differences and SARS-CoV-2 fitness has not been fully explained, especially for open reading frame (ORF)-encoded accessory proteins. RNA viruses have a high mutation rate, but how SARS-CoV-2 mutations accelerate adaptation is not clear. This study shows that the host-genome similarity (HGS) of SARS-CoV-2 is significantly higher than that of SARS-CoV, especially in the ORF6 and ORF8 genes encoding proteins antagonizing innate immunity in vivo . A power law relationship was discovered between the HGS of ORF3b, ORF6, and N and the expression of interferon (IFN)-sensitive response element (ISRE)-containing promoters. This finding implies that high HGS of SARS-CoV-2 genome may further inhibit IFN I synthesis and cause delayed host innate immunity. An ORF1ab mutation, 10818G>T, which occurred in virus populations with high HGS but rarely in low-HGS populations, was identified in 2594 genomes with geolocations of China, the USA and Europe. The 10818G>T caused the amino acid mutation M37F in the transmembrane protein nsp6. The results suggest that the ORF6 and ORF8 genes and the mutation M37F may play important roles in causing COVID-19. The findings demonstrate that HGS analysis is a promising way to identify important genes and mutations in adaptive strains, which may help in searching potential targets for pharmaceutical agents.

A Single Dose of Self-Transcribing and Replicating RNA Based SARS-CoV-2 Vaccine Produces Protective Adaptive Immunity In Mice (preprint)

A self-transcribing and replicating RNA (STARR) based vaccine (LUNAR-COV19) has been developed to prevent SARS-CoV-2 infection. The vaccine encodes an alphavirus-based replicon and the SARS-CoV-2 full length spike glycoprotein. Translation of the replicon produces a replicase complex that amplifies and prolong SARS-CoV-2 spike glycoprotein expression. A single prime vaccination in mice led to robust antibody responses, with neutralizing antibody titers increasing up to day 60. Activation of cell mediated immunity produced a strong viral antigen specific CD8+ T lymphocyte response. Assaying for intracellular cytokine staining for IFN-gamma; and IL-4 positive CD4+ T helper lymphocytes as well as anti-spike glycoprotein IgG2a/IgG1 ratios supported a strong Th1 dominant immune response. Finally, single LUNAR-COV19 vaccination at both 2 microgram and 10 microgram doses completely protected human ACE2 transgenic mice from both mortality and even measurable infection following wild-type SARS-CoV-2 challenge. Our findings collectively suggest the potential of Lunar-COV19 as a single dose vaccine.