Tam, J. C. H. | bioRxiv Science

bioRxiv2025

Mechanisms for cross-neutralisation of diverse bat sarbecoviruses

The continuing evolution of SARS-CoV-2 variants of concern, and the increasing spillover potential of sarbecoviruses into the human population presents an important and urgent need to discover cross-reactive monoclonal antibodies (mAbs) for future therapeutic use and identify conserved neutralising epitopes that can be used for rationale design of broadly protective sarbecovirus vaccines. Here we study the neutralising epitopes on WIV-1 Spike of three mAbs that confer broad sarbecovirues and SARS-CoV-2 variant neutralisation, including XEC and JN.1. mAb V1WT_06 binds a highly conserved RBD site V epitope that is mediated by the heavy chain alone. V1WT_06 contact residues are highly conserved in circulating viruses suggesting that the epitope is evolutionarily and functionally constrained. mAbs V1WT_41 and VA14_26 bind overlapping RBD class 4 epitopes with differing angles of approach that impact on the degree of ACE2 competition. We show that neutralisation by these mAbs is maintained when virus entry is via Japanese horseshoe bat and Halcyon horseshoe bat ACE2. These mAbs are ideal candidates for therapeutic antibody development and inform the rational design of pan-coronavirus vaccines.

microbiology↗

bioRxiv2025

Spike-specific IgG4 generated post BNT162b2 mRNA vaccination is inhibitory when directly competing with functional IgG subclasses

The rapid development of vaccines against SARS-CoV-2 during the COVID-19 pandemic proved vital in controlling viral spread and reducing mortality and morbidity. Both neutralising activity and effector function activity of Spike-specific antibodies have been shown to be important for their protective and therapeutic activity. However, several recent studies have reported that vaccination with mRNA based COVID-19 vaccines can lead to elevated levels of Spike-specific IgG4, an isotype which is often considered anti-inflammatory due to its reduced binding to Fc{gamma} receptors on immune cells. Here we show that the level of Spike-specific IgG4 produced following BNT162b2 vaccination is impacted by the interval between and frequency of vaccines boosts, prior SARS-CoV-2 infection (hybrid immunity), breakthrough infection and bivalent vaccine boosters. Despite the increase in Spike-specific IgG4 between the 2nd and 3rd BNT162b2 vaccine dose, neutralisation, ADCD and ADCP activity all increased. Through expression of SARS-CoV-2 monoclonal antibodies cloned as IgG1, IgG2, IgG3 and IgG4, we demonstrated that whilst Spike-specific IgG4 had reduced effector function activity, including ADCC, ADCD and ADCP, IgG4 was only inhibitory when directly competing with functional IgG subclasses binding to an overlapping epitope. In the context of polyclonal plasma, ADCC and ADCD activity could not be depleted by addition of high concentrations of a Spike-specific IgG4 mAb cocktail suggesting the non-stimulatory effect of Spike-specific IgG4 may be hidden in more complex scenarios, such as polyclonal mixes in serum.

immunology↗