Double-blinded, randomised, placebo-controlled trial of convalescent plasma for COVID-19: analyses by neutralising antibodies homologous to recipients' variants

INTRODUCTION

Convalescent plasma (CP) emerged as potential treatment for COVID-19 early in the pandemic. While efficacy in hospitalised patients has been lacklustre, CP may be beneficial at the first stages of disease. Despite multiple new variants emerging, no trials have involved analyses on variant-specific antibody titres of CP.

METHODS

We recruited hospitalised COVID-19 patients within 10 days of symptom onset and, employing a double-blinded approach, randomised them to receive 200 ml convalescent plasma with high (HCP) or low (LCP) neutralising antibody (NAb) titre against the ancestral strain (Wuhan-like variant) or placebo in 1:1:1 ratio. Primary endpoints comprised intubation, corticosteroids for symptom aggravation, and safety assessed as serious adverse events. For a preplanned ad hoc analysis, the patients were regrouped by infused CP's NAb titers to variants infecting the recipients i.e. by titres of homologous HCP (hHCP) or LCP (hLCP).

RESULTS

Of the 57 patients, 18 received HCP, 19 LCP and 20 placebo, all groups smaller than planned. No significant differences were found for primary endpoints. In ad hoc analysis, hHCPrecipients needed significantly less respiratory support, and appeared to be given corticosteroids less frequently (1/14; 7.1%) than those receiving hLCP (9/23; 39.1%) or placebo (8/20; 40%), (p = 0.077).

DISCUSSION

Our double-blinded, placebo-controlled CP therapy trial remained underpowered and does not allow any firm conclusions for early-stage hospitalised COVID-19 patients. Interestingly, however, regrouping by homologous - recipients' variant-specific - CP titres suggested benefits for hHCP. We encourage similar re-analysis of ongoing/previous larger CP studies.

TRIAL REGISTRATION

ClinTrials.gov identifier: NCT0473040.

DUF2285 is a novel helix-turn-helix domain variant that orchestrates both activation and antiactivation of conjugative element transfer in proteobacteria

Horizontal gene transfer is tightly regulated in bacteria. Often only a fraction of cells become donors even when regulation of horizontal transfer is coordinated at the cell population level by quorum sensing. Here, we reveal the widespread 'domain of unknown function' DUF2285 represents an 'extended-turn' variant of the helix-turn-helix domain that participates in both transcriptional activation and antiactivation to initiate or inhibit horizontal gene transfer. Transfer of the integrative and conjugative element ICEMlSymR7A is controlled by the DUF2285-containing transcriptional activator FseA. One side of the DUF2285 domain of FseA has a positively charged surface which is required for DNA binding, while the opposite side makes critical interdomain contacts with the N-terminal FseA DUF6499 domain. The QseM protein is an antiactivator of FseA and is composed of a DUF2285 domain with a negative surface charge. While QseM lacks the DUF6499 domain, it can bind the FseA DUF6499 domain and prevent transcriptional activation by FseA. DUF2285-domain proteins are encoded on mobile elements throughout the proteobacteria, suggesting regulation of gene transfer by DUF2285 domains is a widespread phenomenon. These findings provide a striking example of how antagonistic domain paralogues have evolved to provide robust molecular control over the initiation of horizontal gene transfer.