Search

Measuring immune correlates of disease acquisition and protection in the context of a clinical trial is a prerequisite for improved vaccine design. We analysed binding and neutralizing antibody measurements 4 weeks post vaccination as correlates of risk of moderate to severe-critical COVID-19 through 83 d post vaccination in the phase 3, double-blind placebo-controlled phase of ENSEMBLE, an international randomized efficacy trial of a single dose of Ad26.COV2.S. We also evaluated correlates of protection in the trial cohort. Of the three antibody immune markers we measured, we found most support for 50% inhibitory dilution (ID

Anti-spike IgG binding antibody, anti-receptor binding domain IgG antibody, and pseudovirus neutralizing antibody measurements four weeks post-vaccination were assessed as correlates of risk of moderate to severe-critical COVID-19 outcomes through 83 days post-vaccination and as correlates of protection following a single dose of Ad26.COV2.S COVID-19 vaccine in the placebo-controlled phase of ENSEMBLE, an international, randomized efficacy trial. Each marker had evidence as a correlate of risk and of protection, with strongest evidence for 50% inhibitory dilution (ID50) neutralizing antibody titer. The outcome hazard ratio was 0.49 (95% confidence interval 0.29, 0.81; p=0.006) per 10-fold increase in ID50; vaccine efficacy was 60% (43, 72%) at nonquantifiable ID50 (< 2.7 IU50/ml) and rose to 89% (78, 96%) at ID50 = 96.3 IU50/ml. Comparison of the vaccine efficacy by ID50 titer curves for ENSEMBLE-US, the COVE trial of the mRNA-1273 vaccine, and the COV002-UK trial of the AZD1222 vaccine supported consistency of the ID50 titer correlate of protection across trials and vaccine types.

2716-Pos Board B146 Nuclear Actin Dynamics Regulate Nuclear Organization and Transcription Leo Serebryannyy 1 , Megan Parilla 1 , Paolo Annibale 2 , Christina Cruz 1 , Dmitri Kudryashov 3 , Enrico Gratton 2 , Cara J. Gottardi 4 , Primal de Lanerolle 1 . Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL, USA, 2 Laboratory of Fluorescence Dynamics, University of California at Irvine, Irvine, CA, USA, 3 Chemistry and Biochemistry, Ohio State University, Columbus, OH, USA, 4 Medicine, Northwestern University, Chicago, IL, USA. Actin is an important and elegant mechanotransducer that transfers messages from the extracellular environment into the nucleus, thus conferring changes in both the physical properties and the genetic program of the cell. Although actin in the nucleus has been established in a growing number of functions, the form of nuclear actin remains poorly understood as there are no apparent actin filaments in the nucleus. Therefore, we tested how disrupting the form of nuclear actin impacts function and what effects this may have on the nucleus. To do so, we formed stable nuclear actin filaments using a variety of methods, including the nuclear enrichment of actin binding proteins supervillin and a-E-catenin and the expression of a mutant form of skeletal a-actin. Using fluorescence recovery after photobleaching (FRAP), we found that stabiliza- tion of nuclear actin filaments significantly impairs actin dynamics within the nucleus. The formation of nuclear actin filaments coincides with striking changes in nuclear structure and overall nuclear topography as determined by confocal microscopy and raster image correlation spectroscopy. Using a com- bination of FRAP analysis, structured illumination microscopy and immuno- logical assays, we found that nuclear actin filaments reduce the association of actin with RNA polymerase II and this correlates with impaired RNA poly- merase II dynamics, localization and gene recruitment. Moreover, we were able to recapitulate our findings in purified nuclear extract by using in vitro transcription assays with the covalent actin crosslinking domain (ACD) of V. cholerae MARTX toxin. Based on our data, which help explain the absence of nuclear actin filaments in the interphase mammalian nucleus, we propose a model where nuclear actin dynamics are critical for maintaining proper nu- clear function.