Systematic screening of kidney transplant patients points towards deficits in neutralizing antibody capacity against sars-cov-2

ABSTRACT

Purpose: The majority of kidney transplant recipients (KTR) is able to develop SARS-CoV-2 antibodies (Abs). Little is known about the virus neutralizing capacity of these Abs. Methods: KTR were systematically screened for SARS-CoV-2 at the Antwerp University Hospital by nasopharyngeal swab and serum sampling for the detection of respectively SARS-CoV-2 RNA and SARS-CoV-2 IgG Abs using an in-house Luminex assay. Results of Abs against the nucleocapsid protein (NP) and Receptor- Binding Domain (RBD) of the spike protein were expressed as Median Fluorescence Intensities (MFI). Virus neutralisation assays were performed on serum samples of patients with SARS-CoV-2 Abs or a positive RT-PCR test and on samples of an age and sex matched control group of 23 COVID-19 positive immunocompetent patients. Results: 135 KTR were included;13 were known to be RT-PCR positive. Of these 13, 10 (77%) tested positive for SARS-CoV-2 Abs. Antibody screening revealed two (2%) additional KTR with detectable Abs. Virus neutralizing capacity was observed in 11/12 (92%) antibody positive KTR vs. 22/23 (96%) immunocompetent antibody positive controls (p = 0.63). In patients who showed virus neutralizing capacity (expressed as sample dilution reducing the number of infected wells by 50% (NT50)), significantly higher neutralizing antibody capacity was observed in immunocompetent controls vs. KTR (median NT50 1027 (IQR 395-1601) vs. 217 (IQR 108-534);p=0.01). There was no difference in IgG-NP MFI and IgG-RBD MFI values between both groups (median IgG NP MFI 24554 (IQR 11218-27017) vs. 11387 (IQR 3062-24825);p = 0.13);median IgG RBD MFI 20302 (IQR 13464- 24251) vs. 21736 (6288-24993);p = 0.85). Conclusions: Our results suggest that KTR have lower neutralizing antibody capacity compared to immunocompetent subjects. The latter might be of high importance for future COVID-19 vaccine trials.