*Purpose: The purpose of this study was to determine the effect of SARS-CoV-2 infection on the immune response in Kidney Transplant Waitlist Candidates (KTWC) and its clinical impact on their ability to get transplanted.

*Methods: Initial kidney transplant work-ups were performed including high resolution HLA typing, Flow PRA and single antigen bead assessment of anti-HLA antibody specificities pre-COVID-19 pandemic. Our study group contained 12 KTWC with known positive COVID tests ranging in age from 29-71 years, predominantly Hispanic (75%) and all were male gender. Serum samples were tested pre COVID-19 pandemic and at the time of a positive COVID-19 test using the Luminex based LABScreen COVID Plus assay (One Lambda). IgM and IgG immune responses to SARS-CoV-2 were assessed for a panel of spike, RBD and nucleocapsid determinants as well as other common coronaviruses.

*Results: KTWC who tested positive for SARS-CoV-2 by RT-PCR (92%) developed robust IgG responses to all five SARS-CoV-2 antigens expressed in the bead panel. Furthermore, 66% additionally produced IgM responses to SARS-CoV-2 antigens with predominance towards spike proteins and only 17% positive for nucleocapsid protein. 33% of KTWC lost their IgM antibody positivity to SARS-CoV-2 antigens while maintaining significantly strong IgG reactivity suggesting patients were in various phases of SARS-CoV-2 infection. Within other coronaviruses tested KTWC produced strong responses to the spike proteins from common human coronaviruses 229E, NL63, OC43 and HKU1. Surprisingly, 67% of KTWC also had significant IgG immunity to the SARS-CoV Spike S1 protein. Pre-pandemic sera did not show any antibody responses to SARS-CoV-2 proteins however, immunity to common coronaviruses remained high. We did not observe a change in KTWC PRA levels or subsequent rise in anti-HLA antibodies in post SARS CoV-2 infection. There was no association between HLA antigens and degree of either IgM or IgG responses to SARS-CoV-2 or common coronaviruses.

*Conclusions: During the COVID-19 pandemic it is critical to have the tools to accurately detect immunity to the SARS-CoV-2 virus. The unintended consequences of SARS-CoV-2 infection in patients awaiting transplant needed to be explored. KTWP were able to mount an effective immune response to 5 distinct protein domains on SARS-CoV-2. Patients with active infection produced both IgM and IgG antibodies against SARS-CoV-2. Despite mounting a stong immune response to SARS-CoV-2 no additional HLA sensitization was observed. Tracking how long these IgG antibodies to SARS-CoV-2 domains persist in patient sera will continue to inform us in how long a patient might remain protected and the effectiveness of a SARS-CoV-2 vaccine once administered.

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