24. Longitudinal Assessment of Immune Responses to COVID-19 Vaccines in Solid Organ Transplant Recipients

Abstract Background mRNA vaccines for coronavirus disease 2019 (COVID-19) illicit strong humoral and cellular responses and have high efficacy for preventing and reducing the risk of severe illness from COVID-19. Since solid organ transplant (SOT) recipients were excluded from the phase 3 trials, the efficacy of the COVID-19 vaccine remains unknown. Understanding the serological responses to COVID vaccines among SOT recipients is essential to better understand vaccine protection for this vulnerable population. Methods In this prospective cohort study, a subset of SOT recipients who were part of our center’s larger antibody study were enrolled prior to receipt of two doses of the BNT162b2 (Pfizer, Inc) vaccine for high resolution immunophenotyping. To date, plasma has been collected for 10 participants on the day of their first dose (baseline), day of their second dose, and 28 days post second dose. 23 healthy participants planning to receive either BNT162b2 or mRNA-1273 (ModernaTX, Inc) were also enrolled, providing plasma at the same timepoints. Ultrasensitive single-molecule array (Simoa) assays were used to detect SARS-CoV-2 Spike (S), S1, receptor-binding domain (RBD) and Nucleocapsid (N) IgG antibodies. Results Participant demographics and SOT recipient characteristics are summarized in Table 1. Low titers of anti-N IgG at all timepoints indicate no natural infection with COVID-19 during the study (Fig 1A). There were significantly lower magnitudes for anti-S (p< 0.0001), anti-S1 (p< 0.0001), and anti-RBD (p< 0.0001) IgG titers on the day of dose 2 and day 28 post second dose for SOT recipients compared to healthy controls (Fig 1B,C,D). Using the internally validated threshold of anti-S IgG >1.07 based on pre-pandemic controls, only 50% of the SOT sub-cohort responded to vaccine after series completion (Fig 2). There was a positive trend between months from transplant and anti-S IgG titer (Fig 3). Table 1: Demographics Figure 1: Anti-N, Anti-S, Anti-S1, Anti-RBD and Anti-N Ig G for healthy v. SOT cohort Black error bars denote median and 95% CI. The dotted line on panel B denotes an internally validated cutoff of 1.07; anti-S IgG titers greater than 1.07 denote a positive response. Figure 3: Time from Transplant v. anti-S IgG Titer SOT recipients further out from transplant tend to have a higher anti-S IgG response. The dotted line denotes an internally validated cutoff, with anti-S IgG titers greater than 1.07 indicating a positive response. Conclusion SOT recipients had a significantly decreased humoral response to mRNA COVID-19 vaccines compared to the healthy cohort, with those further out from transplant more likely to respond. Further research is needed to evaluate T-cell responses and clinical efficacy to maximize the SARS-CoV-2 vaccine response among SOT recipients. Disclosures Ann E. Woolley, MD, MPH, COVAX (Consultant) David Walt, PhD, Quanterix Corporation (Board Member, Shareholder)


Session: O-05. Clinical Quandries in Viral Infections in ICH
Background. mRNA vaccines for coronavirus disease 2019 (COVID-19) illicit strong humoral and cellular responses and have high efficacy for preventing and reducing the risk of severe illness from COVID-19. Since solid organ transplant (SOT) recipients were excluded from the phase 3 trials, the efficacy of the COVID-19 vaccine remains unknown. Understanding the serological responses to COVID vaccines among SOT recipients is essential to better understand vaccine protection for this vulnerable population.
Methods. In this prospective cohort study, a subset of SOT recipients who were part of our center's larger antibody study were enrolled prior to receipt of two doses of the BNT162b2 (Pfizer, Inc) vaccine for high resolution immunophenotyping. To date, plasma has been collected for 10 participants on the day of their first dose (baseline), day of their second dose, and 28 days post second dose. 23 healthy participants planning to receive either BNT162b2 or mRNA-1273 (ModernaTX, Inc) were also enrolled, providing plasma at the same timepoints. Ultrasensitive single-molecule array (Simoa) assays were used to detect SARS-CoV-2 Spike (S), S1, receptor-binding domain (RBD) and Nucleocapsid (N) IgG antibodies.
Results. Participant demographics and SOT recipient characteristics are summarized in Table 1. Low titers of anti-N IgG at all timepoints indicate no natural infection with COVID-19 during the study (Fig 1A). There were significantly lower magnitudes for anti-S (p< 0.0001), anti-S1 (p< 0.0001), and anti-RBD (p< 0.0001) IgG titers on the day of dose 2 and day 28 post second dose for SOT recipients compared to healthy controls ( Fig 1B,C,D). Using the internally validated threshold of anti-S IgG >1.07 based on pre-pandemic controls, only 50% of the SOT sub-cohort responded to vaccine after series completion (Fig 2). There was a positive trend between months from transplant and anti-S IgG titer (Fig 3).    Background. Allogeneic stem cell transplant (SCT) recipients are at an increased risk of poor outcomes from COVID-19. While the mRNA-1273 (Moderna) and BNT162b2 (Pfizer) COVID-19 mRNA vaccines are highly immunogenic in the general population, the immune response in SCT recipients is poorly understood. We characterized the immunogenicity and reactogenicity of COVID-19 mRNA vaccines in a cohort of SCT patients.

Methods.
We performed a prospective cohort study of 16 allogeneic SCT patients and 23 healthy controls. Blood samples for both cohorts were collected prior to first vaccination (baseline), at the time of second vaccination, and approximately 28 days post-second vaccination. Anti-Spike (S), anti-S1, anti-receptor binding domain (RBD), and anti-Nucleocapsid (N) IgG levels were measured quantitatively from plasma using a multiplexed single molecule array (Simoa) immunoassay. Reactogenicity was captured for the SCT cohort via a self-reported post-vaccination diary for 7 days after each dose.
Results. Demographics and SCT recipients' characteristics are shown in Table 1. In the SCT cohort, we observed a significantly lower anti-S (p< 0.0001), S1 (p< 0.0001), and RBD (p< 0.0001) IgG responses as compared to healthy controls, both at the time of dose 2 and 28 days post-vaccine series (Fig 1). Overall, 62.5% of SCT recipients were responders after vaccine series completion, as compared to 100% of healthy controls (Fig  2). While no patients had a reported history of COVID-19 diagnosis, 2 patients in the SCT cohort had elevated anti-S IgG levels and 1 showed elevated anti-N at baseline.
10/16 participants in the SCT cohort completed at least one post-vaccination diary. Local and systemic reactions were reported by 67% and 22% of participants, respectively, after dose 1, and 63% and 50% after dose 2 ( Figure 3). All reported events were mild. Table 1 Anti-Spike (A), anti-S1 (B), anti-RBD (C), and anti-nucleocapsid (D) IgG titers were measured at baseline, time of second dose, and approximately 28 days after second