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Durability of variant neutralization in solid organ transplant recipients following Omicron-containing boosters is unknown. We report wane in XBB.1.5 neutralization by 3 months following a first bivalent booster, improved by a second booster; hybrid immunity improved peak, and duration of neutralization. Boosting at 3 to 6 months appears necessary to maintain neutralization., Competing Interests: Potential conflicts of interest. D. L. S. reports receiving consulting and/or speaking honoraria from Sanofi, Novartis, Veloxis, Mallinckrodt, Jazz Pharmaceuticals, CSL Behring, Thermo Fisher Scientific, Caredx, Transmedics, Kamada, MediGO, Regeneron, AstraZeneca, Takeda/Shire, Novavax, and Bridge to Life. W. A. W. has received consulting and/or speaking fees from AstraZeneca, GlobalData, China Medical Tribune, Medical Learning Institute (CME), and advisory board fees from AstraZeneca and Novavax. A. H. K. has received consulting fees from Hologic Inc. and speaking fees from PRIME Education (CME). All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: Kidney transplant recipients (KTRs) generate lower antibody responses to messenger RNA (mRNA)-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination, yet precise mechanisms for this poor response remain uncertain. One potential contributor is suboptimal spike antigen (sAg) translation and expression owing to transplant immunosuppression, which might lead to insufficient exposure to develop humoral and/or cellular immune responses., Methods: Within a single-arm clinical trial, 65 KTRs underwent ultrasensitive plasma sAg testing before, and 3 and 14 days after, the third mRNA vaccine doses. Anti-SARS-CoV-2 spike antibodies (anti-receptor binding domain [anti-RBD]) were serially measured at 14 and 30 days post-vaccination. Associations between sAg detection and clinical factors were assessed. Day 30 anti-RBD titer was compared among those with versus without sAg expression using Wilcoxon rank sum testing., Results: Overall, 16 (25%) KTRs were sAg positive (sAg+) after vaccination, peaking at day 3. Clinical and laboratory factors were broadly similar in sAg(+) versus sAg(-) KTRs. sAg(+) status was significantly negatively associated with day 30 anti-RBD response, with median (interquartile range) 10.8 (<0.4-338.3) U/mL if sAg(+) versus 709 (10.5-2309.5) U/mL if sAg(-) (i.e., 66-fold lower; p = .01)., Conclusion: Inadequate plasma sAg does not likely drive poor antibody responses in KTRs, rather sAg detection implies insufficient immune response to rapidly clear vaccine antigen from blood. Other downstream mechanisms such as sAg trafficking and presentation should be explored., (© 2024 The Authors. Transplant Infectious Disease published by Wiley Periodicals LLC.)

Kidney transplant recipients (KTRs) develop decreased antibody titers to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination compared to healthy controls (HCs), but whether KTRs generate antibodies against key epitopes associated with neutralization is unknown. Plasma from 78 KTRs from a clinical trial of third doses of SARS-CoV-2 vaccines and 12 HCs underwent phage display immunoprecipitation and sequencing (PhIP-Seq) to map antibody responses against SARS-CoV-2. KTRs had lower antibody reactivity to SARS-CoV-2 than HCs, but KTRs and HCs recognized similar epitopes associated with neutralization. Thus, epitope gaps in antibody breadth of KTRs are unlikely responsible for decreased efficacy of SARS-CoV-2 vaccines in this immunosuppressed population. Clinical Trials Registration.  NCT04969263., Competing Interests: Potential conflicts of interest. D. L. S. reports receiving consulting and/or speaking honoraria from AstraZeneca, CareDx, Moderna Therapeutics, Novavax, Regeneron, Springer Publishing, Houston Methodist, Northwell Health, Optum Health Education, Sanofi, and WebMd. W. A. W. has received consulting and/or speaking fees from AstraZeneca, GlobalData, China Medical Tribune, Medical Learning Institute (CME), and advisory board fees from Novavax. A. H. K. has received consulting fees from Roche Diagnostics and Hologic, Inc; and speaking fees from PRIME Education (CME). H. B. L. is an inventor on an issued patent (US20160320406A) filed by Brigham and Women's Hospital that covers the use of PhIP-Seq for antiviral antibody detection; and is a founder of ImmuneID, Portal Bioscience, Alchemab, and Infinity Bio. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination are reduced in solid organ transplant recipients (SOTRs). We report that increased levels of preexisting antibodies to seasonal coronaviruses are associated with decreased antibody response to SARS-CoV-2 vaccination in SOTRs, supporting that antigenic imprinting modulates vaccine responses in SOTRs., Competing Interests: Potential conflicts of interest. D. L. S. reports consulting and speaking honoraria from Sanofi, Novartis, CSL Behring, Jazz Pharmaceuticals, Veloxis, Mallinckrodt, Regeneron, AstraZeneca, and Thermo Fisher Scientific; consulting fees from Sanofi, Novartis, CSL Behring, Jazz Pharmaceuticals, Veloxis, Mallinckrodt, Thermo Fisher Scientific, Regeneron, and AstraZeneca; and speaking honoraria from Sanofi and Novartis (paid to author). A. L. C. reports consulting fees from Janssen. A. H. K. reports consulting fees from Roche. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

We compared antibody and T-cell responses against the severe acute respiratory syndrome coronavirus 2 vaccine strain spike protein to responses against the Omicron variant in 15 messenger RNA vaccine recipients. While these individuals had significantly lower levels of antibodies that inhibited Omicron spike protein binding to ACE2, there was no difference in T-cell responses., Competing Interests: Potential conflicts of interest. A. L. C. reports support from the National Institutes of Health for the present manuscript and outside of the submitted work and consulting fees from Janssen paid to hepatitis B virus cure strategies. A. H. K. reports consulting fees from Roche. All other authors report no potential conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Humoral responses to coronavirus disease 2019 (COVID-19) vaccines are attenuated in solid organ transplant recipients (SOTRs), necessitating additional booster vaccinations. The Omicron variant demonstrates substantial immune evasion, and it is unknown whether additional vaccine doses increase neutralizing capacity versus this variant of concern (VOC) among SOTRs., Methods: Within an observational cohort, 25 SOTRs with low seroresponse underwent anti-severe acute respiratory syndrome coronavirus 2 spike and receptor-binding domain immunoglobulin (Ig)G testing using a commercially available multiplex ELISA before and after a fourth COVID-19 vaccine dose (D4). Surrogate neutralization (percent angiotensin-converting enzyme 2 inhibition [%ACE2i], range 0%-100% with >20% correlating with live virus neutralization) was measured against full-length spike proteins of the vaccine strain and 5 VOCs including Delta and Omicron. Changes in IgG level and %ACE2i were compared using the paired Wilcoxon signed-rank test., Results: Anti-receptor-binding domain and anti-spike seropositivity increased post-D4 from 56% to 84% and 68% to 88%, respectively. Median (interquartile range) anti-spike antibody significantly increased post-D4 from 42.3 (4.9-134.2) to 228.9 (1115.4-655.8) World Health Organization binding antibody units. %ACE2i (median [interquartile range]) also significantly increased against the vaccine strain (5.8% [0%-16.8%] to 20.6% [5.8%-45.9%]) and the Delta variant (9.1% [4.9%-12.8%] to 17.1% [10.3%-31.7%]), yet neutralization versus Omicron was poor, did not increase post-D4 (4.1% [0%-6.9%] to 0.5% [0%-5.7%]), and was significantly lower than boosted healthy controls., Conclusions: Although a fourth vaccine dose increases anti-spike IgG and neutralizing capacity against many VOCs, some SOTRs may remain at high risk for Omicron infection despite boosting. Thus, additional protective interventions or alternative vaccination strategies should be urgently explored., Competing Interests: D.L.S. has received consulting and speaking honoraria from Sanofi, Novartis, CSL Behring, Jazz Pharmaceuticals, Veloxis, Mallinckrodt, and Thermo Fisher Scientific. A.H.K. has received consulting fees from Roche. The other authors declare no conflicts of interest., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc.)