A study has begun to assess the antibody response to an additional dose of a COVID-19 mRNA vaccine in kidney and liver transplant recipients, either alone or with a concurrent reduction in immunosuppressive medication. The clinical trial will enroll people for whom two-to-four doses of a COVID-19 mRNA vaccine did not elicit a detectable antibody response. The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), is sponsoring and funding the phase-II trial, called COVID Protection After Transplant–Immunosuppression Reduction (CPAT-ISR), as per a statement from NIH.

“Eliciting a protective immune response to COVID-19 vaccines in some organ transplant recipients continues to be a challenge,” Anthony S Fauci, MD, Director, NIAID, said in the statement.

Organ transplant recipients must take life-long immunosuppressive therapy to prevent organ rejection, and this therapy blunts their immune responses to pathogens and vaccines. Research has shown that many organ transplant recipients do not develop antibodies against SARS-CoV-2 after receiving a primary COVID-19 vaccine regimen. Even after receiving a third dose of a COVID-19 mRNA vaccine, many transplant recipients still fail to produce an antibody response. Those who do develop antibodies tend to have much weaker responses than immunocompetent people. The lack of robust antibody responses, along with a high prevalence of risk factors such as obesity and diabetes, leaves kidney and liver transplant recipients at high risk for SARS-CoV-2 infection and severe COVID-19, the statement added.

It further noted that the purpose of the new study is to determine if temporarily reducing immunosuppressive medication taken during the days before and after an additional dose of an mRNA COVID-19 vaccine safely allows for better antibody responses to vaccination in kidney and liver transplant recipients. Research has shown that pausing immunosuppressive medication in people with autoimmune disease can safely improve their antibody responses to vaccinations for both COVID-19 and influenza, suggesting that this approach might also work for some transplant recipients.

The new trial builds on NIAID’s CPAT pilot study, which is assessing the antibody response to a third dose of a COVID-19 mRNA vaccine in kidney transplant recipients. The CPAT-ISR trial will take place at approximately 15 transplant centres across the US. The study team will enroll up to 400 adults aged 18 years or older who received a kidney or liver transplant a year or more prior to enrollment. All participants will have received two-to-four doses of either the Moderna COVID-19 vaccine or the Pfizer-BioNTech COVID-19 vaccine at least 30 days before enrollment and will have a negative or indeterminate antibody response 30 days or more after the most recent dose. Participants must be taking one of two specific tacrolimus-based immunosuppressive medication regimens and have no recent transplant rejection or change in immunosuppression, emphasised the statement.

It also mentioned that the study team will assign participants at random to one of two groups. One group will receive an additional dose of a COVID-19 mRNA vaccine with no further intervention. The other group will take a reduced dose of their immunosuppressive therapy for five days before and two weeks after receiving an additional dose of a COVID-19 mRNA vaccine. Investigators will measure each participant’s antibody response to vaccination 30 days after the additional vaccine dose. The goal is to determine the proportion of participants who achieve a pre-defined antibody response at the 30-day mark. The study team will follow participants for one year after enrollment.