Real-world experience of tixagevimab/cilgavimab prophylaxis in Japanese patients with immunodeficiency.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes severe illness and mortality in patients with immunodeficiency. Although vaccination has been recommended, the induction of protective antibodies by immunization, and thus the disease-preventive effect, has proven insufficient in immunodeficient patients, especially in those with predominantly antibody deficiency. A monoclonal antibody combination of tixagevimab and cilgavimab (TIX/CIL) was developed as a pre-exposure prophylaxis (PrEP). In this study, we investigated the post-PrEP increase in antiviral antibody titers and detailed the breakthrough infections that occurred despite PrEP in Japanese immunodeficient patients who had received TIX/CIL.

Methods: Blood samples were collected before and after TIX/CIL administration between November 2022 and August 2023. Antibody titers against the S-protein of SARS-CoV-2 were measured to evaluate TIX/CIL-induced protection. Information regarding breakthrough infection, as evidenced by positive antigen and/or PCR tests, was collected.

Results: A significant increase in the anti-S antibody titer was observed in all 89 immunodeficient patients who had received TIX/CIL. However, 14 (16 %) patients experienced breakthrough SARS-CoV-2 infections, of which one died of respiratory failure.

Conclusion: The shift in the SARS-CoV-2 circulating strain might have reduced the efficacy of TIX/CIL, leading to an increased number of breakthrough infections.