Abstract
The SARS-CoV-2 pandemic highlighted the potential of mRNA vaccines in rapidly responding to emerging pathogens. However, immunity induced by conventional mRNA vaccines wanes quickly, requiring frequent boosters. Self-amplifying RNA (saRNA) vaccines, which extend antigen expression via self-replication, offer a promising strategy to induce more durable immune responses. In this study, we developed an saRNA vaccine encoding Zika virus (ZIKV) membrane and envelope proteins and evaluated its efficacy in mice. A single vaccination elicited strong humoral and cellular immune responses and reduced viral loads but only for 28 days. By day 84, antibody titers and T cell responses had significantly declined, resulting in reduced efficacy. To address this, we evaluated agonist antibodies targeting the T cell costimulatory molecules OX40 and 4-1BB. Coadministration of agonist antibodies enhanced CD8+ T cell responses to vaccination, resulting in sustained immunity and reduced viral loads at day 84. Depletion and passive transfer studies verified that long-term antiviral immunity was primarily CD8+ T cell dependent, with minimal contributions from antibody responses. These findings suggest that agonists targeting members of the tumor necrosis receptor superfamily, such as OX40 and 4-1BB, might enhance the durability of saRNA vaccine–induced protection, addressing a key limitation of current mRNA vaccine platforms.
Authors
Hsueh-Han Lu, Rúbens Prince dos Santos Alves, Qin Hui Li, Luke Eder, Julia Timis, Henry Madany, Kantinan Chuensirikulchai, Krithik V. Varghese, Aditi Singh, Linda Le Tran, Audrey Street, Annie Elong Ngono, Michael Croft, Sujan Shresta
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