A single dose of self-transcribing and replicating RNA-based SARS-CoV-2 vaccine produces protective adaptive immunity in mice

de Alwis, Ruklanthi; Gan, Esther S.; Chen, Shiwei; Leong, Yan Shan; Tan, Hwee Cheng; Zhang, Summer L.; Yau, Clement; Low, Jenny G.H.; Kalimuddin, Shirin; Matsuda, Daiki; Allen, Elizabeth C.; Hartman, Paula; Park, Kyoung-Joo Jenny; Alayyoubi, Maher; Bhaskaran, Hari; Dukanovic, Adrian; Bao, Yanjie; Clemente, Brenda; Vega, Jerel; Roberts, Scott; Gonzalez, Jose A.; Sablad, Marciano; Yelin, Rodrigo; Taylor, Wendy; Tachikawa, Kiyoshi; Parker, Suezanne; Karmali, Priya; Davis, Jared; Sullivan, Brian M.; Sullivan, Sean M.; Hughes, Steve G.; Chivukula, Pad; Ooi, Eng Eong

A self-transcribing and replicating RNA (STARR)-based vaccine (LUNAR-COV19) has been developed to prevent SARS-CoV-2 infection. The vaccine encodes an alphavirus-based replicon and the SARS-CoV-2 full-length spike glycoprotein. Translation of the replicon produces a replicase complex that amplifies and prolongs SARS-CoV-2 spike glycoprotein expression. A single prime vaccination in mice led to robust antibody responses, with neutralizing antibody titers increasing up to day 60. Activation of cell-mediated immunity produced a strong viral antigen-specific CD8(+) T lymphocyte response. Assaying for intracellular cytokine staining for interferon (IFN)γ and interleukin-4 (IL-4)-positive CD4(+) T helper (Th) lymphocytes as well as anti-spike glycoprotein immunoglobulin G (IgG)2a/IgG1 ratios supported a strong Th1-dominant immune response. Finally, single LUNAR-COV19 vaccination at both 2 μg and 10 μg doses completely protected human ACE2 transgenic mice from both mortality and even measurable infection following wild-type SARS-CoV-2 challenge. Our findings collectively suggest the potential of LUNAR-COV19 as a single-dose vaccine.