Arcturus says sa-mRNA COVID boosters induced immune response in small phase 1/2 study

A dwindling COVID-19 vaccine market is not stopping Arcturus Therapeutics from pressing ahead with its own mRNA candidate, as the biotech touts new early data indicating its shot lights up the immune system.

The company said Tuesday that three iterations of its self-amplifying-mRNA (sa-mRNA) shots elicited an immune response against the D614G variant in patients from a small phase 1/2 trial. The study recruited 36 previously vaccinated patients in the U.S. and Singapore who were randomized to receive one of three Arcturus vaccines targeting the ancestral strain, B.1 variant including the D614G mutation or the Beta variant. There was no placebo control included in the study. 

Patients receiving the B.1-variant targeting booster (ARCT-154) performed best, with a 36.7 geometric mean fold rise (GMFR), a measurement of the increase in antibodies before and after vaccination. Patients receiving the ancestral strain booster (ARCT-021) and Beta variant booster (ARCT-165) saw GMFR of 20 and 23.5, respectively. 

Arcturus added that ARCT-154 induced a “broad, cross-neutralizing immune response, which persisted up to one-year post-booster” without an additional shot. The company didn’t expand on the data behind that response and was vague on the safety profile, saying that side effects were mild or moderate but “rates of related or severe AEs were low.” 

The San Diego biotech, alongside partner CSL Behring, recently asked European regulators to approve ARCT-154 as a new vaccine for COVID-19. Data from a phase 3 trial found that the shot had 56.6% efficacy against symptomatic COVID-19 and 95.3% efficacy against severe COVID-19. A separate phase 3 booster trial found that ARCT-154 passed a non-inferiority test against Pfizer’s Comirnaty when tested against the ancestral strain. 

Though the recent approval filings have put Arcturus’ vaccine business front and center, it’s not the only clinical-stage work in the pipeline. The company is working on two clinical-stage treatments for ornithine transcarbamylase (OTC) deficiency and cystic fibrosis. Arcturus used to be partnered with CureVac on the OTC med before rights were handed back in 2019.