SARS-CoV-2 mRNR vaccines induce microglial proliferation in mixed neuronal-glial cultures

Abstract

Development of mRNA vaccines was major discovery that helped stop COVID-19 pandemic. All developed vaccines against SARS-CoV-2 showed that they can cause various neurological effects like headache, brain fog and dizziness. Recent research states that mRNA vaccines like Comirnaty (Pfizer) tend to cause side effects after repeated vaccination, though developers did not investigate if there is a direct interaction of vaccine and brain cells. In our study, we aim to investigate whether SARS-CoV-2 mRNA vaccines can directly affect viability of mixed neuronal-glial cells and microglia proliferation. We used primary neuronal-glial cell cultures that we prepared from 6-7 days Wistar rat cerebella. Cell cultures were treated with single injections of 5 different concentrations of Comirnaty (Pfizer) mRNA Original/Omicron B.A. 4-5 and Tozinameran/Riltozinameran vaccines for 3 and 7 days. We also treated cells with three repeated standard 5 ng/ml mRNA vaccine injections every 24 hours incubating for 7 days. Cell viability was evaluated with fluorescent microscope using Hoechst 33342 and Propidium Iodide. Isolectin GS IB4 AlexaFluor 488 was used to identify microglial cells. We showed that single injections of both mRNA vaccines did not affect viability and number of neurons in mixed neuronal-glial cultures after 3 days and 7 days of incubation. After 7-day incubation with singular doses of mRNA vaccines (in the range of 50 ng/ml – 100 ng/ml concentrations) microglial number significantly increased compared to control cultures at the same time while after 3 days there was no effect on microglial number with all concentrations. Repeated injections of standard 5 ng/ ml mRNA vaccines increased microglial number in mixed neuronal glial cultures, but had no significant effect on neuronal number and viability. In conclusion, our data show that mRNA vaccines can induce microglial proliferation, though it does not affect neuronal viability in mixed neuronal-glial co-cultures.