Lipid nanoparticles employed in mRNA-based COVID-19 vaccines: An overview of materials and processes used for development and production

Abstract

In the light of the recommended application of the third dose, both public and professional community would benefit from a detailed repor t on the technological advances behind the developed messenger ribonucleic acid (mRNA) based COVID-19 vaccines. Although many vaccine developers are yet to reveal their precise formulations, it is apparent they are founded on nanotechnology platforms similar to the one successfully used for registered drug Onpattro TM (INN: patisiran). Optimal encapsulation of mR NA requires the presence of four lipids: an ionizable cationic lipid, a polyethylene-glycol (PEG)-lipid, a neutral phospholipid and cholesterol. Together with other excipients (mainly buffers, osmolytes and cryoprotectives), they enable the formation of lipid nanoparticles (LNPs) using rapid-mixing microfluidic or T-junction systems. However, some limitations of thermo stability testing protocols, coupled with the companies’ more or less cautious approach to predicting vaccine stability, led to rigorous storage conditions: -15° to -25°C or even -60° to -80°C. Nevertheless, some inventors recently announced their mRNA-LNP based vaccine candidates to be stable at both 25° and 37°C for a week. Within the formulation design space, further optimizati on of the ionizable lipids should be expected, especially in the direction of increasing their branching and optimizing pKa values, ultimately leading to the second generation of mRNA-LNP COVID-19 vaccines.

U susret preporučenoj tre ćoj dozi, razumevanje tehnološkog napretka koji je doveo do razvoja vakcina na bazi informacione ribonukleinske kiseline (iRNK) od interesa je kako stručne tako i šire javnosti. Iako mnoge kompanije koje stoje iza razvoja ovih vakcina još uvek nisu učinile dostupnim podatke o formulaciji, o čigledno je da se dominantno oslanjaju na nanotehnološke platforme slične onoj uspešno primenjenoj za registrovani lek OnpattroTM (INN: patisiran). Zadovoljavaju ća inkapsulacija iRNK zahteva prisustvo četiri lipida: jonizujućeg katjonskog lipida, PEGilovanog lipida, neutralnog fosfolipida i holesterola. Zajedno sa ostalim ekscipijensima (puferima, sredstvima za podešavanje toni čnosti i krioprotektantima), pažljivo odabrani lipidi omogućavaju obrazovanje lipidnih nanočestica (LNPs) mikrofluidnim ili T- junction tehnikama mešanja velike brzine. Me đutim, odre đena ograni čenja u primenjenim protokolima procene stabilnosti vakcina, zajedno sa povećanim oprezom kompanija od kojih se željno očekivalo plasiranje vakcina na tržište, dovelo je do rigoroznih uslova čuvanja: -15° do - 25°C ili čak -60° do -80°C. Ipak, pojedine kompanije izveštavaju o zadovoljavajućoj stabilnosti svojih iRNK-LNP vakcina kako na 25°, tako i na 37°C tokom ne delju dana. Dalji formulacioni razvoj će svakako obuhvatiti optimizaciju jonizuju ćih lipida, naročito u smeru pove ćanja broja bočnih lanaca i podešavanja pKa vrednosti, te dovesti do pojave tzv. drugegeneracije iRNK-LNP vakcina za prevenciju COVID-19.