Modified mRNAs were produced by in vitro transcription using T7 RNA polymerase (Megascript, Ambion) on linearized plasmids encoding codon-optimized CH848 10.17DT gp160s, CH848 10.17DT SOSIP trimers, or CH848 10.17DT trimer-ferritin NPs. All the HIV-1 modified mRNA constructs used in this study and their corresponding plasmids were listed in Table S1. One-methylpseudouridine (m1Ψ)-5’-triphosphate (TriLink, Cat# N-1081), instead of UTP was used to produce nucleoside-modified mRNAs. Modified mRNAs contain 101 nucleotide-long polyadenylation tails for optimized expression. Modified CH848 10.17DT SOSIPv4.1 trimer and CH848 10.17DT SOSIPv5.2.8 trimer mRNAs were capped using ScriptCap m7G capping system and ScriptCap 2′-O-methyl-transferase kit (ScriptCap, CellScript) (Pardi et al., 2013 (link)). Capping of all other in vitro transcribed mRNAs was performed co-transcriptionally using the trinucleotide cap1 analog, CleanCap (TriLink, Cat# N-7413). All mRNAs were purified by cellulose purification, as described (Baiersdorfer et al., 2019 (link)). All mRNAs were analyzed by agarose gel electrophoresis and were stored frozen at −20 °C.