This study reports on the design of mRNA and adjuvant-loaded lipid nanoparticles for therapeutic cancer vaccination. The use of nucleoside-modified mRNA has previously been shown to improve the translational capacity and safety of mRNA-therapeutics, as it prevents the induction of type I interferons (IFNs). However, type I IFNs were identified as the key molecules that trigger the activation of antigen presenting cells, and as such drive T cell immunity. We demonstrate that nucleoside-modified mRNA can be co-delivered with the clinically approved TLR agonist monophosphoryl lipid A (MPLA). As such, we simultaneously allow high antigen expression in vivo while substituting the type I IFN response by a more controllable adjuvant. This strategy shows promise to induce effective antigen-specific T cell immunity and may be useful to enhance the safety of mRNA vaccines.