Modular Integration of Self‐Adjuvanting mRNA Delivery with Real‐Time Vaccine Efficacy Tracking for Timely Optimization of Cancer Immunotherapy

Abstract Messenger RNA (mRNA) vaccines revolutionize cancer immunotherapy, offering powerful tools to elicit precise, antigen‐specific immune responses. However, the limited efficiency of current mRNA delivery systems and the lack of real‐time immune monitoring tools hinder their full therapeutic potential. In this study, a modular platform that integrates a self‐adjuvanting mRNA delivery system with a self‐targeting vaccine efficacy reporter (VER), allowing for optimized therapeutic regulation in real‐time is developed. This platform utilizes peptide‐lipid nanoparticle (PLNP) incorporating cathepsin B‐activatable melittin lipidoid to deliver mRNA encoding ovalbumin (mOVA), which triggers robust immune activation through the STING pathway, significantly enhancing both transfection efficiency and vaccine potency. The VER probe features a leucine‐caged near‐infrared fluorescent moiety designed to detect antigen presentation by exploiting endoplasmic reticulum aminopeptidase 1 (ERAP1), a key enzyme upregulated during antigen processing. Following vaccination with PLNP/mOVA, ERAP1 activation leads to fluorescence emission by VER, enabling real‐time, non‐invasive tracking of immune activation. Through this modular integration, the system provides both self‐adjuvanting mRNA delivery and precise immune activation reporting. This approach supports the timely optimization of therapeutic strategies in cancer immunotherapy, offering the potential for more effective and personalized vaccination and treatment regimens.