Cascade amplification of therapeutic payloads for cancer immunotherapy.

Achieving sufficient therapeutic payload delivery remains a significant challenge in gene therapy, particularly for cancer immunotherapy, where payload thresholds are critical for efficacy. To address this, we developed a Cascade Amplification of Therapeutic Payloads (CATP) system, leveraging lipid nanoparticles (LNPs) to co-deliver self-amplifying mRNA (SamRNA) and modified mRNA encoding alphavirus capsids and envelopes. The CATP system initiates a dual-amplification process: SamRNA amplifies therapeutic payloads within transfected cells, while capsid and envelope proteins package SamRNA into defective viral particles to infect neighboring cells, enabling secondary payload amplification. This single-cycle infection ensures enhanced efficacy while maintaining safety. In vitro and in vivo studies demonstrated the CATP system's superiority over conventional SamRNA delivery. In a B16F10 melanoma model, CATP achieved a 525-fold increase in intratumoral IL-12 levels, resulting in tumor regression and long-term immune memory. The platform also showed broad applicability, effectively treating MC38 colorectal cancer, CT26 colon cancer, and P53