Fractalkine mRNA-LNPs Enable In Vivo CD8 T-Cell Reprogramming : Sci Immunol | May 2026

Introduction

Adoptive cellular immunotherapies have transformed cancer treatment, but current strategies generally require ex vivo cell engineering, manufacturing complexity and individualized processing. The ability to selectively reprogram cytotoxic effector CD8 T cells directly in vivo represents a major next frontier in immunotherapy and RNA-based medicine.

Problem Statement

Existing lipid nanoparticle (LNP) platforms lack precise targeting specificity for cytotoxic effector T-cell subsets, limiting their ability to selectively manipulate immune responses in vivo. Developing efficient, transient and clinically scalable approaches for targeted CD8 T-cell reprogramming remains a critical unmet challenge in immunotherapy.

Summary

This study introduces a highly innovative ligand-directed mRNA-LNP platform capable of selectively targeting CX3CR1-positive cytotoxic effector CD8 T cells in vivo using fractalkine (CX3CL1)-conjugated nanoparticles. By exploiting the natural interaction between fractalkine and the CX3CR1 receptor expressed on effector T cells, the investigators achieved remarkably efficient and selective mRNA delivery in both murine models and nonhuman primates. In mice, fractalkine-conjugated mRNA-LNPs targeted up to 95% of circulating and splenic effector CD8 T cells, enabling successful transient cellular reprogramming. Delivery of IL-2–encoding mRNA induced robust exogenous IL-2 secretion, while CD62L-encoding mRNA restored lymphoid homing receptor expression on differentiated effector cells. Importantly, the platform demonstrated impressive translational potential in rhesus macaques, where nearly all peripheral effector CD8 T cells were successfully targeted and reprogrammed to express human CD62L, including trafficking into lymphoid tissues. The work establishes proof-of-concept that endogenous immune cells can be rapidly modified in vivo without ex vivo manipulation or viral engineering. The transient nature of mRNA expression may also offer important safety advantages compared with permanent genetic modification approaches. Beyond oncology, this platform may have broad applications in infectious disease, vaccine development, autoimmunity and immune modulation. Overall, the study represents a major advance in targeted RNA therapeutics and demonstrates the feasibility of highly selective in vivo immune-cell engineering using receptor ligand–guided mRNA nanoparticle technology.