Virus-Like Particles Overcome Challenges in Correcting Immune Cells, Accelerating the Development of Next-Generation CAR-M Therapies
Background
Myeloid immune cells, including monocytes, macrophages, and dendritic cells (DCs), which are responsible for the primary immune response in our body, are considered a new key to treating intractable diseases. However, myeloid cells possess a strong self-defense mechanism that specifically detects and destroys external invaders, making gene delivery very challenging.
Conventional nucleofection methods cause severe toxicity due to the physical shock applied to the cell membrane, reducing cell survival rates. Furthermore, even surviving cells often exhibit abnormally activated cGAS-STING pathways, intracellular DNA sensors, leading to a loss of their inherent immune characteristics.
Another alternative, lentivirus, is also significantly limited by the SAMHD1 blocking protein in myeloid cells. Even when bypassing this barrier with the VPX auxiliary protein, it is difficult to avoid the risk of off-target modifications caused by the continuous expression of gene editing tools. This highlights the need to establish a precise technology that can safely and efficiently correct genes while fully preserving the characteristics of immune cells.
Key Findings
Researchers from the University of California, San Francisco (UCSF) and the Gladstone Institutes, led by Professor Julia Carnevale and Professor Jonathan Weissman, respectively, have developed and reported a novel delivery system based on virus-like particles (VLPs) called 'SLICeVLP'. This system sequentially delivers VPX lentivirus carrying guide RNA (sgRNA) and engineered VLPs (eVLPs) containing the Cas9 protein, effectively overcoming the immune resistance of myeloid cells.
In experiments using human macrophages, this approach demonstrated its advantages by correcting the CD274 gene, which blocks PD-L1 (Programmed Death-Ligand 1) expression. The system exhibited remarkable efficiency, achieving over 95% knockout (KO) while minimizing cell death. Furthermore, it eliminated the cytoplasmic detection signal side effects, such as interferon induction, which were frequently observed with nucleofection. This system is versatile, accommodating base editing (BE) and epigenetic silencing techniques, as well as the insertion of specific sequences in conjunction with adeno-associated virus (AAV).
The researchers conducted a pooled CRISPR screening using this platform to analyze a large number of functional genes in human macrophages. This yielded significant insights, providing a detailed map of candidate molecules that regulate the secretion of tumor necrosis factor (TNF) and the expression of CD80, an immune activation marker. Through screening analysis, the TNFAIP3 gene, a key regulator of inflammation, was identified as the top candidate. Macrophages that have undergone this process maintain their immune activity even in the presence of inhibitory signals released by cancer cells. Human epidermal growth factor receptor 2 (HER2)-targeted chimeric antigen receptor macrophage (CAR-M) cells incorporating this gene also showed enhanced anti-cancer activity.
Significance and Prospects
This research represents a significant breakthrough in macrophage research, which has been hindered by cell toxicity and defense mechanisms that have previously prevented gene manipulation. The demonstration of a technique for efficiently correcting myeloid cells is expected to greatly improve the efficiency of disease genome analysis.
The newly discovered TNFAIP3 inhibition technology aims to prevent macrophages from turning into tumor-protective cells in the vicinity of cancer cells. By maintaining strong immune activity even in the tumor center, this approach strengthens the strategic foundation for increasing the effective survival period of anti-cancer cell therapies.
However, the standardization of the production process and the establishment of large-scale VLP manufacturing methods remain challenges. The validation process to minimize potential minor immune responses induced by the extracellular delivery vehicle in vivo also requires careful attention. Once these barriers are overcome, the new myeloid cell correction platform is expected to become a driving force in revolutionizing the development of next-generation CAR-M therapies.
Nature Biotechnology, Published online: 17 August 2026; doi:10.1038/s41587-026-03258-2Primary human myeloid cells are efficiently edited using virus-like particles.
The utility of this platform will be fully realized in the widespread adoption of next-generation immune cell therapies targeting solid tumors. Existing therapies have been limited by the physical density and immunosuppressive environment of solid tumors, making it difficult for them to penetrate and function effectively. In response, macrophage-based CAR-M therapies, which have superior mobility, have emerged, but they face the challenge of losing activity near the tumor. The VLP delivery method and TNFAIP3 deficiency treatment demonstrated in this study create robust macrophages that maintain their activity even in the tumor center, significantly enhancing therapeutic efficacy. This paves the way for precise targeted cancer therapies that can safely deliver gene-corrected macrophages with preserved characteristics into the bodies of patients with solid tumors.
Furthermore, it can be immediately utilized to enhance productivity in the drug discovery phase. This contrasts with the previous reality, where research in the field relied for a long time on indirect responses in mouse models due to the difficulty of manipulating human primary immune cells. By using SLICeVLP, it is possible to establish a large-scale in vitro environment that closely mimics the in vivo response of actual patients, allowing for the proactive acquisition of early efficacy data. This will establish an industrial development framework that reduces the budget allocated to candidate validation and increases the success rate of clinical trials.