Comment on "In vivo CAR T cell generation to treat cancer and autoimmune disease"
Science. 2025 June 19, Theresa L Hunter et al.
Comment by Alex Rampotas, Academic Clinical Lecturer, University College London Hospitals, London, United Kingdom.
Background:
CAR T-cell therapies have transformed treatment of B-cell malignancies and recently shown promise in B-cell–mediated autoimmune diseases. However, current approaches rely on complex ex vivo manufacturing, lymphodepleting chemotherapy, and integrating viral vectors, which restrict scalability, accessibility, and significantly raise their cost to healthcare systems.
Methods and Findings:
The authors developed a targeted lipid nanoparticle (tLNP) platform that delivers mRNA encoding CAR constructs directly into T cells in vivo, eliminating the need for ex vivo manipulation. A novel ionizable lipid (L829) reduced off-target liver uptake and improved tolerability in preclinical models. By conjugating tLNPs to anti-CD8 antibodies, the approach selectively engineered CD8⁺ T cells, minimizing CRS-associated CD4⁺ CAR T activation.
Key results included:
- Efficient CAR expression and cytotoxicity in human T cells from both healthy donors and patients with autoimmune diseases.
- Rapid and profound B-cell depletion in humanized mice within hours of dosing, with complete tumour clearance in leukaemia xenograft models after repeated dosing.
- In cynomolgus monkeys, CD8-tLNP-CAR treatment induced deep B-cell depletion across tissues. On B-cell reconstitution, the returning population was predominantly naïve, consistent with an “immune reset” effect previously seen in ex vivo CAR T clinical trials.
- Two- or three-dose regimens were effective, with acceptable tolerability and manageable cytokine responses.
Significance:
This study introduces an off-the-shelf, nonviral, in vivo CAR T generation strategy capable of achieving potent B-cell depletion and immune resetting without chemotherapy or ex vivo manipulation. The platform may broaden CAR T accessibility, reduce long-term risks linked to integrating vectors, and expand applicability to autoimmune disease as well as cancer.
Comment:
For transplant and cellular therapy clinicians, this work represents a potentially transformative step toward scalable, off the shelf, hospital-ready CAR T treatments. By bypassing manufacturing bottlenecks and conditioning, such approaches could make immune-resetting cellular therapy feasible for large autoimmune patient populations. Compared to autologous ex vivo CAR T cells, this approach may have several limitations. The transient nature of mRNA expression could reduce durability of response, potentially requiring repeat dosing. In vivo dosing allows less control over product quality and phenotype than ex vivo manufacturing, where CAR⁺ cells can be expanded, characterized, and selectively infused. Off-target effects, variability in in vivo transfection efficiency, and risks of uncontrolled immune activation also remain concerns. By contrast, autologous ex vivo CAR T therapies provide a defined cell product with long-term persistence but are hindered by cost, logistics, and manufacturing time. This approach as the authors highlight may be most suited for the use of CAR-T cells in autoimmune disease where persistence is not desirable. Clinical translation will need to confirm safety, durability of response, and optimal dosing schedules, but this discovery seems to be a step towards a more wider adoption of CAR-T cell therapy.