Key Findings
Residual CAR transgene levels measured at the time of allogeneic hematopoietic stem cell transplant (allo-HSCT) are associated with the persistence of CAR-T donor cells and the subsequent development of mixed chimerism with cytopenia (MCC). In a report published in Biomarker Research on 16 October 2026, researchers found that patients with detectable CAR transgenes at transplantation experienced MCC, while a patient with undetectable levels showed stable complete donor chimerism and normal hematopoietic recovery.
Technical Details
The study utilized three-party short tandem repeat (STR) analysis to distinguish between the CAR-T donor, the transplant donor, and the recipient. The correlation between transgene copies and outcomes was as follows:
- Patient 1: CAR transgene was undetectable; resulted in stable complete donor chimerism.
- Patient 2: 240 copies of CAR transgene per microgram of genomic DNA; developed MCC with the CAR-T donor contributing 47.72% of the measured compartment.
- Patient 3: 22,162 copies per microgram; developed mixed chimerism with a CAR-T donor contribution of 14.23%.
To rescue these patients, the team administered donor lymphocyte infusion using cells engineered to knock out the CAR target (KO-DLI). Patient 2 received this as a rescue treatment for established MCC, while Patient 3 received it preemptively. Both became CAR-undetectable and achieved complete donor chimerism.
Background & Context
Patients with relapsed or refractory T-cell malignancies often receive both CAR-T therapy and allo-HSCT. A complication arises when CAR-T cells and the transplant originate from the same donor, as standard chimerism testing cannot differentiate the two populations. This study specifically examined cases where the CAR-T and stem cells came from different donors.
Significance & Outlook
All three patients remain in complete remission with follow-up periods of 713, 335, and 201 days. While the findings are hypothesis-generating due to the small sample size, the authors propose that KO-DLI warrants prospective validation as a salvage approach. Larger cohorts are required to confirm the predictive value of CAR transgene levels and the causal therapeutic benefit of KO-DLI.
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