Minority Report: Why detecting microchimerism can make the biggest difference

In the evolving field of transplantation and histocompatibility testing, chimerism monitoring remains a fundamental part of post-transplant care. However, the tools we use to measure donor and recipient DNA are evolving.

The once‑dominant short tandem repeat (STR) method, robust, familiar, and dependable, has gradually given way to newer technologies capable of detecting microchimerism with significantly greater sensitivity and accuracy. Next-generation sequencing (NGS) and digital PCR (dPCR or ddPCR) platforms are revolutionising how laboratories and clinicians interpret engraftment, relapse risk, and treatment response.

Why sensitivity matters

STR‑based chimerism assays have historically served well, providing clear, reproducible data at moderate sensitivity. But STR’s limit of detection, typically around 1 to 5%, meant that low‑level recipient DNA or ‘microchimerism’ often escaped detection. By the time STR flags mixed chimerism, the underlying biological shift was already well underway. Microchimerism methods, such as NGS, close this diagnostic gap, routinely achieving limits of detection between 0.05 to 0.5%. That extra decimal point can mean the difference between pre-emptive intervention and clinical relapse.

Clinical value: When small signals save lives

Studies consistently show that early detection of rising recipient DNA (≥0.05% in the first 90 days) can precede clinical relapse by days or weeks; lineage‑specific monitoring (e.g., tracking CD33+ myeloid fractions in AML) adds even greater predictive power. Sensitive chimerism detection enables earlier intervention, such as immunomodulation, donor lymphocyte infusion, or molecular MRD assessment, at a stage when they are most effective.

ASHI’s verdict: NGS outperforms STR

The 2024 ASHI Engraftment Monitoring (EMO) survey provided one of the strongest profession‑wide validations yet of NGS technology for chimerism monitoring. Participating H&I laboratories demonstrated that NGS‑based chimerism results showed markedly less inter‑laboratory variability across the entire chimeric range (0.1 to 100%) compared with STR; interestingly, NGS assays also produced significantly fewer discrepant results. ASHI’s official conclusion was unambiguous: NGS appears more suitable for detecting incremental changes in chimerism and more accurately identifies relapse or evaluates response to treatment.

In short, one of the field’s governing bodies has spoken; NGS isn’t just the next generation of testing, it’s the better one.

NGS in practice: One Lambda Devyser Chimerism

Among the commercially available NGS assays, the One Lambda Devyser Chimerism NGS kit stands head-and-shoulders above the rest for its blend of analytical performance and practical workflow. The manufacturer and validation data report limits of detection as low as 0.05 to 0.1%, with excellent reproducibility across the chimeric spectrum. The single‑tube workflow, short hands‑on time, and supplied Advyser Chimerism analysis software make it highly suitable for busy H&I or molecular laboratories looking to modernise their post‑HSCT monitoring.

From data to decision: Turning detection into action

Of course, greater sensitivity must be matched by thoughtful interpretation. Low‑level findings require confirmation and clinical context through repeat samples, lineage‑specific testing, and coordination with MRD results. However, the benefits are clear; earlier awareness gives clinicians the chance to act before relapse becomes irreversible. As the ASHI EMO survey confirmed, NGS methods aren’t just more sensitive… they’re more consistent, more reliable, and better aligned with modern precision‑medicine principles.

The bottom line

The evidence, the technology, and the professional consensus now point in the same direction. STR served the field well, but its era has ended. As laboratories assess more sensitive and precise assays for post-transplant monitoring, streamlining methodologies, platforms, and service agreements becomes essential. A straightforward, combinable NGS assay maintains technical competence and expertise while maximising the use of existing equipment, avoiding the need for extra bench space and training. Microchimerism-sensitive NGS assays, led by platforms like One Lambda Devyser Chimerism, offer the precision, reproducibility, and early warning that transplant clinicians and patients need.

When it comes to post-transplant surveillance, it’s time to start seeing the smaller picture.

References

Blouin AG, Askar M. Chimerism analysis for clinicians: a review of the literature and worldwide practices. Bone Marrow Transplant, 2022 Mar;57(3):347-359. doi: 10.1038/s41409-022-01579-9.

Haugaard AK, Madsen HO, Masmas TN, Vettenranta K, Buechner J, Mellgren K, Turkiewicz D, Rosthøj S, Marquart HV, Heilmann C, Müller KG and Ifversen M. Highly-sensitive chimerism analysis in blood after allogeneic hematopoietic cell transplantation in childhood leukemia: Results from the Nordic Microchimerism Study. Frontiers in Hematology, 2023. 2:1055484. doi: 10.3389/frhem.2023.1055484

American Society for Histocompatibility and Immunogenetics (ASHI). Engraftment Monitoring (EMO) Proficiency Testing Survey Report 2024. ASHI Proficiency Testing Program, 2024.
DOI: N/A (internal ASHI report).

Kim JJ, Kwon SS, Choi YJ, Kang Y, Park YJ, Shin S, Lee ST, Choi JR. Real-world clinical experience with NGS-based chimerism analyses in haematopoietic stem cell transplant patients. British Journal of Haematology, 2025 Aug;207(2):475-483. doi: 10.1111/bjh.20191.