Measurement Uncertainty in Quantitative Chimerism Monitoring after Stem Cell Transplantation

Abstract

Following allogeneic stem cell transplantation, graft status is often inferred from values for DNA chimerism in blood or bone marrow. Timely assessment of graft status is critical to determine proper management of post cell transplantation. A common methodology for chimerism testing is based on STR-PCR, i.e. PCR amplification of Short Tandem DNA Repeats. This is a complex technology platform for indirect DNA measurement. It is however associated with inherent variability originating from preparation, amplification of the DNA, and uncalibrated product detection. Nonetheless, these semi-quantitative measurements of DNA quantity are used to determine graft status from estimated percent chimerism [%Chim]. Multiplex PCR partially overcomes this limitation by using a set of simultaneously amplified STR markers, that enables computing a [mean%Chim] value for the sample. Quantitative assessment of measurement variability and sources of error in [mean%Chim] is particularly important for longitudinal monitoring of graft status. In such cases, it is necessary to correctly interpret differential changes of [mean%Chim] as reflective of the biological status of the graft, and not mere error of the assay. This paper presents a systematic approach to assessing different sources of STR measurement uncertainty in the tracking of chimerism. Severe procedural and cost constraints are making this assessment non trivial. We present our results in the context of Practical Statistical Efficiency (PSE), the practical impact of Statistical work, and InfoQ, the Information Quality encapsulated in ChimerTrack®;, a software application tracking chimerism.