1037-LBP: Lineage marker “Negative” Fraction resolves discrepancy in lineage specific chimerism

Donor Chimerism (DC) analysis documents engraftment, disease persistence and/or recurrence post allogeneic hematopoietic stem cell transplantation (HSCT). Typically, unfractionated analysis (UA) is performed but lineage-specific chimerism analysis (FC) can document specific cell engraftment or early relapse. However, loss or alteration of cell surface marker expression may hamper selection of relapsed cells and results inaccurately show only donor genotype. We present two Acute Myelogenous Leukemia (AML) patients with discordant results between FC and UA where analysis of Negative Fraction (NF) furnished evidence of relapse. Demonstrate utility of NF analysis to resolve discrepant UA/FC results. DC was evaluated using commercially available STR reagents (Life Tech. and Promega). Sequential separation of B, T and myeloid cells was performed on post HSCT blood (RoboSep, StemCell, Inc.). Cells remaining after selection were saved, i.e. Negative Fraction (NF). Chimerism analysis was performed on UA and cell fraction DNA. NF was analyzed if discrepant results between UA and FC were found. HSCT patients were tested for DC at 30 days post txp and for cause. Pt#1, whose 30 day analysis was missed, was tested 5 months post txp. FC showed no B cells, >95% DC in T and myeloid fractions, but 11% DC in UA. NF was predominantly recipient genotype. For Pt#2, 90 day analysis showed 19.5 % DC in UA, >92% in T and myeloid fractions with negligible B cells. NF showed 9% DC. In both patients, relapsed cells escaped the fractionation process. Both patients were diagnosed with relapse. FC is useful in detecting relapse post HSCT but recurrent tumor cells may not express separation markers and results will be inaccurate. Concurrent UA analysis is recommended. NF testing may resolve discrepancies between UA and FC.