Abstract LB063: Duplex Sequencing reveals ubiquitous clonal hematopoiesis and complex donor-recipient clonal dynamics following HSCT
Authors: Ueda Masumi , Higgins Jake , Smith Thomas , Schmidt Elizabeth , Lo Fang Y. , Valentine Charles C. , Salk Jesse J. , Storb Rainer , Radich Jerald P. 
Published: June 2022

Abstract
Clonal hematopoiesis (CH aka CHIP) is the process whereby otherwise healthy individuals accumulate clones bearing low-frequency somatic mutations in hematologic malignancy (HM) driver genes. Historically thought to be a phenomenon of the elderly that is associated with increased risk of HM and cardiovascular disease, CH has been observed in increasingly younger cohorts as sequencing technology has advanced. CH in hematopoietic stem cell transplant (HSCT) donors has also been associated with adverse recipient outcomes.
In this retrospective analysis, we asked whether CH mutations preferentially expanded in recipients vs. donors in paired samples collected a median of 34 years post-HSCT (range 6-45). 16 donor-recipient pairs were analyzed, 11 of which had a donor sample collected pre-HSCT. All individuals were healthy at the time of contemporary sampling. Median donor age was 26 years (range 12-84) at time of HSCT. We took advantage of the ultra-low error rate (&lt;1-in-10-million) of Duplex Sequencing (DS) to comprehensively assess CH in genomic DNA from blood. We targeted 29 genes recurrently mutated in acute myeloid leukemia (AML) plus 48 kilobases of randomly chosen neutral genomic regions.
The mean DS error-corrected molecular depth across all samples was 26,731x for AML-associated genes and 32,812x in the neutral regions. CH was detected in 100% of donors and recipients, with a trend toward more CH clones in older vs. younger donors. We defined CH as mutations observed in at least 2 unique DNA molecules, rather than by a threshold variant allele frequency (VAF). Among the 11 donors with matched historical and contemporary DNA samples, CH mutations in the latter had a higher average VAF and comprised more unique mutations than in the former, reflecting clonal expansions over time. The magnitude of CH expansions was greater for the AML-associated genes than for neutral loci, consistent with positive selection.
Post-HSCT the overall number of unique mutations was similar between donors and recipients. Most donor CH variants did not preferentially expand in the recipient. A minority of recipients had a modestly increased overall average VAF relative to paired donors in AML genes. While the VAF of some likely pathogenic variants increased in the recipient vs the donor, this was not the case for most CH mutations in most recipients and the reciprocal was sometimes observed.
DS represents a powerful tool for the high-resolution study of CH evolution. In a unique historical cohort comprising longitudinal samples from some of the earliest patients and donors to undergo HSCT, we observed limited instances of accelerated CH in recipients relative to donors. While this cohort is biased due to enriched inclusion of long-term survivors, our data exemplifies how healthy hematopoiesis, indistinguishable between donors and recipients, can be maintained almost half a century following transplant.
Citation Format: Masumi Ueda, Jake Higgins, Thomas Smith, Elizabeth Schmidt, Fang Y. Lo, Charles C. Valentine, Jesse J. Salk, Rainer Storb, Jerald P. Radich. Duplex Sequencing reveals ubiquitous clonal hematopoiesis and complex donor-recipient clonal dynamics following HSCT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB063.