Clonal Hematopoiesis in AML Patients in Hematological CR Is Present in Many Patients with Intermediate Risk AML and Is Associated with a High Prevalence of DNMT3A gene Mutations

Background De novo acute myeloid leukemia (AML) is a malignant disorder of hematopoietic stem and progenitor cells usually characterized by a rapid clinical onset. Despite this clinical manifestation, recent evidence suggests that premalignant stem cells might be present in patients with AML, which can persist after chemotherapy in some patients and induce clonal hematopoiesis. Little is known about the prevalence of clonal persistence and about the molecular basis. In order to study the prevalence of this phenomenon and to better understand the underlying molecular mechanisms, we investigated AML patients in remission for clonal persistence of cells after chemotherapy.

Patients and methods: All patients included in this analysis were treated within a prospective treatment protocol of the Study Alliance Leukemia (SAL). The primary study cohort consisted of 61 female patients with intermediate risk cytogenetics achieving hematologic complete remission (CR), whose DNA material was available at CR. Clonality analysis was based on X-chromosome inactivation testing using the HUMARA assay. DNA from diagnostic samples of patients presenting with evidence for X-chromosome skewing in CR was analyzed using amplicon based resequencing on a MiSeq next generation sequencing (NGS)-system for DNMT3A, ASXL1, ASXL2, TET1, TET2, EZH1, EZH2, IDH1 and IDH2.

Results: Of the 61 patients included, 52 were heterozygous for the STR in the human androgen receptor gene. In CR, 22 of these 52 patients (42%) showed evidence for a skewed X-chromosome representation, indicating persistence of clonal hematopoiesis in remission. The NGS-based analysis of genes involved in epigenetic regulation revealed mutations in 13/22 (59%) of the patients. DNMT3A was most frequently mutated (11/13 patients), either alone or in combination with other alterations (TET2, EZH2). Interestingly, two patients showed somatic alterations in the TET1 gene. In remission, clonal persistence of these alterations was detected in all 13 patients with mutations at diagnosis at levels between 0.8 and 50% as documented using ultradeep-NGS. To get an idea on the prevalence of clonal persistence in other cytogenetic groups, we analyzed 22 low risk (i.e. CBF-leukemias) as well as 18 poor risk (-7, complex karyotype) patients using the HUMARA assay. Here we observed similar results, with 13/19 informative patients showing clonal persistence in low-risk group (68%) compared to 7/14 patients (50%) in the poor risk population. Since all these analyses were confined to female patients and potentially limited by the sensitivity of the HUMARA method, we went on to look for persistence of clonal molecular markers using more sensitive ultra-deep NGS. Because DNMT3A exon 23 was the common alteration in this initial analysis, we screened a cohort of 48 patients with mutations in NPM1 and comutations in DNMT3A. In this separate cohort, persistence of the DNMT3A mutations at CR or during follow-up (FU) was detected in 42 patients (87.5%) at levels between 0.5 and 50% (median 11.1%). No difference was seen between male and female patients, the median age was 51 years, persistence was seen even in young patients at 26 years of age. During FU, the DNMT3A VAF level rose further in all patients analyzed, arguing for a clonal advantage of the mutant cells. All patients with relapse and available material showed high levels of DNMT3A at time of relapse. However, correlation of DNMT3A mutant allele levels at CR1 with the incidence of relapse showed no significant impact of the VAF for the development of relapse.

Conclusions: Our data indicate that clonal persistence of premalignant cells carrying clonal alterations in epigenetic regulator genes is a common phenomenon in patients in continuous CR. DNMT3A is the most common lesion persisting, the majority of patients with this mutations retain it at CR and during FU. These data indicate that de novo AML develops from preleukemic stem and progenitor cells in many patients. Preliminary data indicate that this persistence per se is not associated with inferior outcome.