Low numbers of pre-leukemic fusion genes are frequently present in umbilical cord blood without affecting DNA damage response

Abstract

Despite widely accepted notion that many childhood leukemias are likely developed from hematopoietic stem/progenitor cells (HSPC) with pre-leukemic fusion genes (PFG) formed in embryonic/fetal development, the data on PFG incidence in newborns are contradictive. To provide a better understanding of a prenatal origin of leukemia, umbilical cord blood from 500 newborns was screened for the presence of the most frequent PFG associated with pediatric B-cell acute lymphoblastic leukemia. This screening revealed relatively high incidence of ETV6-RUNX1, BCR-ABL1 (p190) and MLL-AF4 at very low frequencies, averaging ~14 copies per 100,000 cells. We assume that most of these PFG might originate relatively late in embryonic/fetal development and will be eliminated later during postnatal development. The obtained results suggested that higher PFG copy numbers originating in specific time windows of the hematopoietic stem cell hierarchy may define a better prognostic tool for the assessment of leukemogenic potential. We have observed no significant effect of low-copy PFG on radiation-induced DNA damage response, accumulation of endogenous DNA double-stranded breaks, and apoptosis in either lymphocytes or HSPC. Imaging flow cytometry showed lower level of γH2AX foci in HSPC in comparison to lymphocytes suggesting better protection of HSPC from DNA damage.

Insights into the prenatal origin of childhood acute lymphoblastic leukemia

“…The frequency in investigated adults was markedly lower, but that is in line with the reduced risk for ETV6-RUNX1 + leukemia in adults [48]. However, all studies confirming the presence of ETV6-RUNX1 in healthy newborns that looked at the frequency found it to be much lower [37,39]. Lausten-Thomsen et al [46] initially found1 % of ETV6-RUNX1-positive samples with a frequency of ≤ 10 −5 , therefore this study is very important in challenging the proposed frequency of the preleukemic cells.…”

“…The real discussion might not be whether the ETV6-RUNX1 fusion is present in healthy newborns but at what frequency. Originally, Mori et al [6] reported frequencies of 10 −4 to 10 −3 , but those frequencies were not confirmed by later studies [36,37,39,46,48]. The frequency in investigated adults was markedly lower, but that is in line with the reduced risk for ETV6-RUNX1 + leukemia in adults [48].…”

“…Initially identified in umbilical cord blood of one healthy newborn and the peripheral blood of 13 healthy children and adults [32], ETV6-RUNX1 was shown to be present in~1% of newborns [6]. Several Danish studies later challenged these findings [36,[44][45][46][47], but newer reports confirmed the original results [7,[37][38][39].…”

Five percent of healthy newborns have an ETV6-RUNX1 fusion as revealed by DNA-based GIPFEL screening

“…It has been shown to be associated with monocytic AML phenotypes and proven to be of functional relevance for leukemogenesis. [13][14][15] It is interesting to note that RKIP loss has also been observed in a variety of solid cancers and has been described as a bona fide…”

“…Since this initial investigation, several studies have carefully analyzed the incidence of the translocation in newborns, children, and adults using fresh or frozen cord blood or peripheral blood (summarized in supplemental Table 1, available on the Blood Web site). [4][5][6][7][8][9][10][11][12][13][14] Remarkably, the suggested incidence ranged from 0.01% (equaling the corresponding leukemia rate) [7][8][9] to 8% (exceeding it by a factor of 800). 5 Because the investigated cohorts and specimens were similar, the variation was assumed to have technical explanations.…”