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Frequent RUNX1 mutations in acute leukemia + pDC
a bipotent progenitor with DC (pDC and cDC) and with monocyte potential such as the MDP. The expression of CD22, CD2 and CD5 on pDC and blasts in some cases could also suggest that they derive from a granulocyte- monocyte-lymphoid progenitor or from AXL+ SIGLEC6+ DC, recently identified.41
The mutation status obtained does not highlight specific genes for all cases. Many of them are frequently mutated in other myeloid malignancies, involved in epigenetics (ASXL1 and TET2), splicing (SRSF2, SF3B1, U2AF1) or the RAS pathway (CBL, KRAS, PTPN11). This mutation pro- file is only partially similar to BPDCN, because BPDCN can also be mutated for ETV6, TP53, ZEB2, MET, ATM, IKZF3, JAK, NOTCH2 and CXCR4, plus TET2 with a high frequency (Figure 4). Cases classified as M4/5-AML were always transformations of MDS/MPN and had a similar molecular profile including ASXL1, TET2, SRSF2, CBL or PTPN11 mutations, sometimes with additional mutations responsible for acute transformation (NPM1 mutation for N35). Remarkably, RUNX1 is the most frequently mutated gene in pDC-AML (73% of cases), as already described.17 Moreover, it only concerned M0-AML cases in our study and all cases of M0-AML exhibited this mutation (100%). This point is particularly puzzling considering that this prevalence is markedly different from the described epi- demiology of 20-30% of RUNX1 mutations in M0- AML42,43 and knowing that RUNX1 mutation has only been reported once in BPDCN.44 Although, this study only analyzed a small number of cases and the recruitment bias precludes us from determining the frequency of M0-AML and RUNX1 mutations in pDC-AML. Our 11 PDCP-M0- AML cases were 71 years old on average, with a male/female sex ratio of 2.67, consistent with the RUNX1-mutated AML provisional entity.8,42 Unfortunately, given the advanced age of patients with palliative care and low number of cases, prognostic con- clusions are impossible. RUNX1 mutations were not detected in the non-neoplastic T-cell fraction, demonstrat- ing that these mutations are somatic. WGA prevented us from definitely obtaining copy number variations, but VAF were higher than 50% for six patients (N8, N9, N11, N12, N16, N19) and a seventh (N13) was double mutated for RUNX1, suggesting secondary alteration of RUNX1, as already described.45
Notably, inhibition of RUNX1 is considered to increase RUNX2 and RUNX3 protein levels, following a comple- mentary compensation mechanism that maintains the entire RUNX family at a constant level.46 Then, RUNX1 invalidation could promote a RUNX2 switch and then a pDC commitment because RUNX2 plays a crucial role in pDC diffentiation.47,48 Further experiments are neverthe- less required to confirm this hypothesis.
To conclude, our study identifies a group of pDC-AML requiring a differential diagnosis with BPDCN. They are characterized by an immature myeloid population
(CD34+, CD117+/- CD123+low without expression of pDC markers) associated with an excess of pDC (CD123+high, CD4+) that clearly differ from BPDCN neoplastic cells by no expression of CD56, the possible expression of CD34, higher expression of CD303 and lower expression of cTCL1. Molecular data show that these pDC are neoplas- tic and not reactive, and the mutational landscape of pDC- AML appears distinct from BPDCN, notably with fre- quent RUNX1 mutations. Moreover, a continuous matura- tion pattern suggests that these pDC as well as monocytes could arise from the immature CD34+ blasts, potentially with MDP properties (Figure 5B). Finally, this study addresses (i) the frequency with which RUNX1-mutated AML are associated with an excess of pDC, (ii) the type of progenitors involved and (iii) its prognostic or therapeutic impact. These questions warrant investigation in an inde- pendent and larger cohort of AML.
Disclosures
No conflicts of interest to disclose.
Contributions
FGO designed the study; FGO and FR supervised the study; ED, ED, SB, ED, VB, MLG, DRW, OWB, VS, JF, SB, BD, CMR, PO, VD, MT, JR, MTR, MCJ, VR, ES and FGO pro- cured patient specimens; SB performed cell sorting; TP performed anatomopathological analysis and MACR cytogenetics analysis; LZ, FR and LS performed the molecular experiments; PJV pro- vided assistance in bioinformatics analysis; LZ and FR analyzed NGS data; FR performed statistical analysis; LZ, FR and FGO wrote the original manuscript; CP, CR, MC, FAD, SG, FJ, CF, PS and OA revised the manuscript and provided guidance and expertise. All authors provided input and approved the final ver- sion of the manuscript.
Acknowledgments
The authors would like to thank Hugues Faucheu for helping on the design panel, Véronique Yerly-Motta for helping on the NGS platform and Fiona Ecarnot for English proofreading.
Funding
This work was supported by Ligue régionale contre le Cancer (CCIRGE-BFC-2016), Fondation ARC (Aides Individuelles DOC20170505805) and Association Laurette Fugain (ALF 2018/08).
References
1. Banchereau J, Briere F, Caux C, et al. Immunobiology of dendritic cells. Annu Rev Immunol. 2000;18767-811.
2. Jegalian AG, Facchetti F, Jaffe ES. Plasmacytoid dendritic cells: physiologic roles and pathologic states. Adv Anat Pathol. 2009;16(6):392-404.
3.Naik SH, Sathe P, Park H-Y, et al. Development of plasmacytoid and conven- tional dendritic cell subtypes from single precursor cells derived in vitro and in vivo. Nat Immunol. 2007;8(11):1217-1226.
4. Onai N, Obata-Onai A, Schmid MA, Ohteki T, Jarrossay D, Manz MG. Identification of clonogenic common Flt3+M-CSFR+ plasma- cytoid and conventional dendritic cell pro-
genitors in mouse bone marrow. Nat
Immunol. 2007; 8(11):1207-1216.
5. Chaperot L, Bendriss N, Manches O, et al. Identification of a leukemic counterpart of the plasmacytoid dendritic cells. Blood.
2001;97(10):3210-3217.
6. Garnache-Ottou F, Feuillard J, Ferrand C, et
al. Extended diagnostic criteria for plasma- cytoid dendritic cell leukaemia. Br J
haematologica | 2021; 106(12)
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