Tracking clonal hematopoiesis in patients with classical hodgkin's lymphoma

Introduction: Clonal hematopoiesis (CH) is frequent in the elderly and predisposes to hematological malignancies, mostly of myeloid and T-cell origin. CH incidence and tissue trajectories are not well characterized in classical Hodgkin lymphoma (cHL), a B-cell neoplasm frequent in the young and uniquely featuring a small tumor clone of Hodgkin/Reed-Sternberg (HRS) cells interspersed in a tumor-supportive microenvironment largely infiltrated by hematopoietic cells. Methods: 40 cHL cases were studied for CH, by whole-exome and/or targeted sequencing (mean unique coverage ∼150X and ∼1000X, respectively) of microdissected tumor cells, and matched non-neoplastic blood cells (n = 27 cases) and/or lymphoid cells microdissected from the tissue biopsy (n = 14 cases). Results: 5/40 cases (12.5%) had blood and/or tissue CH, including 3/5 with >70 years and 2/35 < 70 years (Fig. 1A). In 3/5 CH cases (aged 30, 45 and 73 years), CH extensively spread through the non-neoplastic tissue microenvironment (32%, 92%, and 60% of cells), being respectively driven by DNMT3A R882H (Case 1), mutant KRAS G60D (Case 2) and DNMT3A R882H + TET2 Q1274* (Case 5). Notably, in Case 5 (73 years old), CH originated also the tumor cell clone, which was infected by the Epstein-Barr virus and had almost no other somatic mutations exome-wide; this is the first description, in a cHL tumor cell clone, of mutant DNMT3A R882, a hotspot in myeloid and T-cell neoplasms. In Case 1 (45 years old), the same mutation determined a massive blood CH (DNMT3A R882H in 94% leukocytes and in 96% B cells) that was surprisingly absent from the tumor cell clone (instead carrying STAT6 and SOCS1 mutations, typical of cHL) and led, 6 years after therapy for cHL, to a likely therapy-unrelated NPM1-mutated acute myeloid leukemia (with normal karyotype, wild-type TP53 and PPM1D) (Fig. 1B). Thus, CH trajectories must be carefully disentangled to correctly interpret the histogenesis and pathogenesis of multiple blood cancers arising in patients with CH. Interestingly, all 3 cases with extensive CH propagation in cHL tissue microenvironment, showed a polyclonal status of T-cell receptor gene rearrangement, thus proving that CH-associated mutations occurred in a bone marrow stem/progenitor cell before T-cell lineage commitment. Finally, all these 3 cases progressed after first-line chemotherapy, versus 11/35 (31%; p-value 0.043) evaluable cases with absent or non-extensive tissue CH, who otherwise had similar clinical features and received the same first-line therapy. EA – previously submitted to AACR and EHA 2021. The research was funded by: This research was funded by a grant on cHL to ET from AIRC (IG 2019- ID. 23732 project – P.I. Tiacci Enrico); a grant on AML to BF from AIRC (IG 2019 n. 23604); a grant on AML to BF from ERC (Advanced Grant 2016 n. 740230), the Leopold Griffuel prize from ARC to BF; and a grant on cHL to GS from the Department of Medicine - University of Perugia (Ricerca di Base 2017-2019). Keywords: Tumor Biology and Heterogeneity, Hodgkin lymphoma No conflicts of interest pertinent to the abstract.