S238: CLONAL ARCHITECTURE OF RELAPSED OR REFRACTORY ANGIOIMMUNOBLASTIC T-CELL LYMPHOMA: AN ANCILLARY STUDY OF THE ORACLE TRIAL, A LYSA STUDY (2023)

Background: The lymphomagenesis of TFH peripheral T-cell lymphoma (TFHL) notably involves altered TCR signaling and epigenetic regulation in follicular T-helper lymphocytes resulting from recurrent mutations in key components of these pathways such as RHOA and TET2, DNMT3A, or IDH2 respectively. Previous studies also identified some of these mutations in B cells or hematopoietic progenitors in TFHL patients suggesting that TFHL derives from clonal hematopoiesis. Aims: This study aims to characterize the clonal hierarchy of TFHL further and estimate the frequency of TFHL derived from clonal hematopoiesis (CH-TFHL) in an ancillary study of the randomized Phase 3 clinical trial, ORACLE (NCT03593018), evaluating the efficacy and safety of oral 5-azacitidine (CC-486) compared to single-agent chemotherapy in patients with relapsed or refractory TFHL. Methods: To determine the clonal architecture of refractory TFHL, bone marrow myeloid progenitor cultures from 32 patients at inclusion were performed in methylcellulose supplemented with standard growth factors. BFU-E, CFU-GM, and CFU-GEMM were counted and individually harvested. A total of 517 colonies derived from the 32 patients were then individually genotyped by next-generation sequencing (NGS) using a capture-based panel (limit of detection: 1%) covering 43 genes recurrently mutated in CH and TFHL and including TET2, DNMT3A, IDH2R172, RHOAG17V. Meanwhile, total BM cells from 29 patients were sequenced with the same NGS panel and results were compared with those found in cfDNA (n=31 patients) and malignant lymph node biopsies (n=28 patients). Overall, the frequency of clonal hematopoiesis and the phylogenetic link between the myeloid progenitors and the tumor could be evaluated on 30 TFHL patients. Two patients were excluded from the analysis due to an important bone marrow infiltrate of malignant T cells or technical failure. Results: 471/517 (91%) colonies were successfully genotyped. CH defined by at least one somatic mutation detected in at least one myeloid clone or total BM cells was found in 29/30 (97%). The proportion of patients carrying DNMT3A mutations in the BM (75%) was significantly higher (Fisher’s test FET; p = 0.003) as compared with their detection in LN (33%). Conversely, TET2 mutations were more frequent (P = 0.003; FET) in the LN (89%) than in the BM (56%). Three groups of patients were identified according to the distribution of mutations found in the BM and the LN: 16/30 (53.3%) patients had TFHL clonally derived from CH (CH-related TFHL), 13 (43.3%) had CH unlinked to TFHL (CH-unrelated TFHL) (Cf. Figure), and one patient (3.3%) had undetectable CH. The proportion of patients with myeloid colonies carrying a DNMT3R882 mutation, a TET2 mutation, or double hits (two TET2 or TET2+DNMT3A mutations) were significantly more frequent in CH-TFHL as compared with CH-unrelated TFHL (p=0.04, p=0.0001 and p=0.001 respectively, FET). The presence of a DNMT3A mutation in the tumor was highly associated with its detection in myeloid cells (p<0.001, FET, OR= 57.6), while the presence of RHOAG17V and IDH2R172 mutations in the lymph nodes were never linked to CH (p<0.0001 and p<0.01 respectively, FET). Summary/Conclusion: Mutations driving oncogenesis towards AITL arise in a hematopoietic stem cell in more than half of the patients tested and showed a distinct genetic pattern. The prognosis significance of this condition on treatment response is currently evaluated in the ORACLE trial and will be presented at the meeting. Figure: Examples of CH-TFHL and CH-unrelated TFHL Keywords: Epigenetic, Lymphomagenesis, Age related clonal hematopoiesis, Angioimmunoblastic T-cell lymphoma