HL-370 Fragmentóme Profiling Reveals Distinct Molecular Subgroups of Classic Hodgkin Lymphoma

Context: Classic Hodgkin lymphoma (cHL) is a phenotypically heterogeneous disease with enigmatic biology and pathogenesis. By leveraging ctDNA analysis, here we identify molecular groups of cHL with phenotype- and outcome-associated signatures. Objective: Identification and biological characterization of novel cHL subgroups. Methods: We sequenced 202 cHL patients targeting ~344 kb of genomic space. The length of ctDNA mapped reads was extracted, and unsupervised clustering was performed. PET/CT scan and 71 plasma cytokines were obtained for clinical correlation. Single-cell RNA sequencing was performed for 8 patients. Results: To identify molecular subgroups within cHL, we focused on the fragmentation profile of cfDNA, a non-genetic way of detecting tumor-derived DNA in the cfDNA samples. We identified two distinct clusters, one with a fragmentation profile close to healthy (N=135), named mono-nucleosomal, and a submono-nucleosomal cluster characterized by a global shift toward shorter fragments, whose length was less than the typical wrap around the nucleosome (N=67). We explored whether cHL subtypes defined by the cfDNA fragmentation profile are clinically and biologically validated. Patients with the submono-nucleosomal fragmentome showed more frequent advanced-stage B symptoms and elevated ESR at the clinical level, higher tumor volume (TMTV and TLG) at the radiomic level, and lower PFS in terms of outcome. Tumor mutations and immune microenvironment are pathophysiologic features of cHL. The submono-nucleosomal cluster carried a higher tumor mutation burden because of heavier aberrant somatic hypermutation (ASHM). The submono-nucleosomal cluster had an immune-suppressive microenvironment enriched of T-regs and higher plasmatic levels of T-regs chemoattractants and inducers of PD1 expression (IL6, CCL2, CCL4). Conversely, mono-nucleosomal cHL had a microenvironment enriched of T_FH cells and cytotoxic CD8 T_EM cells and associated with cytokines and chemokines that are known for being attractants and activators of effector T cells (IL-1a, CCL21, CXCL12, IL-17A). Conclusions: Our observations indicate that cHL subgroups belonging to the submono-nucleosomal cluster have a more aggressive disease, a higher mutation load and more neoantigens likely due to denser ASHM, and an immune-suppressive microenvironment. Instead, cHL subgroups belonging to the mono-nucleosomal cluster have a less aggressive disease, a lower mutation load and lower neoantigens likely due to lighter ASHM, and a tumor-suppressive microenvironment.