Clinicopathological characteristics of DLBCL-associated HLH and an exploratory transcriptomic investigation of the underlying microenvironment in primary DLBCL

Abstract Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome that can complicate diffuse large B-cell lymphoma (DLBCL), yet its clinicopathological characteristics and inflammatory tumor microenvironment (TME) remain incompletely understood. We retrospectively analyzed 579 newly diagnosed patients with DLBCL, including 22 with HLH and 66 matched controls without HLH, to compare their clinical and pathological characteristics. Because fresh tumor biopsies are rarely available during active HLH, publicly available single-cell RNA sequencing data from treatment-naïve primary DLBCL were used as an exploratory model to characterize inflammatory TME programs. Based on these analyses, a trajectory-derived TME inflammatory signature was developed and subsequently validated in independent bulk transcriptomic cohorts. DLBCL-associated HLH occurred in 3.8% of patients and was associated with severe systemic inflammation, high tumor burden, poor survival, and enrichment of the non-germinal center B-cell-like (non-GCB) subtype and double-expressor lymphoma (DEL). Exploratory single-cell analyses identified inflammatory TME programs characterized by macrophage activation and CD8⁺ T-cell dysfunction, leading to the development of a 29-gene trajectory-derived inflammatory signature. In external validation cohorts, higher inflammatory risk scores were associated with elevated lactate dehydrogenase and International Prognostic Index scores and remained independently associated with inferior overall survival, including within the GCB subtype. These findings indicate that DLBCL-associated HLH is a highly aggressive clinical entity. Exploratory transcriptomic analyses suggest that inflammatory TME programs may represent an additional layer of biological heterogeneity in DLBCL, and the trajectory-derived inflammatory signature provides independent prognostic value across multiple DLBCL cohorts. Further studies are warranted to determine whether these inflammatory programs are associated with susceptibility to DLBCL-associated HLH.