CD161 and LLT1 expression in immune cell populations of Hodgkin lymphoma tumor microenvironment

Hodgkin lymphoma (HL) tumor microenvironment (TME) is composed of an abundant immune cell population, with relatively few neoplastic Reed-Sternberg (RS) cells. These immune cells fail to initiate an anti-tumor response or prevent immune evasion. Both Lectin-like transcript 1 (LLT1) and CD161 are an immune checkpoint axis that modulates immune cells' responses in chronic infections, cancer, and autoimmune diseases. However, their expression within the HL TME is not well studied.

This is a retrospective observational study that was conducted using archived formalin-fixed paraffin-embedded (FFPE) lymph node tissues from tertiary care center in Northern Jordan. A total of 56 HL cases and 60 reactive lymphoid tissue controls (benign lymph nodes and tonsils) were included. Immunohistochemistry (IHC) was performed to assess LLT1 and CD161 expression in background immune cells (BICs). The primary outcomes were the expression levels and localization patterns of LLT1 and CD161. Associations with clinicopathological variables were analyzed using Chi-square, Mann-Whitney U, Kruskal-Wallis, and Spearman correlation tests. Survival analysis was performed using the Kaplan-Meier method.

A significant correlation was observed between LLT1 and CD161 expression in the tumor microenvironment, both in the frequency of positive background immune cells) (BICs (p = 0.030) and in their expression localization patterns (p = <0.001). An enrichment of CD161-expressing immune cells was significantly associated with mixed cellularity cHL (p = 0.047) and with advanced-stage disease (Stage III-IV) (p = 0.010). In contrast, EBV-negative cases exhibited significantly higher LLT1-positive immune cell infiltration than EBV-positive cases (p = 0.036), whereas CD161 expression was not associated with EBV status (p = 0.746).

LLT1 and CD161 expression in HL BICs may suggest an immune-to-immune interaction within TME. CD161 enrichment in advanced disease and the mixed cellularity subtype highlights their potential role in sustaining immune recruitment and retention. Thus, LLT1 and CD161 expression patterns position them as potential targets for immunotherapy in HL.