Expression of the cancer testis antigen PRAME is associated with response to immune checkpoint inhibitor and rituximab priming in treatment-naïve diffuse large B-cell lymphoma

Abstract Introduction Diffuse large B-cell lymphoma (DLBCL) is clinically and biologically heterogenous. Though immune checkpoint inhibitors (ICI) have limited efficacy in unselected, heavily pre-treated DLBCL (Ansell JCO 2019), responses have been reported in select subgroups, e.g. primary mediastinal B-cell lymphoma and EBV-positive DLBCL (Armand Blood 2018, Nayak Blood 2017). In our phase II AvR-CHOP study, treatment-naïve DLBCL patients (pts) received priming with avelumab (anti-PD-L1) and rituximab (AvRp) prior to R-CHOP. Response to AvRp alone was observed in 57%, independent of established prognostic markers including International Prognostic Index, histologic subtype, cell-of-origin and baseline total metabolic tumour volume (TMTV). Novel biomarkers are thus needed to guide ICI use and further define the DLBCL immune landscape. PRAME, a cancer testis antigen expressed in ~30% of DLBCL, is highly immunogenic yet paradoxically linked to immune exclusion and checkpoint expression (Bose Int J Transl Med 2023). Its prognostic impact in chemotherapy-treated DLBCL is unclear, with both overexpression and deletions associated with poor outcomes (Mitsuhashi In J Haem 2014, Takata J Clin Invest 2022). Notably, autologous PRAME-specific T-cells have efficacy in non-Hodgkin and Hodgkin lymphoma, supporting its immunotherapeutic relevance (Vasileiou JCO 2021). We present the pre-specified translational analysis of the AvR-CHOP study. Methods Twenty-eight pts received AvRp x2, followed by R-CHOP x6 and avelumab consolidation. PET metrics (SUVmean, TMTV and total lesion glycolysis [TLG, SUVmean x TMTV]) were calculated with a fixed SUV >4 method (MIMEncore). Gene expression profiling (GEP) was performed using the NanoString PanCancer Immune Panel. Differential expression was analysed via Rosalind and custom pipelines, stratifying pts by >75% TLG reduction (TLG75) post AvRp. Whole exome sequencing (WES) used the Agilent SureSelect All Exon V8 platform. Molecular subtypes were assigned via LymphGen (Wright Cancer Cell 2020). Immune cell deconvolution, pathway enrichment, and gene set variation analysis (GSVA) were performed with CIBERSORTx and custom workflows. Associations with clinical outcomes were assessed by Kaplan-Meier analysis. Results GEP was available in 21 pts. Ten (48%) achieved TLG75, including 4 with complete metabolic response. Responses were seen across histologic subtypes. PRAME was amongst the most significantly differentially expressed genes and was upregulated in TLG75 responders (log2FC=3.84; p<0.001); 71% (10/14) of PRAME-high pts responded vs 0% (0/7) of PRAME-low. PRAME-high expression was associated with improved overall survival (OS; p=0.0314), while PRAME loss correlated with inferior progression-free survival (p<0.001) and OS (p=0.031). All 3 pts with PRAME deletions were refractory to both AvRp and R-CHOP. PRAME expression correlated with other cancer testis antigens CT45A1 (p=0.005) and MAGEA3 (p=0.013), but not PD-L1. PRAME-high tumours trended toward higher immune abundance scores, with enrichment of the immune regulation pathway (p=0.025). Pathway analysis showed upregulation of chemokine (p=0.038), cytokine (p=0.025), and tumour necrosis factor (TNF) signalling (p=0.031) in PRAME-high tumours. In TLG75 responders, GSVA revealed increased PD-1 signalling (p=0.017) and reduced IL-1 (p<0.001) and toll-like receptor signalling (p=0.047). LymphGen classification revealed subtype associations; all ST2 cases were PRAME-high and 5/6 achieved TLG75, whereas EZB and MCD subtypes were PRAME-lowwith no response. Tumours with high tumour mutational burden (TMB>10mut/Mb) were also enriched with PRAME-high expression (p=0.090). PRAME-specific T-cell responses, assessed via TCR sequencing and ELISpot, will be presented. ConclusionHigh PRAME expression identified a biologically distinct, ICI-sensitive DLBCL subgroup marked by co-expression of cancer testis antigens, upregulated immune signalling and enrichment for the ST2 molecular subtype. Despite expression of immune regulatory signatures, PRAME-high tumours respond to PD-L1 inhibition, suggesting a functionally suppressed but ICI-responsive microenvironment. These findings identify PRAME as a potential predictive biomarker in ICI-treated DLBCL and build on prior reports of PRAME-specific T-cell efficacy in lymphoma. Further study is warranted to elucidate the relationship between PRAME expression, tumour immunobiology and response to T cell–directed therapies in DLBCL.