Abstract 4330: A CD5 signature identifies diffuse large B-cell lymphomas (DLBCLs) sensitive to Bruton’s tyrosine kinase (BTK) inhibition

Abstract Introduction: Gene expression profiling has identified DLBCLs that bear transcriptional similarity to either non-malignant germinal center B-cells (GCB-DLBCL) or activated B-cells (ABC-DLBCL, i.e. non-GCB-DLBCL). This cell-of-origin (COO) classification has guided precision medicine strategies, including the use of ibrutinib, a BTK inhibitor (BTKi), with ABC-DLBCLs thought to be sensitive to BTKi due to their constitutive activation of NF-kB downstream of the B-cell receptor (BCR). However, the phase III Phoenix trial testing the addition of ibrutinib to R-CHOP chemoimmunotherapy surprisingly failed to demonstrate a survival benefit in non-GCB-DLBCLs. By employing a newly defined genetic classification algorithm (LymphGen), distinct genetic DLBCL subtypes that benefit from this regimen were identified. However, LymphGen is not utilized in the clinic and fails to classify >40% of DLBCLs. To overcome these challenges, we sought to identify a straightforward biomarker of BTKi sensitivity. CD5 was selected as a potential candidate, given its role as a negative regulator of BCR signaling and expression in other BTKi-responsive B-cell lymphomas. Methods: CD5 IHC was performed on a cohort of 405 DLBCLs, most with paired RNA and targeted mutational sequencing. Comparison of the transcriptomes of CD5+ and CD5− DLBCLs was used to construct a 60-gene CD5 signature (CD5sig), which was applied to large genomic DLBCL datasets, including pre-treatment biopsies from the Phoenix trial (n = 584) to evaluate its utility in predicting improved response to R-CHOP + ibrutinib. Results: Twenty-seven DLBCLs were identified as CD5+ by IHC (6% of cases; 12% of non-GCB). Consistent with previous reports, CD5+ DLBCLs were enriched for a non-GCB COO and exhibited inferior progression-free survival to R-CHOP. CD5+ DLBCLs upregulated genes related to BCR signaling and had a significantly higher incidence of CD79B BCR-activating mutations. A CD5 signature (CD5sig) was created from differentially expressed genes between CD5 IHC+ and CD5 IHC− non-GCB-DLBCLs. When applied to an external dataset of 349 non-GCB-DLBCLs, CD5sig+ DLBCLs (15% of cases) were enriched for BCR-activating mutations and were majority MCD (MYD88 and CD79B) or unclassified by LymphGen. CD5sig+ DLBCLs were largely devoid of BCL10 activating mutations known to drive BTKi resistance. When applied to the Phoenix study, CD5sig+ DLBCLs selectively benefitted from R-CHOP + ibrutinib by event-free and overall survival. This survival difference was preserved even among LymphGen-unclassified DLBCLs. Conclusions: Here, we identify CD5 expression as a simple and useful biomarker to identify high-risk, BCR-driven DLBCLs beyond those identified through genetic classification. Based upon unique transcriptional features of CD5 IHC+ DLBCLs, we developed a novel CD5 signature that identifies DLBCLs vulnerable to BTKi therapy. Citation Format: Alan Cooper, Sravya Tumuluru, Kyle Kissick, Girish Venkataraman, Nikita Kotlov, Aleksander Bagaev, Andrew Lytle, Gerben Duns, David W. Scott, Christian Steidl, Brendan Hodkinson, Srimathi Srinivasan, Justin Kline, James Godfrey. A CD5 signature identifies diffuse large B-cell lymphomas (DLBCLs) sensitive to Bruton’s tyrosine kinase (BTK) inhibition. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4330.