CD19 Expression by IHC Alone Is Not a Predictor of Response to Loncastuximab Tesirine: Results from the LOTIS-2 Clinical Trial and Quantitative Systems Pharmacology Modeling

Abstract

Introduction: CD19 is a clinically-validated target for the treatment of B-cell malignancies, and several CD19-targeted therapies have received approval, including chimeric antigen receptor T-cell (CAR-T) therapy, antibody-drug conjugates (ADCs), monoclonal antibodies, and bispecific agents. However, the optimal sequencing of these treatments has not yet been clarified. Loncastuximab tesirine (loncastuximab tesirine-lypl; Lonca) is an ADC comprising an anti-CD19 antibody conjugated to a pyrrolobenzodiazepine (PBD) dimer cytotoxin, indicated for relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) after ≥2 systemic treatments. Prior CAR-T therapy does not preclude a response to Lonca, and responses were also observed in patients who received CAR-T therapy post-Lonca. The present analysis was performed to determine the contribution of CD19 expression to responses in patients treated with Lonca. Methods: CD19 expression determined by immunohistochemistry (IHC) was evaluated in a cohort of patients enrolled in the LOTIS-2 clinical trial (NCT03589469) with available tissue samples obtained after their last anti-cancer systemic therapy and prior to Lonca. IHC was performed using the LE-CD19 antibody (DAKO), and expression was analyzed using the BenchMark ULTRA platform (Ventana). CD19 expression was assessed by semiquantitative scoring of both the percentage of positive tumor cells and the H-Score (semiquantitative assessment of the percentage of CD19 positive cells and staining intensity). Quantitative Systems Pharmacology (QSP) modeling was used to predict response to Lonca and to test hypotheses regarding patient-specific covariates. Results: The cohort included patients with any prior systemic therapies (n = 59), including patients who received CAR-T as the last therapy prior to biopsy (n = 9). Responses to Lonca were seen in patients across all levels of CD19 expression, including patients with extremely low or no detectable CD19 expression at baseline and extremely low H-Scores. On the basis of the QSP modeling, patients are anticipated to achieve disease response to Lonca with CD19 tumor cell-surface densities as low as 1,000 molecules/cell (Figure 2). Conclusions: Response to Lonca was observed in R/R DLBCL patients with very low CD19 tumor expression as measured by IHC. QSP modeling predicts that CD19 expression level by IHC is not predictive of response to Lonca, whereas the addition of CD19 surface density improves the response prediction. Patients responded to Lonca with estimated tumor cell surface densities as low as 1,000 molecules/cell, normally below the level of IHC detection. Our findings indicate that Lonca is an effective treatment option for patients with R/R DLBCL following ≥ 2 lines of treatment, even in patients expected to have a low level of CD19 expression. These results serve as a basis for future studies addressing sequencing of CD19-targeted agents. Funding: ADC Therapeutics SA; medical writing: CiTRUS Health Group. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal