Abstract
Background: The availability of multiple CD19-targeted agents of different drug classes allows for sequential targeting of the CD19 antigen in relapsed or refractory (R/R) B-cell lymphomas. However, the observation of CD19-negative relapse in approximately 30% of patients following CD19-directed chimeric antigen receptor T-cell (CAR-T) therapy with axicabtagene ciloleucel has raised concerns on the sequencing of CD19-targeted therapies (Plaks V, et al. Blood. 2021). Tafasitamab is an anti-CD19 monoclonal antibody (mAb) approved in combination with lenalidomide (L) for adults with R/R diffuse large B-cell lymphoma (DLBCL) ineligible for autologous stem cell transplant. Several studies have reported that CD19 expression was retained after tafasitamab treatment (Boxhammer R, et al. Blood. ASH 2019; Duell J, et al. Leuk Lymphoma. 2022); however, the assays used were not standardized and sample sizes were limited. We report data from multiple complementary, standardized analyses assessing CD19 expression and mutation status in post-treatment tumor samples from patients who received tafasitamab as part of a clinical trial or in a real-world setting.
Methods: Tumor samples were collected from patients with R/R DLBCL who received tafasitamab in the phase 2 L-MIND (NCT02399085) and phase 3 firmMIND (NCT05429268) studies, patients with R/R follicular lymphoma (FL) or marginal zone lymphoma (MZL) who received tafasitamab in combination with L + rituximab (R) in the phase 3 inMIND study (NCT04680052), patients with chronic lymphocytic leukemia (CLL) enrolled in a phase 1 study (NCT01161511), patients with R/R non-Hodgkin lymphoma or CLL in the topMIND study (NCT04809467), and also from patients with R/R DLBCL who received tafasitamab in a real-world setting. CD19 protein expression was assessed by immunohistochemistry (IHC) or flow cytometry. Next-generation sequencing (NGS) was used to assess CD19 mutation status and RNA expression.
Results: At the data cutoff (June 30, 2025), post-treatment biopsy samples from a total of 64 patients with R/R B-cell malignancies were analyzed by either IHC or flow cytometry (L-MIND, n=6; firmMIND, n=9; inMIND, n=13 [FL, n=12; MZL, n=1]; CLL, n=14; real world, n=22).
Among the 13 inMIND samples collected from patients who received tafasitamab + L + R, 5 (38%) did not contain residual tumor cells. All 59 samples with residual tumor cells were CD19 positive post-treatment, except for 2 samples: one from a patient with DLBCL that was also negative at baseline; the other from a patient with FL from the inMIND study who was refractory to R. This patient achieved a partial response (PR) despite the finding that 80% of tumor cells in the screening sample were CD19-negative and the remaining 20% stained only weakly for CD19. This finding suggests that CD19 positive cells were eliminated by treatment with tafasitamab, resulting in a PR, although it is also possible that tafasitamab resulted in the PR followed by loss of CD19 expression. Among 44 samples with available data, median duration from last tafasitamab dose to post-treatment biopsy collection was 24 days (range, 0–820). Among 48 samples from 45 patients assessed by IHC, all tumor cells were CD19 positive in 67% of samples, at least 70% of tumor cells were CD19 positive in 92% of samples, and 77% of intensity scores were 3+.
NGS was performed on 4 post-treatment samples from patients enrolled in L-MIND, 7 from patients enrolled in topMIND, and 28 from patients who received tafasitamab + L + R enrolled in inMIND who were minimal residual disease-positive post-treatment; no somatic CD19 mutations were observed. CD19 expression was preserved in all 4 samples from L-MIND that were RNA sequenced; although, exon skipping was observed for exons 2 (E1–E3), 5 (E4–E6), and 5/6 (E4–E7).
Conclusions: CD19 protein expression was retained in samples from patients with R/R B-cell malignancies who received tafasitamab in either clinical trial or real-world settings and no somatic CD19 mutations were detected in post-treatment samples. These data support the potential to treat patients with R/R B-cell malignancies who received tafasitamab with subsequent lines of CD19-targeting agents, such as CAR-T therapy.
