Quantitative assessment of the evolution of therapeutic target antigen expression in diffuse large b-cell lymphoma in response to treatment

Abstract Introduction: Variability in expression of B-cell surface antigens could be an important mechanism of treatment failure after immunotherapy in patients with relapsed or refractory (R/R) diffuse large B-cell lymphoma (DLBCL). Understanding the evolution of target antigen expression can guide selection and sequencing of newer therapies targeting CD19 and CD20. We sought to quantitate the change in expression of CD19 and CD20 in R/R DLBCL after Rituximab (R)-based chemo immunotherapy (CIT) relative to pretreatment levels. Methods: Pts. diagnosed with DLBCL after January 2014 who were R/R to R-based CIT (R-CHOP or R-EPOCH), were identified and clinical variables at diagnosis (Dx) and first R/R were recorded. Data from archival flow cytometry assays on Dx and R/R biopsies were accessed. Using FCS Express® software, neoplastic cells were gated, and fluorescence intensity (FI) of CD19 and CD20 expression were reported. Multivariate linear mixed model was used to compare median and geometric mean FI of CD19 and CD20 between Dx and R/R. Results: A total of 51 flow cytometry assays (26 Dx and 25 R/R) were analyzed for 33 pts., of whom paired assays (at both Dx and R/R) were available for 18 pts. Median age at Dx was 64 (range, 41-76) yrs, 24 pts. (73%) were male and 29 (88%) had IPI ≥ 2. Cell of origin at Dx was GCB in 16 (49%), non-GCB in 12 (36%) pts., while two had a double-hit rearrangement. Median time to R/R was 10.4 months. There was a significant reduction in median FI of CD20 from Dx [median: 40,610 (range: 167 - 259,962)] to R/R [median: 11,596 (range: 63 - 79,592)], representing a reduction of 63% at R/R relative to Dx (P= 0.01; 95% CI: 20-73%). Similar change was observed in geometric mean FI of CD20, which was reduced 65% at R/R relative to Dx (P< 0.01; 95%CI: 31-82%). Median and geometric mean FI of CD19 at R/R were 38% and 20% lower compared to Dx, respectively, but these differences were not statistically significant (P= 0.08 and 0.39, respectively). Relative change in FI at R/R in individual cases, compared to the mean FI of all Dx cases, showed that 21 out 25 R/R cases (84%) had reduction of CD20 whereas only 14/25 (56%) had reduction of CD19. Interestingly, 7/25 (28%) R/R cases had an increase in CD19 expression by >80%. Reduction in CD20 geometric mean FI from Dx to R/R was significantly associated with age >60 years (p=0.04), bone marrow involvement (p <0.01) and >1 site of extra nodal involvement (p= 0.03) at Dx. Conclusions: Quantitative assessment by flow cytometry revealed a significant decline in expression of CD20 at R/R compared to Dx in patients with DLBCL treated with R-based CIT. CD19 expression was largely unchanged, although dramatically upregulated in a subset of R/R cases. Given the role of CD19 mediated pathways in B-cell NHL and its association with PI3K pro-survival signaling, these data merit further exploration as a potential mechanism of treatment resistance. Citation Format: Agrima Mian, Narendra Bhattarai, Wei Wei, Manishkumar S. Patel, Paolo F. Caimi, Sarah L. Ondrejka, Brian T. Hill. Quantitative assessment of the evolution of therapeutic target antigen expression in diffuse large b-cell lymphoma in response to treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3480.