CD19 Chimeric Antigen Receptor T-cell Shows Activity in Patients with B-cell Lymphoma Without CD19 Expression by Immunohistochemistry

Abstract Background: Some clinical trials have reported that CD19-negative B-cell lymphoma patients responded to CD19 CART therapy. The mechanism of CD19 CART activating in patients with B-cell lymphoma that do not express CD19 by immunohistochemistry (IHC) remains unknown. Methods: 8 CART treated diffuse large B-cell lymphoma (DLBCL) patients and other 90 DLBCL tissues were tested by IHC using 7 anti-CD19 antibodies. Besides, CD19 mRNA and protein of 6 human DLBCL cell lines were assessed using Reverse Transcription Polymerase Chain Reaction (RT-PCR) and Western blotting analysis, and CD19 expression was evaluated by IHC as well as flow cytometry (FCM). Results: 6 out of 8 (75%) DLBCL patients who received CD19 CART therapy were identified as CD19-negative by at least one antibody. In the 6 patients, 5 objective responses were seen (response rate, 83.3%). For the 90 DLBCL samples, 68 samples were involved in analysis, and 57 out of 68 (83.8%) samples were assessed as CD19 negative by at least one antibody. IHC assay for 6 DLBCL cell lines showed that 3 cell lines CD19 expression by IHC had inconsistent results with CD19 mRNA and Western blotting assays, while FCM assay for the 6 DLBCL cell lines showed high sensitivity and good concordance to CD19 expression. Antibody HIB19 mean fluorescence intensity showed a positive correlation with CD19 expression (R2=0.8125, P=0.0137). Conclusion: These results demonstrate the mechanism that CD19-negaive B-cell lymphoma patients respond to CD19 CART therapy, suggesting that inclusion or exclusion of lymphoma patients for CD19 CART therapy based on current CD19 IHC seems unwarranted. FCM assay is recommended as a complementary diagnostic method to CD19 IHC.