159P Better performance of pan-claudin18 antibodies on claudin18.2 detection in gastric adenocarcinoma than claudin18.2 specific antibody

The claudin18 isoform 2 (CLDN18.2), a member of the tight junction protein family, is a highly selective target for development of novel therapies in various primary malignant tumors. Due to the interference of CLDN18.1, which is highly homologous to CLDN18.2, selection of appropriate antibodies still need to be further identified. Expression of CLDN18.2 was evaluated in a total of 66 gastric adenocarcinoma samples by immunohistochemistry(IHC) using the pan-CLDN18 antibodies (clone 43-14A and clone MM02), which recognizes both CLDN18.2 and CLDN18.1, and the CLDN18.2-specific antibody (clone EPR19202-244). The results were further verified by qPCR and CLDN18.1-specific antibody respectively. The CLDN18.2 expression evaluated by 43-14A and MM02 showed highly consistentat in different eligibility criterions (≥ 2+ membrane staining intensity in ≥ 40% or ≥ 75% of tumor cells) with 95.45% and 90.91% overall percent agreements(OPA) respectively. While EPR19202-244 showed low sensitivity (84.38%) compared with 43-14A, even after readjusting the optimal threshold according to the ROC curve and Youden index. CLDN18, CLDN18.1 and CLDN18.2 mRNAs were further measured via quantative real-time PCR and IHC for CLDN18.1 was applied. It was verified that all those samples determined to be negative for CLDN18.2 by EPR19202-244 but positive for CLDN18 by pan-CLDN18 antibodies should be identified as true positive for CLDN18.2.Table: 159PComparison of clone 43-14A, clone MM02, and clone EPR19202-24443-14A/MM02/EPR19202-244+/+/++/+/-+/-/--/+/--/-/+-/+/+-/-/-TotalSamples29702212566Samples were verified205/210937qPCRpan-CLDN1819420/1*CLDN18.2194200CLDN18.100001*IHCCLDN18.1-specific00000Note: ≥2+ intensity in ≥40% tumor cells defined as CLDN18.2-positive for 43-14A and MM02, and ≥2+ ≥25% for EPR19202-24. *：Possibly due to technical differences in qPCR and IHC Open table in a new tab Note: ≥2+ intensity in ≥40% tumor cells defined as CLDN18.2-positive for 43-14A and MM02, and ≥2+ ≥25% for EPR19202-24. *：Possibly due to technical differences in qPCR and IHC Our results clarify the differences between EPR19202-244, 43-14A and MM02, and suggesting a higher sensitivity and specificity of pan-claudin18 antibodies, which should be used for the dectction of CLDN18.2.