Sera obtained from patients pre-and post-CARTmeso therapy were analyzed for the presence of antibodies reactive with mesothelin and with cell extracts from autologous and allogeneic tumor cell lines. (A) Sera from MPM patient 17510-105 obtained at day −3 and day +64 were analyzed by immunoblotting for reactivity against purified mesothelin protein (MESO), SV40 large T antigen protein (SV), and lysates obtained from seven mesothelioma cell lines (REN, 208, 213, 302, 307, M30 and M60). New bands at ~70 kD (red boxes) and ~45 kD (blue boxes) were seen after CARTmeso cell infusion. (B) Sera from PDA patient 21211-101 obtained at days −7, +57 and +92 were analyzed by immunoblotting for reactivity against mesothelin protein (MESO), SV40 large T antigen protein (SV), lysate from a PDA cell line (Panc1) and lysate from a tumor cell line derived from the patient’s own ascites (21211 Tumor). A strong anti-mesothelin band was noted in the Day +57 sample (blue arrow) and new bands were seen after receiving CARTmeso cell infusion at ~65–80 kD (red boxes) for the autologous 21211 cell line and for the Panc1 cell lines (blue boxes).