Anti-drug antibodies to LMB-100 are enhanced by mAbs targeting OX40 and CTLA4 but not by mAbs targeting PD1 or PDL-1.

LMB-100 is a recombinant immunotoxin being developed for cancer treatment that is composed of a Fab that binds to mesothelin and a portion of Pseudomonas exotoxin A. LMB-100 is in clinical trials for the treatment of mesothelioma and pancreatic cancer. To determine if check point modulating antibodies enhance the formation of anti-drug antibodies (ADA) against LMB-100, we treated mice with LMB-100 and four different immune modulating monoclonal antibodies that have different mechanisms of action; anti-CTLA4, anti-OX40, anti-PD-1 and anti-PDL-1. We found that anti-PD-1 and anti PDL-1 do not increase the formation of ADA, but anti-CTLA-4 and anti-OX-40 do increase the onset of ADA. These results indicate that combining anti-CTLA-4 and anti-OX-40 with antibodies and other protein-based therapeutics may enhance ADA formation in humans.