Bendamustine switches TNF receptor superfamily signal from a survival to a death signal in B-cell lymphomas

Bendamustine is one of the primary chemotherapeutic agents for the treatment of B-cell lymphomas, whereas its toxicity to T cells is associated with a high rate of infectious complications and a potential negative impact on subsequent immunotherapies. Bendamustine has previously been reported to be a potent in vitro inhibitor of HOIP, the catalytic subunit of the linear ubiquitin chain assembly complex (LUBAC). Because LUBAC functions as a checkpoint for tumor necrosis factor receptor superfamily (TNFRSF)-induced cell death, we hypothesized that bendamustine may have specific activity on the CD40 or BAFF-R signaling in B-cell lymphomas. In a cell culture assay, we found that bendamustine not only suppressed CD40L- and BAFF-driven NF-κB signaling in B-cell lymphomas but also induced higher cell death in the presence of these signals, a phenomenon not typical of other chemotherapeutic agents. Bendamustine resistance was shown to be driven by knockout of TRAF3, a mediator of CD40 and BAFF-R signaling. Importantly, the toxic effect of bendamustine on T cells was also found to be associated with another TNFRSF molecule, OX40. Pretreatment with an antibody blocking OX40-OX40L signaling attenuated bendamustine-induced T-cell depletion in mice, whereas preserving the cytotoxic effect of bendamustine on transplanted B-cell lymphoma. In conclusion, both the antilymphoma effect and the T-lymphopenia induced by bendamustine are associated with TNFRSF signaling, and the T-cell toxicity can be separately controlled by blocking OX40 signaling before bendamustine administration.