Abstract 970P
Background
Anti-tumor immunity of therapeutic anti-PD-1 monoclonal antibodies (mAbs), such as nivolumab and pembrolizumab, rely on their ability to antagonize the PD-1/PD-L1 interaction, rescuing exhausted T-cell immunity. However, upon forming a stable sPD-1-antiPD-1mAb immune complex (PD-1 IC), anti-PD-1 mAbs can trigger immunosuppressive activity in fragment crystallizable receptor (FcR)-expressing myeloid cells.
Methods
The binding of anti-PD1 and PD-1-IC is evaluated in vitro by surface plasmon resonance (SRP) (BiacoreTM T200, Cytiva), through the interaction of FcγRI/CD64, FcγRIIa/CD32a, FcγRIIb/CD32b, FcγRIIIa/CD16a and FcγRIIIb/CD16b and anti-PD1 mAbs or IC-PD-1 on a CM5 sensor chip. The presence and quantification of sPD-1 and PD-1 ICs in plasma of anti-PD-1 mAb-treated patients is assessed by customized ELISAs and western-blot approaches.
Results
Sensorgrams analyses revealed that anti-PD1 and PD-1-IC display detectable levels of binding all the FcγRs tested, albeit with diverse degrees. For FcγRIIIa/CD16a and FcγRIIIb/CD16b, dissociation phase was clearly slowest for PD-1 IC with respect to the monomeric mAb. Instead, the interaction with FcγRI/CD64, FcγRIIa/CD32a, FcγRIIb/CD32b have any major difference in the overall affinity of anti-PD-1 mAbs versus PD-1 IC, but at least CD32a/b show a slightly different kinetic of binding that may reflect a different signal for the cells involved. Data concerning the quantitative/semiquantitative evaluation of PD-1 IC concentration in plasma of cancer patients treated with nivolumab or pembrolizumab, will be presented.
Conclusions
Despite the IgG4 subclass is expected to display the lowest binding affinity to Fcγs, we report here that anti-PD-1 therapeutic antibodies bind significantly to FcγRs particularly if stabilized in the IC form by engaging soluble PD-1. This evidence could introduce novel functional properties to these therapeutic agents, with potential detrimental effects on their clinical efficacy. Our findings imply that tools to antagonize PD-1-related exhaustion by Fc-null mAbs or non-mAb-based strategies could be preferred to engage full-fledged antitumor immune responses without unwanted effects related to FcR triggering.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
L. Rivoltini, Immunotherapy of Human Tumor, Fondazione IRCCS Istituto Nazionale dei Tumori Milano.
Funding
5x1000 Funds 2014, Italian Ministry of Health (MoH) Institutional grant from Fondazione IRCCS, Istituto Nazionale dei Tumori [grant number BRI2017]; PRECIOUS Project-Horizon 2020 [grant number 686089].
Disclosure
All authors have declared no conflicts of interest.