Fc-null anti-PD-1 monoclonal antibodies deliver optimal checkpoint blockade in diverse immune environments

Abstract

BackgroundDespite extensive clinical use, the mechanisms that lead to therapeutic resistance to anti-programmed cell-death (PD)-1 monoclonal antibodies (mAbs) remain elusive. Here, we sought to determine how interactions between the Fc region of anti-PD-1 mAbs and Fcγ receptors (FcγRs) affect therapeutic activity and how these are impacted by the immune environment.MethodsMouse and human anti-PD-1 mAbs with different Fc binding profiles were generated and characterized in vitro. The ability of these mAbs to elicit T-cell responses in vivo was first assessed in a vaccination setting using the model antigen ovalbumin. The antitumor activity of anti-PD-1 mAbs was investigated in the context of immune ‘hot’ MC38 versus ‘cold’ neuroblastoma tumor models, and flow cytometry performed to assess immune infiltration.ResultsEngagement of activating FcγRs by anti-PD-1 mAbs led to depletion of activated CD8 T cells in vitro and in vivo, abrogating therapeutic activity. Importantly, the extent of this Fc-mediated modulation was determined by the surrounding immune environment. Low FcγR-engaging mouse anti-PD-1 isotypes, which are frequently used as surrogates for human mAbs, were unable to expand ovalbumin-reactive CD8 T cells, in contrast to Fc-null mAbs. These results were recapitulated in mice expressing human FcγRs, in which clinically relevant hIgG4 anti-PD-1 led to reduced endogenous expansion of CD8 T cells compared with its engineered Fc-null counterpart. In the context of an immunologically ‘hot’ tumor however, both low-engaging and Fc-null mAbs induced long-term antitumor immunity in MC38-bearing mice. Finally, a similar anti-PD-1 isotype hierarchy was demonstrated in the less responsive ‘cold’ 9464D neuroblastoma model, where the most effective mAbs were able to delay tumor growth but could not induce long-term protection.ConclusionsOur data collectively support a critical role for Fc:FcγR interactions in inhibiting immune responses to both mouse and human anti-PD-1 mAbs, and highlight the context-dependent effect that anti-PD-1 mAb isotypes can have on T-cell responses. We propose that engineering of Fc-null anti-PD-1 mAbs would prevent FcγR-mediated resistance in vivo and allow maximal T-cell stimulation independent of the immunological environment.

Penpulimab, an Fc-Engineered IgG1 Anti-PD-1 Antibody, With Improved Efficacy and Low Incidence of Immune-Related Adverse Events

“…The crystallizable fragment (Fc) of IgG antibodies can bind to Fc gamma receptors (FcγRs) and trigger effector functions like antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cell-mediated cytotoxicity (ADCC). Previous study demonstrated that Fc/FcγR interactions contribute to the resistance to PD-1 blockade, as evidenced by the depletion of activated CD8 tumor-infiltrating lymphocytes (TILs) upon application of anti-PD-1 antibody with high affinity for FcγRs ( 5 ). Importantly, blockade of FcγRs before PD-1 antibody administration prolongs PD-1 antibody binding to TILs and enhances immunotherapy-induced tumor regression in mice ( 6 ).…”

The Blocking vs Depletion Model of Immune Checkpoint Inhibitor Therapy for Cancer

“…Although ICI antibody developers claim that they are aware of this potential problem, and have thus modified the Fc region in their products to reduce the degree of FcγR binding, there is no evidence that these ICI antibodies lose the ability to be recognized by macrophages in vivo and antibody-bond ICI antibodies are not removed in vivo. In fact, there is study showing binding of ICI antibodies through Fc segment and depletion of antibody-bond T cells in vivo [19]. This T cell depletion mechanism may well explain the damage caused by ICI therapy in that antitumor T cells that express PD-1 are bond and removed through ADCP process.…”

Tumor-Associated Macrophages Regulate PD-1/PD-L1 Immunosuppression

“…Indeed, studies have demonstrated that after administration, anti-PD-1 mAb binds to tumor-infiltrating T cells at an early stage but is subsequently captured by TAMs due to the presence of Fcγ receptors, which ultimately leads to drug failure ( 53 , 54 ). More importantly, activation of Fcγ receptors by an anti-PD-1 mAb results in depletion of activated CD8 + T cells in vitro and in vivo , reducing the therapeutic effect ( 55 ). Therefore, the design of FC-null anti-PD-1 mAbs ( 55 ) or specific competitive inhibitors is one of the future strategies necessary to block Fcγ receptor-mediated resistance and increase T-cell infiltration.…”

“…More importantly, activation of Fcγ receptors by an anti-PD-1 mAb results in depletion of activated CD8 + T cells in vitro and in vivo , reducing the therapeutic effect ( 55 ). Therefore, the design of FC-null anti-PD-1 mAbs ( 55 ) or specific competitive inhibitors is one of the future strategies necessary to block Fcγ receptor-mediated resistance and increase T-cell infiltration.…”