Du et al. developed human CTLA-4 knock-in homo- and heterozygous mouse models and demonstrated that the immunotherapy-related adverse events (irAEs) could be uncoupled from antitumor immunity. The model recapitulated most irAEs observed with ipilimumab, including severe organ inflammation and anemia. irAEs were related to systemic T cell activation and increased autoreactive Teff/Treg ratio, while the antitumor effect depended on Treg depletion in the tumor. The CTLA-4h/h mouse model could prove useful for identifying safer anti-CTLA-4 therapies.

Anti-CTLA-4 monoclonal antibodies (mAbs) confer a cancer immunotherapeutic effect (CITE) but cause severe immunotherapy-related adverse events (irAE). Targeting CTLA-4 has shown remarkable long-term benefit and thus remains a valuable tool for cancer immunotherapy if the irAE can be brought under control. An animal model, which recapitulates clinical irAE and CITE, would be valuable for developing safer CTLA-4-targeting reagents. Here, we report such a model using mice harboring the humanized Ctla4 gene. In this model, the clinically used drug, Ipilimumab, induced severe irAE especially when combined with an anti-PD-1 antibody; whereas another mAb, L3D10, induced comparable CITE with very mild irAE under the same conditions. The irAE corresponded to systemic T cell activation and resulted in reduced ratios of regulatory to effector T cells (Treg/Teff) among autoreactive T cells. Using mice that were either homozygous or heterozygous for the human allele, we found that the irAE required bi-allelic engagement, while CITE only required monoallelic engagement. As with the immunological distinction for monoallelic vs bi-allelic engagement, we found that bi-allelic engagement of the Ctla4 gene was necessary for preventing conversion of autoreactive T cells into Treg cells. Humanization of L3D10, which led to loss of blocking activity, further increased safety without affecting the therapeutic effect. Taken together, our data demonstrate that complete CTLA-4 occupation, systemic T cell activation and preferential expansion of self-reactive T cells are dispensable for tumor rejection but correlate with irAE, while blocking B7-CTLA-4 interaction impacts neither safety nor efficacy of anti-CTLA-4 antibodies. These data provide important insights for the clinical development of safer and potentially more effective CTLA-4-targeting immunotherapy.

Author Info: (1) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (2) Center for Cancer and Immunology Research

Author Info: (1) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (2) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (3) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (4) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (5) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (6) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (7) OncoImmune, Inc., Rockville, MD, 20852, USA. (8) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (9) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. (10) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. yaliu@cnmc.org. OncoImmune, Inc., Rockville, MD, 20852, USA. yaliu@cnmc.org. (11) Center for Cancer and Immunology Research, Children's Research Institute, Children's National Health System, Washington, DC, 20010, USA. pzheng@cnmc.org. OncoImmune, Inc., Rockville, MD, 20852, USA. pzheng@cnmc.org.

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