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1454 Evaluation of checkpoint inhibitor efficacy in the absence of murine Fc gamma receptors in a humanized immune system mouse model
  1. Nicholas Smith,
  2. Megan MacBride,
  3. Esther Andino,
  4. Emily Sack,
  5. Debra Freer,
  6. Michelle Vedder,
  7. Kathleen Bott,
  8. Louise Baskin and
  9. Janell Richardson
  1. Taconic Biosciences, Inc., Rensselaer, NY, USA
  • Journal for ImmunoTherapy of Cancer (JITC) preprint. The copyright holder for this preprint are the authors/funders, who have granted JITC permission to display the preprint. All rights reserved. No reuse allowed without permission.


Background Humanized immune system (HIS) mice are critical immuno-oncology tools for evaluating antibody-based therapeutic target engagement and efficacy in a human-like context. Most therapeutics have an IgG backbone and thus engage Fc gamma receptors. Traditional HIS mice retain murine immune cells such as neutrophils and macrophages which can interact with human IgG-based therapeutics and confound preclinical results. To determine whether knockout of murine Fc gamma receptors (FcγRs) in a super-immunodeficient mouse model would alter anti-PD1 efficacy compared to the parent strain in a lung adenocarcinoma model, we studied tumor growth kinetics, human reconstitution, and tumor infiltrating leukocytes (TILs) in each strain engrafted with HCC872 tumor cells treated with Pembrolizumab or Vehicle.

Methods HIS NOG (huNOG) or HIS FcγR knockout NOG mice (available as the FcResolv™ huNOG mouse) were created using identical protocols with CD34+ cells from three human donors shared across both strains. Baseline reconstitution was evaluated in naïve animals via flow cytometry. HCC827 cells were inoculated in remaining animals. Animals were randomized on day 7 post-tumor implantation into 12 groups. Body weight, clinical observations, and tumor growth were measured. Mice received treatment from D7, dosed twice weekly for four weeks, and were then euthanized for FACS analysis, collecting blood, spleen, and tumor samples.

Results For a given donor, no significant differences were seen in human immune reconstitution and kinetics between strains. Pembrolizumab treatment showed significant tumor growth inhibition in one donor in FcResolv huNOG, but not in donor-matched huNOG mice. Evaluation of human TILs in pembrolizumab-treated animals showed significant differences between the strains across all donors, with FcResolv huNOG mice showing increased CD8+ T cells and decreased tumor-associated macrophages compared to vehicle-treated mice, and no significant differences in huNOG. Evaluation of murine TILs revealed differences in murine macrophage populations, regardless of treatment, with LyClo dominant in FcResolv huNOG and LyChi dominant in huNOG. In the presence of Pembrolizumab, the murine myeloid and granulocyte population within the tumor was significantly decreased in FcResolv huNOG mice whereas no change was seen in huNOG.

Conclusions Our study demonstrates when treated with anti-PD1, FcResolv huNOG mice show expected pharmacodynamic changes and donor-dependent efficacy whereas, despite identical donors and creation protocols, Pembrolizumab-treated huNOG mice showed neither. These differences are due to the presence or absence of murine FcγRs and their impact on antibody IgG-based therapeutics.

Acknowledgements The authors would like to recognize Oncodesign Services (Dijon, France) who conducted the in-life tumor bearing and dosing portion of this study with recognition to Dr. Caroline Mignard and Damien France.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See

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