MHC class I and II-deficient humanized mice are suitable tools to test the long-term antitumor efficacy of immune checkpoint inhibitors and T-cell engagers

Immunodeficient mice engrafted with peripheral blood mononuclear cells (PBMCs) are models to study new cancer immunotherapy agents. However, this approach is associated with xenograft-versus-host disease (xGVHD), which starts early after PBMC transfer and limits the duration and interpretation of experiments. Here, we explore different approaches to overcome xGVHD and better support the development of cancer immunotherapies.

Humanized MHC-dKO immunodeficient mice allow and refine the preclinical testing of immunotherapy agents for which experimentation is precluded in conventional immunodeficient mice due to severe xGVHD.

Immunodeficient NOD-scid IL2Rgnull (NSG) mice were intravenously transferred with human PBMCs and subcutaneously co-engrafted with HT29 human colon carcinoma cells. Diverse strategies to reduce xGVHD while preserving the antitumor activity of human immune cells were evaluated: (1) ex vivo immune graft modification by depleting CD4+ T cells pre-transfer using magnetic beads, (2) post-transplantation cyclophosphamide administration to eliminate proliferating xenoreactive T-cell clones and (3) using major histocompatibility complex (MHC) class I and II-deficient NSG mice: (Kb Db)null (IA)null (MHC-dKO NSG). Body weight and plasma murine alanine aminotransferase levels were measured as indicators of xGVHD and tumor size was measured every 2-3 days to monitor antitumor activity. The antitumor effects and pharmacodynamics of nivolumab plus ipilimumab and an anti-epithelial cell adhesion molecule (EpCAM)/CD3 T-cell engager (αEpCAM/CD3 bispecific antibody (BsAb)) were evaluated in the model.

CD4+ T-cell depletion attenuates xGVHD but also abrogates the antitumor activity. Cyclophosphamide limits the antitumor response and does not substantially prevent xGVHD. In contrast, xGVHD was significantly attenuated in MHC-dKO NSG recipients, while the antitumor effect of human PBMCs was preserved. Furthermore, the administration of nivolumab plus ipilimumab caused exacerbated xGVHD in conventional NSG mice, thereby precluding the observation of their antitumor effects. Severe xGVHD did not occur in MHC-dKO NSG mice thus enabling the study of complete and durable tumor rejections. Similarly, NSG mice treated with an αEpCAM/CD3 BsAb showed complete tumor regressions, but died due to xGVHD. In contrast, MHC-dKO NSG mice on treatment with the αEpCAM/CD3 BsAb achieved complete tumor responses without severe xGVHD. A significant proportion of mice rendered tumor-free showed tumor rejection on rechallenge with HT29 cells without further treatment. Finally, tumor-infiltrating CD8+ T-cell number increase, activation and CD137 upregulation were observed on αEpCAM/CD3 BsAb treatment.