The Use of a Humanized NSG-β2m-/- Model for Investigation of Immune and Anti-tumor Effects Mediated by the Bifunctional Immunotherapeutic Bintrafusp Alfa.

Y Maurice Ii Morillon,Lucas A Horn,Caroline Jochems,Ariana Sabzevari,John W Greiner,Jeffrey Schlom,Claudia Palena,Nicholas T Roller,Claire Smalley Rumfield,Samuel T Pellom

doi:10.3389/fonc.2020.00549

Y Maurice Ii Morillon, Lucas A Horn + Show 8 more

Open Access

https://doi.org/10.3389/fonc.2020.00549

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Abstract

The lack of serial biopsies in patients with a range of carcinomas has been one obstacle in our understanding of the mechanism of action of immuno-oncology agents as well as the elucidation of mechanisms of resistance to these novel therapeutics. While much information can be obtained from studies conducted with syngeneic mouse models, these models have limitations, including that both tumor and immune cells being targeted are murine and that many of the immuno-oncology agents being evaluated are human proteins, and thus multiple administrations are hampered by host xenogeneic responses. Some of these limitations are being overcome by the use of humanized mouse models where human peripheral blood mononuclear cells (PBMC) are engrafted into immunosuppressed mouse strains. Bintrafusp alfa (M7824) is an innovative first-in-class bifunctional fusion protein composed of the extracellular domain of the TGF-βRII to function as a TGF-β “trap” fused to a human IgG1 antibody blocking PD-L1. A phase I clinical trial of bintrafusp alfa showed promising anti-tumor efficacy in heavily pretreated advanced solid tumors, and multiple clinical studies are currently ongoing. There is still much to learn regarding the mechanism of action of bintrafusp alfa, including its effects on both human immune cells in the periphery and in the tumor microenvironment (TME), and any temporal effects upon multiple administrations. By using the NSG-β2m−/− mouse strain humanized with PBMC, we demonstrate here for the first time: (a) the effects of bintrafusp alfa administration on human immune cells in the periphery vs. the TME using three different human xenograft models; (b) temporal effects upon multiple administrations of bintrafusp alfa; (c) phenotypic changes induced in the TME, and (d) variations observed in the use of multiple different PBMC donors. Also discussed are the similarities and differences in the data thus far obtained employing murine syngeneic models, from clinical trials, and in the use of this humanized mouse model. The results described here may guide the future use of this agent or similar immunotherapy agents as monotherapies or in combination therapy studies.

Highlights

The success of immuno-oncology in the management of subsets of patients with certain tumor types is well-established
In the studies reported here, we describe for the first time: (a) comparative effects of bintrafusp alfa administration on human immune cells in the periphery vs. the tumor microenvironment (TME) using three different human xenograft models; (b) temporal effects upon multiple administrations of bintrafusp alfa; (c) phenotypic changes induced in the TME, and (d) variations observed in the use of multiple different peripheral blood mononuclear cells (PBMC) donors
The parental NSG mouse strain injected with human PBMCs attains adequate levels of peripheral T-cell engraftment for treatment studies between 3 and 4 weeks post-engraftment [21]; between 4 and 5 weeks post-engraftment, severe Graft vs. Host Disease (GvHD) develops [22]

Summary

Introduction

The success of immuno-oncology in the management of subsets of patients with certain tumor types is well-established. Several variants of these parental mouse strains have eliminated murine MHC class I and/or II and exhibit delayed development of GvHD in the PBMC model [1,2,3,4,5] Due to their recent development, few immunotherapeutic studies have utilized these novel lines, and while limitations exist, delayed development of GvHD enables more complete characterization of immunotherapeutic modulation of the human anti-tumor response. The NSG-β2m−/− mouse lacks expression of beta microglobulin (β2m), eliminating murine MHC class I and resulting in the delayed development of GvHD in PBMC humanized mice This advantage was highlighted in a recent study which observed a significant survival advantage in NSGβ2m−/− mice injected with human PBMC when compared to the parental NSG line [1]. This is the first study to utilize the NSG-β2m−/− PBMC model in the investigation of immunotherapeutic modulation of a human anti-tumor response

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