Abstract 5204: Preclinical models for translational immuno-oncology research: Rare patient-derived xenografts on humanized mice
Authors: Stecklum Maria , Wulf-Goldenberg Annika , Brzezicha Bernadette , Walther Wolfgang , Hoffmann Jens 
Published: April 2023

Abstract
Background
The preclinical evaluation of novel immune checkpoint modulators is dependent on models with functional human immune cells. In previous experiments, we have demonstrated, that we can use either peripheral blood mononuclear cells (PBMC), subset of immune cells like NK cells or hematopoietic stem cells (HSC) to establish a humanized immune system on highly immunodeficient 1st and 2nd generation NOG mice with functional T-, B-, and NK cells, as well as monocytes and dendritic cells. Furthermore, we determined PD-L1 expression as a predictive marker and target for immunotherapy on different patient-derived xenografts (PDX). By co-transplantation of rare PDX, like leukemia or Nuclear-protein-in-testis (NUT) carcinoma, we successfully generated a fully human tumor-immune-cell model in mice. Finally, we evaluated the functionality of the model by the treatment with checkpoint inhibitors like Ipilimumab (Ipi), Nivolumab (Nivo) or Pembrolizumab (Pembro). In parallel, we investigated the functionality of the human immune cells and evaluated concepts for combination therapies i.e. with chemotherapy or radiation.
Methods
HSC-humanized mice were generated by i.v. HSC transplantation and engraftment of immune cells was monitored by FACS analysis. For PBMC-humanized mice, immune cells were implanted i.v.. PDX models from different entities (leukemia or NUT carcinoma) were transplanted on HSC-humanized (HIS) mice and treated with Ipi, Nivo and Pembro alone or in combination with radiation. Blood and tumor samples were analysed by FACS for immune cell infiltration and activation.
Results
The transplanted HSC showed engraftment in mice with proliferation and differentiation. 14 weeks after HSC inoculation up to 20% of the human immune cells in the blood were T-cells, characterized by a high PD-1 expression. We have transplanted PDX from different tumor entities on HSC-humanized mice. Most of the investigated PDX (&gt;70%) successfully engrafted on humanized mice and showed no significant difference in tumor growth compared to growth on non-humanized mice. However, for some PDX we observed a delayed tumor growth or a complete rejection. Engraftment delay seems to correlate with the PD-L1 expression of PDX (the higher PD-L1, then the higher growth delay). Furthermore, our results demonstrate the functionality of the engrafted human immune cells against some PDX. Treatment with Ipi, Nivo or Pembro led to a minor tumor growth delay. Response to checkpoint inhibitors showed a correlation to innate immune response and PD-L1 expression of PDX and could further be increased by combination with radiotherapy.
Conclusions
Our humanized immune-PDX models enable appropriate preclinical translational research on tumor immune biology and the evaluation of new therapies and combinations, as well as the identification and validation of biomarkers for immune therapy, especially in rare PDX models.
Citation Format: Maria Stecklum, Annika Wulf-Goldenberg, Bernadette Brzezicha, Wolfgang Walther, Jens Hoffmann. Preclinical models for translational immuno-oncology research: Rare patient-derived xenografts on humanized mice. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5204.