Human Immune System Humanized Modeling of Down Syndrome Immune Responses to Pluripotent Stem Cells

ABSTRACT
People with Down syndrome (DS) have increased susceptibility to immunological pathologies, certain
cancers, congenital heart defects, and cognitive decline, all of which involve immune dysregulation. Elevated
inflammatory cytokines associated with DS may impact disease treatments, such as immunotherapy for
leukemia and organ transplantation. Current mouse models do not fully replicate the unique immunobiology of
human trisomy 21, highlighting the need for more robust animal models to study DS-specific immune
responses to therapies. Humanized mouse models, created by introducing human hematopoietic cells into
immune-deficient mice, offer unique opportunities to evaluate pharmacological and cellular therapies in a DS
context. No DS humanized mouse models of this class have been reported until now.
We developed a DS humanized mouse model, the Thymocyte-Hu, using neonatal thymocytes. Preliminary
data show long-term human T cell engraftment and reduced graft-vs-host disease susceptibility. This R24
project aims to fully characterize the phenotype and function of engrafted T cells in Thymocyte-Hu mice, which
will provide a better understanding of DS T cell maturation and antigen-specific responses in the context of
clinical translation of hypoimmune induced pluripotent stem cell (iPSC) therapies for people with DS.
Additionally, we will leverage another new DS NeoThy model, combining umbilical cord blood hematopoietic
cells and neonatal thymus fragments to study DS T cell development and function within a full immune
repertoire. In our Specific Aims, we will establish multiple biological material and data resources for the DS
research community, by: 1) creating mosaic DS hypoimmune gene-edited iPSC lines. We will differentiate
these cells into cardiovascular cell therapies and assess in vitro DS immune responses; 2) characterizing
Thymocyte-Hu model T cell phenotype and function using bioluminescence imaging, single cell RNA
sequencing, Luminex cytokine assays, and flow cytometry; 3) assessing DS NeoThy humanized mouse T cell
dynamics and immune responses to hypoimmune iPSC cardiovascular cell therapies using single cell RNA
sequencing, epigenomics, bioluminescence imaging, Luminex, flow cytometry, and histology; and 4) sharing
biological and data resources by distributing humanizing tissues, gene-edited iPSC lines, and experimental
data and by providing access to humanized mice through the University of Wisconsin Humanized Mouse Core.
Successful completion of this project will provide novel DS humanized mouse models and data resources to
the research community, fostering high-impact discoveries and potential new therapies for people with DS.

Grant Number: 1R24AI197259-01
NIH Institute/Center: NIH
Principal Investigator: Matthew Brown