Isolation of fresh endothelial cells from porcine heart for cardiovascular studies: a new fast protocol suitable for genomic, transcriptomic and cell biology studies

Modeling human anti-pig xenoimmune responses in a pig artery tissue grafted humanized mouse model

BACKGROUND

Blood vessels that contain endothelial cells (ECs) on the surface are in direct contact with host blood and are the first target of xenograft rejection. Currently, our understanding of human anti-pig vessel immune responses is primarily based on in vitro assays using pig ECs. Therefore, it is necessary to develop an animal model that permits in vivo study of human immunological rejection of pig vessels.

METHODS

Pig artery tissues (PAT) were transplanted into human immune system (HIS) mice or immunodeficient NSG mice (as controls). Intragraft human immune cell infiltration and antibody deposition were quantified using histology and immunohistochemistry. Donor antigen-specific immune responses were quantified using a mixed lymphocyte reaction and a complement-dependent killing assay.

RESULTS

Pig CD31+ ECs were detected and increased 2-fold from weeks 3 to 5 in PAT xenografts from immunodeficient NSG mice. However, compared with NSG mice, PAT xenografts in HIS mice had significantly lower numbers of porcine CD31+ ECs and showed a marked reduction from week 3 to week 5. PAT xenograft rejection in HIS mice is associated with intensive infiltration of human immune cells, deposition of human IgM and IgG antibodies, and the formation of a tertiary lymphoid structure. Robust donor pig antigen-specific human T cells and antibody responses were detected in PAT-transplanted HIS mice.

CONCLUSION

We have developed a humanized mouse model to evaluate human anti-pig xenoimmune responses by PAT transplantation in vivo. This model is expected to facilitate the refinement of pig gene-editing strategies (the expression on EC surface) and the testing of local immunosuppressive strategies for clinical pig organ xenotransplantation.

Characterization of a functional endothelial super-enhancer that regulates ADAMTS18 and angiogenesis

Super-enhancers are clusters of enhancers associated with cell lineage. They can be powerful gene-regulators and may be useful in cell-type specific viral-vector development. Here, we have screened for endothelial super-enhancers and identified an enhancer from within a cluster that conferred 5–70-fold increase in transgene expression. Importantly, CRISPR/Cas9 deletion of enhancers demonstrated regulation of ADAMTS18, corresponding to evidence of chromatin contacts between these genomic regions. Cell division-related pathways were primarily affected by the enhancer deletions, which correlated with significant reduction in cell proliferation. Furthermore, we observed changes in angiogenesis-related genes consistent with the endothelial specificity of this SE. Indeed, deletion of the enhancers affected tube formation, resulting in reduced or shortened sprouts. The super-enhancer angiogenic role is at least partly due to its regulation of ADAMTS18, as siRNA knockdown of ADAMTS18 resulted in significantly shortened endothelial sprouts. Hence, functional characterization of a novel endothelial super-enhancer has revealed substantial downstream effects from single enhancer deletions and led to the discovery of the cis-target gene ADAMTS18 and its role in endothelial function.