Generation of rat-derived lung epithelial cells in Fgfr2b-deficient mice retains species-specific development

Scaling Autologous Epidermal Cell Therapies: iPSC-Derived Keratinocytes and In Vivo Chimerism for Skin Regeneration

Severe skin injuries and genetic disorders such as epidermolysis bullosa present significant clinical challenges due to limitations in current epidermal replacement therapies. While promising, cultured epithelial autografts (CEAs) suffer from prolonged culture times, cellular senescence, and low-quality clinical outcomes, limiting their widespread application. Recent advancements in iPSC-derived keratinocytes (iKeratinocytes) and in vivo chimerism offer transformative potential for scalable and personalised skin regeneration. Advances in understanding transcriptional networks, mRNA delivery, CRISPR-based genome editing, and automated biomanufacturing processes can enable improved and efficient protocols for generating iKeratinocytes. Despite these advances, there are still challenges for scaling iKeratinocytes, including optimising xeno-free culture systems and developing reproducible methods for generating multilayered skin with appendages. Interspecies chimerism utilising lineage-specific ablation systems and targeted in utero delivery of organ progenitor cells can enable human epidermal tissue development within animal hosts, offering an alternative novel platform for scaling epidermal cell and skin generation. This method, however, requires further refinements for complete ablation and detachment of target cells in the animal hosts and improved human cell integration in chimeric models. Together, iKeratinocytes and in vivo chimerism hold great promise for advancing autologous epidermal cell therapies and enabling broader clinical adoption and improved outcomes for patients with severe skin injuries and genetic disorders.

Blastocyst complementation-based rat-derived heart generation reveals cardiac anomaly barriers to interspecies chimera development

The use of pluripotent stem cells (PSCs) to generate functional organs via blastocyst complementation is a cutting-edge strategy in regenerative medicine. However, existing models that use this method for heart generation do not meet expectations owing to the complexity of heart development. Here, we investigated a Mesp1/2 deficient mouse model, which is characterized by abnormalities in the cardiac mesodermal cells. The injection of either mouse or rat PSCs into Mesp1/2 deficient mouse blastocysts led to successful heart generation. In chimeras, the resulting hearts were predominantly composed of rat cells; however, their functionality was limited to the embryonic developmental stage on day 12.5. These results present the functional limitation of the xenogeneic heart, which poses a significant challenge to the development in mouse-rat chimeras.

The perspective for next-generation lung replacement therapies: functional whole lung generation by blastocyst complementation

PURPOSE OF REVIEW

Blastocyst complementation represents a promising frontier in next-generation lung replacement therapies. This review aims to elucidate the future prospects of lung blastocyst complementation within clinical settings, summarizing the latest studies on generating functional lungs through this technique. It also explores and discusses host animal selection relevant to interspecific chimera formation, a challenge integral to creating functional human lungs via blastocyst complementation.

RECENT FINDINGS

Various gene mutations have been utilized to create vacant lung niches, enhancing the efficacy of donor cell contribution to the complemented lungs in rodent models. By controlling the lineage to induce gene mutations, chimerism in both the lung epithelium and mesenchyme has been improved. Interspecific blastocyst complementation underscores the complexity of developmental programs across species, with several genes identified that enhance chimera formation between humans and other mammals.

SUMMARY

While functional lungs have been generated via intraspecies blastocyst complementation, the generation of functional interspecific lungs remains unrealized. Addressing the challenges of controlling the host lung niche and selecting host animals relevant to interspecific barriers between donor human and host cells is critical to enabling the generation of functional humanized or entire human lungs in large animals.

CRISPR-Cas9 Genome Editing Allows Generation of the Mouse Lung in a Rat

Rationale: Recent efforts in bioengineering and embryonic stem cell (ESC) technology allowed the generation of ESC-derived mouse lung tissues in transgenic mice that were missing critical morphogenetic genes. Epithelial cell lineages were efficiently generated from ESC, but other cell types were mosaic. A complete contribution of donor ESCs to lung tissue has never been achieved. The mouse lung has never been generated in a rat. Objective: We sought to generate the mouse lung in a rat. Methods: Clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 genome editing was used to disrupt the Nkx2-1 gene in rat one-cell zygotes. Interspecies mouse-rat chimeras were produced by injection of wild-type mouse ESCs into Nkx2-1-deficient rat embryos with lung agenesis. The contribution of mouse ESCs to the lung tissue was examined by immunostaining, flow cytometry, and single-cell RNA sequencing. Measurements and Main Results: Peripheral pulmonary and thyroid tissues were absent in rat embryos after CRISPR-Cas9-mediated disruption of the Nkx2-1 gene. Complementation of rat Nkx2-1-/- blastocysts with mouse ESCs restored pulmonary and thyroid structures in mouse-rat chimeras, leading to a near-99% contribution of ESCs to all respiratory cell lineages. Epithelial, endothelial, hematopoietic, and stromal cells in ESC-derived lungs were highly differentiated and exhibited lineage-specific gene signatures similar to those of respiratory cells from the normal mouse lung. Analysis of receptor-ligand interactions revealed normal signaling networks between mouse ESC-derived respiratory cells differentiated in a rat. Conclusions: A combination of CRISPR-Cas9 genome editing and blastocyst complementation was used to produce mouse lungs in rats, making an important step toward future generations of human lungs using large animals as "bioreactors."

Chimeric Livers: Interspecies Blastocyst Complementation and Xenotransplantation for End-Stage Liver Disease

Orthotopic liver transplantation (OLT) currently serves as the sole definitive treatment for thousands of patients suffering from end-stage liver disease; and the existing supply of donor livers for OLT is drastically outpaced by the increasing demand. To alleviate this significant gap in treatment, several experimental approaches have been devised with the aim of either offering interim support to patients waiting on the transplant list or bioengineering complete livers for OLT by infusing them with fresh hepatic cells. Recently, interspecies blastocyst complementation has emerged as a promising method for generating complete organs in utero over a short timeframe. When coupled with gene editing technology, it has brought about a potentially revolutionary transformation in regenerative medicine. Blastocyst complementation harbors notable potential for generating complete human livers in large animals, which could be used for xenotransplantation in humans, addressing the scarcity of livers for OLT. Nevertheless, substantial experimental and ethical challenges still need to be overcome to produce human livers in larger domestic animals like pigs. This review compiles the current understanding of interspecies blastocyst complementation and outlines future possibilities for liver xenotransplantation in humans.