Clinical guideline for vascularized composite tissue cryopreservation

Current State and Challenges of Tissue and Organ Cryopreservation in Biobanking

Recent years have witnessed significant advancements in the cryopreservation of various tissues and cells, yet several challenges persist. This review evaluates the current state of cryopreservation, focusing on contemporary methods, notable achievements, and ongoing difficulties. Techniques such as slow freezing and vitrification have enabled the successful preservation of diverse biological materials, including embryos and ovarian tissue, marking substantial progress in reproductive medicine and regenerative therapies. These achievements highlight improved post-thaw survival and functionality of cryopreserved samples. However, there are remaining challenges such as ice crystal formation, which can lead to cell damage, and the cryopreservation of larger, more complex tissues and organs. This review also explores the role of cryoprotectants and the importance of optimizing both cooling and warming rates to enhance preservation outcomes. Future research priorities include developing new cryoprotective agents, elucidating the mechanisms of cryoinjury, and refining protocols for preserving complex tissues and organs. This comprehensive overview underscores the transformative potential of cryopreservation in biomedicine, while emphasizing the necessity for ongoing innovation to address existing challenges.

Composite tissue xenopreservation: Preliminary results of staged VCA in rat to mouse model

BACKGROUND

The time between procurement and transplantation of composite tissues, especially regarding the limited donor pool, is a challenge effecting the outcomes of the transplantation. Current preservation techniques mainly include either cold preservation with a solution or machine perfusion using blood or certain oxygen-carrying solutions. However, none enables preservation beyond 24 h. Increasing this time to several days will provide better usage of the donor pool, safer transplantation of VCA with significant muscle content, and gives time to stabilize a patient before long surgical procedures. Herein, we described a novel strategy of xenopreservation (preservation via xenotransplantation) to preserve composite tissues for 7 days, followed by staged transplantation.

MATERIALS AND METHODS

We used two concordant species, female Sprague Dawley rats (n = 10) and female CF-1 mice (n = 10) in this study. Four of pair of animals are used for anatomical study. The groin flap of the rat was used as a xenograft and xenotransplanted to the neck area of the carrier mouse. Cyclosporine (CsA) was administered used as immunosuppressant. After 7 days of preservation on the mouse neck, xenotransplanted groin flap (called xenopreserved flap) was re-harvested, skin and vessels samples were collected for histopathological evaluation, and the xenopreserved flap was transplanted to the donor rat's opposite groin area. Anastomoses were performed between the flap's pedicle and the femoral vessels. Clinical observation regarding inflammation and tissue perfusion of the xenopreserved flap was monitored daily. Fifteen days after the second surgical procedure, the rats were euthanized, and skin and vessel samples were collected. Histologic evaluation, including inflammatory cell numbers, was performed. Wilcoxon test was used to compare the changes in inflammation severity and p < .05 was set for statistical significance.

RESULTS

All xenopreserved groin flaps except one survived. Mean lymphocyte count before the second operation (at the end of the xenopreservation procedure) was 20,22 ± 0.44 and reduced to 13,14 ± 0.47 at the end of 15 days, and the difference was statistically significant (p < .05).

CONCLUSION

This proof-of-concept study with preliminary results showed that xenotransplantation might be a novel strategy for preservation of VCA for a certain period of time. However, additional translational studies are needed to modulate the tissue changes following xenopreservation.

Cryopreservation of tissues and organs: present, bottlenecks, and future

Tissue and organ transplantation continues to be an effective measure for saving the lives of certain critically ill patients. The organ preservation methods that are commonly utilized in clinical practice are presently only capable of achieving short-term storage, which is insufficient for meeting the demand for organ transplantation. Ultra-low temperature storage techniques have garnered significant attention due to their capacity for achieving long-term, high-quality preservation of tissues and organs. However, the experience of cryopreserving cells cannot be readily extrapolated to the cryopreservation of complex tissues and organs, and the latter still confronts numerous challenges in its clinical application. This article summarizes the current research progress in the cryogenic preservation of tissues and organs, discusses the limitations of existing studies and the main obstacles facing the cryopreservation of complex tissues and organs, and finally introduces potential directions for future research efforts.

Improving the ischemia-reperfusion injury in vascularized composite allotransplantation: Clinical experience and experimental implications

Long-time ischemia worsening transplant outcomes in vascularized composite allotransplantation (VCA) is often neglected. Ischemia-reperfusion injury (IRI) is an inevitable event that follows reperfusion after a period of cold static storage. The pathophysiological mechanism activates local inflammation, which is a barrier to allograft long-term immune tolerance. The previous publications have not clearly described the relationship between the tissue damage and ischemia time, nor the rejection grade. In this review, we found that the rejection episodes and rejection grade are usually related to the ischemia time, both in clinical and experimental aspects. Moreover, we summarized the potential therapeutic measures to mitigate the ischemia-reperfusion injury. Compare to static preservation, machine perfusion is a promising method that can keep VCA tissue viability and extend preservation time, which is especially beneficial for the expansion of the donor pool and better MHC-matching.

A cryopreservation method for bioengineered 3D cell culture models

Technologies to cryogenically preserve (a.k.a. cryopreserve) living tissue, cell lines and primary cells have matured greatly for both clinicians and researchers since their first demonstration in the 1950s and are widely used in storage and transport applications. Currently, however, there remains an absence of viable cryopreservation and thawing methods for bioengineered, three-dimensional (3D) cell models, including patients' samples. As a first step towards addressing this gap, we demonstrate a viable protocol for spheroid cryopreservation and survival based on a 3D carboxymethyl cellulose scaffold and precise conditions for freezing and thawing. The protocol is tested using hepatocytes, for which the scaffold provides both the 3D structure for cells to self-arrange into spheroids and to support cells during freezing for optimal post-thaw viability. Cell viability after thawing is improved compared to conventional pellet models where cells settle under gravity to form a pseudo-tissue before freezing. The technique may advance cryobiology and other applications that demand high-integrity transport of pre-assembled 3D models (from cell lines and in future cells from patients) between facilities, for example between medical practice, research and testing facilities.