Traumatic injuries or cancer resection can result in large soft tissue loss, which can lead to severe functional impairments, including difficulties with mobility and performing daily activities.
Dr. Siba Haykal from the University Health Network and the Toronto General Hospital, Canada specialises in tissue-engineered techniques for tracheal reconstruction of breast and head and neck.
Image Source: Adobe Stock Images / Golubovy
Hello and welcome to Research Pod. Thank you for listening and joining us today.
In this episode, we look at the work of Dr. Siba Haykal from the University Health Network and the Toronto General Hospital, Canada. Haykal is also cross-appointed to the Division of Thoracic Surgery within the University Health Network, and specialises in microvascular oncological reconstruction of breast and head and neck.
Traumatic injuries or cancer resection, resulting in large volumetric soft tissue loss, requires surgical reconstruction. Large soft tissue loss can lead to severe functional impairments, including difficulties with mobility and performing daily activities. Patients typically struggle to regain full functionality, impacting their independence and quality of life. What’s more, patients also require life-long immunosuppression regimens to prevent rejection of the transplanted tissue, rendering the recipient immunocompromised.
Vascularized composite allotransplantation, or VCA for short, is a specialized form of transplantation that involves transplanting multiple tissues as a single functional unit, such as the hand, face, or limb. It differs from normal procedures, which typically involves the transplantation of a single organ, such as the heart, kidney, or liver.
By allowing us to transplant various tissues, VCA and tissue regeneration have transformed patient care and quality of life by providing innovative solutions for complex medical challenges, enabling patients to lead more fulfilling lives and offering hope for those who were previously deemed So, how can we work to make VCA widely accessible to the millions that can benefit from it?
While VCA is a very promising and exciting field for medicine and tissue engineering, it is still relatively new and not as commonly performed as normal organ transplantation. Research and advancements in surgical techniques, immunosuppression, and long-term outcomes are ongoing in the field of VCA. In particular, there are two main areas that require further research; Haykal’s lab focuses on the effect of ischemia reperfusion injury, or IRI, in VCA, as well as the safe monitoring of acute rejection with peripheral markers.
IRI refers to the damage that occurs when blood flow is restored to a tissue or organ after a period of inadequate blood supply. When blood flow is interrupted, the affected tissue becomes deprived of oxygen and nutrients, leading to a decrease in cellular metabolism. This metabolic disturbance can cause the accumulation of waste products and the depletion of energy stores within the cells.
When blood flow is subsequently restored, a series of biochemical and physiological events occur, leading to reperfusion injury. The restoration of blood supply can trigger an excessive inflammatory response, the production of reactive oxygen species, known as ROS, and the release of various pro-inflammatory and cytotoxic molecules. These factors can cause direct damage to the tissue and exacerbate the injury that occurred during ischemia. In some cases, this can result in necrosis, where the tissue experiences cell death.
Another event that may occur with transplantation is acute rejection, which is when the recipient’s immune system mounts an aggressive response against the transplanted organ or tissue, recognizing it as foreign and attempting to destroy it. This type of rejection typically occurs any time from the first week after the transplant to 3 months post-operation. Acute rejection in organ transplantation is prevented primarily through the use of immunosuppressive medications.
Dr. Siba Haykal’s laboratory research focuses on tissue-engineered techniques for tracheal reconstruction and the immunology of vascularized composite allotransplantation. Haykal’s lab aims to directly tackle the problem of IRI and complications associated with immunosuppression through decellularization and recellularization, combined with testing various preservation solutions.
Decellularization is a tissue engineering technique in which the cellular components of tissues and organs are removed, leaving behind the extracellular matrix, which is composed of proteins like collagen and elastin, as well as glycosaminoglycans, or GAGs. This provides structural support and serves as a scaffold for cells to adhere and grow.
Recellularization is a process that follows decellularization and involves repopulating the decellularized extracellular matrix, or ECM, scaffold with new cells. This allows the creation of tissues that can then be used for transplantation or disease modelling.
In transplantation, decellularized scaffolds can come from bioartificial sources, or donor-derived scaffolds. After decellularization, a patient’s stem cells are seeded onto the scaffold in a bioreactor, allowing the cells to repopulate, integrate and eventually differentiate into the target tissue. By using a patient’s own stem cells to recellularize a decellularized scaffold, there is a reduced risk of rejection and other complications commonly associated with traditional transplantation using donor tissues or organs.
Through proof-of-concept studies and animal-based experimentation, Haykal’s lab has developed various protocols and engineered bioreactors that demonstrate the feasibility of decellularization and recellularization.
Haykal’s PhD work explored both de- and re- cellularization of long tracheal segments, comparing three existing decellularization protocols. For recellularization, the team designed a dual-chamber bioreactor for recellularization of tracheal allografts. The method allowed for dynamic perfusion seeding, confirmed adherence of two different cell types and achieved higher cell numbers and homogeneous structures compared to traditional static seeding methods.
Haykal and the team have established a small animal model for de- and re- cellularization of a limb. In the study, the team utilize what’s known as the ‘hindlimb rat model’, developing preliminary data showing preservation of the extracellular matrix following decellularization of these transplants.
The team also explore partial decellularization to preserve muscle function whilst maintaining the immunological advantages of complete decellularization and expediting flap turnaround in the eventual clinical setting.
Furthermore, the team investigate the use of various preservation solutions and developing an ex vivo, meaning outside the body, machine perfusion to allow for longer ischemia time and increasing geographical accessibility for VCA transplant recipients. VCA involves tissues with varying metabolic demands, and muscle tissue is particularly sensitive to IRI due to its need for high blood supply and oxygen demand, so ideal preservation is critical to the outcome success of the operation.
As for testing for acute rejection and IRI using various preservation solutions, the team have established a rat model of VCA. A rat hindlimb, composed of skin, muscle, bone, nerve and vessels, has been successfully transplanted as a perfused flap in both syngeneic and allogeneic rats with survival of the animals when ischemia is minimal. When ischemia time is prolonged in allogeneic animals, the team have observed a significant reduction in survival time.
The molecular events and tissue damage caused by IRI as well as vascular integrity following reperfusion in skin, muscle, nerve, vessels and bone were studied. The team then compared different preservation solutions with static cold storage, or SCS, and found that heparinized saline – which is actually the standard preservation solution in clinical settings – resulted in higher markers of ischemia and decreased vascular integrity, while perfadex appears to be protective. The team are now working on expanding this work to focus on an Ex vivo preclinical model.
In the ex vivo preclinical model, the team aims to upscale their current set-up to a large preclinical model, to add an extracellular oxygen carrier to their current preservation solution, and to examine the effects of ischemia reperfusion injury in an allogeneic transplantation model.
Overall, the lab aims to improve the quality of life of patients who often have no other choice than a transplant, which comes with several complications to one’s health, life, and wellbeing. Sometimes, a traditional transplant may not even be an option for the patient with extreme traumatic injury; VCA gives patients a renewed hope, and has the potential to revolutionize treatment options and quality of life.
Recellularization holds great promise for the future of patient treatment; the ability to customize the tissue or organ to a specific patient’s needs, while reducing the need for life-long immunosuppression, will mitigate the complications associated with transplantation. However, it is essential to address various challenges, such as achieving proper cell integration and vascularization, to ensure the success and clinical viability of recellularized constructs.
That’s all for this episode, thanks for listening. Links to Dr. Haykal’s lab and research can be found in the show notes for this episode. And, as always, be sure to stay subscribed to ResearchPod for more of the latest science.
See you again soon.