The Science of Tissue Transplantation

Amidst the constantly changing world of medicine, innovative research from some of the world’s leading surgeons is finding new ways to use donated human tissue to treat a host of medical conditions. This tissue, referred to as allograft tissue, is donated by registered donors and their families, in the same way organs are donated, and it is used in many life-saving and enhancing medical procedures already, with numerous new opportunities on the horizon.

Donated human tissue is used in many surgical applications, saving peoples’ lives and limbs daily. Allograft tissue is used to replace damaged structures in the body, from the ligaments and tendons of major league sports players, bones and joints of military men and women, to the musculoskeletal structures, teeth, skin, and spinal components of average citizens.

The possibilities for the use of human tissue in modern medicine are exciting. Surgeons are researchers are learning more about the growth biology of the human body, about regenerating bone and tissue and using donor stem cells to re-grow physical structures. More information is coming to light to achieve long-term success with groundbreaking procedures such as full limb transplantation.

Recovery

Allograft safety begins at the point of tissue recovery. Here, knowledgeable and well-trained tissue recovery partners are key. The verification of donor medical and social history and a comprehensive initial donor physical assessment are critical screening steps.

Tissue recovery should be performed in a controlled environment by experienced and trained technicians using aseptic techniques. Procurement time constraints should be adhered to and documented, and microbial cultures should be taken. All donors must undergo rigorous and FDA approved screening serological tests for: Hepatitis B & C, HIV 1 & 2, and Syphilis (T. pallidum). Many processors have now added highly sensitive Nucleic Acid Testing (NAT), which is believed to reduce the window for determining HIV or HCV infection. If these evaluations determine the donor is eligible, a medical director should approve the tissue for processing.

Processing

A tissue processing facility should be accredited by the American Association of Tissue Banks (AATB) that uses Clinical Laboratories Improvement Act (CLIA) certified testing and environmental laboratories.  The facility also must be in full compliance with the FDA current Good Tissue Practices (cGTP). Upon arrival at the facility, donor tissue should be entered into a reliable inventory system and subjected to a robust process for reducing bioburden. This process should be carried out in certified clean rooms. The process by which the tissue’s bioburden is measured and diminished should include:

  • Elimination or reduction of blood, debris and lipids
  • Use of validated bactericidal washes and/or treatments
  • Surface swab tests, solution extraction or destructive tests of companion tissue

According to the FDA cGTP, donor pooling and batching is prohibited. Each donor should be processed individually in a separate processing session. Acceptable providers should have established quality assurance procedures in place, which are “designed to prevent, detect, and correct deficiencies that may lead to circumstances that increase the risk of introduction, transmission, or spread of communicable diseases.” Superior facilities are capable of producing a broad line of standard allografts as well as alternate and customized grafts.

Sterilization

Once processed, the allografts should be sealed in sterile pouches and clearly labeled with a unique donor and tissue ID, product ID code, allograft description, size, expiration date and storage instructions.

After individual allografts are prepared and preserved via freezing to -80ºC or freeze-drying (lyophilization), they should undergo a final review by a highly qualified and specialized individual. This step should include a careful visual inspection of the allograft, verification of its labeling, sizing and expiration date.

Allografts should be exposed to a validated terminal sterilization process. Low-dose, low temperature gamma irradiation between 10 and 15 kGy (1.0 to 1.5 Mrads) can provide a sterility assurance level (SAL) of 10-6 without jeopardizing the structural or biomechanical properties of the allograft. An SAL of 10-6 means there is a less than one in one million chance that a single microorganism survived the sterilization process. This is the same sterility level recommended for all other medical implants.