Why is storing Cord Tissue different from Cord Blood?

Umbilical Cord Blood contains both types of stem cells, the haemopoietic stem cells and the mesenchymal stem cells. Haemopoietic stem cells are blood stem cells. They multiply and differentiate to form the various types of blood cells. These haemopoietic stem cells are used in the field of Stem Cell Transplants. This is a treatment modality proven beyond doubts for many patients with blood disorders and cancers. While not every leukaemia and not every patient can be cured, haemopoietic stem cells had indeed proven its value in curing many such patients since the 1960s (known as Bone Marrow Transplants then). However, this treatment modality, Stem Cell Transplant, cannot be performed with Mesenchymal Stem Cells. As such, cord tissue cannot be used to treat blood disorders and cancers.

On the other hand, cord blood can be used for Regenerative Medicine because it does contain Mesenchymal Stem Cells also. In fact, cord blood had been used in the treatment of Cerebral Palsy, where the neurological damage in the brain is supposedly reversed by these stem cells. Small studies and individual reports had been very impressive with the results. Bigger clinical trials are still undergoing to determine the effectiveness of cord blood in treating Cerebral Palsy.

So, the big difference is that cord blood can be used in both Stem Cell Transplants and Regenerative Medicine while cord tissue can only potentially be used for Regenerative Medicine. As such, not storing cord tissue is not a big disadvantage once cord blood is stored.

 

Is it useful to store?

 

In theory, there are no disadvantages in storing cord tissue other than the expenditure. Any extra quantities of stem cells, be it haemopoietic stem cells or mesenchymal stem cells can only be potentially useful when there is a need to use them. The cord tissue will be discarded if not collected and stored at delivery, much like cord blood. There is no risk or harm at all to both mother and baby during the collection process.

 

Are there any controversies with storage?

 

The main controversy with cord tissue is the methodology of collection and storage. Most cord blood banks that offer cord tissue storage are storing the cord tissue without processing first. This means the cord tissue is brought to the laboratory, cleansed, cut into pieces and frozen with the cryopreservative agent. When there is a need to use Mesenchymal Stem Cells, these frozen pieces of cord tissue are then thawed and the Mesenchymal Stem Cells are then extracted. However, there is no guarantee that extracting these Mesenchymal Stem Cells is always possible. In fact, there are concerns that the freezing technique may kill all the cells in the cord tissue.

In the processing of cord blood, the freezing process is a laborious and careful step that involved a special machine, called the rate-control freezer. This machine freezes at a rate of minus 1 degree Celsius per minute. Also, the cells in cord blood are in the liquid medium and are well mixed with the cryopreservative agent. With cord tissue, the cryopreservative agent may not be able to infiltrate the tissue and hence may not be able to protect the cells during the freezing process. Furthermore, some banks just put the cord tissue in the storage tank without using the rate-control freezer.

Because of this, some banks offer to process the cord tissue first. That means extracting the Mesenchymal Stem Cells, put them into a liquid medium with the cryopreservativeagent and freeze them in exactly the same way as cord blood stem cells. Freezing stem cells in this way is very well accepted amongst all stem cell experts. Stem cells stored this way can be stored indefinitely. But, processing the cord tissue first to extract the Mesenchymal Stem Cells will involve a lot more work that is not so convenient to the laboratory.

In summary, I do agree that Mesenchymal Stem Cells in cord tissue is a wonderful discovery but unfortunately, its usefulness is still limited to clinical research at the moment. Unlike cord blood, cord tissue cannot be useful for stem cell transplants, which is an established treatment modality for blood disorders and cancers. Furthermore, the controversy involving its storage methodology (if unprocessed) does raise concerns over its usefulness in future. More clinical studies have to be conducted to ensure successful retrieval and clinical use before we should consider routine storage.

 

By Dr Teo Cheng Peng

StemCord Medical Director