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Potential participants first need a blood test to determine their tissue type.

However, optimum hormone conditions can vary significantly with plant species, culture conditions, and tissue type.

The NHS hopes that by matching white blood cell type - also known as tissue type or HLA type - as close as possible between the blood donor and the organ transplant patient, it will mean the patient is less likely to reject the "foreign" organ.

The process increases the number of possible matches: if an organ isn't the right blood or tissue type for a donor's intended recipient, it could match someone else in the chain, and another donor in that chain could have an organ that's a good match for the original recipient.

Because the matching process for blood stem cells and bone marrow is dependent on tissue type, not simply blood type, growing the number of donors of different and mixed ethnicities is critical in finding potential matches.