Treatment of a wide range of diseases using stem cells and other types of cell appears promising. Following administration of cells it is often not clear where exactly the cells have gone and how many of them have reached the target site. This has been one of the challenges of developing these treatment options further. We have developed a method of labelling human cells with a magnetic resonance imaging (MRI) "contrast agent" which contains tiny iron filings. Following intravenous administration it is possible to see where the iron-labelled cells have gone using MRI scanning. We would like to do is to demonstrate that these cells behave normally and migrate to a site of inflammation. We plan to induce an area of inflammation in the forearm of healthy volunteers using the Mantoux test (a test of immunity against tuberculosis) before giving the labelled cells intravenously. After the Mantoux test we will give these volunteers iron-labelled cells and do MRI scans of their forearm to determine whether these cells can be seen accumulating in the target site.

Inclusion Criteria:

• Healthy male or female volunteers age 18 to 65 years
• Previous vaccine for tuberculosis more than 5 years ago

Exclusion Criteria:

• pregnancy / breast feeding
• Contra-indication to MRI scanning
• Inability or refusal to give informed consent
• Renal failure (eGFR <25mL/min) or hepatic dysfunction (Child's B or C)
• HIV/hepatitis B/hepatitis C/HTLV/syphilis
• Active malignant disease
• Anaemia
• Blood dyscrasia
• High risk of allergy to protamine sulphate (fish allergy, infertile men, vasectomy)
• Known history of tuberculosis infection.
• History of prolonged residence (> 6 months) in a region or country with a high prevalence of tuberculosis.
• Previous Mantoux reaction of 15mm of greater.