This is a follow up study to a randomised controlled trial comparing a CMV glycoprotein B vaccine with placebo (Trial title: A Phase II Immunogenicity Trial Of Cytomegalovirus Glycoprotein B Vaccine In Allograft Candidate Recipients; CTA ref no 20363/0238/001-0010; REC ref no 5476; UCL sponsor no 05/009) in participants with Chronic renal or liver deficiency sufficient to require transplantation. The study provided encouraging results (data now unblinded and analysed) by reducing the amount of cytomegalovirus that vaccinated patients excreted in blood post transplant (Griffiths et al Lancet 2011). The titre of antibody made against glycoprotein B was a correlate of protection against duration of viraemia (i.e. reduction in CMV levels). 100% of patients given vaccine produced antibody against glycoprotein B although the titres decreased with time. The titres of CMV neutralising antibody were boosted in those with prior natural immunity. The titres of neutralising antibody were low among those who were initially seronegative. However, improved assays for CMV neutralising antibodies have now become available, so we wish to have the samples retested using these different methods. We will also send the blood samples taken in the previous study to the same labs for enzyme immunoassay for antibodies against glycoprotein B. This trial will approach patients that took part in the above referenced study for one further blood sample to determine their current antibody titres and to obtain their consent to test the samples taken in that previous study using these new improved antibody assays. Monoclonal antibodies will be made from purified B lymphocytes to study how these may bind and neutralise cytomegalovirus in the laboratory in order to develop antibodies as potential therapeutic agents.