69DOLLY: A FINAL REPORT

Abstract

Dolly, the first animal to be derived by transfer of a nucleus from an adult somatic cell was euthanized on February 14, 2003, because of the presence of a virally-induced lung tumor resulting in progressive decline in respiratory function. We have carried out full gross and histopathological analysis of tissues and additionally re-examined the length of her telomeres. Dolly was derived from an oocyte recovered from a Scottish Blackface ewe and the nucleus of a cell cultured from mammary tissue of a 6-year-old Finn Dorset ewe. The culture had been through 27 population doublings. Dolly was 5 years and 7 months old at the time of her death. A detailed comparison was made between Dolly and four other ewes of similar breed and age produced by natural mating. Full post mortem examination was carried out and a range of tissues examined histologically. Major findings were the presence of extensive tumor infiltrates in both lungs and bilateral severe stifle arthritis in Dolly. Histopathology confirmed the presence of extensive sheep pulmonary adenomatosis/SPA (syn. ovine pulmonary adeoncarcinoma/OPA) lesions in the lung. This infection is caused by Jaagsiekte sheep retrovirus (JSRV) and is transmitted in respiratory droplets. Other animals in the barn had previously developed SPA. The risk of transmission of infection may have been increased by the fact that the animals were housed in close proximity in a barn. There is currently no reliable diagnostic test before the tumor develops and it is probable that Dolly was infected before we were aware of the presence of the infection in the group of sheep. There is no treatment for the disease. There is no reason to think that Dolly was more vulnerable to infection because she was a clone. The osteoarthritis was first observed during the autumn of 2001 when radiographs of the left stifle revealed osteophytes and osteophytosis associated with the patella, distal femur and proximal tibia. Radiographs of the right stifle were normal at that stage. A regime of anti-inflammatory drugs enabled the ewe to live a normal life. None of the other cloned sheep at the Institute have shown any symptoms of arthritis. Arthritis has been described in a cloned bull, but has not been described in any other cloned sheep. Telomeres in kidney tissue taken from Dolly were found to be shorter than those in kidney of the four control sheep (Dolly’s=15.6kb v. controls=17.9±0.27kb). This confirms the observation that her telomeres were shorter at 1 year of age than those of age-matched controls (Dolly 19.14kb v. controls 24kb). It is not appropriate to contrast these measurements, as they were not made in a single experiment. Dolly was fertile and delivered a total of 6 healthy lambs in three pregnancies. During routine husbandry there were no unusual findings apart from the development of the arthritis. Since the birth of Dolly, experiments in several species have revealed a range of abnormal phenotypes associated with unusual patterns of gene expression.