Lymphoblastoid cell lines 265(L) and 990(O) are monoclonal lymphomas, derived respectively from liver and ovarian tumours, generated in inbred P-line (MHC B(19)/B(19)) chickens infected with RB-1B strain of Marek's disease virus (MDV) and pRB-1B5 BAC clone respectively. These were inoculated into inbred, MDV-susceptible, P-line chickens by intra-venous or intra-abdominal routes. Additional groups of birds were vaccinated using 1000 plaque-forming units of CVI988 vaccine 8 days prior to inoculation of the cell lines. Non-vaccinated birds developed visceral Marek's disease tumours with an increased rate 30 to 60 days post inoculation. Vaccination prevented tumour and disease development in challenged birds. TCRβ repertoire analysis by spectratyping and sequencing of the inoculum was used to track tumour identity in primary tumours and tumour cell lines derived from inoculated birds. These data revealed that the tumours were a consequence of de novo virus infection and not metastasis and expansion of the inoculated tumour cells. Moreover, the data showed that the two MDV-derived cell lines were not transplantable even in syngeneic P-line birds. The data also demonstrated the application of spectratyping as a tool to track tumour identity in lymphoma transplantation studies.