In situ RT-PCR analysis of vTK expression in a representative PTLD tumor sample.

(A) Hematoxylin and eosin (H & E) stain of tumor biopsy showing diffuse infiltration by atypical large lymphocytes. (B) IS-RT-PCR detection of EBER-1 and EBER-2 mRNA. Most of the lymphoma cells in the field are positive for the expression of these abundant EBV transcripts, confirming the presence of EBV. (C) IS-RT-PCR analysis of EBV vTK mRNA. vTK expression is present in a number of lymphoma cells equivalent to those expressing EBER-1 and EBER -2. (D) RNase digestion after IS-RT-PCR analysis of vTK mRNA demonstrates that the signal present in panel C is RNA-based. Original magnification, × 400.