Dear Sir,
Nasopharyngeal carcinoma (NPC) is rare in most part of the world but shows high incidence in South China and Southeast Asia. One of the unique features of this epithelial cancer is its consistent association with Epstein-Barr virus (EBV) infection. Studies have shown that EBV plays a key role in the genesis and maintenance of the tumor phenotype in this disease. 1 Clonal EBV genome and latent gene products are found in almost all cases of NPC expect for the keratinizing type of NPC from nonendemic areas. With the advance of molecular biology, knowledge of molecular alterations and EBV's function in NPC rapidly accumulated in the past 15 years. 1,2 However, most of these studies are based on the EBV-negative NPC cell lines established at 10-20 years ago. Until now, only a few NPC cell lines, such as C666-1, stably harboring the EBV genome were used as EBV-positive NPC model. 3 In addition to the established NPC cell lines, several EBV-positive NPC transplants in nude mice (e.g. C15, C17, xeno-666, xeno-2117 and xeno-1915) were used for identifying the genetic alterations and delineating aberrant signal transduction pathways in NPC. 4,5 Because of the difficulties in manipulating target gene expression in these in vivo models, they are rarely used in functional studies.
Recently, we have performed the array-based CGH analysis on a number of NPC cell lines, xenografts and primary tumors. 6 We observed similar copy number aberrant patterns in some EBV-negative cell lines. Furthermore, these cell lines show distinct transcription profiles from the C666-1 cell line and NPC xenografts in microarray analysis (unpublished observations). It raised the concern for the identity of tumor lines used in NPC study. Thus, we investigated the authenticity of a number of NPC cell lines (C666-1, HK-1, CNE-1 and CNE-2), xenografts (xeno-666, xeno-2117, xeno-1915, C15 and C17) and immortalized nasopharyngeal epithelial cell lines (NP69 and NP460), which are commonly included in our previous works. 1 The DNA samples from these tumors were extracted and subjected to DNA fingerprinting analysis using the AmpF/STR Identifiler 1 PCR Amplification Kit (Applied Biosystems, Foster City, USA). A total of 15 short tandem repeat (STR) loci (D3S1358,