Letter to the Editor Expression of TRAG-3 antigen in non-small-cell lung carcinomas

Specific immunotherapy targeting cancer-testis (CT) antigen is considered to be the promising strategy to treat lung cancer. The expression of CT antigens, such as MAGE, BAGE, NY-ESO-1 and GAGE, were found in non-small-cell lung carcinoma (NSCLC) [1,2]. The taxol resistant associated gene-3 (TRAG-3) antigen, which was initially identified by Duan [3] and associates following comparison of SKOV-3 to SKOV-3TR by differential display, belongs to a growing class of CT antigens. This gene has been found to be overexpressed in the majority of carcinoma cell lines and malignant melanoma, including NSCLC cell lines [4]. However, the expression status of TRAG-3 in lung tumors has yet to be determined. We report here an analysis of TRAG-3 expression in 48 surgical samples of non-small-cell lung carcinomas, containing 20 samples of squamous carcinoma, 22 samples of adenocarcinoma and 6 samples of large cell carcinoma according to WHO classification of cancer. The analysis of TRAG-3 mRNA expression was made by reverse-transcription polymerase chain reaction (RT-PCR). The following oligonucleotide primers were used: sense 5?-GCT GGC CTG CCT TCA CTG TC-3?; antisense 5?-CAC CCT GTT GGC TAT TTA TCT GG-3?. Both primers were synthesized commercially. The TRAG-3 protein expression in lung tumors was evaluated by immunohistochemistry. The first antibody to TRAG-3 antigen, generously provided by Dr Duan Z (Division of Hematology/Oncology, Massachusetts General Hospital, Boston, USA) is a polyclonal, rabbit antibody raised against the human TRAG-3 protein, which was expressed in and purtified from Escherichia coli HistastainTM- Strepcavisin/Peroxidase Kits was from ZYMED company. We obtained the following results in the present study: (1) There was no detectable TRAG-3 expression in normal lung tissues and adjacent tissues. (2) A comparison of TRAG-3 protein and mRNA expression revealed concordance in 48 cases. (3) The TRAG-3 protein was located in the cytoplasm of lung carcinoma cells, while no staining was detectable in adjacent normal cells or tissues. (4) The differences in the proportion of positive tumors between squamous-cell carcinoma and adenocarcinoma were significant. Among 20 samples of squamous carcinoma, only eight (17%) expressed TRAG-3, while 16 (73%) expressed TRAG-3 in 22 samples of adenocareinoma (Table 1). (5) Because TRAG-3 was first identified in a taxol-resistant ovarian carcinoma cell line, we therefore analyzed the difference of TRAG-3 expression between the patients received preoperative chemotherapy and the patients not received. The results showed that there was no significant difference between them. In conclusion, our results indicated that approximately 50% of non-small cell lung tumors expressed TRAG-3 antigen, the percentage of expression in adenocarcinoma was more than in squamous carcinoma. The result suggested that TRAG-3 might be a target for vaccine in the specific immunotherapy to nonsmall-cell lung carcinoma, especially to adenocarcinoma.