Identification of tumor -associated antigens as markers for immunodiagnosis of human cancers
Background and significance. Hepatocellular carcinoma (HCC) is one of the most malignant cancers in the world and is associated with a very poor prognosis. It can be partly attributed to the lack of sensitive and specific diagnostic methods for early detection. During the transition from precursor conditions, such as chronic hepatitis (CH) and liver cirrhosis (LC) to HCC, patients may develop autoantibodies which were not present during the preceding chronic liver disease phase. These novel autoantibodies are assumed to be driven by tumor associated antigens (TAAs) which might be involved in HCC tumorigenesis. The hypothesis is that in sera from HCC patients who show autoantibodies changes during progression from chronic liver disease to HCC, autoantibodies appearing during this transition might likely be the "reporters” of the events associated with the tumorigenesis of HCC. These autoantibodies therefore, can be used as probes in immunoscreening HepG2 cDNA expression library to identify antigens which are potentially involved in liver malignant transformation. Due to the low sensitivity, the use of autoantibody to single TAA as a serological marker in HCC diagnosis is still limited. A mini-array of multiple HCC-specific TAAs, however, may greatly enhance antibody detection. The overall goal of this study is to identify TAAs that are more specific to HCC and to further evaluate the possibility and usefulness of autoantibodies to a mini-array of multiple TAAs, in order to establish a novel approach in the immunodiagnosis of human HCC. Methods. One selected HCC serum was used to immunoscreen a HepG2 cDNA expression library. All the positive cDNA clones were sequenced and compared with known sequences database by Blast search. The immunogenecities of two identified genes Sui1and RalA which might be potentially involved in HCC tumorigenesis were analyzed by immunoassay such as ELISA and Western Blot in the sera with different conditions. Protein expression profiles of both antigens were evaluated by immunohistochemistry study with tissue array. A panel of multiple TAAs including Sui1 and RalA were constituted and the diagnostic values were also evaluated. Results. Twenty-seven individual genes were identified by immunoscreening HepG2 cDNA library including 21 known genes and six unknown genes. Of 21 known genes, 11 were involved in apoptosis, cell differentiation and proliferation as well as antigen processing. Ten genes have been reported to be related to various cancers, and 3 were especially associated with HCC. Based on the functional significance and cancer relevance, HCC-1 (Sui1) and HCC-13 (RalA) were particularly selected for subsequent study. Both antigens showed significantly higher immunoreactivities in HCC (11.9% and 19% for Sui1 and RalA, respectively) compared to liver cirrhosis (3.3%), chronic hepatitis (0%) and normal human sera (0%). A panel of 10 TAAs including Sui1 and RalA greatly increased the cumulative frequency of antibody response in HCC to 66.2%, which is significantly higher compared to that in normal human sera (12.2%). RalA was found to be overexpressed in HCC tissues (63.3%) compared to the expression in normal liver tissues (26.7%). Sui1, however, showed an equivalent expression in HCC (26.7%), LC (22.5%) and normal liver tissues (36.7%). Conclusions. Our study demonstrated that two identified TAAs Sui1 and RalA which were derived from HepG2 cDNA expression library had significantly higher immunoreactivities in HCC compared to the precursor conditions such as LC and CH as well as normal individuals. It suggested that these two antigens might be potential tumor markers in HCC diagnosis. Stepwise increased expression of RalA from the precursor condition to HCC may contribute to liver malignant transformation. A panel of 10 TAAs including Sui1 and RalA greatly increases the antibody detection of HCC and may provide a feasible approach to enhance HCC early diagnosis in high-risk population.
Chen, Yao, "Identification of tumor -associated antigens as markers for immunodiagnosis of human cancers" (2007). ETD Collection for University of Texas, El Paso. AAI3262904.