Characterization of C21ORF100 as a Novel Prostate Differentiation Antigen

ABSTRACT

Differentiation antigens are immunogenic proteins expressed in specific cell lineages or at specific stages of differentiation ina particular tissue. Generally, their expression in normal cells is preserved after neoplasic transformation and this feature hasmade such molecules potential candidates for cancer immunotherapy. Using alignments between expressed sequence tags(ESTs) and the human chromosome 21 sequence, we have identified a novel gene, named C21orf100, which is exclusivelyexpressed in normal prostate and codes for a putative protein of 55 amino acids. Objective: To characterize C21orf100 as anovel prostate differentiation antigen. Material and Methods: C21orf100 mRNA expression was determined by RT-PCR in 22normal tissues and in 65 samples from melanomas and prostate, thyroid, stomach, uterus and breast tumors. The existenceof a humoral immune response against C21orf100 protein in prostate cancer patients was evaluated by immunoblotting usinga His-tagged recombinant protein. Results: As expected for a differentiation antigen, C21orf100 mRNA expression waspredominantly detected in both normal and tumor prostate samples. Antibodies against C21orf100 recombinant protein weredetected in 1 out of 50 (2%) plasma samples from prostate cancer patients and were not detected in the plasma from healthyblood donors. Conclusion: The restricted expression pattern and the detection of antibodies in prostate cancer patients suggestthat C21orf100 is a novel prostate differentiation antigen. However, due to the low frequency of antibody response againstC21orf100 detected among prostate cancer patients, further analysis is necessary to evaluate its potential for cancerimmunotherapy.