Limited SP17 expression within tumors diminishes its therapeutic potential

Abstract

In this study, we have investigated the expression of the tumor antigen sperm protein 17 (SP17) in a large panel of human cancers and compared it with the expression of two well-characterized families of tumor antigens, melanoma-associated antigen-A (MAGE-A) and G antigen (GAGE). We found that SP17 was expressed in many cancer types with an overall frequency of 12%. SP17 was most frequently expressed in a different set of cancer types than MAGE-A and GAGE antigens and rarely overlapped with these proteins. Importantly, SP17 expression was limited to a small number of scattered cancer cells in most positive tumors in contrast to MAGE-A and GAGE proteins, which were homogenously expressed in large foci. Our results suggest that SP17 may not be an optimal target for cancer vaccines.

Analysis of GAGE, NY-ESO-1 and SP17 cancer/testis antigen expression in early stage non-small cell lung carcinoma

“…Patient characteristics are presented in Table 1. GAGE, NY-ESO-1 and SP17 expression was examined using well-characterized antibodies and previously established methods for immunohistochemical staining [17,18]. GAGE and NY-ESO-1 was not detected in normal lung tissues, but SP17 was expressed in a subset of ciliated epithelial cells of the bronchi (Figure 1), in accordance with previously published data [17,18].…”

“…It is also notable that while the frequency of tumors positive for both GAGE and NY-ESO-1 proteins suggested a degree of coordinated expression of these proteins (p = 0.03), neither showed any tendency to co-expression with SP17 (p = 0.65 and p = 1.00) (Figure 2). Unlike GAGE and NY-ESO-1, SP17 is expressed in ciliated normal tissues in addition to testis, indicating that the encoding genes exhibit differences in tissue-specific regulation, which may explain the significant expression dissimilarities observed in NSCLC and other cancers [17]. It further confirms the notion that chromosome X encoded and autosomal encoded CT antigens exhibit different expression profiles in normal and malignant tissues.…”

“…GAGE, NY-ESO-1 and SP17 expression was examined using well-characterized antibodies and previously established methods for immunohistochemical staining [17,18]. GAGE and NY-ESO-1 was not detected in normal lung tissues, but SP17 was expressed in a subset of ciliated epithelial cells of the bronchi (Figure 1), in accordance with previously published data [17,18]. As shown in Table 2, GAGE proteins were detected in 26.0% (44/169) of NSCLC tumors and in 63.6% (28/44) of the positive tumors there were more than 50% positive tumor cells.…”

“…Methods for immunohistochemical staining of GAGE, NY-ESO-1 and SP17 in formalin-fixed, paraffin-embedded tissues and the characteristics of the antibodies used have been described previously [17-19]. Notably, the anti-GAGE antibody likely recognizes all members of the GAGE family.…”

“…In brief, tissue sections were cut, deparaffinized, treated with 1.5% H 2 0 2 in Tris-buffered saline (pH 7.5) for 10 min to block endogenous peroxidase activity, rinsed in distilled H 2 O, demasked for antigen retrieval and washed in TNT buffer (0.1 M Tris, 0.15 M NaCl, 0.05% Tween-20, pH 7.5). Primary monoclonal antibodies (anti-GAGE (clone M3) [18], 1:100; anti-NY-ESO-1 (clone E978) [18] 1:25; anti-SP17 (clone 22) [17] 1:400) were diluted in antibody diluent (DAKO Cytomation, Glostrup, Denmark) and added to sections for 1 h at room temperature. Sections were washed with TNT and incubated with horseradish peroxidase-conjugated Envision or Powervision polymer (DAKO Cytomation) for 30 min, followed by another wash with TNT.…”