Expression of the Cancer-Testis Antigens, SEMG 1 and Protamine 1, in Early CLL: Their Relationship to Disease Stage and Zap 70 Expression.

Despite advances in modern chemotherapy, CLL remains incurable. CLL is an indolent disease. It expresses a panel of Cancer-Testis (CT) antigens. CLL leukemia cells are susceptible to the cytotoxicity of T cells. CLL is, therefore, an ideal disease for immunotherapeutic approaches. Immunotherapy, in addition to being less toxic and more specific than chemotherapy, provides a different mode of cytotoxicity that may synergize with that induced by chemotherapeutic agents. Immunotherapy also offers the prospect of inducing immune memory that may be important for long term disease-free survival of patients with CLL. However, there are obstacles that may prevent successful immunotherapy. CLL patients are generally immunosuppressed even before any therapy is given and the immunosuppression increases as the disease progresses. Therefore, any immunotherapeutic approaches for CLL should be aplied in early disease when immunosuppression is least encountered. We previously demonstrated the expression of a CT antigen, SEMG 1, in 3/9 patients with CLL. Furthermore, we also demonstrated that the presence of high titer IgG in the serum of patients expressing SEMG 1, suggesting the in vivo immunogenicity of SEMG 1 in the cancer-bearing autologous host. We have also recently used SEMG 1 as the bait in a yeast two-hybrid system of testicular cDNA library and identified that Protamine 1 is the interacting ligand of SEMG 1 and that Protamine 1 is also a novel CT antigen, suggesting that both SEMG 1 and Protamine 1 may be suitable antigens for tumor vaccine development. However, the expression of SEMG 1 and Protamine 1 in early CLL is unknown. We have in this study set out to determine whether or not SEMG 1 and/or Protamine 1 could be used for the design of tumor vaccine for the targeting of patients with early CLL, in particular, those with poor risk disease, as predicted by Zap 70 expression. Using pairs of sequence-specific primers in RT-PCR on a cohort of CLL (41 Stage 0/I and 6 Stage II/III), we found that SEMG 1 gene is expressed in 24/47 (51%) and Protamine 1 in 16/47 (34%) of CLL patients. Gene expression in most cases was associated with the detection by immunocytochemistry of SEMG 1 and/or Protamine 1 in the CLL cells. The expression frequency of SEMG1 and Protamine 1 in CLL did not appear to differ between early and late stage disease. 19/41 of patients with early stage disease and 5/6 of patients with late disease expressed SEMG 1; 12/41 of patients with early stage disease and 4/6 patients with late disease expressed Protamine 1. Furthermore, the expression of these antigens was equally distributed between Zap 70+ and Zap 70− CLL. SEMG 1 was expressed in 4/6 of Zap 70+ CLL (all 6 had early disease) and 2/9 of Zap 70− CLL (1/8 early disease and 1/1 late disease). Interestingly, although Protamine 1 expression in CLL predicted for SEMG 1 co-expression, only 67% of SEMG 1+ CLL expressed Protamine 1. Our results, therefore, suggest that both SEMG 1 and Protamine 1 are suitable targets for tumor vaccine development for some patients with early CLL, especially those with high risk disease, as predicted by Zap 70 expression.