Defining tumor antigens: mRNA, protein or cytotoxicity?

Sperm associated antigen 9 expression and humoral response in chronic myeloid leukemia

Early diagnosis and cure for patients with chronic myeloid leukemia (CML) exhibit significant clinical challenges because of the disease progression from chronic phase (CP) into a rapidly fatal blast crisis. Our earlier studies suggested an association of sperm associated antigen 9 (SPAG9) with various human malignancies. The present investigation revealed that SPAG9 mRNA and protein are expressed in CML patients (88%), in K562 and KCL-22 cells. Further, SPAG9 protein expression was also detected on cell surface suggesting that this molecule may be a suitable target for immunotherapy. Interestingly, 90% CML-CP patients showed humoral response against SPAG9, suggesting its important role in early diagnostic of CML-CP. Further investigation is warranted in establishing the potential of SPAG9 as a biomarker and immunotherapeutic target for early treatment of CML-CP patients.

A yeast two-hybrid system using Sp17 identified Ropporin as a novel cancer-testis antigen in hematologic malignancies

Since most intracellular proteins are expressed with their ligands, ligands of cancer-testis (CT) antigens may also be CT in their distribution. Applying Sperm protein 17 (Sp17) as the bait in a yeast 2-hybrid system of a testicular cDNA library, 17 interacting clones were isolated and all encoded Ropporin, a spermatogenic cell-specific protein that serves as an anchoring protein for the A-kinase anchoring protein, AKAP110. Ropporin showed a very restricted normal tissue gene expression, detected only in testis and fetal liver. Ropporin mRNA could also be detected in tumor cells from patients with multiple myeloma, chronic lymphocytic leukemia and acute myeloid leukemia. Interestingly, expression of Sp17 did not necessarily predict for the expression of Ropporin suggesting that their coexpression in these tumor cells was random rather than coordinated. Ropporin gene expression in tumor cells is associated with the presence of high titer IgG antibodies against Ropporin, suggesting the in vivo translation of the mRNA into protein and the immunogenicity of the protein to the autologous hosts. Using a CT antigen as the bait in a yeast 2-hybrid system may, therefore, identify novel tumor antigen. Our results also suggest that Ropporin is a novel CT antigen in hematologic malignancies.

Sperm protein 17 is expressed in human nervous system tumours

Background

Human sperm protein 17 (Sp17) is a highly conserved protein that was originally isolated from a rabbit epididymal sperm membrane and testis membrane pellet. It has recently been included in the cancer/testis (CT) antigen family, and shown to be expressed in multiple myeloma and ovarian cancer. We investigated its immunolocalisation in specimens of nervous system (NS) malignancies, in order to establish its usefulness as a target for tumour-vaccine strategies.

Methods

The expression of Sp17 was assessed by means of a standardised immunohistochemical procedure [(mAb/antigen) MF1/Sp17] in formalin-fixed and paraffin embedded surgical specimens of NS malignancies, including 28 neuroectodermal primary tumours (6 astrocytomas, 16 glioblastoma multiforme, 5 oligodendrogliomas, and 1 ependymoma), 25 meningeal tumours, and five peripheral nerve sheath tumours (4 schwannomas, and 1 neurofibroma),.

Results

A number of neuroectodermal (21%) and meningeal tumours (4%) were found heterogeneously immunopositive for Sp17. None of the peripheral nerve sheath tumours was immunopositive for Sp17. The expression pattern was heterogeneous in all of the positive samples, and did not correlate with the degree of malignancy.

Conclusion

The frequency of expression and non-uniform cell distribution of Sp17 suggest that it cannot be used as a unique immunotherapeutic target in NS cancer. However, our results do show the immunolocalisation of Sp17 in a proportion of NS tumour cells, but not in their non-pathological counterparts. The emerging complex function of Sp17 makes further studies necessary to clarify the link between it and immunopositive cells.

Cancer immunotherapy targeting Sp17: when should the laboratory findings be translated to the clinics?

Despite advances in chemotherapeutic agents, the prognosis for some cancers remains extremely poor, suggesting the need for other treatment modalities. Immunotherapy appears an ideal approach because the mechanisms of tumor cell killing induced by tumor vaccines are different from those from chemotherapy. Various investigations are ongoing to identify suitable targets for this purpose. Sperm protein 17 (Sp17) was originally identified by our group as a novel cancer-testis antigen in various malignancies, including multiple myeloma. Sp17 is a highly immunogenic protein and the observation that more than 90% of vasectomized males develop immunity against Sp17 suggests the opportunity and safety of Sp17 for tumor vaccines. Recent works by other workers suggest a low level of expression of Sp17 in some normal tissues, and investigators have questioned whether Sp17 is in fact a suitable target for immunotherapy. In this paper, we review the general principles of immunotherapy and provide evidence supporting the highly immunogenic nature of Sp17. We also address the discrepancies between the objectives of oncologists involved in treating cancer patients and their familiarity with acceptable levels of toxicity of any effective therapy and those of pure laboratory-based investigators. Finally, we present some early clinical data supporting the rationale for further investigations of Sp17 for tumor vaccines.

The Spermatozoa Protein, SLLP1, Is a Novel Cancer–Testis Antigen in Hematologic Malignancies

PURPOSE

Neoplastic cells often aberrantly express normal testicular proteins. Because these proteins have a very restricted normal tissue expression, they may be suitable targets for immunotherapy. SLLP1 is an intra-acrosomal, nonbacteriolytic, c lysozyme-like protein recently isolated from human spermatozoa. In this study, we determined whether SLLP1 is a novel cancer-testis antigen in hematologic malignancies

EXPERIMENTAL DESIGN

SLLP1 expression in hematologic tumor cells and normal tissues was determined using a combination of reverse transcription-PCR, real-time PCR, and Western blot analysis. The presence of antibodies against SLLP1 was determined by ELISA analysis.

RESULTS

SLLP1 was aberrantly expressed in the tumor cells from 2 of 9 acute myeloid leukemia, 3 of 11 chronic lymphocytic leukemia, 4 of 14 chronic myeloid leukemia, and 6 of 17 multiple myeloma. In contrast, they were not detected in corresponding specimens from any healthy donors. SLLP1 exhibited a very restricted normal tissue expression, being found only in testis/spermatozoa. SLLP1 was expressed in some tumor cells at a level of >25%. High titer IgG antibodies against SLLP1 were also detected in the sera of some of these patients.

CONCLUSIONS

SLLP1 is a novel cancer-testis antigen in hematologic malignancies and is capable of eliciting B-cell immune responses in vivo in cancer-bearing individuals. Our results, therefore, support SLLP1 as a protein target appropriate for additional in vitro study to define its suitability for immunotherapy.

Cancer immunotherapy: avoiding the road to perdition

The hypothesis that human cancers express antigens that can be specifically targeted by cell mediated immunity has become a scientifically justifiable rationale for the design and clinical testing of novel tumor-associated antigens (TAA). Although a number of TAA have been recognized and it has been suggested that they could be useful in the immunological treatment of cancer, the complexity of human beings leads us to reflect on the need to establish new criteria for validating their real applicability. Herein, we show a system level-based approach that includes morphological and molecular techniques, which is specifically required to improve the capacity to produce desired results and to allow cancer immunotherapy to re-emerge from the mist in which it is currently shrouded.

Gene expression and immunologic consequence of SPAN-Xb in myeloma and other hematologic malignancies

Recent studies in tumor immunology indicate that malignant cells frequently express normal testicular-specific proteins. Because these proteins show restricted normal tissue distribution, they are usually highly immunogenic and may be potential targets for immunotherapy. In the present study, we have used a pair of sequence-specific primers in reverse transcription-polymerase chain reaction (RT-PCR) and sequence analysis to demonstrate that the X-linked gene encoding SPAN-Xb is expressed in multiple myeloma and other hematologic malignancies such as chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML), and acute myeloid leukemia (AML). RT-PCR analysis demonstrates that SPAN-Xb is a cancer/testis antigen and shows a restricted normal tissue expression. It is not expressed in any normal tissue except testis. SPAN-Xb recombinant protein was produced and used in enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. High-titer immunoglobulin G (IgG) antibodies, of IgG3 or IgG2 subclass, against SPAN-Xb were detectable in the sera of these patients. In contrast, SPAN-Xb mRNA or antibodies could not be detected in any of the healthy donors. There was a good correlation between SPAN-Xb gene expression and B-cell immune responses. These results suggest the in vivo immunogenicity of the SPAN-Xb protein. The presence of high-titer IgG responses suggests that the B-cell responses are likely to have been generated with CD4 T-cell cognitive help. Based on these data, we conclude that SPAN-Xb is a novel member of the family of cancer/testis antigens aberrantly expressed by, and capable of inducing, immune responses in patients with multiple myeloma and other hematologic malignancies.

Sperm protein 17 (Sp17) is a suitable target for immunotherapy of multiple myeloma

Sperm protein 17 (Sp17) is a protein recently identified as a novel cancer-testis (CT) antigen in multiple myeloma (MM). Because this tumor antigen demonstrates a very restricted normal tissue expression, Sp17 may be an excellent target for tumor vaccine of MM. In this study, we determined the ability to generate Sp17-specific HLA class I-restricted cytotoxic T lymphocytes (CTLs) from the peripheral blood of 4 patients with MM, 3 consecutive Sp17(+) patients, and 1 Sp17(-) patient. Dendritic cells were generated from monocytes of 4 patients with MM and used to present a recombinant Sp17 protein to autologous T cells. Following 4 rounds of antigen stimulation, the CTLs were tested for their ability to kill autologous targets in an Sp17-dependent and HLA-class I- restricted manner in standard cytotoxicity assays. Despite previous chemotherapy and the immunosuppression so often associated with MM, CTL generation was successful in all 4 patients, irrespective of the Sp17 status of their tumors. Most importantly, the CTLs were able to lyse autologous tumor cells that expressed Sp17. Tumor cell lysis in all cases appeared to be mainly mediated by perforin and could be blocked by concanamycin A. We conclude that Sp17 is a suitable target for immunotherapy of MM. Our findings provide the basis for a clinical study aimed at inducing a cellular immune response directed at Sp17(+) MM.