Presence of antibodies to different subunits of replication protein A in autoimmune sera

Serologic laboratory findings in malignancy

Autoantibodies are extremely promising diagnostic and prognostic biomarkers of cancer, and have the potential to promote early diagnosis and to make a large impact by improving patient outcome and decreasing mortality. Moreover, autoantibodies may be useful reagents in the identification of subjects at risk for cancer, bearing premalignant tissue changes. Great efforts are being made in many laboratories to validate diagnostic panels of autoantibodies with high sensitivity and specificity that could be useful in a clinical setting. It is likely that prospective studies of sufficiently large cohorts of patients and controls using high-throughput technology may allow the identification of biomarkers with diagnostic significance, and perhaps of discrete antigen phenotypes with clinical significance. The identification of TAAs may also be essential for the development of anticancer vaccines, because autoantibodies found in cancer sera target molecules involved in signal transduction, cell-cycle regulation, cell proliferation, and apoptosis, playing important roles in carcinogenesis. On this basis, molecular studies of antigenantibody systems in cancer promise to yield valuable information on the carcinogenic process. TAAs identified by serum antibodies in cancer sera can be natural immunogenic molecules, useful as targets for cancer immunotherapy. An important problem encountered in the practice of medicine is the identification of healthy individuals in the general population who unknowingly are at high risk of developing cancer. For the rheumatologist, a related problem is the identification of those patients with rheumatic diseases who are at high risk for developing a malignant process. These problems encountered in the fields of cancer and the rheumatic diseases can in the future be helped by new diagnostic instruments based on antibodies. The need for promoting the early diagnosis of cancer is a recognized major public health problem in need of significant research support for the validation of multiple promising but inconclusive studies, with the intention of producing diagnostic panels of autoantibodies in various types of cancers. Cancer developing in patients with rheumatic diseases is also an important problem requiring prospective longterm follow-up studies of patients with rheumatic diseases, particularly because some of the new biologic therapies seem to increase the cancer risk. It is possible that a panel of autoantibodies common to patients with cancer and the rheumatic diseases may prove to be of value in the identification of those patients with ADs at high risk for neoplasms.

Autoantibodies against the replication protein A complex in systemic lupus erythematosus and other autoimmune diseases

Replication protein A (RPA), a heterotrimer with subunits of molecular masses 70, 32, and 14 kDa, is a single-stranded-DNA-binding factor involved in DNA replication, repair, and recombination. There have been only three reported cases of anti-RPA in systemic lupus erythematosus (SLE) and Sjögren syndrome (SjS). This study sought to clarify the clinical significance of autoantibodies against RPA. Sera from 1,119 patients enrolled during the period 2000 to 2005 were screened by immunoprecipitation (IP) of ³⁵S-labeled K562 cell extract. Antigen-capture ELISA with anti-RPA32 mAb, immunofluorescent antinuclear antibodies (ANA) and western blot analysis with purified RPA were also performed. Our results show that nine sera immunoprecipitated the RPA70–RPA32–RPA14 complex and all were strongly positive by ELISA (titers 1:62,500 to 1:312,500). No additional sera were positive by ELISA and subsequently confirmed by IP or western blotting. All sera showed fine speckled/homogeneous nuclear staining. Anti-RPA was found in 1.4% (4/276) of SLE and 2.5% (1/40) of SjS sera, but not in rheumatoid arthritis (0/35), systemic sclerosis (0/47), or polymyositis/dermatomyositis (0/43). Eight of nine patients were female and there was no racial predilection. Other positive patients had interstitial lung disease, autoimmune thyroiditis/hepatitis C virus/pernicious anemia, or an unknown diagnosis. Autoantibody specificities found in up to 40% of SLE and other diseases, such as anti-nRNP, anti-Sm, anti-Ro, and anti-La, were unusual in anti-RPA-positive sera. Only one of nine had anti-Ro, and zero of nine had anti-nRNP, anti-Sm, anti-La, or anti-ribosomal P antibodies. In summary, high titers of anti-RPA antibodies were found in nine patients (1.4% of SLE and other diseases). Other autoantibodies found in SLE were rare in this subset, suggesting that patients with anti-RPA may form a unique clinical and immunological subset.

Naturally occurring B-cell responses to breast cancer

As demonstrated by the effectiveness of trastuzumab, antibodies against breast cancer antigens are a potentially potent mechanism of tumor control. While trastuzumab is administered exogenously, its efficacy suggests that induction of very high titer antibody responses in vivo might also be therapeutic. Both naturally occurring and vaccine-induced antibody responses to some breast cancer antigens are associated with improved survival in some cases. However, the improvement in survival associated with antibody responses to breast cancer is modest, and tumor regression is not known to be associated with the natural antitumor antibody response, indicating a need for improved understanding of the natural antitumor antibody response. Naturally occurring B-cell responses in the form of serum antibody, tumor reactive lymph node B cells, and tumor-infiltrating B cells have been described, and a variety of breast tumor-associated antigens have been identified based on reactivity of patient antibodies. This review discusses current knowledge of humoral immunity to breast cancer with regard to specific antigens and the basis for their immunogenicity, and the contexts (tumor, lymph node, serum) in which responses are observed. With few exceptions, "tumor-associated antigens" identified with naturally occurring antibodies may be overexpressed on tumor but are in fact nonspecific autoantigens. This suggests that while overexpression or aberrant processing can increase immunogenicity in some cases, the immunogenicity of many or even most tumor-associated antigens is a function of expression in tumor or the result of ancillary tumor factors.

Autoimmunity to the M(r) 32,000 subunit of replication protein A in breast cancer

PURPOSE

We sought to identify autoantigens recognized by antibodies in breast cancer patient sera with potential diagnostic or prognostic significance.

EXPERIMENTAL DESIGN

Serum from a female breast cancer patient exhibiting a high titer antinuclear antibody was used to screen a HeLa cDNA expression library, leading to the cloning of a cDNA for the M(r) 32,000 subunit of replication protein A (RPA32). RPA32 expression and localization were assayed in autologous tumor by monoclonal antibody staining. A specific ELISA using recombinant protein was used to screen sera from 801 breast cancer patients and 65 controls.

RESULTS

A relationship between anti-replication protein A (RPA) antibodies and the ductal breast carcinoma of the proband was suggested by overexpression and aberrant localization of RPA32 in tumor cells as compared with surrounding normal ductal tissue and by the presence of anti-RPA32 antibodies before the diagnosis. The prevalence of anti-RPA32 antibodies was significantly higher (P < 0.01) among breast cancer patients (87 of 801 patients) than among noncancer controls (0 of 65 controls). Similarly, anti-RPA32 antibodies were present in 4 of 39 patients with intraductal in situ carcinoma. No associations were found between anti-RPA antibodies and survival, occurrence of a second tumor, metastases, or antibodies to p53. Reactivity to RPA32 also was detected in sera from 3 of 47 patients with other cancers.

CONCLUSIONS

In view of the central role of RPA in DNA replication, recombination, and repair, we suggest that autoimmunity to RPA32 may reflect molecular changes involved in the process of tumorigenesis. The finding of antibodies to RPA32 before diagnosis and their prevalence in in situ carcinoma suggest that they are potentially useful markers of early disease.

Antibodies against glutathione S-transferase T1 (GSTT1) in patients with de novo immune hepatitis following liver transplantation

Four patients of 283 liver-transplant recipients (1.4%) developed de novo immune-mediated hepatitis approximately 2 years after transplantation. Antibodies showing an unusual liver/kidney cytoplasmic staining pattern were detected in the sera of all four patients and one of them was used to screen a human liver cDNA expression library with the aim of identifying the antigenic target of these newly developed antibodies. After cloning and sequencing the gene, it was identified as the gene encoding the glutathion-S-transferase T1 (GSTT1), a 29-kD molecular weight protein, expressed abundantly in liver and kidney. Sera from the other three patients also contained anti-GSTT1 antibodies, two of them demonstrated by immunoblot analysis against the recombinant antigen and the other, which was negative by immunoblot, gave a positive reaction when used directly to screen the same library, suggesting it to be directed to a conformational epitope. The GSTT1 enzyme is the product of a single polymorphic gene that is absent from 20% of the Caucasian population. When we analysed the GSTT1 genotype of the four patients described above, we found that this gene is absent from all of them. Three donor paraffin embedded DNA samples were available and were shown to be positive for GSSTT1 genotype. In accordance with these results, we suggest that this form of post-transplant de novo immune hepatitis, that has been reported as autoimmune hepatitis by others, could be the result of an antigraft reaction in individuals lacking the GSTT1 phenotype, in which the immune system recognizes the GSTT1 protein as a non-self antigen, being the graft dysfunction not the result of an autoimmune reaction, but the consequence of an alo-reactive immune response.

Affinity selection of cDNA libraries by lambda phage surface display

Bacteriophage lambda surface display was used to isolate cDNA clones encoding autoantigens recognized by sera from patients with Sjögren's syndrome (SS). We made cDNA libraries from human HeLa and HepG2 cells, using the expression vector lambdafoo. By repeating affinity selection of the libraries with the sera immobilized in microtiter wells, we isolated three clones that encode previously unknown antigens as well as four clones previously known as SS autoantigens. The newly identified autoantigens include TRK-fused gene product (TFG), survival motor neuron gene product (SMN) and pM5, which has a similarity to the metal-binding domain of human fibroblast collagenase. Thus, the bacteriophage lambda surface display is powerful for isolating cDNA clones by affinity screening.

Autoantibodies to transcriptional regulation proteins DEK and ALY in a patient with systemic lupus erythematosus

A human cDNA expression library that was used to investigate the nature of autoantigens recognized by the serum from a patient with systemic lupus erythematosus revealed the presence of antibodies directed against two transcriptional regulation protein: DEK, a site-specific 45 kD DNA binding protein, likely involved in signal transduction and transcriptional regulation, and a novel 28 kD protein that showed a 94% homology with murine ALY, a nuclear protein that plays a role in regulating the activity of TCRalpha enhancer complex. Whereas autoantibodies directed to epitopes on DEK are commonly found in patients with pauciarticular onset juvenile rheumatoid arthritis, autoantibodies against ALY have not been described and their occurrence has led to the cloning of the cDNA sequence of the first member of the human ALY family.

Detection of anti-PL-12 autoantibodies by ELISA using a recombinant antigen; study of the immunoreactive region

Autoantibodies to aminoacyl-tRNA synthetases are highly associated with myositis and detection is important in clinical diagnosis; however, current methods of screening limit its clinical utility. In the present study, alanyl-tRNA synthetase (PL-12) recombinant protein was obtained by immunological screening of a HeLa expression library and used in an ELISA with 22 anti-PL-12 sera, 200 autoimmune sera negative for PL-12 and 100 healthy individual sera. Sensitivity of the method was 95% (21/22) and specificity 100%. Mapping of the immunoreactive region was carried out using three anti-PL-12 sera and different recombinant protein-derived peptides. Results show that the same conformational epitope located within amino acids 730-951 of the PL-12 antigen outside the catalytic region was recognized by the three anti-PL-12 sera tested. We conclude that ELISA using recombinant protein is an effective and useful method for routine screening for anti-PL-12 autoantibodies.

Abnormal DNA damage-inducible protein in cells from Sjögren's syndrome patients

Antinuclear antibodies are commonly found in patients with Sjögren's syndrome. It has been suggested that the development of antinuclear antibodies depends on the activation of the spliceosome and other transcription-related subcellular particles, some of which have recently been shown also to function in DNA-modifying processes, such as DNA repair and V(D)J recombination. These observations add weight to a previously proposed model for the aetiology of Sjögren's syndrome. This includes the abnormal processing of the T-cell receptor and immunoglobulin genes. To test this hypothesis further, the present study on DNA-modifying proteins in Sjögren's syndrome was initiated. Gel-shift experiments using protein extracted from UV-treated Sjögren cells provided evidence of high molecular weight DNA-binding protein in six out of 12 Sjögren patients studied (but not among seven healthy controls). Some Sjögren sera displayed antibodies to protein extracts from cells treated with psoralen plus UVA radiation. These results indicate an abnormal DNA damage-inducible response in Sjögren's syndrome. It may therefore be concluded that alterations in nuclear protein may play a role in the aetiology of Sjögren's syndrome.