Antibodies to EGF Receptor Family Members Can Upregulate Tumor Immunity.

Immunologic mechanisms influence how a cancer patient responds to therapy. Monoclonal antibodies (mAbs) to the epidermal growth factor receptor are clinically approved, and a lung cancer vaccine inducing antibodies to epidermal growth factor (EGF) has some beneficial clinical effects. We tested the hypothesis that mAbs to epidermal growth factor receptor, EGF, and tumor growth factor alpha (TGF-α), in addition to any other effects, can facilitate the generation of a tumor-destructive immunologic response. Data from studies with mouse tumors showed that all 3 of these mAbs stimulated the in vitro generation of a Th1 response with tumor cells killed by spleen cells from mice with SW1 melanoma, B16 melanoma, or ID8 ovarian carcinoma. The mAb to TGF-α was most effective, and tumor lines releasing TGF-α were more sensitive than lines not releasing TGF-α. Stimulated by these findings we then performed pilot experiments in which mice with SW1 melanoma were injected with mAbs intraperitoneally or with a combination of the 2. A combination of anti-TGF-α and anti-PD-1 mAbs could cure mice with established tumor while single anti-TGF-α or anti-PD1 mAbs could not.

From the Hellstrom paradox toward cancer cure.

Several decades ago we published some of the first papers showing that both murine and human cancers are recognized in vitro as immunologically foreign and that this is the case also in the presence of a growing tumor. The latter situation, sometimes referred to as the Hellstrom paradox, implies that the tumor is protected in vivo by a highly immunosuppressive environment. After many disappointments, the discovery that tumor-related immunosuppression can be counteracted by administrating monoclonal antibodies (mAbs) to checkpoint inhibitors such as CTLA-4, PD-1, and PD-L1 is now revolutionizing cancer therapy. Over the past several years we have applied mouse models in attempts to further improve the ability of such mAbs to cause long-term complete tumor rejection. This review is focused on that work and emphasizes that successful immunotherapy is associated with a shift from a tumor-promoting Th2 inflammation to a tumor-inhibiting Th1 response.

Ovarian carcinomas express HE4 epitopes independently of each other.

BACKGROUND: The gene encoding HE4 undergoes alternative splicing to yield multiple protein isoforms. We investigated anti-HE4 mAbs which recognize epitopes on the C (2H5 and 3D8) or N (12A2 and 14E2) terminals. METHODS: A Luminex assay was applied to determine mAb affinity. Binding of mAbs to sections from formaline fixed ovarian carcinomas was determined by immunohistology, binding to cultured ovarian carcinoma cells was tested by flow cytometry and immunocytochemistry, and HE4 secretion to patient serum or supernatants of cultured ovarian carcinoma was assayed by ELISA. RESULTS: mAb 12A2 bound to formalin-fixed sections from 18 of 19 ovarian carcinomas, while 14E2, 2H5 and 3D8 bound to sections from 14, 7 and 4 patients, respectively. The mAbs bound independently of each other, i.e. a sample bound one mAb most strongly while another sample with similar affinity strongest bound another mAb. The intensity of binding to sections did not significantly correlate with the serum level of HE4 except for mAb 14E2, but there was a significant correlation between HE4 expression and its detection in supernatants of cultured ovarian carcinomas. CONCLUSIONS: HE4 epitopes are expressed independently of each other and their expression of HE4 by cultured ovarian carcinoma cells correlates with the release of HE4 into culture supernatants. he epitope recognized by mAb 14E2 was significantly more expressed by platinum resistant tumors. IMPACT: Expression of HE4 by most ovarian carcinomas makes it an excellent biomarker.. Further studies are needed to investigate the clinical relevance of overexpression of a particular epitope.

Tumor Regression and Cure Depends on Sustained Th1 Responses.

While immunomodulatory monoclonal antibodies (mAbs) have therapeutic efficacy against many tumors, few patients are cured. Attempting to improve their therapeutic efficacy we have applied the TC1 mouse lung carcinoma model and injected established subcutaneous tumors intratumorally with 3 weekly doses of various combinations of mAbs. Combinations of mAbs to CTLA4/PD1/CD137 (the 3 mAb combination) and to CTLA4/PD1/CD137/CD19 (the 4 mAb combination) were most efficacious to induce complete regression of both the injected tumor and an untreated tumor in the same mouse. Tumor cure was consistently associated with shifting a Th2 to a Th1 response in tumor-draining lymph nodes and spleen and it involved epitope specific and long-lived memory T cells as well as M1 macrophages. This shift and accompanying tumor rejection was harder to achieve as the treated tumors increased in size. Relapse of tumors which had initially regressed following treatment with immunomodulatory mAbs was associated with return of a Th2 microenvironment in tumors, tumor-draining lymph nodes and spleens rather than the emergence of immune-resistant tumor cells. While mAbs to CTLA4 plus PD-1 were therapeutically ineffective, combining the 2 of them with intraperitoneal cisplatin, 10 mg/kg, induced long-term complete tumor regression in most mice with small TC1 tumors and the therapeutic efficacy against larger tumors improved by administrating cisplatin together with the 3 or 4 mAb combination.

Curing tumor-bearing mice by shifting a Th2 to a Th1 anti-tumor response.

Over the past several years remarkable therapeutic responses have been obtained with immunomodulatory monoclonal antibodies (mAbs), both in mice \cite{10,18,20,48,54,61} and human cancer patients \cite{1,3,14,28,30,39,80}. However, complete regressions and cures are infrequent and not predictable and some tumor types respond much worse than others. As an attempt to increase curability, we have investigated in mouse models the therapeutic efficacy of several mAb combinations, focusing on anti-PD-1/CTLA-4/CD137 and anti-PD-1/CTLA-4/CD137/CD19, and we have also combined mAbs with the chemotherapeutic drug cisplatin. Our data demonstrate an important contribution of anti-CD19 mAb to therapeutic efficacy, they show that intratumoral delivery of the mAbs is therapeutically more effective than systemic delivery, and that there is synergy when the mAbs are combined with cisplatin. In an attempt to improve predictability, we developed an in vitro model that may also be employed to search for novel immunomodulatory agents and combinations. This article reviews our data and discusses what is known about the underlying mechanisms.

Selenium-Binding Protein 1 (SBP1) autoantibodies in ovarian disorders and ovarian cancer.

Infertility is a risk factor for ovarian cancer (OvCa). The goal was to determine if antibodies to selenium-binding protein 1 (SBP1), an autoantibody we identified in patients with premature ovarian failure (POF), occurs in both infertility and OvCa patients, and thus could be associated with preneoplasia. Anti-SBP1 was measured by immunoassay against recombinant SBP1, in sera from OvCa (n = 41), infertility (n = 92) and control (n = 87) patients. Infertility causes were POF, unexplained, irregular ovulation or endometriosis. The percent of anti-SBP1-positive sera was higher in POF (P = 0.02), irregular ovulation (P = 0.001), unexplained causes (P = 0.02), late (III-IV)-stage OvCa (P = 0.02) but was not significant in endometriosis, benign ovarian tumors/cysts, early stage (I-II) OvCa or uterine cancer compared to healthy controls. Anti-SBP1 was significantly higher in women with serous (P = 0.04) but not non-serous (P = 0.33) OvCa compared to controls. Also, we determined if anti-SBP1 was associated with CA125 or anti-TP53, markers often studied in OvCa. Anti-TP53 and CA125 were measured by established immunoassays. The ability of anti-SBP1 alone to discriminate infertility or OvCa from controls or when combined with anti-TP53 and CA125, to identify OvCa was evaluated by comparing the area under the curve (AUC) in ROC analysis. Anti-SBP1 alone discriminated infertility (AUC = 0.7; P = 0.001) or OvCa (AUC = 0.67; P = 0.03) from controls. The sensitivity and specificity of OvCa identification was increased by combining CA125, anti-TP53 and anti-SBP1 (AUC = 0.96). Therefore, anti-SBP1 occurs in infertile women with POF, ovulatory disturbances or unexplained infertility and in serous OvCa. This suggests an autoimmune process is associated with the development of serous OvCa.

An In Vitro Model That Predicts the Therapeutic Efficacy of Immunomodulatory Antibodies.

Immunomodulatory monoclonal antibodies (mAbs) have efficacy in patients with advanced cancer and are the focus of intensive research. However, cures are infrequent and responses vary among tumor types and among subjects with the same tumor. An in vitro test would be valuable to determine the most effective mAb combination for a given case and to evaluate novel agents. Toward this goal, we investigated the ability of various mAb combinations to generate a tumor-destructive immune response in vitro in the presence of lymphoid cells from mice with established TC1 lung carcinoma, B16 melanoma, or SW1 melanoma. The data strongly correlate (r=0.9, 0.89, and 0.91, respectively) with the therapeutic efficacy of the respective mAb combinations. Both in vivo and in vitro, tumor destruction was associated with a shift from a Th2 to a Th1 response and included a dramatic increase of long-term memory cells. A combination of mAbs to CD137/PD-1/CTLA4/CD19 was most efficacious.

Immune Mechanisms Are Major Players in Cancer.

Vaccination with sipuleucel-T produced IgG antibodies to secondary prostatic carcinoma antigens and prolonged survival in some patients, and assaying for antibodies may provide prognostic information and identify new vaccine targets. Additional approaches to improve T-cell responses are needed to improve the clinical efficacy. See related article by GuhaThakurta et al., p. 3619.

Detection of the HE4 protein in urine as a biomarker for ovarian neoplasms: Clinical correlates.

OBJECTIVES: To measure HE4 levels in urine from normal donors, patients with LMP tumors and ovarian cancer patients and to correlate levels with clinical factors in ovarian cancer patients. METHODS: Archived samples from controls, patients with LMP tumors and ovarian cancer were tested using commercial assays, including serially collected serum and urine samples from women treated for stage III/IV serous ovarian cancer. RESULTS: Five of 6 patients with stage I/II and 26 of 36 stage III/IV serous ovarian cancer patients had HE4-positive urines, similar to serum samples (4 of 5 stage I/II and 26 of 34 stage III/IV) when tested at the same level of specificity (95%). Urine HE4 was more sensitive in LMP tumors: 9 of 32 urines (28%) HE4-positive versus 3 of 68 sera (4.4%, p=0.002). Mean levels of serum CA125 and HE4 decreased comparably in patients during initial treatment regardless of their primary platinum response, but mean urine HE4 levels decreased only 7% in primary platinum resistant patients while decreasing 68% in those who were sensitive. By 7months after diagnosis, urine HE4 levels were higher in primary platinum resistant patients compared to those who proved to be sensitive (p=0.051) and persisted 12months after diagnosis (p=0.014). HE4 values in urine also became positive in advance of clinical recurrence in several women while serum HE4 and serum CA-125 remained normal. CONCLUSIONS: Measuring HE4 in urine complements serum assays for the detection of ovarian cancer and may allow identification of patients at high risk for primary platinum resistance.

Curing mice with large tumors by locally delivering combinations of immunomodulatory antibodies.

PURPOSE: Immunomodulatory mAbs can treat cancer, but cures are rare except for small tumors. Our objective was to explore whether the therapeutic window increases by combining mAbs with different modes of action and injecting them into tumors. EXPERIMENTAL DESIGN: Combinations of mAbs to CD137/PD-1/CTLA-4 or CD137/PD-1/CTLA-4/CD19 were administrated intratumorally to mice with syngeneic tumors (B16 and SW1 melanoma, TC1 lung carcinoma), including tumors with a mean surface of approximately 80 mm(2). Survival and tumor growth were assessed. Immunologic responses were evaluated using flow cytometry and qRT-PCR. RESULTS: More than 50% of tumor-bearing mice had complete regression and long-term survival after tumor injection with mAbs recognizing CD137/PD-1/CTLA-4/CD19 with similar responses in three models. Intratumoral injection was more efficacious than intraperitoneal injection in causing rejection also of untreated tumors in the same mice. The three-mAb combination could also induce regression, but was less efficacious. There were few side effects, and therapy-resistant tumors were not observed. Transplanted tumor cells rapidly caused a Th2 response with increased CD19 cells. Successful therapy shifted this response to the Th1 phenotype with decreased CD19 cells and increased numbers of long-term memory CD8 effector cells and T cells making IFNγ and TNFα. CONCLUSIONS: Intratumoral injection of mAbs recognizing CD137/PD-1/CTLA-4/CD19 can eradicate established tumors and reverse a Th2 response with tumor-associated CD19 cells to Th1 immunity, whereas a combination lacking anti-CD19 is less effective. There are several human cancers for which a similar approach may provide clinical benefit.

Dual targeting of CD137 co-stimulatory and PD-1 co-inhibitory molecules for ovarian cancer immunotherapy.

We recently demonstrated that simultaneous targeting of CD137 co-stimulatory and programmed cell death 1 (PD-1) co-inhibitory molecules synergistically induced an anticancer immune response in the ID8 syngeneic orthotopic mouse ovarian carcinoma model. We further showed that the therapeutic efficacy was enhanced by treatment with cisplatin. These findings provide a rationale for evaluating dual targeting of CD137/PD-1 co-signaling molecules in ovarian cancer patients.

Human and mouse CD137 have predominantly different binding CRDs to their respective ligands.

Monoclonal antibodies (mAbs) to CD137 (a.k.a. 4-1BB) have anti-tumor efficacy in several animal models and have entered clinical trials in patients with advanced cancer. Importantly, anti-CD137 mAbs can also ameliorate autoimmunity in preclinical models. As an approach to better understand the action of agonistic and antagonistic anti-CD137 mAbs we have mapped the binding region of the CD137 ligand (CD137L) to human and mouse CD137. By investigating the binding of CD137L to cysteine rich domain II (CRDII )and CRDIII of CD137, we found that the binding interface was limited and differed between the two species in that mouse CD137L mainly combined with CRDII and human CD137L mainly combined with CRDIII.

Combinatorial PD-1 blockade and CD137 activation has therapeutic efficacy in murine cancer models and synergizes with cisplatin.

There is an urgent need for improved therapy for advanced ovarian carcinoma, which may be met by administering immune-modulatory monoclonal antibodies (mAbs) to generate a tumor-destructive immune response. Using the ID8 mouse ovarian cancer model, we investigated the therapeutic efficacy of various mAb combinations in mice with intraperitoneal (i.p.) tumor established by transplanting 3 × 10(6) ID8 cells 10 days previously. While most of the tested mAbs were ineffective when given individually or together, the data confirm our previous finding that 2 i.p. injections of a combination of anti-CD137 with anti-PD-1 mAbs doubles overall survival. Mice treated with this mAb combination have a significantly increased frequency and total number of CD8(+) T cells both in the peritoneal lavage and spleens, and these cells are functional as demonstrated by antigen-specific cytolytic activity and IFN-γ production. While administration of anti-CD137 mAb as a single agent similarly increases CD8(+) T cells, these have no functional activity, which may be attributed to up-regulation of co-inhibitory PD-1 and TIM-3 molecules induced by CD137. Addition of the anti-cancer drug cisplatin to the 2 mAb combination increased overall survival >90 days (and was probably curative) by a mechanism which included a systemic CD8(+) T cell response with tumor specificity and immunological memory. Strikingly, combined treatment of cisplatin and CD137/PD-1 mAb also gave rise to the long-term survival of mice with established TC1 lung tumors. A similar combination of the 2 mAbs and cisplatin should be considered for clinical 'translation'.

Anti-HE4 antibodies in infertile women and women with ovarian cancer.

OBJECTIVES: To develop an assay for anti-HE4 antibodies and assess such antibodies in sera from women with increased epidemiologic risk for ovarian cancer (infertility) and patients with ovarian cancer in comparison to controls. METHODS: An ELISA was developed to measure antibodies to recombinant full length HE4 and cut-off values were determined for different levels of specificity (up to 99%). RESULTS: Infertile women more frequently had anti-HE4 antibodies than controls (23% at 98% specificity, p < 0.001) with antibodies most frequent in women with POF (31%) and ovulatory dysfunction (47%). There was also an increased frequency of anti-HE4 antibodies in patients with ovarian cancer (14% at 97% specificity, p < 0.01), but more women with certain types of infertility have anti-HE4 antibodies than women with ovarian cancer. Most patients with ovarian cancer have circulating HE4 antigen, which may interfere with detection of antibodies, while the level of HE4 antigen in sera from infertile women was not higher than in normal controls. There was a statistically significant correlation between antibodies to HE4 and antibodies to mesothelin in the same patients. CONCLUSIONS: Women with certain types of infertility, which have increased risk to develop ovarian cancer, and women with ovarian cancer more frequently than controls have antibodies to HE4, a biomarker for ovarian cancer. The antibodies may reflect a tumor-promoting Th2 type of inflammation.

Long-lasting complete regression of established mouse tumors by counteracting Th2 inflammation.

Mice with intraperitoneal ID8 ovarian carcinoma or subcutaneous SW1 melanoma were injected with monoclonal antibodies (mAbs) to CD137PD-1CTLA4 7-15 days after tumor initiation. Survival of mice with ID8 tumors tripled and >40% of mice with SW1 tumors remained healthy >150 days after last treatment and are probably cured. Therapeutic efficacy was associated with a systemic immune response with memory and antigen specificity, required CD4 cells and involved CD8 cells and NK cells to a less extent. The 3 mAb combination significantly decreased CD19 cells at tumor sites, increased IFN-γ and TNF-α producing CD4 and CD8 T cells and mature CD86 dendritic cells (DC), and it increased the ratios of effector CD4 and CD8 T cells to CD4Foxp3 regulatory T (Treg) cells and to CD11bGr-1 myeloid suppressor cells (MDSC). This is consistent with shifting the tumor microenvironment from an immunosuppressive Th2 to an immunostimulatory Th1 type and is further supported by PCR data. Adding an anti-CD19 mAb to the 3 mAb combination in the SW1 model further increased therapeutic efficacy. Data from ongoing experiments show that intratumoral injection of a combination of mAbs to CD137PD-1CTLA4CD19 can induce complete regression and dramatically prolong survival also in the TC1 carcinoma and B16 melanoma models, suggesting that the approach has general validity.

Th2 type inflammation promotes the gradual progression of HPV-infected cervical cells to cervical carcinoma.

OBJECTIVES: To investigate the role of immunological parameters in tumorigenesis of cervical cancer in women infected with high risk human papillomavirus (hr-HPV), and determine whether key findings with human material can be recapitulated in the mouse TC1 carcinoma model which expresses hr-HPV epitopes. METHODS: Epithelial and lymphoid cells in cervical tissues were analyzed by immunohistochemistry and serum IL10 levels were determined by ELISA. Tumor draining lymph nodes were analyzed in the mouse TC1 model by flow cytometry. RESULTS: The mucosa was infiltrated by CD20+ and CD138+ cells already at cervical intraepithelial neoplasia 1 (CIN1) and infiltration increased in cervical intraepithelial neoplasia 3 (CIN3)/carcinoma in situ (CIS) and invasive cervical cancer (ICC), where it strongly correlated with infiltration by CD32B+ and FoxP3+ lymphocytes. GATA3+ and T-bet+ lymphoid cells were increased in ICC compared to normal, and expression in epithelial cells of the Th2 inflammation-promoting cytokine TSLP and of IDO1 was higher in CIN3/CIS and ICC. As a corollary, serum levels of IL10 were higher in women with CIN3/CIS or ICC than in normals. Finally we demonstrated in the mouse TC1 carcinoma, which expresses hr-HPV epitopes, an increase of cells expressing B cell or plasma cell markers or Fc receptors in tumor-draining than distal lymph nodes or spleen. CONCLUSIONS: hr-HPV initiates a local Th2 inflammation at an early stage, involving antibody forming cells, and fosters an immunosuppressive microenvironment that aids tumor progression.

Silencing of the TGF-ß1 gene increases the immunogenicity of cells from human ovarian carcinoma.

Cells from many tumors produce transforming growth factor (TGF)-ß which facilitates their escape from control by the immune system. We previously reported that nonimmunogenic cells from either of 2 transplantable mouse tumors became effective as therapeutic tumor vaccines after lentivirus-mediated shRNA interference to "silence" the TGF-ß1 gene. We now show that cells from in vitro cultured human ovarian carcinomas (OvC) make large amounts of TGF-ß1 and that this can be prevented by "silencing" the TGF-ß1 gene. We further show that in vitro sensitization of peripheral blood mononuclear cells in the presence of either mitomycin-treated OvC cells whose TGF-ß1 gene was silenced or in vitro matured dendritic cells that had been pulsed with homogenates from OvC cells with silenced TGF-ß1 generated a stronger Th1/Tc1 immune response to the respective wild-type OvC and also to the OvC antigens mesothelin and HE4 as measured by ELIspot assays. The percentage of interferon-γ and tumor necrosis factor-α-producing CD4+ and CD8+ T cells increased while there were fewer cells expressing markers characteristic for regulatory T cells or myeloid-derived suppressor cells. Similar results were obtained when peripheral blood mononuclear cells from a patient with OvC were sensitized to dendritic cells pulsed with homogenate from autologous TGF-ß1-silenced tumor cells, and a cytolytic lymphocyte response was generated to autologous OvC cells. Our results support clinical evaluation of TGF-ß1-silenced tumor vaccines for immunotherapy of OvC.

Elafin selectively regulates the sensitivity of ovarian cancer cells to genotoxic drug-induced apoptosis.

OBJECTIVE: Elafin has been reported to be abundantly expressed in human epithelial ovarian carcinoma (EOC), however, its functions are poorly understood. Here, we evaluated the role of elafin in modulating the sensitivity of human EOC cells to chemotherapeutic drugs. METHODS: Elafin expression was determined by ELISA in 9 established human EOC cell lines. A lentivirus encoding elafin-specific shRNA was used to down-regulate elafin expression in OVCAR3 and OV433 cells, and a plasmid encoding elafin was used to ectopically express elafin in elafin-negative SKOV3 cells. Sensitivity to cisplatin and other genotoxic agents and to paclitaxel, an inhibitor of microtubule depolymerization, was examined in OVCAR3, OV433 and SKOV3 sublines. Cell viability was determined by the MTT assay, apoptosis by annexin V/7-AAD staining and caspase activation by fluorimetric assay. RESULTS: Knockdown of the elafin gene decreases cisplatin IC50 by at least 2-folds in OVCAR3 and OVCAR433 cells (p<0.01) but does not affect paclitaxel IC50. The sensitivity to other genotoxic agents such as carboplatin, cyclophosphamide and 5-fluorouracil was also increased by silencing the expression of elafin. Apoptosis and caspase-3 activation were significantly augmented in cisplatin-treated OVCAR3 cells with silenced elafin. Overexpression of elafin in SKOV3 cells made them more resistant to cisplatin and decreased cisplatin-induced apoptosis and caspase activation (p<0.01). CONCLUSIONS: Expression of elafin decreases the sensitivity of human EOC cells to several genotoxic agents, which may have an important implication in predicting the response of patients with EOC to chemotherapy in the clinic.

Evaluation of ovarian cancer remission markers HE4, MMP7 and Mesothelin by comparison to the established marker CA125.

OBJECTIVE: Evaluate and compare the effectiveness of CA125, HE4, Mesothelin and MMP7 marker levels to monitor ovarian cancer patients after surgery and chemotherapy. Evaluate the lead time of a rise of marker levels before recurrence. METHODS: The study consists of 23 patients with advanced stage ovarian/fallopian tube cancer. Blood was drawn after front line surgery and chemotherapy treatment and at 3 month intervals thereafter. One patient had chemoresistant disease, two patients remained in remission and 20 patients had recurring disease and were used for marker evaluation. RESULTS: In five patients HE4 was the only marker to elevate before recurrence with a lead time of up to 4½ months including one patient who did not have a CA125 response at all. In a further two patients, HE4 increased before CA125 did. In four of these seven patients, HE4 levels were consistently at or above threshold during remission when both CA125 and imaging results were negative. MMP7 elevated before recurrence in one patient who was negative for the other markers. Mesothelin elevated in two patients who were also positive for CA125 and HE4. CONCLUSIONS: HE4 can predict ovarian cancer recurrence earlier than CA125 and it can be elevated in patients that do not express CA125 at sufficient levels to make a clinical decision. MMP7 and Mesothelin have lower potential as markers for ovarian cancer recurrence to complement CA125. A failure of HE4 levels to normalize at completion of standard therapy may indicate a poor prognosis.

Autoantibodies to mesothelin in infertility.

BACKGROUND: According to extensive epidemiologic data, infertility is associated with increased ovarian cancer risk. Previous studies showed that both women with infertility and those with ovarian cancer have autoantibodies to ovarian antigens. The objective was to determine if women with infertility have antibodies to mesothelin, a well-characterized ovarian cancer antigen. METHODS: Sera were obtained from women with infertility (n = 109), ovarian cancer (n = 28), benign ovarian tumors or cysts (n = 24), and from healthy women (n = 152). Infertility included those with a risk for ovarian cancer; endometriosis (n = 23), ovulatory dysfunction (n = 17), premature ovarian failure (POF; n = 25) and unexplained infertility (n = 44). Sera were assayed for mesothelin antibodies and for circulating mesothelin antigen by immunoassay and compared with assay control sera (n = 16) to determine a positive result. RESULTS: Mesothelin antibodies were significantly more frequent in women with prematurely reduced ovarian function including ovulatory dysfunction (59%), ovarian failure (44%) and unexplained infertility (25%) compared with controls. In contrast, women with endometriosis, who also have a high risk for ovarian cancer, did not have mesothelin antibodies. Serum levels of mesothelin were rarely elevated in women with infertility but were high in most patients with ovarian cancer. CONCLUSIONS AND IMPACT: We show for the first time that antibodies to mesothelin, a well-characterized ovarian cancer antigen, occur in some women with epidemiologic risk for ovarian cancer. The results suggest it may be possible to identify which women with infertility have ovarian cancer risk.