ImmunoPET Imaging of Insulin-Like Growth Factor 1 Receptor in a Subcutaneous Mouse Model of Pancreatic Cancer.

The role of insulin-like growth factor-1 receptor (IGF-1R) in cancer tumorigenesis was established decades ago, yet there are limited studies evaluating the imaging and therapeutic properties of anti-IGF-1R antibodies. Noninvasive imaging of IGF-1R may allow for optimized patient stratification and monitoring of therapeutic response in patients. Herein, this study reports the development of a Zirconium-89 ((89)Zr)-labeled anti-IGF-1R antibody ((89)Zr-Df-1A2G11) for PET imaging of pancreatic cancer. Successful chelation and radiolabeling of the antibody resulted in a highly stable construct that could be used for imaging IGF-1R expressing tumors in vivo. Western blot and flow cytometry studies showed that MIA PaCa-2, BxPC-3, and AsPC-1 pancreatic cancer cell lines expressed high, moderate, and low levels of IGF-1R, respectively. These three pancreatic cancer cell lines were subcutaneously implanted into mice. By employing the PET imaging technique, the tumor accumulation of (89)Zr-Df-1A2G11 was found to be dependent on the level of IGF-1R expression. Tumor accumulation of (89)Zr-Df-1A2G11 was 8.24 ± 0.51, 5.80 ± 0.54, and 4.30 ± 0.42 percentage of the injected dose (%ID/g) in MIA PaCa-2, BxPC-3, and AsPC-1-derived tumor models at 120 h postinjection, respectively (n = 4). Biodistribution studies and ex vivo immunohistochemistry confirmed these findings. In addition, (89)Zr-labeled nonspecific human IgG ((89)Zr-Df-IgG) displayed minimal uptake in IGF-1R positive MIA PaCa-2 tumor xenografts (3.63 ± 0.95%ID/g at 120 h postinjection; n = 4), demonstrating that (89)Zr-Df-1A2G11 accumulation was highly specific. This study provides initial evidence that our (89)Zr-labeled IGF-1R-targeted antibody may be employed for imaging a wide range of malignancies. Antibodies may be tracked in vivo for several days to weeks with (89)Zr, which may enhance image contrast due to decreased background signal. In addition, the principles outlined in this study can be employed for identifying patients that may benefit from anti-IGF-1R therapy.

Acute phase cytotoxic T lymphocyte escape is a hallmark of simian immunodeficiency virus infection.

Cytotoxic T-lymphocyte (CTL) responses peak coincident with the decline in acute HIV viremia. Despite two reports of CTL-resistant HIV variants emerging during acute infection, the contribution of acute CTL escape to HIV pathogenesis remains unclear. Difficulties inherent in studying acute HIV infection can be overcome by modeling virus-host interactions in SIV-infected rhesus macaques. We sequenced 21 complete simian immunodeficiency virus (SIV)mac239 genomes at four weeks post-infection to determine the extent of acute CTL escape. Here we show that viruses from 19 of 21 macaques escaped from CTLs during acute infection and that these escape-selecting CTLs were responsive to lower concentrations of peptide than other SIV-specific CTLs. Interestingly, CTLs that require low peptide concentrations for stimulation (high 'functional avidity') are particularly effective at controlling other viral infections. Our results suggest that acute viral escape from CTLs is a hallmark of SIV infection and that CTLs with high functional avidity can rapidly select for escape variants.

Humoral immune responses to testis antigens in sera from patients with prostate cancer.

Tumor vaccines represent one type of molecularly targeted therapy being investigated for the treatment of prostate cancer. Although many prostate-specific proteins are being tested as target antigens for prostate cancer vaccines, most are not natural targets of an immune response in patients with cancer. Using sera from cancer patients, several research groups have identified a large family of immunologically recognized proteins whose expression is normally confined to immune-privileged testis tissue but which may be expressed in cancers of different histological origins. These proteins, so-called cancer-testis (CT) antigens, are appealing targets for immune-based therapies because they are essentially tumor-restricted antigens and there is less risk of preexisting immune tolerance. In addition, specifically targeting these proteins by means of vaccines should reduce the risk of potential autoimmune reactions to normal tissues. In the current study, we hypothesize that prostate CT antigens can be identified using a SEREX screening method with sera from patients with prostate cancer and probing with a human testis cDNA expression library. We have identified several potential prostate cancer antigens with predominantly testis-specific expression in normal tissues, including MAD-CT-1 (protamine 2) and MAD-CT-2. Each was independently identified from different subjects with prostate cancer. Antigens identified by these studies can be investigated further as potential prostate cancer tumor antigens.

DNA vaccine encoding prostatic acid phosphatase (PAP) elicits long-term T-cell responses in patients with recurrent prostate cancer.

Prostatic acid phosphatase (PAP) is a tumor antigen in prostate cancer and the target of several anti-tumor vaccines in earlier clinical trials. Ultimately, the goal of anti-tumor vaccines is to elicit a sustainable immune response, able to eradicate a tumor, or at least restrain its growth. We have investigated plasmid DNA vaccines and have previously conducted a phase 1 trial in which patients with recurrent prostate cancer were vaccinated with a DNA vaccine encoding PAP. In this study, we investigated the immunologic efficacy of subsequent booster immunizations, and conducted more detailed longitudinal immune analysis, to answer several questions aimed at guiding optimal schedules of vaccine administration for future clinical trials. We report that antigen-specific cytolytic T-cell responses were amplified after immunization in 7 of 12 human leukocyte antigen-A2-expressing individuals, and that multiple immunizations seemed necessary to elicit PAP-specific interferon-gamma-secreting immune responses detectable by enzyme-linked immunosorbent spot assay. Moreover, among individuals who experienced a >/=200% increase in prostate-specific antigen doubling time, long-term PAP-specific interferon-gamma-secreting T-cell responses were detectable in 6 of 8, but in only 1 of 14 individuals without an observed change in prostate-specific antigen doubling time (P=0.001). Finally, we identified that immune responses elicited could be further amplified by subsequent booster immunizations. These results suggest that future trials using this DNA vaccine, and potentially other anti-tumor DNA vaccines, could investigate ongoing schedules of administration with periodic booster immunizations. Moreover, these results suggest that DNA vaccines targeting PAP could potentially be combined in heterologous immunization strategies with other vaccines to further augment PAP-specific T-cell immunity.

Safety and immunological efficacy of a DNA vaccine encoding prostatic acid phosphatase in patients with stage D0 prostate cancer.

PURPOSE: Prostatic acid phosphatase (PAP) is a prostate tumor antigen. We have previously demonstrated that a DNA vaccine encoding PAP can elicit antigen-specific CD8+ T cells in rodents. We report here the results of a phase I/IIa trial conducted with a DNA vaccine encoding human PAP in patients with stage D0 prostate cancer. PATIENTS AND METHODS: Twenty-two patients were treated in a dose-escalation trial with 100 microg, 500 microg, or 1,500 microg plasmid DNA, coadministered intradermally with 200 microg granulocyte-macrophage colony-stimulating factor as a vaccine adjuvant, six times at 14-day intervals. All patients were observed for 1 year after treatment. RESULTS: No significant adverse events were observed. Three (14%) of 22 patients developed PAP-specific IFN gamma-secreting CD8+ T-cells immediately after the treatment course, as determined by enzyme-linked immunospot. Nine (41%) of 22 patients developed PAP-specific CD4+ and/or CD8+ T-cell proliferation. Antibody responses to PAP were not detected. Overall, the prostate-specific antigen (PSA) doubling time was observed to increase from a median 6.5 months pretreatment to 8.5 months on-treatment (P = .033), and 9.3 months in the 1-year post-treatment period (P = .054). CONCLUSION: The demonstration that a DNA vaccine encoding PAP is safe, elicits an antigen-specific T-cell response, and may be associated with an increased PSA doubling time suggests that a multi-institutional phase II trial designed to evaluate clinical efficacy is warranted.

Identification of autoantibodies elicited in a patient with prostate cancer presenting as dermatomyositis.

OBJECTIVES: Dermatomyositis is an uncommon autoimmune disease distinguished by proximal muscle weakness and a characteristic skin rash. Dermatomyositis has also frequently been associated with malignancy, typically heralding the diagnosis of ovarian, lung, gastric, or colorectal cancer. We report an unusual case of prostate adenocarcinoma preceded by a diagnosis of dermatomyositis. We hypothesized that in this particular patient, proteins produced by the neoplastic prostatic tissue, which might be normally expressed in muscle tissue, were immunologically recognized as autoantigens. METHODS: Serum from this patient was used to screen a cDNA lambda phage expression library from normal prostate tissue for prostate protein-specific IgG. RESULTS: We identified several immunoreactive plaques encoding known autoantigens, and several encoding known muscle-related proteins, including aldolase C, eukaryotic translation elongation factor 1 alpha 1, transgelin, and acetyl-coenzyme A acyltransferase 1. IgG specific for these proteins were not specifically recognized in sera from other patients with prostate cancer compared with male control blood donors, and were not specifically recognized in a small panel of sera from patients with breast or ovarian cancer and dermatomyositis. CONCLUSIONS: Our results demonstrate that this patient with prostate cancer presenting as dermatomyositis had autoantibodies to specific proteins, possibly associated with his autoimmune myopathy. Moreover, given this patient's history and the multiple treatment options for prostate cancer, the identification of dermatomyositis in men should prompt an evaluation to exclude a concurrent diagnosis of prostate cancer.

Antigen-specific IgG elicited in subjects with prostate cancer treated with flt3 ligand.

Identifying appropriate prostate cancer-associated antigens is critical to the development of immunologic treatments for prostate cancer. Flt3 ligand, a growth and differentiation factor for dendritic cells, has shown modest clinical activity in prostate cancer, presumably by eliciting anti-cancer immune responses. The authors previously reported the results of a clinical trial in which some patients with metastatic prostate cancer treated with flt3 ligand developed autoimmune hypothyroidism with thyroid-specific antibodies. Given these findings, the authors hypothesized that anti-prostate immune responses might also have been elicited in some subjects treated with flt3 ligand. The authors now report the identification of prostate-associated proteins immunologically recognized in 13 prostate cancer patients treated with multiple cycles of flt3 ligand. Using a normal prostate cDNA expression library, and sera from subjects before and after treatment with flt3 ligand, a modified SEREX approach was used to identify six proteins to which IgG immune responses were augmented after flt3 ligand treatment compared with pretreatment. IgG responses to one protein, MAD-CaP-5, were not detectable in any of the subjects' sera before treatment but were elicited after therapy in one subject. The authors suggest that MAD-CaP-5 could be explored as a novel prostate cancer antigen, and that this approach can be used to identify immunologically recognized proteins following any specific intervention.

Identification of antigen-specific IgG in sera from patients with chronic prostatitis.

Antigen-specific vaccines are one of several molecularly targeted approaches under investigation as possible treatments for prostate cancer. Important to the development of vaccines is the identification of appropriate target antigens. We hypothesized that antigens of the prostate might be identified in patients with the chronic prostatitis/pelvic pain syndrome, a syndrome for which an autoimmune pathology has been proposed. Such antigens might represent naturally recognized target antigens of the prostate that could be investigated in the future as prostate tumor antigens. In this report, we used SEREX to identify proteins expressed in a prostate cDNA expression library recognized by IgG from the sera of patients with chronic prostatitis. Candidate proteins were evaluated using a panel of sera from 62 subjects with symptomatic prostatitis and 71 control male blood donors. We identified one protein that was recognized primarily in sera from subjects with prostatitis compared with controls. MAD-PRO-34, a nucleolar autoantigen, was recognized in 6/62 subjects and 0/71 controls (p = 0.00897). This protein had previously been identified as an autoantigen in patients with prostate cancer. In addition, the NY-CO-7 protein was recognized in 9/62 subjects and 3/71 controls (p = 0.0654). Two subjects had IgG specific for both the MAD-PRO-34 and NY-CO-7 gene products. Our results demonstrate that some patients with the chronic prostatitis/pelvic pain syndrome have autoantibodies to specific proteins. Proteins identified, and MAD-PRO-34 in particular, could be further investigated as potential prostate tumor antigens.