Identification of HLA-DRB1*1501-restricted T-cell epitopes from human prostatic acid phosphatase

Experimental autoimmune prostatitis: different antigens induction and antigen-specific therapy

PURPOSE

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) has uncertain etiology and lacks effective treatment. Autoimmunity is an important pathogeny, and experimental autoimmune prostatitis (EAP) models have long been used for studying CP/CPPS. This review presents the detailed current knowledge of EAP models based on evaluation criteria aspects to provide a tool for model selection in pathogenesis studies and therapeutic drug screening.

METHODS

We extensively searched the published literature on CP/CPPS and different antigen-induced EAP models focusing on the histopathology, clinical-related phenotypes, and biochemical indicators. We also cover the changes in the prostate function and other organs in EAP. Finally, we try to get some insights about antigen-based therapeutic approaches for CP/CPPS.

RESULTS

Several inciting autoantigens were reported in EAP, including male accessory gland extracts, prostate extracts (PE), prostatic steroid-binding protein, prostatic spermine-binding protein (p25), prostatic acid phosphatase, seminal vesicle secretory protein 2, and T2 peptide. All of these models mimicked histological prostatitis, however only p25- and T2-induced models developed both pelvic pain and voiding behaviors. PE immunization is the most widely used method. Diminished fertility and mental health disorders can be found in PE model. Oral and intravenous T2 peptide have been studied for antigen-specific therapy and achieved preliminary progress in EAP models.

CONCLUSIONS

PE-induced model is the most commonly used, while T2- or p25-model could serve as a promising CP/CPPS model. Antigen-specific therapy in CP/CPPS deserves further study.

Identification and preliminary study of immunogens involved in autoimmune prostatitis in human males

BACKGROUND

Experimental models have confirmed that autoimmunity is an important factor in the onset of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS); however, there is no conclusive evidence on whether autoimmune prostatitis exists in human males.

METHODS

Rabbits were immunized with either human prostate tissue homogenates or normal saline and the antiserum was collected. Two-dimensional electrophoresis (2-DE) was performed on the homogenates and Western blotting was conducted on the sera. The identified human prostate tissue immunodominant antigens (HPTIAs) were detected by mass spectrometry. The serum immunoglobulin (Ig)G from the immunized rabbits was purified with protein A-agarose, and the purified IgG was linked with Sepharose to purify HPTIAs by affinity chromatography. Non-obese diabetic (NOD) mice were immunized with the purified HPTIAs, and the levels of serum antibodies, INF-γ, and histopathological changes in their prostate tissues were detected. The purified HPTIAs were coated into polystyrene pores and serum autoantibodies in CP/CPPS patients were detected by enzyme-linked immunosorbent assay (ELISA). Meanwhile, serum interleukin 2 (IL-2), interferon gamma (IFNγ), and tumor necrosis factor alpha (TNFα) levels in CP/CPPS patients were also determined by ELISA.

RESULTS

Sixteen HPTIAs were identified. Among them, three types were reported to be associated with prostatic diseases. Prostatitis was induced in mice immunized with the 16-HPTIA complex, with positive serum autoantibody and increased prostatic IFN-γ levels. The positive rate of serum autoantibodies against HPTIAs was significantly higher in CP/CPPS patients (23.1%, 18/78) than in the control (2.7%, 2/75). But there was no significant difference in serum TNFα, IFNγ, and IL-2 levels between the CPPS patients with positive and negative autoantibodies against HPTIAs.

CONCLUSIONS

Autoantibodies against HPTIAs exist in part in CP/CPPS patients, which implies that autoimmunity and the 16 HPTIAs are important factors in the onset of CP/CPPS. The detection of serum autoantibodies could be applied in clinical diagnoses of autoimmune prostatitis; treatment protocols might change. Additional studies are needed to determine which of the 16 HPTIAs is the most important.

Prostate Cancer Immunotherapy: Exploiting the HLA Class II Pathway in Vaccine Design

Prostate cancer is the second most diagnosed cancer in men and current treatment of advanced prostate cancer is ineffective. Immunotherapy has emerged as a promising treatment option for metastatic prostate cancer but its clinical application is still in the early stages of development. In order to treat metastatic prostate tumors, new directions must be taken to improve current immunotherapeutic strategies. These include the identification of effective tumor antigens (Ags), the induction of the HLA class II pathway for Ag processing and CD4⁺ T cell activation, and the ability of tumor cells to act like Ag presenting cells. In this review, we suggest a model for tumor Ag selection, epitope modification and self-processing for presentation by class II proteins as a means of restoring immune activation and tumor clearance. We also outline the importance of a Gamma-IFN-inducible Lysosomal Thiol reductase (GILT) in Ag and modified peptide processing by tumor cells, generation of functional epitopes for T cell recognition, and inclusion of immune checkpoint blockers in cancer immunotherapy. Taken together, this review provides a framework for the future development of novel cancer vaccines and the improvement of existing immunotherapeutics in prostate cancer.

Histopathological classification criteria of rat model of chronic prostatitis/chronic pelvic pain syndrome

OBJECTIVE

A variety of murine models of experimental prostatitis that mimic the phenotype of human chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) have been developed. However, there is still a lack of explicit diagnosis criteria about those animal model. Our study is to establish histopathological classification criteria, which will be conducive to evaluate the animal models.

METHODS

We firstly established a rat model of experimental autoimmune prostatitis that is considered a valid model for CP/CPPS. For modelling, male Sprague-Dawley rats were immunized with autologous prostate tissue homogenate supernatant emulsified with complete Freund's adjuvant by subcutaneous injection into abdominal flank and simultaneously immunized with pertussis-diphtheria-tetanus vaccine by intraperitoneal injection. Three immunizations were administered semimonthly. At the 45th day, animals were killed, and prostate tissues were examined for morphology.

RESULTS

Histologically, the prostate tissues were characterized by lymphoproliferation, atrophy of acini, and chronic inflammatory cells infiltration in the stromal connective tissue around the acini or ducts. Finally, we built histopathological classification criteria incorporating inflammation locations (mesenchyme, glands, periglandular tissues), ranges (focal, multifocal, diffuse), and grades (grade I-IV). To verify the effectiveness and practicability of the histopathological classification criteria, we conducted the treatment study with one of the alpha blockers, tamsulosin.

CONCLUSION

The histopathological classification criteria of rat model of CP/CPPS will serve for further research of the pathogenesis and treatment strategies of the disease.

Structure-guided deimmunization of therapeutic proteins

Therapeutic proteins continue to yield revolutionary new treatments for a growing spectrum of human disease, but the development of these powerful drugs requires solving a unique set of challenges. For instance, it is increasingly apparent that mitigating potential anti-therapeutic immune responses, driven by molecular recognition of a therapeutic protein's peptide fragments, may be best accomplished early in the drug development process. One may eliminate immunogenic peptide fragments by mutating the cognate amino acid sequences, but deimmunizing mutations are constrained by the need for a folded, stable, and functional protein structure. These two concerns may be competing, as the mutations that are best at reducing immunogenicity often involve amino acids that are substantially different physicochemically. We develop a novel approach, called EpiSweep, that simultaneously optimizes both concerns. Our algorithm identifies sets of mutations making such Pareto optimal trade-offs between structure and immunogenicity, embodied by a molecular mechanics energy function and a T-cell epitope predictor, respectively. EpiSweep integrates structure-based protein design, sequence-based protein deimmunization, and algorithms for finding the Pareto frontier of a design space. While structure-based protein design is NP-hard, we employ integer programming techniques that are efficient in practice. Furthermore, EpiSweep only invokes the optimizer once per identified Pareto optimal design. We show that EpiSweep designs of regions of the therapeutics erythropoietin and staphylokinase are predicted to outperform previous experimental efforts. We also demonstrate EpiSweep's capacity for deimmunization of the entire proteins, case analyses involving dozens of predicted epitopes, and tens of thousands of unique side-chain interactions. Ultimately, Epi-Sweep is a powerful protein design tool that guides the protein engineer toward the most promising immunotolerant biotherapeutic candidates.

Serum Antibody Repertoire Profiling Using In Silico Antigen Screen

Serum antibodies are valuable source of information on the health state of an organism. The profiles of serum antibody reactivity can be generated by using a high throughput sequencing of peptide-coding DNA from combinatorial random peptide phage display libraries selected for binding to serum antibodies. Here we demonstrate that the targets of immune response, which are recognized by serum antibodies directed against sequential epitopes, can be identified using the serum antibody repertoire profiles generated by high throughput sequencing. We developed an algorithm to filter the results of the protein database BLAST search for selected peptides to distinguish real antigens recognized by serum antibodies from irrelevant proteins retrieved randomly. When we used this algorithm to analyze serum antibodies from mice immunized with human protein, we were able to identify the protein used for immunizations among the top candidate antigens. When we analyzed human serum sample from the metastatic melanoma patient, the recombinant protein, corresponding to the top candidate from the list generated using the algorithm, was recognized by antibodies from metastatic melanoma serum on the western blot, thus confirming that the method can identify autoantigens recognized by serum antibodies. We demonstrated also that our unbiased method of looking at the repertoire of serum antibodies reveals quantitative information on the epitope composition of the targets of immune response. A method for deciphering information contained in the serum antibody repertoire profiles may help to identify autoantibodies that can be used for diagnosing and monitoring autoimmune diseases or malignancies.

Structure-based redesign of proteins for minimal T-cell epitope content

The protein universe displays a wealth of therapeutically relevant activities, but T-cell driven immune responses to non-"self" biological agents present a major impediment to harnessing the full diversity of these molecular functions. Mutagenic T-cell epitope deletion seeks to mitigate the immune response, but can typically address only a small number of epitopes. Here, we pursue a "bottom-up" approach that redesigns an entire protein to remain native-like but contain few if any immunogenic epitopes. We do so by extending the Rosetta flexible-backbone protein design software with an epitope scoring mechanism and appropriate constraints. The method is benchmarked with a diverse panel of proteins and applied to three targets of therapeutic interest. We show that the deimmunized designs indeed have minimal predicted epitope content and are native-like in terms of various quality measures, and moreover that they display levels of native sequence recovery comparable to those of non-deimmunized designs.

Design and analysis of immune-evading enzymes for ADEPT therapy

The unparalleled specificity and activity of therapeutic proteins has reshaped many aspects of modern clinical practice, and aggressive development of new protein drugs promises a continued revolution in disease therapy. As a result of their biological origins, however, therapeutic proteins present unique design challenges for the biomolecular engineer. For example, protein drugs are subject to immune surveillance within the patient's body; this anti-drug immune response can compromise therapeutic efficacy and even threaten patient safety. Thus, there is a growing demand for broadly applicable protein deimmunization strategies. We have recently developed optimization algorithms that integrate computational prediction of T-cell epitopes and bioinformatics-based assessment of the structural and functional consequences of epitope-deleting mutations. Here, we describe the first experimental validation of our deimmunization algorithms using Enterobacter cloacae P99 β-lactamase, a component of antibody-directed enzyme prodrug cancer therapies. Compared with wild-type or a previously deimmunized variant, our computationally optimized sequences exhibited significantly less in vitro binding to human type II major histocompatibility complex immune molecules. At the same time, our globally optimal design exhibited wild-type catalytic proficiency. We conclude that our deimmunization algorithms guide the protein engineer towards promising immunoevasive candidates and thereby have the potential to streamline biotherapeutic development.

Identification of prostatic acid phosphatase (PAP) specific HLA-DR1-restricted T-cell epitopes

BACKGROUND

Prostatic acid phosphatase (PAP) is a prostate cancer tumor antigen and is an immunological target in several active immunotherapy clinical trials for the treatment of prostate cancer. We and others have demonstrated that PAP-specific T-cell responses can be elicited and augmented following antigen-specific immunization in both humans and animal models. We have previously reported that prostate cancer patients immunized with a DNA vaccine encoding PAP (pTVG-HP) developed both CD4+ and CD8+ T-cell responses. PAP-specific, CD4+ T-cell proliferative responses were generated in three out of four HLA-DRB1*0101 patients suggesting the possibility that DR1-restricted epitopes exist.

METHODS

To identify PAP-specific HLA-DRB1*0101 restricted epitopes, we immunized HLA-A2.01/HLA-DRB1*0101 (A2/DR1) transgenic mice with the pTVG-HP DNA vaccine. To map DRB1*0101-restricted epitopes, splenocytes from immunized mice were screened against a library of overlapping 15-residue, PAP-derived peptides using an IFNγ ELISPOT assay.

RESULTS

We identified four HLA-DRB1*0101 epitopes for PAP in A2/DR1 mice (PAP(161-175) , PAP(181-195) , PAP(191-205) , and PAP (351-365) ). T cells specific for one epitope (PAP(181-195) ) were found to be augmented after immunization in a HLA-DRB1*0101+ prostate cancer patient.

CONCLUSIONS

The identification of MHC class II epitopes may provide tools to directly monitor immune responses after vaccination and may be important for the design of future prostate cancer vaccines.

Tumor-associated antigens for specific immunotherapy of prostate cancer

Prostate cancer (PCa) is the most common noncutaneous cancer diagnosis and the second leading cause of cancer-related deaths among men in the United States. Effective treatment modalities for advanced metastatic PCa are limited. Immunotherapeutic strategies based on T cells and antibodies represent interesting approaches to prevent progression from localized to advanced PCa and to improve survival outcomes for patients with advanced disease. CD8⁺ cytotoxic T lymphocytes (CTLs) efficiently recognize and destroy tumor cells. CD4⁺ T cells augment the antigen-presenting capacity of dendritic cells and promote the expansion of tumor-reactive CTLs. Antibodies mediate their antitumor effects via antibody-dependent cellular cytotoxicity, activation of the complement system, improving the uptake of coated tumor cells by phagocytes, and the functional interference of biological pathways essential for tumor growth. Consequently, several tumor-associated antigens (TAAs) have been identified that represent promising targets for T cell- or antibody-based immunotherapy. These TAAs comprise proteins preferentially expressed in normal and malignant prostate tissues and molecules which are not predominantly restricted to the prostate, but are overexpressed in various tumor entities including PCa. Clinical trials provide evidence that specific immunotherapeutic strategies using such TAAs represent safe and feasible concepts for the induction of immunological and clinical responses in PCa patients. However, further improvement of the current approaches is required which may be achieved by combining T cell- and/or antibody-based strategies with radio-, hormone-, chemo- or antiangiogenic therapy.

Optimization of therapeutic proteins to delete T-cell epitopes while maintaining beneficial residue interactions

Exogenous enzymes, signaling peptides, and other classes of nonhuman proteins represent a potentially massive but largely untapped pool of biotherapeutic agents. Adapting a foreign protein for therapeutic use poses numerous design challenges. We focus here on one significant problem: modifying the protein to mitigate the immune response mounted against "non-self" proteins, while not adversely affecting the protein's stability or therapeutic activity. In order to propose such variants suitable for experimental evaluation, this paper develops a computational method to select sets of mutations predicted to delete immunogenic T-cell epitopes, as evaluated by a 9-mer potential, while simultaneously maintaining important residues and residue interactions, as evaluated by one- and two-body potentials. While this design problem is NP-hard, we develop an integer programming approach that works very well in practice. We demonstrate the effectiveness of our approach by developing plans for biotherapeutic proteins that, in previous studies, have been partially deimmunized via extensive experimental characterization and modification of limited segments. In contrast, our global optimization technique considers an entire protein and accounts for all residues, residue interactions, and epitopes in proposing candidates worth subjecting to experimental evaluation.

CD4 T-Cell-mediated immune response to prostatic proteins in HLA-DRB1*1503 transgenic mice and identification of a novel HLA-DRB1*1503-restricted T-cell epitope from human prostatic acid phosphatase

BACKGROUND

Transgenic mice engineered to express human leukocyte antigen (HLA) alleles are widely used for identification of immunogenic and naturally processed epitopes. Using HLA-DRB1*1501 (DR2b) transgenic mice, we have previously identified epitopes from two prostatic antigens, prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP). These antigens are implicated in the development of autoimmunity in the prostate and also are considered promising targets for prostate cancer immunotherapy. HLA-DRB1*1501 is the most common DR15 allele in Caucasians, while HLA-DRB1*1503 is the most common in African Americans. Hence characterization of peptide immunogenicity for these alleles is important for the development of prostate cancer immunotherapy in white and black patients.

METHODS

HLA-DRB1*1501 or HLA-DRB1*1503 transgenic mice were immunized with human PSA or PAP. Libraries of overlapping 20-mer peptides spanning the entire sequences of these proteins were screened by IFN-γ ELISPOT assay.

RESULTS

PSA and PAP peptides that were previously identified in HLA-DRB1*1501 tg mice were immunogenic in HLA-DR1503 tg mice and induced CD4 T-cell response against whole processed PSA or PAP respectively. However, the hierarchy of the immunodominance among the peptides differed significantly between strains. Using HLA-DRB1*1503 tg mice, a novel immunogenic and naturally processed 20-mer peptide, PAP (233-252) has been identified that showed no reactivity in HLA-DRB1*1501 tg mice.

CONCLUSIONS

Our data demonstrate a disparity in CD4 T-cell immune reactivity to PSA and PAP between HLA-DRB1*1501 and -DRB1*1503 alleles in HLA transgenic mouse models. It is possible that such immunological differences could contribute to racial disparity in prostate cancer outcome.

Optimization algorithms for functional deimmunization of therapeutic proteins

Background

To develop protein therapeutics from exogenous sources, it is necessary to mitigate the risks of eliciting an anti-biotherapeutic immune response. A key aspect of the response is the recognition and surface display by antigen-presenting cells of epitopes, short peptide fragments derived from the foreign protein. Thus, developing minimal-epitope variants represents a powerful approach to deimmunizing protein therapeutics. Critically, mutations selected to reduce immunogenicity must not interfere with the protein's therapeutic activity.

Results

This paper develops methods to improve the likelihood of simultaneously reducing the anti-biotherapeutic immune response while maintaining therapeutic activity. A dynamic programming approach identifies optimal and near-optimal sets of conservative point mutations to minimize the occurrence of predicted T-cell epitopes in a target protein. In contrast with existing methods, those described here integrate analysis of immunogenicity and stability/activity, are broadly applicable to any protein class, guarantee global optimality, and provide sufficient flexibility for users to limit the total number of mutations and target MHC alleles of interest. The input is simply the primary amino acid sequence of the therapeutic candidate, although crystal structures and protein family sequence alignments may also be input when available. The output is a scored list of sets of point mutations predicted to reduce the protein's immunogenicity while maintaining structure and function. We demonstrate the effectiveness of our approach in a number of case study applications, showing that, in general, our best variants are predicted to be better than those produced by previous deimmunization efforts in terms of either immunogenicity or stability, or both factors.

Conclusions

By developing global optimization algorithms leveraging well-established immunogenicity and stability prediction techniques, we provide the protein engineer with a mechanism for exploring the favorable sequence space near a targeted protein therapeutic. Our mechanism not only helps identify designs more likely to be effective, but also provides insights into the interrelated implications of design choices.

HLA Class II Antigen Presentation in Prostate Cancer Cells: A Novel Approach to Prostate Tumor Immunotherapy

Prostate cancer is a deadly disease that is in drastic need of new treatment strategies for late stage and metastatic prostate cancer. Immunotherapy has emerged as a viable option to fill this void. Clinical trials have been conducted that induce tumor clearance through cytotoxic T lymphocyte (CTL) activation, these studies have had mixed outcomes with the overlying problem being the lack of a complete immune response with sustained killing and the formation of tumor specific memory cells. To overcome this, we have outlined the need for activating the HLA class II pathway in inducing a sustained CD8+ T cell response and the development of effective memory. We have also discussed the ability of prostate cancer cells to express stable HLA class II molecules that can be manipulated for tumor antigen (Ag) processing and presentation. This review also sets to outline new directions that exist for the use of class II-restricted Ags/peptides in devising cancer vaccines as well as combined chemoimmunotherapy. A better understanding of these concepts will improve future cancer vaccine studies and further the field of cancer immunobiology.

T-cell recognition of prostatic peptides in men with chronic prostatitis/chronic pelvic pain syndrome

PURPOSE

A potential etiology of chronic prostatitis/chronic pelvic pain syndrome is autoimmunity. We determined whether T cells from men with chronic prostatitis/chronic pelvic pain syndrome would recognize peptides derived from the normal self-prostatic proteins prostate specific antigen and prostatic acid phosphatase.

MATERIALS AND METHODS

CD4 T cells purified from peripheral blood of 31 patients with chronic prostatitis/chronic pelvic pain syndrome and from the buffy coat preparation of 27 normal male blood donors were stimulated in vitro with a panel of immunogenic peptides from prostate specific antigen and prostatic acid phosphatase, and assayed for reactivity with the peptides by interferon-gamma enzyme-linked immunosorbent spot assay. Intermediate resolution HLA typing was done by polymerase chain reaction. Peptides were also tested by binding assay against different class II alleles.

RESULTS

Peptide PAP(173-192) was recognized more frequently by CD4 T cells from patients with chronic prostatitis/chronic pelvic pain syndrome than from healthy donors. The recognition of prostate specific antigen peptides was not statistically different when comparing cases to normal male blood donors individually. Peptide reactivity was more common in patients than in normal male blood donors for any prostate specific antigen peptide or any tested peptide. All peptides showed high promiscuity on binding assays. There was no association of cases with any specific HLA class II phenotype at intermediate resolution.

CONCLUSIONS

CD4 T cells from patients with chronic prostatitis/chronic pelvic pain syndrome have a higher rate of recognizing the self-prostatic proteins prostatic acid phosphatase and prostate specific antigen compared to those from normal male blood donors. Data provide further evidence to support the role of autoimmunity in some men with chronic prostatitis/chronic pelvic pain syndrome.