Accurate identification of paraprotein antigen targets by epitope reconstruction

Waldenström macroglobulinemia: clinical and immunological aspects, natural history, cell of origin, and emerging mouse models

Waldenström macroglobulinemia (WM) is a rare and currently incurable neoplasm of IgM-expressing B-lymphocytes that is characterized by the occurrence of a monoclonal IgM (mIgM) paraprotein in blood serum and the infiltration of the hematopoietic bone marrow with malignant lymphoplasmacytic cells. The symptoms of patients with WM can be attributed to the extent and tissue sites of tumor cell infiltration and the magnitude and immunological specificity of the paraprotein. WM presents fascinating clues on neoplastic B-cell development, including the recent discovery of a specific gain-of-function mutation in the MYD88 adapter protein. This not only provides an intriguing link to new findings that natural effector IgM⁺IgD⁺ memory B-cells are dependent on MYD88 signaling, but also supports the hypothesis that WM derives from primitive, innate-like B-cells, such as marginal zone and B1 B-cells. Following a brief review of the clinical aspects and natural history of WM, this review discusses the thorny issue of WM's cell of origin in greater depth. Also included are emerging, genetically engineered mouse models of human WM that may enhance our understanding of the biologic and genetic underpinnings of the disease and facilitate the design and testing of new approaches to treat and prevent WM more effectively.

Viruses and multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler's murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.

Viruses and Multiple Sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler’s murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.

Association of a dominantly inherited hyperphosphorylated paraprotein target with sporadic and familial multiple myeloma and monoclonal gammopathy of undetermined significance: a case-control study

BACKGROUND

Chronic antigenic stimulation might have a role in the pathogenesis of monoclonal gammopathy of unknown significance (MGUS) and multiple myeloma. The aim of this study was to search for factors underlying the autoimmunogenicity of paratarg-7, a frequent antigenic target of paraproteins in MGUS and multiple myeloma.

METHODS

Between January, 2005, and February, 2009, serum and peripheral blood cells were obtained from consecutive patients with MGUS or multiple myeloma and healthy blood donors, and paratarg-7 was analysed by DNA sequencing, SDS-PAGE, isoelectric focusing, and western blotting.

FINDINGS

Mutations or polymorphisms of paratarg-7 were not noted, but hyperphosphorylation was detected in 35 (13.9%) of 252 patients with MGUS or multiple myeloma, all of whom had an anti-paratarg-7-specific paraprotein. Analysis of eight families showed that hyperphosphorylated paratarg-7 is inherited in a dominant fashion, and that carriers of hyperphosphorylated paratarg-7 have an increased risk of developing MGUS and multiple myeloma (odds ratio [OR] 7.9, 95% CI 2.8-22.6; p=0.0001).

INTERPRETATION

Familial MGUS and multiple myeloma were associated with a dominant inheritance of hyperphosphorylated paratarg-7, enabling family members at increased risk for MGUS or multiple myeloma to be identified. That only patients with MGUS or multiple myeloma who are carriers of hyperphosphorylated paratarg-7 had a paratarg-7-specific paraprotein suggests that the hyperphosphorylation of paratarg-7 induces auto-immunity and is involved in the pathogenesis of MGUS and multiple myeloma; for example, by chronic antigenic stimulation.

FUNDING

Förderverein Krebsforschung Saar-Pfalz-Mosel e.V. (eingetragener Verein: officially registered charity) and HOMFOR (the research programme of the Saarland University Faculty of Medicine).

The microenvironment in mature B-cell malignancies: a target for new treatment strategies

Despite major therapeutic advances, most mature B-cell malignancies remain incurable. Compelling evidence suggests that crosstalk with accessory stromal cells in specialized tissue microenvironments, such as the bone marrow and secondary lymphoid organs, favors disease progression by promoting malignant B-cell growth and drug resistance. Therefore, disrupting the crosstalk between malignant B cells and their milieu is an attractive novel strategy for treating selected mature B-cell malignancies. Here we summarize the current knowledge about the cellular and molecular interactions between neoplastic B lymphocytes and accessory cells that shape a supportive microenvironment, and the potential therapeutic targets that are emerging, together with the new problems they raise. We discuss clinically relevant aspects and provide an outlook into future biologically oriented therapeutic strategies. We anticipate a paradigm shift in the treatment of selected B-cell malignancies, moving from targeting primarily the malignant cells toward combining cytotoxic drugs with agents that interfere with the microenvironment's proactive role. Such approaches hopefully will help eliminating residual disease, thereby improving our current therapeutic efforts.

A frequent target of paraproteins in the sera of patients with multiple myeloma and MGUS

Antigenic targets of monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) paraproteins might play a role in the pathogenesis of these neoplasms. We screened a human fetal brain-derived macroarray with the IgA or IgG containing sera of 192 consecutive MGUS and MM patients. Twenty-nine of 192 (15.1%) paraproteins reacted with paratarg-7, a protein of unknown function which is expressed in all human tissues. Paratarg-7 reactivity was similarly frequent among IgA and IgG paraproteins, but all paratarg-7 reactive IgG paraproteins belonged to the IgG3 subtype with 24/57 IgG3 (42.1%) paraproteins displaying this specificity. Sequence analysis of paratarg-7 derived from patients having a paraprotein with specificity for paratarg-7 revealed no differences to paratarg-7 derived from patients with paraproteins of other specificities or healthy controls, excluding mutations or polymorphisms as a reason for its autoimmunogenicity. Similarly, Western-blot analysis showed identical bands for paratarg-7 derived from patients and controls. The above-random frequency of paratarg-7 as a paraprotein target suggests that paratarg-7 might be involved in the development of the respective clonal proliferations. The identification of paratarg-7 as an antigenic target enables the more detailed analysis of tumor-host interactions in these patients and their role in the pathogenesis of MM and MGUS.

Bioinformatic requirements for protein database searching using predicted epitopes from disease-associated antibodies

We describe a new approach to identify proteins involved in disease pathogenesis. The technology, Epitope-Mediated Antigen Prediction (E-MAP), leverages the specificity of patients' immune responses to disease-relevant targets and requires no prior knowledge about the protein. E-MAP links pathologic antibodies of unknown specificity, isolated from patient sera, to their cognate antigens in the protein database. The E-MAP process first involves reconstruction of a predicted epitope using a peptide combinatorial library. We then search the protein database for closely matching amino acid sequences. Previously published attempts to identify unknown antibody targets in this manner have largely been unsuccessful for two reasons: 1) short predicted epitopes yield too many irrelevant matches from a database search and 2) the epitopes may not accurately represent the native antigen with sufficient fidelity. Using an in silico model, we demonstrate the critical threshold requirements for epitope length and epitope fidelity. We find that epitopes generally need to have at least seven amino acids, with an overall accuracy of >70% to the native protein, in order to correctly identify the protein in a nonredundant protein database search. We then confirmed these findings experimentally, using the predicted epitopes for four monoclonal antibodies. Since many predicted epitopes often fail to achieve the seven amino acid threshold, we demonstrate the efficacy of paired epitope searches. This is the first systematic analysis of the computational framework to make this approach viable, coupled with experimental validation.