CD46 and oncologic interactions: Friendly fire against cancer

One of the most challenging aspects of cancer therapeutics is target selection. Recently, CD46 (membrane cofactor protein; MCP) has emerged as a key player in both malignant transformation as well as in cancer treatments. Normally a regulator of complement activation, CD46 is co-expressed as four predominant isoforms on almost all cell types. CD46 is highly overexpressed on a variety of human tumor cells. Clinical and experimental data support an association between increased CD46 expression and malignant transformation and metastasizing potential. Further, CD46 is a newly discovered driver of metabolic processes and plays a role in the intracellular complement system (complosome). CD46 is also known as a pathogen magnet due to its role as a receptor for numerous microbes, including several species of measles virus and adenoviruses. Strains of these two viruses have been exploited as vectors for the therapeutic development of oncolytic agents targeting CD46. In addition, monoclonal antibody-drug conjugates against CD46 also are being clinically evaluated. As a result, there are multiple early-phase clinical trials targeting CD46 to treat a variety of cancers. Here, we review CD46 relative to these oncologic connections

A C3(H20) recycling pathway is a component of the intracellular complement system

An intracellular complement system (ICS) has recently been described in immune and nonimmune human cells. This system can be activated in a convertase-independent manner from intracellular stores of the complement component C3. The source of these stores has not been rigorously investigated. In the present study, Western blotting identified a band corresponding to C3 in freshly isolated human peripheral blood cells that was absent in corresponding cell lines. One difference between native cells and cell lines was the time absent from a fluid-phase complement source; therefore, we hypothesized that loading C3 from plasma was a route of establishing intracellular C3 stores. We found that many types of human cells specifically internalized C3(H(2)O), the hydrolytic product of C3, and not native C3, from the extracellular milieu. Uptake was rapid, saturable, and sensitive to competition with unlabeled C3(H(2)O), indicating a specific mechanism of loading. Under steady-state conditions, approximately 80% of incorporated C3(H(2)O) was returned to the extracellular space. These studies identify an ICS recycling pathway for C3(H(2)O). The loaded C3(H(2)O) represents a source of C3a, and its uptake altered the cytokine profile of activated CD4(+) T cells. Importantly, these results indicate that the impact of soluble plasma factors should be considered when performing in vitro studies assessing cellular immune function

Development and Optimization of an ELISA to Quantitate C3(H2O) as a Marker of Human Disease

Discovery of a C3(H2O) uptake pathway has led to renewed interest in this alternative pathway triggering form of C3 in human biospecimens. Previously, a quantifiable method to measure C3(H2O), not confounded by other complement activation products, was unavailable. Herein, we describe a sensitive and specific ELISA for C3(H2O). We initially utilized this assay to determine baseline C3(H2O) levels in healthy human fluids and to define optimal sample storage and handling conditions. We detected ~500 ng/ml of C3(H2O) in fresh serum and plasma, a value substantially lower than what was predicted based on previous studies with purified C3 preparations. After a single freeze-thaw cycle, the C3(H2O) concentration increased 3- to 4-fold (~2,000 ng/ml). Subsequent freeze-thaw cycles had a lesser impact on C3(H2O) generation. Further, we found that storage of human sera or plasma samples at 4°C for up to 22 h did not generate additional C3(H2O). To determine the potential use of C3(H2O) as a biomarker, we evaluated specimens from patients with inflammatory-driven diseases. C3(H2O) concentrations were moderately increased (1.5- to 2-fold) at baseline in sera from active systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) patients compared to healthy controls. In addition, upon challenge with multiple freeze-thaw cycles or incubation at 22 or 37°C, C3(H2O) generation was significantly enhanced in SLE and RA patients' sera. In bronchoalveolar lavage fluid from lung-transplant recipients, we noted a substantial increase in C3(H2O) within 3 months of acute antibody-mediated rejection. In conclusion, we have established an ELISA for assessing C3(H2O) as a diagnostic and prognostic biomarker in human diseases

Complement-Dependent Modulation of Antitumor Immunity following Radiation Therapy

Complement is traditionally thought of as a proinflammatory effector mechanism of antitumor immunity. However, complement is also important for effective clearance of apoptotic cells, which can be an anti-inflammatory and tolerogenic process. We show that localized fractionated radiation therapy (RT) of subcutaneous murine lymphoma results in tumor cell apoptosis and local complement activation. Cotreatment of mice with tumor-targeted complement inhibition markedly improved therapeutic outcome of RT, an effect linked to early increases in apoptotic cell numbers and increased inflammation. Improved outcome was dependent on an early neutrophil influx and was characterized by increased numbers of mature dendritic cells and the subsequent modulation of T cell immunity. Appropriate complement inhibition may be a promising strategy to enhance a mainstay of treatment for cancer