Exosome removal as a therapeutic adjuvant in cancer.

Exosome secretion is a notable feature of malignancy owing to the roles of these nanoparticles in cancer growth, immune suppression, tumor angiogenesis and therapeutic resistance. Exosomes are 30-100 nm membrane vesicles released by many cells types during normal physiological processes. Tumors aberrantly secrete large quantities of exosomes that transport oncoproteins and immune suppressive molecules to support tumor growth and metastasis. The role of exosomes in intercellular signaling is exemplified by human epidermal growth factor receptor type 2 (HER2) over-expressing breast cancer, where exosomes with the HER2 oncoprotein stimulate tumor growth and interfere with the activity of the therapeutic antibody Herceptin®. Since numerous observations from experimental model systems point toward an important clinical impact of exosomes in cancer, several pharmacological strategies have been proposed for targeting their malignant activities. We also propose a novel device strategy involving extracorporeal hemofiltration of exosomes from the entire circulatory system using an affinity plasmapheresis platform known as the Aethlon ADAPT™ (adaptive dialysis-like affinity platform technology) system, which would overcome the risks of toxicity and drug interactions posed by pharmacological approaches. This technology allows affinity agents, including exosome-binding lectins and antibodies, to be immobilized in the outer-capillary space of plasma filtration membranes that integrate into existing kidney dialysis systems. Device therapies that evolve from this platform allow rapid extracorporeal capture and selective retention of target particles < 200 nm from the entire circulatory system. This strategy is supported by clinical experience in hepatitis C virus-infected patients using an ADAPT™ device, the Hemopurifier®, to reduce the systemic load of virions having similar sizes and glycosylated surfaces as cancer exosomes. This review discusses the possible therapeutic approaches for targeting immune suppressive exosomes in cancer patients, and the anticipated significance of these strategies for reversing immune dysfunction and improving responses to standard of care treatments.

Modeling hepatitis C virus therapies combining drugs and lectin affinity plasmapheresis.

Hepatitis C virus (HCV) infection can be cured by standard pegylated interferon (IFN) + ribavirin drug therapy in 30-50% of treatment-naïve genotype 1 HCV patients. Cure rate is defined as a sustained viral response measured 6 months after the end of treatment. Recently, Fujiwara et al. [Hepatol Res 2007;37:701-710], using a double-filtration plasmapheresis (DFPP) technique, showed that simple physical reduction in circulating HCV using a 1-week pretreatment increased the cure rate for treatment-naïve type 1 HCV patients from 50 (controls) to 78% (treated). For previous nonresponders, the cure rate increased from 30 to 71%. This effect occurs even though the DFPP per treatment HCV viral load reduction averaged 26%. In clinical studies discussed here, a lectin affinity plasmapheresis (LAP) device caused an estimated 41% decrease in viral load as previously reported. A more detailed analysis using normalized data to correct for any variations in initial viral load gave an average 29% per treatment viral load reduction in 5 HCV-positive dialysis patients. The latter data indicate that continuous application of LAP could bring HCV viral load to undetectable levels in 4.1 days. Compared to DFPP, the LAP approach has the advantage that no plasma losses are incurred. In addition hemopurification can be carried out for extended periods of time analogous to continuous renal replacement therapy for the treatment of acute kidney failure, making the process much more effective. Calculations based on these data predict that continuous hemopurification would substantially increase the rate of viral load reduction (approx. 14-fold) and therefore increase the cure rate for HCV standard-of-care drug therapies without adding additional drugs and their associated side effects.

Reduction of hepatitis C virus using lectin affinity plasmapheresis in dialysis patients.

BACKGROUND/AIMS: To test the safety and efficacy of the Aethlon Hemopurifier, a lectin affinity cartridge, in clearing hepatitis C virus (HCV) from the blood of HCV-positive end-stage renal disease patients undergoing dialysis. Viral RNA was measured using real-time quantitative reverse transcriptase polymerase chain reaction. RESULTS: HCV clearance from plasma or blood was measured using either direct capture on immobilized Galanthus nivalis agglutinin (GNA) or using miniature plasmapheresis cartridges containing immobilized GNA. HCV in plasma samples was rapidly cleared by direct affinity capture (t(1/2) = approx. 20 min) and HCV in human blood was cleared using the Hemopurifier (t(1/2) = 2-3 h). Institutional-review-board-sanctioned clinical safety studies were conducted at the Apollo and Fortis Hospitals in India. At Apollo, 4 patients were treated 3 times/week for 2 weeks. HCV captured on the Hemopurifier averaged 8.9 x 10(8) viral copies/cartridge (n = 5), representing approximately 30% of the initial viral body burden. At Fortis, 3 patients treated 3 times/week for 1 week completed the viral load studies. Two patients showed measurable viral load reduction, while the third showed both increases and decreases in viral load. After Hemopurifier treatment, average HCV viral load was reduced by 57%. Surprisingly, average viral load was also 82% lower 7 days after treatment. Control samples also showed a marked transient reduction in HCV viral load as previously reported. CONCLUSION: The Hemopurifier rapidly cleared HCV from blood treated in vitro. In patients, the combination of the Hemopurifier plus dialysis decreased HCV viral load by 57% in 1 week. Moreover, viral load reduction continued up to 7 days after treatment.

Exosomes as a tumor immune escape mechanism: possible therapeutic implications.

Advances in cancer therapy have been substantial in terms of molecular understanding of disease mechanisms, however these advances have not translated into increased survival in the majority of cancer types. One unsolved problem in current cancer therapeutics is the substantial immune suppression seen in patients. Conventionally, investigations in this area have focused on antigen-nonspecific immune suppressive molecules such as cytokines and T cell apoptosis inducing molecules such as Fas ligand. More recently, studies have demonstrated nanovesicle particles termed exosomes are involved not only in stimulation but also inhibition of immunity in physiological conditions. Interestingly, exosomes secreted by cancer cells have been demonstrated to express tumor antigens, as well as immune suppressive molecules such as PD-1L and FasL. Concentrations of exosomes from plasma of cancer patients have been associated with spontaneous T cell apoptosis, which is associated in some situations with shortened survival. In this paper we place the "exosome-immune suppression" concept in perspective of other tumor immune evasion mechanisms. We conclude by discussing a novel therapeutic approach to cancer immune suppression by extracorporeal removal of exosomes using hollow fiber filtration technology.

Preliminary Study of Plasma Exosomal Tau as a Potential Biomarker for Chronic Traumatic Encephalopathy.

BACKGROUND: Chronic traumatic encephalopathy (CTE) is a tauopathy associated with prior exposure to repetitive head impacts, such as those incurred through American football and other collision sports. Diagnosis is made through neuropathological examination. Many of the clinical features of CTE are common in the general population, with and without a history of head impact exposure, making clinical diagnosis difficult. As is now common in the diagnosis of other neurodegenerative disorders, such as Alzheimer's disease, there is a need for methods to diagnose CTE during life through objective biomarkers. OBJECTIVE: The aim of this study was to examine tau-positive exosomes in plasma as a potential CTE biomarker. METHODS: Subjects were 78 former National Football League (NFL) players and 16 controls. Extracellular vesicles were isolated from plasma. Fluorescent nanoparticle tracking analysis was used to determine the number of vesicles staining positive for tau. RESULTS: The NFL group had higher exosomal tau than the control group (p <  0.0001). Exosomal tau discriminated between the groups, with 82% sensitivity, 100% specificity, 100% positive predictive value, and 53% negative predictive value. Within the NFL group, higher exosomal tau was associated with worse performance on tests of memory (p = 0.0126) and psychomotor speed (p = 0.0093). CONCLUSION: These preliminary findings suggest that exosomal tau in plasma may be an accurate, noninvasive CTE biomarker.