Gene therapy for autoimmune diseases: quo vadis?

Biological therapies using antibodies and cytokines are becoming widespread for the treatment of chronic inflammatory autoimmune diseases. However, these treatments have several limitations - such as expense, the need for repeated injections and unwanted side-effects - that can be overcome by genetic delivery. This review summarizes the ingenuity, sophistication and variety of gene-therapy approaches that have been taken in the design of therapeutic molecules and vectors, the engineering of cells and the regulation of gene expression for the targeting of disease outcome. We focus our attention on multiple sclerosis, type 1 diabetes and rheumatoid arthritis.     

Are rare variants responsible for susceptibility to complex diseases?

Little is known about the nature of genetic variation underlying complex diseases in humans. One popular view proposes that mapping efforts should focus on identification of susceptibility mutations that are relatively old and at high frequency. It is generally assumed-at least for modeling purposes-that selection against complex disease mutations is so weak that it can be ignored. In this article, I propose an explicit model for the evolution of complex disease loci, incorporating mutation, random genetic drift, and the possibility of purifying selection against susceptibility mutations. I show that, for the most plausible range of mutation rates, neutral susceptibility alleles are unlikely to be at intermediate frequencies and contribute little to the overall genetic variance for the disease. Instead, it seems likely that the bulk of genetic variance underlying diseases is due to loci where susceptibility mutations are mildly deleterious and where there is a high overall mutation rate to the susceptible class. At such loci, the total frequency of susceptibility mutations may be quite high, but there is likely to be extensive allelic heterogeneity at many of these loci. I discuss some practical implications of these results for gene mapping efforts.     

B-cell depletion for rheumatic diseases: where are we?

Immune system dysfunction is common to rheumatic disorders, with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) being classic examples. Altered development and function of B cells may play a prominent role. B-cell abnormalities also occur in other rheumatic diseases, eg, Sjogren's syndrome, Behcet's disease, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, and dermatomyositis. Hence, B-cell depletion has been investigated as a therapeutic option. Clinical trials in RA and SLE have shown that rituximab, an anti-CD20 monoclonal antibody, can profoundly reduce disease activity and is generally well tolerated. Reports of rituximab treatment for ANCA-associated vasculitis and dermatomyositis are also promising. These encouraging results validate the strategy of B-cell depletion in various rheumatic diseases. B-cell depletion with rituximab is under study in larger clinical trials for the purposes of regulatory approval to define more closely its place in RA and SLE treatment paradigms, and smaller clinical trials are ongoing or planned in associated inflammatory diseases.     

Is there a role for copper in neurodegenerative diseases?

Copper is an essential metal in living organisms; thus, the maintenance of adequate copper levels is of vital importance and is highly regulated. Dysfunction of copper metabolism leading to its excess or deficiency results in severe ailments. Two examples of illnesses related to alterations in copper metabolism are Menkes and Wilson diseases. Several proteins are involved in the maintenance of copper homeostasis, including copper transporters and metal chaperones. In the last several years, the beta-amyloid-precursor protein (beta-APP) and the prion protein (PrP(C)), which are related to the neurodegenerative disorders Alzheimer and prion diseases respectively, have been associated with copper metabolism. Both proteins bind copper through copper-binding domains that also have been shown to reduce copper in vitro. Moreover, this ability to reduce copper is associated with a neuroprotective effect exerted by the copper-binding domain of both proteins against copper in vivo. In addition to a functional link between copper and beta-APP or PrP(C), evidence suggests that copper has a role in Alzheimer and prion diseases. Here, we review the evidence that supports both, the role of beta-APP and PrP(C), in copper metabolism and the putative role of copper in neurodegenerative diseases.     

A therapeutic role for sirtuins in diseases of aging?

The sirtuins are a group of proteins linked to aging, metabolism and stress tolerance in several organisms. Among the many genes that have been shown to affect aging in model organisms, sirtuin genes are unique in that their activity level is positively correlated with lifespan (i.e. they are anti-aging genes). Sirtuins are a druggable class of enzymes (i.e. amenable to intervention by small molecules) that could have beneficial effects on a variety of human diseases. In view of the many functions of Sirtuin 1 (SIRT1) in cells, this review focuses on its role in regulating important aspects of mitochondrial biology. Mitochondria have been linked to aging, and also to diseases of aging. Thus, sirtuins might provide a key link between mitochondrial dysfunction, aging and metabolic disease.     

PLASMANATE?—A New Plasma Substitute for Pediatric Therapy

Plasmanate®, a human-serum protein solution, appears to have all the attributes of an ideal plasma expander. Freedom from infection, immediate availability in a clear, stable solution and the apparent absence of antigenic properties are particularly valuable qualities. The efficacy and safety of Plasmanate was clinically demonstrated in the treatment of 125 infants and children. This solution seems especially effective in the treatment of acute shock states and for the physiologic correction of hypoproteinemia. Comparison with other plasma expanders makes Plasmanate the agent of choice in the initial treatment of shock states in pediatrics.     

Shh Signaling and Pancreatic Cancer: Implications for Therapy?

Hedgehog signaling has been implicated in the development of several human cancers, including small cell lung carcinomas, medulloblastomas, basal cell carcinomas, and digestive tract tumors. Elevated levels of pathway components are observed in pancreatic ductal adenocarcinoma (PDAC) precursor lesions, and these levels increase further as lesions progress to more advanced stages. Yet the mechanisms by which hedgehog signaling contributes to pancreatic tumorigenesis were poorly understood. We recently published results showing that activated hedgehog signaling enhances the proliferation and survival of pancreatic duct epithelial cells, the presumptive target cells for PDAC development. We also demonstrated that sonic hedgehog (Shh) expression, in cooperation with loss of the Trp53 and Ink4a/Arf tumor suppressor loci, was sufficient to initiate the formation of early pancreatic lesions. Furthermore, Shh signaling enhanced K-Ras-mediated pancreatic tumorigenesis and reduced the dependence of tumor cells on the sustained activation of Ras-stimulated signaling pathways. Here we discuss the significance of these findings and the implications for therapy.     

Aerosols: An underestimated vehicle for transmission of prion diseases?

We and others have recently reported that prions can be transmitted to mice via aerosols. These reports spurred a lively public discussion on the possible public-health threats represented by prion-containing aerosols. Here we offer our view on the context in which these findings should be placed. On the one hand, the fact that nebulized prions can transmit disease cannot be taken to signify that prions are airborne under natural circumstances. On the other hand, it appears important to underscore the fact that aerosols can originate very easily in a broad variety of experimental and natural environmental conditions. Aerosols are a virtually unavoidable consequence of the handling of fluids; complete prevention of the generation of aerosols is very difficult. While prions have never been found to be transmissible via aerosols under natural conditions, it appears prudent to strive to minimize exposure to potentially prion-infected aerosols whenever the latter may arise—for example in scientific and diagnostic laboratories handling brain matter, cerebrospinal fluids, and other potentially contaminated materials, as well as abattoirs. Equally important is that prion biosafety training be focused on the control of, and protection from, prion-infected aerosols.Key words: prion, prion transmission, scrapie, chronic wasting diseases, CWD, Creutzfeldt-Jacob-disease, CJD, TSE, aerosol, pathogens, allergensPrions, the causative agents of transmissible spongiform encephalopathies, can be undoubtedly propagated from one individual organism to another. The specific routes of prion transmission have been subjected to intensive studies over the past two decades. Incidental and iatrogenic transmission has occurred through the intracerebral route in the case of Dura mater implants¹ and the parenteral route in the case of contaminated pituitary hormones.² In addition, the Bovine Spongiform Encephalopathy (BSE) disaster has provided grim evidence that prion can be transmitted enterally as well. Experimental transmission of prions has been routinely achieved via intraperitoneal and intravenous injection^3,4 but also through more exotic routes such as intralingual,⁵ intranerval⁶ and conjunctival inoculation⁷ and via the nasal cavity.⁸In all prion disease paradigms studied so far the propagation, accumulation and dissemination of the prion protein has been mostly shown to depend on a functional immune system.^9–12 This dependence of prion pathogenesis on the lymphoid compartment, however, is only true for peripheral routes of infection—whereas direct inoculation into the brain does not require any components of the adaptive or innate immune system.B cells in secondary lymphoid organs have been shown to be of importance for the neuroinvasion of the prion protein; in contrast, B lymphocytes in the blood do not appear to play a crucial role.^13–15A special role in prion pathogenesis can be assigned to follicular dendritic cells (FDC). The generation, maturation and function of FDC are dependent on cytokines and chemokines predominantly synthesized and secreted by B lymphocytes. Consistently with this role of B cells in prion pathogenesis, B cell deficient mice show a significantly impaired prion replication due to severely impaired maturation of FDCs.¹⁶ Other soluble and membrane-bound immune mediators such as lymphotoxin heterotrimers and TNFalpha^17,18 as well as components of the complement system^19,20 play an important role in prion pathogenesis.While prions mostly reside in tissues, prion infectivity has also been detected in a variety of body fluids including cerebrospinal fluid,²¹ blood,²² saliva,²³ milk²⁴ and urine.²⁵ Although shedding of prions may occur constitutively from these secretions and excretions, many of the latter phenomena are enhanced by chronic inflammatory processes such as granulomas²⁶ and follicular infiltrates,²⁷ which trigger the maturation of lymphotoxin-dependent, prion-replicating cells.²⁶ The presence of prions in fluids begs the question whether nebulization, and subsequent inhalation, of such fluids may trigger prion infections.Aerosols are finely dispersed particles originating from solid material or liquid using air or other gases as carriers. Natural examples of aerosols include dust (e.g., volcano ashes), smoke, haze and sprays (e.g., sneezing or sea water sprays from breaking waves). Aerosols might be formally categorized as primary or secondary, with primary aerosols being generated in mechanical or thermal processes e.g., by whirling up, impact on surfaces, or burning, whereas secondary aerosols are generated during chemical reactions or by using condensation nuclei.Primary aerosols play an important role in microbiology since they can act as efficacious vehicles for pollen, spores, algae, fungi, bacteria and viruses. Of medical importance are also dandruff, fragments of fur, hairs or skin and mites, which can all function as allergens and trigger e.g., allergic asthma.Moreover, aerosols are excellent vehicles for the transportation of drugs into the respiratory tract. The size of the individual droplets is crucial in specifying the target organs of aerosol. Particle sized 3–10 µm are generally deposited in the nasal cavity and in the throat, whereas smaller particles (e.g., 1 µm) tend to deposit within the lower airways. In rodents pulmonary deposition can reach 10%.^28,29 In humans, particles of 5 µm may reach the lung if inhaled orally, but deposition in the alveolar compartment after inhaling via the nose is highly unlikely.^28,29 For the reasons discussed above, we have become interested in exploring the transmission potential of aerosol-borne prions. Indeed, we found that mouse scrapie can be efficiently transmitted via aerosols.³⁰ In addition to results obtained by exposure to aerosols, we found that mice developed prion infections when inoculated intranasally.Interestingly, this route of transmission was entirely independent on immune cells as shown by challenging various transgenic mouse strains lacking defined functions of the immune system.Well-known examples of transmission of pathogens via aerosols are infections by respiratory viruses (e.g., influenza viruses, adenoviruses, rhinoviruses, coronaviruses) and bacterial diseases (e.g., legionellosis, pneumonic plague by Yersinia pestis, Q-fever by Coxiella burnettii, anthrax) and fungal diseases (particularly aspergillosis and candidosis). In stark contrast, aerosols have historically never been regarded as potential vectors for prion diseases—although very little data existed in favor or against this possibility. This attitude goes along with the implicit “conventional wisdom” that prions are not airborne diseases. However, the concept of “airborne disease” in all the bacterial, fungal and viral examples quoted above, encompasses three distinct phases: (1) release of the infectious agent into aerosols by an infected donor, (2) uptake by a healthy recipient and (3) establishment of disease. It is self-evident that little or no natural transmission between individuals will be observed if any one of these three steps is inefficient. The epidemiological evidence from human prion diseases seems to indicate, albeit indirectly, that step #1 does not occur in CJD patients—inter alia because there is a dearth of evidence of proximity clustering of sCJD.³¹ In the case of CWD the situation may be different since saliva and droppings, which might plausibly give rise to powerful aerosols under a variety of conditions, were found to harbor infectivity. Finally, milk from sheep affected by mastitis can carry scrapie infectivity and—again—could conceivably give rise to aerosols. Since both CWD and sheep scrapie can efficiently spread horizontally within animal collectives, it is extremely appealing to speculate whether aerosols may play a role in said transmission.In natural scrapie in sheep horizontal transmission of prion diseases has been long thought to arise from placental contamination. However, in mice suffering from nephritis prion infectivity is shed with the urine.²⁵ Furthermore, sheep having a mastitis can transmit infectious prions with milk.³²In Chronic Wasting disease (CWD) of deer several careful studies have been performed that, together with our present finding, depose in favor of airborne transmission in this naturally occurring disease. Indeed, CWD prions can be transmitted experimentally via aerosol and the nasal route to transgenic cervidized mice.³³ Although no anecdotal or epidemiological evidence has come forward that airborne transmission may be important for the spread of CWD, several lines of thought suggest that this possibility is not implausible. In deer, prions have been detected in urine, saliva, feces and blood of diseased animals. Moreover, it was claimed that pathological prion protein could be recovered from the environmental water in an endemic area.³⁴ Since all fluids can act as sources for the generation of aerosols, any of the body fluids mentioned above may represent the point of origin for airborne transmission of CWD prions.In this context, also the presence of infectious prions in blood of patients should be mentioned which was demonstrated by the transmission of vCJD by blood transfusions.^35,36 The growing body of evidence that prion transmission can be airborne—at least under certain conditions—dictates that the release of potentially contaminated aerosols should be avoided under all circumstances. In this context it is mandatory that reliable precautions be defined and followed in scientific and diagnostic laboratories. In particular, it is self-evident that safety cabinets should be used while processing brain and nerve tissue (or any other potentially contaminated tissue) of man and animals suspected with prion disease. Our experience shows that this necessity is generally very well-understood by prion scientists.A further stone of contention relates to the biosafety level of the laboratory environment. Because prions were hitherto considered not be airborne, so far no specific regulations have been implemented. As a consequence, prion laboratories have been mostly required to adhere to the category “BSL3**.” While it is understood that the airborne transmission of prions has thus far only been observed under extreme conditions, we feel that it is in order to critically reassess biosafety regulations in the light of the recent discoveries. In particular, one might consider implementing more stringent measures towards protecting workers within diagnostic and scientific laboratories from aerosols.The situation in slaughterhouses and plants handling potentially contaminated offal may be even more problematic. Although regulations in slaughterhouses dictate the use of protecting glasses and masks or, alternatively, visors the use of personal protecting equipment should be rigorously controlled. In addition, high-pressure cleaning devices produce massive aerosols and should be strictly avoided in areas of slaughterhouses where prion-containing material may be processed. Regulations concerning cleaning of heads from slaughtered animals do pay attention to aerosol avoidance, e.g., by allowing only water hoses without pressure.A case in point is the severe neurological syndrome arising in swine abattoir workers.³⁷ Here, an immune-mediated polyradiculoneuropathy was reported to be related to a process using high-pressure fluids to remove the brains of swine.³⁷ During this process, high amounts of swine brain tissue became aerosolized and were inhaled and/or gained access to the respiratory tract mucosa of abattoir workers, resulting in immunization with myelin constituents akin to experimental autoimmune encephalitis (EAE). Although significant physiological differences exist concerning breathing, where humans are regarded as mouth breathers and mice as nose breathers, many people indeed show nose breathing under no or only moderate body burden. Therefore, results obtained in mouse experiments might also be extrapolated to a considerable extent to the situation in man.In this context it is of importance to stress again that aerosols might be generated under various conditions and represent a normal entity of the environment in a variety of daily life situations.In our studies of airborne transmission of prion protein in mice³⁰ we took advantage of the fact that mice breathe exclusively through their nostrils^38,39 and therefore could be exposed in groups to aerosolized brain suspensions. Using this system, it was possible to vary both time of exposure as well as concentration of the prion load in the aerosol. We were surprised to discover that exposure times as short as 1 min were sufficient to achieve high attack rates. By extending the time of exposure it became obvious that incubation times were shortened. A possible alternative route of infection via the cornea or the conjunctiva was extremely unlikely, since newborn mice, whose eyelids were still closed, could also be infected. These findings show that the aerogenic transmission of prions is very efficient.But how do prions spread from the airways to the brain? Peripheral replication of prions in the lymphoid system—a characteristic of most other peripheral routes of transmission—appeared to be dispensable. Instead, the results argue for a direct pathway of brain invasion. One anatomical peculiarity of the nasal cavity is the “area cribriformis” of the olfactory epithelium. Here the olfactory bulb sprouts axons of olfactory receptor neurons passing through the cribriform plate of the ethmoidal bone to reach the olfactory mucosa where olfactory cilia extend representing non-myelinated nerve endings. Thus, open nerve endings are located in the nasal cavity through which aerosolized infectious prions might get access to the brain. In this context it is noteworthy that pathological prion protein was found in the olfactory cilia and basal cells of the olfactory mucosa of sCJD patients, as well as in the olfactory bulb and olfactory tract.^40,41 However, it was hitherto never clearly documented that olfactory receptor neurons represent an entry site for infectious prions; this might also be due to the sensitivity threshold of detection assays.In conclusion, aerosols can infect mice with a surprisingly high efficiency. Just how important a role is played by this newly recognized pathway of spread in natural transmission is, as of now, unclear and in need of further studies. Although it was not identified as a route of infection in epidemiological studies thus far, the worryingly high attack rate suggests that we would be well-advised to carefully avoid the inhalation of aerosols from prion-containing materials.     

Why are there no proven therapies for genetic mitochondrial diseases?

Although mitochondrial disease research in general is robust, adequate treatment of these life-threatening conditions has lagged, partly because of a persistence of clinical anecdotes as substitutes for scientifically and ethically rigorous clinical trials. Here I summarize the key lessons learned from some of the “first generation” of randomized controlled trials for genetic mitochondrial diseases and suggest how future trials may benefit from both past experience and exciting new resources available for patient-oriented research and training in this field.     

Natural Products: An Alternative to Conventional Therapy for Dermatophytosis?

The increased incidence of fungal infections, associated with the widespread use of antifungal drugs, has resulted in the development of resistance, making it necessary to discover new therapeutic alternatives. Among fungal infections, dermatophytoses constitute a serious public health problem, affecting 20–25 % of the world population. Medicinal plants represent an endless source of bioactive molecules, and their volatile and non-volatile extracts are clearly recognized for being the historical basis of therapeutic health care. Because of this, the research on natural products with antifungal activity against dermatophytes has considerably increased in recent years. However, despite the recognized anti-dermatophytic potential of natural products, often advantageous face to commercial drugs, there is still a long way to go until their use in therapeutics. This review attempts to summarize the current status of anti-dermatophytic natural products, focusing on their mechanism of action, the developed pharmaceutical formulations and their effectiveness in human and animal models of infection.