Basic biochemical investigations as rationale for the design of original antimalarial drugs. An example of phospholipid metabolism

The future of antimalarial chemotherapy is particulary alarming in view of the spread of parasite cross-resistances to drugs that are not even structurally related. Only the availability of new pharmacological models will make it possible to select molecules with novel mechanisms of action, thus delaving resistance and allowing the development of new chemotherapeutic strategies. We reached this objective in mice. Our approach is hunged on fundamental and applied research begun in 1980 to investigate to phospholipid (PL) metabolism of intraerythrocytic Plasmodium. This metabolism is abundant, specific and indispensable for the production of Plasmodium membranes. Any drug to interfere with this metabolism blocks parasitic development. The most effective interference yet found involves blockage of the choline transporter, which supplies Plasmodium with choline for the synthesis of phosphatidylcholine, its major PL, this is a limiting step in the pathway. The drug sensitivity thereshold is much lower for the parasite, which is more dependent on this metabolism than host cells. The compounds show in vitro activity against P. falciparum at 1 to 10 nM. They show a very low toxicity against a lymphblastoid cell line, demonstrating a total abscence of correlation between growth inhibition of parasites and lymphoblastoid cells. They show antimalarial activity in vivo, in the P. berghei or P. chabaudi/mouse system, at doses 20-to 100-fold lower than their in acute toxicity limit. The bioavailability of a radiolabeled form of the product seemed to be advantageous (slow blood clearance and no significant concentration in tissues). Lastly, the compounds are inexpensive to produce. They are stable and water-soluble.

Babesia divergens vaccine

A vaccine strategy against Babesia divergens bovine babesiosis was sucessfully developed after perfecting of an efficient in vitro culture. Crude supernatants and purified fractions were able to induce a vaccine protection in gerbils against B. divergens infection. More, supernatants induced an effective vaccine protection in cattle. The role of B. divergens exoantigens of 17, 37, 46, 70 and 90 kDa in the development of the immune response was cleary demonstrated in gerbils, cattle, and man.

Field evaluation of an exoantigen-containing Babesia vaccine in Venezuela

Bovine babesiosis is endemic in Venezuela, causing significant losses in highly susceptible imported cattle. Current immunoprphylatic methods include the less desirable use of live parasites. Inactivated vaccines derived from exoantigen-containing supernatant fluids of in vitro Babesia bovis and B. bigemina cultures have been developed and constitute a major improvement in vaccine safety, stability and ease of handling. Vaccination trials conducted under field conditions provide the final evaluation of a culture-derived B. bovis-B. bigemina vaccine. During a 5-year period, approximately 8,000 cattle were vaccinated and 16 clinical trials carried out in. 7 states of Venezuela Clinical, serologic and parasitologic data were collected monthly from 10% of the animals over a 2-year period. Data were also collected from a similar number of nonvaccinated control cattle. Analysis of results from these trials demonstrated a reduction in the incidence of clinical disease among vaccinated animals and complete protection against mortality among vaccinated and nonvaccinated cattle. Use of this inactivated vaccine offers the best combination od safety, potency and efficacy for thew immunoprophylatic control of bovine babesiosis.

Efficience of human Plasmodium falciparum malaria vaccine candidates in Aotus lemurinus monkeys

The protective efficacy of several recombinat and a synthetic Plasmodium falciparum protein was assessed in Aoutus monkeys. The rp41 aldolase, the 190L fragment of the MSA-1 protein and fusion 190L-CS. T3 protein containg the CS. T3 helper "universal epitope were emulsified in Freund's adjuvants and injected 3 times in groups of 4-5 monkeys each one. The synthetic polymer Spf (66)30 also emulsified in Freund's adjuvants was injected 6 times. Control groups for both experiments were immunized with saline solution in the same adjuvant following the same schedules. Serology for malaria specific antibodies showed seroconversion in monkeys immunized with the recombinant proteins but not in those immunized with the polymer nor in the controls. Challenge was performed with the 10 (elevado a quinta potência) parasites from the P. falciparum FVO isolate. Neither rp41 nor SPf (66)30 induced protection, whereas 190L induced significant delay of parasitemia. The fusion of the CS. T3 epitope to 190L significantly increased is protective capacity.

Vaccine strategies against schistosomiasis

In this review the authors analyze the effector and regulatory mechanisms in the immune response to schistosomiasis. To study these mechanisms two animal models were used, mouse and rat. The mouse totaly permissive host like human, show prominent-T cell control in the acquisition of resistance. But other mechanisms like antibody mediated cytotoxity (ADCC) involving eosinophils and IgG antibodies described in humans, are observed in rats. Also in this animal, it is observed specific IgE antibody high production and blood and tisssue eosinophilia. Using the rat model and schistosomula as target, some ADCC features have emerged: the cellular population involved are bone marrow derived inflammatory cell (mononuclear phagocytes, eosinophils and platelets), interacting with IgE through IgE Fc receptors. Immunization has been attempted using the recombinant protein Sm28/GST. Protection has been observed in rodents with significant decrease of parasite fecundity and egg viability affecting the number, size and volume of liver egg granulomas. The association of praziquantel and immunization with with Sm28/GST increases the resistance to infection and decreases egg viability. The authors suggest the possibility of the stablishment of a future vaccine against Schistosoma mansoni.

Vaccine strategies against schistosomiasis

Schistosomiasis, the second major parasitic disease in the world after malaria affects at least 200 million people, 500 million being exposed to the risk of infection. It is widely agreed that a vaccine strategy wich could lead to the induction of effector mechanisms reducing the level of reinfection and ideally parasite fecundity would deeply affect the incidence of pathological manifestations as well as the parasite transmission potentialities. Extensive studies performed in the rat model have allowed the identification of novel effector mechanisms involving IgE antibodies and various inflammatory cell populations (eosinophils, macrophages and platelets) whereas regulation of immune response by blocking antibodies has been evidencial. Recent epidemiological studies have now entirely confirmed in human populations the the role of IgE antibodies in the acquisition of resistance and the association of IgG4 blocking antibodies with increased susceptibility. On the basis of these concepts, several schistosome glutathion S-transferase (Sm 28 GST) appears as a pronising vaccine candidate. Immunization experiments have shown that two complementary goals can be achieved: (a) a partial but significant reduction of the worm population (up to 60//in rats); (b) a significant reduction of parasite fecundity (up in the mice and 85//in cattle) and egg viability (up to 80//). At least two distinct immunological mechanisms account for these two effects. IgE antibodies appear as a major humoral component of acquired resistance whereas IgA antibodies appear as a major humoral factor affecting parasite fecundity. These studies seem to represent a parasite diseases through the identification of potentially protective antigens and of the components of the immune response which vaccination should aim at inducing.

The Design and efficiency of loyalty rewards

The goal of this paper is to reexamine the optimal design and efficiency of loyalty rewards in markets for final consumption goods. While the literature has emphasized the role of loyalty rewards as endogenous switching costs (which distort the efficient allocation of consumers), in this paper I analyze the ability of alternative designs to foster consumer participation and increase total surplus. First, the efficiency of loyalty rewards depend on their specific design. A commitment to the price of repeat purchases can involve substantial efficiency gains by reducing price-cost margins. However, discount policies imply higher future regular prices and are likely to reduce total surplus. Second, firms may prefer to set up inefficient rewards (discounts), especially in those circumstances where a commitment to the price of repeat purchases triggers Coasian dynamics.

Study design for technology assessment: critical issues.

The epidemiological methods have become useful tools for the assessment of the effectiveness and safety of health care technologies. The experimental methods, namely the randomized controlled trials (RCT), give the best evidence of the effect of a technology. However, the ethical issues and the very nature of the intervention under study sometimes make it difficult to carry out an RCT. Therefore, quasi-experimental and non-experimental study designs are also applied. The critical issues concerning these designs are discussed. The results of evaluative studies are of importance for decision-makers in health policy. The measurements of the impact of a medical technology should go beyond a statement of its effectiveness, because the essential outcome of an intervention or programme is the health status and quality of life of the individuals and populations concerned.

Opportunities and constraints in schistosomiasis vaccine development: infection characteristics and industry realities

The notes provided in this article relate to two components of the development of vaccines against schistosomiasis: (1) The characteristics of schistosome infections (eg. features of the schistosome life cycle), and the parasite itself, that have implications for vaccination strategies; (2) The characteristics of the biopharmaceutical industry that have implications for product development. As will be seen, these two topic areas are not vastly disparate.

Schistosomiasis vaccine development: approaches and prospects

Mounting evidence for acquired immunity to schistosomiasis in humans supports the case for immunological intervention. On the other hand, rapid reinfection poses a threat to younger age groups due to the slow maturation of natural resistance. However, rational approaches, based on advances in immunology and molecular biology, have substantially increased the odds of producing an effective vaccine. Since the parasite cannot replicate in the human host and serious morbidity generally occurs only after a relatively long period of heavy worm burden, complete protection against infection is not essential. The chances of success would increase if more than one of the various host/parasite interphases were targeted, for example reducing morbidity through decreased worm loads as well as through suppression of egg production. Several promising schistosome antigens have now reached an advanced phase of development and are currently undergoing independent confirmatory testing according to a standardized protocol. A few molecules are being contemplated for scaled-up production but, so far, only one has reached the stage of industrial manufacture and safety testing. Since schistosomiasis cannot realistically be controlled by a single approach, vaccination is envisaged to be implemented in conjunction with other means of control, notably chemotherapy.

Development of a vaccine strategy against human and bovine schistosomiasis: background and update

Schistosomiasis is a chronic and debilitating parasitic disease that affects over 200 million people throughout the world and causes about 500,000 deaths annually. Two specific characteristics of schistosome infection are of primordial importance to the development of a vaccine: schistosomes do not multiply within the tissues of their definitive hosts (unlike protozoan parasites) and a partial non-sterilizing immunity can have a marked effect on the incidence of pathology and on disease transmission. Since viable eggs are the cause of disease pathology, a reduction in worm fecundity whether or not accompanied by a reduction in parasite burden is a sufficient goal for vaccine induced immunity. We originally showed that IgE antibodies played in experimental models a pivotal role for the development of protective immunity. These laboratory findings have been now confirmed in human populations. Following the molecular cloning and expression of a protein 28 kDa protein of Schistosoma mansoni and its identification as a glutathion S-transferase, immunization experiments have been undertaken in several animal species (rats, mice, baboons). Together with a significant reduction in parasite burden, vaccination with Sm28 GST was recently shown to reduce significantly parasite fecundity and egg viability leading to a decrease in liver pathology. Whereas IgE antibodies were shown to be correlated with protection against infection, IgA antibodies have been identified as one of the factors affecting egg laying and viability. In human populations, a close association was found between IgA antibody production to Sm28 GST and the decrease of egg output. The use of appropriate monoclonal antibody probes has allowed the demonstration that the inhibition of parasite fecundity following immunization was related to the inhibition of enzymatic activity of the molecule. Epitope mapping of Sm28 GST has indicated the prominent role of the N and C terminal domains. Immunization with the corresponding synthetic peptides was followed by a decrease of 70% of parasite fecundity and egg viability. As a preliminary step towards phase I human trials, vaccination experiments have been performed in cattle, a natural model for Schistosoma bovis. Vaccination of calves with the S. bovis GST has led to a reduction of ever 80% of egg output and tissue egg count. Significant levels of protection were also observed in goats after immunization with the recombinant S. bovis GST. Increasing evidence of the participation of IgA antibodies in protective immunity has prompted us toward the development of mucosal immunization. Preliminary results indicate that significant levels of protection can be achieved following oral immunization with live attenuated vectors or liposomes. These studies seem to represent a promising approach towards the future development of a vaccine strategy against one of major human parasitic diseases.

Vaccination against schistosomiasis and fascioliasis with the new recombinant antigen Sm14: potential basis of a multi-valent anti-helminth vaccine?

Molecular cloning of components of protective antigenic preparations have suggested that related parasite fatty acid binding proteins could form the basis of the well documented protective, immune cross reactivity between the parasitic trematode worms Fasciola hepatica and Schistosoma mansoni. We have now confirmed the cross protective potential of parasite fatty acid binding proteins and suggest that it may be possible to produce a single vaccine that would be effective against at least two parasites, F. hepatica and S. mansoni of veterinary and human importance respectively.

Desenvolupament de vacunes peptídiques y dendrímers basats en polietilenglicol per al tractament del càncer

El principal problema de les teràpies actuals contra el càncer es la baixa especificitat envers les cèl•lules tumorals, cosa que comporta gran quantitat d’efectes secundaris. Per això es important el desenvolupament de nous tipus de teràpies i sistemes d’alliberament efectius per als fàrmacs ja existents al mercat. En la immunoteràpia contra el càncer es pretén estimular el sistema immunològic per a eliminar les cèl•lules canceroses de manera selectiva. En aquest projecte s’han sintetitzat derivats de l’antigen peptídic de melanoma NY-ESO1 i s’ha estudiat la seva capacitat per a estimular el sistema immunològic com a vacunes contra el càncer. També s’han encapsulat el antígens peptídics en liposomes com a adjuvants i sistemes d’alliberament. De totes les variants peptídiques la que resultà més immunogènica fou la que contenia el grup palmitoil i el fragment toxoide tetànic en la seva estructura. La utilització de liposomes com a sistema adjuvant sembla una estratègia interessant per al disseny de vacunes contra el càncer donat que l’encapsulació del pèptid en liposomes va augmentar notablement la resposta immunològica de l’antigen. Per altra banda, s’han desenvolupat dendrímers basats en polietilenglicol com a sistemes alliberadors de fàrmacs per al tractament de tumors. El polietilenglicol és àmpliament utilitzat com a sistema d’alliberament de fàrmacs degut a les seves interessants propietats, augment de la solubilitat i dels temps de residència en plasma, entre d’altres. La metodologia química descrita permet la diferenciació controlada de varies posicions en la superfície del dendrímer a més del creixement del dendrímer fins a una segona generació. S’ha sintetitzat la primera generació del dendrímer contenint el fàrmac antitumoral 5-fluorouracil i s’han realitzat estudis de citotoxicitat comprovant que l’activitat del nanoconjugat és del mateix ordre de magnitud que el 5-fluorouracil sense conjugar.