José Luis Pedraz

Cell encapsulation: Promise and progress

In cell encapsulation, transplanted cells are protected from immune rejection by an artificial, semipermeable membrane, potentially allowing transplantation (allo- or xenotransplantation) without the need for immunosuppression. Yet, despite some promising results in animal studies, the field has not lived up to expectations, and clinical products based on encapsulated cell technology continue to elude the scientific community. This commentary discusses the reasons for this, summarizes recent progress in the field and outlines what is needed to bring this technology closer to clinical application.

Biomaterials for promoting brain protection, repair and regeneration

Biomaterials are likely to have an increasingly important role in the treatment of nervous system disorders. Recently developed biomaterials can enable and augment the targeted delivery of drugs or therapeutic proteins to the brain, allow cell or tissue transplants to be effectively delivered to the brain and help to rebuild damaged circuits. Similarly, biomaterials are being used to promote regeneration and to repair damaged neuronal pathways in combination with stem cell therapies. Many of these approaches are gaining momentum because nanotechnology allows greater control over material–cell interactions that induce specific developmental processes and cellular responses including differentiation, migration and outgrowth.

Microcapsules and microcarriers for in situ cell delivery.

In recent years, the use of transplanted living cells pumping out active factors directly at the site has proven to be an emergent technology. However a recurring impediment to rapid development in the field is the immune rejection of transplanted allo- or xenogeneic cells. Immunosuppression is used clinically to prevent rejection of organ and cell transplants in humans, but prolonged usage can make the recipient vulnerable to infections, and increase the likelihood of tumorigenesis of the transplanted cells. Cell microencapsulation is a promising tool to overcome these drawbacks. It consists of surrounding cells with a semipermeable polymeric membrane. The latter permits the entry of nutrients and the exit of therapeutic protein products, obtaining in this way a sustained delivery of the desirable molecule. The membrane isolates the enclosed cells from the host immune system, preventing the recognition of the immobilization cells as foreign. This review paper intends to overview the current situation in the cell encapsulation field and discusses the main events that have occurred along the way. The technical advances together with the ever increasing knowledge and experience in the field will undoubtedly lead to the realization of the full potential of cell encapsulation in the future.

Size dependent immune response after subcutaneous, oral and intranasal administration of BSA loaded nanospheres

BSA was entrapped in particles of different sizes (200, 500 and 1000 nm) prepared from poly(D,L-lactic-co-glycolic) acid by a double emulsion method. The particles were given, either intranasally, orally or subcutaneously, to Balb/c mice and the serum IgG, IgG1 and IgG2a response elicited was compared to that obtained by the subcutaneous administration of either free antigen, free antigen emulsified 1:1 with Freunds Complete Adjuvant (FCA), or free antigen administered with Al(OH)(3). The administration of 1000 nm particles generally elicited a higher serum IgG response than that obtained with the administration of 500 or 200 nm sized nanospheres, the immune response for 500 nm particles being similar than that obtained with 200 nm by the subcutaneous and the oral route, and higher by the intranasal route. PLGA nanoparticles can elicit serum IgG2a responses by the three routes studied. No significant differences on the serum IgG2a/IgG1 ratios were found after the subcutaneous, the oral and the intranasal administration of the different spheres but those were in general higher compared to the administration of either free antigen or free antigen adsorbed to alum. The route of administration influences the serum IgG2a/IgG1 ratio after the administration of free antigen, but not after the administration of the particles. Therefore, differences on the total serum IgG response induced by particles of different sizes do not result in differences on the IgG1 or IgG2a-type immune responses, suggesting that the antigen processing and presentation is similar in all cases tested for PLGA particles.

Biocompatibility of microcapsules for cell immobilization elaborated with different type of alginates

The biocompatibility of alginate-PLL-alginate (APA) microcapsules has been evaluated with respect to impurity levels. The impurity content of three different alginates (a raw high M-alginate, a raw high G-alginate and a purified high G-alginate) has been determined and the in vivo antigenic response of APA beads made with each alginate assessed. Results show that purification of the alginate not only reduces the total amount of impurities (63% less in polyphenols, 91.45% less in endotoxins and 68.5% less in protein in relation to raw high M-alginate), but also avoids an antibody response when microcapsules of this material are implanted in mice. In contrast, raw alginates produced a detectable antibody response though the differences in their impurity content. Consequently, this work revealed that purity of the alginate rather than their chemical composition, is probably of greater importance in determining microcapsule biocompatibility.

Multiscale requirements for bioencapsulation in medicine and biotechnology

Bioencapsulation involves the envelopment of tissues or biological active substances in semipermeable membranes. Bioencapsulation has been shown to be efficacious in mimicking the cells natural environment and thereby improves the efficiency of production of different metabolites and therapeutic agents. The field of application is broad. It is being applied in bioindustry and biomedicine. It is clinically applied for the treatment of a wide variety of endocrine diseases. During the past decades many procedures to fabricate capsules have been described. Unfortunately, most of these procedures lack an adequate documentation of the characterization of the biocapsules. As a result many procedures show an extreme lab-to-lab variation and many results cannot be adequately reproduced. The characterization of capsules can no longer be neglected, especially since new clinical trials with bioencapsulated therapeutic cells have been initiated and the industrial application of bioencapsulation is growing. In the present review we discuss novel Approached to produce and characterize biocapsules in view of clinical and industrial application. A dominant factor in bioencapsulation is selection and characterization of suitable polymers. We present the adequacy of using high-resolution NMR for characterizing polymers. These polymers are applied for producing semipermeable membranes. We present the pitfalls of the currently applied methods and provide recommendations for standardization to avoid lab-to-lab variations. Also, we compare and present methodologies to produce biocompatible biocapsules for specific fields of applications and we demonstrate how physico-chemical technologies such as FT-IR, XPS, and TOF-SIMS contribute to reproducibility and standardization of the bioencapsulation process. During recent years it has become more and more clear that bioencapsulation requires a multidisciplinary approach in which biomedical, physical, and chemical technologies are combined. For adequate reproducibility and for understanding variations in outcome of biocapsules it is advisable if not mandatory to include the characterization processes presented in this review in future studies.

Nanoparticle delivery systems for cancer therapy: advances in clinical and preclinical research.

Conventional anticancer drugs display significant shortcomings which limit their use in cancer therapy. For this reason, important progress has been achieved in the field of nanotechnology to solve these problems and offer a promising and effective alternative for cancer treatment. Nanoparticle drug delivery systems exploit the abnormal characteristics of tumour tissues to selectively target their payloads to cancer cells, either by passive, active or triggered targeting. Additionally, nanoparticles can be easily tuned to improve their properties, thereby increasing the therapeutic index of the drug. Liposomes, polymeric nanoparticles, polymeric micelles and polymer- or lipid-drug conjugate nanoparticles incorporating cytotoxic therapeutics have been developed; some of them are already on the market and others are under clinical and preclinical research. However, there is still much research to be done to be able to defeat the limitations of traditional anticancer therapy. This review focuses on the potential of nanoparticle delivery systems in cancer treatment and the current advances achieved.

Enhanced immune response after subcutaneous and oral immunization with biodegradable PLGA microspheres.

PLGA microspheres containing bovine serum albumin (BSA) as a model antigen, were prepared by a double emulsion/solvent extraction method and their in vitro characterization was performed. The same microspheres were used in a series of in vivo studies to evaluate the immune response induced after subcutaneous or oral inoculation following different immunization protocols. The in vivo data confirm that the immunogenicity of the albumin is not affected by the encapsulation procedure. The subcutaneous administration of microspheres showed an immune response (serum IgG levels by ELISA) statistically above BSA solution, even when the dose administered was 10 times lower. The adjuvanticity of the microspheres was found to be comparable to that of Freunds complete adjuvant (FCA), but in contrast to FCA they are biocompatible and did not induce any adverse reaction at the site of injection. A single oral administration of the microspheres was not a successful strategy for the induction of a reproducible response. Therefore, microspheres of 1 and 5 micrometer were orally administered on 3 consecutive days and the response obtained showed that the use of a boosting dose was not necessary for the 1 micrometer particles. These results suggest the possibility of simplifying the immunization schedule to a primary immunization if 1 micrometer particles are administered.

Survival of different cell lines in alginate-agarose microcapsules

Cell microencapsulation has emerged as a promising therapeutic strategy to treat a wide range of diseases. The optimisation of this technology depends on several critical issues such as the careful selection of the cell line, the controlled manufacture of microcapsules and the suitable adaptation of the construct design to the selected cell line. In this work, we studied the behavior of hybridoma cells once enclosed in solid and liquefied core alginate-agarose beads. Results show that hybridoma cells presented a better growing pattern and improved their viability and antibody production within liquefied beads. However, when these beads were evaluated with a compression resistance study, they were found to be mechanically more fragile than solid ones. To address this problem, we entrapped non-autologous cells (BHK fibroblast and C2C12 myoblast) in solid alginate-agarose beads and observed that they showed an improved growing profile and prolonged their viability up to 70 days in comparison to the 15 days seen for the hybridoma cells.

Novel advances in the design of three-dimensional bio-scaffolds to control cell fate: translation from 2D to 3D

Recreating the most critical aspects of the native extracellular matrix (ECM) is fundamental to understand and control the processes regulating cell fate and cell function. From the ill-defined complexity to the controlled simplicity, we discuss the different strategies that are being carried out by scientists worldwide to achieve the latest advances in the sophistication of three-dimensional (3D) scaffolds, stressing their impact on cell biology, tissue engineering and regenerative medicine. Synthetic and naturally derived polymers like polyethylene glycol, alginate, agarose, etc., together with micro- and nanofabrication techniques are allowing the creation of 3D models where biophysical and biochemical variables can be modified with high precision, orthogonality and even in real-time.