Microcapsule degradation

We implemented microencapsulation of engineered human cells and designed the system for degradation of alginate microcapsules.

Engineered HEK293T cells were succesfully incorporated into alginate microcapsules and extended time viability of the encapsulated cells was demonstrated.

Secretory alginate lyases from Pseudomoalteromonas elyakovii and from Pseudomonas aeruginosa were cloned by replacing the signal peptide of the alginate lyase with the eukaryotic signal peptide.

Alginate lyases were succesfully produced and secreted from HEK293T cells.

Degradation of alginate beads was demonstrated by alginate lyase from Sphingobacterium multivorum.

Degradation of alginate microcapsules

Our biopharmaceutical delivery system is based on microencapsulated mammalian cells which produce the required therapeutics. These cells are safely sealed in the alginate microcapsules, forming an immune-privileged environment for the therapeutic cells, and implanted into the tissue such as e.g. the eye or placenta. The semi-permeable capsule allows free transport of nutrients, signalling molecules, and produced protein therapeutics, while it prevents immune cells from reaching and destroying the implanted therapeutic cells. Therapeutic cells therefore do not need to be immuno-compatible for each individual patient and can threfore be optimized and mass produced to increase their efficiency and affordability of this therapy.

We designed our device to leave no trace after the therapy has been completed, by initiating secretion of an alginate-degrading enzyme to break down the microcapsules followed by the apoptosis of therapeutic cells. This approach should increase the safety and decrease the unwanted effects of treatment and makes the surgical removal of microcapsules or fibrotic tissue around microcapsules obsolete.

Figure 1. Schematic representation of alginate microcapsule and its degradation. Microcapsules serve as a semi-permeable membrane, allowing exchange of therapeutic and inducer molecules as well as nutrients and metabolites between encapsulated cells and the environment. On the other hand the microcapsule prevents the immune cells and immunoglobulin complexes to access the engineered cells while at the same time preventing uncontrolled dissemination of therapeutic cells throughout the body.

Alginate microcapsules

Alginate is the most widely used and clinicaly tested biomaterial for cell encapsulation. It is found in cell walls of brown seaweed. This polysaccharide is made of (1, 4)-linked monomeric units of β-D-mannuronate (M) and α-L-guluronate (G) (Figure 2). Consecutive M or G residues form so called M or G-blocks, whereas the alternating M and G units constitute MG-blocks of alginate (Duan et al., 2009).

Figure 2. Structure of alginate polymer. α-L-guluronate sugar residues is shown on the left and β-D-mannuronate on the right side. Source: http://en.wikipedia.org/wiki/Alginate

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