The cell type chosen for this technique depends on the desired application of the cell microcapsules. The cells put into the capsules can be from the patient (autologous cells), from another donor (allogeneic cells) or from other species (xenogeneic cells). The use of autologous cells in microencapsulation therapy is limited by the availability of these cells and even though xenogeneic cells are easily accessible, danger of possible transmission of viruses, especially porcine endogenous retrovirus to the patient restricts their clinical application, and after much debate several groups have concluded that studies should involve the use of allogeneic instead of xenogeneic cells. Depending on the application, the cells can be genetically altered to express any required protein. However, enough research has to be carried out to validate the safety and stability of the expressed gene before these types of cells can be used.
This technology has not received approval for clinical trial because of the high immunogenicity of cells loaded in the capsules. They secrete cytokines and produce a severe inflammatory reaction at the implantation site around the capsules, in turn leading to a decrease in viability of the encapsulated cells. One promising approach being studied is the administration of anti-inflammatory drugs to reduce the immune response produced due to administration of the cell loaded microcapsules. Another approach which is now the focus of extensive research is the use of stem cells such as mesenchymal stem cells for long term cell microencapsulation and cell therapy applications in hopes of reducing the immune response in the patient after implantation. Another issue which compromises long term viability of the microencapsulated cells is the use of fast proliferating cell lines which eventually fill up the entire system and lead to decrease in the diffusion efficiency across the semi-permeable membrane of the capsule. A solution to this could be in the use of cell types such as myoblasts which do not proliferate after the microencapsulation procedure.