The Development and Characterization of an HEK293-Derived Cell Line for Use in an Intratumoral Cytokine Delivery System

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Release characteristics of cellulose sulphate capsules and production of cytokines from encapsulated cells

The size and speed of release of proteins of different sizes from standard cellulose sulphate capsules (Cell-in-a-Box®) was investigated. Proteins with molecular weights of up to around 70kD can be released. The conformation, charge and concentration of the protein being released play a role in the release kinetics. Small proteins such as cytokines can be easily released. The ability to produce cytokines at a sustained and predefined level from encapsulated cells genetically engineered to overexpress such cytokines and implanted into patients may aid immunotherapies of cancer as well as infectious and other diseases. It will also allow allogeneic rather than autologous cells to be used. We show that cells encapsulated in polymers of cellulose sulphate are able to release cytokines such as interleukin-2 (IL-2) in a stimulated fashion e.g. using phorbol 12-myristate 13-acetate (PMA) plus ionomycin. Given the excellent documented safety record of cellulose sulphate in patients, these data suggest that clinical usage of the technology may be warranted for cancer treatment and other diseases.

Local Effects of Retrovirally Transduced Endostatin-Expressing Human Umbilical Cord Blood CD34+ Cells on Transplanted Malignancy in a Mouse Model of Hepatic Cancer

Antiangiogenesis has been exploited as an effective approach to inhibit the growth of solid tumors. This technique has been evaluated using various vectors in several xenograft animal models to demonstrate the efficacy of endostatin gene therapy against cancer growth. However, previous studies have not examined the use of cord blood CD34+ cells as endostatin-producing cells for gene therapy against hepatoma. This exploratory study was done to investigate the local effects of CD34+ cells transduced with the endostatin gene on a mouse xenograft tumor model. The human endostatin gene was transferred into CD34+ cells using the recombinant retrovirus plasmid, pLncx/endo. Expression was verified by RT-PCR and Western blot analyses, confirming the stable expression and secretion of endostatin from the transferred CD34+ cells. The proliferation of vascular endothelial cells was evaluated by MTT assay and found to decrease by about 59.9% when treated with the supernatant of cultured transfected CD34+ cells in vitro. These genetically modified cord blood CD34+ cells were implanted intratumorally and tumor regression was evaluated after 2 weeks. The average size of a xenograft tumor in the CD34+/endo group was reduced 31.39% compared to that in the untreated mice or those transplanted with CD34+ cells transduced with a control vector. The microvascular density of the tumor decreased 62.45% in the treated group. The expression of proliferation cell nuclear antigen (PCNA) also decreased significantly in the treated group. Moreover, the apoptotic index (AI) of tumors, as evaluated by TUNEL staining, was significantly enhanced in the treatment group. Our findings indicate that angiogenesis of the xenograft tumor in mice may be inhibited by local administration of genetically modified CD34+ cells expressing the endostatin gene. This novel approach may lead to a new direction of cell-based gene therapy for malignancy.