Immune rejection

A major potential flaw in the future development and therapeutic use of HuCNS-SCs is the risk of immune rejection because the stem cells are derived from fetal donors. This risk has not been addressed in the studies reported to date relating to the use of HuCNS-SCs. Allografts require immunosuppressive treatments, such as cyclosporine, to prevent host rejection. These treatments are not very well tolerated by patients, producing side effects such as renal dysfunction, tremor and hypertension. This may well affect the potential benefits of HuCNS-SC therapy. 

Human cells, tissues, or organs implanted or transplanted in animals present a relatively strong and valuable tool, provided that immune rejection of the human material can be avoided. Immune-deficient animals like mice may well be used to develop organ-like structures (teratomas) from transplanted stem cells [13] or with combinations of human cells or human tissue (e.g., synoviocytes and cartilage [14], and activated mononuclear cells and transplanted skin [15]). 

The work by Herzyk et al. [31], however, appears to be unique. To date, there have been no other reports of a human knock-in system being used in risk assessment of neoplasia, and similarly the literature on the use of tumor immunization/rejection models to evaluate the effects on IMBP on neoplasia is very scant. Because of the paucity of data, and because the anti-CD4 antibody studied by Herzyk et al. was never marketed and thus never used widely in patients, it is currently impossible to judge the predictive power of these systems for an increased risk of neoplasia in patients receiving IMBPs. 

Several of these bioactive natural products have been successfully developed as therapeutics for clinical use. For example, Cyclosporin A is a fungal decapeptide principally used to suppress immune rejection in organ transplant patients. Mevinolin and compatin both control cholesterol synthesis in human. The search for enzyme- or receptor-targeted microbial products does not limit itself to medical use. Several commercially important antibiotics such as Nikkomycin and Avermectin have been found for agricultural applications in recent years. 

When autologous cells are not appropriate or available, the cells can come from either another donor of the same species or a different species. The transplantation of cells between similar or dissimilar species is called allotransplantation or xenotransplantation, respectively. Although the supply of these types of grafts is plentiful, immune rejection is very common, so some additional strategy must be utilized to avoid rejection. Cells provided by family members, or... 

One concern with stem cell usage is that transplanted cells derived from stem cells can be tumori-genic owing to undifferentiated stem cells present in the population that proliferate uncontrollably.The use of stem cells, however, is promising because of the limited cell supply for many tissues. Cells that are not autogeneous must be able to avoid immune rejection. Somatic cell and nuclear transfer procedures could provide cells that function appropriately and... 

Fine-tuning of the immune rejection by co-transplantation of human stem cells and stem cells for other oigans might be used for tolerance induction and cell- and organ-specific regeneration of diseased or damaged organs. 

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