Immune implants

Impla.nta.ble Ports. The safest method of accessing the vascular system is by means of a vascular access device (VAD) or port. Older VAD designs protmded through the skin. The totally implanted ports are designed for convenience, near absence of infection, and ease of implantation. Ports allow dmgs and fluids to be deUvered directiy into the bloodstream without repeated insertion of needles into a vein. The primary recipients of totally implanted ports are patients receiving chemotherapy, bolus infusions of vesicants, parenteral nutrition, antibiotics, analgesics, and acquired immune disease syndrome (AIDS) medications. 

Titanium and its compounds are nontoxic and immune to attack by body fluids. These features account for the use of the metal in knee and hip replacements as well as dental implants. 

Ganciclovir intraocular implant plus valganddovir 900 mg once daily until immune recovery from ART (Al)° Ganciclovir 5 mg/kg IV every 12 hours or foscarnet 180 mg/kg/day in two or three divided doses IV for 21 to 28 days (Bll)... 

Recently, it has been possible to grow cells of the human immune system in special mice. These mice carry a genetic defect called severe combined immunodeficiency (SCID), which leaves them with crippled immune systems, much like those in AIDS patients. Because SCID mice lack functional cellular immunity, it is possible to implant them with human cells without tissue rejection taking place. Researchers have recently developed techniques to implant human fetal tissues containing stem cells for the blood into SCID mice. It is then possible to reconstitute these mice with functional human immune system cells, including T lymphocytes and B lymphocytes. They have also found that if these SCID mice are infected by HIV, the virus will establish infection in the human tissue and destroy the T helper lymphocytes, just as it does in humans. Thus, it may be possible to study some of the mechanisms by which HIV attacks the immune system in these mice. In addition, they may be very useful for testing potential antiviral drugs. 

As discussed in Section 4.7, stem cells have the potential to treat medical conditions beyond the scope that can be offered by drugs alone. However, there are many scientific and ethical hurdles to overcome. On the scientific front, stem cell research activities will intensify over the next decade. These challenges can broadly be divided into (1) determining how to develop stem cells into specific tissues and (2) implanting these tissues into the body without rejection by the recipient s immune system. On the ethical front, it is expected that there will be more debates on the ethical issues of stem cell research. Most scientists consent to therapeutic cloning (stem cell research) but not reproductive cloning. The ethical issue of stem cell research concerns harvesting cells from embryos that are a few days old. This action destroys the embryos. Some questions are ... 

The islet cells transplanted into humans are obtained from pancreatic tissue of deceased human donors (Figure 8.9). Implantation of these cells in recipients displaying a competent immune system would, at best, be of transient therapeutic benefit. The ensuing immune response would quickly destroy the foreign cells. Studies conducted thus far in humans have utilized diabetic patients who have received kidney transplants, as these are already subject to immunosuppressive therapy. However, a major stumbling block to the widespread adoption of this therapeutic approach is, predictably, the requirement to induce concurrent immune suppression. 

Any material proposed for implantation, whether for cell transplantation or some other application, must be biocompatible i.e. it must not provoke an adverse response from the host s immune system. If this goal is not met the implant may be rejected. To this end it is important that the material be easily sterilized either by exposure to high temperatures, ethylene oxide vapor, or gamma radiation. A suitable material must therefore remain unaffected by one of these three techniques. However, biocompatibility is not simply a question of sterility. The chemistry, structure, and physical form of a material are all important factors which determine its biocompatibility. Although our understanding of the human immune system is advancing rapidly, it is not yet possible to predict the immune response to a new material. This can only be determined by in vivo experiments. 

Another study in Fischer rats demonstrated that MSCs do not elicit an immune response after transplantation in immunocompetent recipients. Syngeneic Fischer MSCs or allogeneic ACI MSCs were implanted via an osteoconductive matrix into the bilateral femoral gap of Fischer rats who were then sacrificed at 3, 6 and 12 weeks post-implantation (n = 4 per time point). Histological analysis showed there was no difference between the syngeneic or allogeneic implants. Allogeneic implants did not induce significant inflammatory cell infiltration or stimulate alloreactive T-cell responses [656702]. 

Allogeneic rat mesenchymal stem cells do not elicit an immune response after implantation in immunocompetent recipients Archambault, M.P., McIntosh, K.R., Duty, A., Peter, S.J. (2000). Blood, 96 11 Abs 3295. 

Although titanium has a large positive E° for oxidation, and T dust will burn in air, the bulk metal is remarkably immune to corrosion because its surface becomes coated with a thin, protective oxide film. Titanium objects are inert to seawater, nitric acid, hot aqueous NaOH, and even to aqueous chlorine gas. Titanium is therefore used in chemical plants, in desalination equipment, and in numerous other industrial processes that demand inert, noncorrosive materials. Because it is nontoxic and inert to body fluids, titanium is even used for manufacturing artificial joints and dental implants. 

Imagine the possibilities, some of which are just now becoming reality Tools, knife blades, and scalpels coated with diamond remain forever sharp. Eyeglass lenses and wristwatches coated with diamond remain scratch-free. High-fidelity loudspeakers coated with diamond give a nearly perfect, undistorted sound at high frequencies. Hip joints and other biological implants coated with diamond are not rejected by the body s immune system. 

Stochastic responses under conditions of the experiment should be reviewed carefully with respect to the relevance of the evidence to humans (e.g., the occurrence of bladder tumors in the presence of bladder stones and implantation site sarcomas). Interpretation of animal studies is aided by the review of target organ toxicity and other effects (e.g., changes in the immune and endocrine systems) that may be noted in pre-chronic or other toxicologic studies. Time- and dose-related incidence of pre-neoplastic lesions may also be helpful in interpreting animal studies. 

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