Prion diseases or transmissible spongiform encephalopathies (TSEs) are a family of rare progressive neurodegenerative diseases that affect both humans and animals. They are distinguished by long incubation periods, characteristic spongiform changes associated with neuronal loss and an inability to induce an inflammatory response. Infectious protein particles, the prion, were identified by American neurologist Stanley B. Prusiner and colleagues in 1982, derived from the words protein and infection (Stanley B. Prusiner -Autobiography). Prions are known for Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia in humans. In mammals, they cause “mad cow disease” in cattle. Prion diseases affect the structure of the brain or other neuronal tissues and are currently all universally fatal and incurable (Prusiner, 1998). Transmissible spongiform encephalopathies (TSEs) are caused by abnormal folding of prions. The normal prion protein, called PrPc, is a 35 kD membrane glycoprotein, water-soluble and sensitive to proteinase (Laurén, 2009). Abnormal prions, called PrPSc or PrPTSE, result from a change in the folding pattern of PrPc, which makes it resistant to the action of proteases and causes it to precipitate as insoluble amyloid (Robbins, 1999). This conversion leads to neuronal degeneration and loss by an unknown mechanism. PrPc is encoded by the PRNP gene on chromosome 20 and likely plays a role in several cellular functions, including cell adhesion, ion channel activity, and neuronal excitability (Lindquist, 2001). The structure of the PrPC protein is composed of a normal protein found on the cell. membranes. PrP has been reported to play an important role middle of paper ......, suggesting that direct proximity of cells promotes effective infection. The fact that living cells transmit infectivity much more efficiently than dead cells suggests that cellular biological processes are involved in prion transmission (MacKenzie, 2011). Biological bacteria carry some risk of prion contamination, even when generated in cell lines (Brown, 2003). The transmission of CJD through blood and even purified blood products has dramatically highlighted the seriousness of this threat. Therefore, PrPC-deficient livestock (cattle and goats) are well positioned for the production of prion-free therapeutics and will therefore contribute significantly to eliminating the risk of prion contamination in biological organisms..