Abstract: This disclosure provides methods and compositions for treating TTP based on transfusion of a relatively small number of genetically modified red blood cells. The genetically modified red blood cells express a fusion protein including a fragment of ADAMTS13 that is enzymatically active against von Willebrand factor (VWF). The fragments of ADAMTS13 can be resistant to the inhibitors, e.g., the auto-immune antibodies, which are responsible for the acquired form of TTP.

Abstract: Methods and compositions for transforming cells, resulting in efficient and stable site-specific integration of transgenes, are disclosed. Transformation is achieved by providing an acceptor DNA containing two inverted lox sequences and a donor DNA containing the same two inverted lox sequences, and then contacting the acceptor and donor DNA with a recombinase (e.g., Cre or Flp) which causes recombination at the lox sequences contained in the DNAs. Prior to recombination, the acceptor DNA is preferably integrated into the genome of a cell, such as an embryonic stem cell or a fertilized egg. The acceptor DNA optionally may further contain a negatively selectable marker to allow for screening of cells which have undergone the desired site-specific recombination (e.g., DNA cassette exchange).

Abstract: Methods and compositions for transforming cells, resulting in efficient and stable site-specific integration of transgenes, are disclosed. Transformation is achieved by introducing into a cell an acceptor vector, preferably a retroviral vector, which integrates into the genome of the cell. The acceptor vector comprises two incompatible lox sequences, L1 and L2. A donor vector is then introduced into the cell comprising a transgene flanked by the same L1 and L2 sequences. Stable gene transfer is initiated by contacting the lox L1 and L2 sequences with Cre recombinase.