OPTIMIZATION OF THE MAGNETIC-FIELD USED FOR IMMUNOMAGNETIC ISLET PURIFICATION

Purification of islets based on the physical differences in density be tween exocrine and islet tissue reduces islet yields and remains one o f the factors limiting islet transplantation. Immunomagnetic cell sepa ration methods provide an attractive, highly specific alternative capa ble of rapid, gentle, high volume cell separation, but they require mo dification to be applied effectively to separation of the much larger tissue fragments involved in islet purification.In this study, mAb to rat exocrine tissue were coupled to 4.5-mu m magnetic beads (M450 Dyna beads), before incubation with standard aliquots of rat pancreatic dig est. The effect on immunomagnetic islet purification of modifications in the magnetic field and the method of digest release into the field were investigated. The results showed that using vibration to maintain the immunomagnetically labeled digest in suspension in tissue culture medium whose density had been increased by the addition of BSA, signi ficantly improved the purification process, When the digest suspension was slowly released and allowed to drift under gravity through a magn etic field applied across a narrow tube, the use of a quadripole of pe rmanent magnets improved results compared with bipolar or unipolar mag netic fields. By modifying immunomagnetic cell separation techniques i n this way, a median islet yield of 77% could be reliably achieved whi le removing 88% of the contaminating exocrine tissue. The use of such methods in human islet purification would significantly increase the y ield of islets from each donor pancreas and increase the success rate of transplantation from donors.