A method of inhibiting Instant Blood-Mediated Inflammatory Reaction (IBMIR) in a patient, comprises administering a therapeutically effective amount of dextran sulfate, or a pharmaceutically acceptable salt thereof. A method of inhibiting morphological disruption of a transplanted cell transplant in a patient comprises administering a therapeutically effective amount of dextran sulfate, or a pharmaceutically acceptable salt thereof, to a patient. The dextran sulfate, or said pharmaceutically acceptable salt thereof, has an average molecular weight of less than 20,000 Da and an average sulphur content in a range of 10 to 25%, and the inhibition comprises administering said therapeutically effective amount of said dextran sulfate, or said pharmaceutically acceptable salt thereof, resulting in a concentration of said dextran sulfate, or said pharmaceutically acceptable salt thereof, in the blood of said patient of less than 5 mg/ml.
