The present invention refers to use of dextran sulfate, or a pharmaceutically acceptable derivate thereof, for manufacturing of a medicament for treatment of Instant Blood-Mediated Inflammatory Reaction (IBMIR). In addition, the invention refers to the use of dextran sulfate, or a pharmaceutically acceptable derivate thereof, for manufacturing of a medicament for treatment of morphological disruption of cell transplants and graft-rejection of cell transplants caused by IBMIR. The invention may be applied to patients suffering from type I diabetes, in which porcine islets of Langerhans are transplanted in their portal vein. Administration of dextran sulfate according to the invention inhibits and prevents rejection and destruction of the transplanted islets and makes normoglycemia in the patients possible.
