Erythrocytes with covalently bound fibrinogen as a cellular replacement for the treatment of thrombocytopenia

Thrombocytopenia in general, and autoimmune thrombocytopenia in particular, is a disease of high prevalence with a non-satisfactory regime of treatment. The present study aimed to explore the feasibility of an alternative treatment, based on the rationale that autologous erythrocytes modified to bear covalently bound fibrinogen would participate passively in the aggregation of the remaining platelets, thus augmenting the haemostatic needs, while resisting the autoimmune reaction directed towards the platelets. Several procedures for the cross-linking of fibrinogen to red blood cells (RBCs) were tested. Formaldehyde (33 microM) for 10 min at 23 degrees C attached 58 fibrinogen molecules per erythrocyte. These erythrocytes were indistinguishable from untreated erythrocytes in the following properties: osmotic fragility, bound haemoglobin, sedimentation rate, acetylcholinesterase activity, phagocytosis by macrophages, rosette formation with K562 cells. It is shown that RBCs cross-linked with fibrinogen are capable of participating in the in vitro aggregation of platelets and are indeed effective in the in vivo process of arrest of bleeding in an animal model of autoimmune thrombocytopenia.