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Diabetologia (1991) 34:390-396 0012186X9100086Q Diabetologia y Springer-Verlag 1991 Transplantation of purified islet cells in diabetic BB rats D. Pipeleers 1, M. Pipeleers-Marichal 2, H. Markholst 3, A. Hoorens 2 and G. Kl6ppel 2 Department of Metabolism and Endocrinology, 2 Department of Pathology. Vrije Universiteit Brussel, Brussels, Belgium and Hagedorn Research Laboratory, Gentofte, Denmark Summary. The ability to prepare purified islet Beta-cell ag- gregates was used to examine the survival of this cell type after allotransplantation in diabetic BB rats. The aggregates were intraportally implanted in numbers that were pre- viously found to correct a streptozotocin-induced diabetic state in syngeneic or allogeneic Brown Norway recipients. When the grafts were prepared from RT1 ~ donors, which shared the MHC-class I antigen with the BB recipients (RTle~ their implant sites became diffusely infiltrated by inflammatory cells and their metabolic function was com- pletely lost within 5 weeks. MHC-class I incompatible islet Beta-cell allografts (RT1 n~n) exhibited a longer survival, in particular when combined with other islet endocrine cells and/or when covered by a 5-week cyclosporin treatment. In the latter combination, 10 of 12 BB rat recipients remained normoglycaemic over the 10-week observation period, their liver implants presenting a comparable insulin reserve and similarly discrete mononuclear cell infiltration as streptozo- tocin-diabetic Brown Norway rats receiving this treatment. However, administration of cyclosporin to diabetic BB rats was associated with a morbidity that was not observed in drug-treated streptozotocin-diabetic Brown Norway ani- mals or in untreated diabetic BB rats. It is concluded that MHC-incompatible islet Beta cells can induce a long-term normalization in diabetic BB rats provided that they are im- planted under conditions which allow allograft acceptance. The standardized preparation of purified islet Beta-cell grafts can help assessing the conditions for successful trans- plantations in diabetes with an autoimmune origin. Key words: Transplantation, diabetes mellitus, islet cells, BB rats, cyclosporin. Purified endocrine rat islet cells survive transfer across a major histocompatibility barrier markedly better than un- purified islet preparations [1]. As a result of this property, allografts of purified islet cell aggregates can maintain a long-term normoglycaemia in animals with chemically-in- duced diabetes [1]. The implants elicit a mononuclear cell infiltration but the immune response is mild and delayed [1] and hence suppressable by short-term cyclosporin treatment [2]. In addition to their lower immunogenicity, purified islet cell aggregates offer the advantage of a stan- darized preparation, the size and cellular composition of which can be precisely determined in vitro [3]. For these reasons, they appear more appropriate than previously used preparations in assessing the applicability of islet cell transplantation in autoimmune diabetes. In this form of the disease, destructive processes against pancreatic Beta cells can recur as soon as a new pool of islet Beta cells is presented to the immune system [4, 5]. The reappearance and severity of the autoimmune phenomena may, how- ever, depend on the number of grafted Beta cells, on their immunogenicity as well as on the simultaneous transfer of other cell types. Each of these variables can be tested sep- arately with in vitro constructed islet cell implants of se- lected size and cellular composition. In the present study, we have examined whether allografted islet Beta cells can survive after implantation in diabetic BB rats, which are known to have developed autoimmune reactions against their own pancreatic Beta cells [6]. The grafts were com- posed of a fixed number of islet Beta cells that were puri- fied from rat strains with or without disparity in MHC- class I antigens. Materials and methods Preparation of donor tissue Donor tissue was prepared from adult male rats (200-300 g body weight) of the inbred R/A (RTI-p ua, identical in defined histocom- patibility antigens to the RP strain, formerly R1) strain and of the in- bred Brown Norway (BN) (RTI-n njn) strain (colonies of Heverlee, Belgium, [3]). We recently described the methods used for the isola- tion of islets and the preparation of islet cell aggregates composed of