Transplantation of cultured thymic fragments. I. Morphologic and technical considerations.

Thymic fragments were maintained in organ culture until egress or deterioration of the leucocyte component was near completion. These depopulated cultured thymic fragments were then implanted into immunologically competent mouse recipients. Acute immunologic rejection was not observed in mice given cultured thymic allografts. If the organ culture period was approximately 2 weeks, lymphoid repopulation and newly developed Hassall's corpuscles were observed 7-10 weeks after implantation. If the initial culture period was extended to 3 weeks, transplanted fragments developed as unusual repopulation pattern, characterized by eosinophils, macrophages and plasma cells. This finding could be interpreted as a protracted allograft rejection or, more likely, a loss of ability of the thymic epithelium to attract or differentiate the types of precursors usually attracted to the normal gland. When cultured and non-cultured tissues were simultaneously transplanted in a single recipient, the non-cultured tissue was acutely rejected and became fibrous, while the cultured thymus assumed the appearance of a normal lymphoid organ without any neighbouring inflammatory reaction.