Cone fusion confusion in photoreceptor transplantation
Advances in stem cell biology have highlighted the potential for the eye as an ideal model in which to understand the mechanisms of neuronal repair. It is therefore not entirely surprising that the first reported allograft from one human to another also occurred in the eye, but over 100 years ago, with the successful corneal transplant performed by Eduard Zirm (1). Later in the 20th Century, Peter Medawar and colleagues identified the mechanism of immune rejection that prevented survival of skin grafts and whole organ transplantation (2). That led to the first successful kidney transplant in 1955 but between identical twins, thereby proving that the process was surgically feasible when host and donor tissue were genetically matched (3). Immune rejection did however remain the major obstacle to allograft transplantation for a number of years until the discovery of cyclosporine by Jean-Francois Borel whilst working for Sandoz Laboratories in 1969 (4). Although the commercial applications were at the time limited, Roy Calne and David White in the UK tested the newly discovered cyclosporine and found that it prevented transplanted organ rejection (5). The drug was subsequently approved by the US Food and Drug Administration (FDA) for use in transplant patients in 1983, thereby revolutionising the success of organ transplantation to the point where it has almost become a routine procedure.