Successful long-term outcome after renal transplantation in a patient with atypical haemolytic uremic syndrome with combined membrane cofactor protein CD46 and complement factor I mutations

CD46 knock-out using CRISPR/Cas9 editing of hTERT immortalized human cells modulates complement activation

The kidney is especially sensitive to diseases associated with overactivation of the complement system. While most of these diseases affect kidney glomeruli and the microvasculature, there is also evidence for tubulointerstitial deposition of complement factors. Complement inactivating factors on cell membranes comprise CD55, CD59 and CD46, which is also termed membrane cofactor protein (MCP). CD46 has been described as localized to glomeruli, but especially also to proximal tubular epithelial cells (RPTECs). However, human cell culture models to assess CD46 function on RPTECs are still missing. Therefore, we here performed gene editing of RPTEC/TERT1 cells generating a monoclonal CD46^-/- cell line that did not show changes of the primary cell like characteristics. In addition, factor I and CD46-mediated cleavage of C4b into soluble C4c and membrane deposited C4d was clearly reduced in the knock-out cell line as compared to the maternal cells. Thus, human CD46^-/- proximal tubular epithelial cells will be of interest to dissect the roles of the epithelium and the kidney in various complement activation mediated tubulointerstitial pathologies or in studying CD46 mediated uropathogenic internalization of bacteria. In addition, this gives proof-of-principle, that telomerized cells can be used in the generation of knock-out, knock-in or any kind of reporter cell lines without losing the primary cell characteristics of the maternal cells.

Complement regulator CD46: genetic variants and disease associations

Membrane cofactor protein (MCP; CD46) is an ubiquitously expressed complement regulatory protein that protects host cells from injury by complement. This type-I membrane glycoprotein serves as a cofactor for the serine protease factor I to mediate inactivation of C3b and C4b deposited on host cells. More than 60 disease-associated mutations in MCP have now been identified. The majority of the mutations are linked to a rare thrombotic microangiopathic-based disease, atypical hemolytic uremic syndrome (aHUS), but new putative links to systemic lupus erythematosus, glomerulonephritis, and pregnancy-related disorders among others have also been identified. This review summarizes our current knowledge of disease-associated mutations in this complement inhibitor.

Primary disease recurrence—effects on paediatric renal transplantation outcomes

Primary disease recurrence after renal transplantation is mainly diagnosed by examination of biopsy samples, but can also be associated with clinical symptoms. In some patients, recurrence can lead to graft loss (7-8% of all graft losses). Primary disease recurrence is generally associated with a high risk of graft loss in patients with focal segmental glomerulosclerosis, membranous proliferative glomerulonephritis, primary hyperoxaluria or atypical haemolytic uraemic syndrome. By contrast, disease recurrence is associated with a limited risk of graft loss in patients with IgA nephropathy, renal involvement associated with Henoch-Schönlein purpura, antineutrophil cytoplasmic antibody-associated glomerulonephritis or lupus nephritis. The presence of systemic diseases that affect the kidneys, such as sickle cell anaemia and diabetes mellitus, also increases the risk of delayed graft loss. This Review provides an overview of the epidemiology, pathophysiology and management of primary disease recurrence in paediatric renal graft recipients, and describes the overall effect on graft survival of each of the primary diseases listed above. With appropriate management, few paediatric patients should be excluded from renal transplantation programmes because of an increased risk of recurrence.