Recurrent FSGS is a risk factor for graft lost: Recurrence of FSGS can occur rapidly, within minutes of transplantation, and can lead to immediate onset of proteinuria and graft dysfunction. Recurrent FSGS is definitively diagnosed with a kidney biopsy. Early kidney biopsies in recurrent FSGS often demonstrate only extensive foot process effacement with the classic focal sclerosis appearing only after months of proteinuria. Recurrent FSGS is the single most important cause of graft failure in patients with FSGS. Patients with recurrent FSGS have significantly decreased graft survival compared to patients without recurrence and often require multiple kidney transplants in their lifetime. A number of clinical risk factors for recurrent FSGS have been identified including prior recurrence, Caucasian race, rapid progression of primary FSGS to ESRD within 3 years, mesangial hypercellularity on primary biopsy and living donor transplant, however these findings are inconsistent among various small studies. 3 A recent study from Europe identified late steroid resistant FSGS (nephrotic syndrome that is initially responsive to steroids, then later resistant) as a strong risk factor for recurrence. These findings have been replicated in our recent retrospective study of a North American cohort from the Midwest Pediatric Nephrology Consortium (N=116) that showed risk of recurrent FSGS was 70.6% in children with late steroid resistant FSGS compared to 35.8% risk in children with initial steroid resistant FSGS (manuscript in preparation). Genetic risk factors for late steroid resistant FSGS are unknown. In the same study Investigators identified native kidney biopsy findings that may predict risk of recurrence. Unfortunately, an individual's risk of recurrent disease cannot be predicted accurately prior to transplant. Thus, patients with FSGS have a high risk of recurrent disease post-transplant that is difficult to predict and patients have poor kidney transplant outcomes.

Plasmapheresis is utilized as a treatment for recurrent FSGS once it occurs: Several therapies for recurrent FSGS have been attempted with varying degrees of success but there remains no proven treatment for recurrent FSGS post-transplant. 7-10 The demonstration of a possible causative circulating factor by Savin et. al. 11 galvanized the field to attempt plasmapheresis to remove 'the permeability factor' as a therapy for recurrent FSGS. Therefore, recurrent FSGS is most often treated with plasmapheresis to remove the circulating factor and this is effective in a subset of patients. The results of uncontrolled single center case reports and series suggest a benefit from plasmapheresis 12-14 although graft loss from recurrent disease remains unacceptably high. Patients who do not respond to plasmapheresis have rapidly progressive chronic kidney disease. These patients have been treated with alternate agents such as rituximab, abatacept, or high dose cyclosporine with variable responses.15-17 Ideally, therapies will be identified to prevent recurrent FSGS before it occurs. Prevention of recurrent FSGS will lead to longer kidney transplant survival and reduced health care costs.

No treatments are available to prevent the recurrence of FSGS after transplant: Since 2005, there have been 3 published studies that have utilized a variety of protocols of plasmapheresis for the prevention of recurrent FSGS with inconsistent results. 18-20 The University of Minnesota pediatric transplant program has utilized pre-emptive plasmapheresis in children at risk for recurrent FSGS since 2006. In a recent review of our data, the incidence of recurrent FSGS post-transplant was not significantly different in patients who had undergone pre-emptive prophylactic plasmapheresis versus historic controls who had not (31% vs. 23%, p 0.5) (manuscript in press). Although this is a retrospective study, the data seems to suggest that plasmapheresis alone is not effective for preventing recurrence of FSGS. In addition, as stated above, the benefit of plasmapheresis in the treatment of recurrence is reported. 12-14 Thus, plasmapheresis with additional preemptive strategies to prevent recurrent FSGS are needed.

Rituximab has been used to treat recurrent FSGS and is a promising novel therapy to prevent recurrent disease. Rituximab is a chimeric monoclonal antibody against CD20 on B cells that leads to B cell depletion that has been used successfully for the treatment of primary steroid sensitive nephrotic syndrome as well as steroid sensitive and resistant FSGS. 21,22 Rituximab may act in FSGS via alterations in B-cell/T-cell interactions leading to changes in cytokine secretion or co-stimulation. Alternately, rituximab may have a direct effect on podocyte structure and function as it has been found to bind directly to the sphingomyelin phosphodiesterase acid-like 3b protein on the surface of podocytes. 23 Recent systematic reviews on the use of rituximab in the treatment of post-transplant FSGS (either with or without plasmapheresis) demonstrate partial or complete remission in \~60% of treated patients.15,24 The use of preemptive rituximab has been reported to be effective in preventing recurrent FSGS in 4 patients at very high risk due to prior graft loss from recurrent disease, however randomized controlled trials have not been performed. 25 Given the effectiveness of rituximab in the treatment of some patients with both primary and recurrent FSGS and the report of successful preemptive use of rituximab in high risk transplant patients, treatment with Rituximab in patients with FSGS prior to kidney transplant is a promising novel therapy to prevent recurrent disease. Preventing recurrent FSGS, rather than treating it once it has already occurred, is likely to minimize graft injury and prolong graft life, therefore preemptive strategies are needed.