Focal segmental glomerulosclerosis (FSGS) is the leading cause of nephrotic syndrome in adults and commonly progresses to end-stage renal disease (ESRD). FSGS is known to recur after kidney transplantation. FSGS is either idiopathic (ie, primary) or secondary to a variety of etiologies, such as genetic, infections, drugs, and adaptive. In general, only idiopathic FSGS recurs after kidney transplantation. The etiology of idiopathic FSGS remains unknown. However, circulating permeability factors have been suggested in the pathogenesis. The rate of posttransplant idiopathic FSGS recurrence after transplantation is not well defined but it is reported to average around 30%.1-4
Several studies have attempted to identify risk factors for FSGS recurrence. White race, young age at presentation, low serum albumin, mesangial hypercellularity on initial biopsies, rapid progression to ESRD, and pervious failed transplant due to FSGS recurrence, all have been described as risk factors for posttransplant FSGS recurrence.2,5-11
FSGS recurrence is associated with poor outcomes and a graft loss rate as high as 60%.12,13 Management of FSGS recurrence remains a great clinical challenge. Therapeutic plasma exchange (TPE) is the current standard of care with success rate of around 50%.13-15 Rituximab, which is a monoclonal antibody directed against CD-20 expressed in B-lymphocytes, has been used in posttransplant FSGS recurrence. Its beneficial effect on posttransplant FSGS recurrence was reported initially in 2006.16 Subsequently, only few studies14,17-20 have assessed the efficacy of rituximab in the prevention and treatment of FSGS recurrence.
In this article, we report the results of an observational prospective cohort study to evaluate risk factors for posttransplant FSGS recurrence, to describe its course, and to determine the efficacy of rituximab and TPE in its prevention and treatment.
MATERIALS AND METHODS
This a prospective observational cohort study that included patients with ESRD secondary to FSGS who underwent kidney transplantation at our institution. Inclusion criteria for the study are as follows: (1) diagnosis of idiopathic FSGS as original disease or patients who developed “de novo” FSGS after transplant but their pretransplant course is very suggestive of idiopathic FSGS; (2) age, 18 years or older; (3) agree to participate in the study. Double organ transplantation recipients were excluded from the study. The study was approved by the institutional review board at our center. Table 4 shows the type of FSGS in the native kidney.
Subjects who are deemed high risk for recurrence after kidney transplantation received preventative therapy that includes TPE and/or rituximab. We also, evaluated subjects’ response to the preventive therapies and the treatment methods in those who developed recurrence. Response to therapy is defined as reduction of proteinuria to less than 1 g/g. At the end of the study, we assessed risk factors for recurrence and created a 5-point clinical score to predict FSGS recurrence postkidney transplantation and assessed its ability to predict FSGS recurrence.
The study included total of 66 patients; 64 patients with the diagnosis of idiopathic FSGS in their native kidneys and 2 patients who developed “de novo” FSGS after transplant but had a pretransplant course very suggestive of idiopathic FSGS. The transplants were performed between September 2008 and December 2015. Table 1 shows the patients’ characteristics. Donor and baseline recipient clinical variables were collected prospectively and from medical records. Patients were followed up as per routine posttransplant care. Clinical and laboratory variables are collected periodically throughout the follow-up period.
We performed our statistical analyses using STATA 13 statistical software (StataCorp LP, College Station, TX). Descriptive statistics were used to estimate the frequencies, means, medians, and proportions of the study variables. We checked normality of distribution for continuous variables using box plots, normal probability plots, and Shapiro-Wilk normality test. Continuous data were expressed as median and range or mean and standard deviation. We used survival analysis/Kaplan-Meier curve to present all allograft survivals. We used Cox regression models to compare between the recurrence and nonrecurrence groups. Area under the receiver operator curves that predicted recurrence for different values of the scoring system was used. P value less than 0.05 is considered statistically significant.
The study included total of 66 patients. Mean age at diagnosis of FSGS was 29.9 years (range, 18-59 years). Thirty-four (51%) patients were male. Thirty-seven (56%) patients of our cohort were whites, 21 (32%) were African American, 5 (7%) were Asian, and 3 (4%) were Hispanic. The median time from diagnosis of FSGS to initiation of the first renal replacement therapy was 4 years (range, 0-9 years). Data on the treatment of FSGS in the native kidneys were available in 55 patients; 28 (55%) of them received immunosuppressive therapy in the form of corticosteroids, calcineurin inhibitors, cyclophosphamide, or combination of these therapies. In 42 (64%) of the 66 patients this was their first kidney transplantation. In 15 (22%) this was the second, in 7 (10%), this was their third, and in the remaining 2, this was their fourth transplantation. Twenty-five (37%) patients received their allografts from living unrelated donors, 16 (25%) received their allografts from living related donors, and 25 (37%) received their allograft from a deceased donors. Forty-four (65%) recipients were cytomegalovirus immunoglobulin G positive at the time of transplant. Median duration of follow-up from time of transplantation was 29.5 months.
In regard to the therapies used to prevent FSGS recurrence, 37 (57%) received perioperative rituximab and 28 (44%) received both perioperative rituximab and TPE therapies. Rituximab was given in 1 or 2 doses (375 mg/m2 per dose). The perioperative TPE sessions were started anytime between day 7 before transplant to postoperative day 2, depending on the source of donor and the availability of vascular access; and continued for 3 to 10 sessions. Patients were elected to receive a preventative therapy based on their pretransplant risk of recurrence. Risk factors taken into account were white race, young age at presentation defined by disease onset at younger than 30 years, rapid disease progression defined by development of ESRD within 5 years of disease onset in the native kidney, albumin level of less than 3 g/dL during the disease course, and history of failed kidney transplantation due to FSGS recurrence. Patients who had 2 risk factors were deemed high risk and recommended to receive preventative therapy with TPE and rituximab. Nine patients did not receive TPE due to lack of vascular access or due to patients' or providers' preference. Out of the patients who were deemed low risk, 6 received a form of preventative therapy because of presence of donor-specific antibodies at the time of transplant (Table 2).
Excluding patients with de novo FSGS after transplant, 38 (59%) experienced recurrence of FSGS after transplant. Median time to recurrence was 1.25 months (range, 1 day to 30 months). Mean urine protein-creatinine ratio at time of recurrence was 5.81 gram/gram (g/g) of creatinine, with range of 2.1 to 17 g/g. Twenty-three (62%) of the 37 patients who received a preventative therapy developed recurrence. On the other hand, 14 (51%) of the 27 patients who did not receive a preventative therapy developed recurrence. The difference between the 2 groups was not statistically significant (hazard ratio [HR], 1.714; confidence interval [CI], 0.62-4.71; P = 0.21).
The 2 patients who had de novo FSGS after transplant developed proteinuria at 7 and 64 months after transplant. Their allograft biopsies showed severe podocyte effacement (more than 50%). Table 3 shows these 2 patients’ characteristics.
All patients with recurrent FSGS received kidney biopsy to confirm the diagnosis except 1 patient. Table 4 shows all biopsy data before and after transplant.
We assessed the association between several clinical variables and FSGS recurrence, and we created a clinical scoring system to predict FSGS recurrence. The system included 5 clinical parameters with 1 point for each one of them. The clinical parameters are: white race, young age at presentation defined by disease onset at younger than 30 years, rapid disease progression defined by development of ESRD within 5 years of disease onset in the native kidney, albumin level of less than 3 g/dL during the disease course, and history of failed kidney transplantation due to FSGS recurrence. When analyzed as a single factor, we did not detect an association between race, sex, age at diagnosis, time to ESRD, and source of transplant, and risk of recurrence (Table 5). However, when analyzed the performance of the clinical scoring system in predicting FSGS recurrence, the calculated area under the curve (AUC) was 0.7227 when using a score of 3. Using a score of 2, the AUC is 0.614 and using a score of 4, the AUC is 0.581. Figure 1 shows area under the receiver operator curves for the scoring system performance to predict FSGS recurrence.
Treatment and Outcome of Recurrence
All patients who experienced FSGS recurrence and the 2 patients with de novo FSGS received standardized treatment composed of TPE and low-dose IVIg (200 mg/kg). Additionally, 20 (50%) patients received rituximab. TPE course consisted of at least 10 sessions. The first 3 to 5 sessions were daily and followed by IVIg. The remaining sessions were scheduled 3 times a week, 2 of which were followed by IVIg. We used replacement fluids of 100% albumin. TPE sessions are continued for at least 10 sessions. We stop the treatment after that if there is response to treatment (defined by decrease in proteinuria by >50%). Eight patients needed a longer course of TPE (range, 16-35 sessions) at a weaning schedule. Four additional patients required much longer term TPE that has been going on for 1 to 2 years to keep FSGS in remission. These 4 patients received TPE on 1 session every a 2- to 3-week schedule. Thirty-five (87%) patients were placed on angiotensin-converting enzyme inhibitor (after the completion of TPE) or angiotensin receptor blocker. All but 5 (87%) responded to this initial therapy. Four (10%) patients lost their allografts due to FSGS recurrence. These 4 did not receive rituximab.
Fourteen (40%) of the 35 responders developed at least 1 relapse after the initial treatment and 2 of them lost their allograft. There were more relapses in the patients who did not receive rituximab at the time of recurrence (9/18 vs 6/22; HR, 0.285; CI, 0.069-1.167; P = 0.066). Nine of the relapses were observed in patients who did not receive rituximab at the initial treatment.
There were 8 total allografts losses; 4 due to the initial recurrence, 1 due to cardiovascular death, 2 due to subsequent relapse, and 1 due to rejection.
Table 6 shows the differences in serum Creatinine, estimated glomerular filtration rate (eGFR) (calculated by CKD-EPI equation), serum albumin, and urine protein creatinine ratio between the groups of recurrence and without recurrence at the end of the study. Serum creatinine and urine protein-creatinine ratio were higher, and eGFR was lower in the recurrence group. Survival analysis showed that there was a trend toward better renal allograft survival in nonrecurrent group compared to the recurrent group (P log rank of 0.0662) (Figure 2).
Our study is one of the largest prospective studies that describes the natural course of FSGS after transplant and gives insight on the efficacy of using interventions such as TPE and rituximab in the prevention and treatment of posttransplant FSGS recurrence. Idiopathic FSGS remains a challenge to transplant centers because of its high risk of recurrence and associated poor outcomes. Although several studies have assessed different therapies to prevent and treat FSGS recurrence, most of them were small, and more importantly, they included a mixture of FSGS type. Therefore, larger studies that include only patients with idiopathic FSGS are needed so transplant centers can develop strategies to manage such patients. Our study included only patients with high degree of certainty of having idiopathic FSGS.
The etiology of idiopathic FSGS is still unknown. Circulating permeability factors have been suggested in the pathogenesis.21 This is based on the observation of development of proteinuria within hours after transplantation and response to TPE.22-24 In 1 case, kidney transplant recipient developed early recurrence of FSGS with evidence of foot process effacement on biopsy that resolved after retransplanting the same kidney into a second recipient.24 The identity of the circulating permeability factor is yet to be determined, although the serum soluble urokinase receptor has been suggested in several studies.21 Regardless of the type of this factor, TPE seems to be effective in removing it, and therefore, it has been used in its treatment and suggested as a preventative therapy.
The rate of idiopathic FSGS recurrence after transplantation has been difficult to ascertain. In most of the published studies, it is challenging to determine whether FSGS is idiopathic or secondary. The reported FSGS recurrence rate in most of these studies averages approximately 30%.1-4 However, this rate is probably an underestimation given the reasons mentioned above. In our study, which included only patients with idiopathic FSGS, the observed recurrence rate was 59%. This is much higher than what has been previously published. For example, the reported recurrence rate in the European Renal Association-European Dialysis and Transplant Association registry was 24%.25 In a cohort of thirty highly selected idiopathic FSGS patients, the reported recurrence rate was 47%.14
A number of factors have been reported to be associated with an increased risk of recurrence. Patients who develop ESRD rapidly after the onset of the disease are at higher risk compared to those who had their disease for a longer period of time.2,5,6 White race has also been described as a risk factor.3,9 Mesangial hypercellularity on initial renal biopsy has also been described as a risk factor for recurrence.6,7 Patients with recurrence tended to be younger at the onset of the disease when compared with those without recurrence.6,8,9 Also, recurrence of FSGS in previous transplants has been identified as a risk factor.2 Although earlier reports suggested that collapsing FSGS tend to recur more, later studies did not support this finding.10 Lower albumin level is associated with increased risk of recurrence11 and worse outcome.3 We have developed a predictive clinical scoring system that incorporates the most studied risk factors in addition to our clinical observation, to help identify patients with the highest risk of recurrence. Our study is the first one to develop a prediction clinical scoring system. We assessed its prediction for development of FSGS recurrence and we found that using a score of 3 and above, the calculated AUC was 0.7227. This suggests that this system is a fair test to predict risk for posttransplant FSGS recurrence. However, because of the relatively small number of patients, we acknowledge that the scoring system needs to be validated on larger cohorts once such cohorts are available.
There is no proven therapy that has been effective in preventing posttransplant FSGS recurrence. Several studies used TPE and/or rituximab as preventative strategies. TPE has been used for this purpose with variable success. In one study, TPE did not reduce the incidence of FSGS recurrence.26 Rituximab is a chimeric mouse/human monoclonal antibody directed against CD-20 expressed on B-lymphocytes. Rituximab has several applications in treating glomerular conditions, such as acute allograft rejection and nephrotic syndrome. The mechanism by which rituximab affects the FSGS course does not seem to be related to its anti CD-20 activity.19 In vitro studies showed possible cross-reactivity of rituximab with sphingomyelin-phosphodiesterase-acid-like-3b27 and in vitro exposure to rituximab in lymphoma cells regulates the activity of acid-sphyngomyelinase in raft microdomains. These are essential for the organization of receptors and signaling molecules in highly specialized cells such as the podocytes.18 Its beneficial effect on posttransplant FSGS recurrence was reported initially in 2006.16 Subsequently, only few studies assessed the efficacy of rituximab in prevention of FSGS recurrence.17,19,20 However, these studies included only a small number of patients. In one study, rituximab treatment was associated with a lower incidence of posttransplant proteinuria and stabilization of glomerular filtration rate.19 In another study, rituximab was effective in preventing FSGS recurrence in 4 patients who had failed previous kidney transplants due to FSGS recurrence.17
In our study, we did not observe a difference in the rate of posttransplant FSGS recurrence between patients who received a preventative therapy and those who did not (62% vs 51%, P = 0.21). However, this should be interpreted with caution because patients who received preventative therapy were deemed to have a higher risk for recurrence.
The observed average response rate of TPE is 50% to 70% in published literature.13,14,23 We observed a higher rate of response to TPE 87% (35/40). From those 35 patients, 14 needed a long course or became TPE dependent. Half of the patients received rituximab at the time of recurrence. The high response rate to TPE, although it is difficult to prove, could be explained by the additive use of rituximab.
Among patients who responded initially to treatment, 40% developed recurrence. There was a trend toward more relapses in patients who did not receive rituximab at initial recurrence. This is consistent with the findings of Hickson et al14 in which the 4 patients with FSGS recurrence who received TPE at recurrence and rituximab therapy at some time posttransplant sustained remission of proteinuria as well as stable graft function. Graft survival was inferior in patients who developed recurrence compared to those who did not. There were a total of 8 graft losses in the recurrence group, 6 of which were due to FSGS recurrence.
Our study has limitations. Although our data constitute one of the largest prospective analyses of recurrent FSGS postkidney transplant, however it remained small sized study, and a larger multi centers prospective is required to validate the clinical score and the outcome of prevention and therapies that we used in our cohort. Additionally, there are possibly other clinical factors that may predict FSGS recurrence; however, the parameters we utilized in our clinical score were the most relevant and significant in previously published data and our clinical observation.
For different logistic reasons, we were unable to enroll in our study all FSGS patients who were transplanted in our center; in particular patients without recurrence. Therefore, it is possibly that the rate of recurrence is less than the reported rate. Furthermore, complete data of the native biopsies were unavailable to us despite all the effort to obtain these data. A large number of these biopsies were performed in other centers and many years in the past. We have relied on the patients’ nephrology record to confirm the diagnosis of FSGS in native kidney. Another limitation of our findings is the fact that the therapies are heterogeneous and not randomized, the reason is that the therapies depended on patient’s response. Some patients responded to short course of TPE and 1 dose of rituximab; hence the recurrent FSGS therapies were stopped completely and patients were maintained on angiotensin-converting enzyme inhibitor or angiotensin receptor blocker. However, some patients required longer duration of TPE and more than 1 dose of rituximab.
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