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Rituximab or plasmapheresis for prevention of recurrent focal segmental glomerulosclerosis after kidney transplantation: A systematic review and meta-analysis

BACKGROUND Focal segmental glomerulosclerosis (FSGS) is one of the most common glomerular diseases leading to renal failure. FSGS has a high risk of recurrence after kidney transplantation. Prevention of recurrent FSGS using rituximab and/or plasmapheresis has been evaluated in multiple small studies with conflicting results. AIM To assess the risk of recurrence of FSGS after transplantation using prophylactic rituximab with or without plasmapheresis, and plasmapheresis alone compared to the standard treatment group without preventive therapy. METHODS This meta-analysis and systematic review were performed by first conducting a literature search of the MEDLINE, EMBASE, and Cochrane databases, from inception through March 2021; search terms included ‘FSGS,’ ’steroid-resistant nephrotic syndrome’, ‘rituximab,’ and ‘plasmapheresis,’. We identified studies that assessed the risk of post-transplant FSGS after use of rituximab with or without plasmapheresis, or plasmapheresis alone. Inclusion criteria were: Original, published, randomized controlled trials or cohort studies (either prospective or retrospective), case–control, or cross-sectional studies; inclusion of odds ratio, relative risk, and standardized incidence ratio with 95% confidence intervals (CI), or sufficient raw data to calculate these ratios; and subjects without interventions (controls) being used as comparators in cohort and cross-sectional studies. Effect estimates from individual studies were extracted and combined using a random effects model. RESULTS Eleven studies, with a total of 399 kidney transplant recipients with FSGS, evaluated the use of rituximab with or without plasmapheresis; thirteen studies, with a total of 571 kidney transplant recipients with FSGS, evaluated plasmapheresis alone. Post-transplant FSGS recurred relatively early. There was no significant difference in recurrence between the group that received rituximab (with or without plasmapheresis) and the standard treatment group, with a pooled risk ratio of 0.82 (95%CI: 0.47-1.45, I2 = 65%). Similarly, plasmapheresis alone was not associated with any significant difference in FSGS recurrence when compared with no plasmapheresis; the pooled risk ratio was 0.85 (95%CI: 0.60-1.21, I2 = 23%). Subgroup analyses in the pediatric and adult groups did not yield a significant difference in recurrence risk. We also reviewed and analyzed post-transplant outcomes including timing of recurrence and graft survival. CONCLUSION Overall, the use of rituximab with or without plasmapheresis, or plasmapheresis alone, is not associated with a lower risk of FSGS recurrence after kidney transplantation. Future studies are required to assess the effectiveness of rituximab with or without plasmapheresis among specific patient subgroups with high-risk for FSGS recurrence.


INTRODUCTION
Focal segmental glomerulosclerosis (FSGS) is an important glomerular cause of endstage kidney disease, and is associated with a high risk of disease recurrence after kidney transplantation [1][2][3][4][5]. Approximately 30% of patients [6,7] develop recurrent FSGS following kidney transplantation, with studies reporting a range between 17% and 55% [8]. FSGS has been shown to negatively affect overall graft survival [9][10][11][12]. Although the exact pathogenesis of this disease is unknown, it is believed that circulating factors affecting podocytes and glomerular permeability may play an important role. FSGS recurrence presents early after kidney transplantation; thus, supporting the pathophysiological role of circulating factors.
Treatment for recurrent FSGS in kidney transplant recipients is difficult. Steroids have been used as the main therapy in adults. Unfortunately, only 50% of patients achieve remission following a course of steroid treatment [13]. Furthermore, a large proportion of patients relapse, eventually becoming either steroid-resistant, or steroiddependent [14]. Plasmapheresis has been effectively used to treat recurrent FSGS after kidney transplantation, purportedly by removing pathophysiological circulating factors and inducing FSGS remission. Preemptive plasmapheresis following kidney transplantation has been proposed as a preventive measure for FSGS.
Rituximab is a monoclonal, chimeric antibody against CD20+ B lymphocytes, and has been used to both prevent and treat recurrent FSGS after kidney transplantation. In 2020, Hansrivijit and Ghahramani [15] reported promising outcomes after treatment of recurrent FSGS in kidney transplant recipients, using either a combination of rituximab and plasmapheresis, or plasma exchange alone. Their study demonstrated an overall remission rate of 72.7%, determined by a significant reduction in serum creatinine levels and the degree of proteinuria. Nevertheless, the efficacy of rituximab or plasmapheresis as a preventive measure for post-transplant recurrent FSGS remains controversial.
This systematic review and meta-analysis were conducted to explore the effectiveness of rituximab-with or without plasmapheresis-compared with plasmapheresis alone, for the prevention of recurrent FSGS after kidney transplantation.

Search strategy
This systematic review was conducted in accordance with the Meta-analysis of Observational Studies in Epidemiology guidelines [16]. A literature search was performed to identify studies that investigated the effect of preventive use of plasmapheresis and/or rituximab on the risk of recurrent FSGS after kidney transplantation. This was independently conducted by two investigators (Boonpheng B and Hansrivijit P) in the MEDLINE, EMBASE, and Cochrane databases, from inception through March 2021. Search terms included 'FSGS', 'steroid-resistant nephrotic syndrome', 'rituximab', and 'plasmapheresis'. The references of selected articles were manually searched for additional relevant studies. There were no language restrictions.

Inclusion criteria
Studies were eligible for inclusion if they met the following criteria: (1) Original, published, randomized controlled cohort (either prospective or retrospective), casecontrol, or cross-sectional studies; (2) The odds ratio, relative risk, and standardized incidence ratio with 95% confidence intervals (CIs), or sufficient raw data to calculate these ratios, were provided; and (3) Subjects without interventions (controls) were used as comparators in cohort and cross-sectional studies.
Study eligibility was independently assessed by the investigators. Any disagreements were resolved through mutual consensus. The quality of each study was assessed utilizing the Newcastle-Ottawa Quality Scale [17]. This scale assesses each study using three categories: (1) The representativeness of the subjects; (2) The comparability between the study groups; and (3) Ascertainment of the exposure or July 18, 2021 Volume 11 Issue 7 outcome of interest for case-control and cohort studies respectively.

Review process and data extraction
Two investigators independently reviewed the titles and abstracts of all retrieved articles. Articles that did not fulfill the inclusion criteria were excluded. Only potentially relevant articles underwent full-text reviews to determine eligibility. A standardized data collection form was used to extract the following data: First author's name, year of publication, year of study, country of origin, study design, source of population, number of subjects, baseline characteristics of the subjects, and effect estimates. This data extraction process was performed in duplicate to ensure accuracy.

Statistical analysis
All statistical analyses were performed using R version 3.2.0 (the R Foundation for Statistical Computing, Vienna, Austria). The pooled risk ratios for recurrent FSGS in the active intervention group compared with the no intervention group were calculated using the generic inverse method of DerSimonian and Laird [18]. A random effects model was utilized given the high likelihood of between-study variance due to differences in underlying population as well as methodology. Cochran's Q-test, supplemented by the I 2 statistic, was used to evaluate statistical heterogeneity. This statistic quantifies the proportion of total variation across studies due to true heterogeneity rather than chance. An I 2 value of 0-25% represented insignificant heterogeneity, 25%-50% represented low heterogeneity, 50%-75% represented moderate heterogeneity, and > 75% represented high heterogeneity [19].

RESULTS
The initial search yielded 813 articles, all of which underwent both title and abstract reviews. Most were excluded at this step as they did not fulfill our inclusion criteria; i.e., they were case reports, letters to the editor, review articles, or interventional studies. A total of 38 studies underwent full-length article review. Of 17 were excluded, as they did not include controls or report the outcome of interest. A total of 21 observational studies, including 920 patients, met our inclusion criteria [8,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] and were included in the meta-analysis. Figure 1 outlines our search methodology and selection process. The baseline characteristics of the included studies are summarized in Tables 1-4 (detailed characteristics in Tables 3 and 4).
Four studies [24,[29][30][31] selected only patients deemed to be at high-risk of recurrence, based on demographic and clinical criteria. Only the study by Fornoni et al [24] showed a significantly lower recurrence risk in the rituximab group. The remaining three studies reported a numerically higher recurrence in the rituximab group[29-31].
Sensitivity analysis, after excluding three studies [25,27,34] that were published as abstracts and did not report the protocol or regimen of plasmapheresis, did not show a significant change in the risk ratio (1.07, 95%CI: 0.66-1.72, I 2 =22%).  [8] reported the median time to recurrence as 3 and 1.5 mo, respectively. Overall, this data supports the hypothesis that pre-existing circulating factors play a role in FSGS recurrence.

Effects on allograft function
Some studies reported decreased allograft survival in patients who experienced FSGS recurrence compared to those who did not [8,26,[31][32][33]35,39]. Allograft survival appears to depend on response to recurrent FSGS therapy, which variably consists of plasmapheresis with more intensive immunosuppressive regimens. Neither preemptive plasmapheresis or rituximab per se seems to have effects on allograft survival.

Evaluation for publication bias
The funnel plots for the outcomes of rituximab and plasmapheresis are shown in Figures 4 and 5, respectively. They are symmetrical, and do not suggest the presence of publication bias in favor of positive studies. Egger's asymmetry test yielded Pvalues of 0.56 and 0.83 for the rituximab and the plasmapheresis groups, respectively.

DISCUSSION
Primary FSGS often recurs after kidney transplantation, leading to graft loss and morbidity [6][7][8]  to present early and rapidly after kidney transplantation supports the pathophysiologic role of circulating factors [43]. Case reports of successful kidney allograft transfers from recipients with severe, early, refractory recurrent FSGS, to recipients without a history of primary FSGS, also indirectly suggest the role of circulating factors in disease recurrence [44,45]. Plasmapheresis is considered an effective treatment able to induce remission in established recurrent diseases [46]. Likewise, plasmapheresis has been used as a prevention of FSGS after kidney transplant. By rapidly removing pre-existing circulating factors, especially in conjunction with immunosuppressive medication, it is presumed that some of the putative circulating factors can be eliminated or suppressed to the level low enough not to affect glomerular permeability. Plasmapheresis is performed prior to kidney transplantation in an attempt to prevent FSGS recurrence and associated allograft injury, which may affect graft survival [9,10].
More recently, rituximab has been effectively used to treat many glomerular diseases, including FSGS [47]. The exact mechanism of rituximab in the treatment of FSGS is unknown; however, it is believed that rituximab may have a B-cell-independent effect on podocyte cytoskeletal stabilization, in addition to its B-cell depleting effects [48]. Therefore, rituximab is also utilized to prevent FSGS recurrence, either alone or in combination with plasmapheresis.
Our meta-analysis is among the first to report that the use of preemptive rituximab (either alone or in combination with plasmapheresis) or plasmapheresis alone did not alter the recurrence risk of FSGS after kidney transplantation. To increase power, we combined the patients who received rituximab alone and those who received both rituximab and plasmapheresis into the same group. This might have overestimated the effect of rituximab. However, sensitivity analyses in the subgroup that received rituximab alone or rituximab with plasmapheresis did not change the association so this is unlikely to be significant. The timing of recurrence was also not affected by the preventive measure. In contrast, rituximab and plasmapheresis have been shown to be effective for the treatment of recurrent FSGS after kidney transplantation. The efficacy and safety of combined rituximab and plasmapheresis in patients with recurrent FSGS was recently demonstrated in a meta-analysis, reporting that up to 72.7% of patients achieved remission [15]; of these, most patients achieved complete remission. The   authors also described a significant reduction in serum creatinine levels (-0.65 mg/dL) and proteinuria (-4.79 g/d) following treatment [15]. Many studies suggest that recurrent FSGS in kidney transplant recipients is at least partially mediated by circulating factors and/or antibodies [43]. The ineffectiveness of prophylactic rituximab in the prevention of FSGS via suppression of antibody production, or plasmapheresis in the removal of pre-formed circulating factors, suggests either circulating factors may be inactive in quiescent FSGS or that removing the putative circulating factors may not be enough to prevent the immunologic cascades that trigger the onset of disease recurrence. It is possible that yet-to-beidentified B-cell-independent immunologic factors may trigger the onset of FSGS recurrence, which leads to production of circulating factors and stimulation of B cells, which are targeted by plasmapheresis and rituximab. The fact that patients who developed FSGS recurrence despite pre-emptive plasmapheresis or rituximab still responded well to plasmapheresis with or without rituximab supports that the initial triggering event is not the putative circulating factors per se and is likely B-cell independent.
Beyond plasmapheresis and rituximab, low-density lipoprotein (LDL) apheresis has been evaluated as a preventive strategy for recurrent FSGS in a Japanese study [49]. LDL apheresis removes plasma lipids, a source of oxidative stress, as well as multiple circulating humoral factors that contribute to disease recurrence. The authors reported no FSGS recurrence in five patients using this regimen of pre-transplant LDL apheresis, in addition to rituximab and basiliximab induction; however, this finding should be confirmed by larger studies.
The results of this meta-analysis should be interpreted with attention to the study limitations. First, all included studies were observational in design; thus, the risk of    bias was present, and causality could not be established. Second, the sample size of most studies was small. Third, some studies did not report patient characteristics or prognostic factors. Fourth, the treatment regimen, dose of rituximab, and plasmapheresis protocol (frequency, duration, and volume of exchange) were not standardized. Fifth, the use of induction and background immunosuppression varied across studies, depending on the institutional protocol and era of medication availability. Finally, as evidenced by the widely varying recurrence risks reported, it is possible that the different studies enrolled FSGS patients with inherently varying risk of recurrence, resulting in further difficulties regarding the interpretation of posttransplant risk; the eligibility criteria were heterogeneous. Efforts to elucidate the pathogenic mechanisms of FSGS are ongoing. Further clinical research is therefore required, both to accurately identify the subgroup of patients with FSGS who are at a higher risk for disease recurrence, as well as evaluate preventive interventions within this subgroup. At the time of writing, one ongoing randomized controlled trial (clinical trial number: NCT03763643) was identified, with the primary endpoint of preventing recurrent FSGS through the use of preemptive rituximab plus plasmapheresis or plasmapheresis alone.

CONCLUSION
In unselected patients with FSGS, preemptive rituximab with or without plasmapheresis, or plasmapheresis alone, was not associated with a lower risk of FSGS recurrence after kidney transplantation. July 18, 2021 Volume 11 Issue 7

Research background
Focal segmental glomerulosclerosis (FSGS) is one of the most common glomerular diseases leading to kidney failure. FSGS has a high risk of recurrence after kidney transplantation. Prevention of recurrent FSGS using rituximab and/or plasmapheresis has been evaluated in multiple small studies with conflicting results.

Research motivation
FSGS is associated with a high risk of recurrence after kidney transplantation. Plasmapheresis and/or rituximab has been used to prevent recurrence with conflicting results.

Research objectives
This meta-analysis was conducted to assess the effectiveness of rituximab-with or without plasmapheresis-compared with plasmapheresis alone, for the prevention of recurrent FSGS after kidney transplantation.

Research methods
This meta-analysis and systematic review were performed by first conducting a literature search of the MEDLINE, EMBASE, and Cochrane databases, from inception through March 2021; search terms included 'FSGS', 'steroid-resistant nephrotic syndrome', 'rituximab', and 'plasmapheresis'. We identified studies that assessed the risk of post-transplant FSGS after use of rituximab with or without plasmapheresis, or plasmapheresis alone.

Research results
Eleven studies, with a total of 399 kidney transplant recipients with FSGS, evaluated the use of rituximab with or without plasmapheresis; thirteen studies, with a total of 571 kidney transplant recipients with FSGS, evaluated plasmapheresis alone. Posttransplant FSGS recurred relatively early. There was no significant difference in recurrence between the group that received rituximab (with or without plasmapheresis) and the standard treatment group, with a pooled risk ratio of 0.82 [95% confidence intervals (CI): 0.47-1.45]. Similarly, plasmapheresis alone was not associated with any significant difference in FSGS recurrence when compared with no plasmapheresis; the pooled risk ratio was 0.85 (95%CI: 0.60-1.21). Subgroup analyses in the pediatric and adult groups did not yield a significant difference in recurrence risk. We also reviewed and analyzed post-transplant outcomes including timing of recurrence and graft survival.

Research conclusions
The use of rituximab with or without plasmapheresis, or plasmapheresis alone, is not associated with a lower risk of FSGS recurrence after kidney transplantation.

Research perspectives
This meta-analysis is among the first to report that the use of preemptive rituximab, either alone or in combination with plasmapheresis, or plasmapheresis alone, did not alter the recurrence risk of FSGS after kidney transplantation.