Rituximab’s Impact on Antibody-Mediated Rejection After Kidney Transplant: Clinical and Pathological Outcomes

In this retrospective study, we aimed to compare the effects of incorporating rituximab into the standard therapeutic regimen on clinical and histopathological improvement in patients with biopsy-proven AMR. The efficacy of rituximab in the treatment of antibody-mediated rejection remains a subject of ongoing debate in the current literature, and despite some promising findings, its role in AMR management continues to be an area of active investigation.

In our study, rituximab was preferentially administered to patients exhibiting pre-transplantation Class I PRA positivity, who are considered to have a higher immunological risk. The existing literature indicates that patients with elevated Class I PRA titers have an increased risk of antibody-mediated rejection and subsequent graft loss following transplantation[[11, 12]. Furthermore, rituximab treatment was primarily favored in patients who developed early AMR within the first 30 days post-transplantation. Our rationale for this approach is based on the understanding that rituximab may provide an effective intervention by suppressing the immune response in the early stages of AMR[[13]. The literature supports this strategy, as rituximab has been reported to be particularly beneficial in patients with high immunological risk and early rejection, where it aids in controlling the immune response by targeting B cells. Early rejection is believed to progress rapidly, and rituximab may potentially prevent graft damage by exerting its effects swiftly during this critical phase.

In this study, the more favorable findings in the rituximab-treated group were the improvement in both short-term renal indices (trend in ∆SCr and ∆eGFR) and lower SCr at the end of the follow-up. However, these findings should be interpreted with caution, because the follow-up period was significantly shorter in the rituximab-treated group, and it should be taken into account that the difference in serum creatinine levels between the groups may decrease with further follow-up. These findings align with previous literature demonstrating the efficacy of rituximab in treating AMR and improving renal function in kidney transplant recipients[[7, 8, 14, 15]. It is noteworthy that the improvement in serum creatinine reached statistical significance, whereas the improvement in eGFR showed only a trend (p = 0.052). This discrepancy may be explained by the higher variability and broader standard deviation observed in eGFR values compared to serum creatinine, as eGFR is calculated using several demographic and clinical variables. In contrast, serum creatinine reflects a direct biochemical measurement and may therefore be more sensitive to short-term changes. Considering the relatively small sample size of our study, the observed trend in eGFR improvement should still be regarded as clinically relevant, although it did not reach statistical significance. The rate of graft loss was 16.1% in the rituximab-treated group and 36% in the non-rituximab group (p = 0.088). In Kaplan-Meier survival analysis, we showed no statistically significant difference in death-censored graft survival between the groups (p = 0.534), thus failing to derive a durable long-term survival advantage in this cohort. This trend is consistent with the 7-year follow-up data from the RITUX-ERAH study, a multicenter randomized clinical trial, which reported no statistically significant difference in death-censored graft survival or renal function between the rituximab and placebo groups[[15]. Taken together, these results suggest that rituximab may offer potential clinical benefits, particularly in the short term. However, the lack of statistically significant differences in long-term graft survival underscores the need for further large-scale, randomized controlled trials to conclusively determine the efficacy of rituximab in improving long-term outcomes in kidney transplant recipients with AMR. In addition, patient survival was comparable between the two groups, with one death in each group due to sepsis. Because of the limited number of events, no meaningful statistical analysis of patient survival could be conducted.

Polyomavirus BK nephropathy was more prevalent in the rituximab-treated group; however, only one patient in this group experienced subsequent graft loss. Consistent with our findings, several studies have reported low rates of graft loss attributable to Polyomavirus BK nephropathy developing after rejection treatment[[16, 17]. This observation may be related to the meticulous monitoring of BK viremia post-treatment and the controlled reduction of immunosuppression guided by protocol biopsies following rejection therapy[[18]. Notably, no patients in either treatment group developed any type of malignancy during the follow-up period.

In the indication biopsies performed at the onset of rejection, a higher proportion of patients in the non-rituximab group exhibited chronic interstitial inflammation and chronic tubulitis (Ci + Ct > 25%), and the rate of C4d-negative patients was also higher in this group.

Parajuli et al. reported that rituximab was particularly advantageous in patients with low chronicity scores[[9]. In accordance with the literature, we preferentially administered rituximab to patients with low chronicity scores and high C4d positivity at the time of histological diagnosis, considering its potential for better treatment response in the early stages of AMR[[19]. Given the retrospective design of our study, it provides insight into the characteristics of patients who received rituximab and the rationale behind the decision to initiate this therapy.

In both treatment groups, rejection therapy resulted in considerable regression of total inflammation, interstitial inflammation, tubulitis (i + t), glomerulitis, peritubular capillaritis (g + ptc), and microvascular inflammation (MVI), defined as (g + ptc ≥ 2). However, the only statistically significant difference between the groups was the higher rate of conversion to C4d-negative status in the rituximab-treated group, suggesting a potential additive effect of rituximab. These findings are consistent with the RITUX-ERAH study[[20]where both the rituximab and placebo groups showed significant histological improvements after one year, though without significant intergroup differences. Similarly, in our cohort, although inflammation-related parameters improved in both groups, no statistically significant difference in the degree of improvement was found.

In our study, 16 patients presented with C4d-negative AMR. All of these patients exhibited MVI (g + ptc ≥ 2) and were treated accordingly. According to the 2022 Banff classification, microvascular inflammation is now recognized as an integral component of AMR, holding significant importance in both its diagnosis and classification[[21]. The risk of progression to transplant glomerulopathy during follow-up is reported to be higher in patients with MVI compared to those without[[22]. The 2022 Banff classification guidelines recommend that treatment approaches targeting MVI be implemented concurrently with standard AMR therapy[[19]. At our center, microvascular inflammation has long been regarded as a significant pathological finding, and its management has been consistent with the recommendations outlined in the 2022 Banff classification. Protocol biopsy findings from the two groups revealed that a higher number of patients receiving rituximab demonstrated the absence of Ci + Ct and Cg post-treatment. Although a greater number of patients in the rituximab-treatment group showed lower chronicity scores after treatment, these differences did not reach statistical significance, and therefore should be interpreted as a trend rather than a definitive effect of rituximab. Overall, our findings indicate short-term improvements in renal indices and histopathology with rituximab, while definitive long-term benefits were not demonstrated.

What are the key indicators suggesting a patient with antibody-mediated rejection might benefit from rituximab therapy?

Understanding Antibody-Mediated Rejection (AMR)

Antibody-mediated rejection (AMR) remains a significant challenge in kidney transplantation, impacting both graft survival and patient outcomes. Unlike T-cell mediated rejection, AMR is driven by donor-specific antibodies (DSAs) that target the transplanted kidney. These DSAs activate the complement system and trigger inflammation, leading to endothelial injury and ultimately, graft dysfunction. Early detection and effective treatment are crucial for mitigating the damage caused by AMR. Kidney transplant rejection, in general, is a complex immunological process, and AMR represents a particularly insidious form.

The Role of Rituximab in AMR Treatment

Rituximab,a monoclonal antibody targeting the CD20 protein found on B cells,has emerged as a key therapeutic agent in the management of AMR. By depleting B cells, rituximab aims to reduce DSA production and dampen the inflammatory response. It’s use is often considered in cases of acute or chronic AMR, particularly when conventional therapies like plasmapheresis and intravenous immunoglobulin (IVIG) have been insufficient. Rituximab therapy isn’t a standalone solution; it’s typically integrated into a broader immunosuppression regimen.

Mechanism of Action: How Rituximab Works

Rituximab’s effectiveness stems from its targeted B-cell depletion. Here’s a breakdown:

* CD20 Targeting: Rituximab specifically binds to the CD20 antigen expressed on pre-B and mature B lymphocytes, but not plasma cells.

* B-Cell Depletion: Binding triggers several mechanisms leading to B-cell death, including complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), and direct induction of apoptosis.

* DSA Reduction: Reducing the B-cell population ultimately leads to a decrease in DSA production, lessening the attack on the transplanted kidney.

* Immunomodulation: Rituximab can also modulate other immune cells, contributing to its overall immunosuppressive effect.

Clinical Outcomes with Rituximab in AMR

Clinical studies have demonstrated varying degrees of success with rituximab in treating AMR. Factors influencing outcomes include:

* Timing of Treatment: Early intervention, particularly during acute AMR episodes, generally yields better results.

* DSA Strength: Patients with lower DSA titers tend to respond more favorably to rituximab.

* Concomitant Therapies: Combining rituximab with plasmapheresis, IVIG, and other immunosuppressants frequently enough enhances efficacy.

* Type of AMR: Rituximab appears more effective in treating acute AMR compared to chronic AMR, where established fibrosis may limit recovery.

Reported success rates (defined as stabilization of graft function or advancement in eGFR) range from 40% to 70% in various studies. Though, it’s critically important to note that rituximab doesn’t eliminate DSAs entirely in most cases; it aims to reduce their levels and prevent further damage.

Monitoring Response to Rituximab

Close monitoring is essential to assess the response to rituximab therapy. Key parameters include:

1. DSA Levels: Serial monitoring of DSA levels is crucial to track treatment efficacy. A significant reduction in DSA titer is a positive indicator.
2. Kidney Function (eGFR): Changes in estimated glomerular filtration rate (eGFR) reflect the impact of treatment on graft function.
3. Biomarkers of AMR: Monitoring biomarkers like C4d deposition in biopsies and complement activation products can provide insights into the ongoing inflammatory process.
4. B-Cell Reconstitution: monitoring B-cell counts post-rituximab helps understand the degree and timing of B-cell recovery, which can influence the risk of DSA rebound.

Pathological findings & Rituximab’s Influence

Kidney biopsy remains the gold standard for diagnosing AMR and assessing its severity. Pathological features characteristic of AMR include:

* C4d Deposition: C4d deposition in peritubular capillaries is a hallmark of antibody-mediated injury.

* Glomerulitis: Inflammation within the glomeruli, frequently enough accompanied by endothelial cell swelling and damage.

* tubulitis: Inflammation affecting the tubules.

* Arteritis: inflammation of the renal arteries.

* Transplant glomerulopathy (TG): Chronic AMR can lead to TG, characterized by double glomerular basement membrane and progressive fibrosis.

Rituximab treatment can influence these pathological findings. Successful treatment may lead to:

* Reduced C4d Deposition: Decreased antibody binding and complement activation can reduce C4d deposition.

* Diminished Glomerulitis & Tubulitis: Lowering DSA levels can lessen inflammation within the glomeruli and tubules.

* Slowing Progression of TG: While rituximab may not reverse established TG, it can potentially slow its progression.

Benefits and Risks of Rituximab Use

Benefits:

* Improved graft survival rates in selected patients.

* Potential for reversal of acute AMR episodes.

* Reduction in DSA levels and inflammatory markers.

* May allow for reduced doses of other immunosuppressants.

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