Tegoprubart's Phase 3 Bet: Novel Mechanism, No Approved Precedent, Tacrolimus Is a Brutal Bar

Eledon's Tegoprubart Shows Promise, Advances to Phase 3 in Kidney Transplant

Eledon Pharmaceuticals is advancing its investigational immunosuppressive therapy, tegoprubart, a second-generation anti-CD40L antibody, with the goal of replacing tacrolimus as the cornerstone of care in transplantation. Dr. Steve Perrin, President and Chief Scientific Officer, highlighted tegoprubart's promising safety and efficacy data from the BESTOW study in kidney transplant patients, demonstrating improved long-term kidney function and reduced side effects compared to tacrolimus. Eledon is now preparing to launch a large global Phase 3 study in kidney transplantation, randomizing 600 patients against tacrolimus. The company is also developing a subcutaneous formulation and exploring tegoprubart's potential in islet-cell transplantation for type 1 diabetes, xenotransplantation, and immune tolerance, aiming to be the first major innovation in transplant immunosuppression in over 30 years.

• Tegoprubart, a second-generation anti-CD40L antibody, has been engineered to overcome the platelet activation and thromboembolic events observed with earlier molecules. In the BESTOW study, it demonstrated a favorable safety profile in kidney transplant patients, showing meaningful reductions in cardiovascular hypertension, new-onset diabetes, and CNS toxicities (like brain fog and tremors) compared to tacrolimus, while maintaining similar infection rates. This addresses a critical unmet need by mitigating the severe side effects of current standard-of-care immunosuppressants.
• Clinical data from the BESTOW study revealed encouraging efficacy, particularly in long-term kidney function, which is a key predictor of graft survival. By 21 months, while numerically similar in rejection rates to tacrolimus, the tegoprubart arm showed no rejections after six months post-transplant, unlike the tacrolimus arm where rejections continued. Patients who experienced rejection but remained on tegoprubart also exhibited substantially better kidney function, suggesting its potential to protect against difficult-to-treat antibody-mediated rejection and improve long-term outcomes.
• Eledon is preparing to launch a large global Phase 3 study in kidney transplantation, randomizing approximately 600 patients one-to-one against tacrolimus across more than 100 sites in roughly 24 countries. Beyond this, the company is developing a subcutaneous formulation for patient convenience and exploring tegoprubart's application in islet-cell transplantation for severe type 1 diabetes, where it has shown promising results in normalizing HbA1c and enabling patients to come off exogenous insulin. It is also being investigated in immune tolerance studies, aiming to reprogram the immune system to accept donor organs without lifelong immunosuppression.

The Persistent Burden of Tacrolimus in Kidney Transplant

Current treatment approaches for antibody-mediated rejection (AMR) in kidney transplantation face substantial limitations rooted in both mechanistic complexity and the absence of standardized, regulatory-approved protocols. Strategies such as plasmapheresis (PLEX), immunoadsorption (IA), intravenous immunoglobulin (IVIG), and B cell-depleting agents including rituximab have demonstrated variable results, with some small nonrandomized trials identifying modest benefits. More recent histologic follow-ups of patients treated with the proteasome inhibitor bortezomib have not shown significant benefits in terms of allograft outcomes. No specific treatment approaches have been approved by the US Food and Drug Administration, precluding the development of standardized protocols. Several pathways in the AMR cascade remain unknown, which accounts for the lack of efficacy of some currently available agents.

An emerging and particularly difficult clinical challenge is late or chronic active AMR associated with de novo donor-specific antibodies (dnDSA) that emerge more than 100 days posttransplantation. This form of rejection is often resistant to conventional therapies, including rituximab combined with plasmapheresis and IVIG. Newer agents such as daratumumab, an anti-CD38 monoclonal antibody that depletes plasma cells, have shown promising results in refractory cases, but the evidence base remains limited to small case series. Eculizumab, an anti-C5 monoclonal antibody, has been used for more difficult rejections, yet randomized controlled trials are still needed to identify surrogate markers and improve therapeutic efficacy across these approaches.

Beyond AMR-specific therapies, the broader immunosuppressive regimens used to prevent rejection carry their own burden of complications. Calcineurin inhibitors, while associated with substantial reductions in acute rejection and improved one-year graft survival, have not directly correlated with improvements in long-term allograft survival. Chronic immune injury mediated by donor-specific antibodies has been identified as accounting for most late graft losses, and the vast majority of calcineurin inhibitor-sparing studies have short-term follow-up and have not explored the change in the donor-specific antibody profile. Distinguishing patients who will benefit from calcineurin inhibitor-sparing strategies from those at risk of late alloimmune-mediated injury remains one of the biggest challenges in the field.

Tegoprubart's Encouraging Phase 2 Data in Kidney Transplant

Several recent studies have examined interventions targeting kidney transplant rejection, spanning immunosuppressive conversion strategies and rejection-specific therapies. The findings below reflect a range of efficacy and safety profiles across distinct patient populations and clinical settings.

• "Long-term outcomes of tacrolimus conversion to sirolimus in kidney transplant recipients: an eight-year follow-up" — Intervention: Conversion from tacrolimus to sirolimus. Over an 8-year follow-up, the sirolimus cohort demonstrated a superior and more preserved GFR compared to the tacrolimus cohort, with a total GFR change of -1.18 mL/min/1.73 m² (95% CI, -4.86 to 3.06) versus -9.57 mL/min/1.73 m² (95% CI, -16.92 to -7.26), yielding a between-group difference of -8.39 mL/min/1.73 m². Graft loss, patient survival, and de novo donor-specific antibody development did not significantly differ between groups. The sirolimus group showed a numerically but insignificantly elevated biopsy-proven acute rejection rate, significantly lower BK viremia, and significantly lower cancer rates.

• "Conversion from Calcineurin Inhibitor- to Belatacept-Based Maintenance Immunosuppression in Renal Transplant Recipients: A Randomized Phase 3b Trial" — Intervention: Conversion from calcineurin inhibitor (CNI) to belatacept. The 24-month rates of survival with graft function were 98% and 97% in the belatacept and CNI groups, respectively (adjusted difference, 0.8; 95.1% CI, -2.1 to 3.7). Biopsy-proven acute rejection occurred in 8% of belatacept-converted patients versus 4% in the CNI continuation group, while de novo donor-specific antibodies developed in 1% versus 7%, respectively. The 24-month eGFR was higher with belatacept (55.5 versus 48.5 ml/min per 1.73 m² with CNI). Both groups had similar rates of serious adverse events, infections, and discontinuations; one patient in the belatacept group developed post-transplant lymphoproliferative disorder.

• "Tocilizumab Treatment for Microvascular Inflammation and Chronic Active Antibody-mediated Rejection in Kidney Transplantation" — Intervention: Monthly tocilizumab 8 mg/kg intravenous infusions. Among 85 adult kidney transplant patients with histologic features of chronic active antibody-mediated rejection, eGFR declined at a rate of -0.70 mL/min/1.73 m/mo (95% CI, -1.03 to -0.36) preceding tocilizumab initiation and stabilized after treatment onset to a slope of -0.07 (-0.35 to 0.21) mL/min/1.73 m/mo (slope difference: 0.59 [0.22–0.97] mL/min/1.73 m/mo, P = 0.002). Among 65 DSA-positive patients, 14 (22%) no longer had DSA at 1 year, though the distribution of sum mean fluorescence intensity of donor-specific antibodies remained unchanged from baseline to 1 year. There was 1 graft loss and 2 deaths, both COVID-19-related, by 12 months after treatment onset. The study suggested that monthly tocilizumab may stabilize allograft function in this population.

• "Bortezomib for antibody-mediated rejection of kidney transplant in youth" — Intervention: Bortezomib as adjunct therapy for treatment-refractory antibody-mediated rejection. Six pediatric patients (median age 14.6 years) received bortezomib at a mean of 71 months post-kidney transplant. A statistically significant decline in DSA MFI was observed pre- and 12-months post-bortezomib (p = .012, paired t-test) among subjects not on dialysis at the time of treatment, although DSA did not completely resolve. Four patients experienced decline in eGFR from 4% to 42%, and no effects were observed on eGFR trajectory. No adverse effects were reported, and bortezomib was well tolerated.

Expanding Tegoprubart's Reach Across the Transplant Frontier

Beyond kidney transplant rejection, tegoprubart has been investigated in two additional indications: islet allotransplantation and amyotrophic lateral sclerosis (ALS). These programmes span both transplant immunology and neuroinflammation, reflecting the breadth of CD40L-targeted immunosuppression.

• Intrahepatic islet allotransplantation (nonhuman primate model): Tegoprubart (AT-1501) was tested in a cynomolgus macaque model of intrahepatic islet allotransplantation. AT-1501 monotherapy led to long-term graft survival, and AT-1501-based regimens resulted in higher C-peptide, greater appetite leading to weight gain, and reduced occurrence of cytomegalovirus reactivation compared with conventional immunosuppression.

• Kidney allotransplantation (nonhuman primate model): In parallel, AT-1501 was evaluated in a rhesus macaque model of kidney allotransplantation, where monotherapy again led to long-term graft survival, confirming its immunosuppressive potential across transplant types.

• Amyotrophic lateral sclerosis (Phase 2A clinical trial): Tegoprubart was assessed in a multicenter, dose-escalating, open-label Phase 2A study (ClinicalTrials.gov ID: NCT04322149) in 54 participants with ALS. Participants received 6 intravenous infusions of tegoprubart every 2 weeks across 4 dose cohorts: 1 mg/kg, 2 mg/kg, 4 mg/kg, and 8 mg/kg. Tegoprubart demonstrated dose-dependent target engagement and a reduction in 18 pro-inflammatory biomarkers in circulation, and appeared safe and well tolerated in this population.

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Tegoprubart: Reshaping Transplant Care Beyond CNIs

The landscape of transplant medicine stands on the cusp of a significant evolution, driven by the potential emergence of novel immunosuppressive strategies. For decades, calcineurin inhibitors (CNIs) have been the bedrock of post-transplant care, effectively preventing acute rejection but at the cost of substantial long-term toxicities, including cardiovascular, metabolic, and renal complications that ultimately limit graft and patient survival. The advancement of tegoprubart, a second-generation anti-CD40L antibody, offers a compelling vision for a future where these trade-offs are minimized.

Eledon Pharmaceuticals' move to launch a large global Phase 3 study for tegoprubart in kidney transplantation, directly comparing it to tacrolimus, signals a bold ambition to redefine the standard of care. The promise of improved long-term kidney function and a reduced side effect profile could dramatically enhance the quality of life for transplant recipients and extend graft longevity. Furthermore, the strategic development of a subcutaneous formulation addresses a critical logistical challenge, potentially boosting patient adherence and expanding access to this innovative therapy.

However, the path forward is not without its complexities. While CD40L blockade is a promising mechanism, the literature indicates that the CD40/CD40L pathway has seen varied success with other agents, with some showing inferiority or inconsistent efficacy compared to tacrolimus. Moreover, insights from xenotransplantation studies, where tegoprubart was part of the immunomodulatory regimen, highlight that challenges such as antibody-mediated rejection and non-immune graft injury can persist despite CD40L blockade. This suggests that while tegoprubart may be highly effective against cellular rejection, comprehensive strategies to address all facets of immune response, particularly in highly immunogenic contexts, remain crucial. The efficacy of tegoprubart in high-immunological-risk patients, a known limitation for other costimulation blockers, will also be a key factor in determining its ultimate market penetration and broad applicability. As the field looks towards the first major innovation in transplant immunosuppression in over 30 years, tegoprubart represents a beacon of hope, yet one that must navigate intricate immunological hurdles.