Tegoprubart (AT-1501) — SparkNotes

Context

Tegoprubart is Eledon Pharmaceuticals' Fc-engineered anti-CD40L monoclonal antibody designed to replace tacrolimus — the decades-old standard immunosuppressant in organ transplantation. Tacrolimus works but causes serious toxicities: kidney damage, new-onset diabetes, neurotoxicity, and elevated infection risk.

Earlier anti-CD40L antibodies (ruplizumab, toralizumab) were abandoned in the early 2000s after causing fatal blood clots through platelet cross-linking. Tegoprubart was specifically engineered with reduced Fcγ receptor binding to avoid this. Across 150+ human exposures spanning ALS, kidney transplant, islet transplant, and xenotransplantation, zero thromboembolic events have occurred.

The drug has been tested across six clinical programs:

• Phase 2a in ALS (NCT04322149) — completed
• Phase 1b in kidney transplant (NCT05027906) — active, Cohort 2 enrolling
• Phase 2 BESTOW in kidney transplant (NCT05983770) — completed, 127 patients
• Phase 1/2 in islet transplant for T1D (NCT06305286) — active, 6 of 12 patients treated
• Kidney transplant extension study (NCT06126380) — active
• Phase 2a in IgA nephropathy (NCT05125068) — terminated (deprioritized)

Tegoprubart also served as immunosuppression in all four landmark pig-to-human xenotransplants (eGenesis collaboration), including the first-ever porcine kidney transplant at Massachusetts General Hospital in March 2024.

Key Findings

BESTOW Kidney Transplant Trial (Phase 2)

• Primary endpoint missed: 12-month eGFR was 69 mL/min (tegoprubart) vs. 66 mL/min (tacrolimus) — numerically higher but not statistically significant
• Non-inferior on FDA composite: death, graft loss, or biopsy-proven acute rejection met non-inferiority at a 20% margin (22.2% vs. 17.2%)
• Higher acute rejection rate: 20.6% vs. 14.1%, though mostly mild and treatable
• Dramatic safety advantages over tacrolimus:
  • New-onset diabetes: 2.1% vs. 16.7%
  • Tremor: 1.6% vs. 25.0%
  • Sepsis/bacteremia: 4.8% vs. 17.2%
  • Delayed graft function: 14.3% vs. 25.0%
  • Heart failure: 0% vs. 4.7%
• No cases of PTLD, PML, or thromboembolic events in either arm

Phase 1b Long-Term Extension (24-Month Data)

• 8 patients followed for 2 years
• Mean eGFR improved from 67.0 at 12 months to 74.2 mL/min at 24 months
• Zero episodes of acute rejection, graft loss, death, new-onset diabetes, or de novo donor-specific antibodies

Islet Transplant for Type 1 Diabetes (Phase 1/2)

• All 6 evaluable patients achieved insulin independence — 100% success rate
• First patient (~15 months post-transplant): HbA1c of 4.7% (essentially non-diabetic)
• Patient 2 (32-year-old, previously 60 units/day insulin): HbA1c dropped from 8.5% → 4.9% after a single transplant
• Islet engraftment was 3–5× higher than in comparable tacrolimus-treated subjects
• No serious infections, no rejection, no kidney or neurological toxicity
• Trial extended to 12 subjects; Breakthrough T1D funding a second study in T1D + chronic kidney disease

ALS (Phase 2a — Completed)

• Safe across four dose cohorts (1–8 mg/kg IV)
• ~24-day half-life with dose-proportional pharmacokinetics
• Dose-dependent reductions in 20 pro-inflammatory biomarkers
• Trend toward slower disease progression (not powered for efficacy)

Xenotransplantation

• Used in all 4 pig-to-human transplants (3 kidney, 1 heart)
• First patient survived 52 days with no xenograft rejection at autopsy (published in NEJM)
• Second kidney patient discharged off dialysis with creatinine ~1.0 mg/dL

Limitations

• BESTOW missed its primary endpoint — the eGFR difference was not statistically significant, and the stock dropped ~50% on the news (November 2025)
• Higher acute rejection rate (20.6% vs. 14.1%) in BESTOW raises questions about whether tegoprubart alone provides sufficient immunosuppression in kidney transplant
• Small sample sizes across all programs — the islet transplant data (n=6) is striking but far too small for regulatory conclusions
• No Phase 3 trial yet — FDA guidance on Phase 3 kidney transplant trial design is a primary 2026 milestone; design is still TBD
• No Fast Track or Breakthrough Therapy designation obtained for any indication
• Financial constraints — Eledon has cash runway into Q2 2027 (~$140M raised 2024–2025 plus$57.5M in Nov 2025) but a Phase 3 kidney trial will require additional capital
• Islet transplant scalability — even if tegoprubart works perfectly, islet transplantation itself faces donor supply constraints and is not widely accessible
• Xenotransplant data is anecdotal — based on compassionate-use cases, not controlled trials
• IgA nephropathy program terminated — narrowing the pipeline to transplant-focused indications
• Competitive landscape — other Fc-modified anti-CD40L agents (frexalimab, dapirolizumab pegol) are in Phase 3 for autoimmune diseases; if successful, they could expand into transplant indications

Bottom Line

Tegoprubart's safety profile is its strongest argument — dramatically less toxic than tacrolimus across every measured dimension. The islet transplant data (100% insulin independence, 3–5× better engraftment) is the program's most compelling signal but needs replication at scale. The kidney transplant story is muddier: non-inferior efficacy with superior safety, but a missed primary endpoint complicates the regulatory path. Everything now hinges on 2026 FDA discussions about Phase 3 design — specifically whether the agency will accept a safety-differentiation thesis rather than requiring eGFR superiority.