What are B-cell pathway blockers and how might they help?
In IgA nephropathy, the immune system produces abnormal IgA antibodies that deposit in the kidney's filtering units, triggering inflammation and scarring. B cells are the immune cells that make these antibodies, and they also interact with a part of the immune system called the complement cascade—a group of proteins that amplify inflammation. Blocking this pathway is a way to interrupt the damage without wiping out the whole immune system.
The most direct evidence here comes from a drug called iptacopan, which specifically blocks a protein called factor B in the alternative complement pathway [1]. In a phase 3 randomized trial involving over 400 patients, those taking iptacopan had a 38% lower urine protein level at 9 months compared with placebo [1]. Proteinuria (protein in the urine) is a well-established predictor of kidney decline, so this reduction is a meaningful sign that the drug is hitting its target.
Does reducing proteinuria actually slow kidney damage?
Yes—multiple studies confirm that lowering proteinuria is directly linked to better long-term kidney outcomes. A large Swedish registry study of over 1,200 patients found that any reduction in urine albumin (a specific protein) within a year was associated with a 50% lower risk of kidney failure or significant kidney function decline, regardless of starting level [4]. This means that the proteinuria drop seen with iptacopan is not just a lab improvement; it likely translates into real protection.
However, the iptacopan trial has not yet reported the final kidney function results—those come after 2 years of treatment [1]. So while the proteinuria data are encouraging, we don't yet have the definitive proof that this specific drug prevents kidney failure. The trial is ongoing, and the full results are expected to be the deciding factor.
How does this compare to existing treatments?
Current standard care includes corticosteroids (like methylprednisolone) and sometimes tonsillectomy. A large international trial of 503 patients found that oral methylprednisolone reduced the risk of kidney function decline or failure by 47% over 4 years, but it also caused serious infections in about 11% of patients—four times more than placebo [2]. A Japanese study of 941 patients similarly found that corticosteroids reduced kidney events by about half, and adding tonsillectomy further reduced risk by 60% compared with steroids alone [3].
The key difference is safety. Corticosteroids are effective but carry significant side effects, which is why doctors are looking for more targeted options like iptacopan. The iptacopan trial reported no increased risk of infection and similar overall side effects to placebo [1]. If the final results confirm long-term kidney protection, this could offer a safer alternative—but we're not there yet.
What are the caveats and what's still unknown?
The main caveat is that the iptacopan trial's primary outcome—kidney function decline—has not been reported yet. The 9-month proteinuria result is a surrogate marker, not proof of long-term benefit. Also, the trial only included patients with relatively high proteinuria (≥1 g/day), so it's unclear if the drug helps those with milder disease [1].
Another important point: even if B-cell pathway blockers work, they may not prevent disease recurrence after a kidney transplant. A study of 504 transplant recipients found that IgA deposits recurred in 23% of patients within 15 years, and recurrence tripled the risk of graft loss [5]. This suggests that blocking the complement pathway might not fully address the underlying B-cell abnormality that drives the disease.
In summary, the evidence so far is promising but incomplete. Iptacopan reduces proteinuria safely, and proteinuria reduction is strongly linked to better kidney outcomes, but we need the final trial results to know if it truly slows kidney damage in the long run.
About These Sources
This answer is built on 5 peer-reviewed studies — published from 2021 to 2024, 2 from 2024 or later, 5 in Q1 journals, collectively cited 539 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 44 papers retrieved from a database of over 500 million.
Sources used in this answer
Alternative Complement Pathway Inhibition with Iptacopan in IgA Nephropathy
In a phase 3 randomized trial of 443 patients, iptacopan reduced proteinuria by 38% at 9 months compared with placebo, with no increased infection risk, but kidney function outcomes are pending.
Effect of Oral Methylprednisolone on Decline in Kidney Function or Kidney Failure in Patients With IgA Nephropathy
In a randomized trial of 503 patients, oral methylprednisolone reduced the risk of kidney function decline or failure by 47% over 4 years, but serious infections were more common (10.9% vs 2.8%).
Associations of corticosteroid therapy and tonsillectomy with kidney survival in a multicenter prospective study for IgA nephropathy
In a prospective cohort of 941 patients, corticosteroids were associated with a 49% lower risk of kidney events, and adding tonsillectomy further reduced risk by 60% compared with steroids alone.
Albuminuria predicts kidney events in IgA nephropathy
In a Swedish registry study of 1,269 patients, any reduction in urine albumin within a year was associated with a ~50% lower risk of kidney failure or significant decline, regardless of baseline level.
Recurrence of IgA Nephropathy after Kidney Transplantation in Adults
In a multicenter study of 504 transplant recipients, IgA nephropathy recurred in 23% at 15 years, and recurrence was associated with a 3.7-fold higher risk of graft loss.