Pharming Group has reported positive topline Phase II results for leniolisib in genetically identifiable primary immunodeficiencies involving immune dysregulation linked to PI3Kδ signaling, a step the Netherlands-based biotechnology company says could eventually expand the drug’s use well beyond its current approved indication. The results were announced September 22 and have been accepted as a late-breaking abstract at the 22nd Biennial Meeting of the European Society for Immunodeficiencies, taking place October 14-17 in the Netherlands.
What This Trial Actually Tested
The study is a single-arm, open-label, intra-patient dose-escalation Phase II trial evaluating leniolisib in 13 subjects with genetically defined primary immunodeficiencies, or PIDs, tied to abnormal PI3Kδ pathway signaling. Researchers assessed safety, tolerability, pharmacokinetics, pharmacodynamics, and clinical efficacy measures throughout the study.
The Results: Shrinking Spleens and Calmer Immune Systems
The headline finding was a mean 26.4 percent reduction in spleen volume across participants, alongside reductions in the size of index lesions and broader clinical improvements across multiple measures of immune dysregulation, including reductions in lymphoproliferation, the abnormal overgrowth of immune cells that characterizes many of these disorders. Spleen enlargement and lymphoproliferation are common hallmarks of the immune dysregulation seen in these PIDs, so measurable reductions in both offer a fairly direct signal that the drug is addressing the underlying disease process rather than just managing symptoms.
A Familiar Safety Profile
On safety, Pharming reported that leniolisib’s performance in this trial was consistent with its known safety profile, with infections the most commonly observed adverse events among study subjects and no new safety signals identified. That consistency matters because leniolisib already carries a real-world safety track record from its existing approved use, giving regulators and physicians an established baseline to compare this expanded population’s results against.
From APDS to a Broader Family of Rare Immune Disorders
Leniolisib is currently approved as a targeted therapy for activated phosphoinositide 3-kinase delta syndrome, or APDS, in multiple jurisdictions. This Phase II trial represents Pharming’s effort to extend the drug beyond that original indication into a broader group of primary immunodeficiencies sharing a common underlying biological driver: enhanced PI3Kδ signaling that disrupts normal immune regulation. The company has specifically named ALPS-FAS, CTLA4 haploinsufficiency, NFKB1 haploinsufficiency, and PTEN deficiency as conditions within this broader target population, each a distinct genetic disorder that nonetheless converges on the same overactive PI3Kδ pathway APDS itself is driven by.
“These results mark an important step in assessing leniolisib’s potential to address immune dysregulation in PIDs beyond APDS, potentially benefiting a substantially larger patient population.”
— Anurag Relan, Chief Medical Officer, Pharming Group
The CVID Overlap and What’s Coming Next
A notable detail buried in the study’s patient makeup: of the 13 participants enrolled, nine also carried a diagnosis of common variable immunodeficiency, or CVID, a considerably more common condition than APDS itself. Pharming is running a separate, dedicated Phase II trial specifically evaluating leniolisib in CVID patients with immune dysregulation, with or without an identified genetic cause, and expects to report topline results from that study in the fourth quarter of 2026. Because CVID represents a substantially larger patient population than the rare, genetically pinpointed PIDs in this current trial, that upcoming readout carries real significance for how far leniolisib’s commercial reach could ultimately extend if the CVID results prove similarly positive.
Caveats Worth Noting
It’s worth being clear about the limits of what this particular trial demonstrates. With only 13 participants and no placebo or active comparator arm, an open-label, single-arm design like this one is well suited to establishing safety, tolerability, and an initial efficacy signal, but it doesn’t offer the same strength of evidence a larger, randomized, controlled trial would provide. That’s a standard and expected limitation at this stage of drug development, and additional efficacy and safety data are still to be presented at the ESID meeting next month, but it’s a meaningful caveat for anyone weighing how far these “positive” topline results should be read as confirmed clinical benefit versus an encouraging early signal that still needs to be validated at scale.
What Comes Next
For now, Pharming’s leniolisib program sits at an inflection point: positive early data in a small, genetically defined PID population beyond its current APDS approval, a much larger CVID readout due within months, and additional detail from this current trial still to be unveiled at ESID in October. Whether those upcoming data points confirm the trajectory suggested by this week’s topline results will determine how meaningfully leniolisib’s addressable patient population actually grows beyond the rare disease indication it’s approved for today.
This article is for general informational purposes and does not constitute medical advice. Patients with primary immunodeficiencies should discuss treatment options with their physician.