Background

Alzheimer’s disease drug development has long focused on directly targeting amyloid beta (amyloid-β, Aβ) in the brain. IBC-Ab002, an antibody candidate designed to transiently activate the peripheral immune system, showed generally favorable tolerability in a phase 1b trial in people with early Alzheimer’s disease. No drug-related serious adverse events occurred, but immune-related adverse events were reported. The trial did not establish an improvement in cognitive function.

Michal Schwartz and colleagues developed this strategy based on preclinical studies indicating that the peripheral immune system contributes to maintaining brain health and repairing damage. IBC-Ab002 targets programmed death-ligand 1 (PD-L1), which suppresses immune cell activity. In animal models, transient blockade of this pathway was associated with the entry of monocyte-derived macrophages and other cells into the brain and reduced neuroinflammation. However, this trial did not directly establish whether the same processes occur in the human brain.

Key findings

The randomized, double-blind, placebo-controlled trial, published in Nature Medicine, was conducted at 11 centers in the United Kingdom, Israel, and the Netherlands. The 40 participants with early symptomatic Alzheimer’s disease had mild cognitive impairment or mild dementia, with amyloid and tau positivity confirmed using cerebrospinal fluid (CSF) biomarkers. In each of five dose groups—1, 3, 6, 15, and 30 mg/kg—six participants were assigned to the study drug and two to placebo.

The study plan comprised four intravenous infusions at 12-week intervals and approximately 48 weeks of observation. Two participants discontinued the study early. Of the 38 who completed follow-up, two did not receive all four planned infusions because of rash or elevated liver enzymes.

No drug-related serious adverse events or amyloid-related imaging abnormalities (ARIA) were observed. However, immune-related adverse events were reported in 10 of 30 participants in the active-treatment group and one of 10 in the placebo group. One asymptomatic grade 3 elevation in liver enzymes occurred in the active-treatment group, leading to treatment discontinuation; it subsequently resolved spontaneously. Thyroid hormone replacement therapy continued for one case of hypothyroidism. In total, three active-treatment participants discontinued dosing because of adverse events. The absence of drug-related serious adverse events should be distinguished from the occurrence of a grade 3 immune-related adverse event.

IBC-Ab002 was engineered to suppress Fc effector functions that cause cytotoxicity and to reduce binding to the neonatal Fc receptor (FcRn), allowing rapid clearance from the body. Its measured mean half-life was approximately four days. The increase in activated T cells in peripheral blood peaked approximately seven days after dosing, and levels returned close to baseline before the next dose. These findings support the design rationale of brief exposure and transient immune activation, but do not establish that the design prevents immune-related adverse effects.

In an exploratory CSF analysis at week 48, neurogranin, total tau, and phosphorylated tau 181 in the highest-dose group showed changes in the direction of a decrease compared with the pooled placebo group. This comparison was based on data from five participants in the highest-dose group and six in the pooled placebo group who underwent an optional end-of-study lumbar puncture. Statistical significance was not established for this comparison, and no detectable effect was found in plasma biomarkers.

Implications and outlook

The study supports further clinical development of a treatment strategy that intermittently stimulates the peripheral immune system. It demonstrates brief antibody exposure and a transient peripheral immune response in humans. However, CSF changes are indirect indicators of changes in the brain and should not be interpreted as direct evidence of reduced brain inflammation or macrophage entry into the brain.

This phase 1b trial was small and designed primarily to assess safety. Whether the treatment actually slows cognitive decline or is safer than existing therapies remains unknown. Limitations also include the small analysis population resulting from optional CSF collection and exploratory analyses without correction for multiple comparisons. The researchers said they plan adequately powered cognitive assessments in a subsequent phase 2 trial. The original paper provides details of the trial design and results.