 Juan Carlos Lopez |
 Andy Marshall |
The approval of multiple anti-amyloid monoclonal antibodies (mAbs) — aducanumab (Aduhelm; now withdrawn), lecanemab (Leqembi) and donanemab (Kisunla) — over the past five years has opened the era of disease-modifying Alzheimer’s drugs, albeit with only modest benefits in addressing cognitive decline (30% slowing) and associated serious safety risks, such as CNS inflammation and cerebral hemorrhages, which has limited clinical uptake. While many drug development programs target biological processes other than amyloid formation (e.g., tau and tangles, neurotransmitter receptors, neuroinflammation, autophagy, and mitochondrial or metabolic dysfunction), companies continue to optimize anti-amyloid monoclonals, but also look for alternative ways to therapeutically target Aβ.
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One alternative therapeutic modality to antibodies is chimeric antigen receptor (CAR) immune cell therapy. In recent weeks, we have been thinking a lot about in vivo chimeric antigen receptor (CAR)-T therapies, which were one of the dealmaking trends in 2025, and we recommend readers check out an excellent summary of trends in the area from the consultancy firm Scitaris (you don’t even have to give them your details to download the report).
CAR-T treatments have established their clinical niche as last-ditch treatments for B-cell malignancies, with some remarkable outcomes for late-stage patients. In some cases, they have been shown to be at least twice as effective as T-cell engager bispecific antibodies in clinical studies. But they remain rather blunt instruments.
Despite advances in the clinical management of cytokine-release syndrome and immune effector cell neurotoxicity syndrome (ICANS), CAR-T treatments continue to be associated with serious risks. And while there have been advances in managing these adverse events, atypical non-ICANS neurotoxicities (NINTs) can also create serious clinical management issues, with risk factors predisposing patients to development still only poorly understood.
That said, over the past year, we have seen an increasing trend for the use of CAR-T treatments outside oncology. They have started to be applied with promising efficacy in various areas of autoimmunity (systemic lupus erythrematosus, lupus nephritis, systemic sclerosis, Sjögren’s syndrome, antisynthetase syndrome, myasthenia gravis and idiopathic inflammatory myopathies) and neuroinflammatory conditions (multiple sclerosis). In this respect, a recent paper in Science caught our attention. In it, Marco Colonna and his colleagues at Washington University in St. Louis harness astrocytes to clear amyloid plaques by promoting their ability to phagocytize Aβ.
To that end, they used in vivo gene therapy to generate astrocytes carrying chimeric antigen receptors (“CAR-As”), a strategy not unlike the one used in cancer immunotherapy. Although both macrophages (CAR-Ms) and conventional CAR-Ts have been tested in preclinical models of Alzheimer’s disease with limited success, this study reports the first attempt to directly engineer astrocytes in the body to generate CAR-As.
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In broad terms, the construct used to generate CAR-As consisted of an Aβ-binding domain and the phagocytic signaling protein MEGF10 (multiple epidermal growth factor-like domains protein 10). The team examined a variety of constructs and chose two for in vivo testing. One of them combined a fragment from the Aβ-binding antibody crenezumab and MEGF10, which is primarily expressed in astrocytes. The second construct combined a fragment of aducanumab with the phagocytosis receptor Dectin-1, which is primarily expressed in microglia.
The authors packaged the constructs in an adeno-associated viral (AAV) vector under the control of an astrocyte-specific promoter and injected them intravenously into 5xFAD mice (which carry five familial Alzheimer’s disease (FAD) mutations, driving rapid Aβ plaque formation, synaptic loss, and cognitive decline starting around 2–4 months). Both CAR-As reduced amyloid burden and neuritic dystrophy, and the treatment worked both in the prophylactic and therapeutic settings.
Single-nucleus RNA sequencing and immunostaining showed that the CAR-As adopted the transcriptomic profile of activated astrocytes and readily clustered around amyloid plaques. Microglial cells, in turn, also responded to the treatment by showing a reduction of the disease-associated transcriptomic profile that is often seen after administration of monoclonal anti-Aβ antibodies. This is of interest because this disease profile of microglial cells has been suggested to contribute to the inflammatory reaction sometimes seen after Alzheimer’s immunotherapy.
A caveat of the study is that the authos saw no improvements in cognition following therapy, albeit behavioral results in mouse models have been notoriously poor at predicting outcomes in humans. However, the translational questions don’t stop there.
If in clinical practice the CAR-A approach would require an AAV vector, then immunogenicity of the treatment is going to be an issue. Pre-exposure to AAV is often a problem for gene-therapy programs, where patients are much younger. Given that Alzheimer’s is a disease associated with an elderly population, immunogenicity is likely to be exacerbated. Similarly, the delivery of 1013–1014 viral genomes to elderly patients living with Alzheimer’s—many of whom will already have a brain prone to neuroinflammation—makes the specter of unwanted side effects a major concern. In this respect, finding Alzheimer’s patients whose disease stage and age would be appropriate for a therapy with potentially highly toxic consequences for fragile recipients is also difficult to gauge.
That is not to say that CAR-immune cell therapy may not have a place in CNS disease. It just seems like neurological conditions, such as multiple sclerosis where patients are younger and potentially less fragile, are the place where much of the translational groundwork and clinical management for CAR-A or CAR-T therapies must be worked out before moving into neurodegenerative disease for elderly and cognitively compromised patients.
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