Neurological and Cognitive Dysfunction Following CAR-T Treatment. ICANS and Beyond

Neurological symptoms after immune effector cell therapy are poorly understood, even though acute neurological adverse events have been reported for all CAR T-cell products. Adverse events affecting the central nervous system (CNS) during CAR-T-cell treatment-known as Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS)-typically occur about 4-10 days after treatment and cause symptoms such as confusion and speech difficulties. The incidence of ICANS ranges from as low as 2% to as high as 60%-70%. Despite many research projects and clinical trials, the pathogenesis of acute neurological toxicity remains unclear. Although the acute symptoms of ICANS are well characterized, little is known about long-term effects regarding fatigue and cognitive function after this treatment.

We aim to prospectively include patients scheduled to undergo CAR-T therapy at ME CAST, Karolinska University Hospital Huddinge, to study ICANS. Because ICANS develops rapidly, inclusion during this potentially life-threatening phase would not be feasible; patients must therefore be enrolled before they start treatment. We aim to include patients who are clinically at high risk of developing ICANS. The risk of ICANS is assessed based on diagnosis, tumor burden, CAR-T product, and inflammatory status prior to treatment initiation. Although the life-threatening phase may resolve within a few days thanks to rapid diagnostics and optimized treatment, some patients develop more long-lasting symptoms. These patients may experience reduced quality of life and difficulty returning to work and daily routines. Unfortunately, it is currently difficult to quantify and grade these symptoms, which complicates, for example, sickness certification or rehabilitation. Moreover, knowledge is very limited regarding the pathophysiological factors underlying symptoms such as fatigue and cognitive difficulties, and treatment options are limited.

Based on our results in allogeneic stem cell-transplanted patients and prior research on ICANS, our hypothesis is that clinical tools can predict high risk for ICANS and that long-term symptoms are caused by persistent low-grade inflammation in the brain after the acute phase. We believe that patients have dysregulated microglial cells and injury to synaptic function in neurons. Previous research has shown that a reduced number of connections between nerve cells (synapses) causes mental fatigue and cognitive difficulties in several psychiatric and neurodegenerative disorders.

We now plan to compare patients who develop ICANS grade 2-4 with patients who develop no ICANS or at most grade 1. Patients will undergo Positron Emission Tomography (PET) with two different tracers: (1) PBR28 for TSPO, which provides a measure of brain inflammation-this ligand binds to microglial cells-and (2) 11C-UCB-J for SV2A, which provides a measure of synaptic density in the brain. The results will be compared with magnetic resonance imaging. Understanding the relationship between neuroinflammation and synapse loss and how this can lead to cognitive difficulties may ultimately lead to new treatment methods. We will collect blood and cerebrospinal fluid (CSF) samples from this patient cohort. Blood samples will be taken from all patients before, during, and after CAR-T treatment. In the event of ICANS, a lumbar puncture will be performed according to clinical routine and CSF will be collected for microbiological analyses, cell counts, biochemistry, flow cytometry, etc., with the addition of research samples. CAR-T cells will be quantified in blood and CSF. During the acute phase, patients with ICANS will undergo neuroimaging with CT and/or MRI. Much of the above already forms part of routine diagnostics, which we now wish to analyze prospectively. Participation in the study also includes computer-based cognitive testing and genetic testing to determine whether the patient has receptors allowing binding of the TSPO radioligand used during PET imaging.