The chimeric antigen receptor (CAR) T-cell therapy axicabtagene ciloleucel was deemed safe and showed encouraging signs of efficacy in a small pilot trial involving patients with lymphoma of the brain and/or spinal cord, according to findings presented by Caron A. Jacobson, MD, MMSc, and colleagues at the 2022 American Society of Hematology (ASH) Annual Meeting and Exposition (Abstract 440).
The research also features an in-depth, molecular study of individual CAR T cells isolated from patients’ blood and cerebrospinal fluid (CSF). This analysis—presented in another abstract at ASH (Abstract 165) conducted in collaboration with the Cellular Therapeutics and Systems Immunology Lab, directed by Leslie Kean, MD, PhD, at Dana-Farber and Boston Children’s Hospital—revealed a surprising difference between the two CAR T-cell populations: the cells in the CSF display a molecular signature that indicates activation of the interferon pathway, an important step in rallying the immune system.
“For many patients with lymphoma of the central nervous system, there aren’t great treatment options,” said Dr. Jacobson. “Our early results suggest that expanding the applicability of CAR T cells to this indication could improve patient outcomes.”
The underlying biology of primary and secondary CNS lymphomas can be quite different, and these cancers are often difficult to treat, especially once the tumors evade standard treatments. In that case, patients typically do not live more than 2 years.
CAR T cells, which are made from patients’ own disease-fighting T cells and are genetically rewired to bind and destroy tumors, have proven effective in treating other forms of lymphoma, but their efficacy has not been widely studied in disease of the brain and spinal cord. Dr. Jacobson and her colleagues knew CAR T cells can access the brain from previous research, but the neurologic toxicities that can emerge during treatment sparked concerns about deploying the therapy against CNS targets. For this reason, the team embarked on a pilot clinical trial to assess the safety of axicabtagene ciloleucel for primary and secondary CNS lymphoma.
Study Details
The trial was intentionally designed with pauses to assess safety at multiple points, and if at any time two or more treatment-limiting toxicities emerged, the researchers would amend the trial protocol. However, the study was able to proceed without interruption. The researchers enrolled patients into two cohorts: the first for those with lymphoma only in the CNS, and the second for patients with lymphoma in both the body and CNS.
The results for nine patients enrolled in the first cohort were reported at the ASH Annual Meeting and Exposition. To date, all patients have received axicabtagene ciloleucel and are at least 1-month posttreatment. Seventy-eight percent of patients saw their tumors shrink or disappear due to the treatment, and 67% of patients showed a complete response in which their tumors disappeared. The duration of these responses was 10 months. The median progression-free survival was nearly 1 year, and the median overall survival was 19 months. Although further clinical study is required, the data suggest that axicabtagene ciloleucel yields responses that are potentially more durable than current treatments for CNS lymphoma.
Molecular Analysis
The molecular study (Abstract 165) was conducted in Dr. Kean’s laboratory and was led by Dana-Farber’s Ulrike Gerdemann, MD (also of Boston Children’s Hospital); Alexandre Albanese, PhD, of Boston Children’s Hospital; and James Kaminski, PhD, who holds positions at Boston Children’s Hospital and the Broad Institute. The team collected blood and CSF from patients enrolled in the first cohort. CSF samples were collected via a specialized port, known as an Ommaya reservoir, which lies just under the scalp and allows CSF to be accessed more frequently and less painfully than with a traditional spinal tap.
Blood and CSF samples were collected daily during the period when CAR T cells proliferate most rapidly in the body (days 5 through 9 following axicabtagene ciloleucel treatment). Both CAR and non-CAR T cells were isolated and analyzed using advanced single-cell techniques, including single-cell RNA sequencing and single-cell sequencing of T-cell receptors.
“This approach gives us an unprecedented opportunity to explore the immune environment of the central nervous system and determine how that compares to the peripheral blood,” said Dr. Gerdemann. “Moreover, we can compare identical cell populations in both blood and CSF, gaining a high-resolution picture of T-cell dynamics and a deeper understanding of what drives therapeutic responses.”
Drs. Gerdemann, Kaminski, Albanese, and their colleagues analyzed over 125,000 individual cells. The breadth and depth of the researchers’ inquiry enabled them to reveal a molecular signature, unique to CAR T cells in CSF, that could be important for driving antitumor responses. This signature reveals that the CSF CAR T cells are highly activated and have turned on the interferon pathway, which is important for immune activity.
“Further studies of these cells promise to shed even more light on their unique biology and their activities in the body,” said Dr. Kaminski.
Disclosure: For full disclosures of the study authors, visit ash.confex.com.
