Certain cancers that contain organized clusters of immune cells known as tertiary lymphoid structures (TLS) do not respond to treatment as well as expected. Even though they have TLS that support the elimination of cancer cells, they remain resistant to immunotherapy. γ-Aminobutyric acid (GABA), better known as the brain’s major inhibitory neurotransmitter, may play a role in this lack of response by acting as an immunoregulatory metabolite, according to a study led by scientists at Sorbonne Université.