Moreover, CD8 T-cell infiltration was marked as shown by the CD4:CD8 T-cell ratio (1.03), lower than what is usually observed in cerebrospinal fluid (2.2-3.4) and blood (1.5-1.9) in controls, meningitis and multiple sclerosis [14], in keeping with preferential CD8 T-cell recruitment, especially in the Purkinje cell layer where the CD4:CD8 ratio was 0.8. Keywords: CD8 T cells; cerebellitis; CTLA-4 inhibitor; immune checkpoint inhibitors; ipilimumab; paraneoplastic cerebellar degeneration EN CD8 T cells cerebellitis CTLA-4 inhibitor immune checkpoint inhibitors ipilimumab paraneoplastic cerebellar degeneration 1 5 5 02/03/22 20220215 NES 220215 We report a rapidly progressive and fatal CD8 T-cell-mediated cerebellitis after ipilimumab (cytotoxic T-lymphocyte-associated protein 4 inhibitor) for small cell lung cancer. CD8 T-cell-mediated cerebellitis directed against Purkinje cell antigen after ipilimumab for small cell lung cancer A patchy CD8 T-cell infiltrate spatially corresponded to areas of Purkinje cell loss, with occasional CD8 polarisation towards Purkinje cells. [Extracted from the article]