Abstract
Paraneoplastic cerebellar degeneration (PCD) is a rapidly progressive, immune-mediated syndrome characterized by the degeneration of Purkinje cells, often associated with the presence of antibodies targeting intracellular antigens within these cells. These autoantibodies are implicated in the induction of cytotoxicity, leading to Purkinje cell death, as demonstrated in in vitro models. However, the precise roles of antibodies and T lymphocytes in mediating neuronal injury remain a subject of ongoing research, with T cells appearing to be the main effectors of cerebellar injury. Notably, at least 50% of PCD cases involve anti-Yo autoantibodies, also referred to as anti-PCA1 (Purkinje cell antigen 1) antibodies, which specifically target cerebellar degeneration-related protein 2 (CDR2) and its paralogue, CDR2-like (CDR2L). Another recognized antigen is CDR 34, a 34 kDa Purkinje cell antigen characterized by tandem repeats and a B-cell epitope; its detection in non-cerebellar tissues necessitates further in situ hybridization studies. Onconeural antigens are expressed in both Purkinje cells and tumour cells, where they localize in the cytoplasm and associate with membrane-bound and free ribosomes, playing critical roles in regulating transcription and calcium homeostasis. Recent studies suggest that the breakdown of immune tolerance is linked to genetic alterations in tumour cell antigens, leading to the formation of neoantigens that can elicit autoreactive T cells, which may underscore the function of Yo antibodies. In vitro studies indicate that anti-Yo antibodies can induce cell death independent of T lymphocytes. The disease progresses by initial lymphocytic infiltration, followed by a rapid loss of Purkinje cells without significant inflammation. However, in vivo models showcase that anti-Yo PCD is primarily T-cell mediated, with antibodies serving as biomarkers rather than direct effectors of neuronal death. This review examines the mechanisms underlying PCD, focusing on the roles of CDR2 and CDR2L in tumour development and their potential role in the degeneration of cerebellar Purkinje neurons. A comprehensive understanding of these processes is essential for advancing diagnostic, prognostic, and therapeutic strategies for PCD and associated malignancies.