CD4 and small cell lung carcinoma: These peptides are then processed and presented by antigen-presenting cells (APCs) to CD4+ helper T-cells via major histocompatibility complex class II (MHC II), which in turn will activate antigen-specific B cells into Ab-producing plasma cells, leading to the appearance of onconeural antibodies in serum and in CSF; however, additionally, CD8+ cytotoxic T lymphocytes via MHC class I molecules, which will cause the neurological dysfunction [25]. In recent years, chemotherapy for advanced SCLC has been increasingly combined with cytotoxic anticancer agents and ICIs, including atezolizumab.