Previous studies have suggested that common antigens that exist in neurons and tumor cells trigger cross immunoreaction, which attacks the neurons and tumor cells simultaneously. This action leads to paraneoplastic symptoms and slowed tumor growth. The present study co‑cultured peripheral blood mononuclear cells (PBMCs) from anti‑Hu antibody‑associated patients with paraneoplastic neurological syndrome (PNS) and the small cell lung cancer cell line NCI‑H446 (H446) in vitro. In the PNS group, no significant difference was observed in the proliferation index of PBMCs and H446 cells between the mixed or separate cultures. The proportion of CD4+ T cells in patients with PNS (76.54±3.96%) was significantly higher (P<0.05) compared with the healthy control individuals (51.75±17.3%). In conclusion, the sensitized specific T cells in the PBMCs of PNS patients predominantly comprised of CD4+ T cells, which had no inhibitory effect on small cell lung cancer cells in vitro.