Abstract:

Malignant pleural effusion （MPE） is a common complication in patients with advanced malignant tumors，which not only significantly reduces their quality of life but also shortens their survival duration. Despite the widespread use of traditional treatment methods such as thoracentesis and pleurodesis，their efficacy is limited accompanied by high recurrence rates. Therefore，exploring novel therapeutic strategies becomes particularly urgent. In recent years， immunotherapy has attracted extensive attention for its potential in cancer treatment. This article systematically reviews the roles of CD4+T cell subsets，including regulatory T cells （Treg）， T helper cell（Th）17， Th9， and Th22 cells， within the immunosuppressive microenvironment of MPE. These cell subsets are involved in the formation of the immunosuppressive state of MPE through various mechanisms and play key roles in the occurrence and development of the disease. In addition，the article discusses in detail the role of immune checkpoint molecules， such as programmed death protein 1 （PD-1）， PD-1 ligand（PD-L1）， and cytotoxic T-lymphocyte-associated protein 4 （CTLA-4）， in the immune evasion of MPE. The abnormal expressions of these molecules provide opportunity for tumor cells to evade immune system surveillance. At the same time， this article also summarizes the application prospects of novel immunotherapy strategies， such as adoptive cell therapy （ACT） and chimeric antigen receptor T cell （CAR-T） therapy，in the treatment of MPE. These innovative therapies offer possibilities for improving the prognosis of MPE patients through activating and enhancing the anti-tumor immune response.

Key words: Malignant pleural effusion, Immune tolerance, Regulatory T cells, T helper 17 cells, T helper 9 cells, T helper 22 cells