In physiology, regulatory CD4+ T cells or Tregs, are responsible for maintaining immune homeostasis by inhibiting effector T cells, thereby preventing autoimmunity. Tregs do this in different ways, for example, by expressing cell-surface inhibitors, producing inhibitory cytokines, depletion of IL-2, purine-mediated suppression of CD39 dependent conversion of ATP or direct cytotoxicity. However, in tumor microenvironments, a major hindrance to tumor regression is the suppression of anti-tumor immune response by inhibitory populations like Tregs, which are also seen to be enriched in many tumors. Many clinical studies have shown that depletion of Tregs results in tumor regression, but also leads to other complications like autoimmunity and allergies. Therefore, it is important to identify molecular markers associated exclusively with tumor-linked Tregs.
In this publication, Alvisi, et.al have studied the molecular mechanisms of immunosuppression in CD4+ T cells taken from chemotherapy-naive non-small cell lung cancer patients. The authors used a 27-colour flow cytometry panel, encompassing markers of memory and effector T cell differentiation, activation, metabolic activity and exhaustion, as well as Treg markers. Besides, they also used single-cell and bulk RNA sequencing, and fluorodeoxyglucose uptake in positron emission tomography in the study. Their results reveal that human tumors are infiltrated by a large number of CD4+ Tregs with a highly activated phenotype and enhanced suppressive capacity compared to Tregs in healthy tissues. The authors show that this differentiation is brought about by the transcription factor IRF4 and its molecular partner BATF, which are responsible for the regulation of a network of immunosuppressive genes in tumor-infiltrating Tregs.
Read the article in The Journal of Clinical Investigation here.