Exposure to cold physical plasma has been proposed to be of therapeutical value in in oncology via the generation of a number of biologically relevant redox-active molecules. Cancer cells can be recognized and eliminated by cells of the immune system, and accordingly many tumors are populated with these cells, among them T helper cells (TH cells). These lymphocyte population is crucial for effector immune responses against tumor antigens, in response to immunogenic cell death in malignant cells. However, a number of TH populations exists, each having distinct phenotypical features. Using a cold atmospheric pressure argon plasma jet, its redox activity was tested in different TH cell subpopulations to better understand the immunological consequences of potential antitumor plasma treatments in vivo.