With the support of T-regulatory (Treg) cells, the immune system maintains optimal T-effector (Teff) immunological responses against invading microorganisms and tumor antigens while limiting inappropriate autoimmune responses against self-antigens. As a result of their mutual control, Treg and Teff cells contribute to immunological homeostasis. While Tregs can help tumor immune evasion by reducing anti-tumor Teff responses, Treg depletion can lead to Teff responses against self-antigens, which can lead to autoimmune illness. As a result, a breakdown of homeostatic balance between Teff and Treg cells is frequently linked to cancer and autoimmunity. Immune suppression by Treg cells appears to be a key obstacle to successful anticancer immune responses, and their inactivation or elimination is being considered a potential treatment option. Despite the lack of adequate techniques for selective Treg cell modification in humans, a variety of medications and biologicals, as well as reprogramming tumor-infiltrating antigen presentation cells, can modify their number and function.