使用以免疫為基礎的試劑，如T細胞和治療用抗體，或修飾病人的免疫系統使其更好的抵御疾病的方法運用。在正常情況下免疫系統會以抗體和T細胞作為主要武器來消滅入侵者。免疫系統也能夠識別和消滅某些癌癥。當它失靈時，人們可以分離出針對某種疾病的抗體和T細胞，注入病人體內以增強病人的免疫能力。在其它情況下，不正常的免疫反應會造成攻擊自己的組織，引起"自體免疫病"，如糖尿病。這時，免疫治療可以用來關閉這種免疫性免疫反應，用已知的抗體或蛋白質如細胞激動素來影響免疫過程。過激的免疫系統也是引起過敏的原因，本來無害的物質（如花粉）會引起不必要的免疫反應。同樣的，抗體、蛋白質或藥物可以用來改變這種免疫反應。

The use of immune-based reagents such as T cells and antibodies for therapeutic purposes, or the use of methods that will modify a patient’s immune system to better fight disease. Under normal circumstances the immune system will eradicate an infectious agent using antibodies and T cells as its main weapons. The immune system is also capable of recognizing and eradicating certain cancers. When this does not occur, disease-specific antibodies or T cells can be isolated and introduced into a patient to enhance the patients’ immune response. In other cases, an aberrant immune response can lead to an attack on self-tissue and cause a “autoimmune disease”, such as diabetes. Here, immunotherapy may be used to switch off this damaging immune response, using antibodies or proteins such as cytokines that are known to affect the immune process. An over-reactive immune system is also the cause of allergies, where a harmless agent (such as pollen) can lead to an unnecessary immune response. Here again, antibodies, proteins or drugs can be used to modify this immune response.