使用以免疫为基础的试剂，如T细胞和治疗用抗体，或修饰病人的免疫系统使其更好的抵御疾病的方法运用。在正常情况下免疫系统会以抗体和T细胞作为主要武器来消灭入侵者。免疫系统也能够识别和消灭某些癌症。当它失灵时，人们可以分离出针对某种疾病的抗体和T细胞，注入病人体内以增强病人的免疫能力。在其它情况下，不正常的免疫反应会造成攻击自己的组织，引起"自体免疫病"，如糖尿病。这时，免疫治疗可以用来关闭这种免疫性免疫反应，用已知的抗体或蛋白质如细胞激动素来影响免疫过程。过激的免疫系统也是引起过敏的原因，本来无害的物质（如花粉）会引起不必要的免疫反应。同样的，抗体、蛋白质或药物可以用来改变这种免疫反应。

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.