Question: Our antibody candidates are humanized/fully human. Aren’t they inherently non-immunogenic? Why should I screen for immunogenicity?
Answer: The variable framework regions and hyper-variable Contact Determining Regions (CDRs) of human antibodies are created by B cells in the periphery. During B cell maturation antibody variable chains are mutated through a process of recombination and somatic mutation. The resulting antibodies are “human” but also “foreign” in the sense that they cannot be directly transcribed from any particular gene contained within the human genome. The mechanisms of central tolerance, through which autoreactive T cells are recognized and either deleted or rendered anergic, are not capable of suppressing immune response targeting the variable portions of human antibodies [1,2].
The human antibody germline is relatively deimmunized (i.e. it contains relatively few effector T-cell epitopes) so the “average” antibody that is first made in response to an immune stimulus also contains relatively few effector T-cell epitopes. As antibodies mature, even human-derived antibodies deviate from what is called “germline” in the process of affinity maturation. Thus B cells can produce antibodies, which contain significant numbers of new (never been seen by the human body previously) T-cell epitopes. When this happens normal immune surveillance can result in the formation of a human-anti-human antibody response, the so-called HAHA response.
The HAHA response is a normal part of the human adaptive immune system. In a healthy human being this tendency towards auto-antibody responses is held in check by several overlapping mechanisms. First, the germline contains regulatory T-cell epitopes, which can engage and activate immune suppressing regulatory T cells, known as Tregitopes (see our paper in Blood, 2008 ). And so, the “average” human antibody is also relatively rich in regulatory T-cell epitopes that can inhibit the formation of the HAHA response. In addition the human immune system is capable of altering B cells producing autoreactive immunogenic antibodies through the process of receptor “editing” and also through directed apoptosis. Finally, human B cell response is polyclonal and competitive. B cells producing effective antibodies (those strongly binding to the protein target and not subject to autoimmune pressure) may proliferate and dominate immune response in the long run.
Humanized and fully human monoclonal antibodies contain greater or lesser numbers of effector and regulatory T-cell epitopes just as natural antibodies do (see De Groot and Martin, Clinical Immunology, 2009 ). Engineered antibodies which, by chance, contain a relatively large number of effector epitopes and a relatively smaller number of regulatory T-cell epitopes are likely to induce HAHA responses in human subjects. In this case, there is no process of B cell editing, competition, or apoptosis to help reprogram the deleterious immune response. Screening candidate antibodies for immunogenic potential based on the presence or absence of effector and known regulatory T cell epitopes can improve the quality of a biologic product pipeline by reducing the probability of failure due to anti-therapeutic immune response. For more about our immunogenicity screening products, click here.
1. Getts DR “Have we overestimated the benefit of human(ized) antibodies?” mAbs 2:6 Nov./Dec. 2010 682-694
2. Harding FA “The immunogenicity of humanized and fully human antibodies” mAbs 2:3 May/June 2010 256-265.
3. De Groot A.S., L. Moise, J.A. McMurry, Erik Wambre, Laurence Van Overvelt, Philippe Moingeon, W. Scott, W. Martin, Activation of Natural Regulatory T cells by IgG Fc-derived Peptide “Tregitopes”. Blood, 2008,112: 3303. http://tinyurl.com/ASDeGroot-Blood-2008.
4. De Groot A.S., Martin WD. Reducing Risk, Improving Outcomes: Bioengineering less immunogenic protein therapeutics. (Andy Saxon, Ed.). Clin Immunol. 2009 May;131(2):189-201. http://tinyurl.com/ASDeGroot-Clin-Immunol-2009.
For more reading about this topic, see the following references
Antibody humanization: a case of the ‘Emperor’s new clothes’? Mike Clark , Immunology Today Volume 21, Issue 8, 1 August 2000, Pages 397-402. doi:10.1016/S0167-5699(00)01680-7.