The molecular weight of traditional antibody is about 150kDa, and its size is 14.2 nm ×  8.2 nm  ×  3.8 nm, so that the penetration of solid tumor is poor, and the curative effect of solid tumor is not ideal. The molecular weight of nano antibody (heavy chain variable region VHH) from camels and sharks is about one tenth of that of traditional antibody, which shows the hope of solid tumor treatment. This article summarizes eight advantages of nanoantibody and six applications in tumor diagnosis

1.What is nano antibody

There is a natural heavy chain antibody with light chain deletion in camels. Cloning its variable region can obtain a single domain antibody consisting only of heavy chain variable region, called VHH (variable domain of heavy chain of heavy chain antibody), also known as nanoantibody (a single domain antibody), which is the smallest functional antigen-binding segment.

2.The difference between nano antibody and ordinary antibody

In addition to producing monoclonal antibodies, infected or immunized camels or alpacas also secrete a unique and heavy chain only antibody, both of which have the ability to bind to antigens. The heavy chain antibody lacks all the CH1 regions of the common antibody, and CDR1 and CDR3 are longer than VH, which to some extent makes up for the deficiency of the decrease of antigen binding force caused by the loss of light chain. The structural differences between the two are shown in the figure below:

Advantages of nanoantibody：

1）Stable structure and high temperature resistance; The nanoantibody has only one domain and does not contain the traditional connecting peptide sequence. In addition to the conserved disulfide bonds in the domain, the CYS in VHH CDR3 can also form disulfide bonds with the CYS in CDR1 or FR2. These increased sequences and loop structures expand the area of antibody binding with antigen and the diversity of antibody, and at the same time lead to its very stable structure, which can withstand high temperature and harsh extreme environment.

2）The complement reaction caused by Fc segment is avoided: the nano antibody has no traditional Fc segment, thus avoiding the complement reaction caused by Fc segment.

3）Nanoantibodies are easy to carry out gene manipulation. Thus, univalent, bivalent, bispecific and multivalent antibodies can be formed, and fusion proteins can also be formed for targeted treatment.

4）Nano antibody has weak immunogenicity and good compatibility with human body. Compare the VH germline sequence with the germline sequence of the unimodal camel. The former is about 50 species, and the latter is about 40 species. The VHH germline gene sequence of camel is highly homologous with the human VH3 family sequence, so it is relatively simple to humanize VHH.

5）Nanoantibody has small molecular weight and simple structure: it is encoded by a single gene, so it can be expressed in large quantities in bacteriophages, bacteria and yeast.

6）Nanoantibodies have a strong and fast penetration ability, which is conducive to their entry into solid tumors and play a role. At the same time, because they can penetrate the blood-brain barrier, they provide a new method for brain drug delivery.

Conclusion: Compared with ordinary antibody, nanoantibody has small molecular weight, simple structure, easy genetic modification, small volume, good antigenic specificity, strong tissue penetration, high stability, and broad application prospects in disease diagnosis and treatment.

3.Progress in clinical research of nanoantibody

Since the first discovery of heavy chain antibody in 1993, its antigen-binding domain nanoantibody has received widespread attention, and the research literature and reports on nanoantibody have increased exponentially. In 2018, the first nano-antibody drug Cablivi (caplacizumab) was approved by the European Union EMA, and then approved by the FDA and the Canadian Ministry of Health for the treatment of adult patients with acquired thrombotic thrombocytopenic purpura (aTTP). In October 2021, Nvida of Corning Jerry, Suzhou ® It is the world's first subcutaneous injection PD-L1 inhibitor, which can be administered within 30 seconds without intravenous infusion, greatly reducing the time of administration. In February 2022, the BCMA CAR-T product, developed by Janssen and Legendary Biology, was approved by the US FDA for marketing and used to treat adult patients with recurrent/refractory multiple myeloma (MM). In September 2022, Ozooralizumab injection of Daisei Pharmaceutical was approved by Japan PMDA for marketing and applicable to rheumatoid arthritis. Oli Group single antigen research company is Ablynx, which is a human TNF α Nano antibody.

In addition, there are many nano-antibody drugs in different drug development stages in the world, with broad indications, obvious drug innovation and broad prospects for drug development.