Development, expression and characterization of humanized anti-c2 monoclonal antibody / Suba Dharshanan A/L Panja Bernam
Humanized monoclonal antibodies (mAbs) are widely used for diagnosis and treatment of cancer due to their reduced immunogenicity and high specificity. In this project, we aimed to develop procedures to produce, with high efficiency in terms continuity of production, lowered cost and increased spe...
Saved in:
| Summary: | Humanized monoclonal antibodies (mAbs) are widely used for diagnosis and treatment
of cancer due to their reduced immunogenicity and high specificity. In this project, we
aimed to develop procedures to produce, with high efficiency in terms continuity of
production, lowered cost and increased speed, humanized mAbs against C2-antigen
(hum-C2 mAbs), a marker specifically expressed in colorectal and ovarian cancer, from
mAb of mouse origin. The resulting hum-C2 mAbs must still retain their original
specificity and functionality, but possess reduced immunogenicity. Two methods of
humanization were compared to identify potential immunogenic mouse amino acids in
the variable regions: a deimmunization method and a logical approach method using
IgBLAST software. The respective amino acids were then replaced with their
corresponding human residues by overlapping-PCR mutagenesis. The hum-C2 mAbs
were expressed in NS0 mammalian cells. To decrease the time to identify and isolate
high-producing transfectomas secreting hum-C2 mAbs, ClonePix FL which is a highthroughput,
rapid and automated system, was employed to screen large numbers of
transfectomas in a short period of time with increased probability of obtaining rare and
precious high-producing cells. The high-producing NS0 transfectomas were adapted to
serum-free media because the use of serum involves many ethical, safety and scientific
complications. An automated liquid chromatography system, Äktaprime Plus, was used
to purify hum-C2 mAb instead of the conventional method of antibody purification
which is time-consuming, laborious and prone to errors. In terms of functionality, the
hum-C2 mAbs produced by both humanization methods were still able to bind
iv
specifically to C2-antigen expressed on the surface of colorectal cancer cells (SW1116)
in vitro. However, in terms of immunogenicity, only the humanized antibodies
developed by deimmunization method had lower immunogenicity in Macaca
fascicularis compared to chimeric and mouse anti-C2 mAbs. This clearly indicated the
superiority of deimmunization method and demonstrated the fact that it could not be
substituted by the logical approach method. Unfortunately, the use of overlapping-PCR
mutagenesis to humanize mouse residues in the deimmunization method frequently
results in undesired mutations which cause the method to be time-consuming and thus is
not cost-effective. Thus, we substituted the conventional protocol with a method using
synthetic DNA coding for the hum-C2 variable regions which were then transfected into
NS0 and CHO mammalian cells using both pFUSE and UCOE expression systems.
However we found that pFUSE vectors only worked for NS0 cells and UCOE vectors
only for CHO cells. It was also found that the level of expression of hum-C2 mAbs in
CHO cells using UCOE vectors was 100 times higher than NS0 cells transfected with
pFUSE vectors. In addition, the use of UCOE vectors in CHO cells produced a greater
number of high-producing and stable transfectomas. Hence, it was concluded that the
best approach to produce hum-C2 mAbs is by using synthetic DNA coding the variable
regions cloned into UCOE expression vectors and transfected in CHO cells. The use of
ClonePix FL and Äktaprime Plus systems also allows the isolation of high-producing
transfectomas and purification of humanized mAbs to be performed efficiently and
quickly. |
|---|