Biology Reference
In-Depth Information
27
HUMAN ANTIBODIES IN MOUSE
As we have discussed before, among more than 2,500 human and mouse
CDRH3 amino acid sequences each, only one sequence is shared by both.
The question is then whether mouse CDR's are also antigenic in human
patients. Even though the half-lives of humanized mouse antibodies is
approaching that of human antibodies in human patients, they are still not
the same. Thus, recently, transgenic mice carrying human antibody genes
have been constructed. These animals may thus be used to selectively
produce human antibodies with required specificities. However, whether
such transgenic mice use preferably mouse or human genes for the
production of their antibodies requires careful analysis. In other words, it
will be essential to identify the origin of their CDR's. Our finding of nearly
distinct sets of human and mouse CDR's can provide some information by
sequence comparison as illustrated above.
PHAGE DISPLAY LIBRARY
Some filamentous phages can carry extra pieces of DNA. Human antibody
variable regions genes, i.e. V-genes and J-minigenes of the light chains, and
V-genes, D-minigenes and J-minigenes of the heavy chains, can be
incorporated. By various combinations, different phages will display
different V
L
and V
H
on their surfaces. These V
L
and V
H
will associate to
form globular structures known as F
v
with the same specificities of Fab.
Since large numbers of phages can be processed and screened, those
displaying very high binding affinity F
v
can be selected. Separate libraries
can be constructed for human genes, for mouse genes, etc.
After the V
L
and V
H
genes have been selected for specified binding
properties, they can then be joined onto the constant region genes of the
light and heavy chains respectively for the production of biologically active
complete antibody molecules.
In short, there are various biological tools capable of constructing antibodies
with desired properties. However, the binding specificity between antibody
and antigen molecules is not understood, and left to a random selective
process. In order to tackle this basic problem, we have to analyze how
CDR's are folded, how the CDRH3 defines the fine specificity of an
antibody, how the combination of all six CDR's can improve the binding
affinity, etc.
