Clone of cells

Subsequent antigenic stimulation results in high antibody titres (secondary or memory resporrse) as there is now an expanded clone of cells with memory of the original antigen available to proliferate into mature plasma cells (Fig. 14.1). 

Monoclonal antibody, an antibody produced by a single clone of cells (specifically, a single clone of hybridoma cells) and therefore a single pure homogeneous type of antibody that binds to the same target. 

The development of techniques for the production of monoclonal antibodies by Kohler and Milstein has enormously expanded the potential of antibodies as analytical and therapeutic agents. A monoclonal antibody is one that is produced by a clone of cells all derived from a single lymphocyte. Any lymphocyte can probably produce only a single immunoglobulin and hence the antibody produced by a clone of identical cells is very restricted in the antigens to which it will bind, making it a very specific reagent. 

Monoclonal antibody, mAb Describes an antibody derived from a single clone of cells or a clonally obtained cell line. Its common use denotes an antibody secreted by a hybridoma cell line. Monoclonal antibodies are used very widely in the study of antigens, and as diagnostics. 

Traditionally, immunohistochemical studies have been performed with antibodies of polyclonal origin. Antibodies are said to be polyclonal when they are collected from different clones of cells, after a significant immune response. Specifically, the presence of an antigen causes lymphocytes in an exposed area to... 

A cancer is a clone of cells arising from a single cell. These cells have escaped the usual controls on cell division. Consequently, they have the potential to proliferate and differentiate without control. 

Drugs that act by different mechanisms may have additive or synergistic therapeutic effects. Tumors may contain heterogeneous clones of cells that differ in their susceptibility to drugs. Combination therapy will thus increase log cell kill and diminish the probability of emergence of resistant clones of tumor cells. 

When clones of cells are determined to express aputative protein of interest, a set of small-scale purification procedures is developed to further characterize the biochemical and biophysical properties of the protein.Typically, to isolate sufficiently pure... 

Figure 10.3. Schematic representation of monoclonal antibody production using immortalized hybrid cells that secrete antibodies selective for the target antigen. The mortal, immune B cells Isolated from mice immunized with a target antigen are fused with myeloma, immortal B cells that express defective antibodies. The selecting of antigen-specific, immortal hybrid cells (hybridomas) results in identification of unique clones of cells that express antibodies with high specificity and affinity (monoclonal antibodies). These cells are cloned and expanded for large-scale monoclonal antibody preparations.

Furthermore, it is accepted that the somatic cell-mutation theory underlies chemical carcinogenesis. This theory presumes that there is an interaction between the carcinogen and DNA to cause a mutation (Fig. 6.49). This mutation is then fixed when the DNA divides. Further replication then provides a clone of cells with the mutation, which may become a tumor. 

Many variations of site-directed mutagenesis exist. One can start out with a circular, single-stranded DNA and anneal it to a synthetic primer DNA carrying the desired changes (fig. 27.10). This primer can be extended, and the resulting product can be transfected. Finally, one selects clones of cells containing the plasmid with the desired changes. 

A preparation of antibody molecules that arises from several different clones of cells is called a polyclonal antibody. It is a mixture of antibody molecules that bind to different parts of the antigen and with different binding affinities. 

Antibody produced by a single clone of cells is a monoclonal antibody all the antibody molecules are identical and bind to the same antigenic site with identical binding affinities. Monoclonal antibodies can be generated in large amounts by creating a cell fusion (called a hybridoma) between an antibody-producing cell and a myeloma cell. 

There are several stages to the transformation process. Some cell strains (e.g. mouse 3T3 cells) have gained only the property of immortality, whereas in others this is accompanied by an increased rate of cell division and a decrease in contact inhibition reflected in the ability to grow to high cell densities. NIH 3T3 cells undergo further spontaneous transformation at a rate which depends on their recent history (Rubin and Xu, 1989). Thus late passage cells subcultured into a nutritionally poor medium show very numerous foci representing clones of cells with reduced contact inhibition. Such cells often show reduced nutritional requirements relative to primary cells. 

Other selection systems involve the fusion of proline requiring CHO cells and defective mouse cells in HAT medium lacking proline and the fusion of normal lymphocytes (which do not grow in vitro) with defective mouse cells (which do not grow in HAT medium). It is this latter technique which has allowed the isolation of clones of cells which will synthesise in vitro large amounts of a single antibody (i.e. a monoclonal antibody) (Kohler, 1982). 

Scheme 3). A clone of cells from the midge Cbironomus tentans was found to be resistant to the effects of ecdysteroids because they metabolized 20-hydroxyecdysone rapidly. The initial oxidation product was 20,26-dihydroxyecdysone, but this was oxidized further to 20-hydroxy-26-oxo-ecdysone (21). This aldehyde (21) then formed a tautomeric equilibrium mixture of two cyclic hemiacetals (22) and (23), which were separable, isolated, and their structures determined (Scheme 3) with the use of acetonides (Section 4.03.3.6).32 These are the first examples of ecdysteroids with side-chain hemiacetals. Although 20,26-dihydroxyecdysterone still... 

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