BY: SAI MANOGNA (MSIWM014)

Most antigens include multiple epitopes, thereby inducing the proliferation and differentiation of several B cells’ clones, each derived from a B-cell that recognizes a specific epitope. The serum antibodies resulting from this are heterogeneous, consisting of a mixture of antibodies, each unique to one epitope. This polyclonal antibody response facilitates the localization, phagocytosis, and complement-mediated lysis of the antigen; it thus has strong in vivo benefits for the organism. Sadly, the antibody heterogeneity that improves in vivo immune defense also decreases an antiserum’s effectiveness for different in vitro uses. These monoclonal antibodies derived from a single clone and, therefore, unique to a single epitope are preferable for most research, diagnostic, and therapeutic purposes.

1. It is not possible to specifically biochemically purify a monoclonal antibody from a polyclonal antibody preparation.

2. Georges Kohler and Cesar Milstein created a system for the preparation of monoclonal antibodies in 1975, which soon became a key technology in immunology.

3. They were able to create a hybrid cell called a hybridoma by fusing a regular activated, antibody-producing B-cell with a myeloma cell that possessed the myeloma cell’s immortal growth properties secreted the antibody formed by the B cell.

4. As a result, hybridoma cell clones that secrete massive amounts of monoclonal antibodies can be cultured indefinitely.

5. The invention of monoclonal antibody production techniques has provided immunologists with a robust and flexible research method. When each was awarded a Nobel prize, Köhler and Milstein’s work was remembered.

Catalyze enzymes of Monoclonal Antibodies :

In certain aspects, an antibody’s binding to its antigen is identical to the binding of an enzyme to its substrate. The binding includes weak, noncovalent interactions in both cases and shows high specificity and also high affinity. What separates an antibody-antigen interaction from an enzyme-substrate interaction is that the antibody does not alter the antigen. At the same time, a chemical alteration in its substrate is catalyzed by the enzyme. However, like enzymes, the transition state of a bound substrate can be stabilized by antibodies of approximate specificity, thus reducing the activation energy for substrate chemical modification.

Production of monoclonal antibodies :

The issue of whether some antibodies could act like enzymes and catalyze chemical reactions was raised by the similarities between antigen-antibody interactions and enzyme-substrate interactions. A hapten-carrier complex was synthesized to investigate this possibility, in which the hapten structurally resembled the transition state of an under-going hydrolysis ester.

1. To produce monoclonal anti-hapten monoclonal antibodies, spleen cells from mice immunized with this transition state equivalent were fused with myeloma cells.

2. Some of them accelerated hydrolysis by about 1,000-fold when these monoclonal antibodies were incubated with an ester substrate; that is, they behaved like the enzyme that usually catalyzes the hydrolysis of the substrate.

3. These antibodies catalytic activity was highly specific; i.e., only esters whose transition-state structure closely resembled the transition-state equivalent used in the immunizing conjugate as hapten was hydrolyzed.

4. About their dual function as antibody and enzyme, these catalytic antibodies have been called abzymes.

5. The central goal of catalytic antibody research is the derivation of a battery of abzymes that break peptide bonds at unique amino acid residues, as well as restriction enzymes that cut DNA at particular sites.

6. In both structural and functional analysis of proteins, such abzymes will be invaluable instruments.

7. Besides, it may be possible to manufacture abzymes with the potential to dissolve blood clots or break viral glycoproteins at specific locations, thus blocking viral infectivity.

8. Unfortunately, it has been challenging to derive catalytic antibodies that cleave peptide bonds of proteins.

Most of the latest research in this area is dedicated to solving this critical yet challenging problem.

Clinical Uses :

a. Clinical Medicine: In clinical medicine, monoclonal antibodies prove to be very useful as diagnostic, imaging, and therapeutic reagents. Initially, they were used primarily as in vitro diagnostic reagents. Products for detecting pregnancy, diagnosing various pathogenic microorganisms, measuring the blood levels of different medications, matching histocompatibility antigens, and detecting antigens shed by certain tumors are among the several monoclonal antibody diagnostic reagents now accessible.

b. Radiology: Radiolabeled monoclonal antibodies may also be used in vivo to identify or locate tumor antigens, allowing certain primary or metastatic tumors in patients to be detected early. For example, to detect a tumor’s spread to regional lymph nodes, monoclonal antibodies to breast cancer cells are labeled with iodine-131 and introduced into the blood. This monoclonal imaging technique will expose breast cancer metastases that would be undetected by other, less sensitive scanning techniques.

c. Immunology: Potentially useful therapeutic reagents are immunotoxins consisting of tumor-specific monoclonal antibodies coupled to lethal toxins.

Shigella toxin, diphtheria toxin, and ricin, all of which inhibit protein synthesis, are used in preparing immuno-toxins. These toxins are potent that a single molecule has been shown to kill a cell. Each of these toxins consists of two types of functionally different polypeptide components, an inhibitory chain and one or more binding chains that interact on cell surfaces with receptors; without the binding polypeptides, the toxin does not reach cells and is therefore harmless. By replacing the binding polypeptides with a monoclonal antibody unique to a specific tumor cell, an immuno-toxin is prepared.

The attached monoclonal antibody will, in principle, deliver the toxin chain directly to tumor cells, where it will cause death by protein synthesis inhibition. Initial clinical responses to such immunotoxins have shown promise in patients with leukemia, lymphoma, and other cancer forms. Further research is ongoing to improve and demonstrate their safety and efficacy.

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