Application areas suitable for use of polyclonal antibodies are as follows:
a) Sandwich ELISA for tumor markers or other antigens can be designed with polyclonal antibodies as the coating (trapping) antibody, followed by addition of standard antigen/sample and then addition of relevant MAb conjugated to HRPO.
b) Polyclonal antibodies are useful in histopathological analysis using immunoperoxides staining technique.
c) In some cases of affinity purification of antigens, polyclonals have advantages over MAbs.
Single domain antibodies (dAbs) was developed by scientists at LMB, Cambridge. They consist of just the binding site of the orginal antibody and are produced by injecting the relevant genes, take directly from the mouse, into the bacteria. The small size of dAbs gives them the ability of penetrate tissue quickly, block specific active sites on a virus and rapidly diffuse. Their cheap production (100-10000 times less than mAbs/pAbs) is a major advbantage3. According to Scotgen, U.K., dAbs will not appear in products until the latter half of the decade and will displace mAbs in some applications by year 2000 A.D.
MAbs are used instead of pAbs because of better specificity, sensitivity, ease of applicability and use and availability of instrumentation for automation.
2.4 Bispecific, Chimaeric and Single Chain Antibodies
Bispecific Antibodies are antibodies in which the combining sites of the immunoglobulin molecule react with two distinct antigenic determinants. This property is very useful in therapy and diagnosis. In in vitro diagnosis, bispecific antibodies provide higher signal-to-noise ratios, and the possibility of multiple antigen detection. In therapy, they are less toxic, more active and have a longer half-life.
Chimaeric Antibodies can be obtained by coupling human CH (constant heavy) and CL genes (constant light) with mouse VH (variable heavy) and VL (variable light) genes and then introducing them into myeloma cells. Such combinations may be more therapeutically useful than mAbs of purely murine origin, because of less antigen city. Chimaeric antibodies have potential in the treatment of cancer, auto immunity, graft rejection and infectious diseases where repeated administration of antibody reagents may be required.
Single Chain Antibodies are produced by genetically linking heavy and light chain variable region genes with a DNA sequence encoding a synthetic peptide linker. These antibodies offer reduced toxicity, improved attachment of imaging or therapeutic agents and improved binding performance when immobilized. Production of single chain antibodies are expected to be low cost because the genetically engineered organism can be grown rapidly in large volume fermentors on in expensive media. No products of this technology are expected to reach clinical research by 1992.
3.1 Importance and relationship of monoclonal antibodies to the broader area of biotechnology and other relevant sectors
Monoclonal antibodies is a significant branch of biotechnology that has a pervasive impact on the health care industry and is likely to play a major role in diagnostics, therapeutics and industrial purification of biological and chemical products. Early diagnosis of disease will have a significant impact on (i) quality of life for the patient (ii) survival rate (iii) health care costs. Detection of crop diseases can aid the farmer to use a more specific type of herbicide or fungicide in a smaller dose. This will not only increase the yield but also reduce the cost of raising crops.
3.2 Status of ongoing research in India for development and production of mAbs
National Institute of Immunology (NII), Delhi has reported generation of mAbs to detect typhoid fever, and hepatitis B virus. They are in the process of developing monoclonals against rotavirus and virulent stains of E. Coli. This is under clinical trials. Monoclonals to detect bacteria that are difficult to culture or have very long incubation periods in vitro such as Mycobacterium spp. Brucella spp. Are being developed but research has not been successful so far. Research work in India is yet to be initiated for the diagnosis of life threatening infections such as streptococcus group B in the central nervous system, vibrio cholera infection.
Monoclonals have been raised against variety of antigens related to human medicine including hormones, proteins involved with a tumour, drugs. A pregnancy test kit which detects human chorionic gonadotropin (HCG) in the urine of pregnant women has been developed in India by Ranbaxy laboratories in collaboration with NII, Delhi. These kits are already available in the market. Lupin Laboratories has set up a project 5 years ago in Bhopal to produce monoclonal diagnostic kits using indigenous hybridoma technology and ascitis technology. Some of the kits are undergoing clinical trials. In the second phase they plan to use r-DNA technology to produce therapeutic drugs, hepatitis vaccines and growth hormones. Span Diagnostics, Surat drugs, hepatitis experimenting with the preparation of ELISA kits for Hepatitis B antigen. Monoclonals have also been generated against cancer markers CEA, AFP, feritin by cancer institutes in Madras and Bombay. Indian Institute of Microbial Technology (IMTECH) Chandigarh has developed monoclonals against urokimase, fibrin, rifamycine oxidase, tissue type plasminogen activator. Tata Institute of Fundamental Research (TIFR), Bombay has developed mAbs against neural antigens of Drosophila and Zebra fish and nitrate reductase. P.G. Institute for Medical Research, Chandigarh has developed antibodies against human sperm antigen and leishmania donovani. Back