PHARMACEUTICAL PRODUCTS OF RECOMBINANT DNA TECHNOLOGY: AN OVERVIEW

ABOUT AUTHOR:
Muhammad Mujahed
M.Sc Biotechnology
Swami Ramanand Teerth Marathwada University, Vishnupuri , Nanded.
mujubiotech2011@rediffmail.com

INTRODUCTION:
A few decades ago, it was realized that certain proteins could be used as pharmaceutical agents for the treatment of human diseases. e.g. insulin for diabetes mellitus, interferon for viral diseases. However the availability of such therapeutic/ pharmaceutical products was limited due to costly and cumbersome procedures involved in their isolation. Further, their use in humans was associated with several complications. For instance, administration of pig insulin to diabetic patients results in the development of antibodies.

The advent of recombinant DNA technology heralded a new chapter for the production of a wide range of therapeutic agents in sufficient quantities for human use. The commercial exploitation of recombinant DNA  (rDNA) technology began in late 1970s by biotechnological companies to produce proteins.There are around 400 different proteins being produced  by rDNAtechnologyand as of now around 30 have been approved for human use.

REFERENCE ID: PHARMATUTOR-ART-1866

Recombinant DNA technology involves using microorganisms, macroscopic organisms, or hybrids of tumor cells and leukocytes:

• to create new pharmaceuticals;
• to create safer and/or more effective versions of conventionally produced pharmaceuticals; and
• to produce substances identical to conventionally made pharmaceuticals more cost-effectively than the latter pharmaceuticals are produced.

Recombinant DNA technology enables modifying microorganisms, animals, and plants so that they yield medically useful substances, particularly scarce human proteins (by giving animals human genes, for example). This review, however, focuses not on pharmaceutical biotechnology’s methods but on its products, notably recombinant pharmaceuticals.

TYPES:
The pharmaceutical products of rDNA technology are broadly divided into following three types
1.    Human protein replacements
2.    Therapeutic agents for human diseases
3.    Vaccines

1)   HUMAN PROTEIN REPLACEMENTS
The synthesis of the cellular proteins is ultimately under the control of genes. Any defect in a gene produces an incorrect protein or no protein at all. Thus, gene defects will result in inherited or genetically linked diseases.

Identification of defective or deficient proteins in the causation of inherited diseases is very important. The rDNA technology can be fruitfully employed to produce human proteins that can be used for the treatment of genetically linked diseases. This is referred to as human protein replacement strategy in biotechnology.

EXAMPLES:

INSULIN:
The hormone insulin is produced by the β-cells of islets of Langerhans of pancreas. Human insulin contains 51 amino acids, arranged in two polypeptide chains. The chain A has 21 amino acids while b has 30 amino acids. Both are held together by disulfide bonds.

Insulin is central to regulating carbohydrateand fat metabolism in the body. Insulin causes cells in the liver, skeletal muscles, and fat tissue to absorb glucose from the blood. In the liver and skeletal muscles, glucose is stored as glycogen, and in fat cells (adipocytes) it is stored as triglycerides.

Insulin stops the use of fat as an energy source by inhibiting the release of glucagon. With the exception of the metabolic disorder diabetes mellitus and metabolic syndrome, insulin is provided within the body in a constant proportion to remove excess glucose from the blood, which otherwise would be toxic. When blood glucose levels fall below a certain level, the body begins to use stored sugar as an energy source through glycogenolysis, which breaks down the glycogen stored in the liver and muscles into glucose, which can then be utilized as an energy source. As a central metabolic control mechanism, its status is also used as a control signal to other body systems (such as amino acid uptake by body cells). In addition, it has several other anabolic effects throughout the body.

When control of insulin levels fails, diabetes mellitus can result. As a consequence, insulin is used medically to treat some forms of diabetes mellitus. Patients with type 1 diabetes depend on external insulin (most commonly injected subcutaneously) for their survival because the hormone is no longer produced internally. Patients with type 2 diabetes are often insulin resistant and, because of such resistance, may suffer from a "relative" insulin deficiency. Some patients with type 2 diabetes may eventually require insulin if other medications fail to control blood glucose levels adequately. Over 40% of those with Type 2 diabetes require insulin as part of their diabetes management plan.

 Diabetes mellitus affects about 2-3% of the general population.it is a genetically linked disease characterized by the increased blood glucose concentration (hyperglycemia). Insulin facilitates the cellular uptake and utilization of glucose for release of energy. In the absence of insulin, glucose accumulates in the blood stream at higher concentration, usually when the blood glucose concentration exceeds about 180mg/dl, glucose is excreted into urine. The patients of diabetes ate weak and tired since the production of energy (i,e ATP)  is very much depressed.The more serious complications of uncontrolled diabetis include kidney damage (neuropathy), nerve diseases (neuropathy), and circulatory diseases (atheroscelerosis,stroke).

Production of recombinant insulin:
Attempts to produce insulin by rDNA technology started in late 1970s.the basic technique consisted of inserting human insulin gene and the promoter gene of lac operon on to the plasmids of E.coli. Recently the procedure employed for synthesis involves insertion of genes for insulin A chain and B chain separately to the plasmids of differentE.colicultures.the lac operon system( consisting of inducer gene, promoter gene, operator gene and structural gene Z for –galactosidase)is used for expression of both genes.the presence of llactose in the culture mediuminduces the synthesis of insulin A and B chains in separate cultures. The so formed insulin chains can be isolated, purified and joined together to give a full-fledged human insulin.

Fig:  Production of recombinant insulin in E.coli

Forms of human insulin:
Human insulin is available in two forms, a short acting (regular) form and an intermediate acting (NPH) form. NPH (Neutral Protamine Hagedorn) insulin, also known as isophane insulin, is a suspension meaning that the insulin vial should be rolled or repeatedly turned upside down to ensure the solution is uniformly cloudy.

Some examples of human insulin:

• Regular (short acting): Humulin S, Actrapid, Insuman Rapid
• NPH (intermediate acting):Humulin I, Insuman basal, Insulatard
• Premixed human insulins:Humulin M2, M3 and M5, Insuman Comb 15, 25 and 50

As a medication

Insulin vial
Biosynthetic "human" insulin is now manufactured for widespread clinical use using recombinant DNA technology. More recently, researchers have succeeded in introducing the gene for human insulin into plants and in producing insulin in them, to be specific safflower. This technique is anticipated to reduce production costs.

Several of these slightly modified versions of human insulin, while having a clinical effect on blood glucose levels as though they were exact copies, have been designed to have somewhat different absorption or duration of action characteristics. They are usually referred to as "insulin analogues". For instance, the first one available, Humalog(insulin lispro), does not exhibit a delayed absorption effect found in regular insulin, and begins to have an effect in as little as 15 minutes. Other rapid-acting analogues are NovoRapid and Apidra, with similar profiles. All are rapidly absorbed due to a mutation in the sequence that prevents the insulin analogue from forming dimers and hexamers. Instead, the insulin molecule is a monomer, which is more rapidly absorbed. Using it, therefore, does not require the planning required for other insulins that begin to take effect much later (up to many hours) after administration. Another type is extended-release insulin; the first of these was Lantus(insulin glargine). These have a steady effect for the entire time they are active, without the peak and drop off effect in other insulins; typically, they continue to have an insulin effect for an extended period from 18 to 24 hours. Likewise, another protracted insulin analogue (Levemir) is based on a fatty acid acylation approach. A myristyric acid molecule is attached to this analogue, which in turn associates the insulin molecule to the abundant serum albumin, which in turn extends the effect and reduces the risk of hypoglycemia. Both protracted analogues need to be taken only once-daily, and are very much used in the type 1 diabetes market as the basal insulin. A combination of a rapid acting and a protracted insulin is also available for the patients, making it more likely for them to achieve an insulin profile that mimics that of the body´s own insulin release.Insulin is usually taken as subcutaneous injections by single-use syringes with needles, via an insulin pump, or by repeated-use insulin pens with needles.

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Unlike many medicines, insulin currently cannot be taken orally because, like nearly all other proteins introduced into the gastrointestinal tract, it is reduced to fragments (even single amino acid components), whereupon all activity is lost. There has been some research into ways to protect insulin from the digestive tract, so that it can be administered orally or sublingually. While experimental, several companies now have various formulations in human clinical trials, and one, the India-based Biocon, has formed an agreement with BMS to produce an oral-insulin alternative.

HUMAN GROWTH HORMONE:
Growth hormone is produced by the pituitary gland. It regulates the growth and development. Growth hormone stimulates overall body growth by increasing the cellular uptake of amino acids , and protein synthesis, and promoting the use of fat as body fuel.insufficient human growth hormone  (HGH) in young children results in retarded growth, clinically referred to as pituitary dwarfism.

Growth hormone is used as a prescription drug in medicine to treat children's growth disorders and adult growth hormone deficiency. In the United States, it is only available legally from pharmacies, by prescription from a doctor. In recent years in the United States, some doctors have started to prescribe growth hormone in GH-deficient older patients (but not on healthy people) to increase vitality. While legal, the efficacy and safety of this use for HGH has not been tested in a clinical trial.

Function
Effects of growth hormone on the tissues of the body can generally be described as anabolic (building up). Like most other protein hormones, GH acts by interacting with a specific receptor on the surface of cells.

Increased height during childhood is the most widely known effect of GH. Height appears to be stimulated by at least two mechanisms:
1. Because polypeptide hormones are not fat-soluble, they cannot penetrate cell membranes. Thus, GH exerts some of its effects by binding to receptors on target cells, where it activates the MAPK/ERK pathway. Through this mechanism GH directly stimulates division and multiplication of chondrocytes of cartilage.

2. GH also stimulates, through the JAK-STAT signaling pathway,^[30] the production of insulin-like growth factor 1(IGF-1, formerly known as somatomedin C), a hormone homologous to proinsulin The liver is a major target organ of GH for this process and is the principal site of IGF-1 production. IGF-1 has growth-stimulating effects on a wide variety of tissues. Additional IGF-1 is generated within target tissues, making it what appears to be both an endocrine and an autocrine/paracrine hormone. IGF-1 also has stimulatory effects on osteoblast and chondrocyte activity to promote bone growth.

Main pathways in endocrine regulation of growth.

In addition to increasing height in children and adolescents, growth hormone has many other effects on the body:
* Increases calciumretention, and strengthens and increases the mineralization of bone
* Increases muscle mass through sarcomerehypertrophy
* Promotes lipolysis
* Increases protein synthesis
* Stimulates the growth of all internal organs excluding the brain
* Plays a role in homeostasis
* Reduces liveruptake of glucose
* Promotes gluconeogenesisin the liver
* Contributes to the maintenance and function of pancreatic islets
* Stimulates the immune system

Production of recombinant  HGH
Biotechnologists can now produce HGH by genetic engineering. The technique adopted is quite comparable with that of insulin production. The procedure essentially consists of inserting HGH gene into E.coli plasmid, culturing the cells and isolation of the HGH from the extracellular medium.

Limitation in HGHproduction : The HGH is a protein comprised of 191 amino acids. During the course of its natural synthesis in the body.,HGH is tagged with a single peptide  (with 26 amino acids) The signal peptide is removed during secretion to release the active HGH for biological functions. The entire process of HGH synthesis goes on in an orderly fashion in the body. However, signal peptide interrupts HGH production by recombinant technology. The complementary DNA (cDNA) synthesized from the mRNA encoding HGH is inserted into the plasmid. The plasmid containing E.coli when cultured, produces full length HGH along with signal peptide.ButE.coli cannot remove the signal peptide. Further, it is also quite difficultto get rid of signal peptide by various other means. Theoretically, cDNA encoding signal peptide can be cut to solve these problems. Unfortunately, there is no restriction endonuclease to do this job, hence this is not possible.

HGH Vial

A novel approach for HGH production:
Biotechnologists  have resolved the problem of signal peptide interruption by a novel approach. The base sequence in cDNA encoding signal peptide ( 26 amino acids ) plus the neighbouring 24 amino acids is cut by restriction endonuclease ECoRI. Now a gene (cDNA ) for 24 amino acid sequence of HGH is freshly synthesized and ligated to the remaining HGHcDNA. The so constituted cDNA , attached to a vector, is inserted into a bacterium such as E. coli for culture and production of HGH. In this manner, the biologically functional HGH  can be produced by DNA technology.

2)   THERAPEUTIC AGENTS FOR HUMAN DISEASES
Biotechnology is very useful for the production of several therapeutic products for treating human diseases. A selected list of rDNAderived therapeutic agents along with trade names and their uses in human are given below…..

rDNA Product	Trade name	Application / Uses
Insulin	Humulin	Diabetes
Growth hormone	Protropin/Humatrope	Pituitary dwarfism
Interferon	Intron A	Hairy cell leukemia
Hepatitis B vaccine	Recombinax HB/ Engerix	Hepatitis B
TissuEplasminogen activator	Activase	Myocardial  infarction
Factor vIII	Kogenate/Recombinate	Hemophilia
Dnase	Pulmozyme	Cystic fibrosis
Erythropoietin	Epogen/rocrit	Severe anemia with kidney damage

INTERFERONS:

Interferons(IFNs) are proteins made and released by host cells in response to the presence of pathogenssuch as viruses, bacteria, parasites or tumor cells. They allow for communication between cells to trigger the protective defenses of the immune system that eradicate pathogens or tumors.

IFNs belong to the large class of glycoproteins known as cytokines. Interferons are named after their ability to "interfere" with viral replication within host cells. IFNs have other functions: they activate immune cells, such as natural killer cells and macrophages; they increase recognition of infection or tumor cells by up-regulating antigen presentation to T lymphocytes; and they increase the ability of uninfected host cells to resist new infection by virus. Certain symptoms, such as aching muscles and fever, are related to the production of IFNs during infection.

Functions
All interferons share several common effects; they are antiviral agents and can fight tumors. As an infected cell dies from a cytolytic virus, viral particles are released that can infect nearby cells. However, the infected cell can warn neighboring cells of a viral presence by releasing interferon. The neighboring cells, in response to interferon, produce large amounts of an enzymeknown as protein kinase R(PKR). This enzyme phosphorylates a protein known as eIF-2 in response to new viral infections; the phosphorylated eIF-2 forms an inactive complex with another protein, called eIF2B, to reduce protein synthesis within the cell. Another cellular enzyme, RNAse L— also induced following PKR activation—destroys RNA within the cells to further reduce protein synthesis of both viral and host genes. Inhibited protein synthesis destroys both the virus and infected host cells. In addition, interferons induce production of hundreds of other proteins—known collectively as interferon-stimulated genes (ISGs)—that have roles in combating viruses. They also limit viral spread by increasing p53 activity, which kills virus-infected cells by promoting apoptosis. The effect of IFN on p53 is also linked to its protective role against certain cancers.

Another function of interferons is to upregulate major histocompatibility complex molecules, MHC Iand MHC II, and increase immunoproteasomeactivity. Higher MHC I expression increases presentation of viral peptides to cytotoxic T cells, while the immunoproteasome processes viral peptides for loading onto the MHC I molecule, thereby increasing the recognition and killing of infected cells. Higher MHC II expression increases presentation of viral peptides to helper T cells; these cells release cytokines (such as more interferons and interleukins, among others) that signal to and co-ordinate the activity of other immune cells.

Interferons, such as interferon gamma, directly activate other immune cells, such as macrophages and natural killer cells. Interferons can inflame the tongue and cause dysfunction in taste bud cells, restructuring or killing taste buds entirely.

Interferon therapy

Three vials filled with human leukocyte interferon

The immune effects of interferons have been exploited to treat several diseases. Agents that activate the immune system, such as small imidazoquinoline molecules that activate TLR7, can induce IFN-α. Imidazoquinoline is the main ingredient of Aldara (Imiquimod) cream, a treatment approved in the United States by the Food and Drug Administration (FDA) for actinic keratosis, superficial basal cell carcinoma, papilloma and external genital warts. Synthetic IFNs are also made, and administered as antiviral, antiseptic and anticarcinogenic drugs, and to treat some autoimmune diseases.

New research has shown that imiquimod's anti-proliferative effect is totally independent of immune system activation or function. Imiquimod exerts its effect by increasing levels of the opioid growth factor receptor (OGFr). Blocking OGFr function with siRNA technology resulted in loss of any antiproliferative effect of imiquimod.

Interferon beta-1a and interferon beta-1b are used to treat and control multiple sclerosis, an autoimmune disorder. This treatment is effective for slowing disease progression and activity in relapsing-remitting multiple sclerosis and reducing attacks in secondary progressive multiple sclerosis.

Interferon therapy is used (in combination with chemotherapy and radiation) as a treatment for many cancers. This treatment is most effective for treating hematological malignancy; leukemia and lymphomas including hairy cell leukemia, chronic myeloid leukemia, nodular lymphoma, cutaneous T-cell lymphoma.^[21]Patients with recurrent melanomas receive recombinant IFN-α2b. Type I IFNs have a therapeutic potential for the treatment of a wide variety of leukemias and solid tumors due to their antiproliferative and apoptotic effects, their anti-angiogenic effects and their ability to modulate an immune response specifically activating dendritic cells, cytolytic T cells and NK cells. Research in this area is receiving intensive investigation. Interferon a 2b is also being used for treatment of ocular surface squamous neoplasia (OSSN) in the form of perilesional injection followed by topical interferon a 2b drops at Lahore General Hospital Eye unit II.^[

Both hepatitis B and hepatitis C are treated with IFN-α, often in combination with other antiviral drugs. Some of those treated with interferon have a sustained virological response and can eliminate hepatitis virus. The most harmful strain—hepatitis C genotype I virus—can be treated with a 60-80% success rate with the current standard-of-care treatment of interferon-α, ribavirin and recently approved protease inhibitors such as Telaprevir (Incivek) or Boceprevir (Victrelis). Biopsies of patients given the treatment show reductions in liver damage and cirrhosis. Some evidence shows giving interferon immediately following infection can prevent chronic hepatitis C, although diagnosis early in infection is difficult since physical symptoms are sparse in early hepatitis C infection. Control of chronic hepatitis C by IFN is associated with reduced hepatocellular carcinoma.

Administered intranasally in very low doses, interferon is extensively used in Eastern Europe and Russia as a method to prevent and treat viral respiratory diseases such as cold and flu. However, mechanisms of such action of interferon are not well understood; it is thought that doses must be larger by several orders of magnitude to have any effect on the virus. Although most scientists are skeptical of any claims of good efficacy recent findings suggest that interferon applied to mucosa may act as an adjuvant against influenza virus, boosting the specific immune system response against the virus. A flu vaccine that uses interferon as adjuvant is currently under clinical trials in the US.

When used in the systemic therapy, IFNs are mostly administered by an intramuscular injection. The injection of IFNs in the muscle, in the vein, or under skin is generally well tolerated. The most frequent adverse effects are flu-like symptoms: increased body temperature, feeling ill, fatigue, headache, muscle pain, convulsion, dizziness, hair thinning, and depression. Erythema, pain and hardness on the spot of injection are also frequently observed. IFN therapy causes immunosuppression, in particular through neutropenia and can result in some infections manifesting in unusual ways.

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Drug formulations:

Generic name	Trade name
Interferon alpha 2a	Roferon A
Interferon alpha 2b	Intron A/Reliferon/Uniferon
Human leukocyte Interferon-alpha (HuIFN-alpha-Le)	Multiferon
Interferon beta 1a, liquid form	Rebif
Interferon beta 1a, lyophilized	Avonex
Interferon beta 1a, biogeneric (Iran)	Cinnovex
Interferon beta 1b	Betaseron/ Betaferon
Interferon gamma 1b	Actimmune
PEGylated interferon alpha 2a	Pegasys
PEGylated interferon alpha 2a(Egypt)	Reiferon Retard
PEGylated interferon alpha 2b	PegIntron
PEGylated interferon alpha 2bplus ribavirin(Canada)	Pegetron

Several different types of interferon are now approved for use in humans. By March 10, 2009, Multiferon — a brand name known generically as human leukocyte interferon-alpha (HuIFN-alpha-Le) — was being used in 14 European countries. This drug was approved for treatment of patients with high risk (stage IIb–III) cutaneous melanoma, after two treatment cycles with dacarbazine, following a clinical trial performed in Germany.

In January 2001, the Food and Drug Administration(FDA) approved the use of PEGylated interferon-alpha in the USA; in this formulation, polyethylene glycolis added to make the interferon last longer in the body. Initially used for production of PEGylated interferon-alpha-2b(Pegintron), approval for PEGylated interferon-alpha-2a(Pegasys) followed in October 2002. These PEGylated drugs are injected once weekly, rather than administering three times per week, as is necessary for conventional interferon-alpha. When used with the antiviral drugribavirin, PEGylated interferon is effective in treatment of hepatitis C; at least 75% people with hepatitis C genotypes 2 or 3 benefit from interferon treatment, although this is effective in less than 50% of people infected with genotype 1 (the more common form of hepatitis C virus in both the U.S. and Western Europe).^[36][37][38]Recently, 2 new Protease Inhibitors have been approved which improves the outcomes for Genotype 1 hepatitis C - boceprevirand telaprevir. These drugs are used in addition to PEG-IFN / Ribavirin.

Erythropoietin:
It is  also known as erythropoetin or erthropoyetin and or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production. It is a cytokine(protein signaling molecule) for erythrocyte (red blood cell) precursors in the bone marrow. Human EPO has a molecular weight of 34 kDa.

Also called hematopoietin or hemopoietin, it is produced by interstitial fibroblasts in the kidney in close association with peritubular capillary and tubular epithelial cells. It is also produced in perisinusoidal cells in the liver. While liver production predominates in the fetal and perinatal period, renal production is predominant during adulthood. In addition to erythropoiesis, erythropoietin also has other known biological functions. For example, it plays an important role in the brain's response to neuronal injury. EPO is also involved in the wound healing process.

When exogenous EPO is used as a performance-enhancing drug, it is classified as an erythropoiesis-stimulating agent (ESA). Exogenous EPO can often be detected in blood, due to slight differences from the endogenous protein, for example, in features of posttranslational modification.

Mechanism of action:
Erythropoietin has been shown to exert its effects by binding to the erythropoietin receptor(EpoR).

EPO is highly glycosylated (40% of total molecular weight), with half-life in blood around five hours. EPO's half-life may vary between endogenous and various recombinant versions. Additional glycosylation or other alterations of EPO via recombinant technology have led to the increase of EPO's stability in blood (thus requiring less frequent injections). EPO binds to the erythropoietin receptor on the red cell progenitor surface and activates a JAK2 signaling cascade. Erythropoietin receptor expression is found in a number of tissues, such as bone marrow and peripheral/central nervous tissue. In the bloodstream, red cells themselves do not express erythropoietin receptor, so cannot respond to EPO. However, indirect dependence of red cell longevity in the blood on plasma erythropoietin levels has been reported, a process termed neocytolysis.

Pharmaceutical companies make human recombinanterythropoietin with recombinant technology, in which genes are inserted to create a custom organism. In this particular case, bacteria are modified with recombination so that they will produce human erythropoietin which can be administered to patients. The same technology is used to produce a variety of other human hormones. These hormones are as effective in the body as hormones of human or animal origin, but they are easier and safer to produce.

There are side effects associated with human recombinanterythropoietin, especially in patients who use it for a long time. It can increase the risk of heavy clotting and adverse cardiovascular events, and it can also lead to iron deficiency and high blood pressure. In some young athletes, unexpected death has been linked to EPO usage, which is one of the reasons sports authorities are concerned about blood doping. Recombinant EPO is chemically slightly different from the made in the body version, and this can be used on blood tests to determine whether or not an athlete is doping.

3)  VACCINES:
Vaccination is the phenomenon of preventive immunization. In the modern concept, vaccination involves the administration (injection or oral) of an antigen to elicit an antibody response that will protect the organism against the future infections.

Vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as foreign, destroy it, and "remember" it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters.

Vaccines may be prophylactic (example: to prevent or ameliorate the effects of a future infection by any natural or "wild" pathogen), or therapeutic (e.g. vaccines against cancer are also being investigated; see cancer vaccine).

The term vaccine derives from Edward Jenner's 1796 use of cow pox (Latin variolavaccinia, adapted from the Latin vacc?n-us, from vacca, cow), to inoculate humans, providing them protection against smallpox.

Effectiveness
Vaccines do not guarantee complete protection from a disease.Sometimes, this is because the host's immune system simply does not respond adequately or at all. This may be due to a lowered immunity in general (diabetes, steroid use, HIV infection, age) or because the host's immune system does not have a B cell capable of generating antibodies to that antigen.

Even if the host develops antibodies, the human immune system is not perfect and in any case the immune system might still not be able to defeat the infection immediately. In this case, the infection will be less severe and heal faster.

Adjuvants are typically used to boost immune response. Most often aluminium adjuvants are used, but adjuvants like squalene are also used in some vaccines and more vaccines with squalene and phosphate adjuvants are being tested. Larger doses are used in some cases for older people (50–75 years and up), whose immune response to a given vaccine is not as strong.

Maurice Hilleman's measles vaccine is estimated to prevent 1 million deaths every year.

The efficacy or performance of the vaccine is dependent on a number of factors:

• the disease itself (for some diseases vaccination performs better than for other diseases)
• the strain of vaccine (some vaccinations are for different strains of the disease)
• whether one kept to the timetable for the vaccinations (see Vaccination schedule)
• some individuals are "non-responders" to certain vaccines, meaning that they do not generate antibodies even after being vaccinated correctly other factors such as ethnicity, age, or genetic predisposition.

Recombinant vaccines:
Biotechnology sector has also played its part in developing vaccines against certain diseases. Such vaccine which makes use of recombinant DNA technology is known as recombinant vaccines. It is also known as subunit vaccines.

Recombinant vaccines can be broadly grouped into two kinds:
(i) Recombinant protein vaccines: This is based on production of recombinant DNA which is expressed to release the specific protein used in vaccine preparation

(ii) DNA vaccines: Here the gene encoding for immunogenic protein is isolated and used to produce recombinant DNA which acts as vaccine to be injected into the individual.

Steps involved:
Production of recombinant vaccines involves the following steps:
(i) First and foremost, it is important that the protein which is crucial to the growth and development of the causative organism be identified.
(ii) The corresponding gene is then isolated applying various techniques. Further to this, an extensive study of the gene explains the gene expression pattern involved in the production of corresponding protein.
(iii) This gene is then integrated into a suitable expression vector to produce a recombinant DNA.
(iv) ThisrDNA is used as vaccines or is introduce into another host organism to produce immunogenic proteins which acts as vaccines.

Recombinant protein vaccines:
A pathogen upon infection produces proteins, vital for its functions, which elicit an immune response from the infected body. The gene encoding such a protein is isolated from the causative organism and used to develop a recombinant DNA. This DNA is expressed in another host organism, like genetically engineered microbes; animal cells; plant cells; insect larvae etc, resulting in the release of the appropriate proteins which are then isolated and purified. These when injected into the body, causes immunogenic response to be active against the corresponding disease providing immunity against future attack of the pathogen.

Based on the proteins involved in evoking immune response recombinant protein vaccines are of two types:
Whole protein vaccines: The whole immunogenic protein is produced in another host organism which is isolated and purified to act as vaccines.

Polypeptide vaccines: It is known that in the immunogenic protein produced, the actual immunogenic property is limited to one or two polypeptides forming the protein. The other parts of the protein may be successful in evoking an immune response but do not actually cause the disease. For eg: in the case of cholera caused by Vibrio cholerae, consists of three polypeptide chains like A1, A2, and B. The A polypeptides are toxic while B is non-toxic. Thus while producing vaccines, the polypeptide B is produced by rDNA technology and used for vaccination.

DNA vaccines:
It refers to the recombinant vaccines in which the DNA is used as a vaccine. The gene responsible for the immunogenic protein is identified, isolated and cloned with corresponding expression vector. Upon introduction into the individuals to be immunized, it produces a recombinant DNA. This DNA when expressed triggers an immune response and the person becomes successfully vaccinated. The mode of delivery of DNA vaccines include: direct injection into muscle; use of vectors like adenovirus, retrovirus etc; invitro transfer of the gene into autologous cells and reimplantation of the same and particle gun delivery of the DNA.

In certain cases, the responsible gene is integrated into live vectors which are introduced into individuals as vaccines. This is known as live recombinant vaccines. Eg: vaccinia virus. Live vaccinia virus vaccine (VV vaccine) with genes corresponding to several diseases, when introduced into the body elicit an immune response but does not actually cause the diseases.

Advantages:
(i) Since it does not involve actual pathogen, recombinant vaccines is considered to be safe than the conventional vaccines.
(ii) It induces both humoral and cellular immune response resulting in effective vaccination.

Risks involved:
(i) High cost of production.
(ii) Have to be stored at low temperature since heat destabilizes protein. Hence storage and transportation is tedious.
(iii) Individuals with immunodeficiency may elicit poor immune response.

CONCLUSION:
Recombinant DNA Technology is playing very important role in revolutionizing medicinei.e., enabling mass production of safe, pure, more effective versions of biochemicals that human body produces naturallyexamples includes a variety of products such as hormones, Therapeutic proteins, Vaccines and various Enzymes and also to create new pharmaceuticals..With sensible regulatory requirements and expeditious product review by regulatory agencies, biotech pharmaceuticals can within decades become unprecedented preventers and relievers of human suffering.

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