The first approved clinical gene therapy (1990) treated ADA-deficient severe combined immunodeficiency (SCID) by introducing a functional ADA gene into the patient's lymphocytes using a viral vector.
Dolly was produced by somatic cell nuclear transfer (SCNT): the nucleus of an adult somatic cell was transferred into an enucleated oocyte, which developed into an embryo genetically identical to the nucleus donor.
A permanent cure requires replacement of the defective hematopoietic stem cell population so that all blood cells express ADA. Introducing bone-marrow/hematopoietic stem cells that produce ADA (or correcting them by gene therapy) offers lasting correction; enzyme replacement and periodic infusions are temporary.
Human insulin consists of two polypeptide chains: Chain A has 21 amino acids and Chain B has 30 amino acids, linked by disulfide bonds.
PCR cycles: (1) Denaturation — heat separates DNA strands; (2) Annealing — primers bind to complementary sequences; (3) Synthesis/Extension — DNA polymerase extends primers to synthesize new DNA.
PCR uses heat-stable DNA polymerase (e.g., Taq polymerase) that remains active at high temperatures used for denaturation; this allows automated thermal cycling without adding fresh enzyme each cycle.
ELISA (enzyme-linked immunosorbent assay) detects antigens or antibodies and is widely used for pathogen detection and diagnosis (e.g., HIV, hepatitis), based on antigen–antibody reactions and enzyme color development.
A transgenic animal carries foreign DNA stably integrated into its genome and present in all (or most) cells, often including the germ line so the transgene is heritable.
Subunit (recombinant) vaccines contain only specific antigenic components (proteins) of a pathogen rather than whole organisms, reducing risk while eliciting an immune response.
Two primers (a forward and a reverse) are required each cycle. Primers are short synthetic oligonucleotides complementary to the ends of the target sequence; they provide a free 3'-OH for DNA polymerase to begin synthesis. DNA polymerase (a heat-stable enzyme) extends the primers by adding dNTPs to synthesise new DNA strands (5'→3'). The common enzyme used is Taq polymerase from Thermus aquaticus.
Two primers (a forward and a reverse) are required each cycle. Primers are short synthetic oligonucleotides complementary to the ends of the target sequence; they provide a free 3'-OH for DNA polymerase to begin synthesis. DNA polymerase (a heat-stable enzyme) extends the primers by adding dNTPs to synthesise new DNA strands (5'→3'). The common enzyme used is Taq polymerase from Thermus aquaticus.
PCR amplification: mix template DNA, two specific primers, dNTPs, buffer with Mg2+, and heat‑stable DNA polymerase (Taq). Thermal cycling: (1) Denaturation (~94–95°C) separates strands; (2) Annealing (50–65°C) allows primers to bind target sequences; (3) Extension (~72°C) polymerase extends primers. Repeating 25–35 cycles yields exponential amplification (≈2^n copies). A thermal cycler automates temperature changes and product is analyzed by gel electrophoresis.
PCR amplification: mix template DNA, two specific primers, dNTPs, buffer with Mg2+, and heat‑stable DNA polymerase (Taq). Thermal cycling: (1) Denaturation (~94–95°C) separates strands; (2) Annealing (50–65°C) allows primers to bind target sequences; (3) Extension (~72°C) polymerase extends primers. Repeating 25–35 cycles yields exponential amplification (≈2^n copies). A thermal cycler automates temperature changes and product is analyzed by gel electrophoresis.
Genetically engineered (recombinant) insulin is human insulin produced by rDNA technology: the human insulin gene (or separate A and B chains/proinsulin) is expressed in microbes (E. coli or yeast), purified and processed to active insulin (e.g., Humulin). It is identical to human insulin, reducing immune reactions compared to animal insulin.
Genetically engineered (recombinant) insulin is human insulin produced by rDNA technology: the human insulin gene (or separate A and B chains/proinsulin) is expressed in microbes (E. coli or yeast), purified and processed to active insulin (e.g., Humulin). It is identical to human insulin, reducing immune reactions compared to animal insulin.
“Rosie” is a transgenic cow engineered to express a human milk protein (human alpha‑lactalbumin) in her mammary glands. Unlike normal cows, Rosie's milk contains the human protein due to insertion of a human gene under a mammary‑specific promoter, improving nutritional properties for infant formula or therapeutic protein production.
“Rosie” is a transgenic cow engineered to express a human milk protein (human alpha‑lactalbumin) in her mammary glands. Unlike normal cows, Rosie's milk contains the human protein due to insertion of a human gene under a mammary‑specific promoter, improving nutritional properties for infant formula or therapeutic protein production.
Before rDNA, insulin was extracted from animal pancreases (bovine or porcine). Problems: limited and variable supply, differences in amino acid sequence causing immune/allergic reactions, risk of contamination, expensive purification, and batch inconsistency.
Before rDNA, insulin was extracted from animal pancreases (bovine or porcine). Problems: limited and variable supply, differences in amino acid sequence causing immune/allergic reactions, risk of contamination, expensive purification, and batch inconsistency.
ELISA detects proteins or antibodies, so it could measure enzyme levels (phenylalanine hydroxylase) if a specific antibody is available, but it does not detect DNA mutations. Molecular diagnosis of PKU requires biochemical tests (e.g., elevated phenylalanine in newborn screening) or DNA-based methods (PCR, sequencing) to identify causative mutations. Thus ELISA is of limited use for definitive genetic diagnosis.
ELISA detects proteins or antibodies, so it could measure enzyme levels (phenylalanine hydroxylase) if a specific antibody is available, but it does not detect DNA mutations. Molecular diagnosis of PKU requires biochemical tests (e.g., elevated phenylalanine in newborn screening) or DNA-based methods (PCR, sequencing) to identify causative mutations. Thus ELISA is of limited use for definitive genetic diagnosis.
Gene therapy is preferable when safe and feasible because it can correct the root cause and provide long‑term or permanent production of the missing protein by the patient's own cells. Enzyme replacement therapy (ERT) provides temporary relief, requires repeated administrations, is costly, and can provoke immune responses. However, gene therapy carries risks (vector safety, insertional mutagenesis, immune reactions) and technical challenges; ERT may be better short-term or when gene therapy is not available or safe. Choice depends on disease, availability, and risk–benefit analysis.
Gene therapy is preferable when safe and feasible because it can correct the root cause and provide long‑term or permanent production of the missing protein by the patient's own cells. Enzyme replacement therapy (ERT) provides temporary relief, requires repeated administrations, is costly, and can provoke immune responses. However, gene therapy carries risks (vector safety, insertional mutagenesis, immune reactions) and technical challenges; ERT may be better short-term or when gene therapy is not available or safe. Choice depends on disease, availability, and risk–benefit analysis.
Transgenic animals carry foreign DNA stably integrated into their genome and express the transgene in somatic and often germ cells. Examples: transgenic mice used in research, transgenic goats producing human antithrombin in milk (ATryn), transgenic salmon (AquAdvantage) with growth hormone gene, transgenic cows like Rosie producing human milk proteins, and pigs engineered for xenotransplantation.
Transgenic animals carry foreign DNA stably integrated into their genome and express the transgene in somatic and often germ cells. Examples: transgenic mice used in research, transgenic goats producing human antithrombin in milk (ATryn), transgenic salmon (AquAdvantage) with growth hormone gene, transgenic cows like Rosie producing human milk proteins, and pigs engineered for xenotransplantation.
ELISA detects anti‑HIV antibodies and is useful for diagnosing HIV after the window period (antibodies typically appear within weeks to months). Early after exposure (window period) ELISA may be negative; p24 antigen tests or PCR for viral RNA detect infection earlier. Recommendation: do an initial ELISA and repeat after the window period (or use combination antigen/antibody tests) for reliable diagnosis.
ELISA detects anti‑HIV antibodies and is useful for diagnosing HIV after the window period (antibodies typically appear within weeks to months). Early after exposure (window period) ELISA may be negative; p24 antigen tests or PCR for viral RNA detect infection earlier. Recommendation: do an initial ELISA and repeat after the window period (or use combination antigen/antibody tests) for reliable diagnosis.
ADA deficiency (a form of SCID) can be treated by: (1) Enzyme replacement therapy supplying ADA protein periodically; (2) Hematopoietic stem cell/bone marrow transplant from a matched donor to restore ADA‑producing cells; (3) Gene therapy (ex vivo): patient hematopoietic stem cells or lymphocytes are removed, transduced with a vector carrying functional ADA cDNA, and reinfused, enabling long‑term ADA expression and immune restoration.
ADA deficiency (a form of SCID) can be treated by: (1) Enzyme replacement therapy supplying ADA protein periodically; (2) Hematopoietic stem cell/bone marrow transplant from a matched donor to restore ADA‑producing cells; (3) Gene therapy (ex vivo): patient hematopoietic stem cells or lymphocytes are removed, transduced with a vector carrying functional ADA cDNA, and reinfused, enabling long‑term ADA expression and immune restoration.
DNA vaccines are plasmid DNA constructs encoding antigenic proteins of a pathogen; when administered (often intramuscularly), host cells take up the plasmid, express the antigen in vivo, and present it via MHC pathways, inducing both humoral and cellular immunity. Advantages: stability, ease of production, induction of broad immune responses; several are in development or clinical trials.
DNA vaccines are plasmid DNA constructs encoding antigenic proteins of a pathogen; when administered (often intramuscularly), host cells take up the plasmid, express the antigen in vivo, and present it via MHC pathways, inducing both humoral and cellular immunity. Advantages: stability, ease of production, induction of broad immune responses; several are in development or clinical trials.
Somatic cell gene therapy - Target cells: differentiated somatic cells (e.g., blood cells, liver cells). - Heritability: changes are not transmitted to next generation (non‑heritable). - Purpose: treat or cure disease in the treated individual (e.g., ex vivo correction of hematopoietic cells). - Risk/ethics: fewer ethical concerns than germline; repeated treatments may be needed. - Examples/technique: ex vivo retroviral or lentiviral transduction, in vivo viral/nonviral delivery.
Germline gene therapy - Target cells: gametes or early embryos (sperm, egg, zygote, early embryo). - Heritability: modifications are transmitted to descendants (heritable). - Purpose: eliminate genetic defect from family line or introduce permanent change. - Risk/ethics: major ethical, social and safety concerns; largely prohibited in humans. - Examples/technique: nucleus or genome editing in embryos (theoretical/experimental).
Key distinctions: somatic = treats individual, not inherited; germline = alters lineage, inheritable, ethically controversial.
Somatic cell gene therapy: modifies genes in body (somatic) cells of an affected individual; changes are non‑heritable. Germline gene therapy: modifies genes in gametes or early embryos; changes are heritable and passed to offspring.
Definition and properties - Stem cells: undifferentiated cells capable of long‑term self‑renewal and differentiation into specialised cell types. - Potency categories: totipotent (zygote), pluripotent (embryonic stem cells), multipotent (adult stem cells like hematopoietic stem cells), induced pluripotent stem cells (iPSCs) are reprogrammed somatic cells.
Roles in medicine - Hematopoietic stem cell transplantation (bone marrow transplant): established therapy for leukemias, lymphomas and some genetic blood disorders. - Regenerative medicine: potential to replace damaged tissues (e.g., beta cells for type 1 diabetes, dopaminergic neurons for Parkinson’s, cardiomyocytes after myocardial infarction). - Tissue engineering: combine stem cells with scaffolds to regenerate organs/tissues. - iPSCs: patient‑specific pluripotent cells for autologous cell therapy, reducing immune rejection. - Disease modelling and drug discovery: derive disease‑relevant cell types from patient iPSCs to study pathogenesis and test drugs. - Gene + stem cell therapy: correct genetic defect in patient stem cells ex vivo and reimplant.
Limitations and concerns: immune rejection (for non‑autologous cells), risk of tumour formation (teratomas with pluripotent cells), ethical issues (embryonic stem cells), and challenges in directed differentiation and functional integration.
Stem cells are undifferentiated cells with self‑renewal and potency (totipotent, pluripotent, multipotent) that can differentiate into specialised cell types. In medicine they are used for regenerative therapies (e.g., hematopoietic stem cell transplantation), tissue repair, disease modelling, drug testing and potential cell replacement treatments for conditions like leukemia, diabetes, Parkinson’s and spinal cord injuries.
i) Definition: Gene therapy is the delivery of a normal (functional) gene into a patient’s cells to compensate for a defective or missing gene, or to provide a therapeutic protein.
ii) First clinical gene therapy (1990): Treatment of ADA deficiency (ADA‑SCID) — severe combined immunodeficiency due to adenosine deaminase deficiency. The 1990 protocol is widely cited as the first accepted human gene therapy trial.
iii) Typical steps used in the ADA therapy (ex vivo approach): 1. Diagnosis and selection of patient with ADA deficiency. 2. Isolation of target cells from patient (often peripheral blood lymphocytes or hematopoietic stem cells). 3. Cloning of the functional ADA cDNA into a suitable vector (original trials used retroviral vectors). 4. Ex vivo transduction: infect the patient’s isolated cells with the recombinant viral vector to insert the functional ADA gene. 5. Selection/expansion of corrected cells in culture. 6. Reinfusion of the genetically corrected cells back into the patient. 7. Post‑treatment monitoring for ADA enzyme activity, immune reconstitution and adverse effects.
Key terms: ex vivo gene therapy, viral vector (retrovirus/lentivirus), ADA‑SCID, gene insertion, immune reconstitution.
i) Gene therapy: introduction, replacement or correction of defective genes to treat or prevent disease. ii) First clinical gene therapy: ADA deficiency (adenosine deaminase severe combined immunodeficiency, ADA‑SCID). iii) Steps: isolate functional ADA gene, clone into viral vector, ex vivo transduction of patient lymphoid/hematopoietic cells, selection/expansion, reinfusion into patient, monitor immune function.
How PCR helps early diagnosis - Principle: PCR uses sequence‑specific primers and thermostable DNA polymerase (Taq) to exponentially amplify a target DNA fragment through cycles of denaturation, annealing and extension. - Sensitivity: PCR can detect very low copy numbers of pathogen DNA, allowing diagnosis before antibodies develop or when culture is negative. - Specificity: Primers designed to pathogen‑specific genes (e.g., virulence genes) reduce cross‑reactivity; sequencing of amplicon can confirm identity. - RNA pathogens: Reverse transcriptase PCR (RT‑PCR) converts RNA to cDNA before amplification (used for influenza, HIV, SARS‑CoV‑2). - Quantitation: Real‑time PCR (qPCR) measures fluorescent signal during amplification to quantify pathogen load; useful for monitoring treatment (e.g., viral load in HIV, hepatitis). - Speed: Results can be obtained within hours compared with days for culture.
Typical workflow: sample collection → nucleic acid extraction → set up PCR with specific primers and polymerase → thermal cycling → detection (gel electrophoresis, qPCR fluorescence) → interpretation.
Examples: early detection of TB (PCR for Mycobacterium DNA), HIV RNA in early infection, SARS‑CoV‑2 RT‑PCR.
Limitations: risk of contamination and false positives, need for known target sequences, requirement for specialized equipment and trained personnel, inhibitors in clinical samples can cause false negatives.
PCR (polymerase chain reaction) amplifies pathogen‑specific nucleic acid sequences rapidly and sensitively from clinical samples, enabling early detection even when pathogen load is low. Variants like RT‑PCR detect RNA viruses and real‑time PCR (qPCR) quantifies pathogen load for diagnosis and monitoring.
Definition: Recombinant vaccines use genes encoding pathogen antigens cloned and expressed in heterologous expression systems (bacteria, yeast, insect or mammalian cells) to produce purified antigenic proteins for immunisation. They avoid using whole live pathogens and increase safety.
Major types and examples - Recombinant subunit vaccines: only one or more antigenic proteins are produced and purified. Example: Hepatitis B vaccine (recombinant HBsAg produced in yeast). - Virus‑like particle (VLP) vaccines: self‑assembling viral proteins that form particles resembling the virus but lack viral genome—highly immunogenic. Example: HPV vaccine (L1 VLPs). - Viral‑vectored vaccines: a benign virus (vector) is engineered to express antigens from a target pathogen; vector delivers antigen in vivo (induces strong cellular and humoral responses). Example: adenovirus‑vectored COVID‑19 vaccines. - DNA vaccines: plasmid DNA encoding antigen injected into host cells; host machinery expresses antigen stimulating immunity (still largely experimental for humans). - Recombinant live/attenuated: pathogens attenuated by genetic modification or engineered to express foreign antigens.
Advantages: high safety (no infectious pathogen), precise antigen composition, scalable production, lower risk of reversion. Disadvantages: may require adjuvants and booster doses, sometimes weaker cellular immunity unless delivered with vectors, production complexity and cost for some platforms.
Recombinant vaccines are vaccines produced using recombinant DNA technology to express antigenic proteins without using whole pathogens. Types include recombinant subunit protein vaccines, virus‑like particle (VLP) vaccines, viral‑vectored vaccines, DNA vaccines and recombinant live attenuated vaccines.
Key reasons Dolly was a breakthrough: - Somatic cell nuclear transfer (SCNT): Dolly (born 1996) was the first mammal cloned from an adult differentiated somatic cell nucleus, proving that nuclei from adult cells retain the complete genome necessary for development. - Genomic equivalence: supported the idea that differentiated cells keep the full genetic information (no irreversible loss of genes). - Reprogramming: showed that the egg cytoplasm can reprogram a somatic nucleus back to totipotency/pluripotency. - Impact: opened avenues in developmental biology, cloning technology, therapeutic cloning (patient‑specific stem cells), and regenerative medicine; raised ethical, legal and safety debates about cloning.
Key terms: Dolly, somatic cell nuclear transfer (SCNT), genomic equivalence, reprogramming, totipotency.
Dolly demonstrated that a differentiated adult somatic nucleus can be reprogrammed by an enucleated egg to produce a whole animal, proving genomic equivalence and reprogramming to totipotency (somatic cell nuclear transfer).
Advantages - Propagation of desirable genotypes: produce animals with superior traits (agriculture, livestock). - Conservation: potential tool to help save endangered species (though with limitations). - Biomedical research: generate genetically identical animals for controlled experiments and disease models. - Production of pharmaceuticals: transgenic clones can produce therapeutic proteins in milk (bioreactors). - Therapeutic/medical potential: therapeutic cloning to produce patient‑specific embryonic stem cells for regenerative medicine and organ repair.
Disadvantages - Low efficiency: most cloning attempts fail; many embryos do not develop to term. - High rate of abnormalities: cloned animals often show developmental defects, large offspring syndrome, immune problems. - Health and longevity concerns: some clones show shortened lifespan or premature ageing. - Reduced genetic diversity: widespread cloning of a few genotypes can reduce population variability and increase disease vulnerability. - Ethical and social issues: concerns about welfare, identity, reproductive cloning in humans, and playing 'God.' - Technical and economic: expensive, technically demanding, requires specialized facilities.
Overall: cloning has powerful scientific and practical uses but is limited by biological inefficiency, health risks and serious ethical concerns.
Advantages: reproduce animals with desirable traits, conserve endangered species, create identical research models, produce transgenic animals and therapeutic proteins, therapeutic cloning for regenerative medicine. Disadvantages: low efficiency and high failure rate, developmental abnormalities, reduced genetic diversity, ethical concerns, possible health problems and shortened lifespan, high cost and technical complexity.
Concise production steps 1. Gene design: obtain or synthesize the human insulin gene sequence. Early methods used separate genes for A and B chains; later methods use a proinsulin gene for proper folding. 2. Cloning into expression vector: insert the insulin (or proinsulin) gene into a suitable plasmid vector with a strong promoter. For bacterial expression, genes are often fused to carrier proteins to improve expression and solubility. 3. Transformation of host: introduce the recombinant plasmid into a production host such as Escherichia coli or yeast (Saccharomyces cerevisiae). 4. Expression and fermentation: culture transformed microbes in bioreactors; induce expression of insulin polypeptides. 5. Isolation and purification: lyse cells and purify expressed peptides or fusion proteins using chromatographic techniques. 6. Processing/refolding: - If A and B chains expressed separately: purify chains, chemically oxidize and combine under conditions that allow correct disulfide bond formation to yield active insulin. - If proinsulin expressed: enzymatically cleave connecting peptide to convert proinsulin to mature insulin, then purify. 7. Quality control: test biological activity, purity, sterility, absence of endotoxins and correct folding/disulfide bonds. 8. Formulation and packaging: formulate insulin for therapeutic use (e.g., rapid‑acting, long‑acting preparations).
Historical note: Humulin was the first commercially produced recombinant human insulin (Genentech/Eli Lilly) produced in E. coli. Modern production often uses yeast and proinsulin strategies to improve folding and yield.
Key terms: recombinant DNA technology, expression vector, E. coli/yeast host, proinsulin, disulfide bond formation, purification, quality control.
Recombinant insulin is produced by cloning insulin (A and B chain or proinsulin) genes into expression vectors, expressing them in microbial hosts (E. coli or yeast), purifying the expressed peptides or proinsulin, and chemically or enzymatically processing/refolding them to form active insulin.