The document discusses gene expression systems, particularly viral gene transfer, and outlines the processes involved in gene therapy and gene transfer techniques. It details various viral vectors used in gene delivery, such as retroviral, adenoviral, and lentiviral vectors, highlighting their applications and advantages in treating genetic diseases. The central focus is on the mechanisms of gene therapy as an experimental approach to correct genetic abnormalities and the different methods to achieve effective gene transfer.

1. GENE EXPRESSION SYSTEMS
(VIRAL GENE TRANSFER)
Presented by
Simran
M.Pharmacy 2nd sem
GGSCOP, YNR

2. INTRODUCTION
 GENE EXPRESSION
 It is the process by which a gene’s DNA sequence is converted into the
structures and functions of a cell.
 Non-protein coding genes are not translated into protein.
 Gene expression refers to a complex series of processes in which the
information encoded in a gene is used to produce a functional product such
as a protein that dictates cell function.
 Genetic information, chemically determined by DNA structure is transferred
to daughter cells by DNA replication and expressed by Transcription
followed by Translation.

3.  This series of events is called “Central Dogma” is found in all cells and
proceeds in similar ways except in retroviruses which posses an enzyme
reverse transcriptase which converts RNA into complementary DNA.
 Biological information flows from DNA to RNA, and from there to proteins.

5. WHAT IS GENE THERAPY?
 Gene therapy is an Experimental technique that uses genes to treat or prevent
disease.
 Basically gene therapy is an intracellular delivery of genomic materials
(transgene) into specific cells to generate a therapeutic effect by correcting
an existing abnormality or providing the cells with a new function.

6. GENE TRANSFER
 Gene transfer is the introduction of foreign genes or gene sequences in a target cell
population using nonviral or viral vectors to treat a particular disorder in affected
individual for the sustained expression of a transgene cassette vs application of the
therapeutic product itself that exhibits a short pharmacological half-life.
 There are different reasons to do gene transfer. Perhaps foremost these reasons is the
treatment of diseases using gene transfer to supply patients with therapeutic genes.
 There are different ways to transfer genes. Some of methods involve the use of a
vector such as a virus so it can take the gene along with it when it enters the cell.

7. GENE TRANSFER TECHNIQUES
 Based on the vectors used the gene transfer techniques can be divided as
1. Viral methods
2. Non Viral methods

8. VIRAL METHODS
Retro viral vectors
Adeno virus vectors
Adeno associated virus
Herpes simplex virus
Lenti virus

9. VECTOR AND IT’S IDEAL PROPERTIES
 A Vector can be described as a system fulfilling several functions:
1. Enabling delivery of genes to target cells and their nucleus.
2. Providing protection from gene degradation.
3. Ensuring gene transcription in the cells.

10. VECTOR SYSTEM FOR GENE
DELIVERY
Viral vectors
 Viruses are naturally evolved vehicles that efficiently transfer their genes into
host cells.
 Choice of viral vector is dependent on gene transfer efficiency, capacity to carry
foreign genes, toxicity, stability. Immune responses towards viral antigens and
potential viral recombination.
 One of the successful gene therapy systems available today are viral vectors,
such as retrovirus, adenovirus (types 2 and 5), adeno-associated virus,
herpes virus, pox virus, human foamy virus (HFV), and lentivirus.
 All viral vector genomes have been modified by deleting some areas of their
genomes so that their replication becomes deranged and it makes them more
safe.

12. RETROVIRAL VECTORS
 Retroviral vectors are one of the most frequently employed forms of gene delivery in
somatic and germline gene therapies.
 Commonly employed vectors derived from Murine Leukemia Virus (MuLV).
 Virus genome has two single copy RNA molecules, complexed with viral core proteins,
surrounded by lipid envelope.
 In addition, all of the viral genes have been removed.
 For example, they have been used for human gene therapy of X-SCID successfully.
 Applications: Ex Vivo gene therapy
 In vivo gene transfer using retro viral vectors for suicide gene used in brain tumour
 Treatment of T lymphocyte deficiency ,Tumour Infiltrating Lymphocyte(TIL), bone
marrow cells, Gauchers disease, hepatocytes(LDL receptor deficiency) and melanoma.

14. ADENO VIRUS VECTORS
 These are non enveloped DNA viruses, linear genome and double stranded DNA
molecule of about 36kb.
 Adeno viral vectors have been isolated from a large number of different species and
more than 100 different serotypes have been reported
 Adeno viruses type 2 and type 5 can be utilized the transferring both dividing and no
dividing cells and have low host specificity.
 Application:
 to vivo gene therapy- transduce non dividing and terminally differentiated cells.
 Transfect cells in vivo in the intact organ
 Gene therapy for cystic therapy
 Gene therapy of muscle in liver and therapy of disease of CNS
 Localized cancer gene therapy.

15. ADENO ASSOCIATED VIRUS VECTORS
 Members of Parvovirus family
 Heat stable and resistant to various chemicals
 Depend on virus- cannot replicate its own, another virus is necessary for
replication
 Major disadvantages of these vectors are complicated process of vector
production and the limited transgene capacity of the particles.
 Applications
 Used in hematopoietic stem cells for treatment of B-thalassemia and sickle
cell anemia
 AAVs have been used in the treatment of some diseases, such as CF,
hemophilia B

16. HERPES SIMPLEX VIRUS
 Herpes simplex virus (HSV) is one of the recent viruses candidate in gene
delivery.
 When the defective HSV propagated in complementing cells’ viral particles
are generated, they can infect in subsequent cells permanently replicating
their own genome but not producing more infectious particles.
 Herpes vectors can deliver up to 150 kb transgenic DNA and because of its
neuronotropic features, it has the greatest potential for gene delivery to
nervous system tumors, and cancer cells.

17. LENTIVIRUSES
 Lentiviruses are a subclass of retroviruses. They have recently been used as
gene delivery vectors due to their ability to naturally integrate with
nondividing cells.
 Lentiviral vectors can deliver 8 kb of sequence.
 Used for ex vivo gene transfer in central nervous system with no significant
immune responses and no unwanted side effects.
 Effective for long-term treatment of animal models of neurologic disorders,
such as motor neuron diseases, Parkinson, Alzheimer, Huntington’s disease,
lysosomal storage diseases, and spinal injury.

18. Thank You…