Overview of Gene Therapy

Gene Therapy is a method to introduce DNA / RNA of specific gene into target cell of patients that found to be lacked of that partcular gene in order to correct / disrupt it's pathological process to prevent it to become worsen.

Most common approach used are the replacement/ supplementation of that mutated gene with a correct copy of gene to restore their specific functions.

Strategies of Gene Therapy (GT)

• Replacement GT
• Knock-out GT
• Suicide GT
• Immuno-modulatory GT

Replacement GT

Method of GT that replace the mutated gene in order to keep normal cell growth and division under control with corrected (normal) copy of gene.

eg. Gene coding for p53 have to be replaced in order to prevent gene mutation in cancer that could lead to cell apoptosis, cell death and development of tumor.

Limitation : Large no. target genes have been known to maintain malignancy, not enough cancer cell that could be transduced are limiting the curing process of tumor.

Knock-out GT

GT that targets products of oncogenes in order to inactivate and reduce it's cellular proliferations

eg.  Deliver modified / mutant oncogene to negate / counter-attack the effects of the cancer- causing oncogen (bad) thus inhibiting the oncogene proliferation processes.

Bystander effects may happened as the death of more cells are occur than the no. it have been transduced. (for Knock-out and Replacement GT)

Suicide GT

Transduction of a gene that eventually will transforms into a non-toxic form of drugs / pro-drug into a toxic substances.

Immuno-modulatory GT

GT that inducing cellular immune response to tumor cells. Mechanism that been used are injecting a suspension of irradiated tumor cell that already been transduced with a cytokine gene to skin of patients to stimulate response against tumor-specific antigens (vaccinating against cancer).

principles : 

1. Tumor cell removed from patient's body modified with cytokine gene
2. Transplant the cytokine gene back into patients ( right after the cell have been irradiated to prevent further cell division) 
3. The patient's anti-tumor immune response will be activated.

How we insert " good" gene in patient's body?

By the help of VECTORS

The most used vectors in GT are virus vectors as viruses viruses have evolved to have function to infecting cells with specificity & efficiency. It can transfecting their own DNA into the genome of host cells. In this case, it would allows viruses to produce many new viral particle during period of synthesis of the cell itself.

Which virus is the best?

• Virus that transfer well the genes to cells
• Virus that recognizes and infects specific cells
• Virus that alter the cell's DNA permanently 

Example of virus that have been used in GT :

Retrovirus

Adenovirus

Lentivirus

Poxvirus

Herpes virus

Strategies of Trans-gene delivery

Ex-vivo - Cells are removed from body-transgene delivered-cells cultured--cell return to body

In-vivo - Trangene are delivered directly into host ( cell do not remove from patient's body)

                                  Ex vivo and In vivo of GT by Pedro Laurenco

Targeted cells could be both healthy and cancerous cells.

Eg. targets Healthy cells - replacing mutated gene with a corrected gene

Eg. targets Cancer cells - Cancer cells targeted by gene to destroy the cells  (suicide gene)

                                Gene Therapy principles by Shomu's biology

Problems of GT 

• More efficient ways to deliver the genes to the patient's DNA/ RNA should be identified
• Vectors that could focus specifically on target cells should be developed and produced
• Vectors should be always ensured to successfully insert corrected gene to target cells
• Delivering of gene to target cells in DNA/ RNA should be efficient and focused
• The transplanted gene should be always ensured to specifically controlled by patient's own physiological signalling

Future of cancer GT

• Competence of GT will be increased by transduction
• Advances of technique in order to induce expression of transduced gene
• Advances of method of inducing anti-tumor responses at systematic level of responses
• Advances of vectors study for enhance vector's specification and  quality of works
• Andances in induction of cell death (apoptosis)