All viral vectors which are used to transfer genes induce an immunological response to some degree & may have safety risks (such as insertional mutagenesis & toxicity  problems).

Furthermore their capacity is limited & large scale  production may be difficult to achieve.

Non-viral methods of DNA transfer require only a small number of proteins, have a virtually infinite capacity, have no infectious or mutagenic capability & large scale production is possible using pharmaceutical techniques. 

Viral vectors are costly to maintain 

Has limited cloning capacity 

Viral proteins may induce inflammatory response. 

Limitations:
  
    1. Frequency of transfection is often too low to create a
        therapeutic effect.
  
    2. Duration of therapeutic gene ex-pression is too brief to 
        provide an effective treatment. 
  

There are three methods of non-viral DNA transfer.  namely: 

     1. Naked DNA
  
     2. Plasmid liposomes complex
  
     3. Molecular conjugates 

Naked DNA:

Naked DNA is directly injected inside the target tissue. 

In this procedure the pure DNA constructs are directly inserted into cells of target tissues. 

Therapeutic genes delivered are expressed in targeted tissues and gene products are released into circulatory system. 

Secretion of therapeutic protein into circulatory system should facilitate into target tissue.

DNA construct (genetic DNA) is surrounded by artificial  lipid layers to form a lipid sphere with an aqueous core which facilitates passage of DNA through the cell membrane. 
  

This method is a simple procedure and has shown good expression in target genes.

This technique is used for DNA vaccine productions. 

This technique does not produce immunity against the agents; it is relatively a cheap technique and can be used for multiple deliver. 

By transferring DNA, it is able to immunize with two serologically distinct strains.