Table I.

Materials used as tumor markers.

A, Viral vectors
Examples	Advantages	Disadvantages
• Adenovirus	• High transfection efficiency	• Generation of immune response
• Adeno-associated virus	• Efficient in initiating gene expression	• Toxicity
• HSV-1		• Possibility of proto-oncogene activation
• HSV amplicon	• Specific targeting
• Sindbis
• Poliovirus replicon		• High production cost
• Lentivirus/MoMLV
		• Limitations in deliverable gene size
B, Non-viral vectors
Therapeutic DNA, RNAsa and ODNs	Easy to prepare and to scale-up Flexible with regard to the size of the DNA Do not elicit an immune response Less immunogenic Ease of chemical modification Low cost Can be used in different combinations	Low transfection efficiency Less efficient in initiating gene expression
Anaerobic bacteria	Specific targeting High deliverable gene size Motility Can penetrate deep into tumor Easy to manipulate Low cost Environmental sensing Controlled propagation Immunostimulation	Toxicity Genetic instability

^aIncluding microRNAs, short hairpin RNAs and small interfering RNAs.

HSV, herpes simplex virus; MoMLV, Moloney murine leukemia virus; ODNs, oligodeoxynucleotides.