5-1.1. Introduction
The main gene transfer methods using biological means are as follows:

• Bacterial gene delivery i.e. bactofection.
• Delivery using a viral vector i.e. transduction

5-1.2. Bactofection
It is a method of direct gene transfer using bacteria into the target tissue, organ or organism. Various bacterial strains that can be used as vectors in gene therapy are listed in Table 5-1.2. The genes located on the plasmids of the transformed bacterial strains are delivered and expressed into the cells. The gene delivery may be intracellular or extracellular. It has a potential to express various plasmid-encoded heterologous proteins (antigens, toxins, hormones, enzymes etc.) in different cell types.
Strains that are invasive and having better cell to cell spread are more efficient.

Vector	Target gene	Disease	Model
L. monocytogenes	IL-12	L. major-infection	Mus musculus
L. monocytogenes	CFTR	Cystic fibrosis	CHO-K1 cells
S. typhimurium	VEGFR-2 (FLK-1)	Various carcinomas	Mus musculus
S. choleraesuis	Thrombospondin-1	Melanoma	Mus musculus
S. typhimurium	IFNϒ	Immunodeficiency	Mus musculus
S. typhimurium	CD40L	B-cell lymphoma	Mus musculus

Table 5-1.2: Bactofection in various disease models.