Alphavirus expression systems.

Alphavirus vectors are newcomers in the field of heterologous gene expression. Nevertheless, they have rapidly become popular and are now being used in a wide range of applications. During the past year, new vectors and new methods for their use have improved levels of gene expression. As alphaviruses are capable of infecting humans, biosafety was an important issue during early work with these vectors. The construction of a conditional lethal helper system has now largely overcome this problem, and should further increase the utility of these types of vector in animal cell systems.