Which one of the following is used as vector for cloning genes into higher organisms?

The correct option is A Retrovirus

• Salmonella (S.) typhi is an important intracellular pathogen, exclusively for humans that causes typhoid or enteric fever that make most suitable as a vaccine vector carrying antigens of other pathogens. The hybrids are studied for induced immune response against response to both the Salmonella bacteria and the antigen of the pathogen in under study.
• Retroviral vectors are created by replacing retroviral gag, pol, and env genes with therapeutic gene and used in gene therapy which is the process of introduction of DNA into living human beings in order to treat disease. It is used to replace a missing gene product or to correct mutant alleles.
• Baculoviruses have rod-shaped capsids and large, double-stranded DNA genomes that infect insects. Their polyhedrin gene is replaced with foreign DNA which is expressed at high levels under the control of the endogenous polyhedrin promoter and is mainly used for high-level transient protein expression in insects and insect cells.
• Rhizopus nigricans is used as host vector system for mass synthesis of protein encoded by gene cloned in plasmid vectors.
  
• So, the correct answer is 'Retrovirus'.