Ribozymes, including hammerhead ribozymes, can be used in the study of gene function and gene therapy for diseases.

     Those ribozymes which are designed to target a specific gene transcript (hnRNA, mRNA) would bind and cleave the substrate RNA in vitro, or in vivo. The overall effect is the down-regulation of the expression on that target gene, similar to the gene knock-out. The potential advantage of inactivation by ribozyme over gene knock-out is that, the binding and catalysis efficiency of ribozymes on the target RNA can be flexible through the design and selection of different kinds of ribozymes, while gene knock-out decreases the gene expression to zero. The property of ribozymes make them suitable in the research of genetics and developmental biology.

    The other important application of ribozymes is to develop new drugs and protocols for gene therapy. Ribozymes have been proposed as potentially efficacious therapeutics for treatment of a variety of infectious agents(Looney, 1997). Even targeting of prokaryotic pathogens is possible through the use of phage or other delivery systems. Vectors expressing ribozymes have been used for cleaving essential gene products and work as tentative therapeutics on diseases, such as HIV infection (Sarver, 1990). To date, the achievement of ribozymes for human clinical trials has centered on viral pathogens, and ribozymes appear to offer some unique advantages when compared to traditional antisense or protein expression strategies. By protecting cells against viral cytopathic effects, ribozymes may promote survival of populations of functional trransduced cells in vivo, leading to increased therapeutic effects over time. By producing only therapeutic RNAs, ribozymes are likely to avoid entirely or at least largely (antibodies directed against small nuclear RNAs have been detected in several autoimmune disorders, Bernstein, 1990) the problems of immune eradication of transduced cells or production of autoimmune antibodies. For persistent agents, such as retrovirus infections like HIV-1, gene therapy would appear to offer and ideal route to permanent protection of cells. Two clinical trials with hammerhead ribozyme for treatment of HIV-1 have been advanced in US. These include a protocol for ex vivo transduction and infusion of autologous T-lymphocytes from infected individuals using murine vectors producing a hairpin ribozyme directed against the U5 leader sequence of HIV(Wong) and a protocol for the transduction and transplantation of CD34 peripheral blood-derived stem cells in HIV-1 infected individuals using murine vectors containing a hammerhead ribozyme targeting HIV tat RNA (Rosenberg).

    Ribozyme therapy may also be applied on DNA virus infections. By inhibiting expression of the early genes of many DNA viruses(e.g., herpes simplex virus), it should be possible to block virus replication and the production of progeny virions. This suggests a possible role of ribozymes as antineoplastic agents by targeting of the replication of oncogenic DNA viruses.(Looney,1997)

      There are concerns about the potential toxicity of ribozyme therapy in human use. Similarly, concerns about the oncogenic potential of retroviral vectors have to be answered in extended human trials.

    Undoubtedly, ribozymes represent an unique therapeutic tools with some capabilities not possessed by traditional protein targeted strategy. The future of their application should be broad and exciting.