Philadelphia, Pa. -- A study conducted in cell cultures, headed by a research group at The Children's Hospital of Philadelphia, has shown that inserting a beneficial gene into blood immune cells taken from patients infected with HIV blocked the AIDS virus from replicating in those cells. Blocking replication does not eliminate the virus, but prevents activation of the virus, the process by which it changes from a dormant infection to an active one. "These results suggest that, with further work, this technique may keep HIV-infected patients free of disease symptoms," said the study's senior author, Wenzhe Ho, M.D., of the Division of Immunologic and Infectious Diseases at The Children's Hospital of Philadelphia. The study was published in the second February issue of Gene Therapy.
In collaboration with Julianna Lisziewicz, Ph.D., of the Research Institute for Genetic and Human Therapy in Washington, D.C., the researchers took advantage of the fact that an HIV gene called tat is essential for the virus to replicate in the infected cells. They designed an antitat gene that blocks the function of the tat gene and thereby prevents HIV from replicating. Using genetic engineering techniques, the researchers inserted the antitat gene into a mouse retrovirus that can enter cells that are potential sites for HIV replication.
One group of target cells consisted of HIV-infected U1 and ACH-2 cells, cell lines used in HIV research because of their resemblance to human blood immune cells latently infected by HIV. In those cells, the antitat gene inhibited HIV activation and replication. More importantly, antitat also inhibited virus activation and replication in blood immune cells (peripheral blood mononuclear cells) taken from actual patients with HIV infection. Additionally, the antitat gene prolonged the survival of immune system cells called CD4+ T lymphocytes, an essential part of the body's immune defenses and primary target cells for the AIDS virus. In this way, the antitat gene therapy might contribute to maintaining HIV in a dormant state in latently infected cells.
Further studies will be needed to demonstrate whether this approach will be effective in patients with HIV infection. If so, the strategy could become an alternative to the current standard of AIDS treatment, highly active antiretroviral therapy (HAART). HAART, a combination of drugs, decreases HIV replication to undetectable levels in many patients, confining the virus in a latent state. However, recent studies have suggested that HAART alone will not lead to eradication of the virus in the infected cells. In addition, the treatment is very expensive, requires a difficult regimen (four to six pills, two to three times daily) and has side effects such as loss of appetite and vulnerability to other infections. Furthermore, HAART requires lifelong use. If treatment is interrupted, the latent HIV infection rebounds into active infection.
"The antitat gene offers the possibility of prolonging the latency period indefinitely without the need for long-term antiretroviral treatment," said Stuart E. Starr, M.D., chief of Immunologic and Infectious Diseases at The Children's Hospital of Philadelphia, and a co-author of the study. "Early indications are that the antitat gene does not affect uninfected cells or cause toxic side effects."
The challenge of a gene therapy approach to AIDS is to choose the right viral genes to sabotage the AIDS virus. Gene therapy, the introduction of genetic material into a patient's cells to rewrite genetic instructions and treat disease, is a young field in the early stages of potential applications. "Since potential safety issues exist with gene therapy, the next step will be to test the antitat strategy in animal models," said Dr. Starr.
The antitat research combines gene therapy with another promising approach in genetically based medicine: antisense therapy. Antisense technology uses knowledge of the genetic code by which DNA passes along instructions to messenger RNA, which in turn produces proteins that perform biological functions. Antisense molecules are strands of RNA that are designed to link onto complementary targeted strands of messenger RNA. When an antisense strand such as antisense-tat RNA binds to messenger RNA from the tat gene, it interrupts the production of tat protein needed for HIV replication. Because it is an RNA-based approach, use of the antitat gene is unlikely to induce unwanted host immune responses that might eliminate cells expressing a foreign protein.
The Children's Hospital of Philadelphia, the nation's first children's hospital, is a leader in patient care, education and research. This 373-bed multispecialty hospital provides comprehensive pediatric services, including home care, to children from before birth through age 19. The hospital is second in the United States among all children's hospitals in total research funding from the National Institutes of Health.
Journal
Gene Therapy