LOS ANGELES—Researchers at the University of California, LosAngeles (UCLA) AIDS Institute say they have found a way to engineer human bloodstem cells into "killer" cells that can target and kill HIV-infected cells,which potentially could be used against other chronic viral diseases.
Lead investigator Scott G. Kitchen says the study, publishedDec. 7 in the-peer reviewed online journal PLoS ONE, provides proof-of-principle that human stem cellscan be engineered into the equivalent of a genetic vaccine.
Kitchen says existing CD8 cells that help fight helpinfection can already destroy HIV-infected cells, but there are not enough ofthe "killer" cells to clear the virus from the body.
Kitchen is an assistant professor of medicine in thedivision of hematology and oncology at the David Geffen School of Medicine atUCLA and a member of the UCLA AIDS Institute.
"These studies lay the foundation for further therapeuticdevelopment that involves restoring damaged or defective immune responsestoward a variety of viruses that cause chronic disease, or even different typesof tumors," Kitchen says.
According to the researchers, there is a desperate need foreffective therapies to fight chronic viral infections.
"The immune response is normally fastidious at controllingthe majority of viral infections and a therapeutic strategy aimed atreestablishing immune control represents a potentially powerful approachtowards treating persistent viral infections," they wrote.
The team examined the potential of genetically programminghuman hematopoietic stem cells to generate mature CD8+ cytotoxic T lymphocytesthat express a molecularly cloned, "transgenic" human anti-HIV T cell receptor(TCR).
Kitchen points out that the human immune system is incapableof clearing an infection with HIV largely due to the fact that the virusdirectly targets the immune system itself.
"We wanted to investigate the feasibility of being able toreconstitute the ravaged immune system in HIV infected individuals in a mannerto "program" cells to target and clear HIV infected cells," he says. "In thisproof-of-principle approach, we took T cells from an HIV infected individualand identified a molecule (the T cell receptor) on these cells thatspecifically allows a particular T cell to recognize and kill HIV infectedcells."
While cells that have this molecule on them can kill HIV infectedcells in that individual, Kitchen notes that they do not exist in great enoughquantities or are dysfunctional in clearing the virus from the body.
"To study this and eventually attempt to fix this defect, wecloned this T cell receptor and genetically engineered human blood stem cells,"he says. "These genetically modified stem cells were then placed into humanthymus tissue previously implanted in mice. " These mice serve as a surrogate host that allows the studyof human tissue in a living organism.
The researchers found that the stem cells developed intomature human T cells in the thymus tissue, becoming cells that can specificallytarget cells that contain HIV proteins.
"Our results further indicate that the T cell receptor thatis specific to HIV needs to be 'matched' in an individual in a manner similar to matching human tissuesthat are used in transplantation," Kitchen says. "Thus, these results suggestthat blood stem cells can be manipulated and 'tailored' to produce T cells that can target infectedcells."
Anti-HIV TCR transduction of human hematopoietic stem cellsdirected the maturation of a large population of polyfunctional, HIV-specificCD8+ cells capable of recognizing and killing viral antigen-presenting cells.
According to Kitchen, these cells, while able to destroyHIV-infected cells, do not exist in enough quantities to clear the virus fromthe body. So the researchers cloned the receptor and genetically engineeredhuman blood stem cells, then placed the stem cells into human thymus tissuethat had been implanted in mice, allowing them to study the reaction in aliving organism.
The research wasn't without its hurdles and according toKitchen the biggest challenge involved the identification and molecular cloningof a single HIV-specific T cell receptor.
"This hurdle was overcome in a manner that advanced thetechnology so that it will allow the rapid identification and cloning ofadditional T cell receptors to different proteins belonging to HIV and otherviruses that cause chronic infection in humans," he says. "Further, thedevelopment of this system that allows the examination of virus specific T celldevelopment in human tissue in vivo wasa significant challenge."
Kitchen notes that researchers believe that this system willallow them to further investigate the therapeutic potential of this approach inhumans and will provide insight into mechanisms of virus-specific T celldevelopment and function.
According to Kitchen, the approach could also be used to targetany virus that results in chronic infection and disease in humans, such ashepatitis B and C, herpes viruses (HSV1, HSV2, Epstein-Barr Virus, VZV, etc.),human papilloma viruses as well as different types of cancers or tumors.
"We're very excited of the possibility of expanding this,"adds Kitchen. "We're much closer to understanding aspects to repair damage tothe immune system."
The next step is to test this strategy in a more advancedmodel to determine if it would work in the human body, says co-author Jerome A.Zack, UCLA professor of medicine in the division of hematology and oncology andassociate director of the UCLA AIDS Institute.
The researchers also hope to expand the range of virusesagainst which this approach could be used.
But the results of the study suggest that this strategycould be an effective weapon in the fight against AIDS and other viraldiseases.
"This approach could be used to combat a variety of chronicviral diseases," says Zack, who is also a professor of microbiology, immunologyand molecular genetics. "It's like a genetic vaccine."
The research also could provide new approaches to developnew drug candidates to combat HIV.
"This system could be utilized to examine ways that enhanceor modulate the ability of T cells to interact with HIV and virally infectedcells and ways that allow the rapid characterization of technologies thatenhance stem cell and T cell development," notes Kitchen. "The use of thismouse/human chimeric system allows a great deal of manipulation to occur thatfurther allows the rapid and close assessment of these human cellularprocesses."
Kitchen also points out that these studies set the stage forthe identification and characterization of other T cell receptors that targetdifferent viruses or tumor cells.
"The ultimate goal of these studies is the furtherunderstanding of the human immune response and the development of therapeuticapproaches that allow the individual "tailoring" of immune responses inindividuals requiring treatment," he says. "These studies suggest that inindividuals requiring treatment, we could engineer their immune systems tospecifically fight off infection or cancers."
In addition to Kitchen and Zack, investigators includedMichael Bennett, Zoran Galic, Joanne Kim, Qing Xu, Alan Young, AlexisLieberman, Hwee Ng and Otto Yang, all of UCLA, and Aviva Joseph and HarrisGoldstein of the Albert Einstein College of Medicine in New York.
The California Institute for Regenerative Medicine (CIRM)and the UCLA Center for AIDS Research funded this study.
The UCLA AIDS Institute, established in 1992, is amultidisciplinary think tank drawing on the skills of top-flight researchers inthe worldwide fight against HIV and AIDS, the first cases of which werereported in 1981 by UCLA physicians. Institute members include researchers invirology and immunology, genetics, cancer, neurology, ophthalmology,epidemiology, social science, public health, nursing, and disease prevention.Their findings have led to advances in treating HIV, as well as other diseases,such as hepatitis B and C, influenza and cancer.