Back grey_arrow_rt.gif
 
 
UCLA study: Stem cells can target and kill HIV-infected cells
 
 
 
 
Daily News Wire Services
Updated: 12/08/2009 10:17:11 AM PST
 
"While autologous HIV-specific CTLs placed in infected individuals have been shown to migrate to sites in the body of viral replication and retain some of their ability to respond to virally infected cells, this has not been shown to be effective in treating HIV infected individuals. In these HIV infected individuals, these adoptively transferred CTL persisted in the body for only a relatively short period of time and did not have a significant impact on viral replication[44]-[46]. These cells likely lack complete functional competence and the ability to properly respond to antigen and expand as a direct result of the effects of ongoing HIV infection and CTL clonal exhaustion prior to and following ex vivo expansion.....an alternative strategy to generate naïve antigen specific CTLs that would reconstitute immune function would be beneficial to controlling viral replication. Therefore, augmenting these CTL responses with virus-specific CTL could result in better immune control of viral replication and delay or prevent disease progression.....We now demonstrate the ability to effectively transduce HSCs with an HIV-specific TCR, leading to the development of a large population of mature, functional human T cells able to specifically kill cells presenting viral peptide. This establishes a unique system to examine human TCR transgenic HSC development and facilitates the use of antigen-specific TCRs to enhance human T cell immunity and allows the close examination of the mechanisms of human T cell development and thymic selection"
 
Researchers from the UCLA AIDS Institute and colleagues say they have shown that human blood stem cells can be engineered into cells that can target and kill HIV-infected cells, which potentially could be used against other chronic viral diseases.
 
Their study, published Monday in the-peer reviewed online journal PLoS ONE, provides proof-of-principle -- meaning a demonstration of feasibility -- that human stem cells can be engineered into the equivalent of a genetic vaccine, according to a UCLA statement.
 
"We have demonstrated in this proof-of-principle study that this type of approach can be used to engineer the human immune system, particularly the T- cell response, to specifically target HIV-infected cells," said lead investigator Scott G. Kitchen, assistant professor of medicine in the division of hematology and oncology at the David Geffen School of Medicine at UCLA and a member of the UCLA AIDS Institute.
 
"These studies lay the foundation for further therapeutic development that involves restoring damaged or defective immune responses toward a variety of viruses that cause chronic disease, or even different types of tumors."
 
Taking CD8 cytotoxic T lymphocytes -- the "killer" T cells that help fight infection -- from an HIV-infected individual, the researchers identified the molecule known as the T-cell receptor, which guides the T cell in recognizing and killing HIV-infected cells, the statement said.
 
These cells, while able to destroy HIV-infected cells, do not exist in enough quantities to clear the virus from the body. So the researchers cloned the receptor and genetically engineered human blood stem cells, then placed the stem cells into human thymus tissue that had been implanted in mice, allowing them to study the reaction in a living organism.
 
The engineered stem cells developed into a large population of mature, multifunctional HIV-specific CD8 cells that could specifically target cells containing HIV proteins, according to UCLA.
 
The researchers also found that HIV-specific T-cell receptors have to be matched to an individual in much the same way that an organ is matched to a transplant patient.
 
The next step is to test this strategy in a more advanced model to determine if it would work in the human body, said co-author Jerome A. Zack, UCLA professor of medicine in the division of hematology and oncology and associate director of the UCLA AIDS Institute.
 
The researchers also hope to expand the range of viruses against which this approach could be used, according to the UCLA statement.
 
In addition to Kitchen and Zack, investigators included Michael Bennett, Zoran Galic, Joanne Kim, Qing Xu, Alan Young, Alexis Lieberman, Hwee Ng and Otto Yang, all of UCLA, and Aviva Joseph and Harris Goldstein 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 the study.
 
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0008208
 

"Engineering Antigen-Specific T Cells from Genetically Modified Human Hematopoietic Stem Cells in Immunodeficient Mice"
 
Abstract

 
There is a desperate need for effective therapies to fight chronic viral infections. The immune response is normally fastidious at controlling the majority of viral infections and a therapeutic strategy aimed at reestablishing immune control represents a potentially powerful approach towards treating persistent viral infections. We examined the potential of genetically programming human hematopoietic stem cells to generate mature CD8+ cytotoxic T lymphocytes that express a molecularly cloned, "transgenic" human anti-HIV T cell receptor (TCR). Anti-HIV TCR transduction of human hematopoietic stem cells directed the maturation of a large population of polyfunctional, HIV-specific CD8+ cells capable of recognizing and killing viral antigen-presenting cells. Thus, through this proof-of-concept we propose that genetic engineering of human hematopoietic stem cells will allow the tailoring of effector T cell responses to fight HIV infection or other diseases that are characterized by the loss of immune control.
 
"Previous studies utilizing standard gene transfer technologies have demonstrated that cloned, antigen-specific T cell receptors (TCRs) can be used to target polyclonal mature peripheral blood derived CD8+ T cells towards viral and cancer antigens [2]-[8]. This approach has been utilized in safely treating melanoma-afflicted individuals by "redirecting" peripheral CD8+ T cells following transduction with a vector containing an antigen specific TCR against the MART-1 antigen [9], [10]. The introduction of tumor antigen-specific cells in this instance resulted in successful tumor regression in some treated individuals [9]. However, while cells carrying the transgene in this study appeared to be long-lived, extensive ex vivo manipulation resulted in intrinsic functional defects [9]. In addition, these transduced cells also expressed endogenous TCRs and the introduction of a second TCR bypasses thymic selection and could result in auto-reactivity through cross-pairing of TCR chains or circumventing peripheral tolerance. Thus, the use of a gene therapy approach utilizing hematopoietic stem cells (HSCs) that produces functional, naive CD8+ T cells carrying a single desired antigen-specific TCR, could allow long-term engraftment, continuous generation of new effector cells, and a more efficient response through natural immune mechanisms."
 
"We now demonstrate the ability to effectively transduce HSCs with an HIV-specific TCR, leading to the development of a large population of mature, functional human T cells able to specifically kill cells presenting viral peptide. This establishes a unique system to examine human TCR transgenic HSC development and facilitates the use of antigen-specific TCRs to enhance human T cell immunity and allows the close examination of the mechanisms of human T cell development and thymic selection."
 
Discussion
 
The development of vaccine strategies, particularly therapeutic vaccine strategies, against many viruses that produce chronic infections in humans has proven to be difficult. In HIV-1 infection, the CD8+ T cell CTL response plays a crucial role in controlling viral replication in the infected individual [38], [39]. Inevitably, the CTL response fails and this loss is associated with an increase in viral load and a more rapid progression to AIDS [40], [41]. One method of augmenting CTL responses is to expand autologous antigen-specific CTLs ex vivo followed by the return of these cells into the affected individual. This has been shown to be effective in immunodeficient patients for the generation and enhancement of immunity to infection and control with cytomegalovirus (CMV) and Epstein-Barr virus (EBV)[42], [43]. While autologous HIV-specific CTLs placed in infected individuals have been shown to migrate to sites in the body of viral replication and retain some of their ability to respond to virally infected cells, this has not been shown to be effective in treating HIV infected individuals [5], [44]-[46]. In these HIV infected individuals, these adoptively transferred CTL persisted in the body for only a relatively short period of time and did not have a significant impact on viral replication[44]-[46]. These cells likely lack complete functional competence and the ability to properly respond to antigen and expand as a direct result of the effects of ongoing HIV infection and CTL clonal exhaustion prior to and following ex vivo expansion. Ex vivo expansion of these dysfunctional T cells is therefore insufficient to improve the antiviral CTL response. Thus, an alternative strategy to generate naïve antigen specific CTLs that would reconstitute immune function would be beneficial to controlling viral replication. Therefore, augmenting these CTL responses with virus-specific CTL could result in better immune control of viral replication and delay or prevent disease progression.
 
Generation of antigen-specific T cells from hematopoietic progenitor cells has the potential to generate long-term engraftment of specific immune cells through two different mechanisms: 1) the engraftment of hematopoietic stem cells and the production of progeny cells for extended periods of time, 2) the expansion of antigen reactive cells in the periphery and the differentiation of these cells into long-term memory cells. Our results indicate that introduction of a functional TCR into a hematopoietic progenitor cell can lead to the efficient generation of antigen-specific T cells with cytotoxic capabilities. This suggests that this approach could be useful clinically.
 
The ability of HIV to rapidly escape immune pressure would mandate the need for several TCRs specific for multiple viral epitopes. In the current studies, rather than seeing continuous production of immature thymocytes, we observed an extended wave of thymopoiesis culminating in the appearance of mature CD8+ thymocytes. This lack of long-term engraftment may reflect transduction of a more mature progenitor cell incapable of continuous self-renewal. Alternatively, these results may reflect the inability of these transduced stem cells to locate the correct hematopoietic niche in the SCID-hu model. Consistent with either of these mechanisms, we also observed transient reconstitution in this model using HSCs derived from embryonic sources [47]. Nonetheless, our studies provide proof of principle that this approach has strong merit.
 
Human stem cell gene therapy is a relatively new technology. While its use clinically at the current time is limited to a subset of diseases, its potential in treating multiple human diseases is immense. A relatively new approach is to genetically manipulate hematopoietic stem cells followed by re-infusion of these cells back into the patient. Our previous SCID-hu studies demonstrated that in the context of severe HIV-induced thymocyte depletion, human HSCs can properly differentiate into normal mature thymocytes provided that HIV replication is halted by antiretroviral therapy[48]-[50]. Gene therapy trials have effectively demonstrated that human stem cells can be transduced with a retroviral vector and subsequently form mature human T cells in adult subjects [51]. The recent completion of a large-scale phase 2 clinical gene therapy trial highlights the fact that this type of treatment can be used as a conventional therapeutic approach for people with HIV or a variety of diseases [52]. In all, our data demonstrate that HSC transduction with a human viral antigen-specific TCR can be utilized to generate antigen-specific CTL. Our data strongly suggest that this strategy should be pursued as an effective therapy to combat viral infection in humans.
 
 
 
 
  icon paper stack View Older Articles   Back to Top   www.natap.org