Characterization and Modulation of the Natural Antibody-Mediated Immune Response to Human Embryonic Stem Cells
Cells that originate in human embryos, commonly referred to as human embryonic stem cells (HESCs) present almost unlimited potential to replace damaged cells and tissues in a host of diseases by virtue of their ability to be converted into any cell type. The immune system in humans that is responsible for primary defense against infectious agents may prevent the transplantation of HESCs. Most HESC lines from federal and nonfederal sources are grown using culture systems that require animal products. The use of animal products results in the expression of a foreign sugar on the surface of HESCs that causes them to be destroyed by the human immune system. The antibodies that destroy HESCs are called “natural antibodies.” Healthy humans acquire these antibodies after consuming dairy products and red meat. The persistence of these foreign sugars on cells and tissues made from HESCs would be expected to cause immediate rejection after these cells or tissues are transplanted into humans. Efforts are underway to design alternative animal free culture systems that will prevent HESCS from acquiring animal sugars; however, it is not clear whether use of these new animal free systems will eliminate HESC destruction by the immune system. It is possible that there are other foreign substances that may be present on the surface of HESCs that would also activate the human immune system even though they do not come from animal products. We propose to compare the natural antibody response in HESCs grown with and without animal products to determine whether animal free culture conditions are effective in eliminating the innate immune response of humans to HESCs. We also plan to define the pathways that lead to the destruction of HESCS that are exposed to antibodies in human blood. We will examine HESC lines from federal and nonfederal sources. This proposal would therefore not be eligible for federal funds. In addition, we plan to transfer a protective gene into HESCs in order to prevent them from being destroyed when they come into contact with natural antibodies in human blood. The ability to prevent the immune system from destroying transplanted HESCs by altering the culture conditions or by transferring protective genes into HESCs will be an important first step in advancing HESC research to the point where it could be used to help patients. The experiments in this proposal will also help to develop new diagnostic tools that will be used to confirm that the newly designed animal free culture systems are both safe and effective before using them in clinical trials. Similarly, information from gene transfer experiments and animal free culture systems from this proposal will help to create new therapies that will benefit adults and children with autoimmune and/or degenerative diseases such as diabetes and Parkinson’s disease as well as cardiac injury and spinal cord trauma.
Statement of Benefit to California:
In passing Proposition 71, Californians made the landmark decision to commit $3 billion to human embryonic stem cell (HESC) experiments and in doing so created the largest-ever state-supported scientific research initiative in the country. The projects supported by this measure will likely put California at the forefront of the HESC field, far ahead of existing HESC research programs in the United States, whether privately or publicly funded. By devoting resources to the advancement of HESC research, Californians are ensuring that they will be well positioned to benefit from new technological developments as bench research is carried into translational studies and ultimately into clinical trials. Many Californians suffer from such conditions as diabetes, Parkinson’s disease, cardiac injury or spinal cord trauma. These patients may someday undergo transplantation of HESC-derived cells or tissues as a means of regenerating damaged and/or diseased organs. Until now almost all HESC lines from federal and nonfederal sources have been grown in culture systems that require the use of animal products. Recent reports have revealed that cells grown in this manner possess nonhuman sugars on their surfaces. These animal sugars make the cells vulnerable to destruction by preformed “natural” antibodies in human blood shortly after transplantation. Several groups are working hard to design new animal free systems that may prevent destruction of HESCs bearing these animal sugars. Whether these animal free systems will eliminate HESC destruction by preformed antibodies has not yet been confirmed. HESCs grown in newly designed animal free systems may not possess animal sugars on their surfaces; however, they may possess other targets that fail to be seen as “self” by the immune system. The studies in this proposal will benefit Californians by carefully assessing the safety and efficacy of newly created animal free systems before they are used for therapeutic purposes. Additional studies will focus on preventing attack and destruction of HESCs by preformed antibodies by using gene therapy to help HESCs to make the prototypic protective protein, heme oxygenase 1 (HO-1). By transferring the genetic machinery needed to make HO-1 into cells, tissues and organs before they are transplanted, investigators have been able to prolong survival and prevent rejection. The ability to prevent rejection through the transfer of a protective gene into HESCs will benefit Californians by advancing HESC-related research. The ability to overcome attack and destruction of transplanted HESCs is an important first step that will bring this technology closer to the citizens of California. Studies designed to better understand and prevent destruction of transplanted HESCs by the immune system will ultimately bring the dream of a cure closer to a reality for countless adults and children in California.
SYNOPSIS: This proposal addresses the immune response that would follow transplantation of hESCs. The observation has been made by a number of groups that hESCs cultured under xenotropic influences acquire antigens that would provoke a strong rejection response. The PI proposes to address this by pursuing two specific aims. The first is to compare different measures of natural antibody-mediated cytotoxicity of hESC lines grown in the presence or absence of animal products. The second specific aim is to determine whether natural antibody-mediated cytotoxicity to hESCs can be prevented by overexpression of the prototypical cytoprotective gene heme oxygenase 1 (HO-1). INNOVATION AND SIGNIFICANCE: The issue of immune tolerance following hESCs transplantation is of extreme significance and needs to be addressed. The applicant has proposed a novel method for possibly mitigating the effect of immune rejection following transplantation however all the methodologies proposed are traditional. STRENGTHS: The proposal is written in a relatively clear fashion, and both specific aims are clear, sound, and well-defined. The applicants are qualified to do the proposed experiments. WEAKNESSES: There are several weaknesses with this application. First, the issue of immuno-rejection addressed here targets hESCs lines that have been cultured in the presence of or influences from feeder cells. As the technology improves and hESC lines can be detached, by a variety of approaches, from feeder cells, the significance of the aims declines. If, as advertised, hESCs are immune privileged, culture in the absence of xenotropic influences means the project will no longer be relevant. Second, it is important to remember that IVF technology already exposes human embryos to a variety of animal products and by products, yet these do not have a critical influence in the success of implantation and pregnancies. Thus, while the question is an important one, it was unclear that it would be a primary concern at this stage. Finally, aim 1 is weakened by the purely descriptive nature of the experiments. No experiments are proposed to understand what the biological basis might be of increased immune rejection of ES cultured in the presence of MEFs and animal based medium. Aim 2 is weakened by the limited scope of the experimental approaches to increase the cytoprotection or decrease the immune rejection of ES cells. DISCUSSION: There was no further discussion following reviewers' comments.