Characterization and Modulation of the Natural Antibody-Mediated Immune Response to Human Embryonic Stem Cells

Funding Type: 
SEED Grant
Grant Number: 
ICOC Funds Committed: 
Stem Cell Use: 
Embryonic Stem Cell
Public Abstract: 
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.
Progress Report: 
  • The original goals in the CIRM application were to use molecular DNA shuffling to make an AAV capsid library and then use the library to select for AAV vectors that would efficiently transduce human embryonic stem cells. We spent a long time preparing the capsid library and proving that our library had diverse sequences. In the end, we made two libraries each with about 100,000 variant capsids. We did our first set of screens on cultured cell lines and pulled out several novel AAV capsids. We vectorized them and showed they were much more efficient at transducing cells in culture than any other serotype described to date. There is a large amount of data describing the experiments in detail. These studies were published in a very long article published in the Journal of Virology in mid 2008 (Grimm et al., 2008.. In Vitro and In Vivo Gene Therapy Vector Evolution via Multispecies
  • Interbreeding and Retargeting of Adeno-Associated Viruses . J. Virol. 82:5887-5911
  • We had started using the capsid library in human embryonic stem cells as described. We had some technical problems with titering the right amount of human adenovirus needed as a helper virus in the designed screen. Unfortunately, time ran out and the grant ended and a new proposal to continue the work was not selected for review by CIRM. Nevertheless, since we believe producing the reagents we proposed to make for human ES stem cells are important for the research community and now that we have two very robust and diverse libraries, we are going to attempt another round of capsid screening. If we obtain useful serotypes for human ES cell transduction, we will make them available to the research community.
  • We should point out that we have recently produced DNA minicircle vectors, which are episomal plasmids that lack all bacterial plasmid backbone DNA. These minicircles have been used in collaboration with Joesph Wu and Michael Longaker to convert human adipose derived cells into iPS cells with 10 to 20 times greater efficiency than plasmid DNA. Moreover, these vectors are only transiently present in the iPS cells establishing that they do not permanently alter the genetic makeup of the cells. This work while not funded by the CIRM may turn out to be a more valuable approach for reprogramming all types of stem cells. If it were not for CIRM funding, this collaboration may not have occurred. The CIRM funding brought my group together with Joseph WU and Michael Longaker.

© 2013 California Institute for Regenerative Medicine