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Advances in Stem Cell Research: Induced Pluripotent Stem Cells and Stem Cells Derived from…

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Progress on research creating induced pluripotent stem cells (iPSCs):
I have written several times on the blockbuster breakthrough in stem cell research known as direct reprogramming, a technique for converting (“inducing”) common body cells (“somatic cells”) into pluripotent stem cells or iPSCs.  In November 2007 the team of Shinya Yamanaka of Japan’s University of Kyoto first published on the successful production of human iPSCs [1].  By injecting four select proteins delivered on the back of retroviruses into a skin cell, they were able to reprogram the highly differentiated skin cell back into the state of a pluripotent stem cell.  Amidst the well-deserved enthusiasm generated by the success, questions were raised at once about the retroviral delivery system.  Because the viruses tended to incorporate themselves into the new cell’s DNA, the technique risked tumor formation if ever used in clinical trials with humans.  Finding a harmless delivery system for the reprogramming proteins became the new challenge.

In September 2008, the online version of the journal Science published a study using less risky adenovirus vectors to deliver the four proteins [2].  In this case the viruses were non-integrating, posing less of a tumorigenic threat.  Nevertheless, researchers still wanted to eliminate the need for viral delivery systems altogether.  One possibility that proved successful was delivering the reprogramming proteins using small non-integrating circular pieces of DNA called plasmids [3].  Unfortunately, the non-viral delivery system decreased the efficiency of the cellular reprogramming.  How could we maintain efficiency while eliminating the need for viruses?  Last Spring, the problem of inefficiency was overcome when researchers successfully delivered the proteins using DNA segments called piggyBAC transposons.  The segments were later excised leaving no footprint at all, but their reprogramming efficiency equaled that of viral systems [4].  The most recent and promising success, published last Summer, is to deliver the reprogramming proteins directly into the somatic cells without relying on delivery genes at all [5].  This startlingly swift progress illustrates what the scientific community is capable of when it’s motivated. 

Finally, in October 2009, a method for dramatically improving the reprogramming efficiency of iPSC production was published.  Scientists from The Scripps Research Institute developed a technique that has improved the efficiency of direct reprogramming 200 percent [6]. 

Parthenogenetic creation of pluripotent stem cells
Parthenogenesis (fr. Gk. parthenos—“virgin”) is a form of asexual reproduction occurring in nature in some species of insects, reptiles and birds.  In mammals parthenogenesis is an aberrant process.  Its success is prevented by nature’s requiring bi-parental genetic contribution to the development of offspring.  But mammalian parthenogenetic development can be induced artificially by activating a female egg to divide in the absence of male sperm using chemical or electrical stimuli.  Because an egg’s final stage of maturation – the second meiotic division—takes place at fertilization, an unfertilized egg still possesses 46 chromosomes, albeit all derived from the mother.  Two fascinating studies published in 2007 in the journal Cell Research describe the successful derivation of human pluripotent stem cells from parthenogenetically activated female eggs [7].  Among the eggs that began dividing, a few developed to day five with a visible inner cell mass (ICM).  The ICM was extracted and stem cells were derived.  When analyzed, they were found to possess many properties characteristic of pluripotent embryonic stem cells.

Ethically speaking, we need to ask whether human parthenotes even though non-viable are nevertheless human embryos albeit defective in some way—i.e., badly disabled human beings.  We know that an unfertilized egg is not a human being.  So it is tempting to conclude that neither is a parthenote.  And yet human parthenotes mimic observable embryonic behavior for several days.  Catholic ethicists are divided over the question.  Mark Latkovic of Sacred Heart Seminary in Detroit argues that since human parthenotes behave like embryos early on—they divide and form blastocyst-like structures—we should presume they are embryos [8].  Thus research creating human parthenotes would be immoral.  Nicanor Pier Giorgio Austriaco, O.P. of Providence College argues for the opposite conclusion.  In the absence of chromosomal information derived from the father, the molecular basis of the parthenote cannot effect the transition from the egg cell into a living human organism [9].  Thus stem cell research on human parthenotes would seem to be morally permissible. A similar conclusion is reached by Joachim Huarte and Antoine Suarez [10].  My own thinking on the question is unresolved.  Evidence suggests that human parthenotes have developed humanoid bodies—called in the literature a ‘homunculus’—with small brains, bone structures, and some internal organ development [11].  Although these are unusual, and the majority of naturally occurring parthenotes observed in humans develop into chaotic tumor masses called teratomas; nevertheless, the evidence makes me very uncomfortable ruling out the possibility that in some cases an activated egg can reconstitute itself into an embryo.

In brief on ASCs
Meanwhile, while research on both ESCs and iPSCs has yet to proceed to clinical trials, adult stem cells continue to rack up medical triumphs.  Using adult stem cells taken from the fat tissue of a 14 year old boy with a rare genetic condition called Treacher Collins syndrome causing deformities in the facial bones, doctors were able to grow new cheek bones for the teenage boy [12].  In similar research published in October in Proceedings of the National Academy of Sciences, scientists at Columbia University successfully created part of a human jaw joint known as the temporomandibular joint (TMJ) using adult stem cells derived from bone marrow.  Chief researcher Dr. Gordana Vunjak-Novakovic said: “The availability of personalized bone grafts engineered from the patient’s own stem cells would revolutionize the way we currently treat these defects.”  The doctor said he hoped the new method also could be applied to the creation of other bones in the neck and head, which are particularly difficult to graft [13].

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Notes
[1] Kazutoshi Takahashi, Shinya Yamanaka, et al., “Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors,” Cell 131 (2007), 1–12; doi:10.1016/j.cell.2007.11.019.

[2] Matthias Stadtfeld, Masaki Nagaya, Jochen Utikal, Gordon Weir, Konrad Hochedlinger, “Induced Pluripotent Stem Cells Generated without Viral Integration,” Science, published online September 25, 2008, doi:10.1126/science.1162494

[3] Junying Yu, Kejin Hu, Kim Smuga-Otto, Shulan Tian, Ron Stewart, Igor I. Slukvin, James A. Thomson, “Human induced pluripotent stem cells free of vector and transgene sequences,” Science 324 (May 8, 2009), 797-801; doi: 10.1126/science.1172482; Keisuke Okita, Masato Nakagawa, Hong Hyenjong, Tomoko Ichisaka, Shinya Yamanaka, “Generation of mouse induced pluripotent stem cells without viral vectors,” Science 322 (November 7, 2008), 949-953; doi: 10.1126/science.1164270

[4] Keisuke Kaji, Katherine Norrby, Agnieszka Paca, Maria Mileikovsky, Paria Mohseni, Knut Woltjen, “Virus-free induction of pluripotency and subsequent excision of reprogramming factors,” Nature 458 (April 9, 2009), 771-775, doi: 10.1038/nature07864; Knut Woltjen, Iacovos P. Michael, Paria Mohseni, Ridham Desai, Maria Mileikovsky, Riikka Hämäläinen, Rebecca Cowling, Wei Wang, Pentao Liu, Marina Gertsenstein, Keisuke Kaji, Hoon-Ki Sung, Andras Nagy, “PiggyBac transposition reprograms fibroblasts to induced pluripotent stem cells,” Nature 458 (April 9, 2009), 766-770, doi: 10.1038/nature07863; Kosuke Yusa, Roland Rad, Junji Takeda, Allan Bradley, “Generation of transgene-free induced pluripotent mouse stem cells by the piggyBac transposon,” Nature Methods; published online March 31, 2009, doi:10.1038/nmeth.1323.

[5] Hongyan Zhou, Shili Wu, Jin Young Joo, Saiyong Zhu, Dong Wook Han, Tongxiang Lin, Sunia Trauger, Geoffery Bien, Susan Yao, Yong Zhu, Gary Siuzdak, Hans R. Schöler, Lingxun Duan, and Sheng Ding, “Generation of Induced Pluripotent Stem Cells Using Recombinant Proteins,” Cell Stem Cell 4 (May 8, 2009), 381-384, doi:10.1016/j.stem.2009.04.005; D. Kim, C. Kim, J. Moon, Y. Chung, M. Chang, B. Han, S. Ko, E. Yang, K. Cha, R. Lanza, “Generation of human induced pluripotent stem cells by direct delivery of reprogramming proteins,” Cell Stem Cell 4 (June 5, 2009), 472-476, doi: 10.1016/j.stem.2009.05.005

[6] Tongxiang Lin, Rajesh Ambasudhan, Xu Yuan, Wenlin Li, et al., “A chemical platform for improved induction of human iPSCs,” Nature Methods, published online 18 October 2009, 1-4; DOI:10.1038/ NMETH.1393

[7] Mai Q, Yu Y, Li T, et al. “Derivation of human embryonic stem cell lines from parthenogenetic blastocysts,” Cell Research 17 (2007), 1008–1019; Lin G, OuYang Q, Zhou X, et al., “A highly homozygous and parthenogenetic human embryonic stem cell line derived from a one-pronuclear oocyte following in vitro fertilization procedure,” Cell Research 17 (2007), 999–1007

[8] Mark S. Latkovic, “The Science and Ethics of Parthenogenesis,” National Catholic Bioethics Quarterly, vol. 2, no. 2 (Summer 2002), 245-255, esp. 253.

[9] Nicanor Pier Giorgio Austriaco, O.P., “On Static Eggs and Dynamic Embryos: A Systems Perspective,” National Catholic Bioethics Quarterly 2.4 (Winter 2002), 659-683.

[10] Joachim Huarte and Antoine Suarez, “On the Status of Parthenotes: Defining the Developmental Potentiality of a Human Embryo,” National Catholic Bioethics Quarterly, vol. 4, no. 4 (Winter 2004), 761.

[11] N. Kuno, K. Kadomatsu, M. Nakamura, T. Miwa-Fukuchi, N. Hirabayashi, T. Ishizuka, “Mature Ovarian Cystic Teratoma with a Highly Differentiated Homunculus: A Case Report,” Birth Defects Research, vol. 70 (Part A) (2004), 40-46.

[12] http://www.physorg.com/news174580442.html

[13] http://news.bbc.co.uk/2/hi/health/8290138.stm

 

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