Editing Transdifferentiation

{{short description|Process in developmental biology}}
{{Technical|date=February 2015}}

'''Transdifferentiation''', also known as '''lineage reprogramming''',<ref>{{Cite journal 
| last1 = Orkin | first1 = S. H. 
| last2 = Zon | first2 = L. I. 
| doi = 10.1016/j.cell.2008.01.025 
| title = Hematopoiesis: An Evolving Paradigm for Stem Cell Biology 
| journal = Cell 
| volume = 132 
| issue = 4 
| pages = 631–644 
| year = 2008 
| pmid = 18295580 
| pmc =2628169 
}}</ref> is the process in which one mature [[somatic cell]] is transformed into another mature somatic cell without undergoing an intermediate [[Induced pluripotent stem cell|pluripotent]] state or [[progenitor cell]] type.<ref name="Forcing cells to change lineages">{{Cite journal 
| last1 = Graf | first1 = T. 
| last2 = Enver | first2 = T. 
| doi = 10.1038/nature08533 
| title = Forcing cells to change lineages 
| journal = Nature 
| volume = 462 
| issue = 7273 
| pages = 587–594 
| year = 2009 
| pmid = 19956253 
| bibcode = 2009Natur.462..587G 
| s2cid = 4417323 
}}</ref> It is a type of [[metaplasia]], which includes all cell fate switches, including the interconversion of stem cells. Current uses of transdifferentiation include disease modeling and [[drug discovery]] and in the future may include [[gene therapy]] and [[regenerative medicine]].<ref name="ReferenceA">{{Cite journal 
| last1 = Pournasr | first1 = B. 
| last2 = Khaloughi | first2 = K. 
| last3 = Salekdeh | first3 = G. H. 
| last4 = Totonchi | first4 = M. 
| last5 = Shahbazi | first5 = E. 
| last6 = Baharvand | first6 = H. 
| doi = 10.1002/stem.760 
| title = Concise Review: Alchemy of Biology: Generating Desired Cell Types from Abundant and Accessible Cells 
| journal = Stem Cells 
| volume = 29 
| issue = 12 
| pages = 1933–1941 
| year = 2011 
| pmid = 21997905 
| doi-access = free 
}}</ref> The term 'transdifferentiation' was originally coined by Selman and Kafatos<ref>{{Cite journal|last1=Selman|first1=Kelly|last2=Kafatos|first2=Fotis C.|date=1974-07-01|title=Transdifferentiation in the labial gland of silk moths: is DNA required for cellular metamorphosis?|journal=Cell Differentiation|volume=3|issue=2|pages=81–94|doi=10.1016/0045-6039(74)90030-X|pmid=4277742}}</ref> in 1974 to describe a change in cell properties as cuticle-producing cells became salt-secreting cells in [[Silkworm|silk moth]]s undergoing [[metamorphosis]].<ref>{{Cite journal 
| last1 = Selman | first1 = K. 
| last2 = Kafatos | first2 = F. C. 
| title = Transdifferentiation in the labial gland of silk moths: Is DNA required for cellular metamorphosis? 
| journal = Cell Differentiation 
| volume = 3 
| issue = 2 
| pages = 81–94 
| year = 2013
| pmid = 4277742
 | doi=10.1016/0045-6039(74)90030-x
}}</ref>

==Discovery==
Davis et al. 1987 reported the first instance (sight) of transdifferentiation where a cell changed from one adult cell type to another. Forcing mouse embryonic [[fibroblast]]s to express [[MyoD]] was found to be [[Necessity and sufficiency|sufficient]] to turn those cells into [[myoblast]]s.<ref>{{Cite journal 
| last1 = Davis | first1 = R. L. 
| last2 = Weintraub | first2 = H. 
| last3 = Lassar | first3 = A. B. 
| title = Expression of a single transfected cDNA converts fibroblasts to myoblasts 
| journal = Cell 
| volume = 51 
| issue = 6 
| pages = 987–1000 
| year = 1987 
| pmid = 3690668
 | doi=10.1016/0092-8674(87)90585-x
| s2cid = 37741454 
}}</ref>

==Natural examples==
The only<ref>{{Cite web |date=2022-02-22 |title=Life with no Limits: The Immortal Jellyfish |url=https://youthmedicaljournal.com/2022/02/21/life-with-no-limits-the-immortal-jellyfish%EF%BF%BC/ |access-date=2025-01-30 |website=Youth Medical Journal |language=en}}</ref> known instances where adult cells change directly from one lineage to another occurs in the species ''[[Turritopsis dohrnii#Biological immortality|Turritopsis dohrnii]]'' (also known as the immortal jellyfish) and ''[[Turritopsis nutricula]]''.

In [[newt]]s, when the eye lens is removed, pigmented [[epithelial]] cells de-differentiate and then redifferentiate into the lens cells.<ref>{{Cite journal 
| last1 = Jopling | first1 = C. 
| last2 = Boue | first2 = S. 
| last3 = Belmonte | first3 = J. C. I. 
| doi = 10.1038/nrm3043 
| title = Dedifferentiation, transdifferentiation and reprogramming: Three routes to regeneration 
| journal = Nature Reviews Molecular Cell Biology 
| volume = 12 
| issue = 2 
| pages = 79–89 
| year = 2011 
| pmid = 21252997 
| s2cid = 205494805 
}}</ref> Vincenzo Colucci described this phenomenon in 1891 and Gustav Wolff described the same thing in 1894; the priority issue is examined in Holland (2021). <ref name=Holland>{{citation |title=Vicenzo Colucci's 1886 memoir, Intorno alla rigenerazione degli arti e della coda nei tritoni, annotated and translated into English as: Concerning regeneration of the limbs and tail in salamanders | first=Nicholas | last=Holland | journal=The European Zoological Journal | volume=88 | year=2021| pages=837–890 | doi=10.1080/24750263.2021.1943549 | doi-access=free }}</ref>

In humans and mice, it has been demonstrated that alpha cells in the [[pancreas]] can spontaneously switch fate and transdifferentiate into beta cells. This has been demonstrated for both healthy and diabetic human and mouse [[pancreatic islets]].<ref>{{Cite journal
| last1 = van der Meulen | first1 = T. 
| last2 = Mawla | first2 = A.M. 
| last3 = DiGruccio | first3 = M.R. 
| last4 = Adams | first4 = M.W.
| last5 = Nies | first5 = V.
| last6 = Dolleman | first6 = S.  
| last7 = Liu | first7 = S.  
| last8 = Ackermann | first8 = A.M.  
| last9 = Caceres | first9 = E.
| last10 = Hunter | first10 = A.E.  
| last11 = Kaestner | first11 = K.H.  
| last12 = Donaldson | first12 = C.J.  
| last13 = Huising | first13 = M.O.  
| doi = 10.1016/j.cmet.2017.03.017
| title = Virgin Beta Cells Persist throughout Life at a Neogenic Niche within Pancreatic Islets
| journal = Cell Metabolism
| volume = 25
| issue = 4 
| pages = 911–926 
| year = 2017 
| pmid = 28380380 
| pmc = 8586897 
| url = https://escholarship.org/content/qt85r6t1w6/qt85r6t1w6.pdf?t=oxu8pq| doi-access = free}}</ref> While it was previously believed that [[oesophageal]] cells were developed from the transdifferentiation of smooth muscle cells, that has been shown to be false.<ref>{{Cite journal 
| last1 = Rishniw | first1 = M. 
| last2 = Xin | first2 = H. B. 
| last3 = Deng | first3 = K. Y. 
| last4 = Kotlikoff | first4 = M. I. 
| title = Skeletal myogenesis in the mouse esophagus does not occur through transdifferentiation 
| doi = 10.1002/gene.10198 
| journal = Genesis 
| volume = 36 
| issue = 2 
| pages = 81–82 
| year = 2003 
| pmid = 12820168 
| s2cid = 20010447 
}}</ref>

==Induced and therapeutic examples==

The first example of functional transdifferentiation has been provided by Ferber et al.<ref>Ferber S, Halkin A, Cohen H, Ber I, Einav Y, Goldberg I, Barshack I, Seijffers R, Kopolovic J, Kaiser N, Karasik A (2000) Pancreatic and duodenal homeobox gene 1 induces expression of insulin genes in liver and ameliorates streptozotocin-induced hyperglycemia. http://www.nature.com/nm/journal/v6/n5/full/nm0500_568.html</ref> by inducing a shift in the developmental fate of cells in the liver and converting them into '[[Pancreas|pancreatic]] [[Beta cell|beta-cell]]-like' cells. The cells induced a wide, functional and long-lasting transdifferentiation process that reduced the effects of [[hyperglycemia]] in diabetic mice.<ref name="nature.com">Sarah Ferber, Amir Halkin, Hofit Cohen, Idit Ber, Yulia Einav, Iris Goldberg, Iris Barshack, Rhona Seijffers, Juri Kopolovic, Nurit Kaiser & Avraham Karasik (2000) - "[http://www.nature.com/nm/journal/v6/n5/full/nm0500_568.html Pancreatic and duodenal homeobox gene 1 induces expression of insulin genes in liver and ameliorates streptozotocin-induced hyperglycemia]"</ref> Moreover, the trans-differentiated beta-like cells were found to be resistant to the [[autoimmune]] attack that characterizes [[type 1 diabetes]].<ref>Shternhall-Ron K et al., Ectopic PDX-1 expression in liver ameliorates type 1 diabetes, Journal of Autoimmunity (2007),
doi:10.1016/j.jaut.2007.02.010. http://www.orgenesis.com/uploads/default/files/shternhall-jai-2007.pdf</ref>

The second step was to undergo transdifferentiation in human specimens. By transducing liver cells with a single gene, Sapir et al. were able to induce human liver cells to transdifferentiate into human beta cells.<ref name="pnas.org">Tamar Sapir, Keren Shternhall, Irit Meivar-Levy, Tamar Blumenfeld, Hamutal Cohen, Ehud Skutelsky, Smadar Eventov-Friedman, Iris Barshack, Iris Goldberg, Sarah Pri-Chen, Lya Ben-Dor, Sylvie Polak-Charcon, Avraham Karasik, Ilan Shimon, Eytan Mor, and Sarah Ferber (2005) [http://www.pnas.org/content/102/22/7964 Cell-replacement therapy for diabetes: Generating functional insulin-producing tissue from adult human liver cells]</ref>

This approach has been demonstrated in mice, rat, [[xenopus]] and human tissues.<ref name="Al-Hasani">{{cite journal | last1 = Al-Hasani | first1 = K | last2 = Pfeifer | first2 = A | last3 = Courtney | first3 = M | last4 = Ben-Othman | first4 = N | last5 = Gjernes | first5 = E | last6 = Vieira | first6 = A | last7 = Druelle | first7 = N | last8 = Avolio | first8 = F | last9 = Ravassard | first9 = P | last10 = Leuckx | first10 = G | last11 = Lacas-Gervais | first11 = S | last12 = Ambrosetti | first12 = D | last13 = Benizri | first13 = E | last14 = Hecksher-Sorensen | first14 = J | last15 = Gounon | first15 = P | last16 = Ferrer | first16 = J | last17 = Gradwohl | first17 = G | last18 = Heimberg | first18 = H | last19 = Mansouri | first19 = A | last20 = Collombat | first20 = P | year = 2013 | title = Adult Duct-Lining Cells Can Reprogram into β-like Cells Able to Counter Repeated Cycles of Toxin-Induced Diabetes | journal = Dev. Cell | volume = 26 | issue = 1| pages = 86–100 | doi = 10.1016/j.devcel.2013.05.018 | pmid = 23810513 | doi-access = free | hdl = 11858/00-001M-0000-0014-3C2F-6 | hdl-access = free }}</ref>

Schematic model of the [[hepatocyte]]-to-beta cell transdifferentiation process. Hepatocytes are obtained by liver biopsy from diabetic patient, cultured and expanded [[ex vivo]], transduced with a [[PDX1]] virus, transdifferentiated into functional [[insulin]]-producing beta cells, and transplanted back into the patient.<ref name="pnas.org"/>

[[Granulosa cell|Granulosa]] and [[Theca of follicle|theca cells]] in the [[Ovary|ovaries]] of adult female mice can transdifferentiate to [[Sertoli cell|Sertoli]] and [[Leydig cell]]s via induced knockout of the [[Forkhead box L2|FOXL2]] gene.<ref name="pmid20005806">{{cite journal | vauthors = Uhlenhaut NH, Jakob S, Anlag K, Eisenberger T, Sekido R, Kress J, Treier AC, Klugmann C, Klasen C, Holter NI, Riethmacher D, Schütz G, Cooney AJ, Lovell-Badge R, Treier M | display-authors = 6 | title = Somatic sex reprogramming of adult ovaries to testes by FOXL2 ablation | journal = Cell | volume = 139 | issue = 6 | pages = 1130–42 | date = December 2009 | pmid = 20005806 | doi = 10.1016/j.cell.2009.11.021 | doi-access = free }}</ref> Similarly, Sertoli cells in the [[Testicle|testes]] of adult male mice can transdifferentiate to granulosa cells via induced knockout of the [[DMRT1]] gene.<ref name="pmid21775990">{{cite journal | vauthors = Matson CK, Murphy MW, Sarver AL, Griswold MD, Bardwell VJ, Zarkower D | title = DMRT1 prevents female reprogramming in the postnatal mammalian testis. | journal = Nature| volume = 476| issue = 7358| pages = 101–4|date=July 2011 | pmid = 21775990| doi = 10.1038/nature10239 | pmc = 3150961 }}</ref>

==Methods==

=== Lineage-instructive approach ===

In this approach, [[transcription factor]]s from [[progenitor cell]]s of the target cell type are [[transfection|transfected]] into a somatic cell to induce transdifferentiation.<ref name="Forcing cells to change lineages"/> There exists two different means of determining which transcription factors to use: by starting with a large pool and narrowing down factors one by one<ref name="ReferenceB">{{Cite journal 
| last1 = Ieda | first1 = M. 
| last2 = Fu | first2 = J. D. 
| last3 = Delgado-Olguin | first3 = P. 
| last4 = Vedantham | first4 = V. 
| last5 = Hayashi | first5 = Y. 
| last6 = Bruneau | first6 = B. G. 
| last7 = Srivastava | first7 = D. 
| doi = 10.1016/j.cell.2010.07.002 
| title = Direct Reprogramming of Fibroblasts into Functional Cardiomyocytes by Defined Factors 
| journal = Cell 
| volume = 142 
| issue = 3 
| pages = 375–386 
| year = 2010 
| pmid = 20691899 
| pmc =2919844 
}}</ref> or by starting with one or two and adding more.<ref>{{Cite journal 
| last1 = Vierbuchen | first1 = T. 
| last2 = Ostermeier | first2 = A. 
| last3 = Pang | first3 = Z. P. 
| last4 = Kokubu | first4 = Y. 
| last5 = Südhof | first5 = T. C. 
| last6 = Wernig | first6 = M. 
| doi = 10.1038/nature08797 
| title = Direct conversion of fibroblasts to functional neurons by defined factors 
| journal = Nature 
| volume = 463 
| issue = 7284 
| pages = 1035–1041 
| year = 2010 
| pmid = 20107439 
| pmc =2829121 
| bibcode = 2010Natur.463.1035V 
}}</ref> One theory to explain the exact specifics is that [[ectopia (medicine)|ectopic]] Transcriptional factors direct the cell to an earlier progenitor state and then redirects it towards a new cell type. Rearrangement of the [[chromatin]] structure via [[DNA methylation]] or [[histone]] modification may play a role as well.<ref>{{Cite journal 
| last1 = Ang | first1 = Y. S. 
| last2 = Gaspar-Maia | first2 = A. 
| last3 = Lemischka | first3 = I. R. 
| last4 = Bernstein | first4 = E. 
| title = Stem cells and reprogramming: Breaking the epigenetic barrier? 
| doi = 10.1016/j.tips.2011.03.002 
| journal = Trends in Pharmacological Sciences 
| volume = 32 
| issue = 7 
| pages = 394–401 
| year = 2011 
| pmid = 21621281 
| pmc =3128683 
}}</ref> Here is a list of in vitro examples and [[Examples of in vivo transdifferentiation by lineage-instructive approach|in vivo examples]]. [[In vivo]] methods of transfecting specific mouse cells utilize the same kinds of vectors as [[in vitro]] experiments, except that the vector is injected into a specific organ. Zhou et al. (2008) injected Ngn3, Pdx1 and Mafa into the dorsal splenic lobe (pancreas) of mice to reprogram pancreatic [[exocrine]] cells into β-cells in order to ameliorate hyperglycaemia.<ref>{{Cite journal 
| last1 = Zhou | first1 = Q. 
| last2 = Brown | first2 = J. 
| last3 = Kanarek | first3 = A. 
| last4 = Rajagopal | first4 = J. 
| last5 = Melton | first5 = D. A. 
| title = In vivo reprogramming of adult pancreatic exocrine cells to β-cells 
| doi = 10.1038/nature07314 
| journal = Nature 
| volume = 455 
| issue = 7213 
| pages = 627–632 
| year = 2008 
| pmid = 18754011 
| pmc = 9011918 
| bibcode = 2008Natur.455..627Z 
| s2cid = 205214877 
}}</ref>

=== Initial epigenetic activation phase approach ===

Somatic cells are first transfected with pluripotent reprogramming factors temporarily ([[Oct4]], [[Sox2]], [[Homeobox protein NANOG|Nanog]], etc.) before being transfected with the desired inhibitory or activating factors.<ref>{{Cite journal 
| last1 = Efe | first1 = J. A. 
| last2 = Hilcove | first2 = S. 
| last3 = Kim | first3 = J. 
| last4 = Zhou | first4 = H. 
| last5 = Ouyang | first5 = K. 
| last6 = Wang | first6 = G. 
| last7 = Chen | first7 = J. 
| last8 = Ding | first8 = S. 
| doi = 10.1038/ncb2164 
| title = Conversion of mouse fibroblasts into cardiomyocytes using a direct reprogramming strategy 
| journal = Nature Cell Biology 
| volume = 13 
| issue = 3 
| pages = 215–222 
| year = 2011 
| pmid = 21278734 
| s2cid = 5310172 
}}</ref> Here is a list of [[Examples of in vitro transdifferentiation by initial epigenetic activation phase approach|examples in vitro]].

===Pharmacological agents===
The DNA methylation inhibitor, 5-azacytidine is also known to promote phenotypic transdifferentiation of cardiac cells to skeletal myoblasts.<ref>{{cite journal|last1=kaur|first1=keerat|last2=yang|first2=jinpu|last3=eisenberg|first3=carol|last4=eisenberg|first4=leonard|title=5-azacytidine promotes the transdifferentiation of cardiac cells to skeletal myocytes.|journal=Cellular Reprogramming|date=2014|volume=16|issue=5|pmid=25090621|url=https://www.researchgate.net/publication/264462290|doi=10.1089/cell.2014.0021|pages=324–330}}</ref>

In [[prostate cancer]], treatment with [[androgen receptor]] targeted therapies induces neuroendocrine transdifferentiation in a subset of patients.<ref>{{cite journal |last1=Usmani |first1=S |last2=Orevi |first2=M |last3=Stefanelli |first3=A |last4=Zaniboni |first4=A |last5=Gofrit |first5=ON |last6=Bnà |first6=C |last7=Illuminati |first7=S |last8=Lojacono |first8=G |last9=Noventa |first9=S |last10=Savelli |first10=G |title=Neuroendocrine differentiation in castration resistant prostate cancer. Nuclear medicine radiopharmaceuticals and imaging techniques: A narrative review. |journal=Critical Reviews in Oncology/Hematology |date=June 2019 |volume=138 |pages=29–37 |doi=10.1016/j.critrevonc.2019.03.005 |pmid=31092382|s2cid=131934021 }}</ref><ref>{{cite journal |last1=Davies |first1=AH |last2=Beltran |first2=H |author3=[[Amina Zoubeidi]]|title=Cellular plasticity and the neuroendocrine phenotype in prostate cancer. |journal=Nature Reviews. Urology |date=May 2018 |volume=15 |issue=5 |pages=271–286 |doi=10.1038/nrurol.2018.22 |pmid=29460922|s2cid=4732323 }}</ref> No standard of care exists for these patients, and those diagnosed with treatment induced neuroendocrine carcinoma are typically treated palliatively.<ref>{{cite journal |last1=Aggarwal |first1=R |last2=Zhang |first2=T |last3=Small |first3=EJ |last4=Armstrong |first4=AJ |title=Neuroendocrine prostate cancer: subtypes, biology, and clinical outcomes. |journal=Journal of the National Comprehensive Cancer Network |date=May 2014 |volume=12 |issue=5 |pages=719–26 |doi=10.6004/jnccn.2014.0073 |pmid=24812138}}</ref>

=== Mechanism of action ===

The transcription factors serve as a short term trigger to an irreversible process. The transdifferentiation liver cells observed 8 months after one single injection of pdx1.<ref name="nature.com"/>

The ectopic transcription factors turn off the host repertoire of gene expression in each of the cells. However, the alternate desired repertoire is being turned on only in a subpopulation of predisposed cells.<ref>{{Cite journal 
| last1 = Meivar-Levy | first1 = I. 
| last2 = Sapir | first2 = T. 
| last3 = Gefen-Halevi | first3 = S. 
| last4 = Aviv | first4 = V. 
| last5 = Barshack | first5 = I. 
| last6 = Onaca | first6 = N. 
| last7 = Mor | first7 = E. 
| last8 = Ferber | first8 = S. 
| doi = 10.1002/hep.21766 
| title = Pancreatic and duodenal homeobox gene 1 induces hepatic dedifferentiation by suppressing the expression of CCAAT/enhancer-binding protein β 
| journal = Hepatology 
| volume = 46 
| issue = 3 
| pages = 898–905 
| year = 2007 
| pmid = 17705277 
| doi-access = free 
}}</ref> Despite the massive dedifferentiation – lineage tracing approach indeed demonstrates that transdifferentiation originates in adult cells.<ref>{{Cite journal 
| last1 = Mauda-Havakuk | first1 = M. 
| last2 = Litichever | first2 = N. 
| last3 = Chernichovski | first3 = E. 
| last4 = Nakar | first4 = O. 
| last5 = Winkler | first5 = E. 
| last6 = Mazkereth | first6 = R. 
| last7 = Orenstein | first7 = A. 
| last8 = Bar-Meir | first8 = E. 
| last9 = Ravassard | first9 = P. 
| last10 = Meivar-Levy | first10 = I. 
| last11 = Ferber | first11 = S. 
| editor1-last = Linden 
| editor1-first = Rafael 
| title = Ectopic PDX-1 Expression Directly Reprograms Human Keratinocytes along Pancreatic Insulin-Producing Cells Fate 
| doi = 10.1371/journal.pone.0026298 
| journal = PLOS ONE 
| volume = 6 
| issue = 10 
| pages = e26298 
| year = 2011 
| pmid = 22028850 
| pmc =3196540 
| bibcode = 2011PLoSO...626298M 
| doi-access = free 
}}</ref>

=== Mogrify algorithm ===
Determining the unique set of cellular factors that is needed to be manipulated for each cell conversion is a long and costly process that involved much trial and error. As a result, this first step of identifying the key set of cellular factors for cell conversion is the major obstacle researchers face in the field of cell reprogramming. An international team of researchers have developed an algorithm, called Mogrify(1), that can predict the optimal set of cellular factors required to convert one human cell type to another. When tested, Mogrify was able to accurately predict the set of cellular factors required for previously published cell conversions correctly. To further validate Mogrify's predictive ability, the team conducted two novel cell conversions in the laboratory using human cells, and these were successful in both attempts solely using the predictions of Mogrify.<ref>[http://www.eurekalert.org/pub_releases/2016-01/dms-moc011516.php  Mapping out cell conversion]</ref><ref>{{cite journal | last1 = Owen | first1 = Rackham | last2 = Gough | first2 = Julian  | year = 2016 | title = A predictive computational framework for direct reprogramming between human cell types | journal = Nature Genetics| volume =  48| issue = 3| pages =  331–335| doi = 10.1038/ng.3487 | pmid=26780608| url = https://research-information.bris.ac.uk/en/publications/a-predictive-computational-framework-for-direct-reprogramming-between-human-cell-types(e6490a78-f3e8-4253-acc4-7ee181c79168).html | hdl = 1983/e6490a78-f3e8-4253-acc4-7ee181c79168 | s2cid = 217524918 | hdl-access = free }}</ref><ref>Jane Byrne (Jul 2021). [https://www.biopharma-reporter.com/Article/2021/07/01/Mogrify-looks-to-transform-cell-therapy-development  Mogrify looks to transform cell therapy development]. BIOPHARMA-REPORTER.COM</ref> Mogrify has been made available online for other researchers and scientists.

==Issues==

===Evaluation===

When examining transdifferentiated cells, it is important to look for markers of the target cell type and the absence of donor cell markers which can be accomplished using green fluorescent protein or immunodetection. It is also important to examine the cell function, [[epigenome]], [[transcriptome]], and [[proteome]] profiles. Cells can also be evaluated based upon their ability to integrate into the corresponding tissue in vivo<ref name="ReferenceB"/> and functionally replace its natural counterpart. In one study, transdifferentiating tail-tip [[fibroblasts]] into hepatocyte-like cells using transcription factors [[GATA4|Gata4]], Hnf1α and [[FOXA3|Foxa3]], and inactivation of p19(Arf) restored hepatocyte-like liver functions in only half of the mice using survival as a means of evaluation.<ref>{{Cite journal 
| last1 = Huang | first1 = P. 
| last2 = He | first2 = Z. 
| last3 = Ji | first3 = S. 
| last4 = Sun | first4 = H. 
| last5 = Xiang | first5 = D. 
| last6 = Liu | first6 = C. 
| last7 = Hu | first7 = Y. 
| last8 = Wang | first8 = X. 
| last9 = Hui | first9 = L. 
| doi = 10.1038/nature10116 
| title = Induction of functional hepatocyte-like cells from mouse fibroblasts by defined factors 
| journal = Nature 
| volume = 475 
| issue = 7356 
| pages = 386–389 
| year = 2011 
| pmid = 21562492 
| s2cid = 1115749 
}}</ref>

===Transition from mouse to human cells===

Generally transdifferentiation that occurs in mouse cells does not translate in effectiveness or speediness in human cells. Pang et al. found that while transcription factors [[ASCL1|Ascl1]], [[Brn2]] and [[Myt1l]] turned mouse cells into mature neurons, the same set of factors only turned human cells into immature neurons. However, the addition of [[NeuroD1]] was able to increase efficiency and help cells reach maturity.<ref>{{Cite journal 
| last1 = Pang | first1 = Z. P. 
| last2 = Yang | first2 = N. 
| last3 = Vierbuchen | first3 = T. 
| last4 = Ostermeier | first4 = A. 
| last5 = Fuentes | first5 = D. R. 
| last6 = Yang | first6 = T. Q. 
| last7 = Citri | first7 = A. 
| last8 = Sebastiano | first8 = V. 
| last9 = Marro | first9 = S. 
| last10 = Südhof 
| doi = 10.1038/nature10202 | first10 = T. C. 
| last11 = Wernig | first11 = M. 
| title = Induction of human neuronal cells by defined transcription factors 
| journal = Nature 
| volume = 476 
| issue = 7359 
| pages = 220–223 
| year = 2011 
| pmid = 21617644 
| pmc =3159048 
| bibcode = 2011Natur.476..220P 
}}</ref>

===Order of transcription factor expression===

The order of expression of transcription factors can direct the fate of the cell. Iwasaki et al. (2006) showed that in hematopoietic lineages, the expression timing of [[Gata-2]] and [[(C/EBPalpha)]] can change whether or not a [[lymphoid-committed progenitor]]s can differentiate into [[granulocyte]]/[[monocyte]] progenitor, [[eosinophil]], [[basophil]] or bipotent [[basophil]]/[[mast cell]] progenitor lineages.<ref>{{Cite journal 
| last1 = Iwasaki | first1 = H. 
| last2 = Mizuno | first2 = S. -I. 
| last3 = Arinobu | first3 = Y. 
| last4 = Ozawa | first4 = H. 
| last5 = Mori | first5 = Y. 
| last6 = Shigematsu | first6 = H. 
| last7 = Takatsu | first7 = K. 
| last8 = Tenen | first8 = D. G. 
| last9 = Akashi | first9 = K. 
| doi = 10.1101/gad.1493506 
| title = The order of expression of transcription factors directs hierarchical specification of hematopoietic lineages 
| journal = Genes & Development 
| volume = 20 
| issue = 21 
| pages = 3010–3021 
| year = 2006 
| pmid = 17079688 
| pmc =1620021 
}}</ref>

===Immunogenicity===

It has been found for induced pluripotent stem cells that when injected into mice, the immune system of the [[synergeic]] mouse rejected the [[teratomas]] forming. Part of this may be because the immune system recognized epigenetic markers of specific sequences of the injected cells. However, when embryonic stem cells were injected, the immune response was much lower. Whether or not this will occur within transdifferentiated cells remains to be researched.<ref name="ReferenceA"/>

=== Method of transfection ===

In order to accomplish [[transfection]], one may use integrating [[viral vector]]s such as [[lentivirus]]es or [[retrovirus]]es, non-integrating vectors such as [[Sendai virus]]es or [[Adenoviridae|adenoviruses]], [[microRNA]]s and a variety of other methods including using proteins and [[plasmid]]s;<ref>{{Cite journal 
| last1 = Patel | first1 = M. 
| last2 = Yang | first2 = S. 
| doi = 10.1007/s12015-010-9123-8 
| title = Advances in Reprogramming Somatic Cells to Induced Pluripotent Stem Cells 
| journal = Stem Cell Reviews and Reports 
| volume = 6 
| issue = 3 
| pages = 367–380 
| year = 2010 
| pmid = 20336395 
| pmc =2924949 
}}</ref> one example is the non-viral delivery of transcription factor-encoding plasmids with a polymeric carrier to elicit neuronal transdifferentiation of fibroblasts.<ref>{{Cite journal 
| last1 = Adler | first1 = A. F. 
| last2 = Grigsby | first2 = C. L. 
| last3 = Kulangara | first3 = K. 
| last4 = Wang | first4 = H. 
| last5 = Yasuda | first5 = R. 
| last6 = Leong | first6 = K. W. 
| doi = 10.1038/mtna.2012.25 
| title = Nonviral Direct Conversion of Primary Mouse Embryonic Fibroblasts to Neuronal Cells 
| journal = Molecular Therapy: Nucleic Acids 
| volume = 1 
| issue = 7 
| pages = e32– 
| year = 2012 
| pmid = 23344148 
| pmc =3411320 
}}</ref> When foreign molecules enter cells, one must take into account the possible drawbacks and potential to cause tumorous growth. Integrating viral vectors have the chance to cause mutations when inserted into the genome. One method of going around this is to excise the viral vector once reprogramming has occurred, an example being [[Cre-Lox recombination]]<ref>{{Cite journal 
| last1 = Sommer | first1 = C. A. 
| last2 = Sommer | first2 = A. 
| last3 = Longmire | first3 = T. A. 
| last4 = Christodoulou | first4 = C. 
| last5 = Thomas | first5 = D. D. 
| last6 = Gostissa | first6 = M. 
| last7 = Alt | first7 = F. W. 
| last8 = Murphy | first8 = G. J. 
| last9 = Kotton | first9 = D. N. 
| doi = 10.1002/stem.255 
| last10 = Mostoslavsky | first10 = G. 
| title = Excision of Reprogramming Transgenes Improves the Differentiation Potential of iPS Cells Generated with a Single Excisable Vector 
| journal = Stem Cells 
| volume = 28 
| issue = 1 
| pages = 64–74 
| year = 2009 
| pmid = 19904830 
| pmc =  4848036}}</ref> Non-integrating vectors have other issues concerning efficiency of reprogramming and also the removal of the vector.<ref>{{Cite journal 
| last1 = Zhou | first1 = W. 
| last2 = Freed | first2 = C. R. 
| doi = 10.1002/stem.201 
| title = Adenoviral Gene Delivery Can Reprogram Human Fibroblasts to Induced Pluripotent Stem Cells 
| journal = Stem Cells 
| volume = 27 
| issue = 11 
| pages = 2667–2674 
| year = 2009 
| pmid = 19697349 
| doi-access = free 
}}</ref> Other methods are relatively new fields and much remains to be discovered.

==Differences with pluripotent reprogramming==
*Almost all factors that reprogram cells into pluripotency have been discovered and can turn a wide variety of cells back into [[induced pluripotent stem cells|induced pluripotent stem cells (iPSCs)]]. However, many of the reprogramming factors that can change a cell's lineage have not been discovered and these factors apply only for that specific lineage.<ref name="pmid18940730">{{Cite journal 
| last1 = Zhou | first1 = Q. 
| last2 = Melton | first2 = D. A. 
| doi = 10.1016/j.stem.2008.09.015 
| title = Extreme Makeover: Converting One Cell into Another 
| journal = Cell Stem Cell 
| volume = 3 
| issue = 4 
| pages = 382–388 
| year = 2008 
| pmid = 18940730 
| doi-access = free 
}}</ref>
*The final products of transdifferentiated cells are capable of being used for clinical studies, but iPSCs must be differentiated.<ref name="pmid18940730"/>
*It may become possible in the future to use transdifferentiation in vivo, whereas pluripotent reprogramming may cause teratomas in vivo.<ref name="pmid18940730"/>
*Transdifferentiated cells will require less epigenetic marks to be reset, whereas pluripotent reprogramming requires nearly all to be removed, which may become an issue during redifferentiation.<ref name="pmid18940730"/>
*Transdifferentiation is geared towards moving between similar lineages, whereas pluripotent reprogramming has unlimited potential.<ref name="pmid18940730"/>
*Pluripotent cells are capable of self-renewal and often go through many cell passages, which increases the chance of accumulating mutations. Cell culture may also favor cells that are adapted for surviving under those conditions, as opposed to inside an organism. Transdifferentiation requires fewer cell passages and would reduce the chance of mutations.<ref name="pmid18940730"/>
*Transdifferentiation can also be much more efficient than pluripotency reprogramming due to the extra step involved in the latter process.<ref>{{Cite journal 
| last1 = Passier | first1 = R. 
| last2 = Mummery | first2 = C. 
| doi = 10.1016/j.stem.2010.07.004 
| title = Getting to the Heart of the Matter: Direct Reprogramming to Cardiomyocytes 
| journal = Cell Stem Cell 
| volume = 7 
| issue = 2 
| pages = 139–141 
| year = 2010 
| pmid = 20682439 
| doi-access = free 
}}</ref>
*Both pluripotent and transdifferentiated cells use adult cells, thus starting cells are very accessible, whereas human embryonic stem cells require that one navigate legal loopholes and delve into the morality of stem cell research debate.

==See also==
* [[Epigenetics]]
* [[Induced pluripotent stem cell]]
* [[Induced stem cells]]
* [[Reprogramming]]

==References==
{{Reflist}}

{{Authority control}}

[[Category:Biological processes]]
[[Category:Induced stem cells]]
[[Category:Developmental biology concepts]]