Madridge Journal of Internal and Emergency Medicine

ISSN: 2638-1621

Review Article

Placenta: A Massive Biological Resource for Clinical applications in Regenerative Medicine

Niranjan Bhattacharya1 and Priyodarshi Sengupta2*

1Head of the Department of Regenerative Medicine and Translational Science, Dr. Subhas Mukherjee Chair Professor, Director General, Cord Blood Bank, Calcutta School of Tropical Medicine, India
2Research Associate, Department of Regenerative Medicine and Translational Science, Calcutta School of Tropical Medicine, India

*Corresponding authors: Niranjan Bhattacharya, Head, Department of Regenerative Medicine and Translational Science, Calcutta School of Tropical Medicine, Kolkata, India, Tel: +91 9830038158, E-mail:
Priyodarshi Sengupta, Research Associate, Department of Regenerative Medicine and Translational Science, Calcutta School of Tropical Medicine, Kolkata, India, E-mail:

Received: October 14, 2018 Accepted: October 23, 2018 Published: October 31, 2018

Citation: Bhattacharya N, Sengupta P. Placenta: A massive biological resource for clinical applications in Regenerative Medicine. Madridge J Inter Emerg Med. 2018; 2(3): 84-89. doi: 10.18689/mjiem-1000119

Copyright: © 2018 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Download PDF


The placenta, with the amniotic fluid, umbilical cord, and the cord blood can be often classified as pregnancy specific biological substances with enormous applications in regenerative medicine. The human placenta is chorioallantoic because it can form both the chorion and the allantois. It remains connected to the growing fetus via the umbilical cord. The blood-placental barrier allows the selective exchange of nutrients, gas, helps in maintaining the thermoregulation of the fetus. It also helps in removing the waste from the fetus’s blood. Grossly, the placenta is made up of the amnion, the innermost layer surrounding the fetus, the allantois in the middle and chorion, the outermost fetal layer. Since, 1999, Bhattacharya et al., has been successfully using the application of freshly collected, serologically tested negative, amniotic membrane from the placenta as a biological wound dressing model in patients with burns and nonhealing ulcers.


In Latin, the word Placenta means “Cake”. The importance of placenta as an important barrier between the fetus and the mother was first realized around 5 decade’s back [1]. Broadly the placenta can be divided into two parts, the maternal part known as the decidua basal is which develops from the maternal uterine tissues and the fetal part known as the chorion frondosum developing from the blastocyst [2]. One of the most important functions of the placenta is to provide a micro-environment to the fetus required for its nutrition, growth, and development, and a physical and functional barrier against pathogens and maternal immune system. It also plays a role in helping the secretion of different hormones, cytokines and growth factors required for the fetus [3].

Development of the Placenta

The initial development of the placenta starts with the process of outstripping of the embryo. Invagination of the surrounding deciduas occurs by the syncytiotrophoblasts. This process continues till the blastocyst remains surrounded by the circulating maternal blood. Roughly around 3 weeks time, the cytotrophoblast or the primitive extraembryonic layer starts developing as cellular columns along with the syncytiotrophoblast layer and together they extend into the maternal blood lacunae resembling the primary villi [4]. The development of the secondary villi initiates after the mesodermal invasion into the core of the primary villi. The tertiary villi form after the cellular differentiation in the villi mesoderm results in the formation of a network of blood vessels. At this stage of fetal development, the primitive placenta, the chorionic plate, the developing embryo stalk and each of the vascular villus components gets connected with each other [5].

The cytotrophoblast penetrates through the syncytiotrophoblast layer where many villi reach the decidual region and forms the anchoring villa [6,7]. The villi develop into extensive tree-like branches into the lacunar or intervillous spaces, thereby enabling a larger surface area for gaseous exchange. The cytotrophoblast gets reduced and the distance also shortens between the fetal villi and the maternal intervillous space thus marking the maturation of the villous [5]. The rudimentary umbilical vessels or the allantoic gets formed during this stage. The developing embryo remains attached to the chorion by a body stalk which forms the rudimentary umbilical vessels or the allantoic. During the embryonal growth, due to the shifting of the connecting stalk from the ventral side to its initial posterior position, a large open region is created at the ventral end which gets constricted as the development of the body wall grows and closes. This results in the body wall surrounding the yolk stalk, allantois and the developing vessels to form the primitive umbilicus or the umbilical cord. There is a rapid growth of the placenta from the third month of gestation which continues till term when the matured placenta becomes oval and flat in shape. The placenta at this point, on an average normally weighs 500 grams, with a thickness of 23 mm and an average diameter of 18.5 cm [8].

Development of the fetomaternal circulation and neovascularization

Increased flow of maternal blood towards the placenta is accompanied by vasodilation due to decrease in the resistance of the maternal arterial pressure [9-11]. After decidualisation, the spiral arteries remodel themselves. This remodeling results in the fewer convolutions of the arteries thereby to increase the size of the arteries. During this time, post decidualisation, there is also an increased flow of blood from the maternal side to the placental intervillous space and fetal villi [12]. The maternal and the fetal blood comes directly with each other without the exchange of fluids. The deoxygenated blood flows back into the endometrial valves due to a decrease in the pressure. The umbilical arteries radiate and form the chorionic arteries at the junction of the placenta and the umbilical cord. These umbilical arteries undergo further division at the junction to form the arterio-capillary venous branches in the villi. They bring the fetal blood in close proximity to the maternal blood without their mixing because of the presence of the syncytiotrophoblast [3].

Fetomaternal exchanges of carbon dioxide, water, urea starts normally from the first trimester. They enter into the uterine circulation from the fetal circulatory system accompanied by the exchange of carbohydrates, lipids, amino acids, proteins and vitamins from the maternal side to the fetal end [3]. The deoxygenated blood is carried by the umbilical artery from the fetus to the placenta. During this time, any disruption to the fetomaternal circulation will result in fetal hypoxia [13,14]. During this stage, the hormones control the vascular function of the placenta. This helps in maintaining a balance between the vasoconstrictors and the vasodilators [15,16]. Angiogenesis initiates in the placenta after 4 weeks of gestation and continues till the 25th week. During the 15th week of gestation, regression of the peripheral capillaries occurs. Presence of the vascular endothelial growth factors or VEGF, Placental growth factor or PGF remains high post 25 days of gestation and continues till the second trimester [17,18]. The remaining capillaries develop into the primitive veins and the arteries. The flooding of the placental intervillous space starts by the mid of the first trimester and increases till the end of the first trimester [19,20]. With increase in the gestational week, the levels of the angiogenic factors also increases resulting in the increased sprouting of new blood vessels form the pre-existing ones for transporting blood [21-23]. These further develop into well defined veins and arterioles [23]. Through the placenta, there is exchange of nutrients, gases, oxygenated and deoxygenated blood continuously in a stable manner [24,25]. During the second trimester, the sprouting of multiple villi branches takes place and are continuously replaced by the immediate villi till the term [21,26].

Fetomaternal exchange of the Placenta and its mechanism

The placental exchange between the mother and the fetus normally follows Fick’s law. It is defined as : Q/T = K × A(Cm-Ct)/D where Q/T is the rate of diffusion, K is the diffusion coefficient, A is the area of the membrane, D is the thickness of the membrane and (Cm-Ct) is the concentration gradient [26]. Simple diffusion involving gaseous exchange, active transport for facilitating the transfer of iron, calcium and iodine, and facilitated diffusion for the passage of glucose are some of the different types of mechanism by which fetomaternal exchange occurs in the placenta. Amino acids can pass through secondary active transport system whereas water and other important electrolytes are normally exchanged via the bulk transporter system. IgG, low density lipoprotein enters the placenta by specialized processes like endocytosis and exocytose and can be transported by the vesicles so as to negate the effect of any phagolysosomal degradation before it enters the fetus [27]. Also, lipid-insoluble molecules can facilitate the process of transfer of these molecules via the extracellular pores across the placenta [28,29]. Para-cellular channels and pores allow the diffusion of chloride, phosphate and sulphate ions which remain at a higher concentration in the maternal plasma. Stereo-specificity another important physical property plays an important role in the transfer of the amino acids. During the time of placental development, at different stages of the fetal development, transporters are also expressed as they play a major role in efflux of harmful toxic metabolites and selective feto-maternal exchange. Presence of P-gp a well known efflux transporter and a member of the active binding cassette (ABC), present on the human and mouse syncytiotrophoblast is expressed during the first trimester. It is an important component of the blood-placental barrier as it protects the developing fetus from the harmful toxic effects of drugs and metabolites [30-32]. Pgp, although expressed on both sides of the maternal and fetal villi, its expression on the maternal villi is found to be more [33]. In the second trimester, with the down-regulation in the expression of the Pgp, multidrug resistance or MRP-2 is synthesized more [34,35]. OATP2B1 another anionic transporter along with the breast cancer resistance protein or BRCP is also expressed on the placenta during the first and second trimester [36]. Multidrug resistance transporters, MDR 1 & 2 along with MRP-5 has shown to be highly expressed during the first trimester [37]. The fetal trophoblast also plays an important role in helping the survival of the fetus during the pregnancy period. As the fetus is an allograft in nature, due to the presence of paternal antigens, there is always a possibility of fetal rejection by the maternal immune system. However, this is not the case, during the time of embryo development in the first trimester; over-expression of HLA-G is found on the trophoblast. HLA-A, B remains absent and there is a weak expression of HLA-C during the first trimester [38]. HLA-G expressed on the surface of the trophoblast, binds to killer cell-like Ig like receptors of NK cells or KIR’s which reduces the NK cells activity by blocking it [39]. Leukemia Inhibiting factor or LIF is synthesized by the maternal decidua on the placenta in the first trimester and acts as an immune barrier [40].

The Placenta as an immunological barrier

Presence of secretory immune system (SIS) on the maternal side of the placenta also helps in imparting a barrier between the mother and the fetus [41-45]. During the fetal development in the first trimester, the presence of secretory chains (SC) also functions as a barrier against the entry of foreign pathogens inside the fetal compartment [3]. The development of the placenta resembles tumorogenesis in many ways. A balance between the tumorigenesis and normal placental formation is however maintained by the up-regulation of DNA methylation, his tone modifications of tumor suppressor genes such as Maspin, RASSFIA, and APC in the placenta [46]. Genetic imprintation and its control also affect the formation and development of the placenta [47]. DNA methylation normally remains up regulated in the embryo formation period compared to the placental development stage. However, in the trophectoderm, there remains a lack of DNA methylation [48]. Mutation of the polycomb family, an absence of Asc12, Phlda2 and Peg10 genes fails to form the placenta [49,50].

Applications of amniotic membrane in Regenerative Medicine

The placenta consists of the amniotic membrane and the umbilical cord and together with the amniotic fluid and the fetal umbilical cord blood can be considered as pregnancy specific biological substances as they support the process of pregnancy. The use of placental membranes as biological dressing models for healing of woods and burn injuries have been practiced since long including the corneal dressings [51]. After its proper collection and screening for infections, these biological materials can be widely used for the isolation of stem cells, progenitor cells and applied in the field of regenerative medicine [52]. One of the most important applications of the placenta has been its amniotic membrane and amniotic fluid since the last century or so [52]. Grossly, the amniotic membrane of the placenta reveals three important layers. The innermost thin transparent layer is known as the amnion covering the embryo, the middle layer consisting of a collagen-rich connective tissue layer which remains connected with the third and an outer collagen-rich reticular chorionic layer [53]. Both the amnion and the chorion consist of the basement membrane and a stromal layer [54]. The amnion part is rich in mesenchymal stem cells, amniotic epithelial stem/cells, embryonal like cells and progenitor cells [55]. Some of the important properties of amniotic membrane are good water retention capacity, ability to cover large wound areas due to its large size, can be easily and ethically available post birth from the placenta, hypo-antigenic due to poor expression of HLA-A,B,C & DR [56,57]. The amniotic membrane has a similar structure like that of the skin and has anti-microbial properties due to the presence of Beta-defensins, elafin, lysozymes and can prevent the loss of proteins, electrolytes, water by forming a moist environment essentially required for healing [58]. The epithelial stem cells from the amniotic membrane help in re-epithelialization and closure of large wounds [55]. Fibroblasts and other extracellular matrix substances like fibronectin, proteoglycans, laminins, collagen present in the amniotic membrane helps in providing strength to the tissues and act as a scaffold. These cells also have the capability to home to the site of injury. Both amniotic membrane and amniotic fluid have a cocktail of cytokines and growth factors like FGF, PDGF, EGF, TGF-β [55]. Presence of MMP’s and their inhibitors or TIMP’s are present to counterbalance the excessive growth. The amniotic fluid is rich in amniocytes which are a large pool of self-renewing cells fetal in nature are also present in the amniotic fluid. These amniocytes also have shown to contain pluripotent markers such as TRA 1-60, SSEA-1 – 3, TRA 1-81 [59,60]. Amniocytes have a proliferative capacity, non-tumorigenic in nature, and can grow without feeder layer with a faster doubling rate [61].

The amniotic membrane of the placenta plays an important role in the process of wound healing. The mechanism of a wound, in brief, involves three general steps which are i. Inflammation, ii. Proliferation and iii. Maturation [58]. Amniotic membrane has a tendency for rapid adherence to the site of wound bed along with the release of different cytokines and growth factors. Further, through unknown and yet to be explored mechanisms, amniotic membrane helps in maintaining a balance between the process of angiogenesis, by controlling the production of matrix metalloproteinases (MMP) and their inhibitors or TIMP’s, PMN infiltration, proliferation of mesenchymal stem cells and the secretion of various growth factors from at the wound bed. Together these functions and presence of amniotic epithelial cells are believed to initiate the process of rapid re-epithelialization [62,63]. Application of dry, dehydrated and processed amniotic membrane for treating different disease conditions including burn patients is not new [54]. However, the application of freshly collected and fully screened amniotic membrane was conducted for the first time by Bhattacharya et al., in 1999 in more than 200 patients suffering from different diseases including burns [64].

Applications of amniotic membrane in burn management

Successful treatment of 64 burn patients (age group <10 years to 71 years) with freshly collected amniotic membrane was first reported by Bhattacharya et al., [64] Both male and female patients suffering from chemical and thermal burns were recruited for the study after satisfying the inclusion/exclusion criteria. The process included, application of normal saline water to the infected and wound region to clean and remove the cell debris followed by application of amniotic fluid which was serologically screened for CMV, syphilis, Hepatitis B, C, VDRL, HIV-I & II. In cases where of superficial or partial skin thickness burn injuries the amniotic or fetal side of the amniotic membrane was applied and in case of re-epithelialization and improving angiogenesis the maternal or chorionic side was applied [64,58]. Patients were supplemented with antibiotics intravenously and with improvement were given oral antibiotics. Stabilization, healing were routinely conducted with monthly follow up and physiotherapy. Death was not reported in any of the patients. 6 patients had keloid and hypertrophic scars along with 14 cases of hypo-pigmentation. Further, follow up studies showed no hypo-pigmentation and the rest of the patients reported normal and complete wound healing [64,58].

Amniotic membrane application in Leprosy

Similarly, leprosy patients with gangrene were treated with amniotic membrane. Due to infection, some of the patients were infected with maggots which were removed and treated with normal saline followed by a sprinkling of amniotic fluid as an antiseptic agent after 5 to 10 mins [58]. Freshly collected amniotic membranes were applied in superficial and partial thickness wounds. All patients were on anti-leprosy treatment. 3 months and 6 months follow up study revealed the formation of granulation tissue and re-epithelialization [58]. Freshly collected amniotic fluid was successfully applied in 52 patients suffering from osteoarthritis (age range 39 to 82 years) in the joint spaces. It was a double arm study where one group received intraarticular steroid treatment and the other amniotic fluid [65]. The second group where amniotic membrane was applied showed better prognosis and improved outcome after 4 months of follow up study [65].

Amniotic membrane application in Ophthalmology

In 1940, the first application of amniotic membrane in ocular surgery for managing second-degree chemical burns of the eye was reported [66]. Tusbita et al., reported encouraging results with the amniotic membrane in treating patients with cicatricial pemphigoid and Steven Johnson Syndrome (SJS) [67,68]. Other successful reports where amniotic membrane was successfully applied for treating deep corneal ulceration and their reconstruction has also been reported [69-71]. Positive results using the amniotic membrane in pterygium surgery has also been reported including bullous keratopathy [72-74].


The placenta is an important organ formed during the time of pregnancy. Formation of the placenta is essential for the fetus to survive inside the mother’s womb. Through a series of complex developmental stages, the blood-placental barrier is formed which is essential in not only protecting the fetus from harmful toxic drugs, and metabolites but also in the selective diffusion and exchange of different inorganic salts, gases and even fetal cells. The placenta like the cord blood is an untapped resource which can be successfully applied in regenerative medicine and cell-based therapies. The use of properly screened and freshly collected placenta and using its amniotic membranes, amniotic fluid for cell therapy purposes was first attempted in 1999. Since then follow up studies and intense clinical scrutiny has yielded very encouraging and positive results using placental membranes in treating non-healing ulcers of different etiologies and burn wounds with very few reports of graft rejections by the host’s immune system due to sloughing or due to Pseudomonas aeruginosin infection [75].


  1. Challier JC. The placental barrier: structure, resistance, asymmetry. Reprod Nutr Dev. 1989; 29(6): 703-106.   
  2. Carlson BM. Chapter 7 – Placenta and Extraembryonic Membranes, Page no: 117, Human Embryology and Developmental Biology, 5th edition, 2014, Elsevier, ISBN: 978-1-4557-2794-0.   
  3. Bhattacharya N, Stubblefield P. Human Fetal Growth and Development, First and second trimester, Springer-International, Switzerland, 2016, Chapter no: 35, Priyodarshi Sengupta et al., Structural and Functional Developmental Perspectives of the Placental Barrier, 441-451, ISBN- 978-3-319-14874-8.   
  4. Carter AM, Enders AC, Pijnenborg R. The Role of Invasive Trophoblast in Implantation and Placentation of Primates. Philos Trans R Soc Lond B Biol Sci. 2015; 370(1663): 20140070. doi: 10.1098/rstb.2014.0070   
  5. Zakowski M, Geller A. Chapter 4, The Placenta: Anatomy, Physiology, and Transfer of Drugs, 58-62, David H. Chestnut, Cynthia A Wong, Lawrence C Tsen, Warwick D Ngan Kee, Yaakov Beilin, Jill Mhyre, Chestnut’s Obstetric Anesthesia: Principles and Practice, 2014, 5th edition, Elsevier Health Sciences, ISBN: 978-1-4557-4866-2.   
  6. Kaufmann P, Scheffen I. Placental development. In Polin RA, Fox WW, editors. Fetal and Neonatal Physiology. 2nd edition. Philadelphia, WB Saunders, 1998: 59-70.   
  7. Sadler TW. Langman’s Medical Embryology. 7th edition. Baltimore, Williams & Wilkins, 1995.   
  8. Boyd JD, Hamilton WJ. The Human Placenta. Cambridge, W. Heffer and Sons Ltd., 1970.   
  9. Robertson WB, Brosens IA, Dixon HG. Placental bed vessels. Am J Obstet Gynecol. 1973; 117(2): 294-5.   
  10. Roberts JM, Taylor RN, Musci TJ, Rogers GM, Hubel CA, Mc Laughlin MK. Preeclampsia: an endothelial cell disorder. Am J Obstet Gynecol. 1989; 161(5): 1200-4.   
  11. Babawale MO, Mobberley MA, Ryder TA, Elder MG, Sullivan MH. Ultra structure of the early human feto-maternal interface co-cultured in vitro. Hum Reprod. 2002; 17(5): 1351-7.   
  12. Craven CM, Morgan T, Ward K. Decidual spiral artery remodelling begins before cellular interaction with cytotrophoblasts. Placenta. 1998; 19(4): 241-52. doi: 10.1016/S0143-4004(98)90055-8   
  13. Schneider H, Danko J, Huch R, Huch A. Homeostasis of fetal lactate metabolism in late pregnancy and the changes during labor and delivery. Eur J Obstet Gynecol Reprod Biol. 1984; 17(3): 183-92. doi: 10.1016/0028-2243(84)90142-4   
  14. Blechner JN. Maternal-fetal acid-base physiology. Clin Obstet Gynecol. 1993; 36(1): 3-12.    
  15. Kaufmann P, Mayhew TM, Charnock-Jones DS. Aspects of human fetoplacental vasculogenesis and angiogenesis. II. Changes during normal pregnancy. Placenta. 2004; 25(3): 114-26. doi: 10.1016/j.placenta.2003.10.009   
  16. Mulvany MJ, Aalkjaer C. Structure and function of small arteries. Physiol Rev. 1990; 70(4): 921-61. doi: 10.1152/physrev.1990.70.4.921   
  17. Maynard SE, Min JY, Merchan J, Lim KH, Li J, Mondal S, et al. Excess placental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia. J Clin Invest. 2003; 111(5): 649-58. doi: 10.1172/JCI200317189   
  18. Demir R, Kayisli UA, Seval Y, Celik-Ozenci C, Korgun ET, Demir-Wuesten AY, et al. Sequential expression of VEGF and its receptors in human placental villi during very early pregnancy: differences between placental vasculogenesis and angiogenesis. Placenta. 2004; 25: 560-72. doi: 10.1016/j.placenta.2003.11.011   
  19. Brosens IA, Robertson WB, Dixon HG. The role of the spiral arteries in the pathogenesis of preeclampsia. Obstet Gynecol Annu. 1972; 1: 177-91.   
  20. Huppertz B. The feto-maternal interface: setting the stage for potential immune interactions. Semin Immunopathol. 2007; 29(2): 83-94. doi: 10.1007/s00281-007-0070-7   
  21. Kaufmann P, Sen DK, Schweikhart G. Classifi cation of human placental villi. I. Histology. Cell Tissue Res. 1979; 200(3): 409-23.   
  22. Pijnenborg R, Robertson WB, Brosens I, Dixon G. Review article: trophoblast invasion and the establishment of haemochorial placentation in man and laboratory animals. Placenta. 1981; 2: 71-91. doi: 10.1016/S0143-4004(81)80042-2   
  23. Huppertz B, Abe E, Murthi P, Nagamatsu T, Szukiewicz D, Salafia C. Placental angiogenesis, maternal and fetal vessels-a workshop report. Placenta. 2007; 28 (Suppl A): S94-6. doi: 10.1016/j.placenta.2007.01.015   
  24. Myatt L, Brewer AS, Langdon G, Brockman DE. Attenuation of the vasoconstrictor effects of thromboxane and endothelin by nitric oxide in the human fetal placental circulation. Am J Obstet Gynecol. 1992; 166(1): 224-30. doi: 10.1016/0002-9378(92)91863-6   
  25. Lyall F. Mechanisms regulating cytotrophoblast invasion in normal pregnancy and preeclampsia. Aust N Z J Obstet Gynaecol. 2006; 46(4): 266-73. doi: 10.1111/j.1479-828X.2006.00589.x   
  26. Polin RA, Fox WW, Abman SH. Fetal and neonatal physiology. vol 2 4th ed. Saunders, Elsevier. Chapter, 2 section 11, 2004.   
  27. King BF. Absorption of peroxidase-conjugated immunoglobulin G by human placenta: an in vitro study. Placenta. 1982; 3: 395-406. doi: 10.1016/S0143-4004(82)80032-5   
  28. Sibley CP, Boyd RDH. Control of transfer across the mature placenta. Oxf Rev Reprod Biol. 1988; 10: 382-435.   
  29. Faber JJ. Diffusional exchange between foetus and mother as a function of the physical properties of diffusing materials. In: Comline KS, Cross KW, Dawes GS, Nathanielsz PW, editors. Fetal and neonatal physiology. Cambridge: Cambridge University Press; 1973. p. 306-27.   
  30. Cordon-Cardo C, O’Brien JP, Casals D, Rittman- Grauer L, Biedler JL, Melamed MR, et al. Multidrug-resistance gene (P-glycoprotein) is expressed by endothelial cells at blood-brain barrier sites. Proc Natl Acad Sci U S A. 1989; 86(2): 695-8.   
  31. Nakamura Y, Ikeda S-i, Furukawa T, Sumizawa T, Tani A, Akiyama S-i, et al. Function of P-glycoprotein expressed in placenta and mole. Biochem Biophys Res Commun. 1997; 235(3): 849-53. doi: 10.1006/bbrc.1997.6855   
  32. Tanabe M, Ieiri I, Nagata N, Inoue K, Ito S, Kanamori Y, et al. Expression of P-glycoprotein in human placenta: relation to genetic polymorphism of the multidrug resistance (MDR)-1 gene. J Pharmacol Exp Ther. 2001; 297(3): 1137-43.   
  33. Ushigome F, Takanaga H, Matsuo H, Yanai S, Tsukimori K, Nakano H, et al. Human placental transport of vinblastine, vincristine, digoxin and progesterone: contribution of P-glycoprotein. Eur J Pharmacol. 2000; 408: 1-10. doi: 10.1016/S0014-2999(00)00743-3   
  34. Kalabis GM, Kostaki A, Andrews MH, Petropoulos S, Gibb W, Matthews SG. Multidrug resistance phosphoglycoprotein (ABCB1) in the mouse placenta: fetal protection. Biol Reprod. 2005; 73(4): 591-7. doi: 10.1095/biolreprod.105.042242   
  35. May K, Minarikova V, Linnemann K, Zygmunt M, Kroemer HK, Fusch C, et al. Role of the multidrug transporter proteins ABCB1 and ABCC2 in the diaplacental transport of talinolol in the term human placenta. Drug Metab Dispos. 2008; 36(4): 740-4. doi: 10.1124/dmd.107.019448   
  36. Lagrange F, Pehourcq F, Bannwarth B. Passage of S- (+) – and R- (–) – ketotifen across the human isolated perfused placenta. Fundam Clin Pharmacol. 1998; 12: 286.   
  37. Pascolo L, Fernetti C, Pirulli D. Effects of maturation on RNA transcription and protein expression of four MRP genes in human placenta and in behio cells. Biochem Biophys Res Commun. 2003; 303(1): 259-65.   
  38. King A, Boocock C, Sharley AM, Gardner L, Beretta A, Siccardi AG, et al. Evidence for the expression of HLA-C class I mRNA and protein by human fi rst trimester trophoblast. J Immunol. 1996; 156(6): 2068-76.   
  39. Thellin O, Coumans B, Zorzi W, Igout A, Heinen E. Tolerance to the foetoplacental ‘graft’: ten ways to support a child for nine months. Curr Opin Immunol. 2000; 12(6): 731-7. doi: 10.1016/S0952-7915(00)00170-9   
  40. Oreshkova T, R Dimitrov, Mourdjeva M. A Cross-Talk of Decidual Stromal Cells, Trophoblast, and Immune Cells: A Prerequisite for the Success of Pregnancy. Am J Reprod Immunol. 2012; 68(5): 366-373. doi: 10.1111/j.1600-0897.2012.01165.x   
  41. Ben-Hur H, Gurevich P, Berman V, Tchanyshev R, Gurevich E, Zusman I. The secretory immune system as part of the placental barrier in the second trimester of pregnancy in humans. In Vivo. 2001; 15(5): 429-39.   
  42. Gurevich P, Elhayany A, Ben-Hur H, Moldavsky M, Szvalb S, Zandbank J, et al. An immunohistochemical study of the secretory immune system in human fetal membranes and decidua of the first trimester of pregnancy. Am J Reprod Immunol. 2003; 50(1): 13. doi: 10.1034/j.1600-0897.2003.01201.x   
  43. Goldblum RM, Hansen LA, Brandtzaeg P. The mucosal defense system. In: Stiehm ER, editor. Immunologic disorders in infants and children. Philadelphia: Saunders Publ. Co.; 1996. 159.   
  44. McGhee JR, Kiyono H. The mucosal immune system. In: Paul WE, editor. Fundamental immunology. Philadelphia: Lippincott-Raven Publ; 1999. p. 909.   
  45. Iijima H, Takahashi I, Kiyono H. Mucosal immune network in the gut for the control of infectious diseases. Rev Med Virol. 2001; 11(12): 117. doi: 10.1002/rmv.307   
  46. Wong NC, Novakovic B, Weinrich B, Dewi C, Andronikos R, Sibson M, et al. Methylation of the adenomatous polyposis coli (APC) gene in human placenta and hypermethylation in choriocarcinoma cells. Cancer Lett. 2008; 268: 56-62. doi: 10.1016/j.canlet.2008.03.033   
  47. Reik W, Walter J. Genomic imprinting: parental infl uence on the genome. Nat Rev Genet. 2001; 2: 21-32. doi: 10.1038/35047554   
  48. Santos F, Hendrich B, Reik W, Dean W. Dynamic reprogramming of DNA methylation in the early mouse embryo. Dev Biol. 2002; 241: 172-82. doi: 10.1006/dbio.2001.0501   
  49. O’Carroll D, Erhardt S, Pagani M, Barton SC, Surani MA, Jenuwein T. The polycomb-group gene Ezh2 is required for early mouse development. Mol Cell Biol. 2001; 21: 4330-6. doi: 10.1128/MCB.21.13.4330-4336.2001   
  50. Pasini D, Bracken AP, Jensen MR, Lazzerini Denchi E, Helin K. Suz12 is essential for mouse development and for EZH2 histone methyl transferase activity. Embo J. 2004; 23(20): 4061-71. doi: 10.1038/sj.emboj.7600402   
  51. Eskandarlou M, Azimi M, Rabiee S, Seif Rabiee MA. The Healing Effect of Amniotic Membrane in Burn Patients. World J Plast Surg. 2016; 5(1): 39-44.   
  52. Kerry R. Applications of Amniotic Membrane and Fluid in Stem Cell Biology and Regenerative Medicine. Stem Cells International. 2012; 721538. doi: 10.1155/2012/721538   
  53. Malhotra C, Jain AK. Human Amniotic Membrane Transplantation: Different Modalities of Its Use in Ophthalmology. World J Transplantat. 2014; 4(2): 111-121. doi: 10.5500/wjt.v4.i2.111   
  54. Evangelista M, Soncini M, Parolini O. Placenta-Derived Stem Cells: New Hope for Cell Therapy? Cytotechnology. 2008; 58(1): 33-42. doi: 10.1007/s10616-008-9162-z   
  55. Azizian S, Khatami F, Modaresifar K, Mosaffa N, Peirovi H, Tayebi L, et al. Immunological compatibility status of placenta-derived stem cells is mediated by scaffold 3D structure. Artif Cells Nanomed Biotechnol. 2018; 23: 1-9. doi: 10.1080/21691401.2018.1438452   
  56. Di Germanio C, Bernier M, de Cabo R, Barboni B. Amniotic Epithelial Cells: A New Tool to Combat Aging and Age-Related Diseases? Front Cell Dev Biol. 2016; 22(4): 135. doi: 10.3389/fcell.2016.00135.   
  57. Bhattacharya N, Gupta PN, Malakar D. Freshly Collected Amniotic Fluid and Amniotic Membrane as Dressing Material for Leprosy Patients with Gangrene: A Preliminary Report on an Experience with Six Cases. In: Bhattacharya N, Stubblefield P, eds. Regenerative Medicine. Springer, London, 2015; 26: 257-260.   
  58. Atala A. Chapter No: 36 – Amniotic fluid and placental stem cells. In: Bhattacharya N, Stubblefield P, eds. Regenerative Medicine using Pregnancy-specific biological substances. Springer-Verlag London Limited; 2009: 375-380.   
  59. Maguire CT, Demarest BL, Hill JT, Palmer JD, Brothman AR, Yost HJ, et al. Genome-Wide Analysis Reveals the Unique Stem Cell Identity of Human Amniocytes. Plos One. 2013; 8(1): 53372 doi: 10.1371/journal.pone.0053372   
  60. Moschidou D, Mukherjee S, Blundell MP, Drews K, Jones GN, Abdulrazzak H, et al. Valproic Acid Confers Functional Pluripotency to Human Amniotic Fluid Stem Cells in a Transgene-free Approach. Mol Ther. 2012; 20(10): 1953-67. doi: 10.1038/mt.2012.117   
  61. Guo X, Kaplunovsky A, Zaka R, Wang C, Rana H, Turner J, et al. Modulation of Cell Attachment, Proliferation, and Angiogenesis by Decellularized, Dehydrated Human Amniotic Membrane in In Vitro Models. Wounds. 2017; 29(1): 28-38.   
  62. Dickinson LE, Gerecht S. Engineered Biopolymeric Scaffolds for Chronic Wound Healing. Front Physiol. 2016; 5(7): 341. doi: 10.3389/fphys.2016.00341   
  63. Bhattacharya N. Stubblefield P. Regenerative Medicine using Pregnancy specific biological substances, Springer-Verlag London Limited 2009, Chapter No: 37,Use of Amniotic Membrane, Amniotic Fluid, and Placental dressing in Advanced Burn Patients. 383-393.   
  64. Bhattacharya N. Clinical Use of Amniotic Fluid in Osteoarthritis: A Source of Cell Therapy. Transplantation. 2011; 90: 395-403.   
  65. Bhattacharya N. Stubblefield P. Regenerative Medicine using Pregnancyspecific biological substances, Springer-Verlag London Limited 2009, Introduction, page no: vii.   
  66. Shimazaki J, Yang HY, Tsubota K. Amniotic membrane transplantation for ocular surface reconstruction in patients with chemical and thermal burns. Ophthalmology. 1997; 104(12): 2068-76.   
  67. Lee SH, Tseng SC. Amniotic membrane transplantation for persistent epithelial defects with ulceration. Am J Ophthalmol. 1997; 123(3): 303-12.   
  68. Kruse FE, Rohrschneider K, Volcker HE. Multilayer amniotic membrane transplantation for reconstruction of deep corneal ulcers. Ophthalmology. 1999; 106: 1504-10. doi: 10.1016/S0161-6420(99)90444-X   
  69. Rakowski E, Zagorski Z, Kardaszewska A, Durakiewicz D. Application of amniotic membrane transplantation in severe corneal diseases. Klin Oczna. 1999; 101: 417-21.   
  70. Prabhasawat P, Barton K, Burkett G, Tseng SC. Comparison of conjunctival autografts, amniotic membrane grafts, and primary closure for pterygium excision. Ophthalmology. 1997; 104: 974-85.   
  71. Pires RT, Tseng SC, Prabhasawat P. Amniotic membrane transplantation for symptomatic bullous keratopathy. Arch Ophthalmol. 1999; 117: 1291-7.   
  72. Pruit BA, Lindberg RB. Pseudomonas aeruginosin infection in burn patients. In: Doggett RG, editor. Pseudomonas aeruginosin: clinical manifestations of infection and current therapy. 1st ed. New York:Academic; 1979; 339-66.