Foetal gene therapy is a novel and experimental therapeutic approach which has the potency to prevent the irreversible damage due to manifestation most of the inherited disorders. Application of therapeutic gene to the foetus having genetic disorder, allow the targeting of still expanding population of stem cells that might become inaccessible in post natal life. Moreover, immunogenic naivety of foetus towards the theraupetic vector encourages the success of thethis innovative technique. Invention of highly efficient tools like ultrasound scanning and embryo-fetoscopy has enabled the process of application of therapeutic gene in the foetus with minimally invasive technique. Selection of candidate disease, suitable vectors, routes of delivery and appropriate time of administration of the therapeutic gene are the crucial points that play vital role on foetal gene therapy. Due to its potency to prevent some of the uncurable diseases, foetal gene therapy has chances of emerging as a panacea for many disorders and occupy significant position in the sector of bio business trade as well. However, being still an experimental approach ; and due to some potential risks like mutagenesis, carcinogenesis, and germ line transmission, foetal gene therapy needs extensive research on its unrevealed aspects on different animal models, before applying it in human beings. Similarly, different ethical issues related with foetus and mother, that has made the entire process of foetal gene therapy more complicated, must be taken under consideration.
Gene therapy is one of the most significant discovery of modern medicine which is based on the delivery of genetic material to the cells for theraupetic benefit. Though gene therapy has been applied for the treatment of human disease since last two decades, its efficacy has still been delimited by some of the obstacles. Probably these obstacles could be overcome by a novice approach of gene therapy called foetal gene therapy or in-utero gene therapy. (Roybal et al.,2010)
Foetal gene therapy is an innovative technique of treating a genetic disease by replacing damaged or abnormal gene with normal one in utero condition of foetal life. However, this work is highly controversial due to some ethical and safety concerns. Neverthless, foetal gene therapy has been presumed to be treatment or prevention for serious genetic diseases like cystic fibrosis, Duchenne muscular dystrophy, with the assumption that application of this therapy will provide better results than the contemporary ones. The long term expression of the transgene can be achieved in foetal gene therapy by vector mediated gene transfer with mimimally invasive technique like ultrasound guided injection to target the proliferating stem cells which might be inaccessible after the birth of the foetus. Neverthless, the dark side of this therapy is the potential risk of insertional mutagenesis, vector toxicity, potential germ line transmission of gene and maternal and foetal mobidiy and mortality. Thus foetal gene therapy is still considered to be an experimental approach and needs plethora of researches to understand its risk and benefit before applying it for clinical practice in human beings. (Ahmed Salman et al. 2009)
Since last two decades, extensive attempts have been made to design a technique for prenatal diagnosis of some genetic disorders . As a consequence of this effort, foetal material can now be available for genetic analysis even at the first trimester by invasive techniques like chorionic villus sampling (CVS). (Surbek DV, Holzgreve W., 2001)With the contemporary advancement of molecular biology, different research tools have been emergerd for the prenatal diagnosis of chromosomal defects or single gene disorders from foetal material obtained from CVS or foetal cells or foetal cell free DNA from maternal blood. (Holzgreve W., 1997) Apart from the invasive techniques, some non invasive techniques have been seen to be feasible for prenatal diagnosis for haemoglobinipathies and lymphohaemopoietic diseases and storage diseases. As a result diseases like beta thalassemia, sickle cell anaemia, severe combined immunodeficiency syndrome (SCID), Hurler's syndrome and Krabbe's disease are now likely to be diagnosed at the first trimester of pregnancy. With this rate of progressive advancement, it is possible in near future to screen “at-risk population” with non invasive technique and develop a molecular method like DNA- chip technology that will rapidly increase the rate of diagnosis of such diseases prenatally even on an individual having no familial history of that particular disease.
Post natal treatment of above mentioned genetic disorders is often limited. However, in some of these diseases, allogenic stem cell transplantation has shown some optimistic results towards definitive cure. But several obstacles still persist. Firstly, it is very difficult to find a HLA-compatible donor. Secondly, the process of immuno suppression and bone marrow ablation in the recipient most commonly leads to substantial treatment associated morbidity, particularly, the graft-versus host disease. In case of non related donor stem-cell transplantation, graft failure is also commonly seen. Thirdly, some of these diseases like alpha thalassemia, might have already led to irreversible damage to foetus before the birth. Because of these all reasons, most of the parents prefer the option of termination of pregnancy if they face the diagnosis of a severe genetic defect in a previable foetus. Although the decision of mother is the ultimate for the fate of foetus, but the ultimate goal of prenatal diagnosis must not be termination of pregnancy in all the cases of genetic disorder of foetus. Rather, the range of options must be broadened by introducing therapeutic options for the long- term prospects for the future of child. (Surbek,D. et al ,2008)
There are plenty of reasons that justify that why foetus offers most favourable environment for the transfer of genetic material. The most compelling rationale of foetal gene therapy, known so far, is its potency to prevent certain diseases before their onset thus preventing the irreversible damage of an organ. During the developmental stage of foetus, stem cells and progenitor cells occur at high frequency and they remain exposed within various tissue compartments. At this period, a window of opportunity exists for gene transfer on these exposed cells before they distribute in different organs. Hence a necessary transgene can be targeted to these expanding population of cells before they become inaccessible in later life. (Roybal et al.)Thus, unlike conventional post natal gene therapy, foetal gene therapy has the potency to avoid the process of the severe disease manifestation by applying the gene therapy in utero and targeting otherwise inaccessible organs, tissues or expanding population of stem cell and provides the basis of permanent gene correction.
Additionally, immunogenic vectors and transgenes have the previlage of taking advantage of immature immune system of the foetus. Avoidance of immune sensitization due to gene application to the foetus facilitates the repeated treatment even in post natal condition. (Gregoriadis G., Mc Cormack B., 2000) Thus immunological tolerance not only ensures stable and long-term transduction, but also the post natal treatment with the same vecotor and transgene. (Roybal et al.)
Due to the small size of the foetus, it is easy to achieve the extremely high ratio of vector-to- cell even with limited amount of vector. Consequently, it favours the compartmental and hematogenous distribution of the vector due to increased concentration of vector in the target cell. While summing up all these concepts, it becomes obvious that if successful application of foetal gene therapy becomes possible, it will add a therapeutic option regarding decision making after prenatal diagnosis. Thus, it has the potential to alter the attitude of people towards antenatal screening of genetic diseases. (Coutelle C et al, 1995, Doubar AM et al, 1996)
Foetal gene therapy is one of the promising novel scientific strategies to correct genetic disorders. In current scenario, it has been specifically considered to be an auspicious strategy to overcome the limitation of conventional haematopoietic stem cells (HSC) therapy by evading the allogenic HLA barriers, using genetically corrected autologous HSC in foetus.
Ex vivo versus In vivo appraoch
Depending on the mode of application, foetal gene therapy can be categorized into ex vivo and in vivo approach. Major concern of ex vivo approach is to target autologous haematopoietic stem cells in vitro, enabling them to be highly proliferative and able to give enhanced gene expression. In this approach, the therapeutic gene is transduced to the autologous HSC in vitro and transplanted back to the foetus. This type of strategy has been used in human neonates using cord blood stem cells to correct ADA deficiency disorder; and resulted in partial success. However, same experiment became highly successful while using autologous bone marrow instead of cord stem cells. The advantage of ex vivo approach is that it has relatively less risk for germ line transduction than the in vivo delivery of transgene where the whole foetus gets direct exposure to a high titre of gene-vector construct. The major critical issue of ex vivo gene therapy is to achieve a competitive advantage of transduced autologous cells over the resident foetal cells. Hence, genetically corrected autologous HSC are supposed to gain selective advantage compared to the non corrected cells. (Wngner AM, Schoeberlein A.,Surbek D, 2009)
In vivo approach of foetal gene therapy involves the direct transfer of vector -gene construct into the foetus. Here, the vector of interest is transferred directly to the foetus. This approach is technically much easier than the ex vivo approach but it has the threat of germ line transduction of the gene. To the date no comparison of the two techniques using similar delivery system has been performed.(Wngner AM, Schoeberlein A.,Surbek D, 2009)
Being an experimental concept, foetal gene therapy can currently be targeted for future application in the life threatening monogenic diseases which are caused by absence or inactivation of essential gene product and which manifest themselves in foetal life. Similarly, diseases having tendency to cause irreversible damage to organs in prenatal or early post natal life, are also the candidate diseases of the foetal gene therapy. Genetic disorders like cystic fibrosis, Phenylketonurea, Haemophilia, Epidermolysis Bullosa ,DMD, ADA deficiency and different haemoglobinopathies are the potential candidate diseases for foetal gene therapy. (Gregoriadis G., Mc Cormack B., 2000).
Cystic fibrosis is one of common autosomal recessive monogenic disorder having incidence of 1 in 2000 in new borns. ( Jacksin ADM, 1989 ) The genetic cause behind the onset of this disease is the mutation of gene coding Cystic Fibrosis Transmembrane Regulator (CFTR) protein. This disease mainly affects lungs, pancreas biliary tract and intestine, causing shortened expectancy. Appearance of CFTR protein in human embryo occurs by 7 weeks of gestation in the yolk sac and shortly afterwards in ciliated tracheal cells. This protein is expressed in intestine at 12th week, and apical domain of ciliated airway epithelia in 24th to 25th week of gestation. (Gaillard D.et al,1994) Thus it shows its vital role during the development of human foetus. Hence gene therapy in case of cystic fibrosis is most relevant during prenatal rather than post natal life.
Another lung disease caused by deficiency of surfactant protein B affects the expansion of neonatal lung after birth. This is another candidate disease for foetal gene therapy and can be treated by delivering the gene encoding this protein, in utero. Similarly, metabolic disorders (e.g. phenylketonuria), or storage diseases that occur during prenatal life are other pathological conditions that manifest themselves in foetal life and ideal target for gene therapy in utero.
In the scenario of expensive treatment and problems associated with repeated transfusions, haemophilia is also one of the best examples of candidate disease for the application of foetal gene therapy. Due to the immune responses, post natal gene therapy does not seem to prevent manifestation of haemophilia (Zaiss AK, Muruve DA,2008). The other factors that make haemophilia an ideal candidate disease for foetal gene therapy are: availability of its prenatal diagnosis, aetiology being loss of function of a single gene, and its known pattern of inheritance.
Generally vectors used for the gene delivery to the cells bind specifically to the targeted organ and require just a single application. Ideally foetal gene therapy requires a vector system of specific gene construct that reach to the required organs and leave its permanent expression avoiding the germ line transmission. Unfortunately no single vector is available to meet this goal. (Gregoriadis G., Mc Cormack B., 2000).
Though the non viral vectors such as gene gun have been proposed to be safer mode of transduction, but the transgene introduced by them remains episomal or lost with cell division, and thus renders limited expression. (Yoshizawa J, Fujino M, 2004) Hence viral vectors are considered to be more efficient vehicles for gene delivery due to their ability to penetrate host cells and replicate inside the host cell. Before transfection, they are engineered to attenuate their genome so that only the transgene , not the viral genes are copied. There are several factors like immunogenicity, packing capacity, targeted tissue and desired duration of expression that play vital role on the choice of a viral vectors. Till now, viral vectors like adeno viruses, retro virus and adeno associated viruses are considered to be relatively more suitable options for foetal gene therapy.
Adenoviruses have been used as vectors in many experiments due to their higher efficiency to transfer genes. Past experiments show that Adenoviruses have been used in some of the models of foetal gene transfer. But they were not found to integrate into host genome. As a result transgene expression was found to be instantaneous in rapidly dividing foetal cells. Moreover, their high imunognecity prevented them to be a good vector for gene therapy. However due to immunological naivety of the foetus, adenoviruses find foetus to be more amenable than the post natal gene therapy.
Retroviruses have the ability to integrate into the genome of host and render permanent gene expression. They infect dividing cells and are therefore better vectors for in vivo gene transfer in a differentiating and quickly generating organs of pre natal life. But non synchronised cell division and relatively short half life of the virus in foetus may cause problems.(Hatzouglou M, Moorman A, Lamers W, 1995) This problem can be overcome by the use of high titre of retroviruses or use of lentiviruses which do not necessarily require actively dividing cells to enter into the nucleus.
Adeno-associated viruses (AAV)
Adeno- associated viruses (AAV) are promising vectors to achieve long lasting gene expression. Adeno associated viruses(AAV) are comparatively less immunogenic and their serotype influences tissue specificity. But due to their tendency to integrate into the genome at low frequency and their slow expression profile, it may take few weeks for AAV to reach to peak expression level. Relatively longer duration of transgene expression can be seen in the tissues like central nervous system, liver and skeletal muscles, where there occurs less turnover of cells. Similarly the vector must integrate into the host genome in order to ensure long term expression of the transgene.
Route of Administration
Foetal gene therapy has been performed in mice, rats, rabbits and sheep so far. Using different rodent models for human genetic diseases and various routes of administration, foetal gene therapy has been aimed to target different organs. However, the models for pre clinical foetal gene therapy are still under investigation. Following routes of administration have been performed on different animal models:
Intra amniotic delivery
Gene delivery in the intra amniotic cavity requires laparotomy of the animal model. (Papaioannou VE,1990.), however it can be carried out transcutaneously with ultrasound guided technique in sheep. Main limitation of this technique is the dilution of the injected vector construct with relatively large volume of amniotic fluid. Another demerit is that large amount of the vector primarily reach the foetal skin and amniotic membranes without any specific organ targeting. The foetus swallows the amniotic fluid, absorbs by gastro intestinal tract and then excretes via kidneys.(Brace R, 1995) Apart from this, episodes of breathing movements are also shown by the foetus (Badalian, SS, Fox HE ,Chao CR, Timor IE , 1994) which leads to influx of amniotic fluid into the lungs. Consequently, marker gene expression is seen in lungs, intestinal system and the skin after intra uterine administration. Similarly, amniotic membrane may be used for the production of human factor IX in mice by intra amniotic delivey of the vector.
Systemic delivery through foetal circulation
Foetal circulation of the animal models can be accessed through inta placental injection, intra cardial application or injection into the yolk sac vessels. (Schachtner S, Buck CA, 1999) Injection into the umbilical vein of the sheep can be achieved by the fetoscopy after laparatomy (Yang E, Cass DL,Sylvester KG, 1999) or ultrasound guided less invasive transcutaneous injections. In an experiment using systemic delivery though foetal circulation, adenoviral vectors carrying beta galactosidase marker gene and hauman factor IX cDNA, have been studied on sheep foetus of gestation age of 130 days . (Themis M et al, 1999) As a result, 30 % cells staining positive for beta galactosidase in liver and adrenal cortex of the foetuses were found. Sililarly, level of factor IX was found to be equivalent to normal human plasma factor IX level in 80% of the treated foetus after their birth. Vector spread was seen in all foetal, and neonatal organs and maternal liver. Thus systemic delivery of vector through foetal circulation has emerged as a promising approach, however needs more detailed investigations.
Other routes of application:
The other techniques involves laparotomy followed by fetoscopy for intratracheal injection of adenovirus. In addition, intraperitoneal application to infect hepatocytes and heamatopoietic stem cells , and direct hepatic injection to infect hepatocytes are other alternative routes of application of vector construct.
Experiments on Animal Models
Since foetal gene therapy has not yet been applied on human beings, it has been carried out only in the experimental animal models. Different experiment carried out on different animal model for different candidate disease has been illustrated hereunder:
Experiment on Cystic Fibrosis as a candidate disease
Though gene therapy to mature lung have undergone through plenty of clinical trials for the potential therapy against cystic fibrosis, foetal gene therapy was carried out for cystic fibrosis in sheep model, for the first time by, Pitt, Schwarz and Bland . They had used adenovirus vector system to deliver their target gene.
Following are the points that will rationalize and justify that why application of adenoviral mediated foetal gene theapy on lung is more advantageous than that in adult lung:
- Limited immune reposnse and minimized inflammatory response on the foetus, prolonging the adenovirus mediated transgen expression
- Accessibility to plenty of dividing cells (may be stem cells) that allow the use of retro viral vectors.
- More expression of CFTR on foetus than adult lungs
- Less complex surface lining of lungs and presence of limited number of macrophages and proteins that facilitate the delivery of DNA.
Material and Methods:
Following is the description of adeno-virus mediated gene transfer protocol in foetal lung, carried out by Pitt, Schwarz and Bland in sheep model.
Production of Retroviral supernant :
MFG retro viral vectors inserted with LacZ or secreted human interleukin receptor antagonist protein cDNA were used. This MGF vector is the simplified retroviral vector derived from M-MuLV devoiding the polymerase and envelope gene sequences. However partial gag sequences were retained to increase the packing efficiency of the unspliced transcript. The inserted cDNA were transcribed from the promoter/enhancer sequences from the retroviral long terminal repeat (LTR). High titre amphotrophic producer of recombinant retroviruses were produced by cotransfection of plasmid (pSV2neo) into the packaging cells(CRIP). NIH3T3 cells were cultivated in DMEM and provided with 4.5 g/L of
(CFTR : Cystic fibrosis transmembrane conductance regulator, UGT 1A1: UDP-glucuronyl transferase, AAV : Adeno associated virus, RPPE 65: Retinal pigment epithelium 65, MPS VII: Mucopolysaccharidosis VII)
glucose and 10% (v/v) heat-inactivated sheep serum, 100 U/ml of penicillin, 200 mg/mL of glutamine, and finally infected with virus. The medium containing viral supernatant was tested for the viral titre and presence of helper virus, concentrated 3X and stored at -70 degree Celsius.
Twin foetal lambs were surgically prepared with catheters and the ewe was sedated intramuscularly with 15 mg/kg ketamine. After that, hysterotomy was performed with halothane and nitrous oxide anaesthesia. The uterus was, then, opened with a small incision and polyvinyl catheters were placed directly into the foetal carotid artery, jugular vein and trachea. Similarly, a fluid- filled catheter was placed in the amniotic sac, and the catheters were sutured to uterus and abdomen of ewe. The wounds were closed with silk sutures, and catheters were placed in a pouch sewn on the flank of the ewe. Amniotic sac was administered with 1000,000 U of penicillin, and 400 mg of kanamycin during and after surgery. Similarly, foetal vein was administered with 300,000 U of penicillin and 10 mg of gentamycin at the time surgery and daily after that. The ewe was given 5 mL mixture of penicillin and dihydrostreptomycin and 600 mg of kanamycin intramuscularly each day.
Administration of Vector to the Foetus:
After 1 day of surgery, blood was withdrawn from the carotid artery catheter for the determination of haematocrit, pH and blood gas tension. 60 mL of tracheal fluid was withdrawn into a sterile syringe. After this, 10 mL solution of MFG-viral supernatant having 3x 10 6 particle per mL concentration was brought to room temperature immediately before use and polybrene was added to a final concentration of 2 micro gram per mL. The viral supernatant was delivered directly to the tracheal catheter and flushed to the lungs with 30 to 60 mL of previously withdrawn lung liquid. Same procedure was carried out for other twin with other MFG-vector. All the catheters were flushed with heparinised saline and antibiotics was given as per the pre defined dose. This whole procedure was repeated for three consecutive days.
The ewe and the foetuses were killed with an intravenous overdose of sodium pentobarbital (50 mg/kg).Their lungs were removed and inflated ex vivo to 30 cm H20 trans pulmonary pressure by injecting phosphate buffered solution of pH 7.4 (containing 4% paraformaldehyde and 0.1% gluteraldehyde). After that, lungs were immersed into phosphate buffered saline containing 30% sucrose and incubated at 4 degree Celsius.
For histochemical analysis, small blocks of tissue were obtained from proximal and distal section of each lobe and frozen in liquid nitrogen. Frozen sections were cut with cryostat and mounted on poly-L-lysine -coated glass slides. To localize beta galactosidase activity, small blocks of fixed tissues were rinsed in PBS and incubated in a solution containing 1 mg/mL of 5 bromo 4 chloro 3 indoyl- D-galactopyanoside in Tris-phosphate buffered saline (pH 8.0) in 5mM potassium ferricyanide and potassium ferrocyanide. The tissue sections were further incubated for 8 hours and washed in PBS. After that tissue was frozen and sectioned, followed by counter stain with eosin and haematoxylin. The stained sections were observed under microscope. Similarly, immunohistochemistry was performed on these samples.
Detectable levels of beta galactosidase was noted in the upper and lower airways of some of these animals, for 3 weeks after infection. Localization of beta galactosidase was found to be the most prominent in the epithelial cells of proximal airways with additional histochemical appearance associated with fibroblasts and macrophages in the sub mucosa. Most of the current preclinical approaches relate foetal gene therapy with the transduction of foetal heamopoietic tissue. Many laboratories have been successful on to transfect bone marrow cells in culture. But Problems like longevity of expression, difficulty on obtaining and transducing totipotant stem cells and potential requirement of bone marrow ablation have prompted alternative strategies.
Experiment on Hamophilia as a candidate disease
Haemophilia has been studied extensively in animal models with the transfer of required gene at various gestational age through different routes using different vectors. Schneider et al had compared intraperitoneal, intramuscular, and intravenous injections of human factor IX via Adeno virus and AAV-2, in E 15.5 foetuses of mice. As a result , initial higher level of factor IX was seen in foetuses transfected with adeno viral vectors. It was followed by decrease in the expression of the transgene in both vectors over time. However, adeno viral vector injected mice maintained the therapeutic level for six months. But no antibodies were formed against either vector or transgene.
Similarly, Sabatino et al. detected low-level human factor IX expression after intramuscular injection of AAV-1 and 2 in E14 foetuses and neonatal mice. Tolerance induced to AAV-1 made it possible for the postnatal re-administration of the AAV-1-driven transgene and subsequent therapeutic factor IX levels. The experiment carried out by the use of lentiviral vector for prenatal gene transfer in hemophiliac mice gave impressive results. Similarly, Waddington et al. performed a lenti virus mediated intravenous administration of transgene on E15 foetuses and experiment resulted on therapeutic levels of factor IX expression (9-16%) for 14 months; improved coagulation, and showed no immune response against the protein.
These studies on haemophilia indicate that foetal gene therapy in mice result in low-level transgene expression. These results have therapeutic significance as well as the capacity to induce tolerance for potential postnatal administration of the same vector construct for perpetual expression.
Genteric Inc., Gene Medicine Inc., Gen Vec Inc., etc are some of the pioneering biotechnological companies involved in business of gene therapy. They have been focussed on providing new generation gene therapy and hold the patents of different biotechnological productions.
Due to some of its merits over the post natal gene therapy, foetal gene therapy shows a lot of possibilities to emerge as a promising field of biotechnology market.
Safety and potential risk
Potential risk of germ line transduction of theraupetic gene in foetal therapy raises a large number of social, legal and moral questions. Similarly the possibility of insertional mutagenesis in foetal cells leading to gene defect or formation of malignant tumour is another aspect of foetal gene therapy that creates ethical problem.( Noble,R., Rodeck C.H., 2008).
Gene delivery in utero encpunters some specific procedural risks that are not encountered in postnatal gene delivery . The major risks include infection, loss of foetus and induction of preterm labour. In addition, transplacental spread of vector to the mother is another risk factor, which might create the potential risk of oncogenesis and germ-line transduction.
The safety issue of gene therapy is of major ethical concern during the development of clinical trials. History records show that, there were around 400 gene therapy trials during the 1990s, which involved more than 4000 patients internationally. By 2000, the National Institutes for Health of United States recorded that 691 serious adverse events had occurred during these trials, including death of 6 patients.
During the process of foetal gene therapy, the injection of viral vectors into the amniotic fluid or peritoneal cavity of developing foetus leads to exposure of foetus to the organism and causes the risks of oncogenesis ,insertional mutagenesis, and ultimately the disruption of normal development. Due to the compulsion of repeated application of foetal gene therapy
through out the life time, there are chances of increased risk and burden that can be the part of any risk-benefit analysis. Like potential merits of foetal gene therapy are substantial, the potential risks are also considerable. Hence every research trials should be conducted with caution. However, it is not yet clear that how such trials must be conducted, because the experiments on foetal gene therapy do not seem to be compatible as per the standard protocol of clinical trials as it is performed on other assays.
Generally, phase 1 clinical trials for any experiment are conducted specifically to determine the range of safe dose, side effects and coping mechanism of body to the treatment. This type of clinical trials are generally conducted when there are plethora of preclinical evidence to prove that the treatment is likely to work. Since foetal gene therapy has been carried out so far , only in animal models, indicatiors of safety noticed in animal models are uncomparable with human beings and difficult to transfer to human pregnancy, especially while interpreting results on safety concerns in an model like foetal sheep where chances of abortion are rare despite robust pregnancy.
Foetus as a Patient: Conflict of duty
In foetal gene therapy, there is probability of conflict between the perceived duties and obligation of clinician and those of pregnant woman. Similarly the potential conflict between duties owed by clinician to the pregnant women and perceived obligation to the well being of the foetus might create ethical problems. Such situation might arise when the pregnant woman refuses a therapeutic procedure that has been recommended by the clinician for the well being of the foetus. ( Noble,R., Rodeck C.H., 2008)
Informed Consent and Human Trials
Informed consent is a basic concept of medical research involving human participants where potential harms and benefits of the research are thoroughly informed to the participant and they are considered to be the beneficiaries of the research. But in foetal gene therapy, pregnant woman who is considered to be the participant of the therapy is not the direct beneficiary of the therapy, but her future child. Since these participants might have to carry a burden of risk, it might be unethical to recruit them for a therapy that might benefit their offspring, until we are uncertain about the success of this therapy. ( Noble,R., Rodeck C.H., 2008)
Despite its some of merits over the post natal gene therapy, foetal gene therapy is still under experiment. This therapy has been demonstrated in many animal models for many genetic disorders. Safety concerns including risk of insertional mutagenesis and potential germ line transmission are the aspects that need to be investigated extensively. Hence, this technique must undergo a series of trials in suitable animal models to prove its safety and efficacy before initiating clinical trials on human beings. Similarly, ethical issue is another disputable issue of foetal gene therapy that also must be resolved by logical conclusion.
- Roybal, J. L., Santore, M. T. and Flake, A. W. ,2010. Stem cell and genetic therapies for the fetus. Seminars in Fetal and Neonatal Medicine. 15(1): pp.46-51.
- Ahmed Salman, M. S. M., James, D. K. and Bugg, G. J. 2009. Advances in foetal therapy. Obstetrics, Gynaecology & Reproductive Medicine. 19(11): pp.308-314.
- Surbek DV, Holzgreve W., 2001. Why do we need non invasive prenatal diagnosis?In: Hahn S, Holzgreve W, editors. Foetal cells and foetal DNA in maternal blood. New developments in new millennium. New York: Karger, pp. 21e7.
- Holzgreve W., 1997. Will ultrasound -screening and ultrasound-guided procedures be replaced by non-invasive techniques for the diagnosis of foetal chromosomal anomalies? Ultrasound Obstet Gynecol.9 : pp. 21e9.
- Surbek,D,Schoeberlein A., Wagner,A., 2008. Perinatal stem -cell and gene therapy for hemoglobinopathies. Seminars in Fetal and Neonatal Medicine. 13: pp. 282-290.
- Jacksin ADM, 1989. The natural history of cystic fibrosis. In : Goodfellow P, editor. cystic fibrosis. USA: Oxford University Press, pp. 1-11.
- Gaillard D., Lallemand A.,Dallemans W.,Hinnarski J., Puchelle E., 1994. Immunochemical localization of cystic fibrosis transmembrane conductance regulator in human fetal airways and digestive mucosa. Pediatr. Res. 36: pp. 137-143.
- Gregoriadis,G., Mc Cormack, B., 2000. Targeting of drugs: strategies for gene constructs and delivery, Marathon: IOS press: pp. 69-79.
- Coutelle ,C. et al, 1995. The challenge of foetal gene therapy, Nature Med 1: pp. 846-866.
- Doubar, AM et al, 1996. Foetal somatic gene therapy, Human Molecul. Reprod. 2: pp. 633-641.
- Wngner,A.M.,Schoeberlein,A.,Surbek,D,2009. Fetal gene therapy: Opportunities and risk, Advanced Drug delivery reviews. 61: pp. 813-821.
- Noble,R., Rodeck C.H., 2008. Ethical considerations of fetal therapy.Advanced Drug delivery reviews: pp.219-231.
- Zaiss AK, Muruve DA, 2008. Immunity to adeno-associated virus vectors in animals and humans: a continued challenge. Gene Ther.15: pp.808-816.
- Yoshizawa J, Fujino M, 2004. Successful in utero gene transfer using a gene gun in midgestational mouse foetuses. J Pediatr Surg. 39: pp 81-4.
- Pitt BR, Schwarz MA, Bland RD, 1997. Methods of retrovirus mediated gene transfer to fetal lung. In : Paul D. Robbins, edotor. Gene therapy protocols. New Jersey: Humana Press.
- Hatzouglou M, Moorman A, Lamers W, 1995.Persistant expression of genes transferred in the foetal rat liver via retroviruses. Somatic Cell and Molec. Biol. 2: pp. 265-278.
- Papaioannou VE,1990. In utero manipulations. In : Copp AJ,Cockroft DL, editors. Postimplantation mammalian embryos. Apractical approach. IRL press: pp. 61-80.
- Brace R, 1995. Progress towards understanding the regulation of amniotic fluid volume : water and fluxes in and through the fetal membranes, Placenta . pp 1-18.
- Badalian, SS, Fox HE,Chao CR, Timor IE , 1994. Foetal breathing characteristics and postnatal outcome in cases of congenital diaphragmatic hernia. Am. J. Obstetr. Gynnecol . 171: pp. 970-975.
- Schachtner S, Buck CA, 1999.Temporally regulated expression patterns following in utero adenovirus-mediated gene transfer. Gene Therapy. 6: 1249-1257.
- Yang E, Cass DL,Sylvester KG, 1999. Foetal gene therapy: efficacy, toxicity and immunologic effects of early gestation recombinant adenovirus. J Pediatr. 34: pp 235-241.
- Themis M et al, 1999. High level expression of beta galactosidase and factor IX transgenes in foetal and neonatal sheep after ultrasound -guided transcutaneous adenovirus vector administration into the umbilical vein. Gene therapy. 6: 1239-1248.
- Nichols 1988. Human Gene therapy. National academy of sciences. pp. 168
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