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1 R&D 동향분석보고서 세포치료의연구동향 손은수

2 < 목차 > Ⅰ. 서론 1 Ⅱ. 기술개발동향 1 1. 기술의개요 1 2. 연구개발동향 3 1) 배아줄기세포 (embryonic stem cell) 동향 3 2) 성체줄기세포 (Adult stem cell) 동향 8 Ⅲ. 기술개발의문제점 윤리적인문제해결과줄기세포의확보 의약품으로서정부의인가 줄기세포연구지원및기술경쟁력확보 15 Ⅳ. 결론및전망 16 < 표차례 > < 표 1> 줄기세포의자원 2 < 표 2> 배아줄기세포의성질및특징 4 < 표 3> 인간배아줄기세포분화배지조건의예 5 < 표 4> 성체줄기세포의분화유연성 9 < 표 5> 공급원에따른줄기세포의특성비교 11 < 표 6> NIH에등록된인간배아줄기세포 13 < 그림차례 > < 그림 1> The embryonic stem cells generated by this procedure could be genetically corrected either by gene insertion or gene replacement strategies. In the scheme, cells from a patient biopsy are obtained and their nuclei transferred into enucleated oocytes. In a second step, embryonic stem cells are

3 generated and expanded stem cells are subjected to genetic correction. Finally, genetically corrected cells are differentiated toward the tissue of interest and then transplanted into the patient60). 7 < 그림 2> Adult stem cell plasticity. Adult stem cell plasticity has been described as the unexpected potential of cells from bone marrow, muscle or brain to give rise to cells of tissues other than the tissue of origin. Examples include bone-marrow-derived cells or even purified hematopoietic stem cells that can give rise to endothelium, skeletal muscle, cardiac muscle or hepatocytes8)

4 Ⅰ. 서론 줄기세포 (stem cell) 는분화가끝나지않은미성숙세포로서적당한조건에서특정조직이나기관으로성장할수있는능력을갖고있는세포다 1). 무한히증식할수있는자가재생산능력과다양한세포로분화되는특성때문에줄기세포는최근장기기능을재생할수있는획기적인세포치료제 (cell therapy) 로인식되고있어장기이식뿐만아니라그동안치료의한계로생각되었던파킨슨씨병 (Parkinson's disease), 알츠하이머병 (Alzheimer's disease) 등퇴행성질환이나심장, 신장에관련된난치병질환에대한효과적인대안으로부상하고있다 2-4). 줄기세포는시험관에서배양하고분화시킬경우환자가필요로하는특정세포로만들어질수있기때문에손상되거나질병이유발된조직의세포에적합한줄기세포를이식함으로써그조직의세포유형으로분화하여조직재생을유도하는질병의근원적인치료방법으로이용될수있다. Ⅱ. 기술개발동향 1. 기술의개요 줄기세포는포유류배아의초기발달단계에서만들어지는배아줄기세포 (embryonic stem cell) 와성인의다양한조직에제한적으로존재하는성체줄기세포 (adult stem cell) 로구분된다 (< 표 1>). 배아줄기세포는수정된지 5~6 일정도되는초기발달단계에있는배아세포에서분리되는데, 이것은배아, 태아, 태반등에서도발견되며신체의모든세포유형으로분화될수있기때문에 ' 전능세포 (totipotent cell; able to give rise to all embryonic and extra-embryonic cell types)' 혹은 ' 만능세포 (pluripotent cell; able to give rise to all cell types of the embryo proper)' 라고도불린다 2). 배아줄기세포는장기치료에대하여가장우수한효과를나타내며난치병을치료할수있는가장확실한방법으로생각되고있지만, 배아줄기세포의이용은배아의파괴라는생명윤리문제를제기하고있어사회적합의등의신중한접근이요구되고있다. 성체줄기세포는제대혈 (umbilical cord blood, 탯줄혈액 ) 이나다자란성인의골수 (bone marrow) 와혈액등에서추출해낸것으로뼈와간, 혈액등구체적장기의세포로분화되기직전의원시세포로서조혈모세 - 1 -

5 포 (hematopoietic stem cell) 와중간엽줄기세포 (mesenchymal stem cell), 신경줄기세포 (neural stem cell) 등이있다 5,6). 성체줄기세포는성인의조직에제한적으로존재하며, 이들은각각의조직의특정부위에미분화된상태로존재해있다가조직의손상이나질병에의해활성화되어조직을재생시킨다. 배아줄기세포와는달리성체줄기세포는그들이유래된조직에있는세포유형으로만분화가가능하다는특징을가진다. 그러나최근에성체줄기세포도많은종류의세포로분화가가능하다는것이밝혀지면서다양한종류의장기치료를위한연구가진행되고있다 7-11). 성체줄기세포는인간배아에서추출한배아줄기세포와는달리골수나뇌세포등이미성장한신체조직에서추출하기때문에윤리논쟁을피할수있고또한환자의몸에서추출할경우면역거부반응문제를해결할수있는장점이있다. 그러나세포증식이어렵고쉽게분화되는성향이강하기때문에임상적으로세포치료에이용할만큼다량의미성숙줄기세포를분리하기어려운문제점을가지고있다. < 표 1> 줄기세포의자원 줄기세포 l 내용 embryonic cell Spare embryos stem cells can come from leftover embryos stored at fertility clinics that were not used by couples to have children. adult cell Special purpose bryos Cloned embryos embryos are created in vitro fertilization (artificially in the lab) for the sole purpose of extracting their stem cells. embryos are cloned in labs using somatic nuclear transfer method in order to harvest their stem cells. Aborted fetuses stem cells are taken from fetuses in early development that have been aborted. Umbilical cords this after-childbirth tissue holds potential for research. Adult tissue or organs Cadavers stem cells are obtained from the tissue or organs of living adults during surgery. isolation and survival of neural progenitor cells from human post-mortem tissues (up to 20 hours after death) has been reported and provides an additional source of human stem cells(14) 이와같이배아줄기세포를치료에사용할경우면역거부반응과윤리문제가생기고, 성체줄기세포를이용할경우증식력이낮다는장벽을극복해야하기때문에줄기세포에대한연구는이러한문제점을동시에해결할수있는방법으로배아복제 (embryo cloning) 에대한관심이고조되었다 12,13). 환자자신의체세포핵을인간난자에이식하는동종간핵이식기술의경우복제 - 2 -

6 된배아로부터얻어진줄기세포가자신의유전물질을거의완벽하게갖고있어환자본인에게이식했을때면역거부반응이거의없는치료용세포를얻을수있는치료법으로서모든과학자들이시도하려는연구분야이며, 치료용배아복제 (therapeutic cloning) 를주장하는것은바로이와같은엄청난의학적, 의료적효용성때문이다. 줄기세포를이용한세포치료기술은초기단계로서아직해결해야할문제점들이많다. 현재배아줄기세포와성체줄기세포는세포치료제로서각각의장단점을가지고연구개발되고있으며, 이에본논문에서는줄기세포의임상적응용및문제점과산업적인전략등을검토하고줄기세포의기술개발전망을살펴본다. 2. 연구개발동향 1) 배아줄기세포 (embryonic stem cell) 동향 1998년이전까지과학자들은줄기세포가배아가성장하는짧은단계에만존재하고, 이를몸에서격리해서살아있게하는데는특별한장치가필요하기때문에, 격리 배양이불가능하다고믿었다. 그렇지만 1998년 Thomson, Shamblott 등은인간배아줄기세포를착상전배아의내세포덩어리 (inner cell mass; ICM) 로부터분리하고배양하는데성공했다 2,4). 수정후 5일이경과한배난포시기에일부의세포가외부에서떨어져세포덩어리를형성하게되고이세포는모든형태로분화한다. 외부의세포들은외배엽 (trophoectoderm) 이되어결국에는태반 (placenta) 으로발달하게된다. 가운데세포덩어리는나중에분화하여성체를만들게되며이세포가배아줄기세포이다 14). Thomson 등은시험관아기시술후남은배양초기신선 ( 수정후 2~3일된배아 ) 혹은냉동잔여배아를환자의동의를받고사용하여배아줄기세포를제작하였으며, 그배아줄기세포를면역력이결핍된생쥐에주입함으로써외배엽 ( 신경과부세포 ), 중배엽 ( 근육조직, 연골조직, 뼈 ) 및내배엽 ( 내장상피세포 ) 으로의분화능력을간접적인분화유도방법을통해확인하였다. 또한 Shamblott 등은 5~9주령의유산된태아의원시생식세포에서분화되지않은원시생식세포를배양함으로써줄기세포를얻는데성공하였다. 이후 2000년 Reubinoff 등은수정후 6일된배반포기배에서얻어진배아줄기세포가생체내및생체외에서원하는특정조직세포로의분화가가능함을발표하였다. 이와같이생체내배양으로는면역력이결핍된생쥐에서외배엽, 중배엽및 - 3 -

7 내배엽으로의분화능력을간접적으로확인하였고, 생체외배양으로는신경세포로의분화능력을직접적인분화유도배양방법을통해확인하였다 3,15). 이와같은인간배아줄기세포의배양및분리기술의성과는초기인간배아연구뿐만아니라다양한세포배양을통한신규성장인자및의약품개발, 세포대체요법 (cell replacement therapy) 을통한파킨슨씨병, 알츠하이머형치매, 척추손상에의한사지마비, 중풍, 소아당뇨병, 심근경색, 간경화등의난치병치료에획기적으로사용될수있는 21세기가장핵심적인생명공학기술중의하나로주목을받게되었다. 재생의학에서배아줄기세포가중요한이유는배아줄기세포가분화를유도하는인자에따라다양한세포로분화가가능하기때문이다 (< 표 2>). 배아줄기세포는한번분리되면영구적인보관이가능할뿐아니라체외에서 2년이상염색체이상없이배양할수있기때문에오랜배양증식후에도그증식및분화잠재력이변형되지않으므로이세포를세포대체요법에사용할경우세포공급에대한문제도해결이가능하다 16,17). < 표 2> 배아줄기세포의성질및특징 배아줄기세포는외배엽 (ectoderm), 중배엽 (mesoderm), 내배엽 (endoderm) 의세개의배엽으로발달하며, 외배엽은신경이나피부로, 중배엽은근육뼈나생식세포로, 그리고내배엽은소화관이나체내부장기로분화할수있는성질을가지고있다. 일반세포는일정한횟수를분열하면그이상은분열하지않게되는데비해배아줄기세포는계속해서분열할수있는성질을유지하고있다. 배아줄기세포는분열하면서도염색체수에이상이없이일반체세포와동수인상태를유지하고있다. 암세포나다른불사화한세포는분열을하면서염색체의수가통상의수에서증감하는것이보통이다. 배아줄기세포특유의분자생물학적인특징을갖고있어어느특정의효소의활성이높거나낮은경우를공통으로볼수있다 ; 배아줄기세포는암세포와비슷하게염색체끝부분에붙어있는반복된 DNA 의이중나선이다른체세포보다긴것이특징이다. 이들세포에는텔로메라아제 (telemerase) 효소의활성이높아세포가여러차례분열하더라도텔로미어 (telomere) 의길이가유지되는것으로알려져있다 18,19). 배아줄기세포는모두장기간배양이가능하며 pluripotent 한세포의 marker 가발현된다. 배아줄기세포는반복증식이가능하다 ; 배아줄기세포가배아생식세포 (embryonic germ cell) 보다더광범위한분화능력을갖고있는데, 배아줄기세포는 번의반복증식이가능하고배아생식세포는 회정도의분화능력이보고된다. *1981 년에생쥐의배반포의 ICM 세포에서모든조직으로분화할수있는세포가최초로분리되었는데이를배아줄기 (embryonic stem, ES) 세포라하고, 배란후 5-10 주사이에태아가자라면서고환이나난소의생식기관으로발달할세포를배아생식 (embryonic germ, EG) 세포라하였다. 실제로 ES 세포와 EG 세포는특성이다르지만복제분화를통해조직이나기관으로발달할수있다는점에서배아줄기세포에포함시킨다. 인간배아줄기세포의연구분야는다음과같이특징지을수있다. 첫째는인간배아줄기세포가갖는고유한특성을규명하는것이다. 초기배아줄기세포연구자들은대부분의정보를생쥐의배아줄기세포로부터얻었으나 20,21), 실 - 4 -

8 제로인간배아줄기세포와는많은차이가있었다. 예를들면인간과생쥐의배아발달단계의유전자발현이서로다르게나타났는데 22), 장배형성시기에태반및 germ layer 배열을포함하는배아외층형성과 egg cylinder 대신에 embryonic disc를형성하는등인간배아줄기세포는생쥐와다르게나타났다 23-26). 또한세포표면 marker도인간과배아줄기세포에서다르게발현되는데, 인간배아줄기세포에서는단계별특이항원인 SSEA-3, SSEA-4, 당단백 TRA-1-60, TRA-1-81, GCTM-2가발현되고생쥐배아줄기세포에서는발견되지않았으며 2,3), 반면에생쥐의배아줄기세포에서는 SSEA-1이발현되었으나인간세포에서는발견되지않았다 2,27). 또한 LIF(leukaemia inhibitory factor), IL-6 (interleukin) 등사이토카인에대해반응하는것도다르게나타났다 28-30). 둘째는배아줄기세포를이용한다양한분화유도법의개발로서초기인간배아줄기세포가갖는분화능을증명하고생체내이식시기형종 (teratoma) 이형성되지않는세포치료제로이용할수있도록다양한세포분화기술을개발하는것이다. 최근몇년동안다양한성장인자첨가에따라인간배아줄기세포가특정세포로변환하는과정을규명하는논문들이발표되었고 31), 인슐린을생산하는세포의분화 32), 기능성심근세포로의분화 33), 혈액세포의생성 34) 및신경세포를질환동물에이식 35,36) 등의결과가증명되었다 (< 표 3>). < 표 3> 인간배아줄기세포분화배지조건의예 세포형태 성장인자 문헌 Insulin-producing None (32) Cardiomyocytes None (37) Cardiomyocytes None (38) Cardiomyocytes 5-aza-dC (39, 40) Neural precursors 주 ) (36) Neural precursors EGF, bfgf (35) Hematopoietic None (34) Endothelial None (41) Trophoblast BMP4 (39, 40) 주 ) FGF-2, insulin, transferrin, progesterone, putrescine, sodium selenite, heparin. 더최근에는 Austin-Smith와 Yamanaka에의해배아줄기세포를어떤특정세포로분화시키는분화조절마스터유전자 'Nanog' 가발견되었다 42,43). 배아줄기세포가특정세포로분화되지않고무한하게자기분열을반복하도록만드는핵심인자로평가되는마스터유전자는줄기세포를어떤장기로발전시킬것인지를총괄하여조정하는분자조절유전자로서일종의사령탑역할을 - 5 -

9 하는데줄기세포로부터원하는특정세포를자유자재로얻을수있는수단을획득했다는점에서의미가크다. 지금까지는줄기세포로부터예측불허의다양한세포가얻어졌기때문에절반의성공에불과하다는평가를받아왔으나, 마스터유전자의발견으로줄기세포에서의사와환자에게필요한세포만골라서배양할수있게됨으로써배아줄기세포의분화조절연구에큰영향을줄것으로기대된다. 셋째는분화유도된세포의생체내이식시기능회복가능성과이식을위한기반기술개발로서다양한동물모델에대한광범위한이식연구이다. 신경이상동물모델에대한이식 44), 당뇨병동물모델에대한이식 45), 심근경색동물에대한이식 46-48) 등다양한동물모델에대한이식방법이최근에보고되었다. 임상적으로인간배아줄기세포가세포치료제로서활용되기위해서는이식시거부반응이없어야하므로이식거부반응을유발하는유전자를 knock-out시켜 universal stem cell로제작하려는연구도진행중이다 49). 배아줄기세포를배양하는방법에는신선배아또는폐기처분될냉동잔여배아를이용하는법, 인간의체세포핵을핵이없는인간난자에이식하는동종 ( 同種 ) 간핵이식수술법또는동물난자에이식하는이종 ( 異種 ) 간핵이식기술법등네가지방법이있다. 윤리적인측면에서신선혹은냉동잔여배아로부터얻어진줄기세포를이용하는연구가좀더자유롭지만환자에이식시면역거부반응이생길수있다. 배아세포는 2주가지나면스스로줄기세포로급변하면서다양한신체장기로분화해가는데, 배아줄기세포가장기이식에비해거부반응이덜일어난다고는하지만, 이것이배아줄기세포에서얻은장기이식에도적용될지는아직미지수이다. 따라서배아줄기세포를이용한세포치료법에서이식거부반응을극복하려는연구가활발하게진행중이다 50-53). 거부반응은혈액세포에일어나는데혈액세포와이식조직세포가동일배아줄기세포에서유래할경우발생하지않기때문에배아줄기세포에서유래한혈액줄기세포를먼저이식한후동일배아줄기세포에서유래한조직세포를이식하면거부반응을피할수있다 54,55). 또한줄기세포의유전자조작을통해거부반응을없애려는실험도진행중이다 56-58). 환자의체세포핵을핵이제거된난자에이식하는동종간핵이식수술에의해얻는배아줄기세포의경우, 환자에서유래된조직이나장기의체세포를이용하면복제된배아로부터얻어진줄기세포가자신의유전물질을거의완벽하게갖고있기때문에환자본인에게이식했을때이론상거부반응이일어나지않을것으로추정된다 59) (< 그림 1>). 그러나환자의질환이유전자이 - 6 -

10 상에의해발생한것이라면그비정상유전자를함유하고있는핵을체세포핵이식에사용하는것은바람직하지않으며, 이식된핵과세포질미토콘드리아내유전물질과의상호작용에대한가능성을갖고있다. < 그림 1> The embryonic stem cells generated by this procedure could be genetically corrected either by gene insertion or gene replacement strategies. In the scheme, cells from a patient biopsy are obtained and their nuclei transferred into enucleated oocytes. In a second step, embryonic stem cells are generated and expanded stem cells are subjected to genetic correction. Finally, genetically corrected cells are differentiated toward the tissue of interest and then transplanted into the patient 60). 배아줄기세포를이용한세포치료는이식거부반응외에도종양형성, 감염, 윤리문제등이해결해야할과제로남아있다. 배아줄기세포는기본적으로무한증식이가능한세포로이는종양세포의특징이기도하다. 생쥐에인간배아줄기세포를주사할경우기형종이형성될수있다는보고가있는데 61,62), 이는배아줄기세포가종양세포로전환될수있다는우려를뒷받침한다. 또한, 인간배아줄기세포를배양할때생쥐의배상태섬유아세포 (embryonic fibroblast cell) 가필요한데, 이경우정상적으로인간에게존재하지않는바이러스나다른감염원이배아줄기세포를통해이식받는사람을감염시킬수있다. 줄기세포의재료인배아는생명체가될수있는윤리적한계를갖고 - 7 -

11 있어그자체만으로도사회적으로수급 제작에많은어려움을갖고있다. 현재시도되고있는거의모든배아줄기세포도불임치료용으로쓰다남은잉여수정란을분화시켜만든것이다. 인간배아줄기세포에대한연구는전세계적으로도초기단계에머물러있다. 배아줄기세포가환자에적용되기위해서는배아에서추출된줄기세포를분화시켜선택분리하고, 거부반응을없앤뒤환자에이식해손상부위가살아나는지까지확인해야하는여러단계의실험이필요하기때문이다. 국내의현재기술은배아에서줄기세포를추출하는단계를넘은상태이며, 세포배양의어려움, 유전자도입기술의확보, 세포주의분배등의문제및생체내이식시종양형성등의문제로더많은연구가필요하다. 이러한문제점들이있음에도불구하고인간배아줄기세포는향후난치병을치료할수있는해결책으로예상되며이와같은무한한잠재력으로인해다양한연구가빠르게시도되고있다. 2) 성체줄기세포 (Adult stem cell) 동향 성체줄기세포는우리신체를구성하는장기조직에극소수로존재하면서장기조직의정상적기능을수행하고유지해주는근간세포이다. 배아줄기세포연구가이제시작단계인데비해성체줄기세포연구는 40년정도되는긴역사를갖고있다. 악성빈혈이나백혈병과같은혈액질환이나면역질환의치료를위해골수세포나태아조혈모세포를이용한세포치료기술은이미보편화되어치료방법으로적용되고있다. 최근에성체줄기세포도다양한분화능력이입증되었는데, 1998년 Ferrari는뼈속줄기세포가근육세포로변환될수있다는연구결과를 Science지에발표했고 63), 2000년 Lagasse는뼈속줄기세포가간장세포로분화한다는사실을 Nature Medicine지에발표했다 64). 단순히골수이식에만활용되던뼈속줄기세포가배아줄기세포처럼다양한분화능력을갖고있다는사실이입증되기시작하면서, 성체줄기세포는단순히그장기조직으로분화하는것뿐만아니라다른장기조직으로분화할수있다는성체줄기세포의분화유연성 (plasticity) 이밝혀졌다 (< 그림 2>, < 표 4>). 이에성체줄기세포는이식된후각장기의특성에맞게분화할수있는특성때문에치료의학에서장기재생에이용될수있는세포치료제로서, 그리고배아줄기세포의윤리적문제를해결할수있는대안으로떠오르게되었다

12 < 그림 2> Adult stem cell plasticity. Adult stem cell plasticity has been described as the unexpected potential of cells from bone marrow, muscle or brain to give rise to cells of tissues other than the tissue of origin. Examples include bone-marrow-derived cells or even purified hematopoietic stem cells that can give rise to endothelium, skeletal muscle, cardiac muscle or hepatocytes 8). < 표 4> 성체줄기세포의분화유연성 기원조직새로형성된조직문헌 Bone marrow Brain(65, 66), Kidney, Skeletal muscle (63, 67) Mesenchymal/Stromal Brain, Bone, Fat, Heart(69, 70) Hematopoietic stemcell (sorted) MAPC (multipotent adult progenitor cells) Liver, Lung, Skin(74), Gastero-intestinal tract Brain(76-78), Retina(68), Lung, Heart, Skeletal muscle, Liver(79), Intestine, Kidney, Marrow, Blood, Skin (68) (71-73, 59-60) (64, 74, 75) Brain Heart, Skeletal muscle Kidney, Stomach, Instestine, Liver, Blood (81-83) Skeletal muscle Heart (84-86) Liver Bile duct (87) Skin Bone, Skeletal muscle (88) Pancreas Ft, Brain, Muscle, Liver (89) (80) 성체줄기세포는배아줄기세포와같이인체의모든종류세포로분화되지는않지만추출기원에따라다양한종류의조직세포로분화될수있다. 성체줄기세포는골수이외의장기즉, 유방, 간장, 피부, 위장관, 정소, 눈, 췌장등자체재생능력이있는장기조직에전부존재하기때문에이런조직이나 - 9 -

13 장기가상처를입었을때정상적으로재생될수있기때문이다. 현재까지가장많이연구된성체줄기세포는뼈속의골수이며혈액및림프구를생산할수있는조혈모세포를비롯하여중간엽줄기세포등여러종류의줄기세포를가지고있다 76,90,91). 조혈모세포는원래여러가지혈액세포로분화되는능력이있으나체외에서골격근, 심근상피, 간세포로도분화될수있다. 그외신경줄기세포 (neuronal stem cell) 간엽줄기세포도혈액, 골격근, 심근, 신경, 간, 혈관등으로분화되는능력을나타낸다 71-73,59-60,92,93). 이에성체줄기세포는조직이식거부반응이없는장기생산에이용할수있는데, 예를들면당뇨병환자를위하여췌장줄기세포를환자의췌장내에주입함으로써인슐린의존성당뇨병을치료한다든지, 연골세포나근육에문제가있는환자에게줄기세포를주입해치료해줄수있다. 피부화상인경우피부의줄기세포를떼어내시험관내에서증식한후화상부위에발라주어화상치료에도활용할수있다. 최근에는분화에대한연구가많이진행되어더이상재생이불가능하다고여겨진성인의뇌에서도줄기세포군이있다는사실이확인되었다 94,95). 줄기세포를얻을수있는또하나의방법은버려지는제대혈로부터추출하는것이다. 제대혈은태반과탯줄안에있는혈액으로서산모의출산시쉽게얻을수있어채취가용이하고산모와신생아에게영향을주지않으며, 조혈모세포를다량함유하고있으며줄기세포의좋은공급원이되고있다. 그밖에도제대혈은뼈, 연골, 골수간질세포, 지방세포, 건, 신경세포등으로분화할수있는간엽줄기세포를포함하고있어이를이용한조직재생용세포치료제의개발가능성이높아지고있다 96-98). 제대혈줄기세포를이용한세포치료방법은윤리적인문제를피하는동시에기술적으로원하는양만큼의줄기세포를얻을수있는장점이있어매우유리하다 (< 표 5>)

14 < 표 5> 공급원에따른줄기세포의특성비교 줄기세포의특성 줄기세포의공급원배아제대혈성체 분화능력 가장우수함 우수함 우수함 기형종발생가능성 있다 없다 없다 획득의용이성 어렵다 쉽다 어렵다 생명윤리문제 있다 없다 없다 거부반응해결방법 어렵다 가능하다 어렵다 그러나분만시제대혈을보관하는비용이비싸고보관기간도짧아쉽게이용되지않는문제점이있다. 제대혈을이용한중간엽줄기세포는중간엽줄기세포의효과적인분리, 세포특성을유지한상태의대량증식, 배양및증식에소요되는시간의단축, 증식비용의절감및효율적관리등의문제가해결된다면세계적으로매우경쟁력있는세포치료제가될수있다. 성체줄기세포를이용한세포치료기술의핵심은성체조직이나장기에서정확히줄기세포만을분리할수있는기술과이를이용한체외증폭기술개발에있다. 성체줄기세포를실제로임상에적용하려면많은수의줄기세포가필요하지만성체줄기세포는생체내에존재하는줄기세포의양이매우적어성체조직에서줄기세포를획득하기가어려우며, 이를분리할수있는정확한 marker가개발되지못하여순수한줄기세포의분리도쉽지않다. 체외배양을통한골수이식치료에있어서도이식에필요한양의혈액줄기세포를확보하기가용이하지않은데, 10,000개의골수세포중 1개의혈액줄기세포를분리하는것이어렵기때문에골수이식시줄기세포뿐만아니라다른골수세포도같이이식되는경우가많아심각한부작용을야기할수있다. 또한배아줄기세포에비해배양이어렵고성체줄기세포를체외배양으로증폭할수있는기술적시스템이완성되지않았다. 성체줄기세포를이용한기술의또하나의핵심분야는분화의유연성을파악하고활용하는데있다. 성체줄기세포는자신과똑같은세포를만드는자체재생능력과모든계통으로분화할수있는유연성을가진세포다. 따라서어떤조직에서성체줄기세포를분리하려면세포를분리해시험관내에서자체재생능력이있는지, 그리고다른세포로분화할능력이있는지를증명하여야한다. 그러나시험관내에서이런세포의성질을밝히는것은쉽지않다. 또한, 성체줄기세포가갖는분화의유연성이곧생체내의이식가능한충분한양의세포로분화될수있는지의기술도아직완성되지않았다. 성체줄기세포연구에서미국은독보적인자리를차지하고있다. 대표적으

15 로미국의벤처기업 Osiris 社는성체줄기세포를이용한손상된뼈와심장근육을재생시키는실험을임상단계에올려놓았다 99,100). 국내에서도관절연골손상치료에대한임상실험을하고있으며, 특정질환에대해서성체줄기세포를이식하고신체손상부위를회복시킨사례도있다. 이와같은연구성과에도불구하고성체줄기세포기술이성공하기까지는앞에서기술한바와같이골수등체내에서성체줄기세포를채취하는기술, 채취한성체줄기세포를체외에서증식시키는기술, 증식된성체줄기세포를원하는세포로분화시키는기술및분화시킨성체줄기세포를체내이식시키는기술등해결해야할문제가많이남아있어현재로서는아직갈길이멀다. 이에실제로성체줄기세포기술이나배아줄기세포기술들이척추손상마비, 당뇨병, 심장병난치병등환자에게적용하려면최소한 10년은소요될것으로전망하고있다. Ⅲ. 기술개발의문제점 1. 윤리적인문제해결과줄기세포의확보 줄기세포의연구에서앞으로해결해야할많은문제점들중에서가장기본적인문제는적절한줄기세포의확보이다. 현재가장많이이용되는것이배아줄기세포이지만이것은원천적인생명윤리문제를야기시키며, 특히체세포복제기술을통한난치병치료차원의치료용배아복제기술은인간복제와직결되기때문에종교계와많은시민단체가강력히반대하고있다. 특히, 미국에서는 1997년복제양돌리의탄생을계기로인간복제에대한윤리성이거론되었으며인간배아실험은허용하되자궁에이식하는것은금지해왔다. 미국하원은아기를얻기위한출산용배아복제는물론연구목적의배아복제도모두금지하는법안을통과시켰으며이법안은상원에서통과를늦추고있다. 이와같은많은반대는인간복제라고하는악영향만을우려한나머지생명과학의기술개발의위축을가져오게될수도있다. 이에 2001년미국대통령부시는특정한경우에한하여사람의배아줄기세포연구를지원하게함으로써미국국립보건원 (NIH) 산하에위원회를구성하였고 2001년 8월이전에확립된전세계배아줄기세포의등록을받아 NIH Stem Cell Registry를설립하여총 78종류의배아줄기세포가확립되었음을발표하였다 (< 표 6>). 미국의지원금허용범위는배아줄기세포연구에사용할사람의배를얻는공급원은불임치료를위해채취하여쓰고남은것으로국한하고, 2001년발표

16 하기전에불임치료이외의채취한배는사용하되이후부터는배아세포를만들기위하여배를파괴하지못하도록하였다. 그리고배를제공하는경우는반드시충분한설명과이해를확인하는동의 (informed consent) 를통해서만이뤄지며배를제공하는데대한대가는없어야한다는점등이었다. 현재등록된세포주에대해미국 NIH에서는연구비를제공하고있고, 일부세포주에대해서는연구진에게분양이진행되고있다. < 표 6> NIH 에등록된인간배아줄기세포 회사명 보유국가 배아줄기세포주수 * 현재이용가능한배아줄기세포주수 ** BresaGen, Inc. USA 4 1 CyThera, Inc. USA 9 0 ES Cell International, Melbourne Australia 6 4 Geron Co. USA 7 0 Goteborg University, Goteborg, Sweden 19 3 Karolinska Institute Sweden 6 0 Maria Biotech Co Korea 3 3 MizMedi Hospital Korea 1 1 NationalCentre for Biological Sciences India 3 0 Pochon CHA University Korea 2 0 Reliance Life Sciences India 7 0 Technion University Israel 4 3 University of California, San Francisco USA 2 0 Wisconsin Alumni Research Foundation USA 5 1 * 2001 년 8 월 9 일부시미국대통령이줄기세포연구자금지원방침을발표한이후 NIH 는 i) 2001 년 8 월 9 일오후 9 시이전에생식목적으로더이상이용될수없는배반포배아에서내부세포덩어리가제거된것 ii) 배아기증동의를받은것 iii) 배아제공에따른금전적관계가없는등의조건을충족하는배아줄기세포주에한해서등록함. ** 미국 Science 가보도한 2002 년 8 월현재이용가능한배아줄기세포주수 < 표 6> 에나타낸바와같이우리나라에서도 3개기관에서배아줄기세포주를등록하고있으며, 시험관아기시술후폐기될냉동배아의이용이환자의동의하에허용되고있어현재약 15종류의배아줄기세포주가확립되어있다. 이에국내에서는 30여개연구기관에분양되어연구하고있어줄기세포에대한국내기술수준은세계적이며매우높다. 최근보건복지부가마련한생명윤리법에서는질병치료를위한연구목적으로체세포배아복제가일부허용될것으로전망되지만반대목소리가높아국회통과는확실치않다. 또한, 인공수정후폐기될냉동배아의이용은부분적으로허용되고있지만면역거부반응때문에크게실효성이없다. 절대다수가우려하는인간배아복제에관한연구는엄격한정부차원의법령하에서규제하고, 체세포복제기술을통한난치병치료차원의치료용배

17 아복제등의연구문제도심도있게다루어져야할것이다. 특히수정후 2 주이내의배아에대해서는의학발전을위한기초적연구와난치병환자를치료하려는목적의연구를위해서국가차원의법적, 제도적장치가마련되어허용되어야한다는목소리가높다. 이에생명공학분야의분명한가이드라인이설정되고불임센터에서이식하고남은냉동잔여배아를이용한배아줄기세포의연구가장기기증용복제인간같은생명복제와는근본적으로다른세포치료제차원의연구로이루어져야할것이다. 2. 의약품으로서정부의인가 현재새로운치료법으로부상하고있는세포치료제에대해의약품이아닌의료행위로규정해야한다는주장이제기되면서논란이일고있다. 세포를추출한뒤환자에게주입해질병을치료하는세포치료제에대해정부는의약품이라고규정하고있지만일부전문가들은시술이라하여논란이되었다. 이러한논란은세포치료제가의약품으로서안전성에대해허가를받아야하는문제와민감하게연결되어있다. 2004년 3월 KFDA( 식품의약품안전청 ) 에따르면사전승인없이임상시험을실시한벤처기업 4개가형사고발되었다. 전임상결과도없었고세포치료제제조과정의품질향상성을보증할수있는제조과정의문서화또는표준화가없이환자에게투여되었다. 따라서줄기세포를이용한세포치료는과학적안전성, 유효성및품질관리, 제조시설체계가없어위험성을갖고있다. 국내는외국의임상적용기술이조기에도입되어골수및제대혈이식등과같은세포치료의임상적용이시행된지오래되었으며최근에벤처기업을중심으로태아제대혈보관이활성화되면서조혈모세포및간엽줄기세포를이용한임상결과가산발적으로보고되었다. 자가골수를이용한퇴행성관절염치료및제대혈세포를이용한간경화치료, 뇌경색치료가그예이다. 그러나이런임상시험의시도는충분한안전성을검사하지않고시행한것으로서향후줄기세포를이용한이식치료의안전성확보에대한많은논란이예상된다. 이에 KFDA는세포치료에대한 `의약품임상시험계획승인지침`을개정하여 2004년부터시행할계획으로 6월에입안예고했다. KFDA는승인요건을완화하더라도환자사망시연구자와병원이상당한책임을져야하고환자에게진료비를청구하지못하게명문화했기때문에돈벌이수단으로악용될가능성이적고, 안전성 유효성이어느정도알려진세포치료제가실제로유용한지 `긴박하게생명을위협하는응급상황`에한정시켰던응급임상

18 적용범위를 `치료시기를놓치면치료효과를기대하기어렵거나대체치료수단이없는상태`까지완화함으로써말기암환자등이상업적임상단계의세포치료제로치료받을수있는기회를갖게하도록한것이라고발표하였다. 이러한정부지침은시판허가전이라도선택여지가없는환자에게치료기회를확대시키고세포치료제에대한기초연구의활성화를꾀하여생명공학발전을촉진할것으로기대하고있다. 3. 줄기세포연구지원및기술경쟁력확보 줄기세포를제작하고분화시켜세포치료법에사용하는사업은 1998년이후그가능성이제시되어전세계의많은연구자들이같은실험결과를목표로매진하고있으나아직까지는세포치료단계에서뚜렷한결과가없다. 특히, 배아줄기세포는만능세포로의이용가능성때문에전세계적으로의료및생명공학벤처회사에서집중적인투자를하고있다. 미국 일본등선진국을중심으로연구가활발하게진행되고있는데국가차원에서윤리적문제를극복하고기술개발을이루려는노력이뚜렷하게나타나고있다. 최근영국에서는배아연구뿐만아니라배아복제에대한연구도의학적 의료적효용성때문에윤리적문제를최소화하면서정부차원에서허용되고있고, 2001년미국정부도어쩔수없이폐기될잔여배아를사용하는배아줄기세포연구에대해서연방정부차원의연구비를적극적으로지원하기로하였다. 늦게나마우리나라에서도줄기세포연구가보건복지부 ( 바이오보건기술개발사업 ) 와과학기술부 (21세기프런티어사업중하나로세포응용연구사업단선정 ) 등에서줄기세포의연구를향후연구하고투자해야할국가기간산업항목으로간주하고있으며, 정부차원에서조혈모세포나줄기세포를이용해손상된심장근육 관절을재생하거나암을치료하는기술개발에대해바이오벤처기업들에게임상시험비용등을지원하고상용화에주력하고있다. 선진국과비교해볼때우리나라는전반적으로생명공학분야가경험이나규모면에서취약하지만기술적수준이높아배아줄기세포제작기술의경우도선진국과크게차이나지않고있다. 오히려폐기될냉동잔여배반포기배아의이용에대하여효율적인줄기세포주생산이라는한발앞선세계적기술로평가받고있다

19 Ⅳ. 결론및전망 세계적으로차세대바이오산업에대한관심과열기가높아지면서국내에서도배아줄기세포를이용하여당뇨병, 심장병등의난치병을치료하는산학연합동연구가활발히진행되고있다. 배아줄기세포를이용한세포치료제는비교적소수의인원과적은자본을통해연구개발이가능하기때문에자본이취약한국내신약개발환경에적합한기술분야로서평가되고있으며, 인간배아줄기세포배양에세계최초로성공하면서더욱큰기대를모으고있다. 국내에서는학계가먼저그성과를인정받았고, 이를구체적으로실용화시켜야할제약, 바이오기업들또한계속적인투자를통해가시적인성과로발전시키고자노력하고있다. 인간배아줄기세포배양에성공한서울대의황우석, 문신용교수연구팀에서도동아제약, 제일약품, 삼진제약등의국내중견제약기업들과협동연구또는독자연구를통해활발한연구를진행시키고있으며다수의바이오벤처기업들또한세포치료제의응용가능성을다각도로모색하고있다. 학계의연구방향이주로줄기세포주를확립하는방향으로세포치료제개발의기초를닦고있는반면제약, 바이오기업들은그와연계해세포치료법의구체화, 즉심장병, 당뇨병, 관절염등의난치성질환치료에대한응용연구에주로초점이맞추어져있다. 향후국내기술은줄기세포분화연구가지속적으로이루어져다양한조직으로의분화기술경쟁력이확보된다면세포대체요법에의한난치병치료시장에서선진국과대등한위치에오를것으로예상하고있다. 현재국내마리아의학연구소에서심근세포, 신경세포및근육세포로의분화연구에일부성공적인결과를얻고있고, 특정유전자가도입된인간배아줄기세포를파킨슨씨병모델에이식하여행동개선을보고하는등의연구결과가이러한국내기술개발의전망을더욱밝게하고있다

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