讨 论
采用上述方案,我们从供体气管基质中成功去除了HLA抗原,随后将受体的上皮细胞和软骨细胞源性间充质干细胞种植于内。该移植物经过适度处理后被移植到一例患有左主支气管软化患者的气管部位,构成一段新的气道,使患者的生活质量得以改善。
与实质性器官的移植发生在无菌的间叶细胞环境中不同,气管移植发生在管腔内外表面间的环境中。可以肯定的是,气管黏膜的免疫活性细胞在气管移植中具有非常重要的作用[14],可导致急性同种异体移植物排异反应,从而需要高剂量的术后免疫抑制剂治疗[15]。与其他器官移植不同,气管移植不属于挽救生命的唯一治疗方法[1],所以一个保留气管功能和机械特性的完全无免疫原性的气管移植物是气管移植成功的最低要求。
胞外基质在调节多种细胞生物活性方面发挥了积极作用,而这也正是保持组织正常功能所必需的[16]。因此,近来的生物工程研究重点是应用细胞外基质衍生材料作为具备生物活性的支持物。研究表明,来自组织去细胞化后获得的构架可提供若干种细胞的体外黏附、生长并发挥细胞功能[8,17–18],还已成功运用于动物和人体实验[19]及作为组织器官生长和重塑的范本[20–23]。
生物工程器官的一个潜在主要的问题是能否保证功能性的血供。在本项研究中,激光多普勒检测显示,术后第4天可见移植气管邻近部位正常的微血管床,术后第30天出现移植段气管黏膜出血。虽未将血管生长因子列入本研究,但我们认为血管生长因子(碱性成纤维细胞生长因子、转化生长因子β[8])在去细胞化的气管基质中依然表达,并假定类似的表达将有助于及时的血运重建。为支持这一观点,将经过酶洗涤处理后猪的气管植入到Balb/c小鼠背部皮肤中,2周后发现移植气管局部有新血管形成[9]。
25次循环酶洗涤方法可完全去除细胞膜、所有的MHCⅠ类分子和几乎所有的MHCⅡ类分子,但仍有其他一些细胞成分残留于软骨区。基于组织工程实验[24–25]的结果,作者推测,这些残存的细胞成分可同时对移植物和宿主细胞提供有益的信号,并可能降低炎症反应;相反,残存的细胞成分可能表达微量抗原,从而诱导慢性排异反应。然而,微量抗原在临床移植中仅起到极为有限的作用,本例患者术后2个月时并无炎症征象或抗供体的抗体出现。
尽管既往研究[26]已描述了鼻黏膜上皮细胞如何培养才能运用于组织工程,但在本研究中,这些细胞生长过快以至于细胞凋亡的发生也先于支气管细胞,如果减少酶洗涤时间,鼻腔上皮细胞可能会成为将来气道组织工程的首选[26]。虽然1个月时气管移植物被活性黏膜完全覆盖,仍不能肯定这些细胞是来源于种子细胞还是来源于毗邻的健康气管细胞。虽然动物实验研究[27]提供了间接证据,即植入的种子细胞有可能通过一个重要途径发挥作用,但在使用现有的实验方法进行全面临床试验之前有必要更深入了解这些种子细胞的作用。
体外试验中,24 h后上皮细胞与软骨细胞已经深植在移植物基质中,这一结果提示移植物基质具有高度容受性,可以作为以上细胞理想的生长环境。事实上,移植物在生物反应器中作用24 h后,培养介质中已不能检测到任何细胞(存活或死亡的),提示将近100%的细胞已经黏附于移植物基质上。移植后第4天,移植物表面清晰可见的活性上皮细胞和软骨细胞证实了这一结果,显示细胞在体内持续发挥功能。尽管两种细胞的生物反应器舱室结构明显隔离,但从气管内外表面收集的细胞学标本经分析后均可发现这两种类型的细胞。一种解释是细胞能够在短时间内自由迁移并通过移植物管壁,如果这种解释成立,将会对将来的组织工程设计产生影响。Zani[27]通过动物实验证明,对功能性愈合而言,不同细胞之间没有必要形成一个有序的构架。我们的研究结果将这一观察延伸到了人类。
为尽量减少患者和移植物的损伤,对手术前和术后第4天细胞学分析的次数进行了限制,对何时行支气管镜检查的临床适应证也作了限定。猪的异位移植实验[9]表明,一些去细胞化的移植物在没有自体细胞再种植情况下获得成功,我们无法将这些自体细胞的作用加以量化,但也不排除这种可能性,即实际上分辨自体细胞的这些作用是没有必要的。然而,本研究结果与动物模型结果完全一致,表明自体细胞在其中似乎发挥了重要作用[27]。
功能性的生物工程气道的建立,主要的挑战在于有统一、高效的种子细胞种植于三维管状移植物基质的内外表面、不同类型细胞的共同培养以及细胞群如何以最佳的方式在培养介质和生长的组织之间转输。为解决这些难题,我们开发出了一种适用于体外构建较长气道移植物的新型生物反应器。早期认为这两种类型的细胞需要不同的培养条件,因此为临床前期试验设计的生物反应器原型机提供了两个单独的无菌舱室,每个无菌舱室设有旋转的空气–培养介质界面,每个舱室内都要保持细胞活性状态直至移植之时。生物反应器中的这种动态培养环境、良好的可控性和重现性,是细胞营养供应和废物清除以维持庞大的三维构架所必需的。生物反应器的旋转提供了必要的流体切应力,以促进细胞新陈代谢活动和适度的种子细胞分化。
尽管与临床前研究相比,在本临床移植中采用的酶洗涤次数更多,而且猪与人气管结构具有明显差异,但术前与术后自体气管在组织处理和弹性方面的变化与临床前研究的结果非常相似,而且在生物力学性能方面与临床前研究相当[9]。尤其值得一提的是,气管移植物具有的弹性可以使其调整管腔大小以适应受体。
在本项研究中,我们对患者进行了为期4个月的随访,在完成全面临床试验之前,超过6个月的随访是必要的。需要特别提出的是,我们希望评价气管移植物的远期生物力学性能,以及软骨种子细胞能否继续形成新的软骨组织(或骨组织)。然而,气管移植物的早期功能和患者的一般状况良好,尤其移植部位出现新的血供,因此应该不可能出现大的并发症或气管远期再狭窄。在临床移植中,2个月内不出现并发症时,抗供体的抗体就很少出现[28],因此预期不可能出现任何排异反应征象。
本文中,我们描述了一个创新的方法在人体内运用组织工程手段行大气道置换,从而大大改善了患者的生活质量。结果表明,含有受体细胞的组织工程气管可以产生具有机械性能和正常功能的气道,并且无排异反应。该例患者提供了新的证据,即将来通过自体细胞结合适当的生物材料可成功治疗某些严重临床的疾病。
Lancet 2008;372:2023–30
(哈肖别克·卡斯木 译)
Acknowledgments:
This work was supported by the Ministerio de Sanidad y Consumo, Instituto de Salud Carlos III, Fondo de Investigación Sanitaria (PI050987), Spain, and the Charles Courtenay-Cowlin Fund, University of Bristol, UK. APH is funded in part by an endowed chair from the UK Arthritis Research Campaign. SCD is funded by a Research Fellowship from the James Tudor Foundation. We thank Laura Morte for her excellent organisation and trouble-shooting; Victor Peinado, and others in his team, for their superb assistance, to whom we are indebted; John Armitage of the Human Tissue Working Group and the Research Enterprise Development team, including Christine Nileshwar, Sean Jauss, Ginny Hope, and Birgit Whitman at the University of Bristol for providing exceptional support and advice on this project; and all the medical and nurse staff at the Institute Clinic of Thorax and Transplant Foundation Services of the Hospital Clinic of Barcelona, without whom accomplishment of this success would have been impossible. None of the authors have any financial interest in the present work.
Department of General Thoracic Surgery, Hospital Clinic, Barcelona, Spain (Prof P Macchiarini MD, P Jungebluth MD, T Go MD); Fundació Clínic, Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain (P Macchiarini); CIBER Enfermedades Respiratorias, Universitat de Barcelona, Barcelona, Spain (P Macchiarini); Bioengineering, Politecnico di Milano, Milan, Italy (M A Asnaghi MSc, S Mantero PhD); Pharmaceutical Sciences, University of Padua, Padua, Italy (S Bellini PhD, Prof P P Parnigotto PhD, M T Conconi PhD); Immunology, Hospital Clinic, Barcelona, Spain (J Martorell PhD); Department of Cellular and Molecular Medicine, University of Bristol, Bristol, UK (T A Cogan PhD, S C Dickinson PhD, Prof A P Hollander PhD); and Clinical Sciences at South Bristol, Faculty of Clinical Medicine and Dentistry, University of Bristol, Bristol, UK (Prof M A Birchall MD, L E Rees PhD, A Dodson BSc)
Correspondence to: Prof Paolo Macchiarini, Department of General Thoracic Surgery, Hospital Clinico de Barcelona, University of Barcelona, c Villarroel 170, E-08036 Barcelona, Spain (e-mail: pmacchiarini@ub.edu)
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