爱华网最近一期的《自然综述-遗传学》发表了一篇观点文章，题为《诱导多能干细胞和重编程：透过忽悠看科学》。
Perspectives
Nature Reviews Genetics 10,878-883 (December 2009) | doi:10.1038/nrg2700
Viewpoint: Induced pluripotentstem cells and reprogramming: seeing the science through thehype
该文由对以下四位iPS细胞的大腕的问答组成：
Juan Carlos Izpisúa Belmonte1,James Ellis2,Konrad Hochedlinger3& Shinya Yamanaka4
其摘要（Abstract）写道：
No-one can have failed to notice the splash that inducedpluripotent stem (iPS) cells have made in the few years sincesomatic cells were first reprogrammed to pluripotency. But whatis their real promise, where should research efforts befocused, and are we at a stage where we can replace embryonicstem cells? Four pioneering iPS cell researchers offer theirpersonal insights into these and other questions of current debate.As well expressing hope for the improved understanding andtreatment of human disease, they urge caution over safetyand propose the establishment of iPS cell banks.
下面我将其他三位跟班的回答暂不考虑，只是将iPS细胞之父Yamanaka（哑马拉卡）的答复集中如下（其中加粗的语句是我认为值得注意的要点）：
What has been the most significant recent discovery ininduced pluripotent stem (iPS) cell research?
Shinya Yamanaka： I would like to highlight the findings from oneof our own papers — 'Variation in the safety of inducedpluripotent stem cell lines'17— regarding the future clinical applications of iPS cells. We foundthat the origin of the iPS cells had a profound influence on theteratoma-forming propensity in a cell transplantationtherapy model using mouse secondary neurospheres differentiated from iPS cells. This propensitycorrelates with the number of undifferentiated cells that persistin the secondary neurospheres. Tail-tip fibroblast-derived iPScells showed the highest propensity, whereas those from embryonicfibroblasts showed the lowest. In addition, hepatocyte- andstomach-derived iPS cells showed intermediate results. Until now,numerous human iPS cell clones have been generated from a varietyof cells, including skin fibroblasts, bone marrow cells,keratinocytes, neural stem cells, peripheral blood cells and fatcells. It is therefore extremely important to examine and elucidatethe impact of such origins on both the safety and the properties ofhuman iPS cells.
How far do we need to understand the basic biology ofreprogramming and iPS cells to be able to use thesecells?
Shinya Yamanaka： There are two distinct types of applicationsfor iPS cells — regenerative medicine and in vitro usage. In vitroapplications — including the development of disease models, drugscreening and toxicology — are just around the corner. By contrast,for the use of iPS cells in regenerative medicine, safetyremains the highest hurdle still to be overcome. Moreprecisely, we need to double-check that we would not see anytumour formation after transplantation into patients. Two typesof tumours should, therefore, be distinguished: tumours caused bytransgene integration and teratomas caused by the persistence ofundifferentiated cells. To avoid transgene-initiated tumours, thegeneration of iPS cells without transgene integration is consideredto be important. Although several methods, such as those usingplasmids or recombinant proteins, have been reported, theefficiency of integration-free iPS cell generation still continuesto be too low. We need to elucidate the process of iPS cellgeneration more fully to increase the efficiency to a morepractical level. As for teratomas, we need to understand whyeach iPS cell clone demonstrates a different proportion ofundifferentiated cells after in vitro differentiation, as well aswhy such clones have a propensity to form teratomas.
How far are we from using iPS cells in theclinic?
Shinya Yamanaka： The clinical application of iPS cells dependson regulatory frameworks, which are different in each country. Somecountries, including Japan, have to establish new guidelines for EScells and iPS cells. The clinical use of iPS cells will also dependon the results of preclinical studies using animals, and manytechnical challenges still need to be overcome.
We aim to solve the technical challenges discussed above, whichare specific to iPS cells, within a few years. However, there aremany more challenges that are common to both ES and iPS cells. Weneed to develop efficient and specific protocols to induce in vitrodifferentiation into specific lineages from ES and iPS cells. Wealso need to establish safe and effective methods for transplantingthose differentiated cells into patients. Thereafter, vigorouspreclinical tests would be needed to evaluate the safety andefficacy of pluripotent cell-derived cells in animalmodels.
What improvements do we need to push iPS cell researchforwards?
Shinya Yamanaka： iPS cells are generated from various origins byvarious methods. In each experiment, multiple iPS cell lines areestablished. We need to determine the best origins, best inductionmethods and best evaluation methods.
To further advance iPS cell research towards variousapplications, we need the following technical improvements: thedetermination of the best original cells in terms of bothsafety and efficacy; the development of reproducible, efficient andintegration-free methods that can fully reprogram human adultsomatic cells; and the establishment of simple but sensitive andreliable methods for evaluating the safety of the myriad iPScell clones and subclones. To achieve these goals, the mechanism ofdirect reprogramming must first be further elucidated.
The generation of iPS cells from each patient in accordance withgood manufacturing principle (GMP) standards would be veryexpensive. It would take at least a few months and would not bepractical for patients suffering from acute disease and injuries,such as spinal cord injury. We therefore might need to considerthe establishment of an iPS cell bank. Previous estimationspredict that the collection of 50 unique iPS cell lines that arehomozygous for the three major human leukocyte antigen loci wouldcover ~90% of the Japanese population with perfect matches.
Should we continue to work on ES cells, or have they beenreplaced by iPS cells?
Shinya Yamanaka： ES cells are at least a few years more advancedthan iPS cells in terms of safety. Therefore, preclinical andclinical trials using ES cells should be continued. A few yearsmeans a lot for patients who are urgently waiting for newtreatments. I would expect that iPS cells will eventuallyreplace ES cells in most, if not all, applications in thefuture. Even thereafter, however, ES cells are still expectedto have an important role as a control in both experiments andtrials. I have a great interest and high expectations in regards tothe first clinical trials using human ES cells for patientssuffering from spinal cord injuries, which are presently beingconducted by Geron, although the US Food and Drug Administrationhas temporarily postponed these trials.
从上面的问答看，现在缠绕哑马拉卡的主要问题是iPS细胞的安全性，因为他终于“发现”了很多iPS细胞致癌（但还没直接承认iPS细胞就是人造的癌细胞）。因此要双倍核实（double-check）iPS细胞不会形成肿瘤（但他能保证得了吗？）。哑马拉卡搞了这么几年的iPS细胞研究，说他的方法可使任何成年体细胞变为iPS细胞，但现在却想起要发现最佳来源细胞（bestoriginal cells）和理解为何每一iPS细胞克隆会显示出不同比例的未分化细胞（each iPScell clone demonstrates a different proportion of undifferentiatedcells）。
看来，这哑马拉卡的捂性还是不高，因为他的这些发现其实在我批驳他过去错误的文章里都已说得一清二楚，他的那些不解我也早就给了他答案（是把文章直接给他的！）。或许他还是想继续装昏？
如今诱导多能干细胞的“多能”已被看作是“多余”，而更多的人也开始明白我说的iPS重编程就是一个癌化过程。但即使这样，在问答的最后哑马拉卡还期望iPS细胞最终会在所有或大部应用中取代胚胎干细胞（expectthat iPS cells will eventually replace ES cells in most, if notall, applications in thefuture）.你说这不是痴人说梦还是啥？
哑马拉卡，你的iPS再生医学大忽悠是该收场了。如非要闹出人命才肯放手的话，那可就太晚了！
刘实
2010年2月26日星期五
