244 hESC Lines and Their Use in International Research Number of studies performed with the cell line (published 1998–2008) Percent of publications 1999–2008 Number of studies Number of studies performed with performed with the cell line Percent of the cell line (published in 2007) publications 2007 (published in 2008) Percent of publications 2008 36.7 30.8 10.2 8.6 7.7 6.4 5.8 4.6 3.7 3.2 3.2 89 71 18 21 20 15 15 9 14 12 8 39.2 31.3 7.9 9.2 8.8 6.6 6.6 4.0 6.2 5.3 3.5 111 85 25 19 19 18 12 7 21 13 6 37.4 28.6 8.4 6.4 6.4 6.1 4.0 2.4 7.1 4.3 2.0 Table 4. Most frequently used hESC lines hESC line H9 H1 H7 BG01 HES-3 HES-2 HSF-6 BG02 HUES9 HUES7 I6 Producer WiCell WiCell WiCell Bresagen ESI ESI UCSF BresaGen HSCI HSCI Technion 363 305 101 85 76 63 57 45 37 32 32 Shown is the number of papers (published 1998–2008) that report on the derivation or experimental use of the particular hESC line. Data for 2007 and 2008 are also listed separately. The percentage values present the share of publications using the particular cell lines in the total number of publications in the given period. Note that in many studies more than one hESC line was used. Sublines were allocated to the respective parental hESC line. other producers were less frequently used. However, there are signiﬁcant country-speciﬁc differences in the use of hESC cell lines from certain providers (Fig. 2B). Whereas 75% of US- based research was performed with at least one WiCell line, only a small percentage of papers originating from Australia, Korea, or Sweden (which together account for more than 14% of hESC research papers) was based on these hESC lines (1.8%, 3.3%, and 4.8%, respectively). More than 80% of hESC research published by Australian groups was performed with hESC lines of ESI. Similarly, work reported by Swedish groups was mainly performed with hESC lines from Cellartis AB and from another Swedish provider, Karolinska Institute. Korean groups nearly exclusively used hESC lines provided by Korean producers. In Japan, Singapore, and China, 16.7%, 40%, and 46.7% of reported research was exclusively or par- tially performed with WiCell lines, respectively (Fig. 2B), whereas a large portion of hESC work was performed with hESC lines derived in the respective country. For example, 23 of 31 hESC research papers from Japanese groups reported work performed with hESC lines provided by Kyoto Univer- sity. These lines have not been used outside Japan for legal reasons. In contrast, all hESC research reported from Germany by the end of 2008 was performed involving hESC lines from WiCell (data not shown). Although hESC research is strictly regulated in Germany by the Stem Cell Act, it was permitted to use any of the hESC lines originally registered at the NIH. Therefore, it seems unlikely that the preferential use of just the WiCell lines is only due to a restrictive stem cell research policy. This view is supported by the fact that a high percent- age of hESC work was also based on WiCell lines in coun- tries with a highly permissive hESC research policy, such as Great Britain and Canada (74.5% and 90%, respectively). Moreover, we wished to determine whether the wide use of WiCell lines could be a direct consequence of a possible interdependence of international hESC research, which could lead to an indirect transmission of US stem cell research poli- cies to collaborative research in other countries. We therefore performed an analysis of authors’ afﬁliations in the 989 research papers investigated here. This analysis revealed that, even in those countries with predominant use of WiCell lines, only a relatively low percentage of hESC papers evolved from direct collaboration with US groups (Canada, 20%; Israel, 13.1%; United Kingdom, 10.6%). Similarly, only 22% of hESC work published by US groups was the result of a direct collaboration with groups outside the United States. Of all hESC lines reported in the literature by the end of 2008, H9 and H1 (including their derivatives) were the most frequently used (36.7% and 30.8% of published studies, respectively) (Table 4). In published research from US groups, these two cell lines were used even more often (52.6% and 47.4% of hESC publications, respectively). We therefore wondered whether the preferential use of these two cell lines over other NIH-approved cell lines might be a con- sequence of preferential NIH funding. This seems not to be the case. According to information from the 989 papers inves- tigated here, 69.1% and 70.9% of studies performed with hESC lines H1 and H9 in the US had NIH or other govern- mental funding. Similarly, publications based on work with two other NIH approved cell lines frequently used in the United States (BG01 and UC06) were funded by the NIH to a comparable degree (72.8% and 81.5%, respectively). On the other hand, our data show that non-WiCell lines have also been widely used. For example, the Harvard Stem Cell Institute (HSCI) line HUES9, which has been available for only 5 years, was used in more than 7% of experimental hESC work published in 2008. Overall, cell lines from HSCI have been used in 12.3% and 12.9% of published work from 15 countries in 2007 and 2008, respectively, indicating diver- siﬁcation of cell lines used in international hESC research. DISCUSSION In this study, we have analyzed the scale and impact of hESC research on a global level, including the use of hESC lines. We found evidence for at least 1,071 original hESC lines, a large portion of which has been reported in the scientiﬁc liter- ature so far. However, despite this multitude of hESC lines, only cell lines from a few providers have been extensively used in published international research, with remarkable dif- ferences between countries. Although we found evidence for more than 1,000 supposed hESC lines, the number of available and well-characterized lines is probably considerably lower. It even remains an open