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作者：Fumiaki Nakajimaa, Katsushi Tokunagab, Norio Nakatsujic作者单位：aResearch and Development Department, Central Blood Institute, Japanese Red Cross Society, Tokyo, Japan;bDepartment of Human Genetics, Graduate School of Medicine, University of Tokyo, Tokyo, Japan;cStem Cell Research Center, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan
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【摘要】
. B9 A! ]; |: K! j& l7 [ Human embryonic stem (hES) cell lines are of great potential in cell transplantation therapy. However, recipients of such allogeneic transplants probably need treatment with immunosuppressants. Recently, Taylor et al. proposed banking of hES cell lines and estimated the required number of hES cell lines for beneficial human leukocyte antigen (HLA) matching in the U.K. population. Here, we carried out such an estimation in the Japanese population. We calculated the proportion of patients who can find at least one HLA-matched donor at three loci of HLA-A, -B, and -DR. With a bank of hES cell lines from 170 randomly selected donated embryos, 80% of patients were expected to find at least one hES cell line with a single mismatch at one HLA locus or a better match. Furthermore, 80% of patients are expected to find at least one donor with complete matching at the three HLA loci if parthenogenetic homozygous hES cell lines are established from 55 randomly selected donated oocytes. The relatively low ethnic diversity of the Japanese population may have resulted in a high success rate in beneficial matching. Moreover, parthenogenetic hES cell lines can greatly reduce the number required for a higher degree of HLA matching.
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Disclosure of potential conflicts of interest is found at the end of this article.
& S8 O4 N5 w: H 【关键词】 Embryonic stem cells Human leukocyte antigen matching Major histocompatibility complex antigens Transplantation Cell therapy8 M9 _" f+ m0 Y: M
INTRODUCTION/ G! q* P. K4 A& T5 F
; F# @2 P7 y* M; @# }7 U sThe derivation of human embryonic stem (hES) cell lines capable of rapid long-term proliferation and differentiation into almost all cell types is envisioned to pave the way for the production of an unlimited number of various human cell types for use in cell transplantation therapy and drug screening .
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/ k9 w3 F% L: x( C8 XIn allogeneic transplantation, mismatches in histocompatibility antigens may result in immunological rejection, although there is a possibility that such immunological reaction might be weaker than that observed in organ transplantation . In the near future, preadministration of immunosuppressive drugs will most likely be part of cell-based therapies for Parkinson disease and spinal cord injury. However, high doses of immunosuppressive drugs frequently result in side effects, including a greater susceptibility to infectious diseases.4 t+ V Z4 b% _7 m: r8 `& i# e( |
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The best way to avoid immunological rejection is to use the patient's own cells. In theory, one way to accomplish this is by reprogramming a patient's somatic cells into pluripotent stem cells, which can then be allowed to differentiate into the required cell type for retransplantation therapy. However, the technology of somatic cell reprogramming is still far from perfect .2 X8 ~6 a3 P4 X2 k7 B+ ?
& ^* [ u D/ |" d s# wImmunological responses to organ transplants are variable depending on the site and type of organ, and the degree of immunological response from allogeneic transplants correlates with the extent of matching of human leukocyte antigen (HLA) antigens . Even a partial match in HLA types may result in beneficial HLA matching, thus reducing the dose requirement for immunosuppressive drugs.
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In cases when stem cells cannot be obtained from the patients themselves, hES cell lines derived from unrelated donated embryos may become alternative sources of various cell types for transplantation therapy. However, complete or at least beneficial matching of histocompatibility antigens of patients with those of hES cell lines is necessary to avoid graft rejection.
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Recently, Taylor et al. . In this present study, we estimated the number of donor cell lines required for anticipated cell transplantation therapy using hES cell lines in the Japanese population.% S& ?! _4 T, F( O/ ~
# x9 _0 g( R% CMATERIALS AND METHODS x4 ^' Y) U& v
" D4 w+ K7 I$ J9 ?; {6 K ~2 sThe data set of HLA types is composed of HLA-A, -B, and -DR from a total of 2,578 unrelated individuals, including unrelated parents in an extensive family study for hematopoietic cell transplantation and donors for a cord blood cell bank . For the present study, the resolution of the HLA types used for the data set adopted the following low-resolution types: 8 antigens in HLA-A, 20 antigens in HLA-B, and 10 antigens in HLA-DR. All the individuals are Japanese people living in Tokyo and its neighboring prefectures. Our assumption is that the distribution of HLA types in our study will be similar to that of donated spare embryos from fertility clinics.7 h4 [2 m# s# n {0 e/ B
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Based on the above data set, we calculated the proportion of patients who can find at least one HLA-matched donor in relation to the number of randomly selected donors. Unrelated individuals in the data set were assumed to be both patient and donor populations. We also calculated what percentage of the individuals (patients) could find the HLA-matched individual(s) from the various numbers of randomly selected individuals (donors), with different levels of matching. For each patient, donors were randomly selected 1,000 times from the individuals other than the patient, and then we calculated the accumulated frequency of donor finding for all the individuals (patients). The following four levels of HLA matching were considered: full match; a single mismatch at the HLA-A, -B, or -DR locus; single mismatches at any two loci of HLA-A, -B, or -DR; and single mismatches at all three loci.
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RESULTS AND DISCUSSION3 |. V8 F7 `. t- p- D0 {
! ^' S' f) a$ C: AFigure 1 shows the results of the calculation. If a bank includes hES cell lines derived from 100 randomly selected donated embryos, 19% of patients were expected to find at least one hES cell line with complete matching at the three HLA loci, HLA-A, -B, and -DR. At the same time, 67% of patients find hES cell line(s) with a single mismatch at one locus or better match, 97% with single mismatches at two loci or better match, and almost 100% with single mismatches at the three HLA loci or better match. When the donor size reaches 170, 80% of patients were expected to find at least one donor (hES cell line) with a single mismatch at one HLA locus or better match. In contrast, even with the donor size of 850, only 60% of patients could find hES cell line(s) with complete matching. Taylor et al. .0 _; O- C, ^1 z% ?' o, B
) \7 Y3 S6 o# T. ~% DFigure 1. Cumulative proportion of patients with at least one human leukocyte antigen (HLA)-matched donor for human embryonic stem cell transplantation: , full match; , single mismatch at one locus of HLA-A, -B, or -DR or better match; , single mismatches at two loci or better match; x, single mismatches at the three loci or better match.
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$ O/ `3 ^3 f- g+ A8 \, wUntil now, the degree of HLA mismatch acceptable for cell transplantation therapy using hES cell lines has not been elucidated. It is well known that the required level of HLA matching differs among organs or tissues to be transplanted. For example, unrelated bone marrow transplantation requires a stricter matching of HLA genes at the sequence level . If a single mismatch at the serological typing level is clinically acceptable for many cases of cell transplantation therapy using hES cell lines, a bank established from 200 randomly selected donated embryos should become beneficial to more than 80% of patients in the Japanese population.3 J# m! b( B1 I# N; O5 s" w6 o
9 E% \# z- {1 }: a! lEstablishment of 200 hES cell lines is a feasible task. Even with underestimation, more than 5,000 embryos are discarded annually from fertility clinics in Japan. Donation and use of spare embryos already destined for destruction causes less bioethical and social concern than somatic nuclear transfer technology, as reflected by existing policies and guidelines in many countries. Also, derivation efficiency of hES cell lines is usually high, even reaching a 100% success rate from a small number of blastocysts . However, such high success rates might be difficult to achieve when hES cell lines will be established for clinical application by excluding use of animal derivatives in the medium and feeder cells. Thus, banking of 200 or more hES cell lines may be a realistic and favorable option after cell therapy using hES cell lines and immunosuppressive drugs become part of routine therapy.
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' } X9 o; p% O; v3 N/ D9 QFor further consideration, we have carried out another calculation to present an additional option with the assumption that parthenogenetic hES cell lines have similar and sufficient abilities of pluripotency and no greater safety risks compared with the conventional hES cell lines derived from zygotic embryos. There have been reports that embryonic stem (ES) cell lines can be established from parthenogenetic mouse and monkey embryos and that such ES cell lines have similar long-term proliferation and pluripotency to differentiate into various cell and tissue types .
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# j! [, Z- J6 o2 y/ \ hThus, it is very likely that hES cell lines can be established from parthenogenetic human embryos with relative ease and that they have similar pluripotency to produce an unlimited number of the various human cell types. One potential concern is that the epigenetic status of such hES cell lines is different from normal somatic cells. In particular, genomic imprinting patterns may be entirely of the maternal state. In spite of such apparent abnormality, studies have suggested that they still retain the pluripotency to produce derivatives of all three germ layers . Additional studies are required to evaluate the stability and safety of such cells and tissues for transplantation therapy.
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/ X( Y! A" C3 _5 Y* b4 F( D# XHuman ES cell lines with uniparental disomy (UPD) have unique advantages in transplantation therapy. Since they have complete homozygosity at all genomic loci, their derivative cells can be transplanted into both homozygous and heterozygous recipients without rejection. This significantly reduced the required number of matching donor cell lines, as our calculation clearly indicated. Figure 2 shows the results of the estimation based on the assumption that randomly donated oocytes from individuals in the HLA type data set are used to produce parthenogenetic embryos for hES cell line derivation. The proportion of patients who can find at least one completely HLA-matched UPD-hES cell line is between that for a single mismatch at one locus and that for single mismatches at two loci in the conventional hES cell transplantation (Fig. 1). If UPD-hES cell lines are established from 55 randomly selected donated oocytes, 80% of patients are expected to find at least one donor with complete matching at the three HLA loci.0 c2 a" Y% y! Q9 Q, q3 `. j
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Figure 2. Cumulative proportion of patients with at least one human leukocyte antigen (HLA)-matched parthenogenetic donor for human embryonic stem cell transplantation: , parthenogenetic donors with full match; , single mismatch at one locus of HLA-A, -B, or -DR or better match; , single mismatches at two loci or better match.4 `1 Q4 V& J* N2 {) e; v
, G' l0 T. F5 V; ?, X8 i1 ?In conclusion, first, banking of a feasible number of hES cell lines, such as 200 lines, derived from randomly donated embryos may be a realistic and favorable option to reduce immunological rejection in the anticipated cell therapy using hES cell lines, because such banking could provide the hES cell line with beneficial HLA matching to more than 80% of Japanese population. Also, if parthenogenetic hES cell lines prove to be useful and safe for cell therapy, the required number of hES cell lines for a higher degree of HLA matching should be greatly reduced, thus benefiting a large majority of patients. This is clearly one important option to be evaluated in the coming years.% V, g2 Q# U" W" @& z
& y3 F# m' ~+ G6 oDISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST
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The authors indicate no potential conflicts of interest.$ N$ w7 W( ?0 m2 U( p" o
* _: X6 l# y# c+ IACKNOWLEDGMENTS: |7 ~. Y& w7 _/ {5 H D8 z/ I
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Although this study did not receive specific funding, we received core funding from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese government.
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发表于 2009-3-5 00:56
发表于 2015-5-25 08:00
