Problems and possible solutions in finding an unrelated bone marrow donor. Results of consecutive searches for 240 Dutch patients

Bone Marrow Transplantation, (1997) 20, 1011 1017 1997 Stockton Press All rights reserved 0268 3369/97 $12.00 Problems and possible solutions in finding an unrelated bone marrow donor. Results of consecutive searches for 240 Dutch patients M Oudshoorn 1,2, JJ Cornelissen 3, WE Fibbe 4, ER de Graeff-Meeder 5, JLWT Lie 2, GMTh Schreuder 1, K Sintnicolaas 6, R Willemze 4, JMJJ Vossen 7 and JJ van Rood 1,2 1 Department of Immunohaematology and Blood Bank, 2 Europdonor Foundation, 4 Department of Haematology, 7 Department of Paediatrics, Leiden University Medical Centre, Leiden; 3 Department of Haematology, Dr Daniel den Hoed Cancer Centre, Rotterdam; 5 Department of Immunology/Haematology, University Children s Hospital, Het Wilhelmina Kinderziekenhuis, Utrecht; and 6 Red Cross Blood Bank Rotterdam, Rotterdam, The Netherlands Summary: Correspondence: M Oudshoorn, Europdonor Foundation, Bldg 1, E3-Q, Leiden University Medical Centre, POB 9600, 2300 RC Leiden, The Netherlands Received 24 April 1997; accepted 14 July 1997 planted. In summary, of the 240 patients for whom the Europdonor office searched for a donor, about onethird were transplanted, one-third had a potential donor but did not reach transplantation, while for the remaining one-third of patients no suitable donor could be found. Keywords: unrelated donors; BMT; donor search To evaluate the efficiency of our protocol for finding an HLA matched unrelated bone marrow donor, search results obtained between 1990 and 1995 for 240 Dutch patients were analyzed. The percentage of patients for whom, according to information given by the registries, a fully split-hla antigen matched donor is available, increased from 24% in 1990 to over 70% in 1995. As a result the percentage of patients transplanted rose from about 24% in 1990 1991 to 44% in 1994 1995. The median time between the start of the search and trans- plantation was about 6 months. The systematic use of Bone Marrow Donors Worldwide (BMDW) which com- prises the HLA groups of all volunteer bone marrow donors in Europe, Israel, South Africa, North America, Canada, India, Australia and New Zealand has been essential in this context. While searching for a suitable donor several problems were encountered such as unavailability of donors (12%) and discordant typing results (8%; range 1% to 25%). Thus it is advisable to select several donors for a patient. For 86% of patients with at least one HLA identical donor on the serological level for HLA-A,-B,-DR,-DQ, an HLA- DRB1/3/4/5, and -DQB1 identical donor could be ident- ified. As expected, patients with two frequent haplotypes in strong linkage disequilibrium had the best chance of obtaining an HLA matched donor. Unexpectedly, patients with only one such haplotype had an almost similar chance. It could be calculated that HLA-DR typing of HLA-A,-B identical donors was rarely costeffective after 1992. Only 12 of the 75 transplanted patients (16%) typeable at DNA level for class II, turned out to be completely matched for HLA-A,-B,-C,- DRB1/3/4/5,-DQB1,-DPB1 and had a negative MLC test. In the group of patients transplanted with a fully matched donor and for whom a CTLp test was performed, only 7% (4/54) of the tests were negative. Search results for patients of non-european origin were dismal, with only four of 26 patients referred being trans- Only one out of three patients in need of a bone marrow transplant has a suitable sibling donor. Allogeneic bone marrow transplantation with marrow from unrelated but HLA matched donors has proven to be a suitable alternative for such patients. 1,2 Small and large registries have been formed to facilitate the search for an unrelated donor. 3 7 Over half of potential donors are coordinated by the National Marrow Donor Program (NMDP) and approxi- mately 40% are included in the European Donor Secretariat (EDS) or European Marrow Donor Information System (EMDIS). According to the IMUST study 8 a suitable donor can be found for 10% of patients only, if the search is restricted to a large registry such as the British Bone Mar- row and Platelet Donor Panel (BBMPDP) with 40 000 donors at the time of analysis. This figure is much higher if other registries are contacted as well. 9 12 Selection criteria by which a suitable donor is identified, are still in a state of flux as a result of the introduction of new HLA typing technologies, extension of the registries and the introduction of new bone marrow transplant protocols. In this report we describe the results of search requests for 240 Dutch patients reported to Europdonor in an attempt to document successes and failures of the search process, and if possible their causes. Patients and methods The analysis concerned the donor searches for 240 consecutive Dutch patients registered by the Europdonor Foundation from 1990 till 1995. Patients originated from the following transplant centres: the University Hospital Leiden (adults n = 50 and children n = 105), Dr Daniel den Hoed Cancer Centre Rotterdam (n = 64) and the University Chil-

1012 Table 1 Patients characteristics After a patient has been reported to Europdonor, the HLA data of his/her siblings and parents are requested in No. of patients 240 order to establish the patient s haplotypes. The patient is Sex (male/female) 144/96 retyped in the national reference laboratory for histo- Age (years) compatibility. median 14.4 range 0.1 52.1 If the patient has a haplotype with a high frequency the under 16 years/over 16 years 131/109 chance of finding a phenotypically identical family member Diagnosis (No. of patients) (eg cousins, aunts, uncles etc) is calculated. 13 If the chance Chronic myelogeneous leukaemia 51 is around 5 10% or higher a search for an extended family Acute myelogeneous leukaemia 41 donor is initiated. A search for an extended family donor Acute lymphocytic leukaemia 39 is also initiated if there is a consanguinous marriage in the Other malignant diseases 6 patient s family. Severe aplastic anaemia 31 Fanconi anaemia 10 At the same time, Bone Marrow Donors Worldwide Myelodysplastic syndromes 25 (BMDW) which contains the HLA phenotypes and number Severe combined immune deficiency 10 of donors per phenotype from bone marrow donor registries Other non-malignant diseases 27 all over the world is consulted. 14 The 2nd edition (March 1990) to 25th edition (December 1995) is screened for donors with suitable phenotypes. In consultation with the dren s Hospital, het Wilhelmina Kinderziekenhuis in transplant centres a selection of (a) donor(s) is made. Utrecht (n = 21). All patients were in need of an allogeneic The first choice of unrelated donors are HLA-A,-B, bone marrow transplant but had no HLA identical sibling. -DRB1 typed donors, second HLA-A,-B,-DR typed donors Patients characteristics shown in Table 1 did not differ identical at the split level to the patient, and third, donors from other studies. who are as yet not typed at the level of the split antigens but are identical for the broad HLA-A,-B,-DR antigens. If Search protocol only HLA-AB identical donors are reported in BMDW, the chance that HLA-DR typing will identify an HLA-A,-B,- The outline of the process for selecting a bone marrow DR identical donor is calculated. 15 If the chance is higher donor for patients in need of an allogeneic bone marrow donor but lacking an HLA (genotypically) identical sibling donor is given in Figure 1. than 1%, which implies that if 10 donors are HLA-DR typed there is a chance of almost 10% that one donor is HLA-A,-B and -DR identical, HLA-DR typing is initiated. I. Patient reported to ED II. HLA-retype patient III. Establish haplotypes of patient IV. Consider extended family search Va. Extended family search Often done simultaneously Vb. Search for unrelated donor No donor VI. Only AB id. donor(s) VII. No donor Vb. *Histocompatibility testing HLA-DR typing Search 1 antigen mismatch donor HLA retyping (serol) No donor No donor DNA typing (HLA-A2,C,DRB1/3/4/5, DQB1,DPB1) VII MLC test CTLp test Figure 1 Outline of the process for selecting a bone marrow donor.

HLA serology All HLA-A,-B and -C typings of patients and retypings of donors were done using the standard NIH lymphocytotoxicity assay and the HLA-DR and -DQ was performed with the two colour fluorescence assay 16 using allo-antisera. DNA typing HLA-DRB1 typing was performed using biotinylated sequence-specific oligonucleotides from 1992 to 1993 17 and from 1994 to 1995 using the PCR-SSP technique. 18 The HLA-DPB1 typing was done with similar methods using three primer sets, one generic set and the other two separating the DPB1 specificities into two groups. Twenty-one DPB1 sequence-specific oligonucleotides were used to detect 36 different DPB1 specificities. HLA-C typing was performed according to the method of Bunce et al. 19 Whenever possible, patient/donor pairs not yet typed at the DNA level, were typed retrospectively. Mixed lymphocyte culture (MLC) test The mixed lymphocyte cultures were performed according to Keuning et al. 20 Tests were defined as negative when the relative response value was equal to or less than 10%. Cytotoxic T lymphocyte precursor (CTLp) test To establish whether the linkage disequilibrium of the patients haplotypes would be helpful in predicting whether an HLA-A,-B,-DRB1/3/4/5,-DQB1 identical donor could be identified, the 97 patients described above were subdiv- ided into those with two (FF), one (FN) or no haplotypes (NN) in strong linkage disequilibrium. A frequent haplotype in this analysis was defined as a haplotype belonging to the 10 haplotypes with strongest linkage disequilibrium in the Dutch population. 22 The 11 patients with two haplotypes in strong linkage disequilibrium had, as expected, a very high success rate (100%) in locating an HLA-A,-B, -DRB1/3/4/5,-DQB1 identical donor, but also those patients (n = 45) who had only one such haplotype had a high success rate (91%). The chance of finding such a donor for patients (n = 41) with no haplotype in strong linkage disequilibrium was 78% (P = NS). The chance of finding an HLA-DPB1 identical donor was significantly increased in the FF group (63%; P = 0.04) compared to the combined FR and RR group (23%). The CTLp test was performed as described by Zhang et al 21 with minor modifications. In each test, donor cells were used as responder cells and patient cells as stimulator and target cells. A negative CTLp test was defined as less than 2 CTLps per 10 6 peripheral blood lymphocytes, a doubtful positive result was defined as 2 and 8 and a positive result as 8 CTLps per 10 6 peripheral blood lymphocytes. Results Number of potentially available donors Table 2 illustrates the rise of potentially HLA-A,-B,-DR identical donors (at the split level) available for patients in the years 1990 1995 in either the Dutch Europdonor registry or in BMDW. From these potentially acceptable donors a mean number of 6.7 donor blood samples per patient were If HLA identical donors are not available, a search pro- requested. Twelve percent of donors requested for testing gram is used which identifies donors who have one antigen were unavailable due to medical or personal reasons mismatched at the split level or a cross-reacting antigen (Table 3). mismatch (eg HLA-A24 instead of -A23, HLA-A2 instead Following retyping, discordant results of 8% were of -A28, respectively). At the same time, the chance of observed (Table 3). This number did not change during the finding a one locus antigen mismatched family donor is period studied. It did, however, vary between the registries calculated. 13 All donors requested for a patient are retyped from less than 1% to over 25% (mean = 8%; median = using serological methods. From 1992 onwards, patient and 11%). Donors from registries with more than 50 000 donors donors have also been subtyped at DNA level for HLA- had on average more discordant results (mean = 10%; DRB1/3/4/5 and increasingly for HLA-DQB1, -DPB1, -A2 median = 12%) than registries with less than 50 000 donors and -C. The mixed lymphocyte culture test is performed (mean = 3%; median 8%). In 37 out of 73 (51%), the discordant routinely and the cytotoxic T lymphocyte precursor (CTLp) results involved homozygosity, ie donor centre test performed if possible. typed the donor as homozygous while the donor was heterozygous and visa versa, ie the donor was typed as heterozygous but was in fact homozygous for that locus. For 8% of patients the only donor thought to be present, turned out to be either not available (4%) or mistyped (4%). Percentage of patients for whom an HLA-A,-B, -DRB1/3/4/5,-DQB1 identical donor could be found Analysis is restricted to the years 1992 1995, because DNA typing was introduced as a routine technique in the middle of 1992. The data analysed consisted of 441 HLA-A,-B, -DR,-DQ serologically split matched donors tested for 97 patients. The mean number of donors tested per patient was 4.5; the median 5.0 and the range 1 17 donors. Seventy- five percent of all HLA-A,-B,-DR,-DQ split identical donors based on serology were also identical to the patient for HLA-DRB1/3/4/5 and 13% for HLA-DRB1/3/4/5, -DQB1 and -DPB1. For 86 of the 97 patients (89%) one (or more) HLA-,A,-B,-DRB1,-DQB1 identical donor(s) were identified. This figure was only reduced by 3% to 86% when identity for DRB3/4/5 was also included in the analysis. Of these, only 28% were also HLA-DPB1 identical. Impact of linkage disequilibrium on the outcome of the search process 1013

1014 Table 2 The number of HLA-A,-B,-DR identical donors (typed at split level) available at time of initial search request in Europdonor and Bone Marrow Donors Worldwide (BMDW) for 240 Dutch patients Year in which search Europdonor Foundation BMDW was started No. of donors No. of patients with No. of donors No. of patients with registered typed at a donor (% of total registered typed at split a donor (% of total split level patients) level patients) 1990 n = 42 1430 1 (2%) 26 181 10 (24%) 1991 n = 28 1754 1 (4%) 48 932 11 (39%) 1992 n = 56 2942 3 (5%) 64 638 30 (54%) 1993 n = 28 5930 5 (18%) 179 389 16 (57%) 1994 n = 36 7977 14 (39%) 332 764 27 (75%) 1995 n = 50 10 250 16 (32%) 515 651 36 (72%) n = 240 1430 10 250 40 (17%) 26 181 515 651 130 (54%) Total 1990 1995 n = No. of patients Table 3 The number of HLA-A,-B,-DR typed donors requested, their availability and discordant HLA typing of the donors requested Year in which search No. of donor blood No. of donors No. of donor No. of donors with was started samples requested a unavailable b samples retyped c discordant HLA typing 1990 128 9 (7%) 107 8 (7%) 1991 75 7 (9%) 60 4 (7%) 1992 307 30 (10%) 250 25 (10%) 1993 169 19 (11%) 135 11 (8%) 1994 189 26 (14%) 148 9 (6%) 1995 255 44 (17%) 195 16 (8%) 1990 1995 1123 135 (12%) 895 73 (8%) a Not only HLA-A,-B,-DR split identical donors were requested but also broad and a few minor mismatched donors. b Donor unavailable due to donor withdrawal for medical or personal reasons. c Ninety-three donor samples received were not retyped. HLA-DR typing of HLA-A,-B identical donors received an HLA mismatched graft. HLA typing at the DNA level was performed for some of the patient/donor HLA-DR typing was effective in the years 1990 1992 combinations retrospectively. Most patient/donor pairs when 12 donors were identified for eight out of 30 patients were found to be either mismatched for class I (A,B or C) after 215 HLA-DR typing procedures. In contrast, in the and/or class II (DRB1/3/4/5,DQB1 or DPB1) or had a posiyears 1993 1995, HLA-DR typing was requested sporaditive MLC or CTLp test. In the majority of the cases studied, cally and was always unsuccessful in identifying an HLAthe class I mismatches could be shown to be due to mis- A,-B,-DR identical donor. matches at the HLA-C locus (18/24). Twelve patients (16%) appeared to be transplanted with a well matched Percentage of patients who did not reach transplantation donor, ie identical for HLA-A,-B,-C,-DRB1/3/4/5,-DQB1, and the reasons why -DPB1, MLC negative (Table 4). Ten out of these 12 patients survived and are remarkably well (manuscript in Eighty-six (36%) out of the 240 patients were transplanted. preparation). Thirty-one patients (13%) were actively withdrawn from the search process, generally because of a reassessment of the indication for transplantation. Seventeen percent of Length of time between search request and patients died or were not transplantable due to advanced transplantation disease status. The percentage of patients who could not be transplanted because a donor was not found dropped from Less than 1 day was needed to identify a potential donor 50% in 1990 1991 to 21% in 1994 1995. The percentage in Europdonor due to the computer register being on site. of patients who could be transplanted rose from an average For the other registries, where transmission of requests and of 24% in 1990 1991 to 44% in 1994 1995. results was necessary, this interval decreased between 1990 and 1995 from a median of 11 days to 4 days. The time Donor recipient disparities for HLA needed to obtain a blood sample from a potential donor differed substantially between registries but was a median Although the a priori aim of the search was to find HLA of 9 days (range 1 38) for donors from the Europdonor file split identical donors, a large percentage of patients actually and 19 days (range 3 149) from elsewhere. It should be

Table 4 Degree of matching in 75 transplanted patient/donor pairs a more precisely and including HLA-DR typing as also suggested by Speiser et al. 11 HLA match category No. of pairs matched/ There is a large difference between the percentage of Total No. of pairs tested patients for whom a donor seems to be available (50% in 1990 1991 and 79% in 1994 1995) and the percentage of A B DR (serology, split) 65/75 = 87% patients actually transplanted (24% in 1990 1991 and 44% A B DRB1/3/4/5 DQB1 60/75 = 80% A B C DRB1/3/4/5 DQB1 42/75 = 56% in 1994 1995), even though in this study the percentage of A B C DRB1/3/4/5 DQB1 DPB1 12/75 = 16% patients transplanted is higher than reported elsewhere. 8,10,24 A B C DRB1/3/4/5 DQB1 DPB1 12/75 = 16% For 8% of patients this is due to donor withdrawal (4%) or MLC negative incorrect typing of the donor (4%). A disturbing trend in A B C DRB1/3/4/5 DQB1 DPB1 4/54 b = 7% MLC negative, CTLp negative this respect is the increase of donors (7% in 1990 vs 17% in 1995) who are unavailable mainly due to withdrawal of a For the remaining 11 transplanted patient/donor pairs no material was left the donor for personal reasons. According to a recent analy- sis by the National Marrow Donor Program blood trans- fusion donors and apheresis donors have a lower unavailability rate (16.7%) than donors recruited by community drives (26.4%). In Europdonor, where mostly blood trans- to perform retrospective typing at DNA level. b The CTLp test was only performed successfully in 54 patient/donor pairs. noted that samples from other registries were obtained fusion donors who have donated at least twice are recruited much faster in 1993 1995 than before 1993. The time as bone marrow donors, no increase in donor withdrawal needed for donor identification and the time to transplan- rate is seen over the years (9% in 1990 and 10% in 1995). tation was substantially shorter for donors residing in The The overall percentage of donors with HLA typing errors Netherlands compared to international donors; 3.0 vs 5.1 is 8% but varies between the different registries from less months for donor choice and 5.1 vs 7.0 months for time to than 1% to over 25%. Homozygosity either missed or incortransplantation. It is unclear to what extent this difference rectly assumed to be present, was the cause of almost half in time interval is caused by the fact that for patients with of the mistypings. It is thus advisable to request a higher a common phenotype there will be several potential donors number of donors for testing when the patient is homoin the national file. zygous for one or more loci. The inclusion of the MLC and CTLp test in our protocol Search outcome for patients from non-european origin deserves a comment. Several publications stress that an MLC test is often uninterpretable and taken alone is not a predictor of a better transplant prognosis. 25 27 We agree that the outcome of the MLC test alone is not a useful criterion for donor selection. We still perform the MLC test as a control for HLA-DRB1 typing as new alleles may not be detected by the PCR-based typing technique used, and to answer the question whether it is a predictor of GVHD or relapse in combination with HLA-DPB1. The outcome of the CTLp test is useful for selecting the best donor as has been documented by others. 28 30 It recog- nizes mismatches for class I, including HLA-C alleles, and serves as a check for the correctness of HLA class I typing. Theoretically, it could recognize minor histocompatibility mismatches but we have not encountered that. 31 The percentage of patients of non-european origin rose from 5% in 1990 to 16% in 1995. In total, 26 of the 240 patients were of non-european origin. For seven patients (27%) an HLA-A,-B,-DR split identical donor could be identified in BMDW. Only four out of the 26 patients, of whom two were an identical twin, were transplanted. For the remaining three patients with a potential donor, the search was stopped; one patient for personal reasons, for one patient HLA subtyping of the donor revealed too many mismatches and for one patient due to advanced disease status. Discussion This study has been useful in pinpointing some of the obstacles encountered when searching for an HLA matched unrelated donor. The analysis of the 240 searches showed that in 1995 for over 70% of the patients an HLA-A,-B,-DR split identical donor was available among the more than 500 000 split typed donors reported in BMDW. This is approximately 10% higher than predicted by Beatty et al 23 in 1988. Less than 20% of the total number of donors reported in BMDW is HLA-A,-B,-DR split typed but 86 out of 87 (99%) patients transplanted received a graft from an already HLA- A,-B,-DR typed donor. Similar findings have been observed in the file of the NMDP (P Coppo, personal communication). One might conclude that the best way to proceed is not to enlarge the registries further by recruiting new donors but in contrast, by retyping available donors Thirteen percent of patients (n = 31) were withdrawn during the search process for reasons other than the unavailability of an unrelated donor. The reasons (n = 20) were therapy-resistant leukaemia, unwillingness of the patient to be transplanted (n = 6), or the identification of a suitable related donor after an extended family search (n = 5). For 17% of patients for whom an unrelated donor was available the patient may have been referred to the transplant centre too late or the search process took too long. They were either deceased or were no longer transplantable due to advanced disease status. This ought to be an incentive to reorganize the search process drastically in order to shorten the time needed to identify a suitable donor. It has been shown that this can, if necessary, be reduced to 1 week in at least some cases (Ref. 32, and Cleaver, personal communications). An additional reason why some patients with an HLA-A,-B,-DR serologically typed donor are not 1015

1016 transplanted is the presence of too many mismatches an agreement is reached for the different matching categories. detected at DNA level. It is obvious that this should be discussed and agreed For 89% of patients with at least one HLA-A,-B,-DR by the World Marrow Donor Association (WMDA). and -DQ identical donor as determined by serology, one (or Finally, we should like to re-emphasize that in the com- more) HLA-A,-B,-DRB1,-DQB1 donor(s) were identified. plicated process of finding and selecting an unrelated donor This figure is much higher than is reported in the literature. and obtaining, transporting and transplanting the bone marect 11 One reason may be that we, whenever possible, sel- row, intensive interaction between the registry staff, the donors beforehand who are also identical for HLA-C immunogeneticist, immunologist and clinician is essen- and -DQ. Testing for DRB3,4 or 5 did not change the num- tial. 32 It is only in this way that the patient can be optimally bers while DPB1 was only matched in 28% of the patients helped and that opportunities such as finding a suitable who were HLA-A,-B,-DRB1/3/4/5,-DQB1 identical. This family donor outside the core family through an extended figure is higher than reported elsewhere, 9,12,33 possibly family search are not missed. because of a larger number of donors tested per patient by us (mean 6.7). These figures were reduced markedly for donors with either an HLA-A or -B locus mismatch. In this Acknowledgements situation only 50% of patients had at least one HLA-A or -B, -DRB1/3/4/5, -DQB1 identical donor and 9% of these This work has been supported in part by the Immunology Workwere also DPB1 identical. This is probably a reflection of ing Party from the European Group for Blood and Marrow Trans- linkage disequilibrium. plantation (EBMT) (EC Grant BMHI-CT 94 0300), the JA Cohen We can only speculate why patients with one haplotype Institute for Radiopathology and Radiation Protection (IRS), the Dutch National Reference Centre for Histocompatibility, the in linkage disequilibrium (F) and one haplotype without World Marrow Donor Association, the Nijbakker Morra Foun- (N) appear to do almost equally well in finding a donor as dation, the Roche Diagnostic Systems and Mrs J Baaij. We would patients with two haplotypes in linkage disequilibrium. like to thank Dr A Brand and Professor FHJ Claas for critically Most probably this is due to the fact that the chance of reviewing the manuscript and Professor H Kolb for useful suggesfinding a donor is directly correlated to the product of the tions. frequencies of the two most common haplotypes out of the six possible. If one haplotype is very frequent and the number of donors is large, we can equal the chance to one. In other words, finding a donor with that haplotype is not References restricted. As a result, the frequency of the less frequent 1 Stroncek D. Results of bone marrow transplants from unrelated haplotype is the only limiting factor. The number of haplotypes donors. Transfusion 1992; 32: 180 189. is still very large, but only a square root function of 2 Kernan NA, Bartsch G, Ash RC et al. Analysis of 462 trans- the phenotypes, and apparently does not function as a plantations from unrelated donors facilitated by the National restraint if a large donor pool is available. Marrow Donor Program. New Engl J Med 1993; 328: 595 For 81 patients (34%) no donor was available. Of this 602. 3 Van Rood JJ, van Leeuwen A, van den Tweel JG et al. Typing group, 19 patients originated from Morocco, Turkey or for the MLC determinants and its possible impact on Europ- (former) Dutch colonies. In general, the search outcome for donor. Transplant Proc 1974; VI: 411 415. 26 patients of non-european origin was unsatisfactory as 4 McCullough J, Rogers G, Dahl R et al. Development and expected; only four patients, of whom two were identical operation of a program to obtain volunteer bone marrow twins, were transplanted. This is in accordance with the donors unrelated to the patient. Transfusion 1986; 26: 315 data of Beatty et al 34 and the IMUST study. 8 There is an 323. increase of patients of non-european origin (5% in 1990 to 5 McCullough J, Hansen JA, Perkins HA et al. The NMDP: 16% in 1995) reported to Europdonor and this has an effect how it works, accomplishments to date. Oncology 1989; 3: on the search outcome. The slight decrease of available 63 72. donors in 1995 (72%) compared to 1994 (75%), despite the 6 Cleaver SA. The Anthony Nolan Research Centre. Bone Mar- row Transplant 1993; 11 (Suppl. 1): 38 40. increase of potential donors, is due to the higher percentage 7 Stroncek D, Bartsch G, Perkins HA et al. The National Marof patients of non-european origin. row Donor Program. Transfusion 1993; 33: 567 577. These patients, children in particular, may be better 8 Howard MR, Gore SM, Hows JM et al. A prospective study helped by increasing the availability of cord blood units of factors determining the outcome of unrelated marrow donor from non-european populations. 35,36 searches: report from the International Marrow Unrelated While writing this report we were confronted with the Search and Transplant Study Working Group on behalf of collack of a generally accepted term to indicate the extent to laborating centres. Bone Marrow Transplant 1994; 13: 389 which donor and recipient are matched. This makes it dif- 396. ficult to compare the success rate in locating a matched 9 Anasetti C, Howe C, Petersdorf EW et al. Marrow transplants donor as reported in the different publications. It is often from HLA matched unrelated donors: an NMDP update and the Seattle experience. Bone Marrow Transplant 1994; 13: not clear whether donor and recipient are identical on the 693 695. basis of the serologically defined broad HLA antigens or 10 Ottinger H, Grosse-Wilde M, Schmitz A, Grosse-Wilde H. whether splits were also tested for. The same holds true for Immunogenetic marrow donor search for 1012 patients: a the use of the different DNA-based typing techniques. We retrospective analysis of strategies, outcome and costs. Bone would like to propose that in analogy to the grading of the Marrow Transplant 1994; 14 (Suppl. 4): S34 S38. severity of acute graft-versus-host disease in five classes 37 11 Speiser DE, Tiercy J-M, Rufer N et al. Relation between the

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