World Marrow Donor Association guidelines for use of HLA nomenclature and its validation in the data exchange among hematopoietic stem cell donor registries and cord blood banks

Since the advent of the European Marrow Donor Information System in the first half of the last decade, fully automated data exchange between registry computer systems has been playing an ever-increasing role in the international search for unrelated donors of blood progenitor cells. This exchange, however, was hampered by different local conventions used to present HLA data and complicated by the need to extend the official WHO nomenclature to accommodate the registries' information systems and to cross-validate HLA data obtained with different methods and/or at different loci. The guidelines presented here have been developed by the World Marrow Donor Association to standardize the nomenclature to be used and the validation checks to be applied in the international electronic exchange of HLA-typing data among unrelated volunteer hematopoietic stem cell donor registries and umbilical cord blood banks. Two reference web sites have been designated to maintain and update the approved HLA nomenclature and all the ancillary information needed by the conventions described here.

Typing of potential and selected donors for transplant: methodology and resolution

The goal was to establish the best typing techniques and strategies for donors selected as potential donors for a specific patient. Complete sequence of exons 2 and 3 for class I and exon 2 for class II molecules by sequencing-based typing was deemed the best technique in reducing problems with ambiguities and null alleles as well as the possibility to establish a completely automated system. Focusing on multiple approaches for typing was regarded as a better strategy than continued usage of serological methods although the latter technique was still considered to be useful by some for detection of null alleles. The patient and finally the selected donor, including the back-up donor, should be typed for at the highest level and typing ambiguities should be resolved. In very difficult cases, race, haplotype information and allele frequency in the population should help to decide whether or not to resolve the ambiguity. Cellular techniques such as the cytotoxic T lymphocyte precursor test may help to choose between single class I mismatched donors in experienced laboratories only.

KIR ligands and prediction of relapse after unrelated donor hematopoietic cell transplantation for hematologic malignancy

Recurrent malignancy remains a significant complication after allogeneic hematopoietic cell transplantation (HCT). Efforts to decrease relapse have included donor lymphocyte infusion to stimulate donor anti-recipient T-cell allorecognition of major and minor histocompatibility differences. Recently, alloreactive effects of donor natural killer cell-mediated inhibitory killer immunoglobulin-like receptor (KIR) recognition of recipient HLA-C and -B ligands have been described. We examined KIR ligand effects on risk of relapse in 1770 patients undergoing myeloablative T-replete HCT from HLA-matched or -mismatched unrelated donors for the treatment of myeloid and lymphoid leukemias. KIR ligands defined by HLA-B and -C genotypes were used to determine donor-recipient ligand incompatibility or recipient lack of KIR ligand. Among HLA-mismatched transplantations, recipient homozygosity for HLA-B or -C KIR epitopes predicted lack of KIR ligand and was associated with a decreased hazard of relapse (hazard ratio, 0.61; 95% confidence interval, .043-0.85; P = .004). Absence of HLA-C group 2 or HLA-Bw4 KIR ligands was associated with lower hazards of relapse (hazard ratio, 0.47; 95% confidence interval, 0.28-0.79, P = .004; hazard ratio, 0.56; 95% confidence interval, 0.33-0.97; P = .04, respectively). The decrease in hazard of relapse in patients with acute myelogenous leukemia was similar to that in patients with chronic myelogenous leukemia and acute lymphoblastic leukemia (P = .95). Recipient homozygosity for HLA-B or -C epitopes that define KIR ligands is likely to be a predictive factor for leukemia relapse after myeloablative HCT from HLA-mismatched unrelated donors. This effect was not observed in HLA-identical unrelated transplants.

Outcomes after myeloablative unrelated donor stem cell transplantation using both in vitro and in vivo T-cell depletion with alemtuzumab

HLA-matched unrelated donor (MUD) stem cell transplantation (MUD) is complicated by a high incidence of graft-versus-host-disease (GVHD) resulting in significant morbidity and mortality. To circumvent this problem we included alemtuzumab for in vivo and in vitro T-cell depletion in a myeloablative MUD-SCT regimen. After SCT, no severe acute GVHD was observed in the 30 transplanted patients. Donor lymphocyte infusion administered at a later time point resulted in sustained anti-tumor responses in most patients with chronic myeloid leukemia. After donor lymphocyte infusion three patients developed severe acute GVHD. Due to good responsiveness to immunosuppressive therapy only two patients developed persistent chronic GVHD. The main advantage of the transplantation regimen including alemtuzumab is that not only mortality due to GVHD is limited but also extensive chronic GVHD, which potentially leads to chronic morbidity and diminished quality of life, is hardly observed.

The Effect of KIR Ligand Incompatibility on the Outcome of Unrelated Donor Transplantation: A Report from the Center for International Blood and Marrow Transplant Research, the European Blood and Marrow Transplant Registry, and the Dutch Registry

Matching for HLA class I alleles, including HLA-C, is an important criterion for outcome of unrelated donor transplantation. However, haplotype-mismatched transplantations for myeloid malignancies, mismatched for killer immunoglobulin-like receptor (KIR) ligands in the graft-versus-host (GVH) direction, is associated with lower rates of graft-versus-host disease (GVHD), relapse, and mortality. This study investigated the effect of KIR ligand mismatching on the outcome of unrelated donor transplantation. The outcomes after 1571 unrelated donor transplantations for myeloid malignancies where donor-recipient pairs were HLA-A, -B, -C, and -DRB1 matched (n = 1004), GVH KIR ligand-mismatched (n = 137), host-versus-graft (HVG) KIR ligand-mismatched (n = 170), and HLA-B and/or -C-mismatched but KIR ligand-matched (n = 260) were compared using Cox regression models. Treatment-related mortality (TRM), treatment failure, and overall mortality were lowest after matched transplantations. Patients who received grafts from donors mismatched at the KIR ligand in the GVH or HVG direction and mismatched at HLA-B and/or C but matched at the KIR ligand had similar rates of TRM, treatment failure, and overall mortality. There were no differences in leukemia recurrence between the 4 groups. These results do not support the choice of an unrelated donor on the basis of KIR ligand mismatch determined from HLA typing.

Hematopoietic Stem Cell Donor Selection: the Europdonor Experience

International collaboration is essential for the optimal selection of unrelated hematopoietic stem cell donors. This review focuses on the benefit of a joint worldwide donor file called Bone Marrow Donors Worldwide and the experience of the Europdonor Foundation in selecting strategies to identify the best human leukocyte antigen-matched donor in the shortest time.

Differential Immunogenicity of HLA Class I Alloantigens for the Humoral versus the Cellular Immune Response: “Towards Tailor-Made HLA Mismatching”

The immunogenicity of an individual human leukocyte antigen (HLA) class I mismatch is different for the cellular and the humoral alloimmune responses. The consequence is that the same antigen can induce a strong antibody response and no cytotoxic T lymphocyte reactivity, but the reverse can occur also. Exact knowledge of the immunogenicity of an HLA mismatch for an individual patient can lead to a strategy of tailor-made HLA mismatching if no HLA identical donor is available. Depending on the clinical situation, one should select a donor with HLA mismatches according to the humoral or cellular mismatch algorithm.

Allogeneic MHC Class I Molecules With Numerous Sequence Differences Do Not Elicit a CTL Response

CD8+ T cell-mediated alloreactivity is generally believed to involve recognition of the alpha1/alpha2 domains of donor-type class I MHC molecules as well as the peptides they bind. Using the CTLp assay outcome as a parameter for the induction of alloreactivity, we have retrospectively surveyed 80 haematopoietic stem cell donor/patient pairs that feature a range of allelic differences at single HLA-A, -B, and -C loci in an attempt to probe the predictive value of such mismatches. In contrast to the expectation that greater degree of allelic disparity would lead to more alloreactivity, we found that in a substantial number of cases, class I MHC molecules with numerous sequence differences did not elicit an allogeneic CTL response. We propose that in generating a T cell repertoire with a sufficiently narrow responsive for self-MHC, positive thymic selection limits the capacity to recognize allogeneic MHC molecules whose structure and sequence have diverged extensively. These findings are important for donor and patient MHC matching strategies and our understanding of T cell-MHC interaction after haematopoietic stem cell transplantation.

Role of NK cells in mismatched unrelated haematopoietic stem-cell transplantation: fact or fiction?

The role of alloreactive NK cells in haematopoietic stem-cell transplantation is a controversial topic. Different studies come up with different conclusions. This is mainly due to heterogeneous patient populations, differences in the sources of haematopoietic stem cells and various conditioning regimens. International collaboration is essential to reveal in which situation NK cell alloreactivity plays a role and, if so, whether it is beneficial or detrimental for patient survival.

Differential immunogenicity of HLA mismatches in clinical transplantation

Although HLA matching is beneficial in clinical transplantation, it is not feasible to select a completely HLA matched donor for every potential recipient because of the enormous polymorphism of the HLA system. As a consequence, the majority of the recipients will be transplanted with a mismatched donor organ or hematopoietic stem cell transplant. For this large group of patients it is important to take advantage of the differential immunogenicity of HLA mismatches and to select for them a donor with HLA mismatches of low immunogenicity, the so-called acceptable mismatches. The differential immunogenicity of HLA mismatches can be determined by either retrospective analysis of graft survival data or by in vitro assays measuring T-cell and B-cell alloreactivity. A recently developed computer algorithm (HLAMatchmaker) can be instrumental in selecting donors with HLA mismatches, which do not lead to alloantibody formation. The theoretical background and practical implications of this acceptable mismatch approach are discussed.

Isolated HLA-C mismatches in unrelated donor transplantation for CML

HLA-incompatibility is a major factor associated with outcome of allogeneic stem cell transplantation, but little is known on the impact of isolated HLA-C mismatches. We analyzed the outcome of 114 CML patients transplanted with marrow from unrelated donors of whom 24 were mismatched for HLA-C only (9/10 match). Univariate estimates of 5-year survival (SRV) (median follow-up: 47 months) in the HLA-matched group were 68+/-12 vs 42+/-20% (P=0.03) for the patients mismatched for HLA-C only and 33+/-33% in the mismatched group (non-HLA-C single mismatches and multiple mismatches) (P=0.0004). Disease stage, GVHD-prophylaxis (T-cell depletion), CMV-status and HLA-incompatibility were the risk factors associated (all P< or =0.005) with poor outcome. In the multivariate analysis, patients mismatched for loci other than HLA-C were at high risk of an adverse outcome (death: RR, 2.9; CI, 1.6-5.4, P=0.008, transplant-related mortality (TRM): RR, 3; CI, 1.5-5.9, P=0.0015). For patients mismatched for HLA-C only, the increased risk was of borderline significance (death: RR, 1.9; CI, 1-3.9, P=0.06, TRM: RR, 2.1; CI, 1-4.5, P=0.07). In spite of their lower expression, HLA-C antigens still represent relevant transplantation barriers that should be considered when searching for an unrelated donor.

How to improve the search for an unrelated haematopoietic stem cell donor. Faster is better than more!

Many patients do not reach haematopoietic stem cell transplantation. Shortage of unrelated donors (UDs) is still seen as the main cause. However, with a worldwide UD pool containing more than 8 million donors, it is possible that other impediments are becoming more important. We analysed 549 UD searches for Dutch patients, performed between 1987 and 2000, in order to find the reasons for failure or success to reach transplantation. Between 1996 and 2000, 59% of the patients of Northwest European origin received a graft from an UD with a median time span of 4.4 months from the start of the search. In all, 11% of the patients lacked a compatible donor, while 30% became medically unfit for transplantation. This is in contrast to the patients of non-Northwest European origin for whom UD shortage is still the most important impediment; only 32% were transplanted while 50% lacked a compatible donor. We conclude that the shortage of donors is no longer the biggest constraint in unrelated stem cell transplantation for patients of Northwest European origin. It may be more effective to optimize the chance on transplantation by making the search process more efficient.

The importance of identifying a back-up donor for unrelated stem cell transplantation

The importance of identifying a back-up donor, once a primary suitable unrelated stem cell donor has been found, is often underestimated. Transplant centres erroneously count on the unrelated volunteer donors to be willing, available and medically fit for actual donation. According to our data, which includes 502 unrelated donor work-up procedures performed for 425 Dutch patients between 1987 and 2002, one of 11 work-ups ended in the primary requested donor failing to donate. Of all donor-related cancellations (N=46), 78% of the procedures were deferred due to medical reasons and 22% due to nonmedical reasons. Most of the donors deferred for medical reasons were female (P=0.005). In 50% of the cases for which a back-up donor was already identified, the patients were transplanted with a delay of less then 2 weeks; when no back-up donor was available, the median delay increased to 18 weeks. We strongly encourage implementing a search for at least one back-up donor in the primary search. Identifying a back-up donor can save precious time and complicated logistic rescheduling.

Towards functional transplant donor matching by measurement of granzyme A and granzyme B production levels

Graft-versus-host disease (GvHD) can be a major complication after allogeneic stem cell transplantation (SCT) especially when donor and recipient are unrelated. The latter serious complication, together with the growing number of available unrelated stem cell donors, demand a simple in vitro assay for functional stem cell donor selection. Activated donor cytotoxic T lymphocytes (CTLs) and natural killer cells produce granzymes (Gr) that are involved in the pathogenesis of GvHD. We measured granzymes A and B (GrA and GrB) production levels in the supernatants of 96 h pretransplant mixed lymphocyte cultures (MLC) of 26 sibling and 31 unrelated patient/donor pairs by enzyme-linked immunosorbent assay (ELISA). In detail, the GrA and GrB production levels from a selected cohort of 37 potential patient/donor pairs were correlated with relative responses (RR) of MLC and with human leukocyte antigen (HLA) class II mismatches and with the development of acute GvHD in a second, consecutive cohort of 20 sibling SCT recipients. In vitro measurement of GrA and GrB production levels significantly correlated with the RR of pretransplant MLC (r=0.492, p< or =0.01 and r=0.853, p< or =0.01, respectively) and increased with the number of HLA class II mismatches between patient and donor. Pretransplant GrA production levels were significantly associated with the in vivo development of acute GvHD grades II-IV in patients transplanted with an HLA-identical sibling donor (p< or =0.001). In conclusion, in vitro GrA and GrB production levels can be measured by a quantitative and sensitive ELISA. This novel and simple method may be used for functional selection of unrelated stem cell donors and for the identification of patients who are at risk for acute GvHD grades II-IV.

HLAMatchmaker Algorithm is not a Suitable Tool to Predict the Alloreactive Cytotoxic T-Lymphocyte Response in vitro

Both donor-specific anti-human leukocyte antigen (HLA) antibodies and cytotoxic T lymphocytes are important mediators of graft rejection. HLAMatchmaker determines the amino acid triplets on antibody-accessible sites of the HLA molecule that are not shared between patient and donor. A previous study showed a strong positive correlation between the number of triplet mismatches and the percentage of individuals producing HLA antibodies. In the present study, we tested whether the number of triplet mismatches is predictive for the cytotoxic T-lymphocyte precursor (CTLp) frequency in vitro. The analysis was performed on 108 HLA-DRB1 and DQB1 identical patient-donor combinations registered by the Europdonor foundation, with a single HLA class I mismatch and in healthy responder-stimulator combinations mismatched for at least one HLA class I antigen. The results show that there is no strong correlation between the number of triplet mismatches and the CTLp frequency. Even in the case of zero triplet mismatches, a high CTLp frequency can be found. This lack of correlation is probably caused by the fact that HLAMatchmaker considers only triplets on antibody-accessible positions, whereas CTLs also recognize other epitopes on the HLA molecule, including the bound peptides.

A special report: suggested procedures for international unrelated donor search from the donor registries and quality assurance working groups of the World Marrow Donor Association (WMDA)

This special report details the World Marrow Donor Association's recommended procedures regarding the international search for an unrelated donor for hematopoietic stem cell transplantation. The responsibilities of the national hubs, transplant center and donor registry staff are outlined for all actions associated with the preliminary search, formal search, donor confirmatory typing and final donor selection.

Five newly identified HLA alleles: A*0310, A*2907, B*4435, Cw*0206, Cw*0506, and confirmation of A*3106, B*3924, Cw*0314, DRB1*0322, and DRB1*1433 alleles

A number of HLA alleles have been newly identified. This concerns HLA-A*0310, A*2907, B*4435, Cw*0206, Cw*0506, of which Cw*0206 was found in three unrelated individuals, all B*4002 positive. Some other alleles are also presented but confirm earlier detected sequences: A*3106, Cw*0314, DRB1*0322, and DRB1*1433. Moreover, we identified B*3924 in a bone marrow transplant recipient and in five of six unrelated stem cell donors, selected for this patient. In all cases, B*3924 was found on a haplotype combining A*0201, B*3924, Cw*0701, and DRB1*1303. The observation of this extended haplotype is of importance for the selection for stem cell transplantation. Cells expressing B*3924 and B*4435 were typed by serology as B39 and B44, respectively. Cells expressing HLA-A*0310 do not express A3 but type as A-Blank.

Hematopoietic stem cell donor registry strategies for assigning search determinants and matching relationships

Registries and cord blood banks around the world collect and store the HLA types of volunteers in order to identify matched unrelated donors for patients requiring hematopoietic stem cell transplantation. This task is complicated by the many formats in which HLA types are provided by the testing laboratories (types obtained by serology vs by DNA-based methods; high vs intermediate vs low resolution) and by the need to identify which of these diverse types are most likely to match the HLA assignments of a searching patient as closely as possible. Conversion of the assignments to 'search determinants' may be included within the algorithm used to select and prioritize a list of potentially suitable donors, either as an aid to matching or as a tool to optimize the performance of comparisons within large data files. The strategies used by registries to create search determinants are described. A set of search determinants, utilized by the National Marrow Donor Program, is provided as an example and is intended to initiate further discussion aimed at understanding the process used by each registry with the possibility of developing a standard process among registries worldwide.

The World Marrow Donor Association (WMDA): its goals and activities

The major goal of the World Marrow Donor Association (WMDA) is to facilitate the transfer of hematopoietic cells for transplantation purposes across international borders. It also has the goal of establishing guidelines on ethical, technical, medical, and financial aspects that concern the donor and donor-cell transfer. It has a Board and five Working Groups, namely the Donor Registry Working Group, the Quality Assurance Group, the Ethic Working Group, the Finance Working Group, and the Clinical Working Group. It has three types of membership, that is, full organizational membership, nonvoting organizational membership, and individual corresponding membership. Current important projects are speeding up the search process, accreditation of registries and collecting information about severe adverse effects in donors.

Are human platelet alloantigens (HPA) minor transplantation antigens in clinical bone marrow transplantation?

The role of human platelet alloantigens (HPA) in clinical bone marrow allotransplantation was investigated. The leading hypothesis was that HPA alloepitopes act as minor histocompatibility antigens and aggravate graft-versus-host disease (GVHD). To exclude the effect of MHC disparity, only HLA identical donor-recipient pairs were entered into the study. The influence of HPA compatibility on overall survival, occurrence of relapses and haematopoietic recovery was also investigated. A total of 223 patients who received a graft from an HLA-identical sibling, genotyped for HPA -1, -2, -3, -4 and -5, were observed over a post-transplant period of 24 months following the protocol recommended by EBMT. The data from patients having received grafts from HPA compatible donors were compared to data from patients having received grafts that were mismatched in HPA allotypes in the GVH direction. Analysis of the incidence of acute and chronic (GVHD), overall survival, relapse incidence, haematopoietic recovery and some other clinical parameters did not reveal any significant difference between the HPA-matched and -mismatched groups of patients, regardless of their age. Our results give no evidence that HPA-1, -2, -3 and -5 alloantigens should be considered minor transplantation antigens in clinical bone marrow transplantation.

Future HLA matching strategies in clinical transplantation

BACKGROUND

HLA matching has shown to be beneficial in clinical transplantation. Due to the enormous polymorphism of the HLA system, however, it is not feasible to select a completely HLA-matched donor for every potential recipient. Only for patients with frequently occurring HLA phenotypes is it realistic to expect a well-matched donor within a reasonable waiting time. The majority of patients will be transplanted with a partially mismatched donor. In order to select the optimal donor for this category of patients, it is important to take advantage of the differential immunogenicity and thus differential importance of mismatched HLA antigens.

METHODS

Based on retrospective analyses of graft survival data and in vitro tests measuring T-cell alloreactivity, the relative importance of different mismatches was evaluated.

RESULTS

It has been possible to define acceptable or permissible mismatches with a low immunogenicity, which are associated with a good graft survival, versus taboo mismatches with a high immunogenicity and a poor graft survival.

CONCLUSIONS

Further developing this new line of permissible versus taboo mismatches, a new strategy will emerge for future HLA matching, which will not only suit a rare number of patients with frequent haplotypes but a great percentage of all patients. This principle of different immunogenicity of different mismatches can not only be applied to T-cell alloreactivity as shown here, but also to B-cell alloreactivity, where a recently developed computer algorithm (HLA matchmaker) can be instrumental in selecting donors with HLA mismatches, which do not lead to alloantibody formation.

[Two brothers with familial hemophagocytic lymphohistiocytosis, treated by transplantation of stem cells from a single unrelated donor]

In two Turkish brothers familial haemophagocytic lymphohistiocytosis (FHLH) was diagnosed at 3 years and 2.5 months, respectively. FHLH is a rare autosomal recessive condition with a typical clinical presentation including prolonged fever, failure to thrive, irritability and hepatosplenomegaly. Laboratory evaluations show cytopenia (at least two out of the three cell lines), hypertriglyceridaemia and hypofibrinogenaemia. A pathognomonic sign is haemophagocytosis in bone marrow or tissue biopsy. Both patients were treated with stem-cell transplants using bone marrow and peripheral blood stem cells, respectively, from one unrelated donor. They showed a good haematological recovery, with minor complications, and at follow-up after one year were free of disease. Immune suppression can induce prolonged remission in FHLH, but cure is only achieved after a successful allogeneic stem-cell transplantation. Without transplantation, the prognosis is very poor.

Cost analysis of HLA-identical sibling and voluntary unrelated allogeneic bone marrow and peripheral blood stem cell transplantation in adults with acute myelocytic leukaemia or acute lymphoblastic leukaemia

Allogeneic stem cell transplantation (SCT) is one of the most expensive medical procedures. However, only a few studies to date have addressed the costs of HLA-identical sibling transplantation and only one study has reported costs of unrelated transplantation. No recent cost analysis with a proper follow-up period and donor identification expenses is available on related or voluntary matched unrelated donor (MUD) SCT for adult AML or ALL. Therefore, we calculated direct medical (hospital) costs based on 97 adults who underwent HLA-identical sibling bone marrow transplantation (BMT) or peripheral blood stem cell transplantation (PBSCT), and patients who received a graft from a MUD between 1994 and 1999. The average costs per transplanted patient were Euro 98,334 (BMT), Euro 151,754 (MUD), and Euro 98,977 (PBSCT), including donor identification expenses, 2 years follow-up and costs of patients who were not transplanted after they had been planned to receive an allograft. The majority of these costs was generated during the hospitalisation for graft infusion. For MUD transplants, nearly one-third of these costs was spent on the search for a suitable donor. For patients who were alive after 2 years, cumulative expenses were calculated to be Euro 103,509 (BMT), Euro 173,587 (MUD), and Euro 105,906 (PBSCT).

Human immunodeficiency virus type 1 replication inhibition by the bidentate iron chelators CP502 and CP511 is caused by proliferation inhibition and the onset of apoptosis

BACKGROUND

The iron chelators deferoxamine (DF) and deferiprone (CP20) have been shown to inhibit human immunodeficiency virus type 1 (HIV-1) replication in human peripheral blood lymphocytes (PBL). The orally active bidentate chelators CP502 and CP511, which also belong to the 3-hydroxypyridin-4-one family, but with higher affinities for iron than CP20, were monitored for their antiviral properties by checking for p24 antigen production and nuclear factor (NF)-kappaB activation, and their ability to induce apoptosis.

MATERIALS AND METHODS

Human PBLs were isolated from HIV-1 seronegative donors and subsequently infected with HIV-1(Ba-L) for 2 h. After 5 days' incubation, HIV-1 replication was monitored by p24 antigen production. Cellular proliferation as well as caspase-3 activity were monitored in uninfected cells after a period of 5 days and after 1 day infection, respectively. NF-kappaB activity was also monitored by electromobility shift assays (EMSA) performed on nuclear extracts of Jurkat cells treated with the different chelators for 4 h.

RESULTS

CP502 and CP511 decrease HIV-1 replication by decreasing cellular proliferation in a similar manner to DF and CP20. CP511 seemed to be more potent than either CP502 or CP20. Due to the reduction in cellular proliferation, there was an increase in caspase-3 activity after 24 h incubation. NF-kappaB activity was not affected by any of the chelators.

CONCLUSIONS

Iron chelators with high affinities for iron, which are under development for the treatment of iron overload, could contribute to the reduction of HIV-1 replication in infected patients by cellular proliferation inhibition rather than by a direct antiviral action.

Functional versus structural matching: can the CTLp test be replaced by HLA allele typing?

Human leukocyte antigen (HLA) incompatibilities are the most important immunological barriers to bone marrow transplant success when using unrelated donors. Until recently, standards for donor selection included serological methods for HLA class I antigens and DNA-based typing for HLA class II alleles. In our center cytotoxic T-lymphocyte precursor (CTLp) assays have been an integrated part of the search selection procedure as well. More recently, DNA-based typing for HLA class I became available. This allowed us to determine the correlation of CTLp frequencies directed against incompatibilities at the HLA-A, -B, and -C locus in 211 donor-recipient pairs. HLA class I incompatibilities are significantly (p < 0.001) associated with high CTLp frequencies. Exceptions did occur, high CTLp frequencies are seen in 14% of the HLA-A, -B, and -C allele matched pairs, whereas in 7% of the pairs mismatched for HLA-A or -B a low CTLp frequency occurred. The successful outcome of transplants performed in the latter cases suggest that the CTLp test can be used as a tool to detect permissible mismatches when no fully matched donor is available. The influence of HLA-C mismatches on the CTLp outcome was less clear. Although in the majority of mismatched pairs (64%) the CTLp frequency was high, in 36% of the pairs the CTLp frequency was low. Analysis of HLA amino acid sequences was performed on the HLA-C allele mismatched group. An amino acid difference was always found at five polymorphic positions 97, 99, 113, 114, and 116 situated at the peptide binding groove in the high CTLp frequency group, whereas in the low CTLp frequency group this was observed in only 9 of 17 combinations (p < 0.001). However, this is mainly due to Cw*0303-0304 mismatches. In conclusion, although there is a highly significant correlation between the outcome of the CTLp frequency test and HLA allele class I typing, exceptions occur. It is unclear whether they are all clinically relevant but they certainly provide additional insight in allograft recognition.

Effect of tolerance to noninherited maternal antigens on the occurrence of graft-versus-host disease after bone marrow transplantation from a parent or an HLA-haploidentical sibling

In haploidentical transplantation, the mismatched haplotype of the donor can originate from either of the parents. We refer to such mismatched haplotypes as noninherited maternal antigens (NIMA haplotype) or noninherited paternal antigens (NIPA haplotype). To determine whether exposure to maternal HLA antigens benefits patients undergoing bone marrow transplantation, we analyzed graft failure and graft-versus-host disease (GVHD) after transplantations from parental or haploidentical sibling donors. We studied 269 patients receiving 1 or 2 HLA-A, -B, -DR antigen-mismatched sibling or parental non-T-cell-depleted bone marrow transplants for acute myelogenous leukemia, acute lymphoblastic leukemia, or chronic myelogenous leukemia between 1985 and 1997 that were reported to the International Bone Marrow Transplant Registry. Included were 121 (45%) NIMA-mismatched and 148 (55%) NIPA-mismatched transplantations. Sixty-three (52%) of the NIMA-mismatched transplants and 69 (47%) of the NIPA-mismatched transplants were from haploidentical sibling donors. Sibling transplantations mismatched for NIMA had similar rates of graft failure but lower rates of acute GVHD (P <.02) than NIPA-mismatched sibling transplantations. In the first 4 months after transplantation, mother-to-child transplantations involved significantly less chronic GVHD than father-to-child transplantations (P <.02). Treatment-related mortality (TRM) was significantly higher after parental transplantations (P =.009 for mother; P =.03 for father) than after haploidentical sibling transplantations mismatched for the NIMA. Non-T-cell-depleted bone marrow transplants donated by haploidentical siblings to recipients mismatched for NIPA and transplants donated by parents caused more acute and chronic GVHD and TRM than transplants donated by haploidentical siblings mismatched for NIMA.

The chemotherapeutic agent bleomycin in a two-drug combination with zidovudine, ritonavir or indinavir synergistically inhibits HIV Type-1 replication in peripheral blood lymphocytes

It has been suggested that the combination of cancer chemotherapy with antiviral therapy is helpful for the containment of lymphomas in HIV-infected patients. Since we have recently shown that the nucleic acid binding chemotherapeutic agent bleomycin in itself has antiviral properties, we looked to see if there was any possible synergy with current anti-HIV agents. Combinations of zidovudine, indinavir or ritonavir with bleomycin, synergistically inhibited HIV-1(AT) replication in stimulated peripheral blood lymphocytes (combination index at 50% virus inhibition was 0.427, 0.604 and 0.535, respectively) and this synergism was not accompanied by any synergistic effects on cytotoxicity. We conclude from these data that further studies to investigate the clinical efficacy of combinations of antiviral and cancer chemotherapeutic agents are warranted in relation to viral load improvement.

Permissible and immunogenic HLA-A mismatches: cytotoxic T-cell precursor frequencies reflect graft survival data

Analysis of the in vivo immunogenicity of single HLA mismatches, in the context of a patient's own human leukocyte antigen (HLA) phenotype, has been used to define permissible and immunogenic HLA mismatches. Kidney graft survival in the case of permissible mismatches was similar to that of completely HLA matched combinations, whereas immunogenic mismatches lead to a significantly poorer graft survival. The present study tested whether such permissible and immunogenic HLA mismatches are reflected in the in vitro cytotoxic T-lymphocyte (CTL) allorepertoire. Limiting dilution experiments were performed to analyze the number of precursor CTL directed against individual HLA class I antigens. In general, the frequency of CTLp directed against permissible HLA-A antigens (n = 70, mean frequency 27 CTLp per million peripheral blood lymphocytes [PBL]) was found to be significantly lower compared with the CTLp directed against immunogenic HLA-A antigens (n = 73, mean frequency 59 CTLp per million PBL). The difference was found both in healthy individuals and a population of renal transplant candidates. These results were confirmed by a retrospective analysis of CTLp frequencies performed between partly mismatched unrelated bone marrow donors and their potential recipients. In conclusion, on the population level the permissible and immunogenic HLA-A mismatches are indeed reflected in the CTL allorepertoire. However, due to the big overlap of the CTLp frequencies in these populations, the permissible or immunogenic nature of a mismatch for a particular patient should be determined on an individual basis.

Three newly identified HLA-B alleles: B*5124, B*5306, B*5307 and confirmation of B*0809 and B*5606

Five HLA-B sequences are described which have been detected as irregular patterns during routine molecular typing. Sequencing of HLA-B exon 2 and 3, both heterozygous and after group specific amplification, revealed three new HLA-B alleles: B*5124, B*5306 and B*5307, whereas the sequences of B*0809 and B*5606 were confirmed. Serological typing showed that B*0809 is expressed as a regular B8, B*5124 as a regular B51, B*5306 as a B51/B53-like variant and B*5606 as a B"blank"-Bw6.

Anti-HIV effect of iron chelators: different mechanisms involved

BACKGROUND

Drugs for the treatment of AIDS have been directed to specific events in the human immunodeficiency virus (HIV-1) life cycle, aimed to stop viral replication by inhibition of reverse transcriptase or protease activity. Studies showing that oxidative stress and iron may be important in the activation of HIV-1 have focused attention on the potential therapeutic use of iron chelators.

OBJECTIVES

The goal of this review is to describe several possibilities as to how iron is involved in the replication of HIV and how iron chelation may interfere in this process.

STUDY DESIGN

First some physico-chemical properties of iron concerning solubility, oxidation-reduction potential, catalysis, and chelation will be discussed. In the second part, the role of iron in various biochemical systems is explained.

RESULTS

Nuclear factor kappa B (NF-kappaB) activation, regulating proviral transcription, can be influenced by iron through the production of reactive oxygen species. A second route by which iron chelation could influence HIV replication, is by inhibition of DNA synthesis through inactivation of iron-dependent ribonucleotide reductase. Another strategy which can be employed in targeting iron chelators against HIV-1, is direct oxidative viral RNA/DNA attack. This could be achieved by bleomycin, a cytostatic agent with the ability to form a complex with DNA and RNA.

CONCLUSION

Chelation may withhold iron from viral metabolism but on the other hand may also favor catalysis of reactive oxygen species directed to viral constituents. In combination with existing antivirals, iron chelation could add to improve the treatment of HIV-disease.

In vitro CTL precursor frequencies do not reflect a beneficial effect of cross-reactive group (CREG) matching

Adjustment of histocompatibility-based allocation criteria in kidney transplantation from HLA matching to matching on the basis of cross-reactive groups (CREG), was recently suggested to be a good alternative to transplant with more "well-matched" kidneys, without negatively influencing graft survival. Because graft rejection is often mediated by cytotoxic T cells (CTLs), we investigated whether a beneficial effect of CREG matching is reflected in vitro by lower CTL precursor frequencies (CTLpf). Therefore, CTLpf were determined in a group of healthy individuals and analyzed with respect to the number of HLA and CREG mismatches. A clear correlation was found between the number of HLA mismatches and the CTLpf, that is, the lowest mean frequency in case of 0 HLA-A, B mismatches (66 CTL precursors per 10(6) cells) and the highest in combinations with 4 HLA mismatches (mean = 303 CTLp/10(6) cells). The situation was different in the case of CREG mismatches. Although the highest frequency was found in the group of 4 CREG mismatches, no significant differences were observed between 0, 1, and 2 CREG mismatches. High CTLpf, up to 430/10(6), were even seen in the case of 0 CREG mismatches. Also within a well-defined group of single HLA-A or HLA-B mismatches no difference in CTLpf were observed between the subgroups with 0 vs. 1 CREG mismatches. The present study showed that in vitro the CTLpf correlates better with HLA than with CREG matching. These data are consistent with findings reported by several groups that matching for the CREG does not benefit transplant outcome.

Cross-reactive group matching does not lead to a better allocation and survival of donor kidneys

BACKGROUND

In cadaveric renal transplantation HLA-A, -B, -DR matching of donor and recipient is beneficial for graft survival. However, allocation based on HLA matching seems to favor recipients with more frequently occurring HLA antigens. In this study we investigated whether matching on the basis of cross-reactive groups (CREGs), defined according to the United Network for Organ Sharing (UNOS), would be a good alternative for the allocation of kidneys without negatively influencing graft survival. Theoretically, this approach would provide more recipients with an immunologically well-matched donor organ.

METHODS

The influence of CREG matching on graft survival was studied in univariate analyses using the Eurotransplant database.

RESULTS

No beneficial effect of CREG matching was observed, whereas a significant HLA matching effect was observed in the 0 CREG mismatched donor/ recipient combinations. Only in the small subgroup with 1 MM for HLA-A, -B and 0 MM for HLA-DR, a significantly better survival was observed, when this mismatch belonged to the 0 or 1 MM CREG group versus two or more MM CREG group. However, this subgroup concerns only 8% of the transplants performed.

CONCLUSIONS

In contrast to other reports, our study showed that HLA matching is by far more beneficial than CREG matching. In the homogenous Eurotransplant population, adjusting the matching criteria toward CREG matching would not lead to an improved graft survival.

HLA-DR4 is associated with a diminished risk of the development of chronic myeloid leukemia (CML). Chronic Leukemia Working Party of the European Blood and Marrow Transplant Registry

CML is characterized by the chromosomal translocation t(9;22) (q34;q11) resulting in the chimeric bcr-abl oncogene that encodes P210 fusion proteins with novel amino acid sequences in the breakpoint region. If these peptides derived from P210 are presented by HLA molecules on the cell membrane of leukemic cells an immunological response may occur. Recent studies using synthetic peptides identical to the bcr-abl fusion region revealed that some peptides are capable of binding to the class I molecules HLA-A2,-A3,-A11 and -B8 and the class II molecules HLA-DR1, -DR2, -DR3, -DR4 and -DR11. Moreover T cell responses have been induced against bcr-abl-derived synthetic peptides bound to some of these HLA molecules. For HLA class I, we have previously shown that individuals expressing HLA-A3 and -B8 have a diminished risk of development of CML. To assess a similar protective effect of class II molecules we performed a large multi-center study. This study compared the frequencies of HLA-DR1, -DR2, -DR3, -DR4 and -DR11 of patients with CML from the database of the EBMT (n = 1462) with unaffected individuals from the registry of Bone Marrow Donors Worldwide (n = 500 596). Patients and controls were matched per country. This analysis yielded significantly lower odds ratios (ORs) of 0.86 (95% CI 0.75-0.98) for HLA-DR3 and of 0.80 (95% CI 0.71-0.89) for HLA-DR4. The OR was 0.91 (95% CI 0.80-1.04) for HLA-DR1, 1.05 (95% CI 0.94-1.18) for HLA-DR2 and 0.87 (95% CI 0.74-1.01) for HLA-DR11. To assess a possible effect of the linkage disequilibrium between HLA-B8 and HLA-DR3 we found that coexpression of HLA-B8 and HLA-DR3 gave an OR of 0.84 (95% CI 0.72-0.98), whereas HLA-DR3 positive/HLA-B8 negative individuals showed an OR of 1.02 (95% CI 0.84-1.24). This means that the protective effect of HLA-DR3 of the development of CML was probably caused by its linkage disequilibrium with HLA-B8. In contrast, as there is no linkage disequilibrium of HLA-DR4 with HLA-A3 or HLA-B8, the results indicate that HLA-DR4 expression itself is associated with a diminished incidence of CML possibly by the presentation of bcr-abl breakpoint peptides in these HLA molecules on the membrane of the leukemic cells.

Inhibition of human immunodeficiency virus type 1 replication in human mononuclear blood cells by the iron chelators deferoxamine, deferiprone, and bleomycin

Replication of human immunodeficiency virus type 1 (HIV-1) can be influenced by iron. Hence, decreasing the availability of iron may inhibit HIV-1 replication. Deferoxamine and deferiprone, both forming catalytically inactive iron-chelator complexes, and bleomycin, by use of which iron catalyzes oxidative nucleic acid destruction, were investigated. Expression of p24 antigen in human monocyte-derived macrophages and peripheral blood lymphocytes (PBL) was reduced by all 3 iron chelators. In PBL, p24 reduction was mirrored by a decrease in proliferation after incubation with deferoxamine or deferiprone, suggesting that viral inhibition is closely linked to a decrease in cellular proliferation. In contrast, clinically relevant bleomycin concentrations reduced p24 levels by approximately 50% without affecting proliferation. When deferoxamine and the nucleoside analogue dideoxyinosine were used in combination, they acted synergistically in inhibiting HIV-1 replication. These observations suggest that iron chelators with different mechanisms of action could be of additional benefit in antiretroviral combination therapy.

Histocompatibility testing guidelines for hematopoietic stem cell transplantation using volunteer donors: report from The World Marrow Donor Association. Quality Assurance and Donor Registries Working Groups of the World Marrow Donor Association

The World Marrow Donor Association has formulated guidelines for establishing the extent and quality of histocompatibility testing for unrelated donor registries, umbilical cord blood banks, and transplant centers involved in international exchange of hematopoietic stem cells for allogeneic transplantation. The ability to identify unrelated stem cell donors in one country for patients in another country requires cooperation and standardization in many areas. The adoption of guidelines for histocompatibility testing, such as those summarized in this report, will facilitate these opportunities and rapidly provide accurately typed donors for patients in need.

HLA-B8 and HLA-A3 coexpressed with HLA-B8 are associated with a reduced risk of the development of chronic myeloid leukemia. The Chronic Leukemia Working Party of the EBMT

Chronic myeloid leukemia (CML) is characterized by the chromosomal translocation t(9;22) resulting in the chimeric bcr-abl oncogene that encodes the P210 fusion protein, which contains a unique amino acid sequence. If peptides derived from the leukemia-specific part of P210 are expressed in HLA molecules on the cell membrane of leukemic cells, an immunological response may occur. Recent studies using synthetic peptides identical to the bcr-abl fusion region showed that some peptides are capable of binding to HLA-A3, -A11, and -B8 molecules. Cytotoxic T-cell responses have been induced against bcr-abl-derived synthetic peptides bound to HLA-A3 and -B8. We hypothesized that if antigen processing of the P210 fusion protein leads to presentation of peptides from the fusion region by major histocompatibility complex (MHC) molecules in vivo, this may be reflected in a diminished incidence of CML in individuals expressing HLA-A3, -A11, or -B8. Consequently, lower frequencies of these antigens would be expected in patients with CML compared with unaffected individuals. A case-control study and a meta-analysis were performed to test this hypothesis. The multicenter case-control study compared patients with CML from the data base of the European Group for Blood and Marrow Transplantation (EBMT) with unaffected individuals from the registry of Bone Marrow Donors Worldwide. Patients and controls were matched per country. The meta-analysis consisted of five studies reported in the literature. The multicenter case-control study consisting of 1,899 patients and 512, 363 bone marrow donors as controls yielded odds ratios (ORs) of 0.90 (95% confidence interval [CI], 0.80 to 1.00) for HLA-A3, 1.16 (95% CI, 1.02 to 1.33) for HLA-A11, and an OR of 0.73 (95% CI, 0.65 to 0. 82) for HLA-B8. Coexpression of HLA-A3 and HLA-B8 gave an OR of 0.51 (95% CI, 0.40 to 0.67). This can be translated in a protective effect of 27% for HLA-B8, 10% for HLA-A3, and 49% protection for the combination of HLA-A3 and HLA-B8. The meta-analysis comprising 463 CML patients and 4,912 controls showed a 29% risk reduction for individuals expressing HLA-B8 (OR of 0.71; 95% CI, 0.52 to 0.97), but an OR of 1.19 (95% CI, 0.90 to 1.56) for HLA-A3 and an OR of 1. 09 (95% CI, 0.80 to 1.50) for HLA-A11. In conclusion, these results indicate that HLA-B8 expression, in particular when HLA-A3 is coexpressed, is associated with a diminished incidence of CML. A biological mechanism may be that presentation of bcr-abl breakpoint peptides in these HLA molecules can induce a protective immune response.

Canine mammary growth hormone gene transcription initiates at the pituitary-specific start site in the absence of Pit-1

Growth hormone (GH) gene expression has been reported in the mammary glands of various mammalian species. The mechanism by which the GH gene becomes activated in extrapituitary tissues is currently unclear. We have characterized the canine mammary and pituitary GH gene transcripts by Northern blot, 5'- and 3'-RACE (rapid amplification of cDNA ends), and DNA sequence analysis. Northern blot analysis detected GH gene transcripts in mammary glands of dogs which were exposed to high levels of progestins. The mammary and pituitary GH cDNAs were shown to be identical in both the coding region and untranslated regions. Pituitary GH gene expression is highly dependent upon the transcription factor Pit-1. Analysis of Pit-1 gene expression using RT-PCR followed by Southern hybridization revealed a strong pituitary signal but faint, weak or no hybridization signals in mammary gland samples. Among the negative samples were progestin-treated dogs with high mammary GH gene expression. These findings indicate that mammary and pituitary GH gene transcripts originate from the same transcription start site but are regulated differentially.

A special report: histocompatibility testing guidelines for hematopoietic stem cell transplantation using volunteer donors

The World Marrow Donor Association has formulated guidelines for establishing the extent and quality of histocompatibility testing for unrelated donor registries, umbilical cord blood banks, and transplant centers involved in international exchange of hematopoietic stem cells for allogeneic transplantation. Registry and cord blood bank guidelines suggest that, at a minimum, initial HLA typing should be performed for three HLA loci, HLA-A, -B, and -DR, at low resolution/split antigen level. DNA-based testing methods should be utilized for HLA-DR typing. DNA-based testing for HLA-A and -B should replace serologic testing of new volunteer donors and cord blood units as robust protocols and reagents become available to the laboratories. Transplant center guidelines for typing of patient, family and to confirm the HLA types of potential unrelated donors should include, at the minimum, typing HLA-A, B, and -DR loci using primarily DNA-based testing methods at allele level resolution for DRB1 and low resolution/ split antigen level for HLA-A and -B. It is strongly recommended that the typing of a patient and the selected donor be performed using the same set of reagents, methodology, and interpretation criteria with fresh tissue samples to ensure HLA identity. Guidelines for laboratory accreditation, approaches to quality assurance and quality control for HLA testing, and suggestions for the format of the HLA database of donor types are also outlined.

A special report: histocompatibility testing guidelines for hematopoietic stem cell transplantation using volunteer donors. Quality Assurance and Donor Registries Working Groups of the World Marrow Donor Association

The World Marrow Donor Association has formulated guidelines for establishing the extent and quality of histocompatibility testing for unrelated donor registries, umbilical cord blood banks, and transplant centers involved in international exchange of hematopoietic stem cells for allogeneic transplantation. Registry and cord blood bank guidelines suggest that, at a minimum, initial HLA typing should be performed for three HLA loci, HLA-A, -B, and -DR, at low resolution/split antigen level. DNA-based testing methods should be utilized for HLA-DR typing. DNA-based testing for HLA-A and -B should replace serologic testing of new volunteer donors and cord blood units as robust protocols and reagents become available to the laboratories. Transplant center guidelines for typing of patient, family and to confirm the HLA types of potential unrelated donors should include, at the minimum, typing HLA-A, B, and -DR loci using primarily DNA-based testing methods at allele level resolution for DRB1 and low resolution/split antigen level for HLA-A and -B. It is strongly recommended that the typing of a patient and the selected donor be performed using the same set of reagents, methodology, and interpretation criteria with fresh tissue samples to ensure HLA identity. Guidelines for laboratory accreditation, approaches to quality assurance and quality control for HLA testing, and suggestions for the format of the HLA database of donor types are also outlined.

Validation of haplotype frequency estimation methods

In order to investigate the performance of haplotype frequency estimation methods using unrelated individuals, we compared the results of three estimation methods with those from the haplotypes deduced from family pedigrees. To that end we used the HLA phenotypes of the parents of 1040 families as data for the estimation methods and the full pedigree information as data for the deductive method. We evaluated the results of the following estimation methods: the method using two by two tables described by Mattiuz et al., the maximum likelihood method described by Yasuda and Tsuji and a crude method that uses the information on homozygosity in the phenotypes. All estimation methods generate reliable haplotype frequencies for the more frequent haplotypes, but are unreliable for the less frequent haplotypes. The maximum likelihood estimation method shows the best overall correlation with the results of the deductive method.

Bone Marrow Donors Worldwide and cord blood stem cell transplantation

Stem cell transplantation using cord blood donors mismatched for one or two HLA antigens can be successful. A simulation study was performed to assess the percentage of patients for whom a matched and/or a one or two antigen mismatched donor is available. Using either bone marrow donors worldwide (BMDW) (n = 925109) or the cord blood donor file in BMDW (n = 11049). As a donor source, for 97% of the Dutch patients a 0 or 1 antigen mismatched cord blood donor was available, for patients from the minority groups this percentage was 55%. These percentages compare favourably with the fraction of 0 mismatched donors found in BMDW.

An HLA matched donor! An HLA matched donor? What do you mean by: HLA matched donor?

The term 'an HLA matched donor' is in general used without giving exact information on the level of resolution of the HLA typing. This can lead to misunderstandings. A proposal is formulated to agree on using six match categories according to the HLA typing technique used to indicate the level of confidence of the matching.

D6STNFa microsatellite locus correlates with CTLp frequency in unrelated bone marrow donor-recipient pairs

The use of unrelated donors for bone marrow transplantation is associated with an increased morbidity and mortality when compared with HLA identical siblings, primarily due to an increased rate of graft-versus-host-disease. HLA matching for donors and recipients is the most important factor influencing the outcome of BMT. However, unrelated donor selection generally relies on matching only for HLA antigens without considering potential incompatibility for other MHC loci. Cellular assays have been developed to predict incompatibility that cannot be detected by current typing methods. The CTLp frequencies correlate with the degree of incompatibility of patient/donor and the clinical grade of GVHD. Since the CTLp assay is expensive and time consuming, an alternative is wanted. We studied the means of matching for microsatellites in determining MHC identity and possible correlation with CTLp frequencies. Therefore, 26 recipient/donor pairs were analysed for eleven microsatellite loci within and around the MHC region. Our study provides evidence that the D6STNFa locus correlates with CTLp frequency. The D6STNFa locus provides an additional marker that may help to improve the matching of unrelated donors and bone marrow recipients.

Unrelated donor bone marrow transplantation in Fanconi anaemia: the Leiden experience

Fanconi anaemia (FA) is an accepted indication for treatment with allogeneic HLA-identical BMT. Most patients, however, lack a suitable HLA-identical donor. In our centre, six FA patients were transplanted with a matched unrelated donor. Due to hypersensitivity to DNA cross-linking agents, a low-dose cyclophosphamide (CY) and thoraco-abdominal irradiation (TAI) regimen is recommended for conditioning in FA. We added Ara-C upfront and anti-T cell antibodies to enhance engraftment and to prevent GVHD, in combination with T cell depletion in four out of six of the first transplants. One patient did not engraft. In three patients rejection was observed. In three of these four patients a second BMT, using full bone marrow grafts, resulted in successful engraftment. The other patient died before a second BMT could be performed. The incidence and severity of acute GVHD was low: only one patient with grade III acute GVHD was seen. Two out of four surviving patients suffered from chronic GVHD. Four patients survived (median survival time 43 months after BMT), three with good and one with acceptable quality of life. Two patients died, one patient due to adenoviral reactivation with multi-organ failure, and one due to sepsis complicated by ARDS. In conclusion, MUD BMT is feasible in FA patients with bone marrow failure in whom no HLA-identical sibling donor is available. In our study group, the major problem was graft rejection, despite the administration of a combination of graft enhancing anti-T cell antibodies. Multicentre studies are needed to determine a more intensive, but still tolerable, conditioning regimen.

The role of different histocompatibility testing methods for selection of related and unrelated bone marrow donors

Bone marrow transplantation has become the treatment of choice for many hematological malignancies. Approximately 30% of the patients lack an HLA-identical sibling donor, for them alternative donors have to be found. The chances of finding an unrelated donor can be estimated by consulting the Bone Marrow Donors Worldwide file and grouping the patients according to whether they have frequent or rare haplotypes. If the HLA-ABDR split antigens are taken into account, for less than 25% of the patients identical donors can be identified. In order to select the best matched donor for a patient, sensitive HLA typing techniques should be employed including DNA typing techniques, but for optimal selection of a suitable donor one should not only study genetics but also determine the immunological repertoire recognizing the histocompatibility differences between donor and recipient. Several promising cellular techniques such as the HTLp and CTLp test have recently become available and should also be used to select the best donor.

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

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 transplantation was about 6 months. The systematic use of Bone Marrow Donors Worldwide (BMDW) which comprises 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 identified. 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 cost-effective 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 transplanted. In summary, of the 240 patients for whom the Europdonor office searched for a donor, about one-third 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.