Maximizing optimal hematopoietic stem cell donor selection from registries of unrelated adult volunteers

Factors Associated with Opting Out of Donation among Registered Young Unrelated Hematopoietic Stem Cell Donors

Young adults enrolled in hematopoietic stem cell (HSC) donation registries, including the Be The Match registry in the United States, often opt out of the registry when a potential recipient is identified. This results in a limited supply from the most desirable allogeneic source of HSCs used in transplantation to treat serious health conditions. The differences in demographic, psychosocial, registry-related, and donation-related characteristics between those who continue to donation and those who opt out may elucidate the modifiable risk factors for attrition, but these characteristics have not been extensively studied in young donors up to age 30 years. Our goal was to study demographic, psychosocial, registry-related, and donation-related characteristics in a group of young HSC donor registry members who had recently been contacted about a potential recipient, to determine the key characteristics that differ between those who continued toward donation and those who opted out and to examine the extent of these differences. We conducted a cross-sectional survey in a random sample of young (age 18 to 30 years) current and former registry members, stratified by race/ethnicity and sex. Demographic, psychosocial (eg, life goals, HSC allocation mistrust), registry-related (eg context and motive for joining the registry), and donation-related (eg, ambivalence, religious objections to donation, knowledge about donation) characteristics were assessed. Chi-square and 2-sample t tests were used to examine differences between those who continued (CT-C group) and those who opted out (CT-NI group). Hierarchical logistic regression was used to estimate adjusted covariate effects on the odds of opting out. A total of 935 participants were surveyed. Donation-related knowledge was higher in the CT-C group than in the CT-NI group. HSC allocation mistrust, religious objections, and concerns about donation were higher in the CT-NI group. After adjusting for covariates in a logistic regression model, we found that having more intrinsic life goals, having more ambivalence, and talking with registry staff only once/twice were significantly associated with opting out of the registry. Ambivalence had the strongest association with opting out. In contrast, remembering joining the registry, believing that parents would support donation, and having medical concerns were significantly associated with continuing toward donation. This effect of medical concerns on donation was discovered only after adjusting for the related but distinct ambivalence variable, with the remaining effect of medical concerns relating to engagement with the donation process and information-seeking. The model had strong discriminative ability (area under the receiver operating characteristic curve = .92) and classification accuracy (86.6%). Our data indicate that among young adult members of a national HSC donor registry, ambivalence and limited contact with registry staff were more strongly associated with opting out of donation. Medical concerns were associated with continuing toward donation. Further studies are needed to confirm a causal link between medical concerns and continuing to donation among young donors. Our study suggests that these concerns might not be directly related to attrition, whereas other factors (eg, ambivalence, low donation-related knowledge) are associated with attrition and thus should be targeted for attrition reduction strategies.

Hapl-o-Mat: open-source software for HLA haplotype frequency estimation from ambiguous and heterogeneous data

BACKGROUND

Knowledge of HLA haplotypes is helpful in many settings as disease association studies, population genetics, or hematopoietic stem cell transplantation. Regarding the recruitment of unrelated hematopoietic stem cell donors, HLA haplotype frequencies of specific populations are used to optimize both donor searches for individual patients and strategic donor registry planning. However, the estimation of haplotype frequencies from HLA genotyping data is challenged by the large amount of genotype data, the complex HLA nomenclature, and the heterogeneous and ambiguous nature of typing records.

RESULTS

To meet these challenges, we have developed the open-source software Hapl-o-Mat. It estimates haplotype frequencies from population data including an arbitrary number of loci using an expectation-maximization algorithm. Its key features are the processing of different HLA typing resolutions within a given population sample and the handling of ambiguities recorded via multiple allele codes or genotype list strings. Implemented in C++, Hapl-o-Mat facilitates efficient haplotype frequency estimation from large amounts of genotype data. We demonstrate its accuracy and performance on the basis of artificial and real genotype data.

CONCLUSIONS

Hapl-o-Mat is a versatile and efficient software for HLA haplotype frequency estimation. Its capability of processing various forms of HLA genotype data allows for a straightforward haplotype frequency estimation from typing records usually found in stem cell donor registries.

Comparison of high-resolution human leukocyte antigen haplotype frequencies in different ethnic groups: Consequences of sampling fluctuation and haplotype frequency distribution tail truncation

High-resolution haplotype frequency estimations and descriptive metrics are becoming increasingly popular for accurately describing human leukocyte antigen diversity. In this study, we compared sample sets of publically available haplotype frequencies from different populations to characterize the consequences of unequal sample size on haplotype frequency estimation. We found that for low samples sizes (a few thousand), haplotype frequencies were overestimated, affecting all descriptive metrics of the underlying distribution, such as most frequent haplotype, the number of haplotypes, and the mean/median frequency. This overestimation was a result of random sample fluctuation and truncation of the tail end of the frequency distribution that comprises the least frequent haplotypes. Finally, we simulated balanced datasets through resampling and contrasted the disparities of descriptive metrics among equal and unequal datasets. This simulation resulted in the global description of the most frequent human leukocyte antigen haplotypes worldwide.

Fluoxetine reduces murine graft-versus-host disease by induction of T cell immunosuppression

Serotonin reuptake inhibitors (SRIs) are widely used drugs in the treatment of depression and anxiety disorders. Although SRIs are generally regarded as safe drugs with relatively few side effects, literature suggests that high concentrations of SRIs may alter immune function. We investigated whether high-dose treatment with fluoxetine was able to suppress acute graft-versus-host disease (GvHD) in a MHC-matched, minor histocompatibility antigen mismatched murine bone marrow transplantation model. We found that high doses fluoxetine induce a significant reduction of clinical symptoms and increase survival of these animals. The amelioration of clinical GvHD was accompanied by a reduced expansion of alloreactive T cells. We further analyzed the direct in vitro effect of six SRIs on the viability and proliferation of human T cells and found an anti-proliferative and pro-apoptotic effect that was significantly larger in activated than in resting T cells. We discuss these results in the light of potential future exploration of SRIs as a novel class of T cell immunosuppressive drugs.

The role of human leukocyte antigen matching in the development of multiethnic "haplobank" of induced pluripotent stem cell lines

Among the tools of regenerative medicine, induced pluripotent stem cells (iPSCs) are interesting because the donor genotype can be selected. The construction of banks of iPSC cell lines selected from human leukocyte antigen (HLA) homozygous donors has been proposed to be an effective way to match a maximal number of patients receiving cell therapy from iPSC lines. However, what effort would be required to constitute such a bank for a worldwide application has remained unexplored. We developed a probabilistic model to compute the number of donors to screen for constituting banks of best-chosen iPSC lines with homozygous HLA haplotypes (haplobanks) in four ancestry backgrounds. We estimated what percentage of the patients would be provided with single HLA haplotype matched cell lines. Genetic diversity leads to different outcomes for the four sets in all terms. A bank comprising iPSC lines representing the 20 most frequent haplotypes in each population would request quite different number of donors to screen, between 26,000 for European Americans and 110,000 for African Americans. It would also match different fractions of the recipient population, namely, more than 50% of the European Americans and 22% of African Americans. Conversely, a bank comprising the 100 iPSC lines with the most frequent HLA in each population would leave out only 22% of the European Americans, but 37% of the Asians, 48% of the Hispanics, and 55% of the African Americans. The constitution of a haplobank of iPSC lines is achievable through a large-scale concerted worldwide collaboration.

Does high-resolution donor typing of HLA-C or other loci upon registration confer advantages to patients?

Our study compared all requests for confirmatory typing (CT requests) received in our center between May 2007 and December 2009 (n = 134) for donors issued from 3 groups defined by different human leukocyte antigen (HLA) loci typed at different levels of resolution. We observed a significant advantage for volunteers when HLA-C 2-digit typing was available or with HLA-A, -B, -C, -DRB1 4-digit typing compared with generic HLA-A, -B, -DRB1, -DQB1 DNA typing: increased percentage of CT requests (p < 0.001), increased rate of donor selection for donation (p < 0.001), and decreased time frame for donor search (p = 0.025). The time frame for a successful search (donation) is similar among the 3 groups, indicating that the search might be concluded more rapidly when the pathology is clinically active or when the patient is at a high risk of relapse (76% of our cases) or for pediatric patients (24% of our cases), regardless of HLA typing resolution. Improvement of HLA typing for volunteers could be a great advantage for first selection in the absence of emergency or high-risk disease. Knowledge of HLA-C should be used to prioritize the selection of donors for further testing and could allow a better donor selection process, reducing search duration and increasing efficiency. In most cases, 2-digit typing for HLA-C associated with specific tools to estimate the probability of finding a matched donor could be sufficient.

Umbilical cord blood transplantation for thalassemia major

Hematopoietic cell transplantation is curative therapy for thalassemia major. Although the clinical application of hematopoietic cell transplantation has relied on marrow collected from related and unrelated donors as the primary source of donor hematopoietic cells, umbilical cord blood (UCB) is an alternative source of hematopoietic cells and represents a suitable allogeneic donor pool in the event that a marrow donor is not available. Progress in developing UCB transplantation for thalassemia is reviewed and the most likely areas of future clinical investigation are discussed.

Analysis of high-resolution HLA-A, -B, -Cw, -DRB1, and -DQB1 alleles and haplotypes in 718 Chinese marrow donors based on donor-recipient confirmatory typings

High-resolution human leucocyte antigen (HLA)-A, -B, -Cw, -DRB1, and -DQB1 alleles and haplotype frequencies were analysed from 718 Chinese healthy donors selected from the Chinese Marrow Donor Program registry based on HLA donor-recipient confirmatory typings. A total of 28 HLA-A, 61 HLA-B, 30 HLA-Cw, 40 HLA-DRB1 and 18 HLA-DQB1 alleles were identified, and HLA-A*1101, A*2402, A*0201, B*4001, Cw*0702, Cw*0102, Cw*0304, DRB1*0901, DRB1*1501, DQB1*0301, DQB1*0303 and DQB1*0601 were found with frequencies higher than 10% in this study population. Multiple-locus haplotype analysis by the maximum-likelihood method revealed 45 A-B, 38 Cw-B, 47 B-DRB1, 29 DRB1-DQB1, 24 A-B-DRB1, 38 A-Cw-B, 23 A-Cw-B-DRB1, 33 Cw-B-DRB1-DQB1 and 22 A-Cw-B-DRB1-DQB1 haplotypes with frequencies >0.5%. The most common two-, three-, four- and five-locus haplotypes in this population were: A*0207-B*4601 (7.34%), Cw*0102-B*4601 (8.71%), B*1302-DRB1*0701 (6.19%), DRB1*0901-DQB1*0303 (14.27%), A*3001-B*1302-DRB1*0701 (5.36%), A*0207-Cw*0102-B*4601 (7.06%), A*3001-Cw*0602-B*1302-DRB1*0701 (5.36%), Cw*0602-B*1302-DRB1*0701-DQB1*0202 (6.12%) and A*3001-Cw*0602-B*1302-DRB1*0701-DQB1*0202 (5.29%). Presentation of the high-resolution alleles and haplotypes data at HLA-A, -B, -Cw, -DRB1 and -DQB1 loci will be useful for HLA matching in transplantation as well as for other medical and anthropological applications in the Chinese population.

Prediction of duration and success rate of unrelated hematopoietic stem cell donor searches based on the patient's HLA-DRB1 allele and DRB1-DQB1 haplotype frequencies

Rapid identification of a matched unrelated donor is essential for patients in need of hematopoietic SCT. We carried out a retrospective evaluation of 549 unrelated donor searches (UDSs), which were completed in 2005 for 23 German transplant centers. On the basis of the patient's HLA-DRB1 allele and DRB1-DQB1 haplotype frequencies, UDSs were divided into four groups with different search success probability predictions. For 90.5% of the patients, an acceptable HLA-matched, and for 61.6% an HLA-A-B-Cw-DRB1-DQB1-identical (10/10 matched) unrelated donor was found. The median search duration was 22 days. In the groups with high (n = 318), medium (n = 157), low (n = 56) and very low (n = 18) UDS success probability, an acceptable donor was found for 99.1, 86.6, 75.0 and 22.2% of the patients, and a 10/10-matched donor was found for 78.3, 49.7, 17.9 and 4.5% of the patients, respectively. The median search duration was 20, 27, 45 and 477 days in the groups with high, medium, low and very low probability, respectively. The search success rate and duration can be predicted on the basis of the patient's HLA-DRB1 allele and HLA-DRB1-DQB1 haplotype frequencies. An unrelated donor can be found for most of the patients, even if the indication for transplantation is urgent.

HLA-A, -B, -C, and -DRB1 allele and haplotype frequencies distinguish Eastern European Americans from the general European American population

Sequence-based typing was used to identify human leukocyte antigen (HLA)-A, -B, -C, and -DRB1 alleles from 558 consecutively recruited US volunteers with Eastern European ancestry for an unrelated hematopoietic stem cell registry. Four of 31 HLA-A alleles, 29 HLA-C alleles, 59 HLA-B alleles, and 42 HLA-DRB1 alleles identified (A*0325, B*440204, Cw*0332, and *0732N) are novel. The HLA-A*02010101g allele was observed at a frequency of 0.28. Two-, three-, and four-locus haplotypes were estimated using the expectation-maximization algorithm. The highest frequency extended haplotypes (A*010101g-Cw*070101g-B*0801g-DRB1*0301 and A*03010101g-Cw*0702-B*0702-DRB1*1501) were observed at frequencies of 0.04 and 0.03, respectively. Linkage disequilibrium values (Dij') of the constituent two-locus haplotypes were highly significant for both extended haplotypes (P values were less than 8 x 10(-10)) but were consistently higher for the more frequent haplotype. Balancing selection was inferred to be acting on all the four loci, with the strongest evidence of balancing selection observed for the HLA-C locus. Comparisons of the A-C-B haplotypes and DRB1 frequencies in this population with those for African, European, and western Asian populations showed high degrees of identity with Czech, Polish, and Slovenian populations and significant differences from the general European American population.

Factors that influence Greeks' decision to register as potential bone marrow donors

Hemopoietic stem cells can be used from bone marrow or blood or umbilical cord blood of matched siblings or appropriately matched unrelated volunteers. Today, large bone marrow registries have been established to help identify volunteer unrelated bone marrow donors for patients lacking a family donor. Despite there being almost 10 million registered potential bone marrow donors (PBMD) worldwide, only 50% of white patients have a suitable bone marrow match. Growth in the number of PBMD increases the likelihood of finding a compatible donor for a patient. The attitudes and knowledge of 250 registered PBMD and 315 not registered PBMD toward bone marrow donation, tissues and organs donation, and blood donation were surveyed, using a questionnaire with 27 items. Multivariate logistic regression identified gender (females more often than males), regular blood donation, having a relative or a friend who has already been registered as PBMD, having a relative or a friend who needs bone marrow transplantation, family discussion about tissue and organ donation, knowledge about bone marrow transplantation, information about bone marrow transplantation, and trust in health professionals were independent predictive factors influencing people's decision to register as PBMD. Knowledge of these factors is important to target recruitment efforts.

Comparable outcomes after nonmyeloablative hematopoietic cell transplantation with unrelated and related donors

We sought to determine whether patients with hematologic malignancies treated by nonmyeloablative hematopoietic cell transplantation (HCT) at a single institution between December 1997 and June 2006 had worse outcomes with grafts from unrelated donors (URDs) (n = 184) compared with HLA-identical related donors (n = 221). The nonmyeloablative preparative regimen consisted of 2 Gy of total body irradiation (TBI) with (78%) or without (22%) fludarabine, along with posttransplantation mycophenolate mofetil (MMF) and cyclosporine (CSa). After adjusting for the HCT comorbidity index, relapse risk, patient age, stem cell source, preparative regimen, previous cytomegalovirus (CMV) infection, and sex mismatch of donor and recipient in multivariate analysis, we found no statistically significant differences between unrelated and related HCT recipients in terms of risk of nonrelapse mortality (NRM; hazard ratio [HR] = 0.98; 95% confidence interval = 0.6-1.6; P = .94), relapse (HR = 1.04; 95% confidence interval = 0.7-1.5; P = .82), or overall mortality (HR = 0.99; 95% confidence interval = 0.7-1.4; P = .94). Overall rates of severe acute and extensive chronic graft-versus-host disease (aGVHD, cGVHD) also were not significantly different between the 2 groups. We conclude that within the limitations of a retrospective study, these results indicate that candidates for nonmyeloablative HCT without suitable related donors may expect similar outcomes with grafts from URDs.

CTLA-4 blockade in murine bone marrow chimeras induces a host-derived antileukemic effect without graft-versus-host disease

We studied the effect of CTLA-4 blockade on graft-versus-leukemia and graft-versus-host responses in a mouse model of minor histocompatibility-mismatched bone marrow transplantation. Early CTLA-4 blockade induced acute graft-versus-host disease. Delayed CTLA-4 blockade resulted in a lethal condition with lymphosplenomegaly, but with stable mixed T-cell chimerism, unchanged alloreactive T-cell frequencies and absent anti-host reactivity in vitro. In contrast, multiorgan lymphoproliferative disease with autoimmune hepatitis and circulating anti-DNA auto-antibodies were documented. Splenic lymphocytes exhibited ex vivo spontaneous proliferation and a marked proliferative response against host-type dendritic cells pulsed with syngeneic (host-type) tissue-peptides. Both phenomena were exclusively mediated by host and not donor T cells, supporting an autoimmune pathogenesis. Selectively host-derived T-cell immune reactivity was equally documented against leukemia-peptide-pulsed dendritic cells, and this was paralleled by a strong in vivo antileukemic effect in anti-CTLA-4-treated and subsequently leukemia-challenged chimeras. In conclusion, delayed CTLA-4 blockade induced a host-derived antileukemic effect, occurring in the context of an autoimmune syndrome and strictly separated from graft-versus-host disease. Both antileukemic and autoimmune responses depended on the allogeneic component, as neither effect was seen after syngeneic bone marrow transplantation. Our findings reveal the potential of using CTLA-4 blockade to establish antileukemic effects after allogeneic hematopoietic stem cell transplantation, provided autoimmunity can be controlled.

HLA Haplotypes in Singapore: A Study of Mothers and Their Cord Blood Units

During 2005, a total of 174 cord blood units with their paired maternal samples from the Singapore Cord Blood Bank were typed for HLA-A, -B, -C at intermediate resolution and DRB1 at allelic resolution. Analysis of allele segregation in mother and child assigned 185 different four locus (HLA-A, -B, -C, -DRB1) haplotypes in Chinese, 66 in Malays, and 34 in Asian Indians. Very few four locus haplotypes were shared among population groups. To evaluate the frequencies of four locus haplotypes, the Expectation Maximization algorithm was used with HLA assignments from 536 unrelated Chinese volunteers from the Singapore Bone Marrow Donor Program registry. The paired maternal and cord blood study identified 75 different B-C associations in Chinese, 52 in Malays, and 24 in Asian Indians. Common B-C associations may be shared among population groups; for example, B*4001g-Cw*0702g was common in Chinese and Malays, whereas B*1502g-Cw*0801g and B*3501g-Cw*0401g were found in all three groups. The high diversity of four locus haplotypes originates from multiple combinations of both HLA-A and -DRB1 alleles with each B-C haplotype.

The HLA system: genetics, immunology, clinical testing, and clinical implications

The human major histocompatibility complex HLA is located on the short arm of chromosome 6. It is known to be the most polymorphic genetic system in humans. The biological role of the HLA class I and class II molecules is to present processed peptide antigens. The HLA system is clinically important as transplantation antigens. Molecular HLA allele typing is routinely performed to provide HLA class I and class II allele matching in unrelated donor hematopoietic stem cell transplantation. Prospective lymphocyte crossmatching is critical in solid organ transplantation to prevent allograft rejection. HLA alloimmunization causes various problems in transfusion therapy. The HLA system is associated with certain diseases, but its underlying mechanisms are not yet fully explained.

Haplotype associations of 90 rare alleles from the National Marrow Donor Program

The National Marrow Donor Program maintains an HLA database of over 4.1 million US adult volunteers, 43,000 cord blood units, and 111,000 patients from which we identified 1,999,424 samples having allele-level HLA-A, HLA-B, or HLA-DRB1 results. We analyzed 811 rare alleles reported at a frequency of less than 1 in 50,000 in this study pool and found strong predicted haplotype associations for 90 of them. The data set includes the number of times the allele was seen, the predicted haplotypes, and the racial or ethnic groups in which it was identified. This information can be helpful in designing search strategies for patients with rare alleles requiring hematopoietic stem cell therapy.

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.

Die Bedeutung der Stammzelltherapie in der Hämatologie und Onkologie

The transplantation of hematopoietic stem cells (HSCT) is an established part of the therapy of hematologic neoplasia and certain solid tumors. In the allogeneic approach hematopoietic stem cells are harvested from healthy donors, while in the autologous setting preparations originating from the patient himself are being used. Both therapies use high dose cytotoxic medication for the induction of higher remission rates in malignant diseases. While autologous HSCT rescues hematopoiesis after high dose chemotherapy, in allogeneic HSCT donor immune cells exert an additional allo-reactivity towards recipient tissue and residual malignant cells. Autologous HSCT is mainly used in relapsed malignant high-grade lymphoma. Allogeneic HSCT results in cure from acute leukemia with unfavorable prognosis in a high percentage of patients. Recent developments target the expansion of the donor pool for allogeneic stem cells and want to reduce chemotherapeutic toxicity of allogeneic transplantation with sustained anti-leukemia efficacy.

Ethnic differences in donation-related characteristics among potential hematopoietic stem cell donors

BACKGROUND

Although the National Marrow Donor Program has been highly successful at recruiting ethnic minorities as potential hematopoietic stem cell donors, there have been no systematic investigations of whether donor characteristics that might be linked to the donation experience vary by ethnicity.

METHODS

Questionnaires assessing four domains-demographic, volunteer-related, general psychosocial, and donation-related-were mailed to potential donors after they were contacted as a preliminary match for a patient and had agreed to donate. In all, 1,679 potential donors completed and returned a predonation questionnaire. Data from potential donors belonging to five major ethnic groups were analyzed; white, black, Asian/Pacific Islander, Hispanic, and Native American.

RESULTS

Bivariate analyses indicated that virtually all factors in the four domains were associated with ethnicity. Direct discriminant function analysis identified three significant functions. The most striking of the three functions indicated that Asian Americans were more highly educated, more ambivalent (reluctant about donation), more concerned (medical, work/family), and more anxious and depressed than all other ethnic groups. Key differences among other ethnic group members were also identified.

CONCLUSIONS

This study provides the first evidence of ethnic group differences in key predonation variables. Findings suggest that Asian/Pacific Islanders possess a number of characteristics that are known psychosocial risk factors for less positive postdonation outcomes and that more intensive pre and postdonation contact with this group may be necessary. Strategies for improving future research in this area are discussed.

Microgeographic variation of HLA-A, -B, and -DR haplotype frequencies in Tuscany, Italy: implications for recruitment of bone marrow donors

HLA-A/B haplotype frequencies were estimated in a sample of 2355 bone marrow donors born in a subregion of Tuscany (Italy), and the HLA-A, -B, -DR haplotype frequencies were estimated in a subset of 809 individuals. This area was divided in 10 subsamples (two-locus haplotypes), or six subsamples (three-locus haplotypes), all with sample size >50, based on administrative boundaries. A considerable level of heterogeneity of haplotype frequency was present among subsamples; this heterogeneity was associated to a large variation (up to 4-fold) of the number of new donors that must be typed in order to reach 50% chance of finding an HLA-A, -B phenotype of intermediate frequency. Knowledge of the genetic structure of the population at a microgeographic level may be useful in directing the search of specific bone marrow donors.

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.

HLA class I allele distribution of a Hong Kong Chinese population based on high-resolution PCR-SSOP typing

A stem cell registry population from Hong Kong, of Chinese ethnicity, was examined for HLA-A and HLA-B alleles using a two-stage sequence-specific oligonucleotide probe system. Comparison of the HLA-A and HLA-B frequencies with different populations showed a close relationship with a Chinese population from Singapore, although there were several differences in the presence/absence of alleles at the HLA-B locus. Having the data available on these registry donors will influence the search strategy and the ongoing compilation of new donors to the registry. In addition, knowing which alleles do/do not occur in this population will aid in the distinction of ambiguities which result from the use of many of the typing kits available.

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.

Allogeneic hematopoietic cell transplantation: from experimental biology to clinical care

PURPOSE

For more than half a century, researchers have explored myeloablative, high-dose chemo/radiotherapy followed by allogeneic hematopoietic stem cell transplantation (HCT) for therapy of malignant and nonmalignant hematological diseases. Continuous advances in the field have changed this approach from one that was initially thought to be fraught by insurmountable complications to one that is now considered standard therapy for many diseases.

METHODS

In order to extend allogeneic HCT to include elderly patients, who represent the main population affected by hematological malignancies, and to those who are medically unfit to undergo conventional HCT, novel non-myeloablative approaches have been developed. These approaches rely on graft-vs-tumor effects for tumor eradication rather than high-dose chemoradiotherapy, and, accordingly, have lower toxicities than conventional regimens.

RESULTS

Results with non-myeloablative regimens have been gratifying, and this may change the future of allogeneic HCT. Advances could not have been possible without basic research and studies in pre-clinical animal models.

CONCLUSION

Further work is focused on improving graft-vs-tumor effects while achieving better control of graft-vs-host disease.

Allogeneic hematopoietic cell transplantation as treatment for hematological malignancies: a review

Allogeneic hematopoietic cell transplantation (HCT) was originally developed as a form of rescue from high-dose chemoradiotherapy, which is given both to eradicate malignancy and provide sufficient immunosuppression for allogeneic engraftment. The first attempts of allogeneic HCT in humans met with little success. However, a better understanding of the complexities of the human leukocyte antigen (HLA) system has allowed selecting compatible sibling donors, and the development of postgrafting immunosuppressive regimens has helped prevent serious graft-versus-host disease, thereby changing the role of allogeneic HCT from a desperate therapeutic maneuver to a curative treatment modality for many patients with malignant hematological diseases. In addition, the establishment of large registries of HLA-typed volunteers has permitted finding suitable unrelated donors for many patients without family donors. Further advances in the immunogenetics of HLA, especially typing by molecular techniques, have improved results after unrelated HCT, which have begun resembling those obtained with HLA-identical sibling grafts, at least in young patients. Important advances have also been made in the prevention and treatment of infectious complications and in other areas of supportive care. Since the late seventies, it has been recognized that allogeneic immunocompetent cells transplanted with the stem cells, or arising from them, mediated therapeutic anti-tumor effects independent of the action of the high-dose therapy, termed graft-versus-tumor (GVT) effects. This has prompted the recent development of non-myeloablative conditioning regimens for allogeneic HCT that have opened the way to include elderly patients and those with comorbid conditions. Remaining challenges include further advances in the prevention and treatment of both severe graft-versus-host disease and infections. Also, progress in adoptive transfer of T cells with relative tumor specificity and disease-targeted therapy with agents such as Imatinib, Rituximab or radiolabeled monoclonal antibodies would make allogeneic HCT even more effective.