Effect of HLA mismatches on the outcome of hematopoietic transplants

Eltrombopag for post-transplant cytopenias due to poor graft function

Persistent cytopenia due to poor graft function (PoGF) is a relatively common complication which may affect up to 20% of patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). Treatment options for PoGF remain limited, and reinfusion of additional HSC is often the only way to rescue hematopoiesis. Here we describe a retrospective single-center experience with the thrombopoietin-mimetic agent eltrombopag for the treatment of PoGF. Thirteen patients have received eltrombopag for either PoGF (n = 12) or primary graft failure (n = 1). In the 12 PoGF patients eltrombopag was started at the median time of 79 days after HSCT, due to persistent thrombocytopenia, with concomitant anemia and neutropenia in 7 and 3 patients, respectively. The treatment was started at the dose of 50 mg per day, and eventually increased up to 150 mg in case of lack of response. Hematological response was seen in 7 patients, with 6 complete responses. Hematological responses were seen both in patients with evidence of immune-mediated pathophysiology, and with possible infectious/iatrogenic causes. In responding patients, eltrombopag was discontinued in 6/7 patients without further relapse. These results suggest that eltrombopag is safe and possibly effective in the setting of the treatment of PoGF, and pave the way for future prospective studies.

Hematopoietic Stem Cell Transplantation: A Bioethical Lens

Hematopoietic stem cell transplantation (HSCT) is one of a range of therapeutic options available to patients suffering from various diseases. HSCT procedure involves important ethical and legal aspects that can occur at every phase of the procedure: the clinical choice of whether to perform the procedure, pretransplantation preparation regimens, donor selection, stem cell harvest procedure, transplantation phase, and short-term and long-term follow-up care. In this discussion paper, we outline the ethical issue-facing physicians involved in HSCT. Currently, HSCT is a widely accepted treatment for many life-threatening diseases. It thus represents a real therapeutic hope for many patients. It does, however, carry a burden of possible morbidity and mortality. Consequently, there are substantial information and communication issues involved in the consent process for HSCT. In the final decision, the judgements of different parties, such as patients, family members, and healthcare professionals, intersect and overlap and this is particularly true when the patient is a minor. Finally, HSCT is a very expensive procedure. The social and economic concerns of HSCT are discussed within the actual contextual framework of the dramatic increase in healthcare costs and inequalities in healthcare in relation to socioeconomic status, educational status, and ethnicity.

Relationship between HLA-DRB1 allele polymorphisms and familial aggregations of hepatocellular carcinoma

OBJECTIVE

We explored the relationship between HLA-DRB1 allele polymorphisms and familial aggregation of hepatocellular carcinoma (fhcc).

METHODS

Polymerase chain reaction sequence-specific primers were used to determine HLA-DRB1 genotypes for 130 members of families with 2 or more liver cancer patients and for 130 members of families without any diagnosed cancers. The genotype profiles were then compared to explore the relationship between HLA-DRB1 gene polymorphism and fhcc.

RESULT

Of 11 selected alleles, the frequencies of DRB1*11 and DRB1*12 were significantly lower in the fhcc group than in no-cancer group (p < 0.05; odds ratio: 0.286; 95% confidence interval: 0.091 to 0.901; and odds ratio: 0.493; 95% confidence interval: 0.292 to 0.893). Differences in the frequencies of the other 9 alleles were not statistically significant in the two groups (p > 0.05).

CONCLUSIONS

Our research suggests that if genetic factors play a role in fhcc, the deficiency in the DRB1*11 and DRB1*12 alleles might be the risk factor at work in Guangxi Zhuang Autonomous Region, P.R.C.

Antibody- and aptamer-strategies for GvHD prevention

Prevention of Graft-versus-Host-Disease (GvHD) by preserved Graft-versus-Leukaemia (GvL) effect is one of the major obstacles following allogeneic haematopoietic stem cell transplantation. Currently used drugs are associated with side effects and were not able to separate GvHD from the GvL-effect because of general T-cell suppression. This review focuses on murine models for GvHD and currently available treatment options involving antibodies and applications for the therapeutic use of aptamers as well as strategies for targeting immune responses by allogenic antigens.

The Impact of HLA-C Matching on Donor Identification Rates in a European-Caucasian Population

The degree of HLA concordance with the patient has long been known to be the major donor-related prediction factor for the success of hematopoietic stem cell transplantations and, with the progress of HLA typing technology, selection criteria became more stringent with regard to the recommended loci and resolution. A late refinement was HLA-C matching, which gained broader acceptance only after the turn of the millennium. The enormous HLA polymorphism has always necessitated registries with a large number of donors in order to be able to provide well-matched donors to a substantial fraction of patients. Using a biostatistical approach, we investigated the impact of adding HLA-C at low or high resolution as a supplementary matching criterion on some key parameters in donor provision for a European-Caucasian population. Starting point is donor selection based on allele level matching for HLA-A, -B, -DRB1, and, optionally, HLA-DQB1. Without typing for HLA-C, 68% of the donors selected based on matching for HLA-A, -B, -DRB1, and -DQB1 at high resolution will also match for HLA-C, 29% will have a single and only 3% will have two HLA-C alleles different from the patient. In order to provide the same fraction of patients with a fully matched donor, a registry would have to be about twice the size if HLA-C is considered in addition to the four other loci, with the exact factor increasing with the registry's size. If the provision of donors with up to a single allele mismatch is considered, this factor doubles due to the strong linkage between HLA-B and -C. These figures only change slightly when HLA-DQB1 is completely ignored or HLA-C matching is only considered at low resolution. Our results contribute to quantifying the medical and economic impact of the progress in donor selection algorithms.

Evaluation of 28 Human Embryonic Stem Cell Lines for Use as Unrelated Donors in Stem Cell Therapy: Implications of HLA and ABO Genotypes

For human embryonic stem cells (hESCs) to be used clinically, it is imperative that immune responses evoked by hESCs and their derivates after transplantation should be prevented. Human leukocyte antigens (HLA) and ABO blood group antigens are important histocompatibility factors in graft rejection. HLA matching between recipient and unrelated donors, in particular, is important in improving outcomes in hematopoietic cell transplantation (HCT). We have established and successfully maintained 29 hESC lines and analyzed the HLA and ABO genotypes of these lines. HLA-A, -B, -C and -DR (DRB1) genotyping was performed by polymerase chain reaction (PCR) sequence-based typing and ABO genotyping was carried out by PCR restriction fragment length polymorphism methods. To determine what proportion of the Korean population would be covered by these cell lines in organ transplantation, 27 cell lines with HLA-A, -B, and -DR data were evaluated for HCT (cord blood) donors and 28 cell lines with HLA-DR and ABO data were evaluated for solid organ (kidney) transplantation donors, and then compared the data with those from 6,740 donated cord bloods. When 2 HLA mismatches are allowed for HCT, as currently accepted for cord blood transplantation, it was estimated that about 16% and 25% of the possible recipients can find one or more donor cell lines with ≤2 mismatches at A, B, DRB1 allele level and at A, B antigen/DRB1 allele level, respectively. When HLA-DR antigen level matching and ABO compatibility was considered for solid organ (kidney) transplantation, it was estimated that about 29% and 96% of the possible recipients can find one or more ABO-compatible donor cell lines with 0 and 1 DR mismatches, respectively. We provided the first report on the HLA and ABO genotypes of hESC lines, and estimated the degree of HLA and ABO matching in organ transplantation for the Korean population.

Haploidentical hematopoietic stem cell transplantation in child hematologic malignancies with G-CSF-mobilized marrow grafts without T-cell depletion: a single-center report of 45 cases

In this report, the authors describe a protocol for haploidentical bone marrow transplantation in children who received G-CSF-mobilized bone marrow grafts without T-cell depletion from HLA-mismatched parents. Forty-two of 45 patients achieved complete donor hematopoietic engraftment; the medium time for neutrophil and platelet recovery was 17 and 19 days, respectively. Three died of early transplantation-associated complications; other causes of death included relapse (11 cases), fungal pneumonia (5), and acute graft-versus-host disease (2). The total disease-free survival rate longer than 2 years was 53.3%. These data suggest that haploidentical hematopoietic transplantation is an alterative strategy for children who lack immediate access to HLA-matched sources.

The new HLA-C allele, Cw*0220, shows a new polymorphism at amino acid position 169

The new human leukocyte antigen (HLA)-C allele, Cw*0220, was identified in a Spanish Caucasian patient by sequence-based typing. HLA-Cw*0220 differs from Cw*020202 by a single amino acid replacement at constant position 169 (R > H).

Prevention of Graft-Versus-Host Disease by Intra-Bone Marrow Injection of Donor T Cells

We have recently found that intra-bone marrow-bone marrow transplantation (IBM-BMT) can be used to prevent graft-versus-host disease (GvHD), even when intensive donor lymphocyte infusion (DLI) is carried out. In the present study, in conjunction with IBM-BMT, allogeneic splenic T cells as DLI were also injected into the bone marrow cavity of lethally irradiated (8.5 Gy) recipients. The extent of GvHD was compared with that of recipients that had received allogeneic IBM-BMT plus i.v. injection of allogeneic T cells (intravenous DLI [IV-DLI]). GvHD in recipients treated with allogeneic IBM-BMT plus IBM-DLI was far milder than in those treated with allogeneic IBM-BMT plus IV-DLI. This was confirmed macroscopically and histopathologically. The frequency of regulatory T cells (Tregs) detected as CD4(+)CD25(+) and CD4(+)Foxp3(+) cells was significantly higher in recipients treated with IBM-BMT plus IBM-DLI than in those treated with IBM-BMT plus IV-DLI. Donor-derived helper T (Th) cells polarized to Th2 type in recipients treated with IBM-BMT plus IBM-DLI, whereas Th1 cells were dominant in recipients treated with IBM-BMT plus IV-DLI. Furthermore, the production of transforming growth factor-beta and hepatocyte growth factor from bone marrow stromal cells was enhanced after IBM-DLI. Thus, IBM-BMT plus IBM-DLI seem to preferentially induce Tregs and Th2, resulting in the prevention of GvHD. Disclosure of potential conflicts of interest is found at the end of this article.

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.

A High Degree of HLA Disparity Arises From Limited Allelic Diversity: Analysis of 1775 Unrelated Bone Marrow Transplant Donor-Recipient Pairs

The allelic diversity and associated human leukocyte antigen (HLA) disparity of 1775 bone marrow recipients and their unrelated donors, matched for six of six (1361/1775,77%), five of six (397/1775, 22%), or four of six (17/1775, 1%) HLA-A, -B, -DR antigens, were retrospectively evaluated. The comprehensive HLA analysis included the class I (A, B, C) and II (DRB1, DQA1, DQB1, DPA1, DPB1) loci. Most (>66%) of the predominantly Caucasian study population carried one or two of five to seven common alleles at each HLA locus. In spite of this limited diversity, 29% of the six of six antigen-matched transplants carried allele mismatches at HLA-A, -B, and/or -DRB1, and 92% carried at least one allele mismatch at one of the eight HLA loci tested. Of the 968 HLA-A,-B,-DRB1 allele-matched pairs, 89% carried mismatches at other HLA loci, predominantly at DP loci. The substantially greater than expected HLA allelic disparity between donor and recipient suggests extensive haplotypic diversity and underscores the importance of enhancing approaches to mitigate the deleterious effect of HLA mismatches.

Molecular construction and characterization of a novel exotoxin fusion protein that selectively blocks the B7:CD28 costimulatory signal system

An important strategy for specifically preventing and treating graft-versus-host and host-versus-graft diseases is to selectively block the B7:CD28/cytotoxic T-lymphocyte A4 costimulatory signal system for induced immune tolerance. In this study, a novel recombinant B7-2-L-PE40KDEL fusion protein was created to target the B7:CD28 system. We used a flexible linker sequence (Gly4Ser)4 and overlapping sequence extension to link the cDNAs encoding a human B7-2 extracellular domain and a mutant truncated form of Pseudomonas exotoxin A (PE), PE40KDEL. This B7-2-L-PE40KDEL fusion gene was then inserted into the pTYB4 expression vector, expressed in Escherichia coli, and purified through Ni-NTA mealty affinity-->MonoQ anion exchange-->Superdex75 gel filtration chromatography 3-step purification protocols. Western blotting demonstrated that the B7-2-L-PE40KDEL fusion protein specifically bound antihuman B7-2 monoclonal antibody and anti-pseudomonas exotoxin A antiserum. We used the Antheprot nucleic acid and protein analyzing software to predict the characteristics of this fusion protein, and showed that the fusion did not confer new antigenicities to the fusion protein. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tests demonstrated that at doses ranging from 0.2 to 2 microg/mL, this fusion protein specifically killed CD28-overexpressing Jurkat cells but even at doses of 2 microg did not kill CD28-negative Hut28 cells. The results of a one-way mixed lymphocyte reaction demonstrated that the fusion protein has a range of suppressive effects on HLA class I and II matched related donors and recipients, and HLA class I and II mismatched unrelated donors. Taken together, these results demonstrate that we have developed a novel recombinant human B7-2-L-PE40KDEL exotoxin fusion protein that specifically blocks the B7:CD28 costimulatory signal system in a manner that may be of significant importance in preventing and treating graft-versus-host or host-versus-graft diseases.

A high-resolution polymerase chain reaction-sequence-specific primer HLA-B*27 typing set and its application in routine HLA-B27 testing

We designed a set of 35 polymerase chain reaction sequence-specific primers (PCR-SSP) in 29 SSP mixtures to assign 29 HLA-B*27 4-digit level alleles (B*2701-B*2721 and B*2723-B*2730). This was used in conjunction with our 41 PCR-SSP primer mixture low-resolution HLA-B typing set to fully differentiate B*27 from all other HLA-B alleles. Successful typing set validation used 521 B*27 samples covering 13 (B*2701-B*2710 and B*2712, B*2717, B*2723) alleles. The distribution of B*27 alleles was determined in a random population of 4020 local blood donors and the use of PCR-SSP B*27 typing in our routine flow cytometry-based HLA-B27/B2708 typing strategy is described.

Constitutional pericentric inversion of chromosome 9 and hematopoietic recovery after allogeneic stem cell transplantation

Recent reports suggest that hemopoietic stem cells with constitutional pericentric inversion of chromosome 9 [inv(9)] may be related to delayed engraftment or hemopoietic defect after stem cell transplantation (SCT). We conducted a retrospective study on five allogeneic SCT in which constitutional inv(9) was detected either in the donor or the recipient. The results showed that hematologic recovery was within the expected time range for all our patients. However, one patient exhibited decreasing blood counts between day +45 and +272 after transplantation, possibly due to protracted cytomegalovirus (CMV) infection and gansiclovir and imatinib treatment. Our findings suggest that constitutional inv(9) may not be associated with delayed hemopoietic recovery after SCT.

Secondary malignancies after hematopoietic stem cell transplantation

Advances in the field of hematopoietic stem cell transplantation have led to an increasing number of cures of malignant and non-malignant diseases with this therapeutic approach. Long-term survivorship may, however, be associated with secondary malignancies, the result of a complex interaction of treatment-, recipient- and immunosuppression-related factors. Furthermore, the increasing use of donors other than human leukocyte antigen-identical siblings is associated with more intense immunosuppression, delayed immune recovery and higher incidence of B-cell post-transplantation lymphoproliferative disorders. Here, we review the incidence and the risk factors associated with these complications of hematopoietic stem cell transplants.

Inferred HLA Haplotype Information for Donors From Hematopoietic Stem Cells Donor Registries

Human leukocyte antigen (HLA) matching remains a key issue in the outcome of transplantation. In hematopoietic stem cell transplantation with unrelated donors, the matching for compatible donors is based on the HLA phenotype information. In familial transplantation, the matching is achieved at the haplotype level because donor and recipient share the block-transmitted major histocompatibility complex region. We present a statistical method based on the HLA haplotype inference to refine the HLA information available in an unrelated situation. We implement a systematic statistical inference of the haplotype combinations at the individual level. It computes the most likely haplotype pair given the phenotype and its probability. The method is validated on 301 phase-known phenotypes from CEPH families (Centre d'Etude du Polymorphisme Humain). The method is further applied to 85,933 HLA-A B DR typed unrelated donors from the French Registry of hematopoietic stem cells donors (France Greffe de Moelle). The average value of prediction probability is 0.761 (SD 0.199) ranging from 0.26 to 1. Correlations between phenotype characteristics and predictions are also given. Homozygosity (OR = 2.08; [2.02-2.14] p <10(-3)) and linkage disequilibrium (p <10(-3)) are the major factors influencing the quality of prediction. Limits and relevance of the method are related to limits of haplotype estimation. Relevance of the method is discussed in the context of HLA matching refinement.

HLA-A gene polymorphism defined by high-resolution sequence-based typing in 161 Northern Chinese Han people

Human leukocyte antigen (HLA) system is the most polymorphic region known in the human genome. In the present study, we analyzed for the first time the HLA-A gene polymorphisms defined by the high-resolution typing methods-sequence-based typing (SBT) in 161 Northern Chinese Han people. A total of 74 different HLA-A gene types and 36 alleles were detected. The most frequent alleles were A*110101 (GF=0.2360), A*24020101 (GF=0.1646), and A*020101 (GF=0.1553); followed by A*3303 (GF=0.1180), A*3001 (GF=0.0590), and A*310102 (GF=0.0404). The frequencies of following alleles, A*0203, A*0205, A*0206, A*0207, A*030101, A*2423, A*2601, A*3201, and A*3301, are all higher than 0.0093. The homozygous alleles include A*020101, A*110101, A*24020101 and A*310102. Heterozygosity (H), polymorphism information content (PIC), discrimination power (DP) and probability of paternity exclusion (PPE) of HLA-A in the samples were calculated and their values were 0.8705, 0.8491, 0.6014, and 0.9475, respectively. These results by SBT analysis of HLA-A polymorphism in Northern Chinese Han population, especially the allele subtypes character, will be of great interest for clinical transplantation, disease-associated study and forensic identification. Implementation of high-resolution typing methods allows a significantly wider spectrum of HLA variation including rare alleles. This spectrum will further be extensively utilized in many fields.

Enhancement of allogeneic hematopoietic stem cell engraftment and prevention of GVHD by intra-bone marrow bone marrow transplantation plus donor lymphocyte infusion

We examined the effect of intra-bone marrow (IBM)-bone marrow transplantation (BMT) in conjunction with donor lymphocyte infusion (DLI) on the engraftment of allogeneic bone marrow cells (BMCs) in mice. Recipients that had received 6 Gy of radiation completely rejected donor BMCs, even when IBM-BMT was carried out. However, when BMCs were IBM injected and donor peripheral blood mononuclear cells (PBMNCs) were simultaneously injected intravenously (DLI), donor cell engraftment was observed 7 days after BMT and complete donor chimerism continued thereafter. It is of interest that the cells of recipient origin did not recover, and that the hematolymphoid cells, including progenitor cells (Lin-/c-kit+ cells) in the recipients, were fully reconstituted with cells of donor origin. The cells in the PBMNCs responsible for the donor BMC engraftment were CD8+. Recipients that had received 6 Gy of radiation, IBM-BMT, and DLI showed only a slight loss of body weight, due to radiation side effects, and had no macroscopic or microscopic symptoms of graft-versus-host disease. These findings suggest that IBM-BMT in conjunction with DLI will be a valuable strategy for allogeneic BMT in humans.

Risk factors in pediatric stem cell transplantation for leukemia

To investigate which factors impact on survival, relapse, relapse free survival, transplant-related mortality (TRM) and graft-versus-host disease (GVHD) in children who undergo allogeneic stem cell transplantation, we included all 181 children transplanted due to leukemia at our unit. At the end of follow up 54% of the patients were alive, 27% had died due to relapse while 19% had died of other causes. Survival was similar in recipients of related (55%) and unrelated grafts (48%). Risk factors identified in univariate analysis were brought into a multivariable analysis. However, an unrelated donor was not identified as a risk factor for any of the five end-points analysed. A donor positive for three to four herpes viruses increased the risk of acute GVHD, TRM and death. A female to male transplant increased the risk of TRM, particularly if combined with a mismatch. Early stage of disease as well as human leukocyte antigen (HLA)-matching independently predicted survival. The risk of relapse increased after 1992. Chronic GVHD independently decreased the risk of relapse (relative risk RR, 0.39) and death (RR 0.42). We conclude that in children with leukemia other specific donor characteristics such as HLA-matching, gender, parity, and exposure to herpes viruses were more important for outcome than relationship.

The impact of cytomegalovirus serostatus of donor and recipient before hematopoietic stem cell transplantation in the era of antiviral prophylaxis and preemptive therapy

In the current era of effective prophylactic and preemptive therapy, cytomegalovirus (CMV) is now a rare cause of early mortality after hematopoietic stem cell transplantation (HSCT). However, the ultimate goal of completely eliminating the impact of CMV on survival remains elusive. Although the direct effects of CMV (ie, CMV pneumonia) have been largely eliminated, several recent cohort studies show that CMV-seropositive transplant recipients and seronegative recipients of a positive graft appear to have a persistent mortality disadvantage when compared with seronegative recipients with a seronegative donor. Recipients of T-cell–depleted allografts and/or transplants from unrelated or HLA-mismatched donors seem to be predominantly affected. Reasons likely include both incomplete prevention of direct and indirect or immunomodulatory effects of CMV as well as consequences of drug toxicities. The effect of donor CMV serostatus on outcome remains controversial. Large multicenter cohort studies are needed to better define the subgroups of seropositive patients that may benefit from intensified prevention strategies and to define the impact of CMV donor serostatus in the era of high-resolution HLA matching. Prevention strategies may require targeting both the direct and indirect effects of CMV infection by immunologic or antiviral drug strategies.

Pyrosequencing trade mark : A one-step method for high resolution HLA typing

While the use of high-resolution molecular typing in routine matching of human leukocyte antigens (HLA) is expected to improve unrelated donor selection and transplant outcome, the genetic complexity of HLA still makes the current methodology limited and laborious. Pyrosequencing™ is a gel-free, sequencing-by-synthesis method. In a Pyrosequencing reaction, nucleotide incorporation proceeds sequentially along each DNA template at a given nucleotide dispensation order (NDO) that is programmed into a pyrosequencer. Here we describe the design of a NDO that generates a pyrogram unique for any given allele or combination of alleles. We present examples of unique pyrograms generated from each of two heterozygous HLA templates, which would otherwise remain cis/trans ambiguous using standard sequencing based typing (SBT) method. In addition, we display representative data that demonstrate long read and linear signal generation. These features are prerequisite of high-resolution typing and automated data analysis. In conclusion Pyrosequencing is a one-step method for high resolution DNA typing.

Nonmyeloablative alternative donor transplants

The advent of nonmyeloablative preparative regimens and the expected lower regimen-related toxicities associated with them hold significant promise for extension of the use of allogeneic hematopoietic stem cell transplantation. Nonmyeloablative hematopoietic stem cell transplantation using human leukocyte antigen matched sibling donor, which carries a relatively low risk of transplant-related complications and can result in impressive antitumor responses, may benefit older patients and patients with preexisting organ impairment. However, more than 65% of patients in need of this procedure lack a human leukocyte antigen matched sibling donor. Therefore, attention has focused on alternative donors such as genotypically matched unrelated donors and partially mismatched related donors. Early clinical results suggest that the use of alternative donors is feasible, therefore potentially allowing full extension of the benefits of allografting to the group of patients in highest need.

Matched and mismatched allogeneic stem-cell transplantation from unrelated donors using combined graft-versus-host disease prophylaxis including rabbit anti-T lymphocyte globulin

PURPOSE

With improved HLA-typing techniques, it is presently unclear what degree of identity is necessary for successful unrelated-donor stem-cell transplantation (UD SCT). Here, we describe the outcome after matched and mismatched UD SCT using a graft-versus-host disease (GVHD) prophylaxis including high-dose rabbit anti-T lymphocyte globulin (ATG).

PATIENTS AND METHODS

One hundred adult patients (median age, 37 years; range, 17 to 65 years) with hematologic malignancies underwent transplantation in early disease (first complete remission [CR1] or first chronic phase [CP1]; n = 34) or in advanced disease (second complete remission or second chronic phase, no remission, refractory; n = 66) with nondepleted bone marrow (n = 87) or peripheral-blood-derived (n = 13) stem cells from an HLA-A, HLA-B, HLA-DRB1*, or HLA-DQB1* identical (n = 75) or mismatched (one antigen, n = 21; two to three antigens, n = 4) unrelated donor. GVHD prophylaxis consisted of rabbit ATG before transplantation in addition to cyclosporine and short-course methotrexate.

RESULTS

The cumulative incidence of acute GVHD degrees II- degrees IV was 21% (95% confidence interval [CI], 14% to 33%) and 20% (95% CI, 9% to 44%) and acute GVHD degrees III- degrees IV was 5.3% (95% CI, 2% to 14%) and 4% (95% CI, 0.6% to 28%) in HLA-matched and HLA-mismatched transplantations, respectively. The risk for extensive chronic GVHD was 43% (95% CI, 32% to 59%) and 44% (95% CI, 26% to 75%) for HLA-matched and HLA-mismatched patients, respectively. The risk of relapse at 4 years was 17% (95% CI, 7% to 43%) and 43% (95% CI, 31% to 60%) for CR1/CP1 and advanced disease patients, respectively. With a median follow-up of 1,068 days (range, 12 to 1,958 days), 3-year disease-free and overall survival for patients who underwent transplantation in CR1/CP1 was 63% (95% CI, 46% to 81%) and 75% (95% CI, 59% to 90%), respectively; and for patients with advanced disease, it was 34% (95% CI, 22% to 46%) and 39% (95% CI, 25% to 53%), respectively.

CONCLUSION

A certain degree of one antigen mismatching may not compromise the outcome after UD SCT when using this rabbit ATG in addition to standard GVHD prophylaxis regimen.

HLA diversity: detection and impact on unrelated hematopoietic stem cell donor characterization and selection

Matching of patient and unrelated donor for HLA molecules significantly decreases the probability of graft rejection, graft vs. host disease, and transplant-related mortality in hematopoietic stem cell transplantation. A significant challenge in the identification of matched donors is the diversity of the HLA system. Almost 1500 alleles have been identified at 12 HLA loci. Significant progress has been made in the application of DNA-based testing to identify this diversity in patients and unrelated volunteer donors; however, the resolution of registry testing remains limited by the need to test many donors inexpensively. Thus, the transplant center must predict which donor might be a match for their patient using incomplete typing information. Design of a typing strategy based on knowledge of allele and haplotype frequencies is critical to speed donor identification. A further challenge is to compare patient HLA assignments to the over 7.7 million volunteer donors on registries carrying both DNA and serologic assignments. The links between alleles and serologic specificities remain unclear in many cases and complicate the design of computer algorithms used to match patients and donors. Finally, since few patients will find donors who are allele matched for all HLA loci, studies are underway to understand which of the HLA loci are most critical to match and to define rules of permissive mismatching to achieve an acceptable outcome.

How H13 histocompatibility peptides differing by a single methyl group and lacking conventional MHC binding anchor motifs determine self-nonself discrimination

The mouse H13 minor histocompatibility (H) Ag, originally detected as a barrier to allograft transplants, is remarkable in that rejection is a consequence of an extremely subtle interchange, P4(Val/Ile), in a nonamer H2-D(b)-bound peptide. Moreover, H13 peptides lack the canonical P5(Asn) central anchor residue normally considered important for forming a peptide/MHC complex. To understand how these noncanonical peptide pMHC complexes form physiologically active TCR ligands, crystal structures of allelic H13 pD(b) complexes and a P5(Asn) anchored pD(b) analog were solved to high resolution. The structures show that the basis of TCRs to distinguish self from nonself H13 peptides is their ability to distinguish a single solvent-exposed methyl group. In addition, the structures demonstrate that there is no need for H13 peptides to derive any stabilization from interactions within the central C pocket to generate fully functional pMHC complexes. These results provide a structural explanation for a classical non-MHC-encoded H Ag, and they call into question the requirement for contact between anchor residues and the major MHC binding pockets in vaccine design.

Durable engraftment of major histocompatibility complex-incompatible cells after nonmyeloablative conditioning with fludarabine, low-dose total body irradiation, and posttransplantation cyclophosphamide

Treatment of leukemia by myeloablative conditioning and transplantation of major histocompatibility complex (MHC)-mismatched stem cells is generally avoided because of the high risk of graft rejection or lethal graft-versus-host disease (GVHD). This study shows that MHC-incompatible cells can engraft stably after nonmyeloablative conditioning with immunosuppressive chemotherapy and low-dose total body irradiation (TBI). Long-term mixed hematopoietic chimerism, clonal deletion of donor-reactive T cells, and bidirectional cytotoxic T-cell tolerance were achieved by transplanting MHC-mismatched marrow cells into recipients conditioned with pretransplantation fludarabine or cyclophosphamide (Cy), 50 to 200 cGy TBI on day -1, and Cy 200 mg/kg intraperitoneally on day 3. In this model, long-term donor chimerism was proportional to the dose of TBI or donor marrow cells. Pretransplantation fludarabine and posttransplantation Cy were both required for alloengraftment, but the drugs had additional effects. For example, fludarabine sensitized host stem cells to the toxicity of TBI, because animals conditioned with both agents had higher chimerism than animals conditioned with TBI alone (P <.05). Also, posttransplantation Cy attenuated lethal and nonlethal GVH reactions, because F(1) recipients of host-reactive, parental spleen cells survived longer (P <.05) and had lower donor cell chimerism (P <.01) if they received posttransplantation Cy than if they did not. Finally, delayed infusions of donor lymphocytes into mixed chimeras prolonged survival after leukemia challenge (P <.0001) without causing lethal GVHD. These results indicate that stable engraftment of MHC-incompatible cells can be induced after fludarabine-based, nonmyeloablative conditioning and that it serves as a platform for adoptive immunotherapy with donor lymphocyte infusions.

Peripheral blood stem cell allograft rejection mediated by CD4(+) T lymphocytes recognizing a single mismatch at HLA-DP beta 1*0901

Little is known about the molecular characteristics of alloantigens recognized by alloreactive T cells mediating hematologic stem cell graft rejection. In particular, it has never been shown that such alloantigens can be encoded by HLA-DP beta alleles. Indeed, matching for HLA-DP antigens is generally not considered to be of functional importance for the outcome of allogeneic bone marrow or peripheral blood stem cell transplantation. In this study, a case of peripheral blood stem cell allograft rejection was investigated in which the patient and donor differed for a single mismatch at HLA-DP in the rejection direction. Patient-derived T lymphocytes circulating at the time of rejection showed direct ex vivo cytotoxic activity against donor-derived B-lymphoblastoid cells as well as other HLA-DP beta 1*0901--expressing targets. The presence of HLA-DP beta 1*0901--specific effectors in vivo was further confirmed by in vitro stimulation experiments. CD4(+) T-cell lines and clones with specific cytotoxic activity against HLA-DP beta 1*0901--expressing targets including donor B-lymphoblastoid cells were generated both by nonspecific and by donor-specific in vitro stimulation. Taken together, these data demonstrate that HLA-DP can be the target antigen of cytotoxic CD4(+) T lymphocytes involved in peripheral blood stem cell allograft rejection. (Blood. 2001;98:1122-1126)

Intravenous injection of apoptotic leukocytes enhances bone marrow engraftment across major histocompatibility barriers

Cross-tolerization of T lymphocytes after apoptotic cell uptake by dendritic cells may be involved in self-tolerance maintenance. Furthermore, immunosuppressive properties are attributed to apoptotic cells. This study evaluated the consequences of apoptotic leukocyte administration in a restrictive engraftment model of murine bone marrow (BM) transplantation. Sublethally irradiated recipients received a limited number of allogeneic BM, with or without irradiated apoptotic leukocytes of different origins. No graft-versus-host disease was observed. Whereas only a low proportion of mice receiving BM cells alone engrafted, addition of apoptotic irradiated leukocytes, independently of the origin (donor, recipient, third-party mice, as well as xenogeneic peripheral blood mononuclear cells), significantly enhanced engraftment. Similar results were obtained after infusion of leukocytes rendered apoptotic by UVB irradiation or by anti-Fas monoclonal antibody stimulation, thus confirming the role of apoptotic cells in engraftment facilitation. Overall, these results suggest that apoptotic leukocytes can nonspecifically facilitate allogeneic BM engraftment. Such a simple approach could be of interest in BM transplantation settings involving an important HLA donor/recipient disparity, a T-cell-depleted graft, or reduced conditioning regimen intensity.

Unrelated donor hematopoietic transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for a range of malignant and non-malignant diseases. Unfortunately, fewer than 30% of patients have a human leukocyte antigen (HLA)-matched sibling. Advances in our understanding of the HLA system and the development of large international donor registries are supporting the increasing use of unrelated donors as an alternative source of stem cells. Unrelated donor transplantation, however, is still associated with higher complication rates than in HLA-identical sibling donor transplants. Improvements in graft-vs.-host disease prevention and treatment, new conditioning regimens and better donor selection will likely expand the indications of unrelated donor HSCT in the next decade.

Unrelated marrow transplantation for adult patients with poor-risk acute lymphoblastic leukemia: strong graft-versus-leukemia effect and risk factors determining outcome

Between 1988 and 1999, 127 patients with poor-risk acute lymphoblastic leukemia (ALL) received a matched unrelated donor transplant using marrow procured by National Marrow Donor Program (NMDP) collection centers and sent out to 46 transplant centers worldwide. Poor risk was defined by the presence of the translocations t(9;22) (n = 97), or t(4;11) (n = 25), or t(1;19) (n = 5). Sixty-four patients underwent transplantation in first remission (CR1), 16 in CR2 or CR3, and 47 patients had relapsed ALL or primary induction failure (PIF). Overall survival at 2 years from transplant was 40% for patients in CR1, 17% in CR2/3, and 5% in PIF or relapse. Treatment-related mortality (TRM) and relapse mortality, estimated as competing risk factors, were 54% and 6%, respectively, in CR1, 75% and 8% in CR2/3, and 64% and 31% in PIF or relapse. Currently 23 CR1 patients are alive and free of disease with a median follow-up of 24 months (range, 3-97). Multivariable analysis showed that CR1, shorter interval from diagnosis to transplantation, DRB1 match, negative cytomegalovirus (CMV) serology (patient and donor), and presence of the Philadelphia chromosome, t(9;22), were independently associated with better disease-free survival (DFS). Transplantation in CR and presence of t(9;22) were associated with lower risk of relapse. Shorter interval from diagnosis to transplantation, DRB1-match, negative CMV, higher marrow cell dose, and Karnofsky score of 90 or higher were associated with less TRM. These results indicate that, despite a relatively high TRM, the low relapse rate resulted in a 37% +/- 13% DFS for CR1 patients, comparing favorably to results obtained with chemotherapy alone and matching results following HLA-identical sibling transplantation.

Acute graft-vs-host disease: pathobiology and management

Acute graft-vs-host disease (GVHD) is a major obstacle to safe allogeneic hematopoietic stem cell transplantation (HSCT), leading to a significant morbidity and mortality. GVHD occurs when transplanted donor T lymphocytes react to foreign host cells. It causes a wide variety of host tissue injuries. This review focuses on the pathobiological basis, clinical aspects, and current management strategies of acute GVHD. Afferent phase of acute GVHD starts with myeloablative conditioning, i.e., before the infusion of the graft. Total-body irradiation (TBI) or high-dose chemotherapy regimens cause extensive damage and activation in host tissues, which release inflammatory cytokines and enhance recipient major histocompatibility complex (MHC) antigens. Recognition of the foreign host antigens by donor T cells and activation, stimulation, and proliferation of T cells is crucial in the afferent phase. Effector phase of acute GVHD results in direct and indirect damage to host cells. The skin, gastrointestinal tract, and liver are major target organs of acute GVHD. Combination drug prophylaxis in GVHD is essential in all patients undergoing allogeneic HSCT. Steroids have remained the standard for the treatment of acute GVHD. Several clinical trials have evaluated monoclonal antibodies or receptor antagonist therapy for steroid-resistant acute GVHD, with different successes in a variety of settings. There are some newer promising agents like mycophenolate mofetil, glutamic acid-lysine-alanine-tyrosine (GLAT), rapamycin, and trimetrexate currently entering in the clinical studies, and other agents are in development. Future experimental and clinical studies on GVHD will shed further light on the better understanding of the disease pathobiology and generate the tools to treat malignant disorders with allogeneic HSCT with specific graft-vs-tumor effects devoid of GVHD.

Allogeneic stem cell transplantation for acute lymphocytic leukemia in adults

Acute lymphocytic leukemia remains a difficult disease to treat in adults. Allogeneic bone marrow transplantation can cure some patients with ALL, but GVHD transplant-related mortality and disease relapse remain problematic. Immunotherapeutic approaches aimed at eliminating minimal residual disease and enhancing the GVL effect may decrease relapse rates and improve overall survival. Because of the rarity of this disease in adults, every new patient should be entered in well-designed, peer-reviewed, investigational trial.

Factors influencing haematological recovery after allogeneic haemopoietic stem cell transplants: graft-versus-host disease, donor type, cytomegalovirus infections and cell dose

Platelet recovery after allogeneic haemopoietic stem cell transplant (HSCT) and predictive factors were analysed in 342 patients with haematological malignancies. All patients were prepared with cyclophosphamide plus total body irradiation, and received an unmanipulated HSCT from an HLA-identical sibling (n = 270), a matched unrelated donor (n = 67) or an identical twin (n = 5). The source of stem cells was peripheral blood (n = 15) or bone marrow (n = 327). Graft-vs.-host disease (GvHD) prophylaxis consisted of cyclosporin A with or without methotrexate. The proportion of patients with < 50 x 10(9)/l platelets on d +50, d +100, d +200 and d +365 after HSCT was 26%, 27%, 14% and 11% respectively. Thrombocytopenia was independent of the degree of complete donor chimaerism. Four variables were predictive of platelet recovery: donor type, acute GvHD, cytomegalovirus (CMV) infection and number of cells infused at transplant. Recipients of an unrelated graft had lower platelet counts (49 x 10(9)/l) on d +50 than identical sibling grafts (10(8) x 10(9)/l) (P < 0.001) and twin grafts (149 x 10(9)/l) (P < 0.001). Patients with GvHD grades 0, I, II, III and IV had significantly different platelet counts on d +50 (153 x 10(9)/l, 102 x 10(9)/l, 85 x 10(9)/l, 32 x 10(9)/l and 22 x 10(9)/l; P < 0.001) and thereafter. Thrombocytopenia was more frequent in patients with high-level CMV antigenaemia (> four positive cells/2 x 105) (P < 0.0001) and in patients who received a low cell dose at transplant (< or = 4.1 x 10(8)/kg) (P = 0.009). Platelet counts predicted transplant-related mortality (TRM) and were higher at all time intervals in patients surviving the transplant. Patients with grade II GvHD and > 50 x 10(9)/l platelets had a lower TRM than patients with grade II GvHD and < or = 50 x 10(9)/l platelets (14% vs. 40%, P < 0.0001). In conclusion, (i) a significant proportion of allogeneic HSCT recipients are thrombocytopenic long-term, irrespective of complete donor chimaerism, (ii) thrombocytopenia identifies patients at greater risk of lethal complications, and (iii) platelet recovery is influenced by GvHD, donor type, CMV infections and cell dose, not by stem cell source or other patient-disease-related variables.

Haemopoietic stem-cell transplantation: recent progress and future promise

Transplantation of haemopoietic stem cells is an increasingly important approach in the management of malignant haematological disease. Recent developments in our understanding of stem-cell biology have profoundly influenced the practice of both autologous and allogeneic stem cell transplantation. The demonstration that cytokines, such as granulocyte colony-stimulating factor, mobilise large numbers of haemopoietic progenitors has resulted in the peripheral blood rather than the bone marrow becoming the preferred source of haemopoietic stem cells in autologous, and increasingly in allogeneic, stem-cell transplantation. This has substantially reduced the morbidity of autografting, so that disease relapse now represents the most important cause of treatment failure. Current efforts are aimed at reducing this risk, either by employing novel conditioning regimens or by tumour purging. With regard to allogeneic transplantation, there is a growing realisation of the importance of a graft-versus-leukaemia effect, and this has encouraged the use of strategies which optimise an immunologically-mediated antitumour effect. This, coupled with increased understanding of the biology of stem-cell engraftment, has resulted in the development of less toxic conditioning regimens, designed to allow the benefits of allografting to be extended to patients in whom this procedure is contraindicated.