The use of unrelated marrow donors for transplantation

Reconstruction of the block matching profiles

Block matching is a valuable tool for selecting donors for bone marrow transplantation. Identical, electrophoretic profiles of unrelated bone marrow donor-recipient pairs have been shown to be associated with long-term survival and a reduction of graft versus host disease (GVHD). This study was undertaken to determine the sequences of the PCR products which are generated. PCR products obtained with beta-block primers following the amplification of DNA extracted from cell lines homozygous for 7.1 and 8.1 ancestral haplotypes were cloned and sequenced. The PCR products were characterised and the beta block profiles reconstructed. The data indicate that the profiles consist of homoduplexes and heteroduplexes which are formed by the products of probably 3 different sequence locations.

Characterization of baboon class I major histocompatibility molecules. Implications for baboon-to-human xenotransplantation

Increasingly strong medical and political pressures are stimulating consideration of the transplantation of baboon organs and cells into humans. Critical to the success of these xenotransplants is management of the immune system such that graft rejection and, in the case of bone marrow transplantation, graft-versus-host disease do not result in transplant failure. The polymorphic products of the major histocompatibility complex (MHC) are the primary barrier to successful allotransplantation, and here we describe class I MHC molecules from baboon (Papio anubis) to gain an understanding of how similarities and differences between baboon and human MHC molecules might affect xenograft survival and function. Comparative analyses of our five novel baboon class I molecules with defined HLA class I molecules demonstrate that the baboon class I molecule are up to 90% identical. Disparity between baboon class I proteins and their human homologues lies predominately at positions in the antigen-binding groove, while C-terminal portions of the class I heavy chain are more conserved between the two species. Such concentration of cross-species differences within the alpha1 and alpha2 domains involves a majority of substitutions at positions demonstrating polymorphism in human alleles; the location of substitutions distinguishing baboon and human molecules thus resembles the positioning of human class I allopolymorphisms. Because this preliminary characterization indicates that both baboon and human T cells with be restricted by xenogeneic class I molecules, immune responses triggered during baboon-to-human transplantation should mimic those arising during MHC mismatched human allotransplantation.

Novel alleles HLA-B*7802 and B*51022: evidence for convergency in the HLA-B5 family

We have characterized two novel HLA-B alleles, B*7802 and B*51022. The Caucasian-derived variant B*7802 most resembles the African-derived variant B*7801, from which B*7802 differs by two nucleotides. Only one of these modifications, however, is translated: a tyrosine for aspartate substitution occurs at residue 74 in B*7802, while the second nucleotide difference reflects a proximal synonymous substitution in codon 23. A second variant, B*51022, differs synonymously only at codon 23 from B*51021. Comparative analysis of the B5 CREG demonstrates that other pairs of B5 alleles differ synonymously only at codon 23 or synonymously at codon 23 and non-synonymously at a second more distal location. Contrary to the genesis of like pairs of B5 alleles via introduction of coordinate yet distant mutagenic events onto a single B5 progenitor, we postulate that synonymously different B5 progenitor molecules, B5ATT and B5ATC, are evolving in convergence to generate homologous B5 allele pairs differing silently at codon 23. Our finding that B*7802 is a single amino acid away from complete convergence with B*7801 and that B*51022 and B*51021 are in complete convergence is exemplary of such evolution.

Bone marrow transplantation for autosomal recessive osteopetrosis. A report from the Working Party on Inborn Errors of the European Bone Marrow Transplantation Group

The outcomes of 69 patients who received allogeneic bone marrow grafts for autosomal recessive osteopetrosis in the period between 1976 and 1994 were analyzed retrospectively. Four patients received bone marrow transplants (BMT) without prior myeloablative conditioning; transient osteoclast function was demonstrated in one of them. Sixty-five patients received myeloablative pretreatment. Recipients of a genotypically human leukocyte antigen (HLA)-identical BMT had an actuarial probability for 5-year survival, with osteoclast function, of 79%; recipients of a phenotypically HLA-identical bone marrow graft from a related or unrelated donor, or one HLA-mismatched graft from a related donor, had an actuarial probability for 5-year survival, with osteoclast function, of 38%; patients who received a graft from an HLA-haplotype mismatched related donor had a probability for 5-year survival of only 13%. The main problems in haplotype-nonidentical BMT were graft failure and BMT-related complications such as sepsis, bleeding, and interstitial pneumonia. Osteoclast function developed in all patients with full engraftment. Recovery of osteoclast function was associated with severe hypercalcemia in 24% of the patients with engraftment, especially those older than 2 years of age. At the time of BMT, severe visual impairment was present in 35% of the patients; of the 15 patients who had visual impairment at the time that a successful BMT was performed, two had improvement after BMT (13%). Within the total group, one patient had neurodegeneration. Engraftment of healthy donor cells had no influence on the progression of that abnormality and BMT thus had no beneficial effect on this phenotype of osteopetrosis. In general, however, early BMT remains the only curative treatment for autosomal recessive osteopetrosis.

Structural heterogeneity in HLA-B70, a high-frequency antigen of black populations

Although the B70 antigen exhibits allele frequencies of 8-23% in African and American black populations, it remains poorly defined. Cloning and sequencing of cDNA encoding B70 antigens from six cell lines has identified a group of three closely related alleles: B*1503, B*1509 and B*1510, that form a subgroup of the B15 family. The sequences of these alleles and, in particular, B*1503, are close to that of the HLA-B consensus consistent with the difficulty in their serological definition. The products of the three alleles correspond to three electrophoretically detected variants of the B70 antigen and some correlation with the B71 and B72 subspecificities of the B70 antigen can be made. A fourth allele, B*7901, previously described by Choo et al. (J. Immunol. 147: 174-180, 1991) that was not serologically typed as B70, differs by a single nucleotide substitution from B*1510. The sensitivity of alloantibodies to single differences in peptide binding residues suggest a role for bound peptides in the HLA-B70 alloantigenic specificities. The heavy chains encoded by the four alleles differ at four peptide binding residues of the antigen recognition site, the evolutionary modification of which can be explained in terms of interallelic recombination events.

Bone marrow transplantation in Europe: major geographical differences. The European Group for Bone Marrow Transplantation [EBMT]

In 1991 171 teams in 21 European countries performed 4976 bone marrow transplants. There were 1829 transplants from an HLA-identical sibling donor, 101 from a nonidentical family member, 30 from a twin, 217 from an unrelated volunteer donor and 2799 autologous transplants. Indications for transplants were leukaemias in 2569 (52%), lymphoproliferative disorders in 1472 (30%), solid tumours in 549 (11%), aplastic anaemia and thalassaemia in 261 (5%), inborn errors in 97 and miscellaneous disorders in 28 patients. There are marked differences between the participating European countries. They relate to absolute numbers, indications and techniques. Less than 10 transplants per 10-million inhabitants are performed in Eastern European countries. Ten to fifty transplants per 10-million inhabitants are done in two, 50-100 transplants per 10-million inhabitants in five, 100-200 transplants per 10-million inhabitants in eight countries and more than 200 per 10-million inhabitants in one country (P < 0.01). The number of transplant teams ranges from less than one to twelve per 10-million inhabitants (P < 0.01). For the continent it becomes 3.3 per 10-million inhabitants. The reasons for these differences are not explained by this survey. The most likely explanation for the differences in transplant activity is availability of transplant beds, trained staff and resources. Bone marrow transplants are expensive. However, the demand is increasing and will increase further with the routine availability of unrelated volunteer donors. Clearly, criteria are required in Europe to define the indications and solutions to meet the legitimate requirements for transplantation in the various regions of Europe.

Bone marrow transplantation for acute non-lymphoblastic leukemia

Most results obtained by different study and analytic designs favor that matched allogeneic BMT is superior to chemotherapy in young adults with ANLL in first remission. The place of ABMT is more difficult to assess and requires further study both compared to chemotherapy and allogeneic BMT. Furthermore, the question of purging needs further study in a controlled fashion. For older patients the choice is more difficult. Transplant related mortality increases with age which makes ABMT an attractive alternative to allogenic BMT. However, recent advances in prophylaxis and treatment of transplant related complications such as cytomegalovirus interstitial pneumonia and veno-occlusive disease of the liver might increase long-term survival after allogeneic BMT in older patients. The role of matched unrelated donors in the treatment of ANLL is unresolved but this procedure should probably be reserved for relatively young patients in second complete remission or later.

PCR-fingerprinting for selection of HLA matched unrelated marrow donors. Collaborating Centres in the IMUST Study

HLA typing contributes to the delays that occur in the search for HLA-matched unrelated marrow donors, and that result in poor patient survival. A new DNA technique for testing DR match between patient and unrelated marrow donors has been assessed. The technique is based on the formation of heteroduplexes between heterologous amplified coding and non-coding DNA sequences during the final annealing stage of the polymerase chain reaction (PCR), and different HLA-DR/Dw types give unique banding patterns ("PCR fingerprints") on non-denaturing polyacrylamide gel electrophoresis. HLA-DR matching is by visual comparison of patients' with donors' fingerprints. Identity can be confirmed by mixing donor and recipient DNA before the final stage of the PCR ("DNA crossmatching"). In an assessment of the technique in 53 unrelated HLA-A and HLA-B matched patient-donor pairs, 42 pairs gave the same results with PCR fingerprinting as with DNA-RFLP analysis. In the 11 other pairs DR/Dw mismatches were detected by PCR fingerprinting but not by the standard DNA-RFLP method; PCR-SSO typing with selected sequence-specific oligonucleotides (SSO) confirmed that mismatches were due to different subtypes of DR4. PCR fingerprinting might thus accelerate the selection of unrelated marrow donors by simplifying the logistics of the donor search.