Expanding the immunotherapeutic potential of minor histocompatibility antigens

Single step multiple genotyping by MALDI-TOF mass spectrometry, for evaluation of minor histocompatibility antigens in patients submitted to allogeneic stem cell transplantation from HLA-matched related and unrelated donor

The outcome of patients underwent to allogeneic stem cell transplantation (allo- SCT) is closely related to graft versus host disease (GvHD) and graft versus leukemia (GvL) effects which can be mediated by mHAgs. 23 mHAgs have been identified and reported to be differently correlated with GVHD or GVL and the aim of this work was develop a method to genotype the mHAgs described so far. For this study we used MALDI-TOF iPLEX Gold Mass Array technology. We tested 46 donor/recipient matched pairs that underwent allo-SCT because of Philadelphia positive (Ph+) chronic myeloid leukemia (n=29) or Ph+ acute lymphoblastic leukemia (n=17). Our data show that sibling pairs had a lesser number of mHAgs mismatches compared to MUD pairs. Notably, donor/recipient genomic mismatch on DPH1 was correlated with an increased risk of acute GvHD and LB-ADIR-1R mismatch on graft versus host direction was correlated with a better RFS with no increase of GvHD risk. Our work provides a simple, accurate and highly automatable method for mHAgs genotyping and suggest the role of mHAgs in addressing the immune reaction between donor and host.

Immunology of hematopoietic stem cell transplant

Hematopoietic stem cell transplantation (HSCT) is a procedure in which infusion of hematopoietic stem cells is used to reestablish hematopoietic function in patients with damaged or defective bone marrow or immune systems. Early and late complications following allogeneic HSCT include acute and chronic graft-versus-host disease (GVHD), donor rejection, graft failure, relapse of primary malignancy, conditioning-related toxicity, immunodeficiency and infections. Immunology has a central role in allogeneic hematopoietic cell transplantation. Any appreciation of the immunological mechanism involved in engraftment, GVHD, the development of tolerance, immune reconstitution, and the control of malignancy requires some understanding of the immunologic basis for immune reactions provoked by grafting tissue from one individual to another. In the future it should be possible to learn what gene(s) must be activated and which must be repressed to force stem cells into division without maturation; to engineer a mechanism into the cells that stops proliferation and sets the stage for amplification; to search if there could be a universal donor cell line, neatly packaged and stabilized in sealed vials and distributed by the pharmaceutical industry; to modify the transplanted cells in such a way that they have a proliferative advantage over those of the host and to deliver the lethal blow against the neoplasm, perhaps the cells that are infused will be engineered in such a way as to be able to distinguish between normal host cells and tumor.

Identification of minor histocompatibility antigens based on the 1000 Genomes Project

Minor histocompatibility antigens are highly immunogeneic polymorphic peptides playing crucial roles in the clinical outcome of HLA-identical allogeneic stem cell transplantation. Although the introduction of genome-wide association-based strategies significantly has accelerated the identification of minor histocompatibility antigens over the past years, more efficient, rapid and robust identification techniques are required for a better understanding of the immunobiology of minor histocompatibility antigens and for their optimal clinical application in the treatment of hematologic malignancies. To develop a strategy that can overcome the drawbacks of all earlier strategies, we now integrated our previously developed genetic correlation analysis methodology with the comprehensive genomic databases from the 1000 Genomes Project. We show that the data set of the 1000 Genomes Project is suitable to identify all of the previously known minor histocompatibility antigens. Moreover, we demonstrate the power of this novel approach by the identification of the new HLA-DP4 restricted minor histocompatibility antigen UTDP4-1, which despite extensive efforts could not be identified using any of the previously developed biochemical, molecular biological or genetic strategies. The 1000 Genomes Project-based identification of minor histocompatibility antigens thus represents a very convenient and robust method for the identification of new targets for cancer therapy after allogeneic stem cell transplantation.

Occurrence and Impact of Minor Histocompatibility Antigens' Disparities on Outcomes of Hematopoietic Stem Cell Transplantation from HLA-Matched Sibling Donors

We have examined the alleles of eleven minor histocompatibility antigens (MiHAs) and investigated the occurrence of immunogenic MiHA disparities in 62 recipients of allogeneic hematopoietic cell transplantation (allo-HCT) with myeloablative conditioning performed between 2000 and 2008 and in their HLA-matched sibling donors. Immunogenic MiHA mismatches were detected in 42 donor-recipient pairs: in 29% MiHA was mismatched in HVG direction, in another 29% in GVH direction; bidirectional MiHA disparity was detected in 10% and no MiHA mismatches in 32%. Patients with GVH-directed HY mismatches had lower both overall survival and disease-free survival at 3 years than patients with compatible HY; also higher incidence of both severe acute GvHD and extensive chronic GVHD was observed in patients with GVH-directed HY mismatch. On contrary, GVH-directed mismatches of autosomally encoded MiHAs had no negative effect on overall survival. Results of our study help to understand why posttransplant courses of allo-HCT from siblings may vary despite the complete high-resolution HLA matching of a donor and a recipient.

Towards effective and safe immunotherapy after allogeneic stem cell transplantation: identification of hematopoietic-specific minor histocompatibility antigen UTA2-1

Donor T cells directed at hematopoietic system-specific minor histocompatibility antigens (mHags) are considered important cellular tools to induce therapeutic graft-versus-tumor (GvT) effects with low risk of graft-versus-host disease after allogeneic stem cell transplantation. To enable the clinical evaluation of the concept of mHag-based immunotherapy and subsequent broad implementation, the identification of more hematopoietic mHags with broad applicability is imperative. Here we describe novel mHag UTA2-1 with ideal characteristics for this purpose. We identified this antigen using genome-wide zygosity-genotype correlation analysis of a mHag-specific CD8⁺ cytotoxic T lymphocyte (CTL) clone derived from a multiple myeloma patient who achieved a long-lasting complete remission after donor lymphocyte infusion from an human leukocyte antigen (HLA)-matched sibling. UTA2-1 is a polymorphic peptide presented by the common HLA molecule HLA-A*02:01, which is encoded by the bi-allelic hematopoietic-specific gene C12orf35. Tetramer analyses demonstrated an expansion of UTA2-1-directed T cells in patient blood samples after several donor T-cell infusions that mediated clinical GvT responses. More importantly, UTA2-1-specific CTL effectively lysed mHag⁺ hematopoietic cells, including patient myeloma cells, without affecting non-hematopoietic cells. Thus, with the capacity to induce relevant immunotherapeutic CTLs, it's HLA-A*02 restriction and equally balanced phenotype frequency, UTA2-1 is a highly valuable mHag to facilitate clinical application of mHag-based immunotherapy.

Leukemia-associated antigens and their relevance to the immunotherapy of acute myeloid leukemia

The graft-versus-leukemia effect of allogeneic hematopoietic stem cell transplantation (HSCT) has shown that the immune system is capable of eradicating acute myeloid leukemia (AML). This knowledge, along with the identification of the target antigens against which antileukemia immune responses are directed, has provided a strong impetus for the development of antigen-targeted immunotherapy of AML. The success of any antigen-specific immunotherapeutic strategy depends critically on the choice of target antigen. Ideal molecules for immune targeting in AML are those that are: (1) leukemia-specific; (2) expressed in most leukemic blasts including leukemic stem cells; (3) important for the leukemic phenotype; (4) immunogenic; and (5) clinically effective. In this review, we provide a comprehensive overview on AML-related tumor antigens and assess their applicability for immunotherapy against the five criteria outlined above. In this way, we aim to facilitate the selection of appropriate target antigens, a task that has become increasingly challenging given the large number of antigens identified and the rapid pace at which new targets are being discovered. The information provided in this review is intended to guide the rational design of future antigen-specific immunotherapy trials, which will hopefully lead to new antileukemia therapies with more selectivity and higher efficacy.

HapMap SNP Scanner: an online program to mine SNPs responsible for cell phenotype

Minor histocompatibility (H) antigens are targets of graft-vs-host disease and graft-vs-tumor responses after human leukocyte antigen matched allogeneic hematopoietic stem cell transplantation. Recently, we reported a strategy for genetic mapping of linkage disequilibrium blocks that encoded novel minor H antigens using the large dataset from the International HapMap Project combined with conventional immunologic assays to assess recognition of HapMap B-lymphoid cell line by minor H antigen-specific T cells. In this study, we have constructed and provide an online interactive program and demonstrate its utility for searching for single-nucleotide polymorphisms (SNPs) responsible for minor H antigen generation. The website is available as 'HapMap SNP Scanner', and can incorporate T-cell recognition and other data with genotyping datasets from CEU, JPT, CHB, and YRI to provide a list of candidate SNPs that correlate with observed phenotypes. This method should substantially facilitate discovery of novel SNPs responsible for minor H antigens and be applicable for assaying of other specific cell phenotypes (e.g. drug sensitivity) to identify individuals who may benefit from SNP-based customized therapies.

Frequencies of 10 autosomal minor histocompatibility antigens in Korean population and estimated disparities in unrelated hematopoietic stem cell transplantation

Disparity of minor histocompatibility antigens (mHAs) is known to induce graft-versus-tumor and graft-versus-host disease reactions in stem cell transplantation. Not much information is available on genotypic and phenotypic distributions of the currently identified mHAs, especially in Korean population. Therefore, we report genotype and phenotype frequency analyses of 10 autosomal mHAs in 329 unrelated healthy Koreans using the Sequenom MassARRAY matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) system and polymerase chain reaction-sequence specific primers (PCR-SSP). Estimates of the probability of immunogenic mismatches between donor/recipient pairs were made from observed phenotypic frequencies. HA-1 was the most favorable mHA for clinical application with the highest disparity of 7.0%. Similar results were obtained in ACC-1. The Korean population can benefit the most in a setting of matched major histocompatibility complex (MHC)-restricted mHAs-mismatched unrelated hematopoietic stem cell transplantations with the disparity rate of 27.5% with eight hematopoietic mHAs. This is the first comprehensive report on the genotypic and phenotypic frequency distributions of human mHAs in the Korean population. It can contribute to not only donor selection before transplantation but also therapeutic approaches after transplantation. It is expected that mHA-based immunotherapy will lead to a new treatment modality tailored for patients at high risk of relapse following allogeneic hematopoietic cell transplantation.

High-throughput identification of potential minor histocompatibility antigens by MHC tetramer-based screening: feasibility and limitations

T-cell recognition of minor histocompatibility antigens (MiHA) plays an important role in the graft-versus-tumor (GVT) effect of allogeneic stem cell transplantation (allo-SCT). However, the number of MiHA identified to date remains limited, making clinical application of MiHA reactive T-cell infusion difficult. This study represents the first attempt of genome-wide prediction of MiHA, coupled to the isolation of T-cell populations that react with these antigens. In this unbiased high-throughput MiHA screen, both the possibilities and pitfalls of this approach were investigated. First, 973 polymorphic peptides expressed by hematopoietic stem cells were predicted and screened for HLA-A2 binding. Subsequently a set of 333 high affinity HLA-A2 ligands was identified and post transplantation samples from allo-SCT patients were screened for T-cell reactivity by a combination of pMHC-tetramer-based enrichment and multi-color flow cytometry. Using this approach, 71 peptide-reactive T-cell populations were generated. The isolation of a T-cell line specifically recognizing target cells expressing the MAP4K1_IMA antigen demonstrates that identification of MiHA through this approach is in principle feasible. However, with the exception of the known MiHA HMHA1, none of the other T-cell populations that were generated demonstrated recognition of endogenously MiHA expressing target cells, even though recognition of peptide-loaded targets was often apparent.

Collectively these results demonstrate the technical feasibility of high-throughput analysis of antigen-specific T-cell responses in small patient samples. However, the high-sensitivity of this approach requires the use of potential epitope sets that are not solely based on MHC binding, to prevent the frequent detection of T-cell responses that lack biological relevance.

Immunological barriers to stem-cell based cardiac repair

Repair of damaged myocardium with pluripotent stem cell derived cardiomyocytes is becoming increasingly more feasible. Developments in stem cell research emphasize the need to address the foreseeable problem of immune rejection following transplantation. Pluripotent stem cell (PSC) derived cardiomyocytes have unique immune characteristics, some of which are not advantageous for transplantation. Here we review the possible mechanisms of PSC-derived cardiomyocytes rejection, summarize the current knowledge pertaining to immunogenicity of such cells and describe the existing controversies. Myocardial graft rejection can be reduced by modifying PSCs prior to their differentiation into cardiomyocytes. Overall, this approach facilitates the development of universal donor stem cells suitable for the regeneration of many different tissue types.

Sensitization to minor antigens is a significant barrier in bone marrow transplantation and is prevented by CD154:CD40 blockade

Sensitization to major histocompatibility complex (MHC) alloantigens is critical in transplantation rejection. The mechanism of sensitization to minor histocompatibility antigens (Mi-HAg) has not been thoroughly explored. We used a mouse model of allosensitization to Mi-HAg to study the Mi-HAg sensitization barrier in bone marrow transplantation (BMT). AKR mice were sensitized with MHC congenic Mi-HAg disparate B10.BR skin grafts. Adaptive humoral (B-cells) and cellular (T cells) responses to Mi-HAg are elicited. In subsequent BMT, only 20% of sensitized mice engrafted, while 100% of unsensitized mice did. In vivo cytotoxicity assays showed that Mi-HAg sensitized AKR mice eliminated CFSE labeled donor splenocytes significantly more rapidly than naïve AKR mice but less rapidly than MHC-sensitized recipients. Sera from Mi-HAg sensitized mice also reacted with cells from other mouse strains, suggesting that Mi-HAg peptides were broadly shared between mouse strains. The production of anti-donor-Mi-HAg antibodies was totally prevented in mice treated with anti-CD154 during skin grafting, suggesting a critical role for the CD154:CD40 pathway in B-cell reactivity to Mi-HAg. Moreover, anti-CD154 treatment promoted BM engraftment to 100% in recipients previously sensitized to donor Mi-HAg. Taken together, Mi-HAg sensitization poses a significant barrier in BMT and can be overcome with CD154:CD40 costimulatory blockade.

Immunomonitoring of graft-versus-host minor histocompatibility antigen correlates with graft-versus-host disease and absence of relapse after graft

BACKGROUND

After HLA-identical hematopoietic stem cell transplantation, minor histocompatibility (mH) antigen alloreactivity plays a dominant role in the development of graft-versus-host disease (GVHD) and graft versus leukemia (GVL).

STUDY DESIGN AND METHODS

We have analyzed the mH alloreactivity (enzyme-linked immunospot [ELISpot] for interferon-gamma[IFN-gamma] assay) from 24 donor/recipient pairs over a period of 2 years of follow-up and correlated such alloreactivity with the development of GVHD or absence of relapse. Circulating specific T cells anti-mH with multimer HLA-peptides were also studied.

RESULTS

We show by ELISpot IFN-gamma assay that alloreactivity during the first 3 months from donor versus recipient or donor versus mismatched identified mH antigens is associated with acute GVHD and GVL effect. In addition, we demonstrate that the donor-versus-recipient reactivity observed after the third month is highly associated with chronic GVHD and GVL (p = 0.0007). Finally, we show by multimer HLA-peptide assay that mH epitope-specific T cells present after 3 months are statistically related to the GVL effect.

CONCLUSIONS

Our results provide a robust method to monitor mH antigen graft-versus-host reaction and suggest that current identified mH have predictive value on GVHD and GVL.

Myeloid leukemic progenitor cells can be specifically targeted by minor histocompatibility antigen LRH-1–reactive cytotoxic T cells

CD8+ T cells recognizing minor histocompatibility antigens (MiHAs) on leukemic stem and progenitor cells play a pivotal role in effective graft-versus-leukemia reactivity after allogeneic stem cell transplantation (SCT). Previously, we identified a hematopoiesis-restricted MiHA, designated LRH-1, which is presented by HLA-B7 and encoded by the P2X5 purinergic receptor gene. We found that P2X5 is significantly expressed in CD34+ leukemic subpopulations from chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) patients. Here, we demonstrate that LRH-1–specific CD8+ T-cell responses are frequently induced in myeloid leukemia patients following donor lymphocyte infusions. Patients with high percentages of circulating LRH-1–specific CD8+ T cells had no or only mild graft-versus-host disease. Functional analysis showed that LRH-1–specific cytotoxic T lymphocytes (CTLs) isolated from 2 different patients efficiently target LRH-1–positive leukemic CD34+ progenitor cells from both CML and AML patients, whereas mature CML cells are only marginally lysed due to down-regulation of P2X5. Furthermore, we observed that relative resistance to LRH-1 CTL-mediated cell death due to elevated levels of antiapoptotic XIAP could be overcome by IFN-γ prestimulation and increased CTL-target ratios. These findings provide a rationale for use of LRH-1 as immunotherapeutic target antigen to treat residual or persisting myeloid malignancies after allogeneic SCT.

HapMap scanning of novel human minor histocompatibility antigens

Minor histocompatibility antigens (mHags) are molecular targets of allo-immunity associated with hematopoietic stem cell transplantation (HSCT) and involved in graft-versus-host disease, but they also have beneficial antitumor activity. mHags are typically defined by host SNPs that are not shared by the donor and are immunologically recognized by cytotoxic T cells isolated from post-HSCT patients. However, the number of molecularly identified mHags is still too small to allow prospective studies of their clinical importance in transplantation medicine, mostly due to the lack of an efficient method for isolation. Here we show that when combined with conventional immunologic assays, the large data set from the International HapMap Project can be directly used for genetic mapping of novel mHags. Based on the immunologically determined mHag status in HapMap panels, a target mHag locus can be uniquely mapped through whole genome association scanning taking advantage of the unprecedented resolution and power obtained with more than 3 000 000 markers. The feasibility of our approach could be supported by extensive simulations and further confirmed by actually isolating 2 novel mHags as well as 1 previously identified example. The HapMap data set represents an invaluable resource for investigating human variation, with obvious applications in genetic mapping of clinically relevant human traits.

A pilot study of allogeneic cellular therapy for patients with advanced hematologic malignancies

Allogeneic hematopoietic stem cell transplantation provides curative therapy for some patients with advanced hematologic malignancies. Disease response after allogeneic transplant is, at least in part, mediated by donor immune cells. In this report we describe a cellular therapy using haploidentical peripheral blood stem cells administered after very low dose total body irradiation (TBI) (100cGy). The donor cells were anticipated to be rejected, so no graft-versus-host (GVHD) prophylaxis was used. Patients with persistent disease beyond 8 weeks could be further treated with infusions of irradiated haploidentical donor cells. Of the 10 patients enrolled in the study, durable engraftment of allogeneic cells was seen in one patient. Two patients with resistant relapsed acute myelogenous leukemia (AML) had a disease response. Analysis of T cell reactivity from one patient who achieved a complete response but did not have durable engraftment of donor cells indicated that disease response was associated with the generation of host-derived anti-leukemic cytotoxic CD8+ T cells that reacted with an AML-associated proteinase 3 epitope. Results from this patient suggest that allogeneic therapy induced a host anti-tumor response associated with cytotoxic T cells reactive with a low affinity self-antigen.

Role of minor histocompatibility antigens in renal transplantation

In hematopoietic stem cell transplantation (HSCT), disparities between recipients and donors for minor histocompatibility antigens (mHags) have been shown to be related to graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effects. We investigated the effect of mHag mismatches on kidney allograft survival. Out of 33 785 kidney transplants on which DNA and clinical data were available to the Collaborative Transplant Study (CTS), 702 recipient/donor pairs could be identified as HLA-A, -B and -DRB1 matched first transplants of Caucasian origin. These pairs were typed for genetic polymorphisms of the mHags HA-1, HA-2, HA-3, HA-8, HB-1, ACC-1 and UGT2B17. Because mHags are presented in an HLA-restricted manner, only HLA-A*02 positive pairs were included in the analysis of HA-1, HA-2 and HA-8. Similarly, only HLA-A*01, HLA-B*44 and HLA-A*24 positive pairs were considered for the evaluation of HA-3, HB-1 and ACC-1, respectively, whereas UGT2B17 compatible transplants were assessed in HLA-A*29 and HLA-B*44 positive pairs. None of the mHag disparities showed a statistically significant effect on death-censored 5-year graft survival. This report represents the first large-scale study on the relevance of mHags in kidney transplantation.

Distribution of the minor histocompatibility antigens in Korean population and disparities in unrelated hematopoietic SCT

Minor histocompatibility antigens (mHags) are polymorphic peptides presented to T lymphocytes restricted by the MHC molecule. It has been reported that disparities of mHags are a potential risk factor for GVHD after hematopoietic SCT (HSCT). Here we observed allelic frequencies of HA-1, -2 and -8 in 139 Korean healthy individuals using PCR-sequence-specific primers, and analyzed the correlation between disparity of these mHags and acute GVHD (aGVHD) in 54 patients who underwent HSCT from unrelated HLA-identical donors. The allelic frequencies in Korean healthy individuals were 39.6 and 60.4% for HA-1(H) and HA-1(R), 92.4 and 7.6% for HA-2(M) and HA-2(V), 36.7 and 63.3% for HA-8(R) and HA-8(P), respectively. The frequencies of mHags incompatibility known to be associated with aGVHD were 16.7% in HA-1, 0% in HA-2 and 25.9% in HA-8. However, the statistically significant association of aGVHD with these mHags incompatibility was not found between healthy donors and leukemia patients after unrelated HSCT. This first report about mHags in Koreans may be helpful in further defining the clinical impact of mHags disparities in HSCT and in comparing with other populations.

Minor histocompatibility antigens as targets for immunotherapy using allogeneic immune reactions

Minor histocompatibility antigens (mHag) were originally identified as antigens causing graft rejection or graft-versus-host disease in human leukocyte antigen (HLA)-matched allogeneic transplantation. Molecular identification has revealed most to be major histocompatibility complex (MHC)-bound short peptide fragments encoded by genes which are polymorphic due to single nucleotide polymorphisms (SNP). Genotypic disparity of SNP between transplantation donors and recipients gives rise to mHag as non-self antigens for both the donor and the recipient. Subsequently, mHag have been explored as immunotherapeutic antigens for use against recurring hematological malignancies after allogeneic hematopoietic cell transplantation (HCT), because mHag expressed only on hematopoietic cells are considered to augment graft-versus-leukemia/lymphoma (GVL) effects without increasing the risk of life-threatening graft-versus-host disease (GVHD). Accumulating evidence suggests that T-cell responses to mHag aberrantly expressed on solid tumor cells are also involved in the eradication of sensitive tumors such as renal cell carcinomas following HCT. Over the past decade, the number of putative GVL-directed mHag has increased to a level that covers more than 30% of the Japanese patient population, so that clinical trials may now be executed in the setting of either vaccination or adoptive immunotherapy. As it is expected that immune responses to alloantigens are more powerful than to tumor antigens mostly derived from overexpressed self-proteins, mHag-based immunotherapy may lead to a new treatment modality for high-risk malignancies following allogeneic HCT.

Phenotype frequencies of autosomal minor histocompatibility antigens display significant differences among populations

Minor histocompatibility (H) antigens are allogeneic target molecules having significant roles in alloimmune responses after human leukocyte antigen-matched solid organ and stem cell transplantation (SCT). Minor H antigens are instrumental in the processes of transplant rejection, graft-versus-host disease, and in the curative graft-versus-tumor effect of SCT. The latter characteristic enabled the current application of selected minor H antigens in clinical immunotherapeutic SCT protocols. No information exists on the global phenotypic distribution of the currently identified minor H antigens. Therefore, an estimation of their overall impact in human leukocyte antigen-matched solid organ and SCT in the major ethnic populations is still lacking. For the first time, a worldwide phenotype frequency analysis of ten autosomal minor H antigens was executed by 31 laboratories and comprised 2,685 randomly selected individuals from six major ethnic populations. Significant differences in minor H antigen frequencies were observed between the ethnic populations, some of which appeared to be geographically correlated.

Alternative splicing due to an intronic SNP in HMSD generates a novel minor histocompatibility antigen

Here we report the identification of a novel human leukocyte antigen (HLA)-B44-restricted minor histocompatibility antigen (mHA) with expression limited to hematopoietic cells. cDNA expression cloning studies demonstrated that the cytotoxic T lymphocyte (CTL) epitope of interest was encoded by a novel allelic splice variant of HMSD, hereafter designated as HMSD-v. The immunogenicity of the epitope was generated by differential protein expression due to alternative splicing, which was completely controlled by 1 intronic single-nucleotide polymorphism located in the consensus 5' splice site adjacent to an exon. Both HMSD-v and HMSD transcripts were selectively expressed at higher levels in mature dendritic cells and primary leukemia cells, especially those of myeloid lineage. Engraftment of mHA(+) myeloid leukemia stem cells in nonobese diabetic/severe combined immunodeficient (NOD/SCID)/gammac(null) mice was completely inhibited by in vitro preincubation with the mHA-specific CTL clone, suggesting that this mHA is expressed on leukemic stem cells. The patient from whom the CTL clone was isolated demonstrated a significant increase of the mHA-specific T cells in posttransplantation peripheral blood, whereas mHA-specific T cells were undetectable in pretransplantation peripheral blood and in peripheral blood from his donor. These findings suggest that the HMSD-v-encoded mHA (designated ACC-6) could serve as a target antigen for immunotherapy against hematologic malignancies.

HLA Class I Epitopes: Recognition of Binding Sites by mAbs or Eluted Alloantibody Confirmed With Single Recombinant Antigens

Development of beads coated with single recombinant HLA antigens has permitted the confirmation and further definition of HLA class I epitopes. In this study, monoclonal antibodies (mAbs) or alloantibodies eluted from recombinant cell lines were tested for reactivity with Luminex beads individually coated with 79 recombinant HLA class I single antigen (rHLA SA). Published amino acid sequences were used to map epitopes common to sets of antigens reactive with each antibody. While several epitopes have already been demonstrated, this study confirmed them by adsorption of allosera with transfectants or SA beads having a single HLA antigen and specific binding of the eluted antibody on SA beads. The allosera and mAbs used in this study recognized a total of at least 58 HLA class I epitopes, as demonstrated by their different adsorption/reactivity patterns. Of these, 25 epitopes were characterized by a single unique common amino acid, 30 shared 2 signature amino acids in close proximity, and 3 epitopes involved 3 specific amino acids in a non-linear sequence. Since these epitopes may be targets for antibody-mediated allograft rejection, epitope analysis should complement HLA and CREG assignment for defining complex antibodies and identifying suitable donors for highly sensitized transplant patients.

Four-year follow-up of a prospective trial of HLA and MICA antibodies on kidney graft survival

In 2002, 1329 patients with functioning transplants were prospectively tested for HLA antibodies in the 13th International Histocompatibility Workshop. Four years after testing, deceased donor graft survival among 806 patients not having antibodies in 2002 was 81% compared to 58% for 158 patients with HLA antibodies (p < 0.0001) and 72% for 69 patients with MICA antibodies (p = 0.02). Hazard ratio (HR) using death-censored graft survival from multivariate analysis of HLA antibodies was 3.3 (p < 0.00001) and 2.04 for MICA (p = 0.01). In the 14th Workshop, at 1 year follow-up, survival for 1319 patients receiving deceased donor grafts and no HLA antibodies was 96% compared to 94% for 344 patients with HLA antibodies (p = 0.0004) and 83% survival for 33 patients with MICA (p = 0.0005). HR from multivariate analysis: HLA antibodies was 3.6 (p < 0.00001) and 6.1 for MICA (p = 0.006). Twelve patients with donor specific antibodies tested by single antigen beads had a 1 year survival of 64% (p = 0.008), and 27 patients with non-donor specific 'strong' antibodies had a 66% survival (p = 0.0003) compared to 92% survival in those with no antibodies. In conclusion, these two prospective trials, after 1 and 4 years, provided strong evidence that HLA and MICA antibodies are associated with graft failure.

A uniform genomic minor histocompatibility antigen typing methodology and database designed to facilitate clinical applications

BACKGROUND

Minor Histocompatibility (H) antigen mismatches significantly influence the outcome of HLA-matched allogeneic stem cell transplantation. The molecular identification of human H antigens is increasing rapidly. In parallel, clinical application of minor H antigen typing has gained interest. So far, relevant and simple tools to analyze the minor H antigens in a quick and reliable way are lacking.

METHODOLOGY AND FINDINGS

We developed a uniform PCR with sequence-specific primers (PCR-SSP) for 10 different autosomal minor H antigens and H-Y. This genomic minor H antigen typing methodology allows easy incorporation in the routine HLA typing procedures. DNA from previously typed EBV-LCL was used to validate the methodology. To facilitate easy interpretation for clinical purposes, a minor H database named dbMinor (http://www.lumc.nl/dbminor) was developed. Input of the minor H antigen typing results subsequently provides all relevant information for a given patient/donor pair and additional information on the putative graft-versus-host, graft-versus-tumor and host-versus-graft reactivities.

SIGNIFICANCE

A simple, uniform and rapid methodology was developed enabling determination of minor H antigen genotypes of all currently identified minor H antigens. A dbMinor database was developed to interpret the genomic typing for its potential clinical relevance. The combination of the minor H antigen genomic typing methodology with the online dbMinor database and applications facilitates the clinical application of minor H antigens anti-tumor targets after stem cell transplantation.

Allogeneic hematopoietic transplantation and natural killer cell recognition of missing self

Although the optimal donor for allogeneic hematopoietic stem cell transplantation (HSCT) is a human leukocyte antigen-matched sibling, 75% of patients do not have a match, and alternatives are matched unrelated volunteers, unrelated umbilical cord blood units, and full-haplotype-mismatched family members. To cure leukemia, allogeneic HSCT relies on donor T cells in the allograft, which promote engraftment, eradicate malignant cells, and reconstitute immunity. Here, we focus on the open issues of rejection, graft-versus-host disease (GVHD), and infections and the benefits of natural killer (NK) cell alloreactivity and its underlying mechanisms. Donor-versus-recipient NK cell alloreactivity derives from a mismatch between inhibitory receptors for self-major histocompatibility complex (MHC) class I molecules on donor NK clones and the MHC class I ligands on recipient cells. These NK clones sense the missing expression of the self-MHC class I allele on the allogeneic targets and mediate alloreactions. HSCT from 'NK alloreactive' donors controls acute myeloid relapse without causing GVHD. We review the translation of NK cell recognition of missing self into the clinical practice of allogeneic hematopoietic transplantation and discuss how it has opened innovative perspectives in the cure of leukemia.