Minor histocompatibility antigens: from transplantation problems to therapy of cancer

Dissection and molecular analysis of alloreactive CD8+ T cell responses in allogeneic haematopoietic stem cell transplantation

We applied a cDNA expression screening procedure with cryopreserved non-clonal CD8+ T cell populations (Lennerz et al., Proc. Natl. Acad. Sci. USA 102:16013-8, 2005) to the identification of candidate antigens for graft-versus-host disease (GvHD) and graft-versus-leukaemia (GvL) effects in allogeneic haematopoietic stem cell transplantation (allo-HSCT). In a patient-donor model system with HLA class I disparities, we identified an HLA-B*44 mismatch allele, HLA-B*4405, as the dominant target of alloreactive T cells expanded in vitro from donor peripheral blood mononuclear cells (PBMC). HLA-B*4405-reactive T cells were detectable after multiple in vitro stimulations in the patient's post-HSCT PBMC. In a patient-donor model with full HLA compatibility, the major target antigen of donor lymphocytes stimulated in vitro with the respective patient's pre-HSCT PBMC was restricted by HLA-A*0201 and was encoded by TRIM22-442 C, a newly detected polymorphic allele of the tripartite motif family member TRIM22 (synonym: STAF50), preferentially expressed in cells of the haematopoietic system. An arginine(R)-to-cysteine(C) exchange at position 442 generated an immunogenic T cell epitope equivalent to a minor histocompatibility antigen (mHag). TRIM22-442C-specific T cells persisted long-term in the patient's post-HSCT PBMC. Approximately, 1.3% of Caucasians carry TRIM22.442 C in association with HLA-A*0201. In particular, the knowledge of a large and diverse panel of such mHags may be crucial for further improvement of donor selection and adoptive T cell transfer strategies. The procedure applied herein will help to accelerate and facilitate their identification.

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.

Peptides from cellular proteins evoking alloimmune responses in human leukocyte antigen–identical transplantation are called minor histocompatibility (H) antigens. Upon hematopoietic stem cell transplantation (HSCT) for hematological malignancies or for solid tumors, responses to minor H antigens may have detrimental effects, e.g., graft-versus-host-disease and graft rejection, but can also significantly contribute to the eradication of the tumor cells. We designated the latter antigens as “tumor” minor H antigens. Current clinical trials aim at using these tumor minor H antigens to boost the graft-versus-tumor response. So far, it is unclear how frequently the HSCT recipient and donor differ in their minor H antigens and thus how many cancer patients are eligible for minor H antigen-based treatment. Therefore, worldwide 31 laboratories joined forces to determine the genotype and phenotype frequencies of ten autosomally encoded minor H antigens in six ethnic populations. The frequencies vary depending upon ethnic background and geographic location of the population, implying that the potential applicability of the tumor minor H antigens differs from one population to another. Depending on the population, the current theoretical percentages of clinical application of the eight tumor minor H antigens in HLA-matched combinations is estimated at 12% to 34%.

Pathophysiology of acute graft-versus-host disease: recent advances

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many malignant and nonmalignant hematologic diseases. Donor T cells from the allografts are critical for the success of this effective therapy. Unfortunately these T cells not only recognize and attack the disease cells/tissues but also the other normal tissues of the recipient as "foreign" or "nonself" and cause severe, immune-mediated toxicity, graft-versus-host disease (GVHD). Several insights into the complex pathophysiology of GVHD have been gained from recent experimental observations, which show that acute GVHD is a consequence of interactions between both the donor and the host innate and adaptive immune systems. These insights have identified a role for a variety of cytokines, chemokines, novel T-cell subsets (naĩve, memory, regulatory, and NKT cells) and for non-T cells of both the donor and the host (antigen presenting cells, delta T cells, B cells, and NK cells) in modulating the induction, severity, and maintenance of acute GVHD. This review will focus on the immunobiology of experimental acute GVHD with an emphasis on the recent observations.

In vivo imaging of T cell delivery to tumors after adoptive transfer therapy

Adoptive transfer therapy of in vitro-expanded tumor-specific cytolytic T lymphocytes (CTLs) can mediate objective cancer regression in patients. Yet, technical limitations hamper precise monitoring of posttherapy T cell responses. Here we show in a mouse model that fused single photon emission computed tomography and x-ray computed tomography allows quantitative whole-body imaging of (111)In-oxine-labeled CTLs at tumor sites. Assessment of CTL localization is rapid, noninvasive, three-dimensional, and can be repeated for longitudinal analyses. We compared the effects of lymphodepletion before adoptive transfer on CTL recruitment and report that combined treatment increased intratumoral delivery of CTLs and improved antitumor efficacy. Because (111)In-oxine is a Food and Drug Administration-approved clinical agent, and human SPECT-CT systems are available, this approach should be clinically translatable, insofar as it may assess the efficacy of immunization procedures in individual patients and lead to development of more effective therapies.

Allorecognition and the alloresponse: clinical implications

The artificial transfer of tissues or cells between genetically diverse individuals elicits an immune response that is adaptive and specific. This response is orchestrated by T lymphocytes that are recognizing, amongst others, major histocompatibility complex (MHC) molecules expressed on the surface of the transferred cells. Three pathways of recognition are described: direct, indirect and semi-direct. The sets of antigens that are recognized in this setting are also discussed, namely, MHC protein products, the MHC class I-related chain (MIC) system, minor histocompatibility antigens and natural killer cell receptor ligands. The end product of the effector responses are hyperacute, acute and chronic rejection. Special circumstances surround the situation of pregnancy and bone marrow transplantation because in the latter, the transferred cells are the ones originating the immune response, not the host. As the understanding of these processes improves, the ability to generate clinically viable immunotherapies will increase.

T cell therapies following hematopoietic stem cell transplantation: surely there must be a better way than DLI?

Advances in the past few years have significantly improved adoptive immunotherapy strategies available following autologous and allogeneic hematopoietic stem cell transplantation (HSCT). Minimal residual disease, relapsed disease and viral infections remain a significant cause of mortality in patients undergoing HSCT. Novel therapies are critically needed to overcome these management dilemmas, while sparing the graft-versus-tumor effect and avoiding graft-versus-host disease. This review focuses on the T-cell strategies currently available to allay disease while minimizing toxicities in patients who have undergone HSCT.

Chronic graft-versus-host disease in the era of reduced-intensity conditioning

In the past decade the field of hematopoietic stem cell transplantation has entered a new era with the introduction of reduced intensity conditioning (RIC) regimens. The impact of RIC on the incidence of chronic graft-versus-host disease (GVHD) has not been evaluated systematically. Factors confounding such analyses include short follow-up in studies, absence of prospective comparison trials, use of a variety of RIC regimens, lack of uniform GVHD prophylaxis and lack of rigorous criteria for the diagnosis and staging of chronic GVHD. This review discusses factors that appear to influence the incidence and clinical presentation of chronic GVHD in the RIC transplantation era. Overall, RIC seems to decrease the incidence and severity of acute GVHD through day 100 post-transplant when compared to conventional conditioning; however, there is little evidence to suggest that chronic GVHD is reduced after RIC. For the more definitive assessments of chronic GVHD after RIC it will be important to study this question in prospective comparison trials with long duration of follow-up. The recent National Institutes of Health chronic GVHD consensus project recommendations provide now the critically needed standardized guidelines for the diagnosis, classification and staging of chronic GVHD.

New directions in the genomics of allogeneic hematopoietic stem cell transplantation

Despite optimal supportive care and high-resolution HLA matching, complications such as GVHD and infection remain major barriers to the success of allogeneic HCT (allo-HCT). This has led to growing interest in the non-HLA genetic determinants of complications after allo-HCT. Most studies have examined genetic predictors of GVHD, relapse, and mortality and have focused on 3 main areas: minor histocompatibility antigen (miHAs), inflammatory mediators of GVHD, and more recently NK cell-mediated allorecognition. The genetic basis of other outcomes such as infection and drug toxicity are less well studied but are being actively investigated. High-throughput methodologies such as single nucleotide polymorphism arrays are enabling the study of hundreds of thousands of genetic markers throughout the genome and the interrogation of novel genetic variants such as copy number variations. These data offer the opportunity to better predict those at risk of complications and to identify novel targets for therapeutic intervention. This review examines the current data regarding the non-HLA genomics of allo-HCT and appraises the promises and pitfalls for integration of this new genetic information into clinical transplantation practice.

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.

Human Leukocyte Antigen DR15 Is Associated with Reduced Relapse Rate and Improved Survival after Human Leukocyte Antigen-Identical Sibling Hematopoietic Stem Cell Transplantation

Human leukocyte antigen (HLA) DR15 is associated with autoimmune cytopenia in patients with aplastic anemia, myelodysplastic syndrome, and paroxysmal nocturnal hemoglobinuria. Presence of this antigen also predicts response to immunosuppressive treatment. If DR15 expression on hematopoietic cells also favors induction of immune responses in an allogeneic setting, a lower relapse rate after hematopoietic stem cell transplantation (HSCT) might result through an enhanced graft-versus-leukemia effect. We retrospectively analyzed outcome of HLA-identical sibling HSCT in 192 consecutive patients with acute or chronic leukemia or non-Hodgkin lymphoma. Patients carrying the DR15 antigen had a higher estimated 5-year overall survival (76%) than did DR15-negative patients (55%; P = .04). Improved survival for DR15 patients was due to a significant decrease in death from relapse (5% for DR15(+) versus 24% for DR15(-); P = .02), whereas no difference was seen for rates of transplant-related mortality (19% and 21%, respectively; P = .76). Findings were confirmed by multivariate analyses. Our results show an association of DR15 with a decreased risk of disease relapse and improved survival after HSCT for leukemia or non-Hodgkin lymphoma. This adds to the growing list of links between DR15 and immune reactions in hematopoiesis.