CD31 mismatching affects marrow transplantation outcome

Systematic identification of minor histocompatibility antigens predicts outcomes of allogeneic hematopoietic cell transplantation

T cell alloreactivity against minor histocompatibility antigens (mHAgs)-polymorphic peptides resulting from donor-recipient (D-R) disparity at sites of genetic polymorphisms-is at the core of the therapeutic effect of allogeneic hematopoietic cell transplantation (allo-HCT). Despite the crucial role of mHAgs in graft-versus-leukemia (GvL) and graft-versus-host disease (GvHD) reactions, it remains challenging to consistently link patient-specific mHAg repertoires to clinical outcomes. Here we devise an analytic framework to systematically identify mHAgs, including their detection on HLA class I ligandomes and functional verification of their immunogenicity. The method relies on the integration of polymorphism detection by whole-exome sequencing of germline DNA from D-R pairs with organ-specific transcriptional- and proteome-level expression. Application of this pipeline to 220 HLA-matched allo-HCT D-R pairs demonstrated that total and organ-specific mHAg load could independently predict the occurrence of acute GvHD and chronic pulmonary GvHD, respectively, and defined promising GvL targets, confirmed in a validation cohort of 58 D-R pairs, for the prevention or treatment of post-transplant disease recurrence.

Extracellular vesicles as potential biomarkers of acute graft-vs-host disease

Acute graft-vs-host disease (GVHD) is a serious complication after allografting. We carried out an exploratory study to investigate a potential correlation of surface antigens on extracellular vesicles (EVs) and acute GVHD. EVs were extracted from serum samples from 41 multiple myeloma patients who underwent allografting. EVs were characterized by flow cytometry using a panel of 13 antibodies against specific membrane proteins that were reported to be predictive of acute GVHD. We observed a correlation between three potential biomarkers expressed on EV surface and acute GVHD onset by both logistic regression analysis and Cox proportional hazard model. In our study, CD146 (MCAM-1) was correlated with an increased risk-by almost 60%-of developing GVHD, whereas CD31 and CD140-α (PECAM-1 and PDGFR-α) with a decreased risk-by almost 40 and 60%, respectively. These biomarkers also showed a significant change in signal level from baseline to the onset of acute GVHD. Our novel study encourages future investigations into the potential correlation between EVs and acute GVHD. Larger prospective multicenter studies are currently in progress.

CD31 signals confer immune privilege to the vascular endothelium

Constitutive resistance to cell death induced by inflammatory stimuli activating the extrinsic pathway of apoptosis is a key feature of vascular endothelial cells (ECs). Although this property is central to the maintenance of the endothelial barrier during inflammation, the molecular mechanisms of EC protection from cell-extrinsic, proapoptotic stimuli have not been investigated. We show that the Ig-family member CD31, which is expressed by endothelial but not epithelial cells, is necessary to prevent EC death induced by TNF-α and cytotoxic T lymphocytes in vitro. Combined quantitative RT-PCR array and biochemical analysis show that, upon the engagement of the TNF receptor with TNF-α on ECs, CD31 becomes activated and, in turn, counteracts the proapoptotic transcriptional program induced by TNF-α via activation of the Erk/Akt pathway. Specifically, Akt activation by CD31 signals prevents the localization of the forkhead transcription factor FoxO3 to the nucleus, thus inhibiting transcription of the proapoptotic genes CD95/Fas and caspase 7 and de-repressing the expression of the antiapoptotic gene cFlar. Both CD31 intracellular immunoreceptor tyrosine-based inhibition motifs are required for its prosurvival function. In vivo, CD31 gene transfer is sufficient to recapitulate the cytoprotective mechanisms in CD31(-) pancreatic β cells, which become resistant to immune-mediated rejection when grafted in fully allogeneic recipients.

An immunologist's guide to CD31 function in T-cells

Although it is expressed by all leukocytes, including T-, B-lymphocytes and dendritic cells, the immunoglobulin-like receptor CD31 is generally regarded by immunologists as a marker of endothelial cell lineage that lacks an established functional role in adaptive immunity. This perception has recently been challenged by studies that reveal a key role for this molecule in the regulation of T-cell homeostasis, effector function and trafficking. The complexity of the biological functions of CD31 results from the integration of its adhesive and signaling functions in both the immune and vascular systems. Signaling by means of CD31 is induced by homophilic engagement during the interactions of immune cells and is mediated by phosphatase recruitment or activation through immunoreceptor tyrosine inhibitory motifs (ITIMs) that are located in its cytoplasmic tail. Loss of CD31 function is associated with excessive immunoreactivity and susceptibility to cytotoxic killing. Here, we discuss recent findings that have brought to light a non-redundant, complex role for this molecule in the regulation of T-cell-mediated immune responses, with large impact on our understanding of immunity in health and disease.

Impact of CD31 mismatches on the outcome of hematopoeitic stem cell transplant of HLA-identical sibling

Graft-versus host disease (GVHD) complicating allogeneic hematopoeitic stem cell transplantation (HSCT) is often attributed to mismatching of minor histocompatibility antigens (mHags), which are poorly defined in humans. CD31 is a candidate human mHag relevant to acute GVHD (aGVHD), but reports disagree about its level of significance. Therefore, we examined the impact of CD31-matching on the outcome of HSCT in different hematological and immunological diseases. About 60 patients receiving HSC from their respective HLA-ABCDR and DQ-identical sibling were studied. DNA was used to study the CD31 allele polymorphism at the codon 125 (LL, LV or VV) in the patient-donor pairs using the principle of allele-specific PCR amplification. Four primer were used; two primers (forward and reverse) for the L allele and another two for the V allele. The CD31 identity was tested for correlation with HSCT outcome measures of aGVHD, chronic GVHD, and relapse. The gene frequency of CD31 alleles (LL, VV and LV) was 28.3, 20 and 51.7%, respectively. CD31 identity was found in 31 pairs (51.7%) versus 29 pairs (48.3%) for nonidentity. The CD31 noncompatibility showed statistical non-significant relation with aGVHD (G 0-I, and G II-IV) and chronic GVHD (De-novo and chronic on acute) (p = 0.59, p = 0.62, p = 036 and p = 0.83, respectively). The CD31 nonidentity had statistical significant relation with aGVHD versus no aGVHD (p = 0.008 and OR = 4.46). The CD31 nonidentity showed statistical significant relation with aGVHD (II-IV) versus no aGVHD (p = 0.012 and OR = 7.14) and also, aGVHD (0-I) versus the no aGVHD (p = 0.03, OR = 3.13, respectively). A statistical significant relation was found between CD31 nonidentity in patient-donor pairs and relapse (p = 0.014 and OR = 4.21). In conclusion, the donor-recipient CD31 nonidentity is a significant risk factor for aGVHD and relapse in HLA-identical sibling.

Biologic markers of chronic GVHD

Biologic markers of chronic GVHD may provide insight into the pathogenesis of the syndrome, identify molecular targets for novel interventions, and facilitate advances in clinical management. Despite extensive work performed to date largely focused on prediction and diagnosis of the syndrome, little synthesis of findings and validation of promising candidate markers in independent populations has been performed. Studies suggest that risk for subsequent chronic GVHD development may be associated with donor-recipient genetic polymorphism, deficiency in regulatory immune cell populations (NK, Treg, DC2), and variation in inflammatory and immunoregulatory mediators post-HCT (increased TNFα, IL-10 and BAFF, and decreased TGFβ and IL-15). Established chronic GVHD is associated with alteration in immune cell populations (increased CD3(+) T cells, Th17, CD4(+) and CD8(+) effector memory cells, monocytes, CD86 expression, BAFF/B cell ratio, and deficiency of Treg, NK cells, and naïve CD8(+) T cells). Inflammatory and immunomodulatory factors (TNFα, IL-6, IL-1β, IL-8, sIL-2R, and IL-1Ra, BAFF, anti-dsDNA, sIL-2Rα, and sCD13) are also perturbed. Little is known about biologic markers of chronic GVHD phenotype and severity, response to therapy, and prognosis.

Association between genetic variants in adhesion molecules and outcomes after hematopoietic cell transplants

Allogeneic hematopoietic cell transplant (HCT) is associated with a high morbidity and mortality. Adhesion molecules play an important role in endothelial activation and initiation of inflammatory response. We hypothesized that single nucleotide polymorphisms (SNPs) in the endothelial molecules may contribute to heterogeneity in HCT outcomes. We evaluated the association of 4 SNPs in ICAM1 (rs5498), PECAM1 (rs668 and rs1131012) and SELL (rs2229569) genes with acute and chronic graft-versus-host disease (GvHD) and those experiencing transplant-related mortality (TRM) within 1 year among 425 allogeneic HCT recipient-donor pairs. Using a Fine and Gray proportional hazards model to evaluate the association between genetic variants and clinical outcomes, after adjustment for recipient age, race, diagnosis, disease status, gender mismatch, cytomegalovirus serostatus, gender, donor type, conditioning regimen and year of transplant, only rs5498 in the ICAM1 gene among both recipients and donors was associated with a decreased risk of TRM (P ≤ 0.02). None of the SNPs were associated with acute or chronic GvHD risk. These findings suggest that genetic variants in the vascular adhesion molecules may be used to identify patients at high risk for TRM.

Do FY antigens act as minor histocompatibility antigens in the graft-versus-host disease paradigm after human leukocyte antigen-identical sibling hematopoietic stem cell transplantation?

FY antigens are candidate minor histocompatibility antigens relevant to renal allograft rejection, but no data have been reported about their role in graft-versus-host disease (GVHD) incidence after human leukocyte antigen (HLA)-identical siblings hematopoietic stem cell transplantation (HSCT). The aim of this study was to examine the effect of donor/recipient disparity at FY antigens on the incidence of GVHD in Tunisian patients receiving an HLA-identical HSCT. This work enrolled 105 Tunisian pairs of recipients and their HLA-identical sibling donors of HSCs. FY genotyping was performed with the polymerase chain reaction-sequence-specific primer method and donor/recipient disparity for these antigens was analyzed at two levels: incompatibility and nonidentity. The case-control analyses showed no significant correlation between FY disparity and the incidence of either acute or chronic GVHD. Sample size calculation showed that 572 cases and 1716 controls would be necessary to be able to detect a significant association with 80% power and two-sided type I error level of 5% (α=0.05). The lack of association in the studied cohort may be explained by the low immunogenicity of FY antigens in HSCT context, compared with other antigens such as HA-1 and CD31.

NCI, NHLBI first international consensus conference on late effects after pediatric hematopoietic cell transplantation: etiology and pathogenesis of late effects after HCT performed in childhood--methodologic challenges

Hematopoietic cell transplantation (HCT) is now a curative option for certain categories of patients with hematologic malignancies and other life-threatening illnesses. Technical and supportive care has resulted in survival rates that exceed 70% for those who survive the first 2 years after HCT. However, long-term survivors carry a high burden of morbidity, including endocrinopathies, musculoskeletal disorders, cardiopulmonary compromise, and subsequent malignancies. Understanding the etiologic pathways that lead to specific post-HCT morbidities is critical to developing targeted prevention and intervention strategies. Understanding the molecular underpinnings associated with graft-versus-host disease (GVHD), organ toxicity, relapse, opportunistic infection, and other long-term complications now recognized as health care concerns will have significant impact on translational research aimed at developing novel targeted therapies for controlling chronic GVHD, facilitating tolerance and immune reconstitution, reducing risk of relapse and secondary malignancies, minimizing chronic metabolic disorders, and improving quality of life. However, several methodological challenges exist in achieving these goals; these issues are discussed in detail in this paper.

Minor histocompatibility antigens in Tunisians: could platelet endothelial cell adhesion molecule 1 marker be one of them?

Platelet endothelial cell adhesion molecule 1 (PECAM-1/CD31) is one of the human minor histocompatibility antigens that are the main targets of alloreactive T-cells after hematopoietic stem cells or solid organs transplantation. In order to investigate its polymorphism in Tunisians, three single nucleotide polymorphisms (SNPs) (rs668, rs12953 and rs1131012) were selected to perform an allele and haplotype analysis. Hundred-and-forty-two healthy and unrelated subjects were enrolled in this survey. Genomic DNAs were extracted using salting out method. SNP genotyping assays were performed with home-designed sequence-specific primers polymerase chain reaction (SSP-PCR). As a result, molecular analysis showed that PECAM-1 is one of the most polymorphic markers in the Tunisian population because minor allele frequency was 0.3, and minimum haplotype frequency was 0.03. A low linkage disequilibrium (D' = 0.45) between rs12953 and rs1131012 was noticed, although all other loci were in the Hardy-Weinberg equilibrium (minimum P value = 0.07). The frequencies were close to those reported in African-American and Caucasian groups.

Investigation of the effect of donor platelet endothelial cell adhesion molecule 1 polymorphism on the graft-vs.-host disease occurrence in Tunisian recipients of hematopoietic stem cells

OBJECTIVE

The aim of this study is to examine the effect of donor PECAM-1 alleles and haplotypes for the SNPs L98V, S536N, and R643G on the occurrence of GVHD in Tunisian recipients of HSCs.

DESIGN AND METHODS

This study enrolled 102 patients and their 102 respective HLA-identical sibling donors of HSCs. The PECAM-1 SNPs genotyping assay was performed using sets of sequence specific primers (SSP-PCR).

RESULTS

The single marker association analysis showed that the L98 allele, in a recessive genetic model, may be a potential risk factor only for acute GVHD (p=0.036, OR=2.580, 95% C.I. = 1.053-6.326). However, the haplotype analysis showed a lack of association between donor's PECAM-1 SNPs and GVHD incidence in recipient.

CONCLUSION

The homozygosity state for donor PECAM-1L98 allele may be a significant risk factor for acute GVHD. This is probably due to its action on the function of donor leukocytes especially during the extravasation process.

Acute graft-vs.-host disease correlates with the disparity for the PECAM-1 S536N polymorphism only in the HLA-B44-like positive Tunisian recipients of HSCs

GVHD is the major cause of mortality after HLA-identical HSCT. Such complication has been widely linked to donor/recipient disparity for minor histocompatibility antigens (MiHAgs). PECAM-1 is one of potential human MiHAgs but its effect on the GVHD occurrence remains not clear. In order to examine such association in the Tunisian cohort of HSCs recipients, we performed a retrospective study on patients who undergone HLA-identical HSCT between 2000 and 2009. Genotyping of the three selected PECAM-1 polymorphisms (rs668, rs12953 and rs1131012) was performed with SSP-PCR method. Univariate analyses showed that grades II-IV acute GVHD were considerably linked to the non-identity for rs12953 only in HLA-B44-like positive patients (p=0.010, OR=10.000). Multivariate analysis for chronic GVHD showed that this outcome may be affected only by the adulthood and the conditioning regimen. Our findings support the previously reported data suggesting a significant association between the PECAM-1 disparity and the risk of acute GVHD.

Genetic polymorphisms of adhesion molecules and kidney transplant survival

BACKGROUND.: Adhesion molecules play a key role in the recruitment of leukocytes to sites of inflammation. Genetic polymorphisms of adhesion molecules may alter their expression or function and may thereby influence the process of leukocyte infiltration in the transplanted organ. It has also been suggested that polymorphic adhesion molecules may act as minor histocompatibility antigens. METHODS.: In two randomly selected cohorts (954 and 1002 kidney transplants), the effect of L-selectin/CD62L (codon 206 and 213), platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31; codon 125, 563, and 670), and activated leukocyte cell adhesion molecule (ALCAM/CD166; codon 258) single nucleotide polymorphisms on 5-yr allograft survival was investigated. DNA samples and clinical data were provided by the Collaborative Transplant Study. Recipients and donors were genotyped by polymerase chain reaction sequence-specific primer. A multivariate analysis was performed using a Cox regression model. RESULTS.: Incompatibility for L-selectin at codon 213 was significantly associated with better graft survival in the first cohort, but the effect could not be replicated in the second cohort. Polymorphisms of PECAM-1 and ALCAM had no impact on graft outcome. CONCLUSIONS.: This is the first comprehensive and large-scale study on the relevance of L-selectin, PECAM-1, and ALCAM genetic polymorphisms in kidney transplantation, showing no significant associations of recipient or donor genotypes with allograft survival. Because the effect of L-selectin mismatch was not reproducible, a putative role of adhesion molecules as minor histocompatibility antigens cannot be confirmed. Our results demonstrate the importance of testing large sample sizes and of performing confirmation studies to validate genetic associations.

Effects of mismatching for minor histocompatibility antigens on clinical outcomes in HLA-matched, unrelated hematopoietic stem cell transplants

Several studies in HLA-matched sibling hematopoietic stem cell transplantation (HSCT) have reported an association between mismatches in minor histocompatibility antigens (mHAg) and outcomes. We assessed whether single and multiple minor mHAg mismatches are associated with outcomes in 730 unrelated donor, HLA-A, B, C, DRB1, and DQB1 allele-matched hematopoietic stem cell transplants (HSCT) facilitated by the National Marrow Donor Program (NMDP) between 1996 and 2003. Patients had acute and chronic leukemia or myelodysplastic syndrome (MDS), received myeloablative conditioning regimens and calcineurin inhibitor-based graft-versus-host-disease (GVHD) prophylaxis, and most received bone marrow (BM; 85%). Donor and recipient DNA samples were genotyped for mHAg including: HA-1, HA-2, HA-3, HA-8, HB-1 and CD31(125/563). Primary outcomes included grades III-IV acute GVHD (aGVHD) and survival; secondary outcomes included chronic GVHD (cGVHD), engraftment, and relapse. Single disparities at HA-1, HA-2, HA-3, HA-8, and HB-1 were not significantly associated with any of the outcomes analyzed. In HLA-A2-positive individuals, single CD31(563) or multiple mHAg mismatches in the HVG vector were associated with lower risk of grades III-IV aGVHD. Based on these data, we conclude that mHAg incompatibility at HA-1, HA-2, HA-3, HA-8, HB-1, and CD31 has no detectable effect on the outcome of HLA matched unrelated donor HSCT.

Haematopoietic stem cell transplantation: can our genes predict clinical outcome?

Haematopoietic stem cell transplantation (HSCT) is currently the only curative treatment for many patients with malignant and non-malignant haematological diseases. The success of HSCT is greatly reduced by the development of complications, which include graft-versus-host disease (GVHD), relapse and infection. Human leukocyte antigen (HLA) matching of patients and donors is essential, but does not completely prevent these complications; non-HLA genes may also have an impact upon transplant outcome. Polymorphisms within genes that are associated with an individual's capability to mount an immune response to alloantigen and infectious pathogens and/or response to drugs (pharmacogenomics) are all currently being studied for their association with HSCT outcome. This review summarises the potential role of non-HLA polymorphisms in predicting HSCT outcome, from studies on retrospective transplant cohorts of HLA-identical siblings and matched unrelated donors. The clinical relevance and interpretation of non-HLA genetics, and how these could be used alongside clinical risk factors in HSCT, are also discussed.

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.

CD31/PECAM-1 genotyping and haplotype analyses show population diversity

Using direct sequencing of complementary DNA products, the sequences of human CD31 from exon 1 through exon 16 of 179 individuals (139 unrelated) were systematically examined. Of the 14 biallelic single nucleotide polymorphic sites detected, 7 polymorphic sites involved amino acid substitution. These 14 polymorphic sites yielded 18 observed CD31 alleles and 9 predicted CD31 polypeptide sequences. Based on molecular haplotyping and family pedigree analysis, linkage disequilibrium among some single nucleotide polymorphic sites was observed. Single nucleotide polymorphism frequencies between populations were also measured using dot-blot hybridization with DNA or peptide nucleic acid probes.

Toward biomarkers for chronic graft-versus-host disease: National Institutes of Health consensus development project on criteria for clinical trials in chronic graft-versus-host disease: III. Biomarker Working Group Report

Biology-based markers that can be used to confirm the diagnosis of chronic graft-versus-host disease (GVHD) or monitor progression of the disease could help in the evaluation of new therapies. Biomarkers have been defined as any characteristic that is objectively measured and evaluated as an indicator of a normal biologic or pathogenic process, a pharmacologic response to a therapeutic intervention, or a surrogate end point intended to substitute for a clinical end point. The following applications of biomarkers could be useful in chronic GVHD clinical trials or management: (1) predicting response to therapy; (2) measuring disease activity and distinguishing irreversible damage from continued disease activity; (3) predicting the risk of developing chronic GVHD; (4) diagnosing chronic GVHD: (5) predicting the prognosis of chronic GVHD; (6) evaluating the balance between GVHD and graft-versus-leukemia effects (graft-versus-leukemia or GVT); and (7) serving as a surrogate end point for therapeutic response. Such biomarkers can be identified by either hypothesis-driven testing or by high-throughput discovery-based methods. To date, no validated biomarkers have been established for chronic GVHD, although several candidate biomarkers have been identified from limited hypothesis-driven studies. Both approaches have merit and should be pursued. The consistent treatment and standardized documentation needed to support biomarker studies are most likely to be satisfied in prospective clinical trials.

PECAM-1, a key player in neuroinflammation

Platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) is a 130-kDa protein, which plays a significant role in the adhesion cascade. It is therefore involved in leucocyte endothelium interaction and in leucocyte transendothelial migration during inflammation. As neuroinflammation and subsequent blood brain barrier disruption are integral processes in many neurological disorders, PECAM-1 and its soluble form (sPECAM-1) have been investigated in a number of conditions, rising hopes as a potential marker of disease activity, a possible target in treatment and a prognostic factor. It has been shown that serum and CSF levels of PECAM-1 and sPECAM-1 are increased in patients in active stages of multiple sclerosis. Similarly, they rise in individuals after ischaemic stroke. PECAM-1 has also been shown to be involved in the pathogenesis of Abeta-related cerebral vascular disorders, such as Alzheimer disease. It participates in the pathomechanism of paraneoplastic neurological disorders and in neuroinflammation in NeuroAIDS. A number of experiments on animal models were carried out in order to investigate PECAM-1 role in the above-mentioned conditions and more, including brain trauma and nerve root injury. In this review most recent investigations on PECAM-1 biology and its role in neuroinflammation have been described and discussed from a multidisciplinary point of view.

Mismatch of minor histocompatibility antigen contributes to a graft-versus-leukemia effect rather than to acute GVHD, resulting in long-term survival after HLA-identical stem cell transplantation in Japan

We determined the alleles of five polymorphic molecules including HA-1 and four adhesion molecules for 106 patients transplanted with HLA-identical stem cell grafts and investigated the association of mismatches as correlates of relapse and graft-versus-host disease (GVHD). All 106 recipients underwent stem cell transplantation (SCT) after myeloablative conditioning between 1985 and 2002. Risk status of disease at SCT was standard (n=63) and high (n=42). After SCT, 36, 49 and 33 developed acute GVHD, chronic GVHD and relapsed, respectively. Our patients relapsed at rates of 16.7 and 38.6% with one or more and without incompatibilities (P=0.013). The relapse rates of patients with CD62L, CD31 codon 563, CD31 codon 125, HA-1 and CD49b incompatibilities were 5.9, 11.8, 15.4, 16.0 and 33.3%, respectively. The frequency of acute GVHD did not differ regardless of incompatibilities. In standard-risk group, the accumulated relapse rates of 19 and 44 patients with and without minor histocompatibility antigen incompatibility were 22% and unexpectedly 66%, respectively (P=0.02). The probability of 12-year survival was 88% in the former and 66% in the latter patients (P=0.03). Our data suggest that incompatibility of CD62L, CD31 codon 563 and CD31 codon 125 contributes to a graft-versus-leukemia effect rather than to GVHD, resulting in prolonged survival after HLA-identical SCT.

The alleles of PECAM-1

Previous studies have reported the existence of eleven different single nucleotide polymorphisms (SNPs) within human PECAM-1 mRNA, several of which have recently been associated with disease. Though SNPs in the PECAM-1 gene have been known for some time, the genetic background on which they exist, and their association into distinct allelic isoforms has not yet been established. To identify the major allelic isoforms of PECAM-1, we determined the nucleotide sequence of individual full-length cloned cDNAs derived from anonymous, unrelated volunteer individuals. Initial sequence analysis of 34 alleles from 17 individuals confirmed the presence of two distinct human PECAM-1 alleles (L(98)S(536)R(643) and V(98)N(536)G(643)) within the human population. Each of these were found, upon more detailed analysis, to be superimposed on a previously unreported a2479g nucleotide polymorphism within the 3' untranslated region (3'UTR) that occurred on both allelic isoforms - yielding a total of four major alleles. Multiplex Luminex bead analysis of an additional 259 individuals allowed identification of 117 individuals homozygous for either the L(98)S(536) or V(98)N(536) allele, and sequence analysis around the R643G and a2479g polymorphic sites permitted accurate determination of significant differences in the gene frequencies of LSRa, LSRg, VNGa, and VNGg among Caucasian individuals. Identification of these PECAM-1 allelic isoforms should facilitate future detailed examination of PECAM-1-related disease associations, and may help resolve previously disparate results.

Multiplex Genotyping of Human Minor Histocompatibility Antigens

Minor histocompatibility antigens (mHAg) induce major histocompatibility complex-restricted, T cell-mediated immune responses that may contribute to increased risk of graft-versus-host disease and graft-versus-leukemia effects. Unlike human leukocyte antigen genes, mHAg are encoded by genetically and functionally unrelated genes located throughout the chromosome. The role of mHAg in stem cell transplantation and the population frequencies of mHAg alleles remain unknown due in part to the lack of suitable high throughput methods for genotyping these diverse genes. Here we describe the development and utility of a multiplexed Luminex assay for genotyping human mHAg, including HA-1, HA-2, HA-3, HA-8, HB-1, CD31(125), and CD31(563). The assay uses a multiplexed, allele-independent, gated amplification of mHAg genes followed by differential detection of allele-specific primer extension products using the MultiCode PLx system (EraGen Biosciences, Madison, WI). The alleles are interrogated using a multiplex allele-specific primer extension reaction using primers tagged with EraCodes. The products are hybridized to Luminex beads and the hybridization duplexes are detected using streptavidin-phycoerythrin. The assay resolved the mHAg genotypes of 259 Caucasian donors and provided population estimates of mHAg gene and phenotypic frequencies. All mHAg alleles evaluated in this study exhibited Hardy-Weinberg equilibrium, although some mHAg phenotypes were present in large majority of individuals tested (HA-2, HB-1). This assay will provide a valuable tool for determining mHAg frequencies in other ethnic populations, as well as for establishing the clinical importance of mHAg disparities in stem cell transplantation.

Hematopoietic stem and progenitor cells: clinical and preclinical regeneration of the hematolymphoid system

A vast literature exists on the biology of blood formation and regeneration under experimental and clinical conditions. The field of hematopoiesis was recently advanced by the capacity to purify to homogeneity primitive hematopoietic stem and progenitor cells. Isolation of cells at defined maturational stages has enhanced the understanding of the fundamental nature of stem cells, including how cell fate decisions are made, and this understanding is relevant to the development of other normal as well as malignant tissues. This review updates the basic biology of hematopoietic stem cells (HSC) and progenitors, the evolving use of purified HSC as grafts for clinical hematopoietic cell transplantation (HCT) including immune tolerance induction, and the application of HSC biology to other stem cell fields.

Donor CD31 genotype and its association with acute graft-versus-host disease in HLA identical sibling stem cell transplantation

CD31 gene polymorphisms are implicated in the pathogenesis of graft-versus-host disease (GvHD) following haematopoietic stem cell transplantation (HST). We investigated the influence of CD31 genotype on the incidence of GvHD following HST from an human leukocyte antigen (HLA)-identical sibling donor. Donor and recipient CD31 codons 125, 563 and 670 DNA polymorphisms were determined in 85 cases of HLA identical sibling HST from two transplant centres. A correlation between CD31 genotype and acute GvHD was considered significant if observed in patients from both transplant centres independently. A strong correlation was identified between donor CD31 codon 125 genotype and the incidence of acute GvHD. Acute GvHD grades II-IV occurred in 27 of 46 (59%) recipients with a CD31 codon 125 leucine / valine heterozygous donor compared to nine of 39 (23%) recipients with a CD31 codon 125 homozygous donor (P=0.0019, relative-risk 2.45, 95% confidence interval 1.3-4.5). This correlation was significant in patients from both transplant centres (P=0.015 and P=0.019). We suggest that CD31 genotype may influence the function of donor-derived leukocytes and may be informative when there is a choice of comparable donors.

The FcγRIIa-polymorphic site as a potential target for acute graft-versus-host disease in allogeneic stem cell transplantation

Graft-versus-host disease (GVHD) is a serious complication of allogeneic stem cell transplantation for hematologic diseases. Antigen mismatches due to polymorphic differences between the patient and donor are central in the mechanisms of GVHD. Polymorphisms are known for FcgammaRIIa, and this molecule is present on endothelial, dendritic, and Langerhans cells. Donor cells reacting against the patient as GVHD can also react against the malignancy of the patient, and this is known as the graft-versus-leukemia (GVL) effect. Because the FcgammaRIIa molecule is also present on acute myeloid leukemia (AML) cells, an FcgammaRIIa mismatch could be a target for both GVHD and GVL. We retrospectively studied 73 AML patients and analyzed the differences in GVHD and relapse incidence between patients with and without a pro-GVHD/GVL FcgammaRIIa allotype mismatch. We observed a difference in FcgammaRIIa receptors with a pro-GVHD/GVL mismatch in 18 patient/donor pairs (25%). Univariate and multivariate analyses demonstrated the pro-GVHD mismatch to be a significant risk factor for the development of acute GVHD. There was no effect on the occurrence of chronic GVHD. The relapse incidence was not significantly different for patients with or without the pro-GVL mismatch, although there was a trend for fewer relapses in standard-risk AML patients with the pro-GVL mismatch. We conclude that the polymorphism of the FcgammaRIIa receptor may be a candidate target for acute GVHD.

Association of polymorphic MHC microsatellites with GVHD, survival, and leukemia relapse in unrelated hematopoietic stem cell transplant donor/recipient pairs matched at five HLA loci

In order to determine whether matching/mismatching for microsatellite polymorphism provides useful information on acute graft-vs-host disease (GVHD), survival, and leukemia relapse in hematopoietic stem cell (HSC) transplantation, we genotyped for polymorphisms at 13 microsatellite loci within the major histocompatibility complex (MHC) of 100 unrelated HSC transplant donor-recipient pairs who were matched at five classical human leukocyte antigen (HLA) loci. A high percentage of allele matching was obtained for five microsatellite loci, DQCARII (96%), MICA (93%), MIB (89%), C1-3-1 (93%), and D6S510 (97%), that are localized within 100 kb of the HLA-DR, HLA-DQ, HLA-B, HLA-C, or HLA-A locus. In contrast, the other eight microsatellites are located farther away from the HLA classical loci and have much lower percentages of allele matching [e.g. tumor necrosis factor a (TNFa) (73%), TNFd (74%), D6S273 (64%), C3-2-11 (46%), C5-3-1 (50%), C5-4-5 (63%), C5-2-7 (68%), and D6S265 (81%)]. Therefore, there were at least eight microsatellite markers with relatively high percentages of mismatches in the donor/recipient pairs with acute or chronic GVHD, poor graft survival, and leukemia relapse. However, there were no statistically significant associations between mismatched donor-recipient pairs at the 13 microsatellite loci and acute or chronic GVHD, graft survival, and leukemia relapse. Nevertheless, allele matching at the microsatellite TNFd locus near the TNFa gene was found by the Fisher's exact double-sided test to be significantly associated with decreased survival in the grade III/IV acute GVHD group. Overall, these results suggest that the matching of microsatellite polymorphisms within the HLA region, especially the ones farthest from the classical HLA loci, was not useful indicator for the outcome of HSC transplantation from unrelated donors. In this regard, the future determination of the genome-wide microsatellite genotypes in HLA-matched donor-recipient pairs, outside the MHC, may be a better possibility for identifying minor histocompatibility genes in linkage disequilibria with microsatellites as potential predictive markers for the occurrence of acute GVHD and survival rate in HSC transplantation.

Minors come of age: minor histocompatibility antigens and graft-versus-host disease

Minor histocompatibility antigens (miHA) are responsible for the occurrence of graft-versus-host disease in the setting of a major histocompatibility complex matched sibling allogeneic stem cell transplantation. These miHA are peptide fragments that are associated with major histocompatibility complex class I or class II antigens. Elegant experiments have led to the molecular characterization of these antigens. Efforts to prevent graft-versus-host disease could be targeted through this pathway by matching for these miHA or by preventing antigen recognition. Alternatively, these miHA could be exploited as targets for a more potent graft-versus-malignancy effect. This area of miHA promises to continue to be an exciting area of continued research.

Novel therapeutic approaches in sickle cell disease

In this update, selected clinical features of sickle cell disease and their management are reviewed. In addition, the current status of interventions that have curative potential for sickle cell disease is discussed, with particular attention focused on indications, methodology, recent results, and challenges to wider clinical application. In Section I, Dr. Nienhuis describes recent improvements in vector technology, safety, and replacement gene expression that are creating the potential for clinical application of this technology. In Section II, Dr. Vichinsky reviews our current understanding of the pathophysiology and treatment of pulmonary injury in sickle cell disease. The acute and chronic pulmonary complications of sickle cell disease, modulators and predictors of severity, and conventional and novel treatment of these complications are discussed. In Section III, Dr. Walters reviews the current status of hematopoietic cell transplantation for sickle cell disease. Newer efforts to expand its availability by identifying alternate sources of stem cells and by reducing the toxicity of transplantation are discussed.

A novel rapid single nucleotide polymorphism (SNP)-based method for assessment of hematopoietic chimerism after allogeneic stem cell transplantation

A major end point of nonmyeloablative hematopoietic stem cell transplantation is the attainment of either mixed chimerism or full donor hematopoiesis. Because the majority of human genetic disparity is generated by single nucleotide polymorphisms (SNPs), direct measurement of SNPs should provide a robust tool for the detection and quantitation of chimerism. Using pyrosequencing, a rapid quantitative sequencing technology, we developed a SNP-based assay for hematopoietic chimerism. Based on 14 SNPs with high allele frequencies, we were able to identify at least 1 informative SNP locus in 55 patients with HLA-identical donors. The median number of informative SNPs in related pairs was 5 and in unrelated pairs was 8 (P <.0001). Assessment of hematopoietic chimerism in posttransplantation DNA was shown to be quantitative, accurate, and highly reproducible. The presence of 5% donor cells was reliably detected in replicate assays. Compared with current measures of engraftment based on identification of short tandem repeats (STRs), variable number of tandem repeats (VNTRs), or microsatellite polymorphisms, this SNP-based method provides a more rapid and quantitative assessment of chimerism. A large panel of SNPs enhances the ability to identify an informative marker in almost all patient/donor pairs and also facilitates the simultaneous use of multiple markers to improve the statistical validity of chimerism measurements. The inclusion of SNPs that encode minor histocompatibility antigens or other genetic polymorphisms that may influence graft-versus-host disease or other transplantation outcomes can provide additional clinically relevant data. SNP-based assessment of chimerism is a promising technique that will assist in the analysis of outcomes following transplantation.

Host defense and inflammatory gene polymorphisms are associated with outcomes after HLA-identical sibling bone marrow transplantation

We made the hypothesis that donor and recipient gene polymorphisms that drive the host response to microorganisms could be associated with infections after bone marrow transplantation (BMT). HLA-identical BMT was performed for patients with acute (n = 39) or chronic leukemia (n = 68). Genotyping was performed in 107 D/R DNA pairs for gene polymorphisms of cytokines (tumor necrosis factor-alpha [TNF-alpha] and TNF-beta, interleukin-1 receptor antagonist [IL-1Ra], IL-6, and IL-10), adhesion molecules (CD31 and CD54), Fcgammareceptors (FcgammaRIIa, IIIa, IIIb), mannose-binding lectin (MBL), and myeloperoxidase (MPO). First infection (overall) and first episodes of bacterial, viral, or invasive fungal infection were studied retrospectively for 180 days after BMT. Univariate and multivariate analyses, using death as a competing event, were performed to study risk factors. In multivariate analysis, first overall infections were increased in patients with the FcgammaRIIa R-131 genotype (hazard ratio [HR] = 1.92; P =.04), and severe bacterial infections were increased when the MPO donor genotype was AG or AA (HR = 2.16; P =.03). Viral and invasive fungal infections were not influenced by any genetic factor studied. Interestingly, we also found that (1) time to neutrophil recovery was shorter when donors were FcgammaRIIIb HNA-1a/HNA-1b (HR = 1.77; P =.002); (2) donor IL-1Ra (absence of IL-1RN*2) increased the risk for acute graft-versus-host disease (GVHD) (II-IV) (HR = 2.17; P =.017); and (3) recipient IL-10 (GG) and IL-1Ra genotypes increased the risk for chronic GVHD (P =.03 and P =.03, respectively). Finally, 180-day transplantation-related mortality rates were increased when donors were FcgammaRIIIb HNA-1a/HNA-1a or HNA-1b/HNA-1b (HR = 2.57; P =.05) and donor MPO genotype was AA (HR = 5.14; P =.004). In conclusion, donor and recipient gene polymorphisms are informative genetic risk factors for selecting donor/recipient pairs and could help in the understanding of mechanisms involved in host defenses of BM transplant recipients.

Minor histocompatibility antigens as targets of graft-versus-leukemia reactions

The main advantage of allogeneic stem cell transplantation over autologous stem cell transplantation for hematologic malignancies is the ability to perform cellular immunotherapy using donor-derived immune effector cells after transplantation. In HLA-matched allogeneic stem cell transplantation, the beneficial graft-versus-leukemia effect of donor lymphocytes appears to be caused mainly by alloreactive T cells that are capable of recognizing minor histocompatibility antigens on the malignant cell population from the patient. The tissue distribution of minor histocompatibility antigens probably determines the clinical result of T-cell responses against these antigens. Whereas T cells recognizing broadly expressed antigens cause not only graft-versus-leukemia but also graft-versus-host disease, T cells recognizing minor histocompatibility antigens specifically expressed on hematopoietic cells may mainly eliminate hematopoietic cells from the recipient, including the malignant cells, without affecting donor hematopoiesis or normal nonhematopoietic tissues. Graft-versus-host disease may still occur because of the induction of inflammatory responses against hematopoietic cells in the tissues. Vaccination of patients after transplantation or vaccination of stem cell donors before transplantation using minor histocompatibility antigen-specific peptides, production of minor histocompatibility antigen-specific T cells, and redirection of T-cell specificity by gene transfer of T-cell receptors may be strategies to eradicate specifically the malignant cells after allogeneic stem cell transplantation.