Female-versus-male alloreactivity as a model for minor histocompatibility antigens in hematopoietic stem cell transplantation

Effects of female bone marrow transplantation on male reproductive organs

Graft-versus-host disease (GVHD), an adverse effect after bone marrow transplantation (BMT), may affect male reproductive function. It is hypothesized that a sex-mismatched BMT induces GVHD in male reproductive organs because female immune cells are not immunologically tolerant to specific antigens of the male organs. However, this hypothesis has not been experimentally verified using male (M) recipient animals following BMT from the female (F) donors. Therefore, the aim of the present study is to examine whether the female BMT to males (F→M group) induces some GVHD reactions in the testis and the other male reproductive organs. The results showed that no inflammation was found in recipients of the male BMT to males (M→M group), whereas significant inflammatory cell responses lasting for at least 4 months were induced in testis, epididymis, prostate and preputial gland in some mice of F→M group. The most severe lesion was found in the preputial gland, in which lymphocytic inflammation was accompanied by loss of glandular acini, thickening of the interstitum and increased cytokines such as TNF-α and IFN-γ. Western blot analyses revealed that sera from the F→M group reacted with various antigens of the male reproductive organs. These results indicate that transplanted female immune cells may recognize the male reproductive organs as immunologically foreign ones and induce chronic GVHD, which may affect male reproductive function.

Effective Immunosurveillance After Allogeneic Hematopoietic Stem Cell Transplantation in Acute Myeloid Leukemia

The number of patients receiving allogeneic hematopoietic stem cell transplantation (alloHCT) has increased constantly over the last years due to advances in transplant technology development, supportive care, transplant safety, and donor availability. Currently, acute myeloid leukemia (AML) is the most frequent indication for alloHCT. However, disease relapse remains the main cause of therapy failure. Therefore, concepts of maintaining and, if necessary, reinforcing a strong graft-versus-leukemia (GvL) effect is crucial for the prognosis and long-term survival of the patients. Over the last decades, it has become evident that effective immunosurveillance after alloHCT is an entangled complex of donor-specific characteristics, leukemia-associated geno- and phenotypes, and acquired resistance mechanisms. Furthermore, adoption of effector cells such as natural killer (NK) cells, alloreactive and regulatory T-cells with their accompanying receptor repertoire, and cell–cell interactions driven by messenger molecules within the stem cell and the bone marrow niche have important impact. In this review of pre- and posttransplant elements and mechanisms of immunosurveillance, we highlight the most important mechanisms after alloHCT.

Impact of mother donor, peripheral blood stem cells and measurable residual disease on outcomes after haploidentical hematopoietic cell transplantation with post-transplant cyclophosphamide in children with acute leukaemia

Haploidentical hematopoietic-cell transplantation using post-transplant cyclophosphamide(Haplo-PTCy) is a feasible procedure in children with haematologic malignancies. However, data of a large series of children with acute leukaemia(AL) in this setting is missing. We analysed 144 AL Haplo-PTCy paediatric recipients; median age was 10 years. Patients had acute lymphoblastic(ALL; n = 86) or myeloblastic leukaemia(AML; n = 58) and were transplanted in remission(CR1: n = 40; CR2: n = 57; CR3+: n = 27) or relapse (n = 20). Bone marrow was the graft source in 57%; donors were father (54%), mother (35%), or sibling (11%). Myeloablative conditioning was used in 87%. Median follow-up was 31 months. At day +100, cumulative incidence (CI) of neutrophil recovery and acute GVHD (II-IV) were 94% and 40%, respectively. At 2-years, CI of chronic GVHD and relapse, were 31%, 40%, and estimated 2-year overall survival (OS), leukaemia-free survival (LFS) and graft-versus-host-relapse-free survival (GRFS) were 52%, 44% and 34% respectively. For patients transplanted in remission, positive measurable residual disease (MRD) prior to transplant was associated with decreased LFS (p = 0.05) and GRFS (p = 0.003) and increased risk of relapse (p = 0.02). Mother donor was associated with increased risk of chronic GVHD (p = 0.001), decreased OS (p = 0.03) and GRFS (p = 0.004). Use of PBSC was associated with increased risk of chronic GVHD (p = 0.04). In conclusion, achieving MRD negativity pre-transplant, avoiding use of mother donors and PBSC as graft source may improve outcomes of Haplo-PTCy in children with AL.

Female Sex Is Associated with Improved Long-Term Survival Following Allogeneic Hematopoietic Stem Cell Transplantation

Life expectancy for long-term survivors of allogeneic hematopoietic stem cell transplantation (alloHSCT), defined as those living ≥5 years post-transplantation, is significantly lower compared with that of the age-matched general population despite a relatively low primary disease relapse rate at >2 years post-transplantation. Among several factors, patient sex is increasingly recognized as a prognostic indicator of long-term survival. We examined the influence of patient sex and donor-recipient sex matching on overall survival (OS) in a landmark analysis of long-term survivors. Using our institutional database supplemented with individual patient record review, we retrospectively investigated the relative influence of recipient sex and donor-recipient sex matching on outcomes of long-term survivors of alloHSCT between 1994 and 2014. Over this 20-year period, 247 met inclusion criteria for analysis; males and females had similar demographic and treatment characteristics. However, significantly more deaths after the 5-year landmark occurred in male recipients. Interestingly, donor sex did not have a significant impact on OS in multivariate analysis, and differences in OS of donor-recipient sex pairs was driven by recipient sex. In addition to recipient sex, only chronic graft-versus-host disease (cGVHD) retained significance as a covariate with an impact on OS in multivariate analysis. Men experienced slightly higher, but statistically nonsignificant, rates and increased severity of cGVHD, and had higher cGVHD-related mortality compared with females. In this long-term survival analysis of adult alloHSCT recipients, one of the only to include follow-up to 15 years, our results show that women survive significantly longer than men irrespective of their age at transplantation. This outcome is independent of other common pretransplantation prognostic indicators, such as donor sex or performance status at transplantation. The inferior survival in males is consistent with survival outcomes described in the transplantation literature. Increasing evidence suggests a biological basis for long-term sex-determined outcomes, possibly owing to differing rates or severity of cGVHD or sustained alloimmune tolerance in females. Larger studies are warranted to validate these retrospective clinical results.

Increased Expression of Y-Encoded Demethylases During Differentiation of Human Male Neural Stem Cells

Human neural stem cells (hNSCs) have long been used as an in vitro model to study neurogenesis and as candidates for nervous system therapy. Many parameters have been considered when evaluating the success of transplantation, but sex of donor and recipients is often not discussed. We investigated two commercial NSC lines, the female hNSC-H9 and male hNSC-H14, and we observed faster growth rates in the male cells. At 4 days of differentiation, male cells presented a significant increase in expression of DCX, an immature neuronal marker, while female cells showed a significant increase in RMST, a long noncoding RNA, which is indispensable during neurogenesis. In addition, expression of neural markers MAP2, PSD95, SYP, DCX, and TUJ1 at day 14 of differentiation suggested a similar differentiation potential in both lines. The most significant differences at day 14 of differentiation were the expression levels of RELN, with almost 100-fold difference between the sexes, and MASH1, with more than 1,000-fold increase in male cells. To evaluate whether some of the observed differences may be sex related, we measured the expression of gametologous genes located on the X- and Y-chromosome. Most noticeable was the increase of Y-encoded demethylases KDM6C (UTY) and KDM5D during differentiation of male cells. Our results indicate that attention should be paid to sex when planning neurogenesis and transplantation experiments.

Equally Interchangeable? How Sex and Gender Affect Transplantation

Organ transplantation as an option to overcome end-stage diseases is common in countries with advanced healthcare systems and is increasingly provided in emerging and developing countries. A review of the literature points to sex- and gender-based inequity in the field with differences reported at each step of the transplant process, including access to a transplantation waiting list, access to transplantation once waitlisted, as well as outcome after transplantation. In this review, we summarize the data regarding sex- and gender-based disparity in adult and pediatric kidney, liver, lung, heart, and hematopoietic stem cell transplantation and argue that there are not only biological but also psychological and socioeconomic issues that contribute to disparity in the outcome, as well as an inequitable access to transplantation for women and girls. Because the demand for organs has always exceeded the supply, the transplant community has long recognized the need to ensure equity and efficiency of the organ allocation system. In the spirit of equity and equality, the authors call for recognition of these inequities and the development of policies that have the potential to ensure that girls and women have equitable access to transplantation.

Chromosome Y-encoded antigens associate with acute graft-versus-host disease in sex-mismatched stem cell transplant

Allogeneic hematopoietic stem cell transplantation (allo-HCT) is a curative option for blood cancers, but the coupled effects of graft-versus-tumor and graft-versus-host disease (GVHD) limit its broader application. Outcomes improve with matching at HLAs, but other factors are required to explain residual risk of GVHD. In an effort to identify genetic associations outside the major histocompatibility complex, we conducted a genome-wide clinical outcomes study on 205 acute myeloid leukemia patients and their fully HLA-A-, HLA-B-, HLA-C-, HLA-DRB1-, and HLA-DQB1-matched (10/10) unrelated donors. HLA-DPB1 T-cell epitope permissibility mismatches were observed in less than half (45%) of acute GVHD cases, motivating a broader search for genetic factors affecting clinical outcomes. A novel bioinformatics workflow adapted from neoantigen discovery found no associations between acute GVHD and known, HLA-restricted minor histocompatibility antigens (MiHAs). These results were confirmed with microarray data from an additional 988 samples. On the other hand, Y-chromosome-encoded single-nucleotide polymorphisms in 4 genes (PCDH11Y, USP9Y, UTY, and NLGN4Y) did associate with acute GVHD in male patients with female donors. Males in this category with acute GVHD had more Y-encoded variant peptides per patient with higher predicted HLA-binding affinity than males without GVHD who matched X-paralogous alleles in their female donors. Methods and results described here have an immediate impact for allo-HCT, warranting further development and larger genomic studies where MiHAs are clinically relevant, including cancer immunotherapy, solid organ transplant, and pregnancy.

Review of Haploidentical Hematopoietic Cell Transplantation

Use of haploidentical (haplo) donors for hematopoietic cell transplantation (HCT) has significantly increased in the last decade. The major advantage with this strategy is universal availability and faster acquisition of the donor, along with affordability and provision of immunotherapy in post-transplantation period. Historically, haplo-HCT was associated with compromised outcomes because of high rates of graft-versus-host disease and graft failure, but after the development of a post-transplantation high-dose cyclophosphamide strategy, which results in selective T-cell depletion, these issues have been addressed to a large extent. Nevertheless, graft failure, high treatment-related mortality due to graft-versus-host disease, infections, delayed immune reconstitution, and disease relapse remain significant concerns. As the experience with haplo-HCTs grows, the clinical outcomes are becoming more at par with those seen with fully matched unrelated donor allogeneic HCTs.

The European Society for Blood and Marrow Transplantation (EBMT) consensus recommendations for donor selection in haploidentical hematopoietic cell transplantation

The number of HLA-haploidentical hematopoietic cell transplants continues to increase worldwide due to recent improvements in outcomes, allowing more patients with hematological malignancies and non-malignant disorders to benefit from this procedure and have a chance to cure their disease. Despite these encouraging results, questions remain as multiple donors are usually available for transplantation, and choosing the best HLA-haploidentical donor for transplantation remains a challenge. Several approaches to haploidentical transplantation have been developed over time and, based on the graft received, can be grouped as follows: T-cell depleted haploidentical transplants, either complete or partial, or with T-cell replete grafts, performed with post-transplant cyclophosphamide-based graft-versus-host disease (GVHD) prophylaxis, or G-CSF-primed bone marrow graft and enhanced GVHD prophylaxis. Carefully selecting the donor can help optimize transplant outcomes for recipients of haploidentical donor transplants. Variables usually considered in the donor selection include presence of donor-specific antibodies in the recipient, donor age, donor/recipient gender and ABO combinations, and immunogenic variables, such as natural killer cell alloreactivity or KIR haplotype. Here we provide a comprehensive review of available evidence for selecting haploidentical donors for transplantation, and summarize the recommendations from the European Society for Blood and Marrow Transplantation (EBMT) on donor selection for different transplant platforms.

Who is the best donor for haploidentical stem cell transplantation?

Recent advances in haploidentical stem cell transplantation have enabled the use of human leukocyte antigen-half matched related donors for allogeneic stem cell transplantation and helped overcome one of the most important limitation in transplantation, which is donor availability, especially for the non-Caucasian population and mixed race individuals, extending allogeneic stem cell transplant for almost all patients in need. As many multiple potential related donors may now be available, it is increasingly clear that not all of these donors can provide equivalent transplant outcomes. Here we review the current available evidence of donor characteristics known to be associated with transplant outcomes for different types of haploidentical transplants using unmanipulated grafts (with post-transplant cyclophosphamide-based graft-vs-host prophylaxis and G-CSF and anti-thymocyte globulin approach) as well as modified grafts (with either selective or complete T-cell depletion). While various platforms use haploidentical donors, graft manipulation and approach to prevent graft-vs-host post-transplant may impact on donor selection and transplant outcomes.

Relative Impact of HLA Matching and Non-HLA Donor Characteristics on Outcomes of Allogeneic Stem Cell Transplantation for Acute Myeloid Leukemia and Myelodysplastic Syndrome

Increasing donor-recipient HLA disparity is associated with negative outcomes of allogeneic hematopoietic stem cell transplantation (HSCT), but its comparative relevance amid non-HLA donor characteristics is not well established. We addressed this question in 3215 HSCTs performed between 2005 and 2013 in Germany for acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Donors were HLA-matched related (MRD; n = 872) or unrelated (10/10 MUD, n = 1553) or HLA-mismatched unrelated (<10/10 MMUD, n = 790). Overall survival (OS) was similar after MRD compared with 10/10 MUD HSCT, reflecting opposing hazards of relapse (hazard ratio [HR], 1.32; P < .002) and nonrelapse mortality (HR, .63; P < .001). After UD HSCT, increasing HLA disparity was associated with inferior OS (HR, 1.21 [P < .02] and HR, 1.57 [P < .001] for 9/10 and ≤8/10 MMUD, respectively, compared with 10/10 MUD). Among non-HLA donor characteristics, age, sex mismatching (male recipient-female donor), and cytomegalovirus (CMV) mismatching (positive recipient-negative donor) impacted OS. Multivariate subgroup analysis showed that OS was similar after HSCT from the youngest 9/10 MMUD (<30 years) compared with the oldest 10/10 MUD (>40 years) (HR, 1.18; P = .25) and also in male patients transplanted from female 10/10 MUD compared with male 9/10 MMUD (HR, .89; P = .46). In contrast, OS of CMV-positive patients tended to be better with CMV-negative 10/10 MUDs compared with CMV-positive 9/10 MMUDs (HR, 1.31; P = .04). Because of low patient numbers in subgroups, definite conclusions and establishment of a hierarchy among HLA matching and non-HLA donor characteristics could not be made. Our data suggest that the impact of donor age and sex mismatch but not CMV mismatch on outcome of allogeneic HSCT may be comparable with that of single HLA disparity.

European Group for Blood and Marrow Transplantation Risk Score Predicts the Outcome of Patients with Acute Leukemia Receiving Single Umbilical Cord Blood Transplantation

The European Group for Blood and Marrow Transplantation (EBMT) risk score has been implemented as an important tool to predict patient outcomes after allogeneic hematopoietic stem cell transplantation. However, to our knowledge, this score has never been applied in cases of single umbilical cord blood transplantation (sUCBT). We retrospectively analyzed 207 consecutive patients with acute leukemia who received sUCBT at our center between February 2011 and December 2015. The probabilities of 3-year overall survival (OS) and leukemia-free survival (LFS) of the entire cohort were 65.0% and 59.8%, respectively, whereas the cumulative incidences of 3-year nonrelapse mortality (NRM) and relapse rate were 19.5% and 20.3%, respectively. In the univariate analysis, a higher EBMT risk score was associated with worse OS and LFS and higher NRM and relapse rate, ranging from 81.7%, 75.9%, 7.3%, and 15.3%, respectively, for patients with a score of 1 to 43.8%, 44.3%, 31.7%, and 23.9%, respectively, for patients with scores of 4 to 6. Hazard ratios of OS, LFS, and NRM all steadily increased for each additional score point. Importantly, the prognostic value of the EBMT risk score on OS, LFS, NRM, and relapse was maintained in the multivariate analysis. Moreover, considering the univariate analysis results of donor-recipient gender and mismatched allele-level HLA-A, -B, -C, and -DRB1 loci on patient outcomes and the fairly strong interaction between time from diagnosis to sUCBT and disease status, we developed a modified sUCBT-EBMT risk score by using degrees of 8-allele HLA match instead of donor type, donor-recipient gender combination, and time from diagnosis to sUCBT, and found that the modified score could also be used as a predictor for patient outcomes after sUCBT. The EBMT risk score is a good predictor of outcomes of patients with leukemia after sUCBT. The modified sUCBT-EBMT risk score can also be used as a pretransplant risk assessment, but this metric still requires further evaluation with a larger cohort.

Bone Marrow Graft-Versus-Host Disease in Major Histocompatibility Complex-Matched Murine Reduced-Intensity Allogeneic Hemopoietic Cell Transplantation

BACKGROUND

Most clinical allogeneic hemopoietic cell transplants (alloHCT) are now performed using reduced-intensity conditioning (RIC) instead of myeloablative conditioning (MAC); however, the biology underlying this treatment remains incompletely understood.

METHODS

We investigated a murine model of major histocompatibility complex-matched multiple minor histocompatibility antigen-mismatched alloHCT using bone marrow (BM) cells and splenocytes from B6 (H-2) donor mice transplanted into BALB.B (H-2) recipients after RIC with fludarabine of 100 mg/kg per day for 5 days, cyclophosphamide of 60 mg/kg per day for 2 days, and total body irradiation (TBI).

RESULTS

The lowest TBI dose capable of achieving complete donor chimerism in this mouse strain combination was 325 cGy given as a single fraction. Mice that underwent RIC had a reduced incidence and delayed onset of graft-versus-host disease (GVHD) and significantly prolonged survival compared with MAC-transplanted recipients (TBI of 850 cGy plus cyclophosphamide of 60 mg/kg per day for 2 days). Compared with syngeneic controls, RIC mice with GVHD showed evidence of BM suppression, have anemia, reduced BM cellularity, and showed profound reduction in BM B cell lymphopoiesis associated with damage to the endosteal BM niche. This was associated with an increase in BM CD8 effector T cells in RIC mice and elevated blood and BM plasma levels of T helper1 cytokines. Increasing doses of splenocytes resulted in increased incidence of GVHD in RIC mice.

CONCLUSIONS

We demonstrate that the BM is a major target organ of GVHD in an informative clinically relevant RIC mouse major histocompatibility complex-matched alloHCT model by a process that seems to be driven by CD8 effector T cells.

Can we make a better match or mismatch with KIR genotyping?

Natural killer (NK) cell function is regulated by a fine balance between numerous activating and inhibitory receptors, of which killer-cell immunoglobulin-like receptors (KIRs) are among the most polymorphic and comprehensively studied. KIRs allow NK cells to recognize downregulation or the absence of HLA class I molecules on target cells (known as missing-self), a phenomenon that is commonly observed in virally infected cells or cancer cells. Because KIR and HLA genes are located on different chromosomes, in an allogeneic environment such as after hematopoietic stem cell transplantation, donor NK cells that express an inhibitory KIR for an HLA class I molecule that is absent on recipient targets (KIR/KIR-ligand mismatch), can recognize and react to this missing self and mediate cytotoxicity. Accumulating data indicate that epistatic interactions between KIR and HLA influence outcomes in several clinical conditions. Herein, we discuss the genetic and functional features of KIR/KIR-ligand interactions in hematopoietic stem cell transplantation and how these data can guide donor selection. We will also review clinical studies of adoptive NK cell therapy in leukemia and emerging data on the use of genetically modified NK cells that could broaden the scope of cancer immunotherapy.

How do we choose the best donor for T-cell-replete, HLA-haploidentical transplantation?

In haploidentical stem cell transplantations (haplo-SCT), nearly all patients have more than one donor. A key issue in the haplo-SCT setting is the search for the best donor, because donor selection can significantly impact the incidences of acute and chronic graft-versus-host disease, transplant-related mortality, and relapse, in addition to overall survival. In this review, we focused on factors associated with transplant outcomes following unmanipulated haplo-SCT with anti-thymocyte globulin (ATG) or after T-cell-replete haplo-SCT with post-transplantation cyclophosphamide (PT/Cy). We summarized the effects of the primary factors, including donor-specific antibodies against human leukocyte antigens (HLA); donor age and gender; killer immunoglobulin-like receptor-ligand mismatches; and non-inherited maternal antigen mismatches. We also offered some expert recommendations and proposed an algorithm for selecting donors for unmanipulated haplo-SCT with ATG and for T-cell-replete haplo-SCT with PT/Cy.

The effect of donor characteristics on survival after unrelated donor transplantation for hematologic malignancy

There are >24 million registered adult donors, and the numbers of unrelated donor transplantations are increasing. The optimal strategy for prioritizing among comparably HLA-matched potential donors has not been established. Therefore, the objective of the current analyses was to study the association between donor characteristics (age, sex, parity, cytomegalovirus serostatus, HLA match, and blood group ABO match) and survival after transplantation for hematologic malignancy. The association of donor characteristics with transplantation outcomes was examined using either logistic or Cox regression models, adjusting for patient disease and transplantation characteristics associated with outcomes in 2 independent datasets: 1988 to 2006 (N = 6349; training cohort) and 2007 to 2011 (N = 4690; validation cohort). All donor-recipient pairs had allele-level HLA typing at HLA-A, -B, -C, and -DRB1, which is the current standard for selecting donors. Adjusting for patient disease and transplantation characteristics, survival was better after transplantation of grafts from young donors (aged 18-32 years) who were HLA matched to recipients (P < .001). These findings were validated for transplantations that occurred between 2007 and 2011. For every 10-year increment in donor age, there is a 5.5% increase in the hazard ratio for overall mortality. Increasing HLA disparity was also associated with worsening survival. Donor age and donor-recipient HLA match are important when selecting adult unrelated donors. Other donor characteristics such as sex, parity, and cytomegalovirus serostatus were not associated with survival. The effect of ABO matching on survival is modest and must be studied further before definitive recommendations can be offered.

Sirolimus as Long-term Graft-versus-host-disease Prophylaxis in Haploidentical Hematopoietic Stem Cell Transplant Recipients for Non-malignant Disorders is Associated with High Incidence of Acneiform Lesions

Background:

Sirolimus has provided the option for calcineurin inhibitor (CNI)-free immunosuppressive therapy in both solid organ transplant (SOT) and hematopoietic stem cell transplantation (HSCT). However, long-term use of sirolimus has been reported to be associated with a high incidence of cutaneous side effects in SOT, particularly acneiform lesions.

Materials and Methods:

We studied the incidence of acneiform lesions and the risk factors in 41 HSCT recipients between ages 4 and 64 years, undergoing HSCT for malignant (n = 29) and non-malignant diseases (n = 12) from haploidentical family donors.

Results:

Seven patients developed acneiform lesions at the median of 85 days (range, 45–105 days). Acneiform lesions occurred in 6/11 patients on sirolimus and in only 1/30 patients not receiving sirolimus (P = 0.001). This was more frequent in patients with non-malignant disorders (5/12 versus 2/29, P = 0.01) and those receiving graft from female donors (7/23 versus 0/18, P = 0.01).

Conclusions:

Despite being frequently reported in SOT, this is the first such report in HSCT. Our study suggests that prolonged use of sirolimus might be associated with high incidence of acneiform lesions in haploidentical HSCT recipients with non-malignant diseases, particularly in those receiving graft from a female donor. We discuss the possible reasons for these findings and the putative mechanism of acneiform lesions in these patients

Donor parity no longer a barrier for female-to-male hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a widely applied treatment for disorders mainly involving the hematopoietic system. The success of this treatment depends on many different patient- and donor-specific factors. Based on higher CD34+ yields and superior clinical outcomes associated with the use of male donors, males are generally seen as the preferred HSCT donor. In addition, female donors are notorious for bearing memory type lymphocytes induced by previous pregnancies; such alloimmune cells may provoke unwanted immune reactions such as graft-vs.-host disease in transplant recipients. Consequently, many transplant centers try to avoid parous donors, particularly when searching the best unrelated donor for a male patient. We recently showed that parous women with female offspring have an anti-male directed tolerogenic immune status comparable to that of nulliparous donors. As discussed in this article addendum, the sex of the donor's offspring combined with the presence of HY-specific T regulator cells are possibly better selection criteria than parity status per se.

Can a female donor for a male recipient decrease the relapse rate for patients with acute myeloid leukemia treated with allogeneic hematopoietic stem cell transplantation?

The mismatched minor histocompatibility antigens present on Y chromosome (H-Y) in male recipients receiving stem cells from female donors may contribute to the graft-versus-leukemia effect and results in a reduced relapse rate, especially in patients with high-risk disease. We retrospectively compared the outcomes of male patients with acute myeloid leukemia who received an allogeneic hematopoietic stem cell transplant (HSCT) from female donors (F-M) (174 patients) versus other gender combinations (667 patients). Median age was 50 years (range, 18 to 74 years). For the whole group, the 1-year cumulative incidence of relapse was significantly lower in F-M group (34.1% versus 41.3%, P = .044), whereas nonrelapse mortality (NRM) was higher (23.2% versus 15.7%, P = .004). For patients younger than 50 years beyond first complete remission, the F-M group was associated with lower relapse rate (42.5% versus 55.2%, P = .045) whereas NRM was not significantly different (35.8% versus 25.5%, P = .141). Although survival was not significantly improved, transplantation from a female donor for male recipient was associated with a lower relapse rate. When relapse is the most common concern for treatment failure, especially for younger patients, a female donor for a male recipient might be beneficial to decrease relapse rate after transplantation. Future studies are needed to explore how the H-Y mismatch may improve survival after transplantation.

Adult stem cell transplantation: is gender a factor in stemness?

Cell therapy now constitutes an important area of regenerative medicine. The aging of the population has mandated the discovery and development of new and innovative therapeutic modalities to combat devastating disorders such as stroke. Menstrual blood and Sertoli cells represent two sources of viable transplantable cells that are gender-specific, both of which appear to have potential as donor cells for transplantation in stroke. During the subacute phase of stroke, the use of autologous cells offers effective and practical clinical application and is suggestive of the many benefits of using the aforementioned gender-specific cells. For example, in addition to being exceptionally immunosuppressive, testis-derived Sertoli cells secrete many growth and trophic factors and have been shown to aid in the functional recovery of animals transplanted with fetal dopaminergic cells. Correspondingly, menstrual blood cells are easily obtainable and exhibit angiogenic characteristics, proliferative capability, and pluripotency. Of further interest is the ability of menstrual blood cells, following transplantation in stroke models, to migrate to the infarct site, secrete neurotrophic factors, regulate the inflammatory response, and be steered towards neural differentiation. From cell isolation to transplantation, we emphasize in this review paper the practicality and relevance of the experimental and clinical use of gender-specific stem cells, such as Sertoli cells and menstrual blood cells, in the treatment of stroke.

Acute graft-versus-host disease: a bench-to-bedside update. Blood. 2014;124:363-373. [PMID: 24914140 DOI: 10.1182/blood-2014-01-514786]

Over the past 5 years, many novel approaches to early diagnosis, prevention, and treatment of acute graft-versus-host disease (aGVHD) have been translated from the bench to the bedside. In this review, we highlight recent discoveries in the context of current aGVHD care. The most significant innovations that have already reached the clinic are prophylaxis strategies based upon a refinement of our understanding of key sensors, effectors, suppressors of the immune alloreactive response, and the resultant tissue damage from the aGVHD inflammatory cascade. In the near future, aGVHD prevention and treatment will likely involve multiple modalities, including small molecules regulating immunologic checkpoints, enhancement of suppressor cytokines and cellular subsets, modulation of the microbiota, graft manipulation, and other donor-based prophylaxis strategies. Despite long-term efforts, major challenges in treatment of established aGVHD still remain. Resolution of inflammation and facilitation of rapid immune reconstitution in those with only a limited response to corticosteroids is a research arena that remains rife with opportunity and urgent clinical need.

Clinical impact of H-Y alloimmunity

H-Y antigens are a group of minor histocompatibility antigens encoded on the Y-chromosome with homologous H-X antigens on the X-chromosome. The disparate regions of the H-Y antigens are highly immunogenic and play an important role in understanding human alloimmunity. In this review, we investigate the history of H-Y antigen discovery along with their critical contributions in transplantation and pregnancy. In hematopoietic cell transplantation, male recipients with female donors who become seropositive for B-cell responses as H-Y antibodies following transplantation have increased rates of chronic graft-versus-host disease and decreased rates of relapse. Conversely, female patients who receive male kidney allografts are more likely than other gender combinations to develop H-Y antibodies and reject their allografts. Finally, in the setting of pregnancy, mothers who initially gave birth to boys are more likely to have subsequent pregnancy complications, including miscarriages, in association with H-Y antibody development. H-Y antigens continue to serve as a model for alloimmunity in new clinical scenarios. Our development of more sensitive antibody detection and next-generation DNA sequencing promises to further advance our understanding and better predict the clinical consequences of alloimmunity.

CD4(+)and CD8(+)T-cell reactions against leukemia-associated- or minor-histocompatibility-antigens in AML-patients after allogeneic SCT

T-cells play an important role in the remission-maintenance in AML-patients (pts) after SCT, however the role of LAA- (WT1, PR1, PRAME) or minor-histocompatibility (mHag, HA1) antigen-specific CD4(+) and CD8(+)T-cells is not defined. A LAA/HA1-peptide/protein stimulation, cloning and monitoring strategy for specific CD8(+)/CD4(+)T-cells in AML-pts after SCT is given. Our results show that (1) LAA-peptide-specific CD8+T-cells are detectable in every AML-pt after SCT. CD8(+)T-cells, recognizing two different antigens detectable in 5 of 7 cases correlate with long-lasting remissions. Clonal TCR-Vβ-restriction exemplarily proven by spectratyping in PRAME-specific CD8(+)T-cells; high PRAME-peptide-reactivity was CD4(+)-associated, as shown by IFN-γ-release. (2) Two types of antigen-presenting cells (APCs) were tested for presentation of LAA/HA1-proteins to CD4(+)T-cells: miniEBV-transduced lymphoblastoid cells (B-cell-source) and CD4-depleted MNC (source for B-cell/monocyte/DC). We provide a refined cloning-system for proliferating, CD40L(+)CD4(+)T-cells after LAA/HA1-stimulation. CD4(+)T-cells produced cytokines (GM-CSF, IFN-γ) upon exposure to LAA/HA1-stimulation until after at least 7 restimulations and demonstrated cytotoxic activity against naive blasts, but not fibroblasts. Antileukemic activity of unstimulated, stimulated or cloned CD4(+)T-cells correlated with defined T-cell-subtypes and the clinical course of the disease. In conclusion we provide immunological tools to enrich and monitor LAA/HA1-CD4(+)- and CD8(+)T-cells in AML-pts after SCT and generate data with relevant prognostic value. We were able to demonstrate the presence of LAA-peptide-specific CD8(+)T-cell clones in AML-pts after SCT. In addition, we were also able to enrich specific antileukemic reactive CD4(+)T-cells without GvH-reactivity upon repeated LAA/HA1-protein stimulation and limiting dilution cloning.

Role of non-HLA gene polymorphisms in graft-versus-host disease

A large number of reports have associated various non-HLA gene polymorphisms with the risk and severity of graft-versus-host disease (GVHD). To date, candidate gene studies and genome-wide association studies have been performed to investigate such non-HLA gene polymorphisms in relation to GVHD. Candidate gene studies are hypothesis-driven and cost-effective, whereas genome-wide association studies have the potential to discover new gene polymorphisms, including possible biomarkers and therapeutic targets. Some gene polymorphisms have the potential to affect protein function or gene expression, or to encode minor histocompatibility antigens. Non-HLA genotyping for genes influencing GVHD prior to transplantation should provide useful information that will facilitate choosing the donor, type of graft, conditioning treatment, and GVHD prophylaxis. However, attention should be paid to the need for validation studies and ethical issues.

Multicenter analyses demonstrate significant clinical effects of minor histocompatibility antigens on GvHD and GvL after HLA-matched related and unrelated hematopoietic stem cell transplantation

The effect of minor H antigen mismatching on the occurrence of graft-versus-host disease (GvHD) and graft-versus-leukemia (GvL) after HLA-matched hematopoietic stem cell transplantation (HSCT) has mainly been demonstrated in single-center studies. Yet, the International Histocompatibility and Immunogenetics Workshops (IHIW) provide a collaborative platform to execute crucial large studies. In collaboration with 20 laboratories of the IHIW, the roles of 10 autosomal and 10 Y chromosome-encoded minor H antigens were investigated on GvHD and relapse incidence in 639 HLA-identical related donor (IRD) and 210 HLA-matched unrelated donor (MUD) HSCT recipients. Donor and recipient DNA samples were genotyped for the minor H antigens HA-1, HA-2, HA-3, HA-8, HB-1, ACC-1, ACC-2, SP110, PANE1, UGT2B17, and HY. The correlations with the primary outcomes GvHD (acute or chronic GvHD), survival, and relapse were statistically analyzed. The results of these multicenter analyses show that none of the HLA class I-restricted HY antigens were found to be associated with any of the primary outcomes. Interestingly, of the HLA class II-restricted HY antigens analyzed, HLA-DQ5 positive recipients showed a significantly increased GvHD-free survival in female-to-male HSCT compared with male-to-female HSCT (P = .013). Yet, analysis of the overall gender effect, thus independent of the known HY antigens, between the gender groups demonstrated an increased GvHD incidence in the female-to-male transplantations (P < .005) and a decreased GvHD-free survival in the female-to-male transplantations (P < .001). Of all autosomally encoded minor H antigens, only mismatching for the broadly expressed minor H antigen HA-8 increased the GvHD incidence in IRD HSCT (Hazard ratio [HR] = 5.28, P < .005), but not in MUD HSCT. Most striking was the influence of hematopoietic restricted minor H antigens on GvL as mismatching for hematopoietic minor H antigens correlated with lower relapse rates (P = .078), higher relapse-free survival (P = .029), and higher overall survival (P = .032) in recipients with GvHD, but not in those without GvHD. In conclusion, the significant GvHD effect of the broadly expressed minor H antigen HA-8 favors matching for HA-8 in IRD, but not in MUD, patient/donor pairs. The GvHD-GvL association demonstrating a significant lower relapse in hematopoietic minor H antigen mismatched patient/donor pairs underlines their clinical applicability for adoptive immunotherapy, enhancing the GvL effect in a GvHD controllable manner.

A two-step approach to allogeneic haploidentical hematopoietic stem cell transplantation

Strategies that exploit natural killer (NK) cell alloreactivity or attenuate rather than deplete T cells have resulted in improved outcomes after haploidentical hematopoietic stem cell transplantation (HSCT). However, no approach has consistently produced the triad of optimal immune reconstitution, avoidance of significant graft-versus-host disease (GVHD), and durable control of malignancy. We developed a two-step approach to haploidentical HSCT in which the lymphoid and myeloid portions of the graft are given in two separate steps in order to control and optimize T-cell dosing. The initial results from these trials have included robust immune reconstitution, low rates of toxicity and significant GVHD, and durable disease control in good-risk patients, as well as insights regarding a threshold for T-cell dosing above which graft-versus-tumor (GVT) effects might be expected. Patients who were not in remission at the time of HSCT had higher rates of relapse requiring efforts to further strengthen GVT effects. Second-generation trials are underway to further exploit changes in the dosing and timing of administration of T cells and to optimize donor selection in an effort to decrease relapse rates in high-risk patients.

Role of donor and recipient sex in platelet transfusion

BACKGROUND

H-Y proteins are ubiquitously expressed Y chromosome-encoded minor histocompatibility antigens, which are relevant in the transplantation of hematopoietic stem cells (HSCT) and solid organs. No studies have so far analyzed whether H-Y incompatibility influences the outcome of platelet (PLT) transfusion.

STUDY DESIGN AND METHODS

We studied the effect of donor and recipient sex on outcome of 9038 single-donor PLT transfusions.

RESULTS

Using standard corrected count increment or percent PLT recovery (PPR) calculations, male patients showed inferior recovery rates, irrespective of donor sex. Using an adjusted PPR, which takes into account differences in blood volume between males and females, neither donor nor recipient sex played any role in PLT recovery after transfusion. Similarly, the time to next PLT transfusion was unaffected by both donor and recipient sex. In a subgroup analysis of patients with graft-versus-host disease after allogeneic HSCT, male recipients of a female allograft-which may carry anti-H-Y T cells and antibodies-had significantly lower time to next PLT transfusion. However, this occurred after both male donor and female donor PLT transfusions, arguing against an involvement of alloreactivity against H-Y antigens on PLTs.

CONCLUSION

This large analysis found no evidence that donor-recipient sex matching influences the outcome of PLT transfusion.

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.

Association of disparities in known minor histocompatibility antigens with relapse-free survival and graft-versus-host disease after allogeneic stem cell transplantation

Allogeneic stem cell transplantation (allo-SCT) can induce remission in patients with hematologic malignancies due to graft-versus-tumor (GVT) responses. This immune-mediated antitumor effect is often accompanied by detrimental graft-versus-host disease (GVHD), however. Both GVT and GVHD are mediated by minor histocompatibility antigen (MiHA)-specific T cells recognizing peptide products from polymorphic genes that differ between recipient and donor. In this study, we evaluated whether mismatches in a panel of 17 MiHAs are associated with clinical outcome after partially T cell-depleted allo-SCT. Comprehensive statistical analysis revealed that DNA mismatches for one or more autosomal-encoded MiHAs was associated with increased relapse-free survival in recipients of sibling transplants (P = .04), particularly in those with multiple myeloma (P = .02). Moreover, mismatches for the ubiquitous Y chromosome-derived MiHAs resulted in a higher incidence of acute GVHD grade III-IV (P = .004), whereas autosomal MiHA mismatches, ubiquitous or restricted to hematopoietic cells, were not associated with severe GVHD. Finally, we found considerable differences among MiHAs in their capability of inducing in vivo T cell responses using dual-color tetramer analysis of peripheral blood samples collected after allo-SCT. Importantly, detection of MiHA-specific T cell responses was associated with improved relapse-free survival in recipients of sibling transplants (P = .01). Our findings provide a rationale for further boosting GVT immunity toward autosomal MiHAs with a hematopoietic restriction to improve outcomes after HLA-matched allo-SCT.

Effect of MHC and non-MHC donor/recipient genetic disparity on the outcome of allogeneic HCT

The outcome of allogeneic hematopoietic cell transplantation is influenced by donor/recipient genetic disparity at loci both inside and outside the MHC on chromosome 6p. Although disparity at loci within the MHC is the most important risk factor for the development of severe GVHD, disparity at loci outside the MHC that encode minor histocompatibility (H) antigens can elicit GVHD and GVL activity in donor/recipient pairs who are otherwise genetically identical across the MHC. Minor H antigens are created by sequence and structural variations within the genome. The enormous variation that characterizes the human genome suggests that the total number of minor H loci is probably large and ensures that all donor/recipient pairs, despite selection for identity at the MHC, will be mismatched for many minor H antigens. In addition to mismatch at minor H loci, unrelated donor/recipient pairs exhibit genetic disparity at numerous loci within the MHC, particularly HLA-DP, despite selection for identity at HLA-A, -B, -C, and -DRB1. Disparity at HLA-DP exists in 80% of unrelated pairs and clearly influences the outcome of unrelated hematopoietic cell transplantation; the magnitude of this effect probably exceeds that associated with disparity at any locus outside the MHC.

Allogeneic hematopoietic stem cell transplantation for intermediate cytogenetic risk AML in first CR

Allogeneic hematopoietic SCT (allo-HCT) from matched sibling donor (MSD) is recommended for younger patients with intermediate cytogenetic risk AML in first CR (CR1), whereas the role of alternative donor transplants in these patients is unknown. We retrospectively analyzed 605 patients with intermediate-risk AML, who received myeloablative allo-HCT in CR1. The 4-year OS for MSD (n=290) and matched unrelated donor (MUD; n=141) was 65% and 68% (P=0.50), respectively. In multivariate analysis, MUD had a similar risk of overall mortality as MSD (hazard ratio=0.90; 95% confidence interval, 0.62-1.30; P=0.58), whereas older age, female donor/male recipient (FDMR) combination, and requiring more than one course of induction chemotherapy to achieve CR1 were poor prognostic factors for OS. Thus, OS after MUD HCT with sex combinations other than FDMR was significantly higher than that after MSD HCT from female donors to male recipients (4-year OS 72% versus 55%, P=0.04). These results suggest that HCT, not only from MSD, but also from MUD, should be considered in younger patients with intermediate-risk AML in CR1, and that the donor-recipient sex combination is more important than the donor type in donor selection.

Anti-thymocyte globulin for conditioning in matched unrelated donor hematopoietic cell transplantation provides comparable outcomes to matched related donor recipients

Rabbit anti-thymocyte globulin (ATG) is used as prophylaxis against GVHD following allogeneic hematopoietic cell transplantation (HCT). At our institution, ATG is exclusively used in the conditioning of matched unrelated donor (URD) transplant recipients. A total of 50 URD HCT recipients who received ATG (ATG group) were retrospectively compared with 48 matched related donor (MRD) HCT recipients who did not receive ATG (no ATG group). There were no significant differences between the groups in rates of day 100 mortality, acute GVHD or relapse. Chronic GVHD incidence was significantly lower in the ATG group (P = 0.007). At a median follow-up of 36 months in the entire cohort, 50% patients are alive in the ATG group and 63% of the patients are alive in the no ATG group (P = 0.13). We conclude that the administration of ATG to patients undergoing URD HCT preserves the anti-leukemia benefit of the transplant, while reducing the risk of developing GVHD, resulting in OS rates that are comparable to MRD HCT recipients.

Clinical options after failure of allogeneic hematopoietic stem cell transplantation in patients with hematologic malignancies

Disease recurrence is the single most common cause of death after allogeneic or autologous hematopoietic stem cell transplantation (HSCT). Disease status and chemosensitivity at the time of transplantation, as well as the development of graft-versus-host disease (GVHD), are factors known to influence the risk of relapse post-HSCT. Both acute and chronic GVHD have been associated with decreased relapse rates; however, owing to toxicity, overall survival is not consistently improved in these patients. Furthermore, there is a transient period of immunodeficiency after HSCT, which may permit residual malignant cells to proliferate early in the post-transplant course, before the donor immune system can establish a graft-versus-tumor response. Patients who fail an initial HSCT have an extremely poor outcome; therefore, maneuvers to prevent, identify and treat recurrent disease as early as possible in these situations are necessary. Strategies to distinguish graft-versus-tumor from GVHD, to enhance both general and disease-specific immune reconstitution after transplantation, and to increase donor-mediated anti-host immune reactions are being investigated in clinical trials. Single agent nontoxic post-HSCT chemotherapy, cellular therapies and second allogeneic HSCT using reduced intensity regimens are among the modalities under investigation.

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.

Donor characteristics affecting graft failure, graft-versus-host disease, and survival after unrelated donor transplantation with reduced-intensity conditioning for hematologic malignancies

We examined the effect of donor characteristics on graft failure (<5% donor chimerism within 3 months after transplantation), acute and chronic graft-versus-host disease (aGVHD, cGVHD), and survival after unrelated donor reduced-intensity conditioning (RIC) transplantation in 709 patients with hematologic malignancies. Donor-recipient pairs were HLA typed at HLA-A, -B, -C, and -DRB1 (allele-level). A total of 501 patients were >95% donor chimerism, 145 patients were 5% to 95%, and 63 patients were <5%. The only donor characteristic associated with transplantation outcome was donor-recipient HLA matching. One- or 2-loci mismatched transplants led to higher grade 2-4 (relative risk [RR] = 1.27, P = .035) and grade 3-4 (RR = 1.85, P < .001) aGVHD and 2-loci mismatched transplants higher mortality (RR = 2.22, P < .001). Graft failure was higher after transplantation of bone marrow (RR = 2.33, P = .002). Donor age, parity, and donor sex match were not associated with transplantation outcome. Donor-recipient HLA matching is the only donor characteristic predictive for survival after RIC regimens for hematologic malignancies.

The EBMT risk score. Bone Marrow Transplant. 2012;47:749-756. [PMID: 21643021 DOI: 10.1038/bmt.2011.110]

The European Group for Blood and Marrow Transplantation (EBMT) risk score provides a simple tool to assess instantly chances and risks of hematopoietic SCT(HSCT) for an individual patient pre-transplant. Five factors, age of the patient, stage of the disease, time from diagnosis, donor type and donor recipient gender combination augment risk for an individual patient with increasing score from 0 as best to 7 as worst in an additive way. The score holds for all acquired hematological disorders, for allogeneic and autologous HSCT (score 0-5), is independent of the HSCT technology and is valid for standard or reduced intensity conditioning. Survival is uniformly worse for older patients, transplanted in advanced disease stage after a long-time interval and with a mismatched donor than for younger patients, transplanted soon in early stage with a well matched donor. Additional risk factors such as performance score, CMV serostatus or cytokine polymorphisms improve prediction but to different extents for low or high-risk patients. Comparative assessment of disease risk and global pre-transplant risk should guide decisions for each patient with his/her specific disease between HSCT and a non-transplant approach and replace the traditional 'donor vs no donor' with such a risk-adapted individualized strategy.

Donor-recipient gender difference affects severity of dry eye after hematopoietic stem cell transplantation

PURPOSE

To determine whether the incidence rate and severity of dry eye after hematopoietic stem cell transplantation varies with donor vs recipient gender.

METHODS

We limited this study to patients received bone marrow transplantation (BMT). In all, 172 patients received BMT at Keio University School of Medicine between January 2000 and May 2007. Of them, 136 recipients who survived at least 70 days were studied prospectively. We classified the 136 patients according to the gender of the donor and the recipient (group I: female to female; group II: male to male; group III: male to female; group IV: female to male). The incidence and severity of chronic graft-vs-host disease-associated dry eye were determined for each group. The donor gender was masked when we assessed dry eye and calculate the incidence.

RESULTS

The incidence of dry eye was 47.4% for group I, 37.5% for group II, 58.6% for group III, and 42.9% for group IV. The percentage of patients with severe dry eye was 44.4, 50.0, 35.3, and 77.8% respectively. There was a significant difference between the percent severe dry eye/total dry eye incidences in groups III and IV (P=0.0375) (odds ratio, 7.6; 95% confidence interval, 1.00-101.01).

CONCLUSIONS

Close attention must be paid to the development of dry eye in cases of female to male BMTs, because the ratio of severe/total dry eye is more common in cases of female to male BMTs than in other gender combination.

Defining genetic risk for graft-versus-host disease and mortality following allogeneic hematopoietic stem cell transplantation

PURPOSE OF REVIEW

This review explores what is known about the genetics of hematopoietic stem cell transplantation (HCT) and how genetic polymorphism affects risk of graft-versus-host disease (GVHD) and mortality.

RECENT FINDINGS

Genetic variation found across the human genome can impact HCT outcome by causing genetic disparity between patient and donor and modifying gene function. Single nucleotide polymorphism (SNP) and structural variation can result in mismatching for cellular peptides known as histocompatibility antigens. At least 25-30 polymorphic genes are known to encode functional histocompatibility antigens in mismatched individuals, but their individual contribution to clinical GVHD is unclear. HCT outcome may also be affected by polymorphism in donor or recipient. Association studies have implicated several genes associated with GVHD and mortality, however results have been inconsistent most likely due to limited sample size, and differences in racial diversity and clinical covariates. New technologies using DNA arrays genotyping for a million or more SNPs promise genome-wide discovery of HCT-associated genes, however adequate statistical power requires study populations of several thousand patient-donor pairs.

SUMMARY

Available data offers strong preliminary support for the impact that genetic variation has on risk of GVHD and mortality following HCT. Definitive results however await future genome-wide studies of large multicenter HCT cohorts.