Determining the extent of maternal-foetal chimerism in cord blood.

During pregnancy, maternal T cells can enter the foetus, leading to maternal-foetal chimerism. This phenomenon may affect how leukaemia patients respond to transplantation therapy using stem cells from cord blood (CB). It has been proposed that maternal T cells, primed to inherited paternal HLAs, are present in CB transplants and help to suppress leukaemic relapse. Several studies have reported evidence for the presence of maternal T cells in most CBs at sufficiently high numbers to lend credence to this idea. We here aimed to functionally characterise maternal T cells from CB. To our surprise, we could not isolate viable maternal cells from CB even after using state-of-the-art enrichment techniques that allow detection of viable cells in heterologous populations at frequencies that were several orders of magnitude lower than reported frequencies of maternal T cells in CB. In support of these results, we could only detect maternal DNA in a minority of samples and at insufficient amounts for reliable quantification through a sensitive PCR-based assay to measure In/Del polymorphisms. We conclude that maternal microchimerism is far less prominent than reported, at least in our cohort of CBs, and discuss possible explanations and implications.

Exposure to non-inherited maternal antigens by breastfeeding affects antibody responsiveness.

The observation, by Ray Owen and colleagues in 1954, that D-negative women were less likely to form anti-D antibodies against their D-positive fetus if their mother possessed the D-antigen, was not found in all later studies. We hypothesized that breastfeeding, received by the mother, may affect her immunity against non-inherited maternal red blood cell antigens. We studied a cohort of 125 grandmother-mother-child combinations, from a follow-up study of mothers after intrauterine transfusion of the fetus for alloimmune hemolytic disease. For mismatched red blood cell antigens the mother was exposed to, whether or not antibodies were formed, we determined whether her mother, the grandmother, carried these antigens. The duration for which the mothers were breastfed was estimated by way of a questionnaire. Using multivariate logistic regression analyses, the interaction term (non-inherited maternal antigen exposure by categorized breastfeeding period) showed that a longer breastfeeding period was associated with decreased alloimmunization against non-inherited maternal antigens (adjusted odds ratio 0.66; 95% confidence interval 0.48-0.93). Sensitivity analysis with dichotomized (shorter versus longer) breastfeeding periods showed that this lower risk was reached after two months (aOR 0.22; 95% CI 0.07-0.71) and longer duration of breastfeeding did not seem to provide additional protection. These data suggest that oral neonatal exposure to non-inherited maternal red blood cell antigens through breastfeeding for at least two months diminishes the risk of alloimmunization against these antigens when encountered later in life.

The effect of NIMA matching in adult unrelated mismatched hematopoietic stem cell transplantation - a joint study of the Acute Leukemia Working Party of the EBMT and the CIBMTR.

Hematological malignancies can be cured by unrelated donor allogeneic HSCT and outcomes are optimized by high-resolution HLA matching at HLA-A, -B, -C, -DRB1 and -DQB1 (10/10 match). If a 10/10 match is unavailable, 9/10 matches may be suitable. Fetal exposure to non-inherited maternal antigens (NIMA) may impart lifelong NIMA tolerance modulating the immune response, as shown in adult haploidentical transplantation. In cord blood transplantation, NIMA matching lowered rates of aGvHD and TRM; in haploidentical transplantation, sibling donors with non-shared maternal antigens showed less grade II-IV aGvHD. This retrospective analysis examined if 9/10 matched unrelated donor HSCT benefits from NIMA matching. DKMS contacted 1,735 donors and obtained 733 (42%) maternal samples. NIMA-matched and -mismatched cases with a minimum follow-up of 1 year were compared by univariate and multivariate analyses adjusted for co-variates for OS, DFS, relapse, TRM and a/cGvHD. The study population (N = 445) comprised 31 NIMA-matched and 414 NIMA-mismatched cases. No significant differences between NIMA-matched and NIMA-mismatched groups were found for any outcomes with similar OS and TRM rates within both groups. This study provides the proof of principle that NIMA matching is possible in the unrelated donor HSCT setting; larger studies may be able to provide significant results.

Kidney allocation based on proven acceptable antigens results in superior graft survival in highly sensitized patients.

Highly sensitized renal transplant candidates accumulate on transplant waiting lists since they produce antibodies to many HLA antigens, which in this way become unacceptable. Organ allocation to these patients is usually based on avoiding transplantation of organs bearing these unacceptable antigens. In contrast, allocation through the Eurotransplant Acceptable Mismatch (AM) program is based on extension of the patient's own HLA type with so-called acceptable HLA antigens to which strictly no antibodies are formed, as shown by extensive laboratory testing. We questioned which type of allocation results in the best long-term graft survival. Therefore, we selected 58,727 cadaveric single renal transplant recipients transplanted within Eurotransplant between 1996 and 2015 and determined factors influencing graft survival for patients transplanted through the AM program. Next, we compared ten-year graft survival of patients with various sensitization grades who received a renal transplant through regular allocation to that of highly sensitized patients transplanted through the AM program. Unlike regular allocation, no effect for HLA mismatches existed for AM patients, while factors that did affect graft survival were similar to those of the general kidney transplant population. AM patients had significantly superior ten-year graft survival compared to highly sensitized patients transplanted on the basis of avoidance of unacceptable mismatches. Strikingly, graft survival of AM patients receiving a repeat transplant was similar to that of nonsensitized repeat transplant recipients. Thus, allocation of kidneys to highly sensitized patients based on proven acceptable antigens results in a significantly better graft survival compared to mere avoidance of unacceptable mismatches.

Modification of host dendritic cells by microchimerism-derived extracellular vesicles generates split tolerance.

Maternal microchimerism (MMc) has been associated with development of allospecific transplant tolerance, antitumor immunity, and cross-generational reproductive fitness, but its mode of action is unknown. We found in a murine model that MMc caused exposure to the noninherited maternal antigens in all offspring, but in some, MMc magnitude was enough to cause membrane alloantigen acquisition (mAAQ; "cross-dressing") of host dendritic cells (DCs). Extracellular vesicle (EV)-enriched serum fractions from mAAQ+, but not from non-mAAQ, mice reproduced the DC cross-dressing phenomenon in vitro. In vivo, mAAQ was associated with increased expression of immune modulators PD-L1 (programmed death-ligand 1) and CD86 by myeloid DCs (mDCs) and decreased presentation of allopeptide+self-MHC complexes, along with increased PD-L1, on plasmacytoid DCs (pDCs). Remarkably, both serum EV-enriched fractions and membrane microdomains containing the acquired MHC alloantigens included CD86, but completely excluded PD-L1. In contrast, EV-enriched fractions and microdomains containing allopeptide+self-MHC did not exclude PD-L1. Adoptive transfer of allospecific transgenic CD4 T cells revealed a "split tolerance" status in mAAQ+ mice: T cells recognizing intact acquired MHC alloantigens proliferated, whereas those responding to allopeptide+self-MHC did not. Using isolated pDCs and mDCs for in vitro culture with allopeptide+self-MHC-specific CD4 T cells, we could replicate their normal activation in non-mAAQ mice, and PD-L1-dependent anergy in mAAQ+ hosts. We propose that EVs provide a physiologic link between microchimerism and split tolerance, with implications for tumor immunity, transplantation, autoimmunity, and reproductive success.

CD4 T-cell cytokines synergize to induce proliferation of malignant and nonmalignant innate intraepithelial lymphocytes.

Refractory celiac disease type II (RCDII) is a severe complication of celiac disease (CD) characterized by the presence of an enlarged clonal population of innate intraepithelial lymphocytes (IELs) lacking classical B-, T-, and natural killer (NK)-cell lineage markers (Lin-IELs) in the duodenum. In ∼50% of patients with RCDII, these Lin-IELs develop into a lymphoma for which no effective treatment is available. Current evidence indicates that the survival and expansion of these malignant Lin-IELs is driven by epithelial cell-derived IL-15. Like CD, RCDII is strongly associated with HLA-DQ2, suggesting the involvement of HLA-DQ2-restricted gluten-specific CD4+ T cells. We now show that gluten-specific CD4+ T cells isolated from CD duodenal biopsy specimens produce cytokines able to trigger proliferation of malignant Lin-IEL lines as powerfully as IL-15. Furthermore, we identify TNF, IL-2, and IL-21 as CD4+ T-cell cytokines that synergistically mediate this effect. Like IL-15, these cytokines were found to increase the phosphorylation of STAT5 and Akt and transcription of antiapoptotic mediator bcl-xL Several small-molecule inhibitors targeting the JAK/STAT pathway blocked proliferation elicited by IL-2 and IL-15, but only an inhibitor targeting the PI3K/Akt/mTOR pathway blocked proliferation induced by IL-15 as well as the CD4+ T-cell cytokines. Confirming and extending these findings, TNF, IL-2, and IL-21 also synergistically triggered the proliferation of freshly isolated Lin-IELs and CD3-CD56+ IELs (NK-IELs) from RCDII as well as non-RCDII duodenal biopsy specimens. These data provide evidence implicating CD4+ T-cell cytokines in the pathogenesis of RCDII. More broadly, they suggest that adaptive immune responses can contribute to innate IEL activation during mucosal inflammation.

Milestones of Hematopoietic Stem Cell Transplantation - From First Human Studies to Current Developments.

Since the early beginnings, in the 1950s, hematopoietic stem cell transplantation (HSCT) has become an established curative treatment for an increasing number of patients with life-threatening hematological, oncological, hereditary, and immunological diseases. This has become possible due to worldwide efforts of preclinical and clinical research focusing on issues of transplant immunology, reduction of transplant-associated morbidity, and mortality and efficient malignant disease eradication. The latter has been accomplished by potent graft-versus-leukemia (GvL) effector cells contained in the stem cell graft. Exciting insights into the genetics of the human leukocyte antigen (HLA) system allowed improved donor selection, including HLA-identical related and unrelated donors. Besides bone marrow, other stem cell sources like granulocyte-colony stimulating-mobilized peripheral blood stem cells and cord blood stem cells have been established in clinical routine. Use of reduced-intensity or non-myeloablative conditioning regimens has been associated with a marked reduction of non-hematological toxicities and eventually, non-relapse mortality allowing older patients and individuals with comorbidities to undergo allogeneic HSCT and to benefit from GvL or antitumor effects. Whereas in the early years, malignant disease eradication by high-dose chemotherapy or radiotherapy was the ultimate goal; nowadays, allogeneic HSCT has been recognized as cellular immunotherapy relying prominently on immune mechanisms and to a lesser extent on non-specific direct cellular toxicity. This chapter will summarize the key milestones of HSCT and introduce current developments.

Development of a diverse human T-cell repertoire despite stringent restriction of hematopoietic clonality in the thymus.

The fate and numbers of hematopoietic stem cells (HSC) and their progeny that seed the thymus constitute a fundamental question with important clinical implications. HSC transplantation is often complicated by limited T-cell reconstitution, especially when HSC from umbilical cord blood are used. Attempts to improve immune reconstitution have until now been unsuccessful, underscoring the need for better insight into thymic reconstitution. Here we made use of the NOD-SCID-IL-2Rγ(-/-) xenograft model and lentiviral cellular barcoding of human HSCs to study T-cell development in the thymus at a clonal level. Barcoded HSCs showed robust (>80% human chimerism) and reproducible myeloid and lymphoid engraftment, with T cells arising 12 wk after transplantation. A very limited number of HSC clones (<10) repopulated the xenografted thymus, with further restriction of the number of clones during subsequent development. Nevertheless, T-cell receptor rearrangements were polyclonal and showed a diverse repertoire, demonstrating that a multitude of T-lymphocyte clones can develop from a single HSC clone. Our data imply that intrathymic clonal fitness is important during T-cell development. As a consequence, immune incompetence after HSC transplantation is not related to the transplantation of limited numbers of HSC but to intrathymic events.

Half a century of Dutch transplant immunology.

The sixties have not only witnessed the start of the Dutch Society for Immunology (NvvI), but were also the flourishing beginning of the discipline of transplant immunology. The interest in immunology in the Netherlands had its start in the context of blood transfusions and not for instance in the field of infectious disease, as in many other countries. It began in the 1950-ties thanks to Joghem van Loghem at that time director of the Central Laboratory of Blood Transfusion in Amsterdam. The discoveries of these times have had major impact for transfusion medicine, hematopoietic stem cell transplantation and organ transplantation. In this review we will look back at some early highlights of Dutch transplant immunology and put them in the perspective of some recent developments.

Noninherited maternal antigens identify acceptable HLA mismatches: benefit to patients and cost-effectiveness for cord blood banks.

Cord blood unit (CBU) transplantations to patients mismatched for only 1 HLA antigen, which is identical to the CBU noninherited maternal antigen (NIMA), are designated as having a 6/6 "virtual" NIMA-matched phenotype and have a prognosis similar to 6/6 inherited HLA-matched CBUs. Such virtual HLA phenotypes of CBUs can be created by replacing the inherited alleles with 1 or more NIMAs. Phenotypes of Dutch patients (n = 2020) were matched against the inherited and virtual HLA phenotypes of the National Cord Blood Program CBU file (with known NIMA, n = 6827). Inherited 6/6 matches were found for 11% of the patients. Including virtual phenotypes resulted in, overall, 19-fold more different phenotypes than were inherited, conferring 6/6 virtual matches for an additional 20% of the patients, whereas another 17% might benefit from CBUs with a 4/6 HLA match and 1 NIMA match (4/6 + 1NIMA or 5/6 virtual match). The elucidation of donors' maternal HLA phenotypes can provide significant numbers of 6/6 and 5/6 virtually matched CBUs to patients and is potentially cost effective.

Naturally acquired microchimerism: implications for transplantation outcome and novel methodologies for detection.

Microchimerism represents a condition where one individual harbors genetically distinct cell populations, and the chimeric population constitutes <1% of the total number of cells. The most common natural source of microchimerism is pregnancy. The reciprocal cell exchange between a mother and her child often leads to the stable engraftment of hematopoietic and non-hematopoietic stem cells in both parties. Interaction between cells from the mother and those from the child may result in maternal immune cells becoming sensitized to inherited paternal alloantigens of the child, which are not expressed by the mother herself. Vice versa, immune cells of the child may become sensitized toward the non-inherited maternal alloantigens of the mother. The extent of microchimerism, its anatomical location, and the sensitivity of the techniques used for detecting its presence collectively determine whether microchimerism can be detected in an individual. In this review, we focus on the clinical consequences of microchimerism in solid organ and hematopoietic stem cell transplantation, and propose concepts derived from data of epidemiologic studies. Next, we elaborate on the latest molecular methodology, including digital PCR, for determining in a reliable and sensitive way the extent of microchimerism. For the first time, tools have become available to isolate viable chimeric cells from a host background, so that the challenges of establishing the biologic mechanisms and function of these cells may finally be tackled.

Birth order and transplantation outcome in HLA-identical sibling stem cell transplantation: an analysis on behalf of the Center for International Blood and Marrow Transplantation.

Allogeneic stem cell transplantation (SCT) is the most effective treatment option for many hematologic malignancies, but graft-versus-host disease (GVHD) remains a major cause of treatment failure. Along with well-established risk factors for transplantation outcomes, recent single-center studies have identified a birth order effect in HLA-identical sibling SCT, with lower rates of acute and chronic GVHD and improved overall survival when the donor is younger than the recipient. One hypothesized mechanism for this effect is microchimerism due to fetomaternal and transmaternal sibling cell trafficking during pregnancy as the donor is exposed to recipient antigens in utero. The aim of the present study was to validate previously reported single-center data in a large, multicenter cohort provided by the Center for International Blood and Marrow Transplantation. All adult and pediatric patients (n = 11,365) with a hematologic malignancy who underwent allogeneic SCT with a graft from an HLA-identical sibling donor between 1990 and 2007 were included. When donors were younger than recipients, there was a significantly lower rate of acute GVHD grade II-IV and chronic GVHD in children, as well as a lower rate of chronic GVHD in adolescents. However, the hypothesized overall positive effect of lower relapse and better survival when donors are younger than recipients was not observed. Our data suggest that if otherwise equally matched, a graft from a younger sibling may be superior to a graft from an older sibling for children and adolescents undergoing SCT.

Effect of HLA-matching recipients to donor noninherited maternal antigens on outcomes after mismatched umbilical cord blood transplantation for hematologic malignancy.

Transplantation-related mortality (TRM) is high after HLA-mismatched umbilical cord blood (UCB) transplantation (UCBT). In utero, exposure to noninherited maternal antigen (NIMA) is recognized by the fetus, which induces T regulator cells to that haplotype. It is plausible that UCBTs in which recipients are matched to donor NIMAs may alleviate some of the excess mortality associated with this treatment. To explore this concept, we used marginal matched-pair Cox regression analysis to compare outcomes in 48 NIMA-matched UCBTs (ie, the NIMA of the donor UCB unit matched to the patient) and in 116 non-NIMA-matched UCBTs. All patients had a hematologic malignancy and received a single UCB unit. Cases and controls were matched on age, disease, disease status, transplantation-conditioning regimen, HLA match, and infused cell dose. TRM was lower after NIMA-matched UCBTs compared with NIMA-mismatched UCBTs (relative risk, 0.48; P = .05; 18% versus 32% at 5 years posttransplantation). Consequently, overall survival was higher after NIMA-matched UCBT. The 5-year probability of overall survival was 55% after NIMA-matched UCBTs versus 38% after NIMA-mismatched UCBTs (P = .04). When faced with the choice of multiple HLA-mismatched UCB units containing adequate cell doses, selecting an NIMA-matched UCB unit may improve survival after mismatched UCBT.

Indirect evidence that maternal microchimerism in cord blood mediates a graft-versus-leukemia effect in cord blood transplantation.

During pregnancy women can develop B- and T-cell immunity against the inherited paternal antigens (IPAs) of the fetus, such as HLA, peptides of minor histocompatibilty antigens, and possibly onco-fetal antigens. The biological and pathological role of these pregnancy-induced immunological events is only understood in part. However, anti-IPA immunity in the mother persists for many decades after delivery and may reduce relapse in offspring with leukemia after HLA-haploidentical transplantation of maternal hematopoietic stem cells (HSC). We hypothesized that maternal anti-IPA immune elements cross the placenta and might confer a potent graft-versus-leukemia effect when cord blood (CB) is used in unrelated HSC transplantation. In a retrospective study of single-unit CB recipients with all grafts provided by the New York Blood Center, we show that patients with acute myeloid or lymphoblastic leukemia (n = 845) who shared one or more HLA-A, -B, or -DRB1 antigens with their CB donor's IPAs had a significant decrease in leukemic relapse posttransplantation [hazard ratio (HR) = 0.38, P < 0.001] compared with those that did not. Remarkably, relapse reduction in patients receiving CB with one HLA mismatch (HR = 0.15, P < 0.001) was not associated with an increased risk of severe acute graft-versus-host disease (HR = 1.43, P = 0.730). Our findings may explain the unexpected low relapse rate after CB transplantation, open new avenues in the study of leukemic relapse after HSC transplantation (possibly of malignancies in general), and have practical implications for CB unit selection.

A proposed algorithm predictive for cytotoxic T cell alloreactivity.

Previously, we showed that with an increasing number of amino acid differences in single HLA class I-mismatched molecules, the probability of T cell alloreactivity decreases. It is unlikely that every amino acid difference will affect T cell alloreactivity in a similar way; we hypothesized that the effect of an amino acid difference may be dependent on its position and/or physicochemical properties. We selected 131 patient/donor pairs with either a single HLA-A or -C mismatch in the graft-versus-host direction and that were compatible for HLA-B, -DRB1, and -DQB1. The alloreactive CTL precursor (CTLp) frequency was determined and associated with the amino acid differences between the single HLA class I mismatches. In the ß sheet, only amino acids that are noncompatible in their physicochemical properties affect T cell alloreactivity, whereas in the α helices, both compatible and noncompatible amino acids affect CTLp outcome. Positions 62, 63, 73, 76, 77, 80, 99, 116, 138, 144, 147, and 163 were bivariately associated with CTLp outcome, irrespective of the total number of amino acid differences. In multivariate analysis, positions 62, 63, 73, 80, 116, 138, 144, and 163 were found to be most predictive for negative CTLp outcome. These results formed the basis for a weighted predictive mismatch score; pairs with the highest mismatch scores are estimated to be 13 times more likely to have a negative CTLp. This new algorithm may be a tool in donor selection for hematopoietic stem cell transplantation.

AIDS-protective HLA-B*27/B*57 and chimpanzee MHC class I molecules target analogous conserved areas of HIV-1/SIVcpz.

In the absence of treatment, most HIV-1-infected humans develop AIDS. However, a minority are long-term nonprogressors, and resistance is associated with the presence of particular HLA-B*27/B*57 molecules. In contrast, most HIV-1-infected chimpanzees do not contract AIDS. In comparison with humans, chimpanzees experienced an ancient selective sweep affecting the MHC class I repertoire. We have determined the peptide-binding properties of frequent chimpanzee MHC class I molecules, and show that, like HLA-B*27/B*57, they target similar conserved areas of HIV-1/SIV(cpz). In addition, many animals appear to possess multiple molecules targeting various conserved areas of the HIV-1/SIV(cpz) Gag protein, a quantitative aspect of the immune response that may further minimize the chance of viral escape. The functional characteristics of the contemporary chimpanzee MHC repertoire suggest that the selective sweep was caused by a lentiviral pandemic.

Reexposure of cord blood to noninherited maternal HLA antigens improves transplant outcome in hematological malignancies.

Cord blood (CB) hematopoietic stem cell transplantation can be successful even if donor and recipient are not fully matched for human leukocyte antigens (HLA). This may result from tolerance-inducing events during pregnancy but to date this concept has not been tested in CB transplantation. Hence we analyzed the impact of fetal exposure to noninherited maternal antigens (NIMA) of the HLA-A, -B antigens, or -DRB1 alleles on the outcome of CB transplants. The 1,121 patients studied were transplanted for hematological malignancy with a single CB unit: 1,059 received grafts mismatched for one or two HLA antigens. Of these patients, 79 patients had a mismatched antigen that was identical to a donor NIMA, 25 with one HLA mismatch (MM), and 54 with two. If there was a NIMA match, transplant-related mortality (TRM) was improved, especially in patients >or=10 years (P = 0.012) as were overall mortality and treatment failure (P = 0.022 and 0.020, respectively, in the older subset), perhaps related to improved neutrophil recovery, especially in patients who received a low total nucleated cell (TNC) dose (P = 0.031). Posttransplant relapse rate also tended to be reduced, especially in patients with myelogenous malignancies given units with a single HLA mismatch (P = 0.074). These findings represent unique evidence that donor exposure to NIMA can improve survival in unrelated CB transplantation and might reduce relapse, indicating that cord blood cells can mount an antileukemic effect. By matching for donor NIMAs in search algorithms of CB inventories, the probability of selecting a graft with an optimal outcome will increase significantly.

When selecting an HLA mismatched stem cell donor consider donor immune status.

Until now, hematopoietic stem cell (HSC) donor selection has been almost exclusively based on selecting a (near) HLA identical donor but many patients fail to find a suitable donor. However all donors have been exposed during fetal life and by breastfeeding to microchimeric maternal cells and molecules, which may induce long lasting T regulator cells. Likewise fetal cells invade the maternal circulation and one-third of the mothers are immunized to the paternal antigens of the child, while part of the mothers become tolerant to them. By taking the alloimmune status of the HSC donor into account, HLA mismatched grafts are an attractive alternative for those patients who do not have an HLA identical sibling donor.

Risk factors for acute graft-versus-host disease after human leukocyte antigen-identical sibling transplants for adults with leukemia.

PURPOSE: Acute graft-versus-host disease (GVHD) causes substantial morbidity and mortality after human leukocyte antigen (HLA)-identical sibling transplants. No large registry studies of acute GVHD risk factors have been reported in two decades. Risk factors may have changed in this interval as transplant-related techniques have evolved. PATIENTS AND METHODS: Acute GVHD risk factors were analyzed in 1,960 adults after HLA-identical sibling myeloablative transplant for acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), or chronic myeloid leukemia (CML) reported by 226 centers worldwide to the Center for International Blood and Marrow Transplant Research from 1995 to 2002. Outcome was measured as time from transplant to onset of grade 2 to 4 acute GVHD, with death without acute GVHD as a competing risk. RESULTS: Cumulative incidence of grade 2 to 4 acute GVHD was 35% (95% CI, 33% to 37%). In multivariable analyses, factors significantly associated with grade 2 to 4 acute GVHD were cyclophosphamide + total-body irradiation versus busulfan + cyclophosphamide (relative risk [RR] = 1.4; P < .0001), blood cell versus bone marrow grafts in patients age 18 to 39 years (RR = 1.43; P = .0023), recipient age 40 and older versus age 18 to 39 years receiving bone marrow grafts (RR = 1.44; P = .0005), CML versus AML/ALL (RR = 1.35; P = .0003), white/Black versus Asian/Hispanic race (RR = 1.54; P = .0003), Karnofsky performance score less than 90 versus 90 to 100 (RR = 1.27; P = .014), and recipient/donor cytomegalovirus-seronegative versus either positive (RR = 1.20; P = .04). Stratification by disease showed the same significant predictors of grade 2 to 4 acute GVHD for CML; however, KPS and cytomegalovirus serostatus were not significant predictors for AML/ALL. CONCLUSION: This analysis confirmed several previously reported risk factors for grade 2 to 4 acute GVHD. However, several new factors were identified whereas others are no longer significant. These new data may facilitate individualized risk estimates and raise several interesting biologic questions.

Protective effect of noninherited maternal HLA-DR antigens on rheumatoid arthritis development.

Rheumatoid arthritis (RA) is a complex genetic disorder in which the HLA-region contributes most to the genetic risk. HLA-DRB1-molecules containing the amino acid sequence DERAA (i.e., HLA-DRB1*0103, *0402, *1102, *1103, *1301, *1302, and *1304) are associated with protection from RA. It has been proposed that not only inherited but also noninherited HLA-antigens from the mother (NIMA) can influence RA-susceptibility. Up to now, no protective NIMAs were described. Here, we studied whether DERAA-containing HLA-DRB1-alleles as NIMA are associated with a protective effect. One hundred seventy-nine families were studied, 88 from the Netherlands and 91 from the United Kingdom. The frequency of DERAA-containing HLA-DRB1-alleles of the Dutch mothers (16.1%), but not of the fathers (26.2%), was lower compared with the general Dutch population (29.3%; P = 0.02). This was replicated in the English set of patients and controls (P = 0.01). Further, of all families, 45 contained at least one DERAA-negative child with RA and at least one DERAA-positive parent. The odds for the DERAA-negative RA patients of having a DERAA-positive mother was significantly lower compared with having a DERAA-positive father (OR 0.25; P = 0.003). These data show a protective NIMA-effect in a human autoimmune disease and indicate that a DERAA-positive mother can transfer protection against RA to her DERAA-negative child.