Search

Transfusion-associated graft-versus-host disease (TA-GVHD) is a rare but hazardous complication caused by transfusion of leucocyte-containing blood. It is not clear why some patients are at risk for TA-GVHD, but others are not. We studied TA-GVHD in immunocompetent individuals by looking at donor-anti-host reactivity after transfusion of leucocyte-containing blood. We tested reactivity in 62 donor-recipient combinations in vitro before and at different times after blood transfusion with mixed lymphocyte culture. One patient was studied in more detail. Reactivity of blood donors against hosts gradually decreased after blood transfusion. This decrease significantly correlated with time (p < 0.001). Studies in a single patient showed that absence of donor-host reactivity was due to host T cells that inhibited the response. These data indicate that an active mechanism exists in immunocompetent individuals which inhibits the graft-versus-host reaction of the donor against the host. This mechanism might be exploited in organ transplantation by pre-transplant blood transfer. [ABSTRACT FROM AUTHOR]

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.

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.

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., (Copyright © 2019 Ferrata Storti Foundation.)

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., (Copyright © 2017 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

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-x L 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., Competing Interests: The authors declare no conflict of interest.

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., Competing Interests: The authors declare no conflict of interest.

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.

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.

We determined whether assessment of the immunogenicity of individual donor-recipient HLA mismatches based on differences in their amino-acid sequence and physiochemical properties predicts clinical outcome following haematopoietic SCT (HSCT). We examined patients transplanted with 9/10 single HLA class I-mismatched grafts (n=171) and 10/10 HLA-A-, -B-, -C-, -DRB1- and -DQB1-matched grafts (n=168). A computer algorithm was used to determine the physiochemical disparity (electrostatic mismatch score (EMS) and hydrophobic mismatch score (HMS)) of mismatched HLA class I specificities in the graft-versus-host direction. Patients transplanted with HLA-mismatched grafts with high EMS/HMS had increased incidence of ⩾grade II acute GVHD (aGVHD) compared with patients transplanted with low EMS/HMS grafts; patients transplanted with low and medium EMS/HMS grafts had similar incidence of aGVHD to patients transplanted with 10/10 HLA-matched grafts. Mortality was higher following single HLA-mismatched HSCT but was not correlated with HLA physiochemical disparity. Assessment of donor-recipient HLA incompatibility based on physiochemical HLA disparity may enable better selection of HLA-mismatched donors in HSCT.

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., (Copyright © 2014 Elsevier B.V. All rights reserved.)

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., (Copyright © 2014 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.)

Introduction: Previously we developed a weighted amino acid (AA) mismatch score predictive for cytotoxic T cell (CTL) alloreactivity (in vitro CTLp assay) based on the structure of the HLA class I molecule. The aim of this study is to confirm the clinical relevance of the CTLp assay and to validate the AA mismatch score as an alternative and easy to use tool to predict permissible mismatches in hematopoietic stem cell transplantation (HSCT)., Methods: We selected patients transplanted with a 9/10 single HLA class I mismatched graft (n=171) at three Dutch HSCT centers. A CTLp assay was performed in 73 donor-recipient pairs. As a control we selected 168 10/10 HLA matched pairs that were matched to the 9/10 single HLA class I mismatched pairs for HSCT year, donor type, patient age and diagnosis., Results: We observed that pairs with negative a CTLp assay had statistically significant decreased incidence of mortality after HSCT comparable to that of 10/10 HLA matched pairs. However, the weighted AA mismatch score did not significantly predict any HSCT end point of interest., Conclusion: Further investigation is needed to unravel the mechanisms involved in causing the beneficial effect of a negative CTLp assay, before other alternative tools to predict HSCT outcome may be developed., (Copyright © 2014 Elsevier B.V. All rights reserved.)

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.

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., (Copyright © 2013 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.)

The MHC region on chromosome 6 contains a large number of non-HLA genes next to the HLA genes. Matching for HLA in unrelated hematopoietic SCT (HSCT) does not necessarily mean that these non-HLA genes are also matched. We selected 348 Northwest European patients transplanted with an HLA-A-, -B-, -C-, -DRB1-, -DQB1-matched unrelated donor (MUD) between 1987 and 2008. Patients' haplotypes were identified via descend. We were unable to determine the haplotypes of the donor; therefore we used frequent haplotypes (FH) in high linkage disequilibrium (LD) as a proxy for haplotype matching. Presence of a FH in a patient positively affected the probability and speed of identifying a matched unrelated donor. Competing risk survival analysis showed that patients with one or two FH have a statistically significantly decreased probability of developing ≥ grade II acute GVDH (aGVHD) without increased risk of relapse compared to patients without FH (HR (95% CI): 0.53 (0.31-0.91)). This association was strongest for those FH with the highest LD between both HLA-A and -C or -B, and HLA-C or -B and -DRB1 (HR (95% CI): 0.49 (0.26-0.92)). These results extend evidence that non-HLA allele coding regions have a significant impact on development of ≥ grade II aGVHD. We conclude that there is more to successful HSCT than matching for HLA genes.

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., (Copyright © 2012. Published by Elsevier Inc.)

To investigate whether all patients in need of an allogeneic hematopoietic SCT (HSCT) are offered one, we retrospectively investigated the policy for all children diagnosed with myelodysplastic syndrome (n=90) or relapsed AML (n=75) between 1998 and 2008. These children are registered at diagnosis and treated according to protocols of the Dutch Childhood Oncology Group, which provides accurate disease incidence data and protocol-indicated appropriateness for HSCT. For 48 (30%) patients, a family donor was identified; for 90 (57%) patients, an unrelated donor (UD) search was performed; and for 21 (13%) patients, no UD search was initiated. Reasons for not initiating an UD search include: progressive disease (n=10), conserve quality of life (n=1), stable disease (n=3), immunosuppressive therapy (n=2), patient death (n=3), patient lives abroad (n=1) and second relapse (n=1). On the basis of the time interval between date of diagnosis and date of death/last follow-up, for eight (5%) patients, it may be questioned why an UD search was not performed. The fact that 95% of all children are given the option of an allogeneic HSCT is encouraging and reasons not to transplant seem fair in most cases.

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 β 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.

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.

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.

Adoptive transfer of T cell receptor (TCR)-transduced T cells may be an attractive strategy to target both hematological malignancies and solid tumors. By introducing a TCR, large numbers of T cells with defined antigen (Ag) specificity can be obtained. However, by introduction of a TCR, mixed TCR dimers can be formed. Besides the decrease in TCR expression of the introduced and endogenous TCR, these mixed TCR dimers could harbor potentially harmful specificities. In this study, we demonstrate that introduction of TCRs resulted in formation of neoreactive mixed TCR dimers, composed of the introduced TCR chains pairing with either the endogenous TCR alpha or beta chain. Neoreactivities observed were HLA class I or class II restricted. Most neoreactive mixed TCR dimers were allo-HLA reactive; however, neoreactive mixed TCR dimers with autoreactive activity were also observed. We demonstrate that inclusion of an extra disulfide bond between the constant domains of the introduced TCR markedly reduced neoreactivity, whereas enhanced effectiveness of the introduced TCR was observed. In conclusion, TCR transfer results in the formation of neoreactive mixed TCR dimers with the potential to generate off-target effects, underlining the importance of searching for techniques to facilitate preferential pairing.

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.

Human leukocyte antigen-C (HLA-C) is the only polymorphic classical histocompatibility antigen expressed by fetal trophoblasts at the fetal-maternal interface. Interactions between HLA-C and decidual natural killer (NK) cells may facilitate trophoblast invasion into maternal tissue. Thus far no evidence has been provided that decidual T cells specifically recognize and respond to fetal alloantigens at the fetal-maternal interface. In this study, we show that pregnancies containing a HLA-C mismatched child induce an increased percentage of CD4(+)CD25(dim) activated T cells in decidual tissue. In addition, HLA-C mismatched pregnancies exhibit a decidual lymphocyte response to fetal cells and contain functional CD4(+)CD25(bright) regulatory T cells in decidual tissue, whereas HLA-C matched pregnancies do not. This suggests that decidual T cells specifically recognize fetal HLA-C at the fetal-maternal interface but are prevented from inducing a destructive immune response in uncomplicated pregnancies.

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.

Patients with hematological malignancies can be successfully treated with HLA-matched T cell-depleted allogeneic stem cell transplantation (alloSCT) and subsequent donor lymphocyte infusions (DLIs). The efficacy of DLI is mediated by donor T cells recognizing minor histocompatibility antigens (mHags) on malignant recipient cells. Because HLA class II molecules are predominantly expressed on hematopoietic cells, mHag-specific CD4(+) T cells may selectively mediate graft versus leukemia (GvL) reactivity without graft versus host disease (GvHD). In this study, we used a recombinant bacteria cDNA library for the identification of the first autosomal HLA class II (HLA-DQB1*0603)-restricted mHag LB-PI4K2B-1S encoded by the broadly expressed phosphatidylinositol 4-kinase type II beta gene. A polyclonal CD4(+) T cell response against LB-PI4K2B-1S was demonstrated in a patient with relapsed chronic myeloid leukemia (CML) who responded to DLI after HLA-matched alloSCT. LB-PI4K2B-1S-specific CD4(+) T cells recognized and lysed the CD34(+) CML cells of the patient and other leukemic cells as well as high HLA-DQ-expressing normal hematopoietic cells. HLA-DQ expression on normal cells of nonhematopoietic origin was moderately up-regulated by IFN-gamma and not sufficient for T cell recognition. We hypothesize that LB-PI4K2B-1S-specific CD4(+) T cells contributed to the antitumor response by both directly eliminating malignant cells as effector cells and stimulating CD8(+) T cell immunity as helper cells.

On 16 November 2005, we celebrated the milestone when 10 million donors had been registered in Bone Marrow Donors Worldwide (BMDW). Since then another million donors have been added in little more than a year. It seems an appropriate time for reassessment and to ask whether we are on the right track or not. We will do so by discussing the strength, weaknesses, opportunities and threats of the unrelated stem cell donor operation.

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.

A fully major histocompatilbility complex (MHC) matched donor is not available for the majority of patients in need of a haematopoietic stem cell transplantation (SCT), which illustrates the need for a tool to define acceptable MHC disparities. Previously, we noticed that a variety of single MHC class I mismatched allogeneic donor-recipient pairs did not elicit an allogeneic cytotoxic-lymphocyte (CTL) response in vitro if the MHC amino-acid sequences had five or more differences in the alpha-helices plus five or more differences in the beta-sheet (> or =5alpha5beta) (7). To address the clinical relevance of this observation, we analysed CTL precursor (CTLp) assay outcome and SCT outcome in 53 Dutch recipients of a single MHC class I mismatched graft from an unrelated donor. Overall patient survival was 44% after 4 years. In multivariate analysis, recipients of a > or =5alpha5beta mismatched graft with negative CTLp frequencies in vitro before transplantation demonstrated superior survival: survival at 4 years was 80% as compared to 47% in recipients of other mismatched grafts with negative CTLp frequencies (hazard ratio=0.131; 95% CI=(0.03-0.61); P=0.009). This option of acceptable mismatches may enlarge the pool of potentially acceptable stem cell donors.

Because of their important role in the maintenance of self-tolerance, CD4(+) regulatory T cells prevent autoimmune diseases but also curtail the efficacy of T cell immune responses against cancers. We now show that this suppressive action of CD4(+) regulatory T cells is not limited to cancers displaying tumor-associated self antigens, such as melanomas, but also extends to human papillomavirus (HPV)-positive cervical cancers that express foreign tumor antigens. HPV-specific CD4(+) T cells isolated from lymph node biopsies of cervical cancer patients were found to suppress proliferation and cytokine (IFN-gamma, IL-2) production by responder T cells. The capacity of HPV-specific CD4(+) T cells to exert this suppressive effect depended on their activation by cognate HPV antigen and on close-range interactions with responder T cells. HPV-specific CD4(+) regulatory T cells were also retrieved from cervical cancer biopsies, suggesting that they interfere with the anti-tumor immune response at both the induction and effector levels. Our findings offer a plausible explanation for the observed failure of the tumor-specific immune response in patients with cervical carcinoma.

The DRB region of the MHC in primate species is known to display abundant region configuration polymorphism with regard to the number and content of genes present per haplotype. Furthermore, depending on the species studied, the different DRB genes themselves may display varying degrees of allelic polymorphism. Because of this combination of diversity (differential gene number) and polymorphism (allelic variation), molecular typing methods for the primate DRB region are cumbersome. All intact DRB genes present in humans and rhesus macaques appear to possess, however, a complex and highly divergent microsatellite. Microsatellite analysis of a sizeable panel of outbred rhesus macaques, covering most of the known Mamu-DRB haplotypes, resulted in the definition of unique genotyping patterns that appear to be specific for a given haplotype. Subsequent examination of a representative panel of human cells illustrated that this approach also facilitates high-resolution HLA-DRB typing in an easy, quick, and reproducible fashion. The genetic composition of this complex microsatellite is shown to be in concordance with the phylogenetic relationships of various HLA-DRB and Mamu-DRB exon 2 gene/lineage sequences. Moreover, its length variability segregates with allelic variation of the respective gene. This simple protocol may find application in a variety of research avenues such as transplantation biology, disease association studies, molecular ecology, paternity testing, and forensic medicine.

Recurrent malignancy remains a significant complication after allogeneic hematopoietic cell transplantation (HCT). Efforts to decrease relapse have included donor lymphocyte infusion to stimulate donor anti-recipient T-cell allorecognition of major and minor histocompatibility differences. Recently, alloreactive effects of donor natural killer cell-mediated inhibitory killer immunoglobulin-like receptor (KIR) recognition of recipient HLA-C and -B ligands have been described. We examined KIR ligand effects on risk of relapse in 1770 patients undergoing myeloablative T-replete HCT from HLA-matched or -mismatched unrelated donors for the treatment of myeloid and lymphoid leukemias. KIR ligands defined by HLA-B and -C genotypes were used to determine donor-recipient ligand incompatibility or recipient lack of KIR ligand. Among HLA-mismatched transplantations, recipient homozygosity for HLA-B or -C KIR epitopes predicted lack of KIR ligand and was associated with a decreased hazard of relapse (hazard ratio, 0.61; 95% confidence interval, .043-0.85; P = .004). Absence of HLA-C group 2 or HLA-Bw4 KIR ligands was associated with lower hazards of relapse (hazard ratio, 0.47; 95% confidence interval, 0.28-0.79, P = .004; hazard ratio, 0.56; 95% confidence interval, 0.33-0.97; P = .04, respectively). The decrease in hazard of relapse in patients with acute myelogenous leukemia was similar to that in patients with chronic myelogenous leukemia and acute lymphoblastic leukemia (P = .95). Recipient homozygosity for HLA-B or -C epitopes that define KIR ligands is likely to be a predictive factor for leukemia relapse after myeloablative HCT from HLA-mismatched unrelated donors. This effect was not observed in HLA-identical unrelated transplants.

Contact between the immune systems of mother and child during pregnancy has an impact on transplantation later in life. Exposure to inherited paternal human leukocyte antigens (HLA) (IPA) and the noninherited maternal HLA antigens (NIMA) can lead to either immunization or tolerization. Exposure to IPA seems to have a more immunizing effect as the mature immune system of a mother can form anti-HLA antibodies against the foreign paternal HLA molecules. On the other hand, exposure of a child to the NIMA antigens during pregnancy may lead to NIMA-specific tolerance. This review provides an overview of the current knowledge on the impact of this fetal-maternal interaction on the alloimmune response and clinical transplantation.

The common marmoset (Callithrix jacchus), a New World monkey species with a limited MHC class II repertoire, is highly susceptible to certain bacterial infections. Genomic analysis of exon 2 sequences documented the existence of only one DRB region configuration harboring three loci. Two of these loci display moderate levels of allelic polymorphism, whereas the -DRB*W12 gene appears to be monomorphic. This study shows that only the Caja-DRB*W16 and -DRB*W12 loci produce functional transcripts. The Caja-DRB1*03 locus is occupied by a pseudogene, given that most of the transcripts, if detected at all, show imperfections and are present at low levels. Moreover, two hybrid transcripts were identified that feature the evolutionarily conserved peptide-binding motif characteristic for the Caja-DRB1*03 gene. Thus, the severely reduced MHC class II repertoire in common marmosets has been expanded by reactivation of a pseudogene segment as a result of exon shuffling.

Reports have shown a worse outcome for donor-recipient pairs mismatched for ABO blood groups in bone marrow transplantation (BMT). These studies, however, included small and heterogeneous study populations, and not all considered bidirectional ABO incompatibility separately. Because the issue remains controversial, we analyzed the effect of ABO mismatch on the overall survival, transplant-related mortality, and occurrence of acute and chronic graft-versus-host disease (GVHD) in a large homogenous group of patients undergoing allogeneic BMT. A total of 3103 patients with early-stage leukemia who underwent transplantation between 1990 and 1998 with bone marrow from an HLA-identical sibling and who were reported to the Center for International Blood and Marrow Transplant Research were studied. The median follow-up was 54 months. A total of 2108 (67.9%) donor-recipient pairs were ABO identical, 451 (14.5%) had a minor mismatch, 430 (13.9%) had a major mismatch, and 114 (3.7%) had a bidirectional ABO mismatch. The groups did not differ significantly in patient or donor characteristics except for more female-to-male sex mismatch in the bidirectional ABO mismatch group (P = .017). In multivariate models of overall survival, transplant-related mortality, and grade II to IV acute GVHD, there were no significant differences among the 4 groups. Bidirectional ABO mismatch was associated with a significantly higher risk of grade III or IV acute GVHD (hazard ratio, 1.869; 95% confidence interval, 1.192-2.93; P = .006). Patients with major ABO mismatch received red blood cell transfusions (P = .001) for a longer timer after transplantation and had a slightly slower neutrophil recovery (P < .001). There was no evidence of a substantial effect of ABO blood group incompatibility on the outcome of conventional BMT among patients with leukemia.

Pre- and/or perinatal exposure to noninherited maternal HLA antigens (NIMA) is associated with a decreased HLA antibody formation against the NIMA and a significantly better graft survival of kidney grafts from siblings or those from unrelated donors who were mismatched for the NIMA haplotype compared with the NIPA (noninherited paternal HLA antigens) haplotype later in life. These observations suggest that some form of immunological tolerance against NIMA is induced. We analyzed the in vitro T cell reactivity of healthy individuals toward their parents and/or siblings expressing the NIMA or NIPA haplotype to explore whether the alloimmune response to NIMA has distinct characteristics compared with NIPA. No differences were detected by mixed lymphocyte reactions (MLR) and supernatants taken from the MLR showed no differences in IFN-gamma and IL-10 production. Additionally, no differences were found with IFN-gamma and IL-10 Elispot analyses. Phenotypic analysis revealed no selective increase in the number of CD3-CD8dim cells (thought to be a NK-like regulator cell) and the number of CD4+CD25+CD152+ cells (naturally occurring regulatory T cells) after stimulation with NIMA-expressing cells when compared with NIPA-expressing cells. In conclusion, no evidence of an influence of a NIMA effect on the cellular level was found in healthy individuals with "standard" immunological techniques.

CD8+ T cell-mediated alloreactivity is generally believed to involve recognition of the alpha1/alpha2 domains of donor-type class I MHC molecules as well as the peptides they bind. Using the CTLp assay outcome as a parameter for the induction of alloreactivity, we have retrospectively surveyed 80 haematopoietic stem cell donor/patient pairs that feature a range of allelic differences at single HLA-A, -B, and -C loci in an attempt to probe the predictive value of such mismatches. In contrast to the expectation that greater degree of allelic disparity would lead to more alloreactivity, we found that in a substantial number of cases, class I MHC molecules with numerous sequence differences did not elicit an allogeneic CTL response. We propose that in generating a T cell repertoire with a sufficiently narrow responsive for self-MHC, positive thymic selection limits the capacity to recognize allogeneic MHC molecules whose structure and sequence have diverged extensively. These findings are important for donor and patient MHC matching strategies and our understanding of T cell-MHC interaction after haematopoietic stem cell transplantation.

Although HLA matching is beneficial in clinical transplantation, it is not feasible to select a completely HLA matched donor for every potential recipient because of the enormous polymorphism of the HLA system. As a consequence, the majority of the recipients will be transplanted with a mismatched donor organ or hematopoietic stem cell transplant. For this large group of patients it is important to take advantage of the differential immunogenicity of HLA mismatches and to select for them a donor with HLA mismatches of low immunogenicity, the so-called acceptable mismatches. The differential immunogenicity of HLA mismatches can be determined by either retrospective analysis of graft survival data or by in vitro assays measuring T-cell and B-cell alloreactivity. A recently developed computer algorithm (HLAMatchmaker) can be instrumental in selecting donors with HLA mismatches, which do not lead to alloantibody formation. The theoretical background and practical implications of this acceptable mismatch approach are discussed.

Many patients do not reach haematopoietic stem cell transplantation. Shortage of unrelated donors (UDs) is still seen as the main cause. However, with a worldwide UD pool containing more than 8 million donors, it is possible that other impediments are becoming more important. We analysed 549 UD searches for Dutch patients, performed between 1987 and 2000, in order to find the reasons for failure or success to reach transplantation. Between 1996 and 2000, 59% of the patients of Northwest European origin received a graft from an UD with a median time span of 4.4 months from the start of the search. In all, 11% of the patients lacked a compatible donor, while 30% became medically unfit for transplantation. This is in contrast to the patients of non-Northwest European origin for whom UD shortage is still the most important impediment; only 32% were transplanted while 50% lacked a compatible donor. We conclude that the shortage of donors is no longer the biggest constraint in unrelated stem cell transplantation for patients of Northwest European origin. It may be more effective to optimize the chance on transplantation by making the search process more efficient.

Confrontation of the unborn child immune system with the noninherited maternal antigens (NIMAs) has a lifelong modulating impact on the immune response of the child against the NIMAs. In this review we summarize the clinical evidence for the existence of the NIMA effect, discuss the possible cellular and molecular basis of the phenomenon, and outline the necessity of further clinical research.