Prognostic value of pretransplantation host thymic function in HLA-identical sibling hematopoietic stem cell transplantation

Mitochondrial DNA sequence heterogeneity of single CD34+ cells after nonmyeloablative allogeneic stem cell transplantation

We applied a single-cell method to detect mitochondrial DNA (mtDNA) mutations to evaluate the reconstitution of hematopoietic stem cells (HSCs) and committed progenitor cells after nonmyeloablative allogeneic stem cell transplantation in humans. In a total of 1,958 single CD34(+) cells from six human leukocyte antigen-matched sibling donor and recipient pairs, individual CD34(+) clones were recognized based on the observed donor- or recipient-specific mtDNA sequence somatic alteration. There was no overall reduction of mtDNA heterogeneity among CD34(+) cells from the recipient after transplantation. Samples collected from two donors over time showed the persistence of certain CD34(+) clones marked by specific mutations. Our results demonstrate the feasibility of distinguishing donor and recipient individual CD34(+) clones based on mtDNA mutations during engraftment. HSCs were not limited in number, and similar mtDNA heterogeneity levels suggested representation of the total stem cell compartment during rapid hematopoietic reconstitution in the recipient. Disclosure of potential conflicts of interest is found at the end of this article.

Risk assessment in haematopoietic stem cell transplantation: Pre–transplant patient and donor factors: non-HLA genetics

Non-HLA genetics involving the study of single-nucleotide polymorphisms (SNPs) and microsatellites of cytokine and cytokine receptor genes, and as well as genes associated with response to infection and therapeutic drugs, are currently being studied for associations with diseases, including autoimmune disease, cancer and solid-organ transplant rejection. This chapter will summarize the potential role of non-HLA genetics in predicting outcome of haematopoietic stem-cell transplantation (HSCT) and how genotyping for non-HLA genes may give insight into the immunobiology of HSCT complications, including GvHD and infectious episodes. Future directions - including the role of pharmacogenomics, use of the research results for individualized medicine, and interpretation of data - will also be discussed.

T cell regeneration in pediatric allogeneic stem cell transplantation

Delayed and/or insufficient T cell recovery post hematopoietic stem cell transplantation (HSCT) leads to an increased risk of morbidity and mortality. We evaluated thymic function and its association with T cell regeneration post HSCT and identified factors involved in the process among pediatric stem cell transplant recipients. T cell regeneration in 66 pediatric patients was prospectively followed by naive T cell phenotyping, measuring of T cell receptor excision circles (TRECs) and expression of Foxp3 by regulatory T cells for the first 18 months post HSCT. TRECs were lower pre-HSCT in children with a malignant than non-malignant primary disease or immunosuppressed controls (P=0.001). Naive T lymphocyte reconstitution and thymic recovery were slow in the recipients of allogeneic stem cell grafts post HSCT. Infections caused by herpesviruses had a prognostic impact on mortality. Children with low TRECs had a high mortality (P=0.05) and low TRECs were also associated with extensive chronic graft-versus-host disease from 6 months onwards. Low amount of Foxp3 pre-HSCT was associated with an increased mortality post HSCT (P=0.03). Our study indicates an association between impaired T cell regeneration and thymic dysfunction and the clinical post transplant complications in pediatric allogeneic stem cell transplantation.

Donor cell reaction to OKT3 as predictor of chronic graft-vs-host disease in hematopoietic stem cell recipients

OBJECTIVE

In the hematopoietic stem cell transplantation setting, granulocyte colony-stimulating factor (G-CSF) administration can reduce donor cell reactivity in vitro, but the clinical significance of this phenomenon was only sparsely defined.

METHODS

We performed lymphocyte transformation tests in 28 related stem cell donors pre and 5 days post G-CSF treatment, respectively, and correlated proliferative responses of donor peripheral blood mononuclear cells with clinical parameters in the corresponding recipients.

RESULTS

In vitro reactions towards 4 mitogens and 12 recall antigens at day 5 post G-CSF administration were predictive for the occurrence of chronic graft-vs-host disease (cGVHD). Here, proliferative responses towards the mitogen anti-CD3 monoclonal antibody (OKT3) above median were most informative; this threshold could be determined by discrimination and receiver operating curve (ROC) analyses. In the whole cohort (18 human leukocyte antigen [HLA]-identical and 10 partially mismatched donor-recipient pairs), OKT3 responses predicted cGVHD with an odds ratio of 33.0, a sensitivity of 79%, and a specificity of 90%. A subgroup analysis of HLA-identical pairs even yielded an odds ratio of 85.0. Furthermore, bivariate analysis defined HLA compatibility and responses towards OKT3 as independent risk factors for cGVHD (p = 0.02 and p = 0.0007, respectively).

CONCLUSION

The proliferative capacity of G-CSF-mobilized donor cells appears as a graft factor that determines the future incidence of cGVHD in the corresponding recipient.

Donor-derived thymic-dependent T cells cause chronic graft-versus-host disease

Chronic graft-versus-host disease (GVHD) is the most common cause of poor long-term outcomes after allogeneic bone marrow transplantation (BMT), but the pathophysiology of chronic GVHD still remains poorly understood. We tested the hypothesis that the impaired thymic negative selection of the recipients will permit the emergence of pathogenic T cells that cause chronic GVHD. Lethally irradiated C3H/HeN (H-2k) recipients were reconstituted with T-cell–depleted bone marrow cells from major histocompatibility complex [MHC] class II–deficient (H2-Ab1−/−) B6 (H-2b) mice. These mice developed diseases that showed all of the clinical and histopathological features of human chronic GVHD. Thymectomy prevented chronic GVHD, thus confirming the causal association of the thymus. CD4+ T cells isolated from chronic GVHD mice were primarily donor reactive, and adoptive transfer of CD4+ T cells generated in these mice caused chronic GVHD in C3H/HeN mice in the presence of B6-derived antigen-presenting cells. Our results demonstrate for the first time that T cells that escape from negative thymic selection could cause chronic GVHD after allogeneic BMT. These results also suggest that self-reactivity of donor T cells plays a role in this chronic GVHD, and improvement in the thymic function may have a potential to decrease chronic GVHD.

Non-HLA immunogenetics in hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) provides a unique environment in which to evaluate the role of immunogenetics of both the donor and the recipient to success of the procedure. The central role of HLA matching in HSCT has been established; however, recipients of allogeneic HSCT incur the risk of graft versus host disease (GVHD) even when the donor is a sibling who shares the major histocompatibility genes. Therefore, the perfect HLA match does not represent the optimal genetic make up. Other genetic systems operate and affect the various outcomes of HSCT, including GVHD, infections, transplant-related mortality, and overall survival. Minor histocompatibility antigens contribute to the control of GVHD as well as graft versus leukaemia reactions. In addition, genes controlling inflammatory processes, including cytokines, chemokines and their receptors, can modulate GVHD, and genes from both arms of the immune response (innate and adaptive) are strong candidates for susceptibility factors to infections in allogenic transplantation.