Blood TRANSPLANTATION

Inducing the tryptophan catabolic pathway, indoleamine 2,3-dioxygenase (IDO), for suppression of graft-versus-host disease (GVHD) lethality

Thu, 03 Dec 2009 09:02:29 PST

During graft-versus-host disease (GVHD), donor T cells become activated and migrate to tissue sites. Previously, we demonstrated a crucial role for the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO) in GVHD regulation. Here, we show that upon arrival in the colon, activated donor T cells produced interferon- that up-regulated IDO, causing T-cell anergy and apoptosis. IDO induces GCN2 kinase, up-regulating a T-cell stress response implicated in IDO immunosuppression. Donor T cells did not require GCN2 kinase to respond to IDO, suggesting toxic IDO metabolites, and not tryptophan depletion, were responsible for suppression. When exogenous metabolites were administered, GVHD lethality was reduced. To determine whether IDO could be induced before transplantation for enhanced GVHD suppression, we first determined whether antigen-presenting cells (APCs) or epithelial cells were primarily responsible for IDO expression and subsequent GVHD suppression. Recipients with wild-type versus IDO^–/– APCs had increased survival, regardless of epithelial-cell expression of IDO, suggesting that APCs were suitable targets for inducing IDO. Administration of an agonist to toll-like receptor-7/8, a receptor expressed primarily on APCs, induced IDO and reduced injury in the colon and ameliorated lethality. We conclude that IDO up-regulation may have therapeutic potential for preventing GVHD in the clinic.

The transfer of adaptive immunity to CMV during hematopoietic stem cell transplantation is dependent on the specificity and phenotype of CMV-specific T cells in the donor

Thu, 03 Dec 2009 09:02:29 PST

The successful reconstitution of adaptive immunity to human cytomegalovirus (CMV) in hematopoietic stem cell transplantation (HSCT) recipients is central to the reduction of viral reactivation-related morbidity and mortality. Here, we characterized the magnitude, specificity, phenotype, function, and clonotypic composition of CMV-specific T-cell responses in 18 donor-recipient pairs both before and after HSCT. The principal findings were: (1) the specificity of CMV-specific T-cell responses in the recipient after HSCT mirrors that in the donor; (2) the maintenance of these targeting patterns reflects the transfer of epitope-specific T-cell clonotypes from donor to recipient; (3) less differentiated CD27⁺CD57^– CMV-specific memory T cells are more likely to persist in the recipient after HSCT compared with more terminally differentiated CD27^– CD57⁺ CMV-specific memory T cells; (4) the presence of greater numbers of less differentiated CD8⁺ CMV-specific T cells in the donor appears to confer protection against viral reactivation in the recipient after HSCT; and (5) CMV-specific T cells acquire a more differentiated phenotype and a restricted functional profile after HSCT. Overall, these findings define the immunologic factors that influence the successful adoptive transfer of antigen-specific T-cell immunity during HSCT, which enables the identification of recipients at particular risk of CMV reactivation after HSCT.

Bone marrow as an alternative site for islet transplantation

Thu, 12 Nov 2009 09:38:06 PST

The liver is the current site for pancreatic islet transplantation, but has many drawbacks due to immunologic and nonimmunologic factors. We asked whether pancreatic islets could be engrafted in the bone marrow (BM), an easily accessible and widely distributed transplant site that may lack the limitations seen in the liver. Syngeneic islets engrafted efficiently in the BM of C57BL/6 mice rendered diabetic by streptozocin treatment. For more than 1 year after transplantation, these animals showed parameters of glucose metabolism that were similar to those of nondiabetic mice. Islets in BM had a higher probability to reach euglycemia than islets in liver (2.4-fold increase, P = .02), showed a compact morphology with a conserved ratio between and β cells, and affected bone structure only very marginally. Islets in BM did not compromise hematopoietic activity, even when it was strongly induced in response to a BM aplasia-inducing infection with lymphocytic choriomeningitis virus. In conclusion, BM is an attractive and safe alternative site for pancreatic islet transplantation. The results of our study open a research line with potentially significant clinical impact, not only for the treatment of diabetes, but also for other diseases amenable to treatment with cellular transplantation.

Superagonistic CD28 stimulation of allogeneic T cells protects from acute graft-versus-host disease

Beyersdorf, N., Ding, X., Hunig, T., Kerkau, T. — Thu, 12 Nov 2009 09:38:06 PST

Acute graft-versus-host disease (aGVHD) often precludes successful immunotherapy of hematologic malignancies with allogeneic T cells. Therefore, we investigated the effect of immunomodulatory superagonistic anti-CD28 monoclonal antibodies (CD28-SA) on the capacity of allogeneic T cells to mediate both aGVHD and the protective graft-versus-tumor (GVT) response. In vivo pretreatment of donor C57BL/6 mice or short-term in vitro culture of donor lymph node cells with a CD28-SA efficiently protected BALB/c recipient mice from aGVHD. This protection strongly relied on the presence of CD28-SA–activated CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells in the donor T-cell inoculum. With respect to the GVT response, CD28-SA–prestimulated T cells were still as potent in clearing lymphoma cells as were T cells without CD28-SA preactivation. Taken together, our data suggest that CD28-SA stimulation of bulk leukocyte cultures in vitro markedly increases the therapeutic window for adoptive immunotherapy with allogeneic T cells in vivo.