expressed on the leading edge of membrane filopodia and colocalizes with a-actinin. Purified recombinant GPR56 extracellular domain protein inhibits glioma cell adhesion and causes abnormal cytoskeletal morphology and cell rounding. These results indicate that the extracellular domain may compete for unidentified ligand(s), and block the normal function of GPR56 in cell attachment. In reporter assays, overexpression of GPR56 activates the NF-jB, PAI-1 and TCF transcriptional response elements. These pathways have been implicated in cytoskeletal signaling, adhesion and tumor biology. The above results indicate that GPR56 serves as an adhesion GPCR and is involved in adhesion signaling.

Regulatory T cells (Tregs) prevent graftversus-host disease (GvHD) by inhibiting the proliferation and function of conventional T cells (Tcons). However, the impact of Tregs on T-cell development and immunity following hematopoietic cell transplantation (HCT) is unknown. Using a murine GvHD model induced by IntroductionNaturally arising CD4 ϩ CD25 ϩ Foxp3 ϩ regulatory T cells (Tregs) are a major regulator of adaptive immunity. 1 Depletion of Tregs enhances microbial and tumor immunity, 2,3 while their adoptive transfer protects animals from autoimmune diseases, 1,4,5 induces tolerance following organ transplantation, 5 and prevents graftversus-host disease (GvHD) following hematopoietic cell transplantation (HCT). 6-8 Given these observations, immunotherapy with Tregs is being explored for clinical applications. 9 However, the impact of Treg transfer on short-and long-term host immunity remains not well understood.In HCT, GvHD damages the stroma of the thymus and secondary lymphoid organs, thereby decreasing thymic output, impairing peripheral expansion of T cells, [10][11][12][13][14][15] and consequently leading to a prolonged immunodeficiency state. 11,16 Given the pathophysiologic link between GvHD and immune reconstitution, protection from GvHD by Tregs would potentially promote timely and complete immune recovery. However, quantitative immune reconstitution does not necessarily translate into recovery of cellular function, 17 and the long-term persistence of transferred Tregs in vivo 18 may diminish or abrogate functional effector responses.Tregs suppress the priming, expansion, and/or function of conventional T cells (Tcons). [19][20][21] However, it is unclear whether this regulation is antigen specific. Following HCT, specific suppression of alloreactive T cells is beneficial, as donor T cells have dual and opposing roles of mounting antitumor and antimicrobial responses and inducing GvHD. Observations from autoimmune disease models that Tregs can induce bystander suppression 5,22,23 and infectious tolerance 24,25 suggest nonspecific inhibition following their activation. Given the multiorgan involvement of GvHD, we anticipate broader nonspecific suppression by polyclonal donor Tregs. Thus, we hypothesized that the adoptive transfer of Tregs would attenuate GvHD via nonspecific suppression of effector responses, which could in turn compromise viral and tumor immunity following HCT.The aims of our studies were to determine if Tregs affect the generation and expansion of thymic-derived naive donor T cells and mature CD4 ϩ and CD8 ϩ T cells transplanted with the allograft, and if effective immune responses can be generated in the presence of Tregs. Our results demonstrate that Tregs prevent damage of the thymus and peripheral lymphoid tissues associated with GvHD. Protection of both central and peripheral lymphoid compartments by Tregs in turn facilitates the development and expansion of an enhanced T-cell repertoire that results in improved reconstitution of functional immune responses following HCT. Meth...

Hematopoietic progenitors committed to the myeloid lineage, the common myeloid and granulocyte-monocyte progenitors (CMP/GMP), have been shown to protect against opportunistic pathogens following myeloablative radiation; however, the efficacy of this approach has not been studied in the setting of chemotherapyinduced neutropenia. In this mouse model, the infusion of CMP/GMP on the day after 5-fluorouracil (5-FU) administration (D؉1) resulted in a significant increase in the number of splenic neutrophils by D؉8 when compared with 5-FUonly controls (P ‫؍‬ .02), the majority of which were CMP/GMP-derived (54%). Moreover, 19% and 28% of neutrophils in the blood and bone marrow, respectively, were CMP/GMP-derived. Survival following intranasal challenge with the fungus Aspergillus fumigatus was significantly higher in CMP/GMP-infused mice than the controls (56% and 33% respectively; P ‫؍‬ .019). Thus, a single infusion of CMP/ GMP enhances tissue neutrophil content and increases survival against a lethal challenge with A fumigatus in the setting of chemotherapy-induced neutropenia.

Invasive fungal infections are a leading cause of morbidity and mortality after myelotoxic chemotherapy or radiation exposure. The resulting depletion of myeloid precursors under these conditions appears to be the factor that limits approaches to accelerate immune reconstitution. In a murine model of myeloablation after radiation exposure, we demonstrated that highly purified common myeloid and granulocyte-monocyte progenitors (CMPs/GMPs) accelerated myeloid recovery and, thus, enhanced innate immunity as measured by survival after a lethal challenge with Aspergillus fumigatus. Of greatest significance was the demonstration that the protection afforded by CMPs/GMPs was not major histocompatibility complex restricted. Furthermore, the effect of CMP/GMP cellular therapy was additive with that of liposomal amphotericin B treatment. These observations greatly expand the potential donor pool and, thus, the clinical utility of CMP/GMP cellular therapy in patients with myeloid depletion.

The reconstitution of immune function after hematopoietic cell transplant (HCT) plays an important role in the control of viral infections. Both donor and recipient cytomegalovirus (CMV) serostatus has been shown to contribute to effective immune function; however, the influence of a nonmyeloablative preparative (NMA) regimen using total lymphoid irradiation (TLI) and antithymocyte globulin (ATG) on antiviral immune reconstitution has not yet been described. In 117 recipients of NMA HCT patients following ATG and TLI, not unexpectedly, CMV viremia was seen in approximately 60% of the seropositive patients regardless of donor serostatus, and recipient seropositivity significantly increased the odds of CMV viremia after transplant in a multivariate analysis. The administration of ATG and TLI resulted in a strikingly earlier viremia in the posttransplant period when compared to the previously reported timing of viremia following myeloablative preparative regimens, especially for transplant recipients who were seropositive for CMV with seronegative donors. Furthermore, early viremia in the setting of a CMV naïve donor was associated with a delay in functional antiviral control. These observations demonstrate the dynamic nature of immunity in relation to CMV antigen exposure in the complex environment resulting from NMA conditions where both donor and residual recipient immune response affect viral control.