Long-term persistence of IL-2-unresponsive allogeneic T cells in sublethally irradiated SCID mice

The miR-17-92 cluster expands multipotent hematopoietic progenitors whereas imbalanced expression of its individual oncogenic miRNAs promotes leukemia in mice

The miR-17-92 cluster and its 6 encoded miRNAs are frequently amplified and aberrantly expressed in various malignancies. This study demonstrates that retroviral-mediated miR-17-92 overexpression promotes expansion of multipotent hematopoietic progenitors in mice. Cell lines derived from these miR-17-92-overexpressing mice are capable of myeloid and lymphoid lineage differentiation, and recapitulate the normal lymphoid phenotype when transplanted to nonobese diabetic/severe combined immunodeficiency mice. However, overexpression of individual miRNAs from this locus, miR-19a or miR-92a, results in B-cell hyperplasia and erythroleukemia, respectively. Coexpression of another member of this cluster miR-17, with miR-92a, abrogates miR-92a-induced erythroleukemogenesis. Accordingly, we identified several novel miR-92a and miR-17 target genes regulating erythroid survival and proliferation, including p53. Expression of this critical target results in marked growth inhibition of miR-92a erythroleukemic cells. In both murine and human leukemias, p53 inactivation contributed to the selective overexpression of oncogenic miR-92a and miR-19a, and down-regulation of tumor-suppressive miR-17. This miR-17-92 expression signature was also detected in p53- B-cell chronic lymphocytic leukemia patients displaying an aggressive clinical phenotype. These results revealed that imbalanced miR-17-92 expression, also mediated by p53, directly transforms the hematopoietic compartment. Thus examination of such miRNA expression signatures should aid in the diagnosis and treatment of cancers displaying miR-17-92 gene amplification.

Rapamycin Promotes Emergence of IL-10-Secreting Donor Lymphocyte Infusion-Derived T Cells Without Compromising Their Graft-Versus-Leukemia Reactivity

BACKGROUND

There are limited data examining the effects of pharmacological immunosuppression on the in vivo fate of donor lymphocyte infusions (DLI)-derived T cells, their function, and their antitumor efficacy.

METHODS

We addressed this question in a murine model in which DLI is given to stable mixed chimeras resulting in lymphohematopoietic graft-versus-host (LH-GVH) response. In this model, LH-GVH potency can be directly measured as the kinetics of conversion to full donor chimerism and can be correlated with associated graft-versus-leukemia (GVL) reactivity.

RESULTS

We found discordance in DLI-mediated LH-GVH reactivity depending on the timing of rapamycin (RAPA) administration. Delayed administration of RAPA in contrast to its early administration at the time of adoptive transfer did not interfere with conversion to full donor chimerism. Moreover, delayed administration of RAPA preserved the GVL reactivity of DLI. Analysis of the long-term chimeras showed that regardless of RAPA administration, adoptively transferred T cells mediating the LH-GVH response contribute minimally to the reconstitution of the peripheral T-cell compartment and exhibit profound hyporesponsiveness and decreased production of interleukin (IL)-2 on restimulation in vitro. However, we observed only in the RAPA-treated chimeras that the remaining hyporesponsive DLI-derived CD4+ T cells secrete large amounts of IL-10, a known immunoregulatory cytokine.

CONCLUSIONS

We conclude that delayed administration of RAPA after DLI does not interfere with their LH-GVH reactivity but promotes the emergence of IL-10-secreting DLI-derived CD4+ T cells that might contribute to the drug's known ability to promote bilateral donor host tolerance without interfering with GVL reactivity.

Reconstructing immunity after allogeneic transplantation

A major goal of our research is to reduce the graft-vs-host disease (GVHD) activity of allogeneic donor T cells in bone marrow transplantation (BMT), while preserving graft-vs-tumor (GVT) effects. Using ex vivo immunosuppressive strategies and cell-separation techniques to modulate the graft prior to transplantation, we examined the roles of different donor immune cells on GVHD and GVT effects in allogeneic mouse models. Our results demonstrate that donor-memory CD4 T cells facilitate posttransplant immunological reconstitution without causing GVHD, whereas transplantation of equal numbers of donor naïve CD4 T cells leads to fatal GVHD. The initial events of donor T cells interacting with antigen-presenting cells (APCs) in the transplant recipient appear to be critical to the development of GVT, GVHD, or anergy to alloantigens. In the setting of clinical BMT, increased numbers of donor type 2 dendritic cells (DCs) were associated with an increased rate of posttransplant relapse, and decreased rates of chronic GVHD. In a mouse transplant model, manipulation of the DC content of bone marrow grafts was achieved by depletion of CD11b+ cells. Mice transplanted with CD11b- depleted marrow showed enhanced posttransplant expansion of memory T cells with markedly improved GVT activity and limited GVHD compared to recipients of unmanipulated marrow. A model that differentiates GVT from GVHD based on interaction of T-cell subsets with DC subsets is proposed.

Aberrant regulation of superantigen responses during T-cell reconstitution and graft-versus-host disease in immunodeficient mice

Acute graft-versus-host disease (GVHD) after allogeneic stem cell transplantation is associated with impaired deletion and anergy of host-reactive T cells. To elucidate the immunoregulatory events that may contribute to such dysregulated T-cell responses in GVHD, we studied superantigen (SAg) responses after adoptive T-cell transfer into severe combined immunodeficient (SCID) mice. SAg responses are normally regulated by mechanisms involving deletion and anergy, with SAg-reactive T cells typically being deleted rapidly in vivo. In a SCID mouse model of GVHD, however, allogeneic host SAg-reactive T cells were not deleted rapidly, but rather persisted in increased numbers for several months. Moreover, depending on the timing of SAg stimulation and the numbers of T cells transferred, dysregulation (impaired deletion and anergy) of SAg responses could be demonstrated following the adoptive transfer of syngeneic T cells into SCID mice as well. Transgenic T-cell receptor-bearing KJ1-26.1+ T cells were then used to determine the fate of weakly reactive T cells after adoptive transfer and SAg stimulation. When transferred alone, KJ1-26.1+ T cells demonstrated impaired deletion and anergy. In the presence of more strongly staphylococcal enterotoxin B (SEB)–reactive T cells, however, KJ1-26.1+ T cells were regulated normally, in a manner that could be prevented by inhibiting the effects of more strongly SEB-reactive cells or by increasing the level of activation of the KJ1-26.1+ T cells themselves. We suggest that the control mechanisms that normally regulate strongly activated T cells in immunocompetent animals are lost following adoptive transfer into immunodeficient hosts, and that this impairment contributes to the development of GVHD.

Aberrant regulation of superantigen responses during T-cell reconstitution and graft-versus-host disease in immunodeficient mice

Acute graft-versus-host disease (GVHD) after allogeneic stem cell transplantation is associated with impaired deletion and anergy of host-reactive T cells. To elucidate the immunoregulatory events that may contribute to such dysregulated T-cell responses in GVHD, we studied superantigen (SAg) responses after adoptive T-cell transfer into severe combined immunodeficient (SCID) mice. SAg responses are normally regulated by mechanisms involving deletion and anergy, with SAg-reactive T cells typically being deleted rapidly in vivo. In a SCID mouse model of GVHD, however, allogeneic host SAg-reactive T cells were not deleted rapidly, but rather persisted in increased numbers for several months. Moreover, depending on the timing of SAg stimulation and the numbers of T cells transferred, dysregulation (impaired deletion and anergy) of SAg responses could be demonstrated following the adoptive transfer of syngeneic T cells into SCID mice as well. Transgenic T-cell receptor-bearing KJ1-26.1+ T cells were then used to determine the fate of weakly reactive T cells after adoptive transfer and SAg stimulation. When transferred alone, KJ1-26.1+ T cells demonstrated impaired deletion and anergy. In the presence of more strongly staphylococcal enterotoxin B (SEB)–reactive T cells, however, KJ1-26.1+ T cells were regulated normally, in a manner that could be prevented by inhibiting the effects of more strongly SEB-reactive cells or by increasing the level of activation of the KJ1-26.1+ T cells themselves. We suggest that the control mechanisms that normally regulate strongly activated T cells in immunocompetent animals are lost following adoptive transfer into immunodeficient hosts, and that this impairment contributes to the development of GVHD.

Characterization of graft-versus-host disease in SCID mice and prevention by physicochemical stressors

BACKGROUND

Graft versus host disease (GVHD) prevents potentially curative allogeneic stem cell transplantation from being offered to cancer patients who lack a suitably matched donor. New methods to prevent GVHD are required to allow successful transplants across major histocompatibility complex barriers.

METHODS

A model of GVHD in C.B-17 SCID mice was developed to allow the study of allo-activated donor T cells without confounding effects of host lymphocytes. The abilities of cyclosporin-A, anticytokine antibodies, and oxidative stress to prevent GVHD in this model was studied.

RESULTS

T cells from major histocompatibility-mismatched donor mice caused severe GVHD in sublethally irradiated SCID hosts that could be ameliorated by coadministration of donor bone marrow but not by cyclosporine-A or anticytokine antibodies. In contrast, three-log more T cells could be injected without clinical consequences if they had been pretreated with a combination of heat, ultraviolet light, and oxygenation. The effect was not the trivial result of donor T cell destruction because T cell reconstitution, although delayed, recovered to normal levels within 2 weeks. Protection from GVHD required oxygenation and was associated with normalization of the CD4/CD8 donor T cell ratio, recovery of host hematopoiesis, and decreased inflammatory cytokine production.

CONCLUSION

Pretreatment of donor T cells with a combination of physicochemical stressors effectively prevents GVHD caused by major major histocompatibility disparities and may facilitate the safe transplantation of patients without HLA-identical donors.