Combined Effects of Interleukin-7 and Stem Cell Factor Administration on Lymphopoiesis after Murine Bone Marrow Transplantation

The decreased ability of the thymus to generate T cells after bone marrow transplantation (BMT) is a clinically significant problem. Interleukin (IL)-7 and stem cell factor (SCF) induce proliferation, differentiation, and survival of thymocytes. Although previous studies have shown that administration of recombinant human IL-7 (rhIL-7) after murine and human BMT improves thymopoiesis and immune function, whether administration of SCF exerts similar effects is unclear. To evaluate independent or combinatorial effects of IL-7 and SCF in post-BMT thymopoiesis, bone marrow (BM)-derived mesenchymal stem cells transduced ex vivo with the rhIL-7 or murine SCF (mSCF) genes were cotransplanted with T cell–depleted BM cells into lethally irradiated mice. Although rhIL-7 and mSCF each improved immune reconstitution, the combination treatment had a significantly greater effect than either cytokine alone. Moreover, the combination treatment significantly increased donor-derived common lymphoid progenitors (CLPs) in BM, suggesting that transplanted CLPs expand more rapidly in response to IL-7 and SCF and may promote immune reconstitution. Our findings demonstrate that IL-7 and SCF might be therapeutically useful for enhancing de novo T cell development. Furthermore, combination therapy may allow the administration of lower doses of IL-7, thereby decreasing the likelihood of IL-7–mediated expansion of mature T cells

Antigen-Specific Inhibition of High-Avidity T Cell Target Lysis by Low-Avidity T Cells via Trogocytosis

Current vaccine conditions predominantly elicit low-avidity cytotoxic T lymphocytes (CTLs), which are non-tumor-cytolytic but indistinguishable by tetramer staining or enzyme-linked immunospot from high-avidity CTLs. Using CTL clones of high or low avidity for melanoma antigens, we show that low-avidity CTLs can inhibit tumor lysis by high-avidity CTLs in an antigen-specific manner. This phenomenon operates in vivo: high-avidity CTLs control tumor growth in animals but not in combination with low-avidity CTLs specific for the same antigen. The mechanism involves stripping of specific peptide-major histocompatibility complexes (pMHCs) via trogocytosis by low-avidity melanoma-specific CTLs without degranulation, leading to insufficient levels of specific pMHC on target cell surface to trigger lysis by high-avidity CTLs. As such, peptide repertoire on the cell surface is dynamic and continually shaped by interactions with T cells. These results describe immune regulation by low-avidity T cells and have implications for vaccine design

Engineering the Human Thymic Microenvironment to Support Thymopoiesis In Vivo

A system that allows manipulation of the human thymic microenvironment is needed both to elucidate the extrinsic mechanisms that control human thymopoiesis and to develop potential cell therapies for thymic insufficiency. In this report, we developed an implantable thymic microenvironment composed of two human thymic stroma populations critical for thymopoiesis; thymic epithelial cells (TECs) and thymic mesenchyme (TM). TECs and TM from postnatal human thymi were cultured in specific conditions, allowing cell expansion and manipulation of gene expression, before reaggregation into a functional thymic unit. Human CD34+ hematopoietic stem and progenitor cells (HSPC) differentiated into T cells in the aggregates in vitro and in vivo following inguinal implantation of aggregates in immune deficient mice. Cord blood HSPC previously engrafted into murine bone marrow (BM), migrated to implants, and differentiated into human T cells with a broad T cell receptor repertoire. Furthermore, lentiviral-mediated expression of vascular endothelial growth factor in TM enhanced implant size and function and significantly increased thymocyte production. These results demonstrate an in vivo system for the generation of T cells from human HSPC and represent the first model to allow manipulation of gene expression and cell composition in the microenvironment of the human thymus

Prevention of graft-versus-host disease by anti–IL-7Rα antibody

Graft-versus-host disease (GVHD) continues to be a serious complication that limits the success of allogeneic bone marrow transplantation (BMT). Using IL-7–deficient murine models, we have previously shown that IL-7 is necessary for the pathogenesis of GVHD. In the present study, we determined whether GVHD could be prevented by antibody-mediated blockade of IL-7 receptor α (IL-7Rα) signaling. C57/BL6 (H2Kb) recipient mice were lethally irradiated and underwent cotransplantation with T-cell–depleted (TCD) BM and lymph node (LN) cells from allogeneic BALB/c (H2Kd) donor mice. Following transplantation, the allogeneic BMT recipients were injected weekly with either anti–IL-7Rα antibody (100 μg per mouse per week) or PBS for 4 weeks. Anti–IL-7Rα antibody treatment significantly decreased GVHD-related morbidity and mortality compared with placebo (30% to 80%). IL-7Rα blockade resulted in the reduction of donor CD4+ or CD8+ T cells in the periphery by day 30 after transplantation. Paradoxically, the inhibition of GVHD by anti–IL-7Rα antibody treatment resulted in improved long-term thymic and immune function. Blockade of IL-7R by anti–IL-7Rα antibody resulted in elimination of alloreactive T cells, prevention of GVHD, and improvement of donor T-cell reconstitution