IL-7 Enhances the Responsiveness of Human T Cells That Develop in the Bone Marrow of Athymic Mice

Abstract

The beige/nude/xid/human (bnx/hu) model of human hematopoiesis provides a unique opportunity to study extrathymic human T lymphocyte development in an in vivo system. Purified human hematopoietic stem cells develop into mature T lymphocytes and immature progenitors in the bone marrow of athymic bnx mice. The human T cells are all TCRαβ+ and display a restricted TCRVβ repertoire. In the current studies, we examined the effects of systemic human IL-7 (huIL-7) administration on the phenotype and the activation status of the bnx/hu T cells. In the majority of the mice that did not have huIL-7 administration, a higher frequency of human CD3+/CD8+ than CD3+/CD4+ T cells developed in the bone marrow. This phenomenon is also frequently observed in human bone marrow transplant recipients. Extremely low levels of IL-2 were expressed by human CD3+ cells isolated from these mice, in response to PMA plus ionomycin and to CD3 and CD28 cross-linking. IL-4 was not expressed by cells exposed to either stimulus, demonstrating a profound inability of the bnx/hu T cells to produce this cytokine. Systemic production of huIL-7 from engineered stromal cells transplanted into the mice increased the human CD4 to CD8 ratios, and increased the ratio of memory to naive CD4+ and CD8+ T cells. The human CD3+ cells recovered from mice that had systemic huIL-7 and equivalent numbers of CD3+/CD4+ and CD3+/CD8+ cells in the marrow were still unable to produce IL-4 in response to any condition tested, but were capable of normal levels of IL-2 production following stimulation.

The AFT024 stromal cell line supports long-term ex vivo maintenance of engrafting multipotent human hematopoietic progenitors

“…We have recently reported that the human T lymphocytes that develop through extrathymic mechanisms are hyporesponsive to anti-CD3 and anti-CD28 or PHA stimuli when recovered from the bnx bone marrow. 18 However, when the human T cells had developed in mice that had systemic human IL-7 production, the responsiveness to in vitro stimuli was restored to levels close to what could be obtained from human peripheral blood T lymphocytes, which had developed with the benefits of thymic selection. 18 In the current studies, we determined that human hematopoietic stem/progenitor cells could retain the capacity to generate T lymphocytes through extrathymic mechanisms to 3 weeks in ex vivo culture.…”

“…18 However, when the human T cells had developed in mice that had systemic human IL-7 production, the responsiveness to in vitro stimuli was restored to levels close to what could be obtained from human peripheral blood T lymphocytes, which had developed with the benefits of thymic selection. 18 In the current studies, we determined that human hematopoietic stem/progenitor cells could retain the capacity to generate T lymphocytes through extrathymic mechanisms to 3 weeks in ex vivo culture. The human stem/progenitor cells that generated the T lymphocytes in the mice were maintained better on AFT024 than on human stroma.…”

“…17,18,25,26 In the current studies, we determined that this phenomenon occurs even when the human hematopoietic stem/progenitor cells were cultured in vitro for up to 3 weeks prior to transplantation into the mice. The average percentage of human CD4 + and CD8 + cells detected in the marrow of mice transplanted with cells cultured for only 24 h prior to transplantation was 4.0 ± 0.8 and 3.0 ± 0.5, respectively.…”

“…Human myeloid cells, erythroid progenitors, B lymphocytes and extrathymically derived T lymphocytes develop in bnx mice following transplantation of purified stem cells. [17][18][19][20][21] The lifespan of the bnx mouse is longer than that of the commonly used NOD/SCID strain, since the bnx does not carry the emv-30 provirus, which causes lethal thymoma in NOD/SCID mice. 22 The bnx mouse was therefore chosen as the xenogeneic host for the cultured human hematopoietic cells in the current studies, so that multilineage long-term engraftment could be examined.…”

New approaches for preventing and treating chronic graft-versus-host disease

“…69 The effects of exogenous IL-7 have been tested on human thymic cultures or human stem cells injected into immunoincompetent mice, showing that T-cell production can be increased. 70,71 Other approaches to T-cell tolerization rely on immunomodulation, such as might be provided by extracorporeal photopheresis (ECP). Subjects who responded to ECP were more likely to have a clonal T-cell population, although these populations were found equally in people with and without chronic GVHD.…”