Physiologic human T-cell responses to OKT3 in the human peripheral blood lymphocyte-severe combined immunodeficiency mouse model

T Lymphocyte Development and Activation in Humanized Mouse Model

Humanized mice, containing engrafted human cells and tissues, are emerging as an important in vivo platform for studying human diseases. Since the development of Nod scid gamma (NSG) mice bearing mutations in the IL-2 receptor gamma chain, many investigators have used NSG mice engrafted with human hematopoietic stem cells (HSCs) to generate functional human immune systems in vivo, results in high efficacy of human cell engraftment. The development of NSG mice has allowed significant advances to be made in studies on several human diseases, including cancer and graft-versus-host-disease (GVHD), and in regenerative medicine. Based on the human HSC transplantation, organ transplantation including thymus and liver in the renal capsule has been performed. Also, immune reconstruction of cells, of the lymphoid as well as myeloid lineages, has been partly accomplished. However, crosstalk between pluripotent stem cell derived therapeutic cells with human leukocyte antigen (HLA) mis/matched types and immune CD3 T cells have not been fully addressed. To overcome this hurdle, human major histocompatibility complex (MHC) molecules, not mouse MHC molecules, are required to generate functional T cells in a humanized mouse model. Here, we briefly summarize characteristics of the humanized mouse model, focusing on development of CD3 T cells with MHC molecules. We also highlight the necessity of the humanized mouse model for the treatment of various human diseases.

Human peripheral blood leukocyte engraftment into SCID mice: critical role of CD4(+) T cells

We examined the influence of donor T lymphocytes on human peripheral blood leukocytes (PBL) engraftment into severe combined immune deficient (SCID) mice. Mice were injected with unfractionated or subset-depleted human PBL, and treated at various times with OKT3, a cytotoxic monoclonal antibody against human CD3(+) T lymphocytes. PBL engraftment, high levels of human Ig, and high incidence of lymphoproliferative disease (lpd) were found in mice transplanted with unfractionated PBL and CD8- or CD14-depleted PBL, and in mice treated with OKT3 at distance from PBL transfer. Animals xenografted with CD3- or CD4-depleted PBL, or treated at transplantation time with OKT3, had very low levels of human Ig and did not develop lpd. PBL engraftment was minimal or absent in these animals, as determined by immunohistochemistry, dot-blot, and RT-PCR analyses. These results demonstrate that the presence of donor CD4(+) T lymphocytes at transplantation time is necessary for observing human PBL engraftment into SCID mice, an essential condition for human Ig production and lpd development.

Prevention of autoimmune attack by targeting specific T-cell receptors in a severe combined immunodeficiency mouse model of myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease targeting the skeletal muscle acetylcholine receptor. We have previously demonstrated a selection bias of CD4+ T cells expressing the Vbeta5.1 T-cell receptor gene in the thymus of HLA-DR3 patients with MG. To evaluate the pathogenicity of these cells, severe combined immunodeficiency mice engrafted with MG thymic lymphocytes were treated with anti-Vbeta5.1 antibody. Signs of pathogenicity (eg, acetylcholine receptor loss and complement deposits at the muscle end plates of chimeric mice) were prevented in anti-Vbeta5.1-treated severe combined immunodeficiency chimeras. Pathogenicity was mediated by autoantibodies against acetylcholine receptor. Thymic cells depleted of Vbeta5.1-positive cells in vitro before cell transfer were nonpathogenic, indicating that Vbeta5.1-positive cells are involved in the production of pathogenic autoantibodies. Acetylcholine receptor loss was prevented by Vbeta5.1 targeting in HLA-DR3 patients only, demonstrating specificity for HLA-DR3-peptide complexes. The action of the anti-Vbeta5.1 antibody involved both the in vivo depletion of Vbeta5.1-expressing cells and an increase in the interferon-gamma/interleukin-4 ratio, pointing to an immune deviation-based mechanism. This demonstration that a selective and specific T-helper cell population is involved in controlling pathogenic autoantibodies in MG holds promise for the treatment of MG.

Treatment of HIV infection with cytoreductive agents

Advances in antiretroviral therapy have resulted in significant improvement in virological markers and clinical end points. However, studies have demonstrated that HIV can be recovered from patients in whom HIV RNA has been undetectable for prolonged periods of time, suggesting that the elimination half-life of latently infected cells may be longer than previously speculated. When used in the appropriate setting, cytoreductive agents may help expedite the elimination of the long-lived viral reservoir, and result in shorter administration of antiviral agents. In this article we discuss the potential use of cytoreductive agents as adjunctive therapy to antiretrovirals. In addition, we review those agents most likely to impact the viral reservoir and describe ongoing clinical trials designed to define the effect of cytoreductive therapy on those reservoirs. If a positive effect is demonstrated, these agents could ultimately be a powerful addition to the potent drugs currently being used to block HIV replication.