Induction of antigen-specific tolerance by intrathymic injection of lentiviral vectors

Abstract

Immune tolerance to self-antigens is established during lymphocyte differentiation in the thymus, but a simple means to induce antigen-specific tolerance in the thymus is still elusive. We show here that intrathymic injection of a lentiviral vector expressing the hemagglutinin antigen (HA) in TCR IntroductionAt least 2 mechanisms are involved in the thymus to establish a self-tolerant although not self-ignorant immune system: negative selection of overtly self-reactive effector T cells and positive selection of a unique subset of self-reactive regulatory CD4 ϩ T cells (Tregs) expressing the ␣-chain of the interleukin-2 receptor (CD25) and the forkhead helix-winged transcription factor foxp3. 1 Injection in the thymus of organs, cells, peptide, or whole antigen, either under native or virally encoded forms, has been successful in the manipulation of T-cell-mediated immunologic tolerance. 2 Seminal findings were that allogeneic grafts of pancreatic islets had a better survival when grafted in the thymus, 3 and provided long-term protection against spontaneous autoimmune diabetes if grafted at birth. 4,5 Other investigators have used intrathymic delivery of adenoviral vectors to establish immune tolerance to viral antigens for ensuing gene therapy protocols. 6 It was later reported that intrathymic injection in neonates established longterm tolerance to adenoviral antigens with no need for prior lymphocyte depletion. 7 To induce T-cell-mediated tolerance, other investigators have relied on the expression of foreign MHC class I 8 or MHC class II alleles, 9 or preproinsulin, 10 on antigen-presenting cells after injection of autologous gene-modified hematopoietic stem cells. However, these studies did not formally demonstrate the involvement of the thymus in the tolerance process. The implication of the thymus has been documented in 2 recent studies related to the prevention of autoimmune responses following bone marrow transplantation. 11,12 In particular, it has been shown that thymic deletion of effector T cells correlated with diabetes protection in NOD mice reconstituted with gene-modified autologous hematopoietic stem cells (HSCs). 12 Besides negative selection (deletion) of overtly self-reactive T cells, a second major mechanism of central tolerance involves positive selection of CD4 ϩ CD25 ϩ foxp3 ϩ Tregs. The importance of Tregs for prevention of autoimmunity is perhaps best exemplified by the widespread autoimmune symptoms seen in patients deficient for FOXP3. 13 In the thymus, CD4 ϩ CD25 ϩ cells are detected during the fetal period in humans 14 and during the perinatal period in mice. 15,16 The regulatory function of Tregs is acquired during thymic selection, as shown by the ability of isolated CD4 ϩ CD25 ϩ thymocytes to suppress lymphocyte proliferation. 17 In most studies, expression of the nominal antigen in the thymus led to increased frequency and/or number of specific Tregs in T-cell receptor (TCR) transgenic mice, suggesting an "instructive" role for the antigen in Treg lineage commitment. [18][19][...

Emerging Role of Regulatory T Cells in Gene Transfer

“…Intrathymic injection of the lentiviral vector also resulted in an enrichment of HA-specific T reg in peripheral lymphoid organs, which prevented diabetes induced in TCR-HA transgenic mice expressing HA under the control of insulin promoter (Ins-HA). This procedure was also capable of preventing autoimmune diabetes in NOD mice [Marodon et al, 2006]. Others infected naïve CD4 + CD25 -T cells with a retrovirus encoding FoxP3 to generate T reg in vitro.…”

Highly Pathogenic Influenza Virus Infection of the Thymus Interferes with T Lymphocyte Development

“…This could be important for oral tolerance against nutrition Ags (41). Also, the evidence arises that an organism is able to develop a tolerance against an i.v., intrathymic, but also intranasal injected high-dose Ag by deletion of Ag-specific thymocytes and induction of apoptosis of T lymphocytes in secondary lymphoid organs (42,43). By reaching the thymus, non-self-Ags can generate a suppressive regulatory T cell (Treg) population, which could also have a suppressive effect on the previously generated existing peripheral T cell precursor population (44).…”

Recent Advances in Immune Modulation

“…Morphogenetic protein-2 (Kaihara et al, 2004) Hemophilia A (Sarkar et al, 2006;Ye et al, 2004) Hemophilia B (Fields et al, 2001;Herzog et al, 2001) HGH reporter gene (Potter et al, 1998) Cyclophosphamide (CTX) Non-specific cyto-toxicity HLPL deficiency (Ross et al, 2006) Hemophilia A long-term expression of a transgene [Marodon et al, 2006]. Transgene expression was detected predominantly in thymic stromal cells for at least 30 days, which mediated negative selection of thymocytes expressing the cognate T-cell receptor.…”