title: Thymic and extrathymic differentiation and expansion of T lymphocytes following bone marrow transplantation in irradiated recipients.
abstract: Thymic function is severely impaired in most marrow transplant recipients. To evaluate the impact of thymic hypoplasia on T cell reconstitution following marrow transplantation, we compared the phenotype and function of T lymphocytes in thymectomized recipients with those of euthymic hosts. Irradiated C57BL/6 mice (Thy1.2+, Ly5.1+) received 10(7) T cell-depleted B6.Ly5.2 bone marrow cells (Thy1.2+, Ly5.2+), with or without 3 x 10(5) B6.PL lymph node cells (Thy1.1+, Ly5.1+) as a source of T lymphocytes. Multiparameter flow cytometry analysis showed that in euthymic mice (group 1), T cell reconstitution was carried out by donor hematopoietic stem cells that differentiated in the host's thymus, whereas the production of chimeric T cells in athymic recipients depended on the presence or absence of T cells in the graft. When T lymphocytes were present in the graft (group 2), their progeny constituted the vast majority of splenic T cells on day 100 posttransplant. When the graft did not contain T lymphocytes (group 3), T cell reconstitution resulted from extrathymic maturation of donor hematopoietic progenitors; T cells differentiating along this pathway expressed lower levels of T cell receptor and a large proportion of the CD8+ subset expressed CD8alpha alpha homodimers. The T cell receptor Vbeta profile of all chimeras was similar to that of normal C57BL/6 mice. Compared with T cells found in euthymic recipients, those in mice from groups 2 and 3 were less abundant (particularly with respect to the CD4+ subset), displayed the CD44/CD45 phenotype of activated memory cells, and expressed high levels of IL-2 receptor beta chain. These results show that both the presence or absence of the thymus and the composition of the grafted inoculum determine the source and extent of posttransplant T cell reconstitution. Because they determine the nature of the differentiation pathway taken during T cell development in the host, these two factors can exert a critical influence on the appearance of graft vs. host disease and the level of host immunocompetence.
authors.affiliation: Department of Medicine, University of Montreal, and Research Center, Maisonneuve-Rosemont Hospital, Quebec, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Dulude
authors.forename: S
authors.initials: S
authors.lastname: Brochu
authors.forename: P
authors.initials: P
authors.lastname: Fontaine
authors.forename: C
authors.initials: C
authors.lastname: Baron
authors.forename: M
authors.initials: M
authors.lastname: Gyger
authors.forename: D C
authors.initials: DC
authors.lastname: Roy
authors.forename: C
authors.initials: C
authors.lastname: Perreault
mesh_terms: D000818:Animals; D016026:Bone Marrow Transplantation; D015704:CD4 Antigens / Q000032:analysis; D016827:CD8 Antigens / Q000032:analysis; D002454:Cell Differentiation; D002455:Cell Division; D003037:Cobalt Radioisotopes; D003602:Cytotoxicity, Immunologic; D005434:Flow Cytometry; D018960:Hyaluronan Receptors / Q000032:analysis; D017493:Leukocyte Common Antigens / Q000032:analysis; D018655:Lymphocyte Count; D051379:Mice; D008810:Mice, Inbred C57BL; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000166:cytology*; D013950:Thymus Gland / Q000166:cytology*; D014916:Whole-Body Irradiation
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D003037:Cobalt Radioisotopes; D018960:Hyaluronan Receptors; D017493:Leukocyte Common Antigens