title: Tumor-induced expansion of regulatory T cells by conversion of CD4+CD25- lymphocytes is thymus and proliferation independent.
abstract: The CD25- and CD25+ CD4 T-lymphocyte compartments are tightly regulated. We show here that tumors break such balance, increasing the number of CD4+CD25+ T cells in draining lymph node and spleen but not contralateral node of tumor-bearing mice. Tumor injection in thymectomized and CD25-depleted mice shows that CD4+CD25+ T-cell expansion occurs even in the absence of the thymus and independently from proliferation of preexisting CD25+ T cells. These newly generated cells are bona fide regulatory T cells (T reg) in terms of Foxp3 expression and suppression of CD3-stimulated or allogeneic effector cell proliferation. Transfer of congenic Thy1.1 CD4+CD25- T cells, from mice treated or not with vinblastine, into tumor-bearing or tumor-free mice and analysis of recovered donor lymphocytes indicate that conversion is the main mechanism for acquiring the expression of CD25 and Foxp3 through a process that does not require proliferation. Although conversion of CD4+CD25- T cells for generation of T regs has been described as a natural process that maintains peripheral T-reg population, this process is used by the tumor for immune escape. The prompt recovery of T regs from monoclonal antibody-mediated CD25 depletion in tumor-bearing mice suggests attempts able to inactivate rather than deplete them when treating existing tumors.
authors.affiliation: Immunotherapy and Gene Therapy Unit, Department of Experimental Oncology, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Valzasina
authors.forename: Silvia
authors.initials: S
authors.lastname: Piconese
authors.forename: Cristiana
authors.initials: C
authors.lastname: Guiducci
authors.forename: Mario P
authors.initials: MP
authors.lastname: Colombo
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D015704:CD4 Antigens / Q000276:immunology*; D003110:Colonic Neoplasms / Q000276:immunology*; D008198:Lymph Nodes / Q000276:immunology; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D013154:Spleen / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D013934:Thymectomy; D013950:Thymus Gland / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D015375:Receptors, Interleukin-2