EXTRATHYMIC MATURATION OF ALPHA-BETA T-CELLS FROM HEMATOPOIETIC STEM-CELLS

The object of the study was to determine whether alpha beta T cells ca n develop from hemopoietic stem cells in the absence of the thymus. C5 7BL/6 (Ly-5.1 and Thy-1.2) mice were thymectomized or sham-thymectomiz ed at 4 wk of age, and received lethal whole body irradiation 2 wk lat er. These mice were reconstituted with an i.v. injection of 500 highly purified hemopoietic stem cells (Mac-1(-), B220(-), TER-119(-), CD3(- ), CD4(-), CD8(-), Thy 1(low), SCA-1(+)) obtained from the bone marrow of C57BL/6 (Ly-5.2 and Thy-1.1) donors. A similar percentage of Ly-5. 2(+) alpha beta T cells (donor) was found in the marrow of thymectomiz ed recipients, sham-thymectomized recipients, and normal donor mice at least 3 mo after stem cell transplantation. The percentage of Ly-5.2( +) alpha beta T cells in the spleens of sham-thymectomized and normal donor mice was similar. The percentage in the spleens of thymectomized recipients was reduced by about 50%, and approximately one-half of th e latter T cells expressed the CD4(-)CD8(-) alpha beta(+) phenotype. A purified population of Ly-5.2(+) alpha beta(-) cells obtained from th e marrow of thymectomized recipients was incubated in vitro for 48 h w ithout exogenous growth factors. After the incubation procedure a prop ortion of the marrow cells acquired alpha beta TCR surface receptors. The results show that alpha beta T cells can develop from hemopoietic stem cells in the absence of the thymus.