Functional clonal deletion of cytotoxic T-lymphocyte precursors in chimeric thymus produced in vitro from embryonic Anlagen.

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Abstract
Chimeric thymus, formed by fusing the prelymphoid 3rd pharyngeal pouches of fetal mice with fetal liver, have been allowed to develop entirely in vitro. Syngeneic and allogeneic chimeras were prepared and both types of thymus were shown to contain substantial numbers of functional cytotoxic T lymphocyte precursors reactive against 3rd-party alloantigens. Alloreactivity specific for H-2 antigens present on the 3rd pharyngeal pouch or the fetal liver was minimal. In 3 different allogeneic chimeric thymuses, the frequencies of cytotoxic T lymphocyte precursors reactive to H-2 antigens present on the 3rd pharyngeal pouches were reduced to 1, 4 and 0 of control values; in the 1 allogeneic chimera tested for alloreactivity to H-2 antigens present on the fetal liver, the cytotoxic T lymphocyte precursor frequency was reduced to < 1% of control values. The phenotype of the H-2 tolerance is one of functional clonal deletion of the cytotoxic T lymphocyte precursor.