Between 10 and 20% of the peripheral gammadelta T cells express cytoplasmic TCR-beta proteins, but whether such TCR-beta chains can partake in alphabeta T-cell development has never been systematically investigated. Therefore, we reconstituted the T-cell compartment of CD3epsilon-deficient mice with Pax5-TCR-beta deficient proB cells expressing, via a retroviral vector, TCR-beta chains from either peripheral gammadelta or alphabeta T cells. Recipient thymi reconstituted with proB cells containing empty vector were small (<15x10(6) cells), contained few gammadelta T but no alphabeta T cells. In contrast, thymi from mice receiving proB cells containing gammadelta or alphabeta T-cell-derived TCR-beta chains contained 80-130x10(6) cells, and showed a normal CD4, CD8 and alphabeta TCR expression pattern. However, regardless of the source of TCR-beta chain, reconstituted mice rapidly showed signs of autoimmunity dying 5-15 wk following reconstitution. Autoimmune disease induction could be prevented by co-transfer of Treg cells thereby allowing the functionality of the generated T cells to be assessed. Results obtained show that TCR-beta chains from gammadelta T cells can efficiently take part in alphabeta T-cell development. The implications of these findings for gammadelta T-cell development will be discussed.