Rat primary T cells expressing HTLV-I tax gene transduced by a retroviral vector: In vitro and in vivo characterization

We prepared a recombinant retroviral vector expressing the human T-lymphotropic virus type-I tax gene. Infection of WKA/H rat splenocytes yielded T-cell lines which proliferated continuously in media supplemented with exogenous interleukin-2 (IL-2) after the control cells ceased to grow. The phenotype of these cells closely resembled that of typical adult T-cell leukemia cells and tax-immortalized human T cells; i.e., positive for CD3, CD4 and IL-2 receptor α-chain. Chromosomal analysis revealed that about 10% of the tax-transduced T cells had several chromosomal abnormalities. We also performed in vivo characterization of tax-transduced splenocytes by injecting them into newborn syngeneic rats soon after in vitro infection. Maintenance of the injected tax-transduced cell population and in vivo expression of the tax gene was confirmed in the splenocytes of the injected rats by polymerase chain reaction. However, development of obvious disease was not observed in these rats for up to 18 months after inoculation. These results indicate that tax is capable of immortalizing rat mature CD4⁺ T cells in vitro but may be insufficient for full transformation of these cells in vivo. Our in vivo system using retrovirally tax-transduced rat T cells could facilitate investigation of the additional genetic events that cooperatively transform T cells transduced with tax gene.