Latent Period in Leukaemia Induction by the Radiation Leukaemia Virus

IN C57BL/6 mice, infection with the radiation leukaemia virus is age dependent and leukaemogenesis is highly effective only when the virus is inoculated shortly after birth^1,2, but several months elapse before the disease is actually manifested. Why is there such a long latent period before the leukaemic cells proliferate into a palpable tumour, especially as in the newborn mouse the target organ for the development of the disease, the thymus, is still in a proliferative stage, with abundance of immature lymphoid cells and an incompetent immunological system?