Age-dependent leukemia produced in thymectomized akr mice by antiserum to leukemic cells

Thymectomized AKR mice, which have a low incidence of leukemia, show a high incidence when treated with rabbit antiserum against leukemic cells. The leukemia-promoting effect of normal rabbit serum and antiserum against non-leukemic cells is less than that of anti-leukemic cell serum. No clear leukemia-producing effect of antiserum was observed in mice over 500 days old. Antisera given to non-thymectomized mice, which have a high incidence of leukemia over a characteristic age-range, did not affect age of leukemia development. Anti-serum against leukemic cells reacted with purified Gross leukemia virus. It is suggested that leukemic transformation represents a response to immunological attack on the virus or against viral-associated cellular antigens, and that an additional age-dependent factor is required for leukemogenesis.