RADIATION CAN INHIBIT TUMOR-GROWTH INDIRECTLY WHILE DEPLETING CIRCULATING LEUKOCYTES

The growth of certain UV-radiation-induced tumors is suppressed by T l ymphocytes, but it has been proposed that non-T lymphocytes stimulate the growth of several of these tumors. In this study, the indirect eff ects of X irradiation on the growth of one such tumor in T-cell-defici ent nude mice was tested. Even when the site of tumor cell injection w as shielded, whole-body irradiation with 6 Gy before tumor challenge i nhibited subsequent tumor growth significantly. The interval during wh ich this indirect inhibition was observed correlated with the depletio n of circulating leukocytes, which did not return to normal levels unt il 12-21 days after irradiation. These data are consistent with earlie r results using an antibody to deplete Gr-1(+) leukocytes and indicate that radiation can inhibit the growth of certain tumors indirectly wi thout direct effects on the tumor cells or the tumor bed. (C) 1996 by Radiation Research Society