Thymic lymphosarcomas obtained by X-rays in association with a weakly leukemogenic virus: cellular studies

Area of Science:

• Oncology
• Virology
• Radiation Biology

Background:

• Subleukemogenic radiation doses and weakly oncogenic retroviruses individually induce thymic lymphosarcomas (TL) in C57BL/6 mice.
• The combined effect of radiation and viral exposure on TL incidence requires further investigation.

Purpose of the Study:

• To investigate the synergistic effects of subleukemogenic radiation and B-tropic retrovirus on thymic lymphosarcoma (TL) development in mice.
• To explore the role of retroviral derepression in radiation-induced lymphomagenesis.

Main Methods:

• Mice were subjected to different protocols involving subleukemogenic radiation (1.75 Gy x 2) and B-tropic retrovirus (1223) injection (VX and XV protocols).
• TL incidence was monitored, and viral presence in thymus and bone marrow (BM) was assessed during the preleukemic period.
• In vitro cell lines from TL were established, and BM restoration experiments were conducted.

Main Results:

• The VX protocol (virus preceding irradiation) resulted in a significantly higher TL incidence (31%) than expected from cumulative effects.
• The XV protocol (virus after irradiation) showed TL incidence (19%) not significantly different from cumulative effects.
• Viral presence correlated with TL incidence in thymus, BM, and established cell lines, suggesting derepressed B-tropic viruses contribute to radio-induced TL.

Conclusions:

• The combination of subleukemogenic radiation and B-tropic retrovirus exhibits a synergistic effect on TL development, particularly when viral exposure precedes irradiation.
• Derepression of B-tropic viruses by radiation appears to play a role in the mechanism of radio-induced TL.
• Bone marrow restoration inhibits radiation or combined radiation-virus induced leukemogenesis, but not TL induced by highly oncogenic viruses, indicating distinct mechanisms.