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Acellular Passage of ³²P-induced Leukemia: An Electron Microscopic Study

Sección Leucemia Experimental, Instituto de Investigaciones Hematológicas, Academia Nacional de Medicina^,3, Melo 3081, Buenos Aires, Argentina

Cell-free extracts of ³²P-induced leukemias were administered to adult and newborn BALB mice; 6 filtrates gave an overall incidence of leukemias of 53 and 41%, respectively, with a latency of approximately 18 months. Cell-free passages, carried out using supernatant centrifuged at 40,000 x g, also gave an increase in the percentages of leukemias with a latency markedly shortened in each successive passage, having fallen to an average of 56 days in the adults and 42 days in the newborn.

Electron microscopic studies revealed the presence of viral particles, type A and C, in the spleen, lymph nodes, and thymus of leukemic mice; their respective concentrations seemed to be well correlated with the latent period: the shorter the latency, the greater the number of C particles and vice versa, the longer the latency, the greater the number of A particles. Both types of virus particles appeared to have a rather well-defined angular form; the possible relationship between the 2 is discussed.

The results obtained with cell-free extracts of ³²P-induced leukemias seem to indicate the presence of a viral agent capable of inducing the disease.

¹ Member of Carrera del Investigador. Consejo Nacional de Investigaciones Cientificas y Técnicas.

² From Instituto de Investigaciones Médicas, Rosario, Santa Fe, Argentina.

³ Partly supported by FUNDALEU (Fundación para combatir la leucemia).

Received 1/ 8/64. Accepted 7/19/66.