Irena Koprowska

Exfoliative cytology as applied to the quantitative evaluation of oncolysis induced by viruses.

The effect of neurotropic viruses upon transplantable mouse tumors was studied by Koprowski and Norton. These workers reported, in 1950, that each of these viruses destroyed or inhibited certain mouse tumors, multiplied without damage in others, and failed to multiply in s0me.l Evaluation of the degree of oncolysis induced by a given virus in a solid transplantable tumor presented certain difficulties for following reasons. The accessibility of cells to viral infection varied in different portions of the tumor because of the presence of central necrosis. Small fragments of neoplastic tissue removed for histological examination and/or transplantation were therefore not sufficiently representative to judge the effect of the virus upon the tumor in toto. Furthermore, the understanding of the mechanism of the viral action suffered, since daily biopsies of the same animal were not feasible. At this early stage of investigation of oncolysis induced by viruses, the virologist was in search of an in z i ~ o suspension of malignant cells similar to that observable in tissue culture techniques in witro. He found such an in viva suspension of malignant cells in ascites tumors of mouse. One of the oldest ascites tumors of mouse, namely, Ehrlich ascites tumor, has been studied by numerous investigators in the past. George and Eva Klein, Goldberg, and Kurnick described some biological aspects of the use of ascites tumors?, 3 , Ehrlich ascites tumor is characterized by a free proliferation of carcinoma in the peritoneal cavity of mouse and, in this respect, it is similar to human malignant neoplasms involving peritoneum. Malignant cells of this carcinoma have an increased value in the Dh-A content as compared to normal cells. Ehrlich ascites tumors maintained in different laboratories may vary in their chromosome numbers. The Ehrlich ascites tumor used in this study had a tetraploid modality of chromosome number. From the standpoint of an exfoliative cytologist, Ehrlich ascites tumor offers excellent opportunities to study material that consists primarily of discr ete and uniformly distributed malignant cells. These cells are distinctly different from histiocytes, polymorphonuclear leukocytes, and lymphocytes, which are also present in smears from perinoneal aspirates. In those circumstances, qualitative changes in cells, as well as variations in differential cell counts, may be evaluated easily and accurately in the course of studies of the effect of various agents upon this tumor. Preliminary morphologic studies of uncontaminated Ehrlich ascites tumors obtained in 1950 from the Carlsberg Foundation in Copenhagen, Denmark, were carried out a t Papanicolaou Cytology Laboratory a t Corncll University Medical College in New York, K. Y. Serial passages of tumors in Swiss Albino and Strong A mice were accomplished by aspirating several cubic centimeters of