{'fraction_non_alphanumeric': 0.02767175572519084, 'fraction_numerical': 0.0057251908396946565, 'mean_word_length': 4.73224043715847, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Letters to the Editor


 Sir: Two recent publications by Fidler, Brodey, and Bech-Nielsen (1, 2) (one of them published in the J. of Immunology) address themselves to the study of the in vitro interaction of tumor cells and lymphocytes from dogs with spontaneous neoplasms. There are two important points that we would like to make concerning these papers.
 Firstly, the method used to establish a tumor cell population does not, in fact, preclude contamination with large numbers of non-tumor cells. In our experience with over 100 canine tumors in culture, virtually all primary isolations consist of a mixed cell population of tumor cells, fibroblasts, and other cell types as determined by morphology and karyotyping (3). The ratio of these cells varies from tumor to tumor. We have been able to obtain pure populations of canine osteosarcoma cells after cloning procedures with confirmation by karyotypic analysis. The assumption made by Fidler et al. that the target cells they used are all (or even mostly) tumor cells is probably incorrect.