Malignant transformation of human non-lymphoid cell line infected by HTLV-I

Human T-cell lymphotropic virus type I (HTLV-I) is an etiological agent of T-cell leukemia and HTLV-I-associated myelopathy/tropical spastic paraparesis. The virus is known to target and transform preferentially CD4+ cells. The aim of this work was to investigate a transforming activity of HTLV-I in non-lymphoid cell line permissive for its replication as well as to establish a convenient model for studying the antiretroviral substances. For this purpose monolayer human osteosarcoma HOS cells were infected with HTLV-I by co-cultivation with HTLV-I-producing rabbit lymphoid Ra-1 cells. Cytogenetic analysis of HTLV-I-infected HOS cell culture (RaHOS) confirmed the human karyotype identical to that of the initial HOS cells. Integration of HTLV-I provirus was detected by polymerase chain reaction (PCR) for HTLV-I gag, env, tax and LTR sequences. Expression of viral antigens and HTLV-I replication in RaHOS cells were confirmed by immunofluorescence assay, RT-PCR and syncytia inhibition assay. The features characteristic of malignant transformation of RaHOS cells developed in the following order: increasing proliferative activity (after 18 passages), colony-forming ability (after 30 passages), appearance of the focuses of multilayer cell growth (after 60 passages). All these features increased progressively throughout passage history of the cells. At the same time the initial HOS cells did not form colonies in soft agar and focuses of multilayer cell growth. Thus, RaHOS cells is the first characterized monolayer cell culture expressing HTLV-I in which HTLV-I transforming activity is observed. This cell line could be a suitable model for studying the changes in expression of different cell genes upon HTLV-I infection as well as the effects of various anti-retroviral compounds.