90 Background: High grade non-Hodgkin's lymphomas (NHL) are associated with individuals infected with HIV. These lymphomas are predominately B-cell origin, although T-cell lymphomas have been described and are increasing in frequency. A subset of these lymphomas have clonal forms of HIV provirus DNA immediately upstream of the c-fes protooncogene that include a T-cell lymphoma, three polyclonal mixed immunophenotype lymphomas, an AILD, and a large cell lymphoma ascites tumor. c-fes expression, which is normally restricted to the granulocytic and monocytic lineages in adults, is integrally involved in cytokine signal transduction pathways. The current study further characterizes the role of HIV in this set of lymphomas. Methods: Fluorescence activated cell sorted tumor associated macrophages were characterized by immunohistochemistry, inverse polymerase chain reaction (IPCR), and western blot analysis. A HIV 3′ LTR was linked 3′ to a set of sequences of the genomic region upstream of the c-fes transcription start site and linked 5′ to a luciferase reporter gene. These constructs were transfected into the K562 human myeloid progenitor cell line, the Jurkat human T-cell leukemia cell line, and primary cultured human macrophages, alone and with a tat expression. Cotransfection studies with a c-fes expression vector were also done in the K562 and Jurkat cell lines. Results: Tumor associated CD14 macrophage populations isolated from the angioimmunoblastic lymphadenopathy (AILD) and the ascites lymphoma cases were positive for HIV p24 and c-fes expression, and found to have clonal HIV provirus integrated in the fur gene exon 16, which is located immediately upstream of c-fes. The c-fes gene product, p93-c-fes was found in a phosphorylated, activated state in the macrophages isolated from the AILD case. The HIV promoter insertion model demonstrated the potential for IIIV 3′LTR mediated cis-activated c-fes expression in K562 and Jurkat cell lines, and in primary cultured human macrophages. The cotransfection of a c-fes expression vector enhanced 3′ LTR cis-activation in both the K562 and Jurkat cell lines. Conclusions: This data implicates HIV cis-activation of c-fes regulation in the induction of cellular transformations in a subset of AIDS-associated lymphomas. We propose a multistep lymphomagenesis model wherein HIV integration upstream of c-fes in a macrophage cis-activates c-fes expression that induces the clonal expansion the cytokine elaborating macrophage, promoting secondary neoplastic lymphoproliferations.