Transformation of owl monkey T cells in vitro with Herpesvirus saimiri.

Abstract

Owl monkey peripheral blood mononuclear cells were treated with phytohemagglutinin and expanded in interleukin 2 (IL-2)-containing medium. The cells were then exposed to Herpesvirus saimiri (HVS strain S295C)-infected owl monkey kidney monolayer cells. Four to 6 weeks later, the lymphocytes showed increased clumping and cell growth and the ability to grow in the absence of IL-2. Control lymphocyte cultures not exposed to HVS eventually died out at '=6-8 weeks, even in the presence of IL-2. Although infected lymphocytes grew 'continuously in the absence of IL-2, their growth was enhanced by addition of IL-2 to the cultures. Natural killer cell-like cytotoxicity and -interferon release were also enhanced by IL-2. All cultures were positive for HVS antigens, infectious centers, or DNA.' The reactivity of monoclonal antibodies to cell surface markers suggested that the resultant cell lines were comprised of activated T cells. The properties of the in vitro-transformed cells were similar to those of cells established from HVS-induced owl monkey tumors. Our results suggest that infection of T lymphocytes with HVS results in decreased dependence of T cells upon exogenous IL-2 for growth.Herpesvirus saimiri (HVS) is a horizontally spread T-cell tropic herpesvirus of squirrel monkeys. As such, it is a member of a large group of primate lymphotropic herpesviruses, which includes the B-cell tropic Epstein-Barr virus (EBV) of man, the EBV-like viruses of Old World monkeys and apes, and the T-cell tropic viruses of New World monkeys (1). HVS is not pathogenic for squirrel monkeys but is potently oncogenic for several other species of New World monkeys and rabbits, where it produces fatal T-cell lymphomas and leukemias (2-8). Although HVS readily produces T-cell (11,12).Previous attempts to transform lymphocytes by cocultivation with HVS producer lymphocytes or by exposure to cellfree HVS have, with the rare exception noted above, been unsuccessful (refs. 3 and 13; unpublished results). Recently, cell lines were established with the aid of IL-2 from owl monkeys bearing HVS-induced tumors (14, 15). These cell lines are not dependent on IL-2 for growth and survival as are normal T cells but respond to it strongly in terms of increased cell growth. Based on this observation and the failure of previous in vitro transformation attempts made without IL-2, it was reasonable to assume that HVS transformation in vitro might also be aided by IL-2. Therefore, a transformation protocol was established in which cells were first activated by phytohemagglutinin (PHA) to induce IL-2 receptors and then were expanded in IL-2-containing medium prior to exposure to virus. The cells were then exposed to HVS and further cultured in IL-2-containing medium prior to 'testing them for IL-2-independent growth, the criterion used for transformation. In this paper we report the establishment and characterization of a series of cell lines established in vitro by HVS transformation of owl monkey lymphocytes. A preliminary account of these result...

Nononcogenic deletion mutants of herpesvirus saimiri are defective for in vitro immortalization

“…All established cell lines were also T8' T4-B1-, suggesting that the T8+-cell population of common marmosets is the major target cell for in vitro immortalization by herpesvirus saimiri. These findings appear to be similar to those obtained with owl monkey cells converted to IL-2 independence by herpesvirus saimiri strain S295C, in which the cells were OKT11a+ (pan-T-cell marker), Leu-5+ (pan-T-cell marker), Leu-3a-(T4-cell marker), and B1- (14); reagents for measuring the T8-cell population were not available to the investigators in this previous study.…”

“…Another approach to achieving in vitro immortalization following infection with herpesvirus saimiri involved growing T cells in interleukin-2 (IL-2) before infection (5,14). After infection, immortalization was assayed by continued cell growth in the absence of exogenously added IL-2.…”

“…After infection, immortalization was assayed by continued cell growth in the absence of exogenously added IL-2. Successful immortalization using this assay has been reported for owl monkey PBL using strain S295-C (14) and for cotton-top tamarin PBL using strain 11 virus (5). However, this process is lengthy, with conversion to IL-2 independence occurring only over the course of several months.…”

“…On two separate occasions the infection of single-cell suspensions and explant cultures prepared from cotton-top tamarin thymus and spleen with strain 11 also did not yield any continuously growing cell lines. Lymphoid cells growing in the presence of IL-2 (Electro-Nucleonics, Inc., Fairfield, N.J.) were established from three different cotton-top tamarins under conditions similar to those described previously (5,14); infection with herpesvirus saimiri strain 11 for as long as 6 months failed to yield any IL-2-independent cell lines.…”

Expression of Interleukin 2 Receptors in T Cells Transformed by Strains of <i>Herpesvirus saimiri</i> Representing Three DNA Subgroups

“…Group A and group C strains can transform peripheral lymphocytes of common marmosets in vitro: group B strains cannot transform [14,16]. Interestingly, group B viruses can also immortalize owl monkey or common marmoset lymphocytes in vitro at low frequency, if the cells are cultured in interleukin 2 (IL-2) containing medium [16,17].…”