An immunopharmacological approach for prevention of retrovirus-associated disease in human pathology

HSP70 production and inhibition of cell proliferation in Molt-4 T-cells after cell-to-cell transmission of HTLV-I: effect of PGA1

Infection with HTLV-I is associated with leukemic transformation of mature CD4+ T lymphocytes. PGA1, a powerful inhibitor of tumour cell proliferation, can prevent the clonal expansion of HTLV-I-infected cells following acute infection of cord blood-derived mononuclear cells. Since the antiproliferative effect of PGA1 on HTLV-I transformed, chronically infected MT-2 cell line was associated with induction of HSP70, we have investigated the effect of PGA1 on cell cycle progression and HSP70 production in a leukemic T-cell line (Molt-4) shortly after exposure to HTLV-I in a cell-to-cell transmission model. Rate of cell proliferation and HSP70 expression were studied within one duplication cycle of Molt-4 cells after exposure to HTLV-I. Growth of both control and virus-exposed cultures was inhibited by treatment with PGA1 (4 micrograms/ml) and cell cycling was arrested preferentially at the G1/S interphase. Synthesis of HSP70 was induced within 3 h by PGA1 in control and virus-exposed Molt-4 cells and became undetectable from overnight onward, though the protein accumulated in the cells. The arrest of growth was observed from overnight up to 48 h so that treated cells almost missed one cycle. Interestingly, HSP70 transcript and protein persisted at remarkably high levels in Molt-4 cells exposed to HTLV-I in the absence of PGA1, showing that HSP70 expression can be directly activated during primary infection with this human retrovirus. Moreover, in these cocultures, treatment with PGA1 or heat shock was not able to increase further the elevated level of HSP70 found in untreated cocultures, suggesting that during the early period of the virus-transmission phase, HTLV-I could interfere with HSP70 induction by other inducers.

Combined treatments with interferon (alpha,beta) plus PGA1 to control early infection with HTLV-I in primary cord blood-derived mononuclear cells

Interferon (IFN) alpha and beta can activate an antiviral and immunomodulating response in primary cord blood-derived mononuclear cells (CBMC) exposed to infection with Human T-cell Leukemia Virus type I (HTLV-I), resulting in partial inhibition of early infection in vitro. On the other hand, PGA1, a PGE1-derived cyclopentenone prostaglandin, can inhibit in vitro the proliferation of virus-infected CBMC, preventing the emergence of the potentially transformed clone. In order to achieve a complete control of HTLV-I infection in this experimental model, we evaluated whether the antiviral activity of IFNs and the antiproliferative activity of PGA1 could be preserved in a combination therapy scheme. Recipient CBMC were treated with IFN alpha or beta (1000 IU/ml) at the onset of the co-culture with lethally irradiated virus-donor MT-2 cells, followed by multiple treatments with PGA1 (4 micrograms/ml every 4 days, starting on day 0) for 6 weeks post infection (p.i.). In PGA1-treated co-cultures the percentage of virus-positive CBMC was constantly doubled during culture time as well as the amount of viral transcripts and p19 virus core protein production were increased. The antiviral effects of IFNs, resulting in about a 50% reduction of the percentage of virus-positive CBMC and consequently in a partial inhibition of virus expression (HTLV-I transcription and p19 production) until 4 weeks p.i., were suppressed by multiple PGA1 treatments. However, the antiproliferative effect of PGA1 was enforced in IFN-treated co-cultures, leading to earlier control of proliferation of virus-infected cells. Interestingly, infection of CBMC with HTLV-I was associated with persistent expression of 70 kDa heat shock protein (HSP70), for at least 4 weeks p.i. IFNs and PGA1 showed antagonistic effects on HSP70 production in infected CBMC. In fact, production of HSP70 was suppressed (or prevented) in IFN-treated co-cultures, tested 2 and 4 weeks p.i. The fact that the expression of HSP70 is apparently suppressed (or prevented) by IFN treatment is surprising, since expression of this protein family has been associated with antiviral immunity. PGA1 could totally reverse the IFN-mediated suppression of HSP70 expression in these co-cultures. It is presently unclear whether HSP70 expression is directly involved in the control of proliferation exerted by PGA1 against virus-infected CBMC or is an epiphenomenon associated with inhibition of cell growth.

Antiviral activity of individual versus combined treatments with interferon alpha, beta and gamma on early infection with HTLV-I in vitro

We have shown previously that infection of mononuclear cells derived from neonatal cord (CBMC) or adult peripheral (PBMC) blood with HTLV-1 can be controlled in vitro by treatment with interferon (IFN) alpha, beta or gamma. The activity of IFNs was mainly related to the induction of an active antiviral competence in host's immune effector cells. The antiviral activity of IFN-boosted CBMC could be ascribed both to a positive regulation of cell-mediated immunity and to inhibition of viral infection. Data described herein provide further information on the mechanisms of the antiviral activity of IFNs and compare the activity of each type of IFN with the association of alpha + beta, alpha + gamma and beta + gamma IFNs, at a concentration of 100 or 1000 IU/ml. When added at the onset of the co-culture of CBMC with lethally irradiated, virus-donor MT-2 cells, IFNs could protect host CBMC by inhibiting HTLV-1 infection in terms of reduced proviral integration and a lower percentage of virus-positive cells, until 4 weeks of culture. Infection of CBMC was inhibited at a comparable extent by either individual or combined IFN treatments. However, a clearcut inhibition of HTLV-I transcription was found only when alpha 100 + beta 1000 IU/ml and especially alpha 1000 + gamma 100 IU/ml combined treatments were tested. When the chronically infected, virus-producing MT-2 cells were treated with IFNs, a remarkable inhibition of HTLV-I transcription was found only after multiple treatments. However, MT-2 cells became resistant to the antiviral activity of IFN gamma, but not to that of IFN alpha or beta. These data provide further information on the control of HTLV-I replication mediated by IFNs at different steps of the viral life cycle, being therefore relevant to the clinical use of combined IFNs in the treatment of acute infection. Moreover, IFNs could be used to prevent the establishment of a persistent infection, which is a prerequisite for developing adult T-cell leukemia (ATL) and/or virus-associated myelopathy.