Differences in time of virus appearance in the blood and virus-specific immune responses in intravenous and intrarectal primary SIVmac251 infection of rhesus macaques; a pilot study.

BACKGROUND: HIV-I can be transmitted by intravenous inoculation of contaminated blood or blood product or sexually through mucosal surfaces. Here we performed a pilot study in the SIVmac251 macaque model to address whether the route of viral entry influences the kinetics of the appearance and the size of virus-specific immune in different tissue compartments. METHODS: For this purpose, of 2 genetically defined Mamu-A*01-positive macaques, 1 was exposed intravenously and the other intrarectally to the same SIVmac251 viral stock and virus-specific CD8+ T-cells were measured within the first 12 days of infection in the blood and at day 12 in several tissues following euthanasia. RESULTS: Virus-specific CD8+ T-cell responses to Gag, Env, and particularly Tat appeared earlier in the blood of the animal exposed by the mucosal route than in the animal exposed intravenously. The magnitude of these virus-specific responses was consistently higher in the systemic tissues and GALT of the macaque exposed by the intravenous route, suggesting a higher viral burden in the tissues as reflected by the faster appearance of virus in plasma. Differences in the ability of the virus-specific CD8+ T-cells to respond in vitro to specific peptide stimulation were also observed and the greatest proliferative ability was found in the GALT of the animal infected by the intrarectal route. CONCLUSIONS: These data may suggest that the natural mucosal barrier may delay viral spreading. The consequences of this observation, if confirmed in studies with a larger number of animals, may have implications in vaccine development.

Differential response to genotoxic stress in immortalized or transformed human T-lymphotropic virus type I-infected T-cells.

Several alterations in the mechanism of cell cycle control have been observed in human T-lymphotropic virus type I (HTLV-I)-infected cells. Here, it is reported that HTLV-I-infected cells both in their immortalized and transformed phase do not undergo apoptosis following ionizing radiation (IR) treatment. However, when IL-2 withdrawal is combined with genotoxic stress, HTLV-I-infected T-cells in their immortalized phase (IL-2-dependent) undergo apoptosis where as their transformed counterparts (IL-2-independent) do not. These results suggest that, during the transformation process, the HTLV-I-infected T-cells become less sensitive to cell death signals through the acquisition of constitutive activation of the IL-2 receptor pathway. The expression of bcl-2 and bcl-XL proteins, which are known to increase cell survival mediated by IL-2, as well as of p21waf1 and p53, was not substantially different in immortalized and transformed cells following IR. All together, these findings suggest that activation of alternative anti-apoptotic pathways, regulated by IL-2, might be responsible for the differential cell death response observed in immortalized versus transformed HTLV-I-infected T-cells.

Limiting amounts of p27Kip1 correlates with constitutive activation of cyclin E-CDK2 complex in HTLV-I-transformed T-cells.

Human T-cells immortalized (interleukin-2 [IL-2] dependent) by the human T-cell lymphotropic/leukemia virus type I (HTLV-I), in time, become transformed (IL-2 independent). To understand the biochemical basis of this transition, we have used the sibling HTLV-I-infected T-cell lines, N1186 (IL-2 dependent) and N1186-94 (IL-2 independent), as models to assess the responses to antiproliferative signals. In N1186 cells arrested in G1 after serum/interleukin-2 (IL-2) deprivation, downregulation of the cyclin E-CDK2 kinase activity correlated with decreased phosphorylation of CDK2 and accumulation of p27Kip1 bound to the cyclin E-CDK2 complex, as seen in normal activated PBMCs (peripheral blood mononuclear cells). In contrast, N1186-94 cells failed to arrest in G1 upon serum starvation, displayed constitutive cyclin E-associated kinase activity, and, although CDK2 was partially dephosphorylated, the amount of p27Kip1 bound to the complex did not increase. This observation, extended to two other IL-2-dependent as well as to three IL-2-independent HTLV-I-infected T-cell lines, suggests that the lack of cyclin E-CDK2 kinase downregulation found in the late phase of HTLV-I transformation may correlate with insufficient amounts of p27Kip1 associated with the cyclin E-CDK2 complex. Reconstitution experiments demonstrated that the addition of p27Kip1 to lysates from N1186-94 starved cells resulted in the downregulation of cyclin E-associated kinase activity supporting the notion that the unresponsiveness of the cyclin E-CDK2 complex to growth inhibitory signals may be due to inadequate amounts of p27Kip1 assembled with the complex in HTLV-I-transformed T-cells. In fact, the amount of p27Kip1 protein was lower in most HTLV-I-transformed (IL-2-independent) than in the immortalized (IL-2-dependent) HTLV-I-infected T-cells. Furthermore, specific inhibitors of the phosphatidylinositol 3-kinase (P13K) induced an increase of p27Kip1 protein levels, which correlated with G1 arrest, in both IL-2-dependent and IL-2-independent HTLV-I-infected T-cells. Altogether, these results suggest that maintaining a low level of expression of p27Kip1 is a key event in HTLV-I transformation.