The Use of Interleukin-2 in Human Immunodeficiency Virus Infection

Insights into the HIV Latency and the Role of Cytokines

Human immunodeficiency virus-1 (HIV-1) has the ability to infect latently at the level of individual CD4+ cells. Latent HIV-1 proviruses are transcriptionally silent and immunologically inert, but are still capable of reactivating productive lytic infection following cellular activation. These latent viruses are the main obstacle in the eradication of HIV-1, because current HIV-1 treatment regimens are ineffective against them. Normal immunological response against an antigen activates CD4+ naïve T cells. The activated CD4+ naïve T cells undergo cell cycle, resulting in further transformation and profound proliferation to form effector CD4+ T-cells. Notably, in HIV-1 infected individuals, some of the effector CD4+ T cells get infected with HIV-1. Upon fulfillment of their effector functions, almost all activated CD4+ T cells are committed to apoptosis or programmed cell death, but a miniscule fraction revert to quiescence and become resting memory CD4+ T cells to mediate a rapid immunological response against the same antigen in the future. However, due to the quiescent nature of the resting memory T cells, the integrated HIV-1 becomes transcriptionally silent and acquires a latent phenotype. Following re-exposure to the same antigen, memory cells and integrated HIV-1 are stimulated. The reactivated latent HIV provirus subsequently proceeds through its life cycle and eventually leads to the production of new viral progeny. Recently, many strategies against HIV-1 latency have been developed and some of them have even matured to the clinical level, but none can yet effectively eliminate the latent HIV reservoir, which remains a barrier to HIV-1 cure. Therefore, alternative strategies to eradicate latent HIV need to be considered. This review provides vital knowledge on HIV latency and on strategies to supplement highly active anti-retroviral therapy (HAART) with cytokine-mediated therapeutics for dislodging the latent HIV reservoirs in order to open up new avenues for curing HIV.

STAT5 Is Essential for Akt/p70S6 Kinase Activity during IL-2-Induced Lymphocyte Proliferation

IL-2R activates two distinct signaling pathways mediated by the adaptor protein Shc and the transcription factor STAT5. Prior mutagenesis studies of the IL-2R have indicated that the Shc and STAT5 pathways are redundant in the ability to induce lymphocyte proliferation. Yet paradoxically, T cells from STAT5-deficient mice fail to proliferate in response to IL-2, suggesting that the Shc pathway is unable to promote mitogenesis in the genetic absence of STAT5. Here we show in the murine lymphocyte cell line Ba/F3 that low levels of STAT5 activity are essential for Shc signaling. In the absence of STAT5 activity, Shc was unable to sustain activation of the Akt/p70S6 kinase pathway or promote lymphocyte proliferation and viability. Restoring STAT5 activity via a heterologous receptor rescued Shc-induced Akt/p70S6 kinase activity and cell proliferation with kinetics consistent with a transcriptional mechanism. Thus, STAT5 appears to regulate the expression of one or more unidentified components of the Akt pathway. Our results not only explain the severe proliferative defect in STAT5-deficient T cells but also provide mechanistic insight into the oncogenic properties of STAT5 in various leukemias and lymphomas.

Cellular immunotherapy for cytomegalovirus and HIV-1 infection

Current antiviral drugs do not fully reconstitute the specific antiviral immune control in chronically human immunodeficiency virus (HIV)-1-infected patients or in cytomegalovirus (CMV)-infected patients after hematopoietic stem cell transplantation. Therefore, immunotherapy in which the patient's immune system is manipulated to enhance antiviral immune responses has become a promising area of viral immunology research. In this review, an overview is provided on the cellular immunotherapy strategies that have been developed for HIV infection and CMV reactivation in immunocompromised patients. As an introduction, the mechanisms behind the cellular immune system and their importance for the development of a workable immunotherapy approach are discussed. Next, the focus is shifted to the immunopathogenesis of CMV and HIV-1 infections to correlate these findings with the concepts and ideas behind the viral-specific immunotherapies discussed. Current and future perspectives of active and passive cellular immunotherapy for the treatment of CMV and HIV-1 infections are reviewed. Finally, pitfalls and key issues with regard to the development of immunotherapy protocols that can be applied in a clinical setting are addressed.