Each year, 55 000 organ transplants are performed worldwide. Cumulatively, the number of living organ recipients is now estimated to be over 300 000. Most of these transplant recipients will remain on immunosuppressive drugs for the remainder of their lives to prevent rejection episodes. Controlled doses of these drugs are required to prevent over-medication, which may leave the patient susceptible to opportunistic infection and drug toxicity effects, or under-dosing, which may lead to shortened graft survival because of rejection episodes. This paper describes the result of a multicenter study conducted at the Universities of Pittsburgh, Alabama and Maryland to evaluate an in vitro assay (CylexTM Immune Cell Function Assay) for the measurement of global immune response in transplant patients receiving immunosuppressive therapy. The assay uses a whole blood sample to maintain the presence of the drug during incubation. Following overnight incubation of blood with phytohemagglutinin (PHA), CD4 cells are selected using paramagnetic particles coated with a monoclonal antibody to the CD4 epitope. The CD4-positive cells are targeted as major immunosuppressive drugs are designed to specifically inhibit T-cell activation which has been implicated in rejection. The data generated at these three sites were submitted in support of an Food and Drug Association (FDA) application for the use of this assay in the detection of cell-mediated immunity in an immunosuppressed population. The assay was cleared by the FDA on April 2, 2002. This cross-sectional study was designed to establish ranges for reactivity of this bioassay in the assessment of functional immunity for an individual solid organ recipient at any point in time.

. By FACS analysis we demonstrate that rapamycin (RAPA), a drug that disrupts IL-2 receptor signaling, reduces CCR5 surface expression on T cells at concentrations as low as 1 nM. In addition, lower concentrations of RAPA (0.01 nM) were sufficient to reduce CCR5 surface expression on maturing monocytes. PCR analysis on peripheral blood mononuclear cells (PBMCs) showed that RAPA interfered with CCR5 expression at the transcriptional level. Reduced expression of CCR5 on PBMCs cultured in the presence of RAPA was associated with increased extracellular levels of macrophage inflammatory protein (MIP)-1␣ and MIP-1␤. In infectivity assays, RAPA suppressed the replication of R5 strains of HIV-1 both in PBMC and macrophage cultures. In total PBMC cultures, RAPA-mediated inhibition of CCR5-using strains of HIV-1 occurred at 0.01 nM, a concentration of drug that is Ϸ10 3 times lower than therapeutic through levels of drug in renal transplant recipients. In addition, RAPA enhanced the antiviral activity of the CCR5 antagonist TAK-779. These results suggest that low concentrations of RAPA may have a role in both the treatment and prevention of HIV-1 infection.

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HIV necessitates host factors for successful completion of its life cycle. Mammalian target of rapamycin (mTOR) is a conserved serine/threonine kinase that forms two complexes, mTORC1 and mTORC2. Rapamycin is an allosteric inhibitor of mTOR that selectively inhibits mTORC1. Rapamycin interferes with viral entry of CCR5 (R5)-tropic HIV and with basal transcription of the HIV LTR, potently inhibiting replication of R5 HIV but not CXCR4 (X4)-tropic HIV in primary cells. The recently developed ATP-competitive mTOR kinase inhibitors (TOR-KIs) inhibit both mTORC1 and mTORC2. Using INK128 as a prototype TOR-KI, we demonstrate potent inhibition of both R5 and X4 HIV in primary lymphocytes (EC50 < 50 nM), in the absence of toxicity. INK128 inhibited R5 HIV entry by reducing CCR5 levels. INK128 also inhibited both basal and induced transcription of HIV genes, consistent with inhibition of mTORC2, whose activity is critical for phosphorylation of PKC isoforms and, in turn, induction of NF-κB. INK128 enhanced the antiviral potency of the CCR5 antagonist maraviroc, and had favorable antiviral interactions with HIV inhibitors of reverse transcriptase, integrase and protease. In humanized mice, INK128 decreased plasma HIV RNA by >2 log10 units and partially restored CD4/CD8 cell ratios. Targeting of cellular mTOR with INK128 (and perhaps others TOR-KIs) provides a potential strategy to inhibit HIV, especially in patients with drug resistant HIV strains.

Vicriviroc (VCV) is a chemokine (C-C motif) receptor 5 (CCR5)antagonist with potent anti-HIV activity that currently is being evaluated in phase III clinical trials. In the present study, donor CCR5 density (CCR5 receptors/CD4 lymphocytes) inversely correlated with VCV antiviral activity (Spearman's correlation test; r ‫؍‬ 0.746, P ‫؍‬ 0.0034). Low doses of the transplant drug rapamycin (RAPA) reduced CCR5 density and enhanced VCV antiviral activity. In drug interaction studies, the RAPA/VCV combination had considerable antiviral synergy (combination indexes of 0.1-0.04) in both multicycle and single-cycle infection of lymphocytes. The synergy between RAPA and VCV translated into dose reduction indexes of 8-to 41-fold reductions for RAPA and 19-to 658-fold reductions for VCV. RAPA enhanced VCV antiviral activity against both B and non-B clade isolates, potently suppressing clade G viruses with reported reduced sensitivities to VCV and to the licensed CCR5 antagonist maraviroc. Importantly, RAPA reduction of CCR5 density in lymphocytes sensitized VCV-resistant strains to VCV, inhibiting virus production by ϳ 90%. We further demonstrated the role of CCR5 density on VCV activity against resistant virus in donor lymphocytes and in cell lines expressing varying CCR5 densities. Together, these results suggest that low doses of RAPA may increase the durability of VCV-containing regimens in patients by enhancing VCV viral suppression, by allowing the use of lower doses of VCV with reduced potential for toxicity, and by controlling emerging VCV-resistant variants.chemokine receptor 5 antagonists ͉ coreceptor density ͉ HIV resistance ͉ vicriviroc resistance ͉ maraviroc H ighly active antiretroviral therapy (HAART) has improved treatment of HIV-1 infected individuals considerably (1). However, the success of current therapies is limited by the emergence of drug-resistant strains, the need for sustained adherence to complex regimens, and the potential for drug toxicity (2, 3). The two new antiretroviral classes of integrase and entry inhibitors may help overcome some of the current limitations of HAART (4, 5). Entry inhibitors are especially attractive because they target HIV at the earliest step of the viral cycle and are effective against strains resistant to inhibitors of protease and reverse transcriptase. Entry inhibitors interfere with HIV binding to CD4 receptor (attachment inhibitors) or chemokine (C-C motif) receptor 5 (CCR5)/chemokine (C-X-C-motif) receptor 4 (CXCR4) coreceptors (coreceptor antagonists) or by preventing fusion between cellular and viral membranes (fusion inhibitors) (5). Currently, the fusion inhibitor T-20 (enfuvirtide) and the CCR5 antagonist maraviroc (Selzentry) are the only licensed entry inhibitors (6, 7). The CCR5 antagonist vicriviroc (VCV) presently is in phase III clinical trials (8). Coreceptor CCR5 antagonists inhibit CCR5-tropic HIV-1 (referred to as ''R5 HIV-1'') strains, which are responsible for most transmissions and generally are present throughout the course of infection. In nor...

Non-toxic concentrations of IM inhibit HIV-1 by blocking viral gene expression mediated by the cellular factor P-TEFb. The drug is effective against wild-type and drug-resistant strains of HIV-1. IM may help control replication of HIV-1 in patients by disrupting a step of the HIV-1 cycle that is not being targeted in current antiretroviral treatments.

Despite some limitations, an 8-week off and on intermittent treatment regimen appeared clinically safe over 96 weeks while sparing half of the drug exposure.

Human immunodeficiency virus (HIV) type 1 infection requires functional interactions of the viral surface (gp120) glycoprotein with cell surface CD4 and a chemokine coreceptor (usually CCR5 or CXCR4) and of the viral transmembrane (gp41) glycoprotein with the target cell membrane. Extensive genetic variability, generally in gp120 and the gp41 ectodomain, can result in altered coreceptor use, fusion kinetics, and neutralization sensitivity. Here we describe an R5 HIV variant that, in contrast to its parental virus, infects T-cell lines expressing low levels of cell surface CCR5. This correlated with an ability to infect cells in the absence of CD4, increased sensitivity to a neutralizing antibody recognizing the coreceptor binding site of gp120, and increased resistance to the fusion inhibitor T-20. Surprisingly, these properties were determined by alterations in gp41, including the cytoplasmic tail, a region not previously shown to influence coreceptor use. These data indicate that HIV infection of cells with limiting levels of cell surface CCR5 can be facilitated by gp41 sequences that are not exposed on the envelope ectodomain yet induce allosteric changes in gp120 that facilitate exposure of the CCR5 binding site.Human immunodeficiency virus type 1 (HIV-1) enters cells by membrane fusion mediated by its envelope (Env) glycoproteins (51). The Env proteins are synthesized as a 160-kDa precursor that is cleaved by a host protease to yield the surface gp120 (SU) and the transmembrane gp41 (TM) glycoprotein subunits. The functional Env structure is a trimer, with the gp120 subunits anchored on the virion surface by noncovalent interactions with the gp41 trimer. The gp120 binds first to CD4 and subsequently to a chemokine receptor/coreceptor (generally CCR5 or CXCR4). The gp41 then interacts with the target cell membrane through its N-terminal fusion domain, promoting lipid mixing and viral entry. An unusual feature of gp41 is its long cytoplasmic domain (CD) or tail of approximately 150 amino acids (aa), in contrast to the TM proteins of other retroviruses, such as avian and murine oncoretroviruses, which have a shorter CD (typically 20 to 30 aa).The HIV gp41 CD region includes a number of domains, the exact functions of which are not well understood. The CD includes one or more palmitoylated cysteines, which may mediate localization of the Env to lipid rafts (4, 55). A tyrosinebased (Yxx⌽) motif in the membrane-proximal region of the CD mediates binding to components of clathrin-associated adaptor complexes, which are involved in trafficking and endocytosis (3,5,7,48,56), and also targets Env to the basolateral membrane in polarized cells, resulting in basolateral budding (38, 49). The CD forms three highly conserved amphipathic ␣-helices, termed lentiviral lytic peptides (LLPs), that have been implicated in interactions that decrease the stability of lipid bilayers, causing pore formation and mediating T-cell death (11,12,22,33,42,43,62). The CD also contains two regions that closely resemble those found in calm...