Hydroxyurea exerts a cytostatic but not immunosuppressive effect on T lymphocytes

Proinflammatory state promotes red blood cell alloimmunization in pediatric patients with sickle cell disease

We examined risk factors for red blood cell (RBC) alloimmunization in pediatric patients with sickle cell disease, focusing on the recipients' inflammatory state at the time of transfusion and anti-inflammatory role of hydroxyurea (HU). Among 471 participants, 55 (11.70%) participants were alloimmunized and formed 59 alloantibodies and 17 autoantibodies with an alloimmunization rate of 0.36 alloantibodies per 100 units. Analysis of 27 participants in whom alloantibodies were formed with specificities showed 23.8% (30/126) of units transfused during a proinflammatory event resulting in alloantibody formation compared with 2.8% (27/952) of units transfused at steady state. Therefore, transfusion during proinflammatory events increased the risk for alloimmunization (odds ratio [OR], 4.22; 95% confidence interval [CI], 1.64-10.85; P = .003). Further analysis of all the 471 participants showed that alloimmunization of patients who received episodic transfusion, mostly during proinflammatory events, was not reduced with HU therapy (OR, 6.52; 95% CI, 0.85-49.77; P = .071), HU therapy duration (OR, 1.13; 95% CI, 0.997-1.28; P = .056), or HU dose (OR, 1.06; 95% CI, 0.96-1.16; P = .242). The analysis also identified high transfusion burden (OR, 1.02; 95% CI, 1.003-1.04; P = .020) and hemoglobin S (HbSS) and HbSβ0-thalassemia genotypes (OR, 11.22, 95% CI, 1.51-83.38; P = .018) as additional risk factors for alloimmunization. In conclusion, the inflammatory state of transfusion recipients affects the risk of RBC alloimmunization, which is not modified by HU therapy. Judicious use of transfusion during proinflammatory events is critical for preventing alloimmunization.

Treating HIV/AIDS by reducing immune system activation: the paradox of immune deficiency and immune hyperactivation

PURPOSE OF REVIEW

To collect published evidence in support of a novel immune therapeutic approach to reduce the excess of immune activation that ultimately turns into immune deficiency in HIV/AIDS.

RECENT FINDINGS

A large body of evidence has been collected in support of the pathogenetic interpretation that prolonged immune overactivation induced by HIV during the course of chronic infection exhausts the immune system and leads to AIDS. Some groups are exploring the possibility of therapeutic interventions to limit the immune system overload. Cytostatic drugs appear promising candidates to achieve the goal, as they restrain cell proliferation without blocking it. At the same time, they do not affect cellular response to antigenic stimulation, and at appropriate dosages are not immune suppressive.

SUMMARY

Presently available antiretrovirals only partially reduce immune system activation during chronic HIV infection. Further clinical research is warranted to test cytostatic drugs to avert immune overactivation and prevent progression to AIDS.

The role of proliferation in the regulation of interferon gamma (IFNγ) expression in foals

Interferon-gamma (IFNγ) plays an important role against viral and intracellular bacterial infections and its production is deficient in foals. Cellular proliferation provides an opportunity for de novo gene expression, though little is known about its role in regulating IFNγ expression in foals. While stimulation of foal peripheral blood mononuclear cells (PBMCs) with concanavalin A (ConA) increased the frequency of IFNγ(+) cells, the overall percentage of IFNγ(+) cells remained below that of adults. By contrast, the proliferative response of foal PBMC was significantly greater than that of the adults. In foals, IFNγ production was predominantly associated with those T cells that underwent proliferation, whereas in adults non-dividing cells also produced IFNγ. While treatment with hydroxyurea inhibited cellular division, it failed to completely block IFNγ production. This residual IFNγ production likely represented memory cells as the proportion of these proliferation-independent IFNγ(+) cells increased with foal age. However, memory cells may not account for all of the IFNγ production as ConA stimulation likely provided additional signals that can control IFNγ expression.

Soluble CD163 made by monocyte/macrophages is a novel marker of HIV activity in early and chronic infection prior to and after anti-retroviral therapy

CD163, a monocyte- and macrophage-specific scavenger receptor, is shed during activation as soluble CD163 (sCD163). We have previously demonstrated that monocyte expansion from bone marrow with simian immunodeficiency virus (SIV) infection correlated with plasma sCD163, the rate of AIDS progression, and the severity of macrophage-mediated pathogenesis. Here, we examined sCD163 in human immunodeficiency virus (HIV) infection. sCD163 was elevated in the plasma of individuals with chronic HIV infection (>1 year in duration), compared with HIV-seronegative individuals. With effective antiretroviral therapy (ART), sCD163 levels decreased in parallel with HIV RNA levels but did not return to HIV-seronegative levels, suggesting the presence of residual monocyte/macrophage activation even with plasma viral loads below the limit of detection. In individuals with early HIV infection (≤1 year in duration), effective ART resulted in decreased sCD163 levels that were comparable to levels in HIV-seronegative individuals. sCD163 levels in plasma were positively correlated with the percentage of CD14+CD16+ monocytes and activated CD8+HLA-DR+CD38+ T lymphocytes and were inversely correlated with CD163 expression on CD14+CD16+ monocytes. With ART interruption in subjects with early HIV infection, sCD163 and plasma virus levels spiked but rapidly returned to baseline with reinitiation of ART. This study points to the utility of monocyte- and macrophage-derived sCD163 as a marker of HIV activity that links viral replication with monocyte and macrophage activation. These observations underscore the significance of monocyte and macrophage immune responses with HIV pathogenesis.

Immunotherapeutic restoration in HIV-infected individuals

While the development of combined active antiretroviral therapy (cART) has dramatically improved life expectancies and quality of life in HIV-infected individuals, long-term clinical problems, such as metabolic complications, remain important constraints of life-long cART. Complete immune restoration using only cART is normally unattainable even in cases of sufficient plasma viral suppression. The need for immunologic adjuncts that complement cART remains, because while cART alone may result in the complete recovery of peripheral net CD4+ T lymphocytes, it may not affect the reservoir of HIV-infected cells. Here, we review current immunotherapies for HIV infection, with a particular emphasis on recent advances in cytokine therapies, therapeutic immunization, monoclonal antibodies, immune-modulating drugs, nanotechnology-based approaches and radioimmunotherapy.

New bis(thiosemicarbazonate) gold(III) complexes inhibit HIV replication at cytostatic concentrations: potential for incorporation into virostatic cocktails

Four bis(thiosemicarbazonate)gold(III) complexes (1-4) with a general formula [Au(L)]Cl {L=L1, glyoxal-bis(N(4)-methylthiosemicarbazone); L2, glyoxal-bis(N(4)-ethylthiosemicarbazone); L3, diacetyl-bis(N(4)-methylthiosemicarbazone); L4, diacetyl-bis(N(4)-ethylthiosemicarbazone)} were synthesised and screened for activity against the human immunodeficiency virus (HIV). Complexes 1-4 were characterised using (1)H-NMR and IR spectroscopy; and their purity established by micronanalysis. Complex 3 inhibited viral infection of TZM-bl cells by 98% (IC(50)=6.8±0.6μM) at a non toxic concentration of 12.5μM while complex 4 inhibited infection of these cells by 72 and 98% (IC(50)=5.3±0.4μM) at concentrations of 6.25 and 12.5μM respectively. The mechanism of inhibition of infection in TZM-bl cells is presumably as a result of the cytostatic or anti-proliferative activity that was observed for complex 4 in real time cell electronic sensing (RT-CES) and carboxyflourescein succinimidyl ester (CFSE) analysis. Treatment of T lymphocytes from HIV infected individuals with 4 decreased CD4+ T cell expression (p=0.0049) as demonstrated by multi-parametric flow cytometry without suppressing cytokine production. None of the ligands (L1-L4) demonstrated anti-viral activity, supporting the importance of metal (gold) complexation in these potential drugs. Complexes 3 and 4 were shown to have ideal lipophilicity values that were similar when shake flask (0.97±0.5 and 2.42±0.6) and in silico prediction (0.8 and 1.5) methods were compared. The activity and drug-like properties of complexes 3 and 4 suggests that these novel metal-based compounds could be combined with virus inhibitory drugs to work as cytostatic agents in the emerging class of anti-HIV drugs known as virostatics.

Hydroxyurea exerts an anti-proliferative effect on T cells but has no direct impact on cellular activation

Hydroxyurea (HU) is a cytostatic drug which has been used as an anti-HIV agent due mainly to its synergistic activity when combined with certain anti-retrovirals. In addition, HU might have a beneficial effect on parameters involved in the pathogenesis of HIV infection, such as immune activation. To test this hypothesis, the effect of HU on T cell proliferation and T cell activation, as well as the potential association between these two phenomena, were examined in an in vitro model. HU exerted a dose-dependent anti-proliferative effect on T cells, and modulated the expression of different activation markers. In cells exposed to HU, expression of CD25 and CD38 diminished in a dose-dependent manner, whereas expression of CD69 increased. However, when the expression of these markers was examined separately on proliferating and non-proliferating lymphocytes, HU did not exert any significant effect. Thus, the effect of HU on T cell activation is not direct and seems to be mediated through its effect on T cell proliferation.

Lowering the dose of hydroxyurea minimizes toxicity and maximizes anti-HIV potency

The goal of this study was to optimize the hydroxyurea dosage in HIV-infected patients, and to minimize the toxicity and maximize the antiviral efficacy of the hydroxyurea-didanosine combination. In a randomized, open-label study (RIGHT 702, a multicenter trial performed in private and institutional practices), three daily doses (600 microg, 800-900 microg, and 1200 microg) of hydroxyurea were administered in combination with didanosine and stavudine to 115 chronically HIV-infected patients, one-third antiretroviral drug naive, with viremia between 5000 and 200,000 copies/ml regardless of CD4+ cell count. The primary efficacy end point was the proportion of patients with plasma HIV-1 RNA levels below 400 copies/ml after 24 weeks of therapy. In the RIGHT 702 intent-to-treat population the lowest (600 mg) dose of hydroxyurea was better tolerated, associated with fewer adverse events, and more potent by all efficacy parameters, including the primary end point (76 versus 60% patients with viremia<400 copies/ml at week 24 for the 600-mg and 800- to 900-mg dose groups, respectively; p=0.027), the mean area under the curve (60.3 versus 65.8; p=0.016), and the mean log10 decrease (-1.95 versus -0.77; p=0.001). Patients receiving 600 mg of hydroxyurea daily also had the highest CD4+ cell count, CD4+/CD8+ cell ratio, and lowest CD8+ cell count and percentage (p=0.035). The RIGHT 702 trial provides an explanation for the increased toxicity and decreased efficacy of hydroxyurea when it was used at high dosage (1200 mg daily). At the optimal dosage of 600 mg daily, hydroxyurea, in combination with didanosine, deserves reevaluation for the long-term management of HIV/AIDS worldwide, because of its excellent resistance profile, durability, and affordability.