Effect of adjunct hydroxyurea on helper T cell immunity in HIV type 1-infected patients with virological suppression

Hydroxyurea for the Treatment of Psoriasis with an Emphasis on HIV-Infected Psoriasis Patients: A Review

Hydroxyurea is a drug that has been long forgotten for the treatment of psoriasis. In addition to its anti-psoriatic effects, it has also been shown to have antiviral effects. This dual effect makes it a drug that dermatologists may want to consider when treating psoriasis in HIV-infected patients. Currently, no studies are available that discuss the safety and efficacy of hydroxyurea in the treatment of psoriasis in this immunocompromised group; however, numerous reports discuss the safety and efficacy of hydroxyurea in psoriasis and HIV separately. This review suggests that hydroxyurea is generally safe and effective. The main risk involves the hematologic adverse events (anemia, leukopenia, thrombocytopenia, and macrocytosis), which appear to be dose dependent. Because of the common hematologic adverse events, hydroxyurea may be considered a viable therapeutic option for patients with generalized psoriasis that is inadequately responsive to other safer options, whether or not the patient is HIV positive.

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.

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.

Hydroxyurea exerts a cytostatic but not immunosuppressive effect on T lymphocytes

OBJECTIVE

To demonstrate that, despite a dose-dependent cytostatic effect, hydroxyurea (HU) does not have immunosuppressive effects.

METHODS

The effects of HU on T lymphocyte proliferation parameters, activation phenotype and cytokine production were examined in vitro after exposure to clinically relevant concentrations of HU (10, 50, and 100 micromol/l). The effects of HU in vivo on CD4 T cell counts, viral load, activation phenotype and virus-specific response were examined in 17 Rhesus macaques infected with SIV(mac251) and randomized into three groups: untreated controls; treated with (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) and didanosine (ddI) only; and treated with PMPA, didanosine, and HU.

RESULTS

The in vitro inhibition of T lymphocyte proliferation confirmed the cytostatic effect of HU, with a linear dose-dependent effect; however, no relevant differences were found in the expression of activation markers between treated and untreated controls. Both T helper type 1 and type 2 cytokine production were enhanced by HU. Consistent with the in vitro results, a blunted increase of peripheral CD4 T cells was observed in vivo in the HU group, without relevant effects on the expression of activation markers, and SIV-specific T cell responses were not affected by HU.

CONCLUSIONS

Hyper-proliferation of T-lymphocytes is a major factor contributing to HIV pathogenesis. HU exerts a cytostatic effect on T lymphocytes, without altering their activation and apparently without having an immunosuppressive effect. The increase in cytokine production at the single cell level might compensate for the decrease in the percentage of activated CD4 T lymphocytes, without overall impairment of HIV-specific immune responses.