Hydroxyurea interferes with antigen-dependent T-cell activation in vitro

The role of hydroxyurea in enhancing the virologic control achieved through structured treatment interruption in primary HIV infection: final results from a randomized clinical trial (Pulse)

BACKGROUND

Structured treatment interruptions (STIs) have been postulated to improve virologic control in primary HIV infection (PHI) by stimulating HIV-specific T-lymphocyte immunity. The addition of hydroxyurea (HU) may reduce viral production from activated CD4 cells.

METHODS

Patients with PHI received a standardized antiretroviral (ARV) regimen consisting of indinavir 800 mg twice daily (BID), ritonavir 100 mg BID, didanosine 400 mg (QD), and either stavudine 40 mg BID or lamivudine 150 mg BID, for up to 12 months and were randomized to HU 500 mg BID or not. If viral suppression (<50 copies/mL) was achieved, up to 3 STIs were undertaken. Two ARV cycles were allowed after each interruption if virologic rebound to more than 5000 RNA copies/mL occurred. Treatment success was defined as maintaining viral loads below 5000 copies/mL for 6 months after ARV interruption.

RESULTS

Sixty-eight male homosexual patients were randomized: 35 to ARV + HU and 33 to ARV-alone. Median baseline HIV RNA was 5.73 log10 copies/mL, and median CD4 T-lymphocyte count was 517 cells/microL. Treatment success was not significantly different between those receiving and not receiving HU, with 9 (26%) and 9 (27%), respectively, maintaining viral load at less than 5000 copies/mL in each group (P = 0.88). Virologic control was achieved by 11 (19%) of 59 after 1 STI, 1 (2%) of 41 after 2 STIs, and 6 (17%) of 36 after the third STI. Serious adverse events were recorded for 9 (26%) of 35 of patients using HU and 3 (9%) of 33 in the ARV-only group (P = 0.28). CD4 cell increases were significantly blunted for the HU group compared to the ARV-alone group after the initial treatment phase (+101 cells vs. +196 cells, respectively, P = 0.006).

CONCLUSIONS

Hydroxyurea was not found to be beneficial when used in association with STIs in patients during PHI.

Enhanced HIV-specific immune responses in chronically HIV-infected patients receiving didanosine plus hydroxyurea

BACKGROUND

The role of hydroxyurea (HU) in the treatment of HIV infection remains controversial. HU potentiates didanosine (ddI) antiviral activity and might exert immunomodulatory effects.

PATIENTS AND METHODS

Immunologic parameters were examined in HIV-infected patients enrolled in a simplification trial in which ddI-HU was provided to subjects who had been on complete virus suppression under highly active antiretroviral therapy (HAART) for longer than 6 months. A total of 84 of these patients showed plasma viraemia repeatedly below 5000 HIV-RNA copies/ml, and were the main study population. A group of 22 patients who continued on HAART and another of 22 drug-naive HIV-positive individuals were taken as controls.

RESULTS

At 12 months, the levels of naive and memory T-cell subsets were similar in patients on ddI-HU and under HAART, whereas immune activation tended to be lower in the former group. The frequency of HIV-specific CD8+ T cells (CTL) directed against 125 peptides derived from Gag, Pol, Env, Nef and HIV regulatory proteins was similar among patients on ddI-HU and untreated controls, and significantly higher than in patients under HAART. This higher CTL response in patients on ddI-HU was seen even when considering only subjects with undetectable viral load. HIV-specific CD4+ T-cell responses were absent in almost all patients on HAART, whereas they were present in up to 19% of patients on ddI-HU.

CONCLUSION

Treatment with ddI-HU provides higher levels of HIV-specific CD8+ and CD4+ T-cell responses than standard triple drug regimens. Thus, hydroxyurea might exert a beneficial immunomodulatory effect in HIV infection.

Time-dependent changes in HIV nucleoside analogue phosphorylation and the effect of hydroxyurea

BACKGROUND

Nucleoside analogues are activated to their triphosphates, which compete with endogenous deoxynucleoside triphosphate (dNTP) pools to inhibit HIV reverse transcriptase. Hydroxyurea has been administered with nucleoside analogues to modulate intracellular dNTP pools and thus the ratio of drug triphosphate:endogenous triphosphate.

OBJECTIVES

To examine changes in drug activation over time and investigate the effects of hydroxyurea on intracellular phosphorylation of antiretroviral nucleoside analogues.

PATIENTS

A total of 229 HIV-infected individuals receiving abacavir, lamivudine and zidovudine were randomly assigned to receive or not nevirapine and hydroxyurea. Twenty-four patients were recruited to an observational substudy measuring intracellular drug triphosphate and dNTP concentrations at 0, 2, 6, 12, 24 and 48 weeks.

METHODS

Drugs were extracted from isolated peripheral blood mononuclear cells before analysis of endogenous dNTP and drug triphosphates by primer extension assays.

RESULTS

Twenty-two out of 24 patients were followed to completion of the substudy. Hydroxyurea had no demonstrable effect on endogenous dNTP or drug triphosphate levels at any timepoint. However, the ratio of zidovudine triphosphate to endogenous deoxythymidine triphosphate was significantly increased with hydroxyurea. A significant decrease in lamivudine triphosphate (3TCTP) and the 3TCTP:endogenous deoxycytidine triphosphate ratio was seen over 48 weeks. In five patients who failed therapy in the first 24 weeks, significantly reduced 3TCTP was seen.

CONCLUSION

Hydroxyurea does not affect measurable pools of endogenous nucleosides in vivo. Decreased lamivudine phosphorylation over time may provide a novel pharmacological explanation for the mechanism of resistance to this drug.

Effect of target cell availability on HIV-1 production in vitro

OBJECTIVE

The recovery of CD4 target cells following antiretroviral therapy may facilitate virus production and escape from antiretroviral suppression. To address this hypothesis, we directly examined whether the CD4 target cell number increases viral production in the presence of suboptimal therapy.

DESIGN

The effect of the CD4 T cell number on HIV-1 replication with a suboptimal dose of zidovudine was studied in vitro.

METHODS

Varying numbers of CD4 T cells were infected with HIV-1 and treated with 1 nM zidovudine. Virus production was measured by p24 antigen capture enzyme-linked immunosorbent assay. Partial sequencing of HIV-1 pol was performed to assess zidovudine-resistant mutations.

RESULTS

Wild type virus production was found to increase eightfold in cultures with 100 x 10(4) cells compared with cultures with 10 x 10(4) cells. The IC90 of zidovudine was 4 logs higher in cultures with 16 x 10(4) cells compared with cultures with 1 x 10(4) cells. No zidovudine-resistant mutations were found.

CONCLUSION

Target cell availability may play a direct role in wild type HIV-1 resurgence following therapy.

In vitro hydroxyurea decreases Th1 cell-mediated immunity

Hydroxyurea (HU) is used in the treatment of hematologic disorders and is sometimes added to antiretroviral combination therapy to potentiate human immunodeficiency virus (HIV) suppression. However, HU has toxic effects on rapidly dividing cells, including the effectors of the immune response. To determine whether HU affects specific T-cell responses, we measured lymphocyte proliferation and cytokine production in response to microbial antigen and mitogen stimulation in the presence of added HU (10 to 1,000 microM). HU treatment of peripheral blood mononuclear cells obtained from HIV-infected patients and uninfected controls decreased lymphocyte proliferation and gamma interferon production compared with untreated cells. Interleukin-2 (IL-2) and IL-10 production was not affected by HU. The HU-mediated decrease of lymphocyte proliferation was similar in peripheral blood mononuclear cells from HIV-infected patients and from uninfected controls. The inhibitory effect of HU required continuous exposure to the drug and could be reverted by washing the drug out of the culture environment. These findings suggest that HU-containing therapeutic regimens might decrease Th1-cell-mediated immune responses in vivo.