Publications

BACKGROUND

The introduction of highly active antiretroviral therapy (ART) as treatment for HIV infection has greatly improved mortality and morbidity for adults and children living with HIV around the world. Two of the most common medications given in first-line ART are the nucleoside reverse transcriptase inhibitor (NRTI) zidovudine (AZT) and the nucleotide reverse transcriptase inhibitor (NtRTI) tenofovir (TDF).

OBJECTIVES

To assess the efficacy, safety, and tolerability of TDF compared with AZT in combination with one NRTI and one non-nucleoside reverse transcriptase inhibitor (NNRTI) as part of first-line ART for HIV-infected people in resource-limited settings

SEARCH STRATEGY

Standard Cochrane methods were used to search electronic databases and conference proceedings with relevant search terms without limits to language.

SELECTION CRITERIA

Randomised controlled trials of HIV-infected patients aged 5 years and older were included. Primary outcomes of interest included mortality, serious adverse events, virologic response to ART, and adherence/tolerance/retention. Secondary outcomes included immunologic response to ART, development of ART drug resistance, and prevention of sexual transmission of HIV.

DATA COLLECTION AND ANALYSIS

Two authors assessed each reference for inclusion and exclusion criteria established a priori. Data were abstracted independently using a standardised abstraction form.

MAIN RESULTS

Two randomised controlled trials contributed to this literature, enrolling 586 participants, and found no critical difference between TDF and AZT in regards to serious adverse events or virologic response. The trials did find higher rates of adherence and immunologic response in TDF-containing regimens compared with those containing AZT. The quality of the literature to support this conclusion is moderate to high. Drug resistance was more common for TDF than AZT, but the quality of this literature is low, with only one study reporting this outcome. It should be noted that the two studies compared two different drugs in addition to TDF and AZT; one had lamivudine (3TC) and nevirapine (NVP) and the other had emtricitabine (FTC) and efavirenz (EFV).

AUTHORS' CONCLUSIONS

We conclude that for the critical outcomes of virologic response and serious adverse events, initial ART regimens containing TDF are equivalent to those containing AZT. However, TDF is superior to AZT in terms of immunologic response and adherence and less frequent emergence of resistance. How much the other drugs in the regimens contributed to these findings is unclear, and true head-to-head trials are still warranted. The role of each drug in initial ART likely will be driven by their specific toxicities.

It is unclear where within tissues subsets of effector and memory CD8 T cells persist during viral infection and whether their localization affects function and long-term survival. Following lymphocytic choriomeningitis virus infection, we found most killer cell lectin-like receptor G1 (KLRG1)(lo)IL-7R(hi) effector and memory cells, which are long-lived and high proliferative capacity, in the T cell zone of the spleen. In contrast, KLRG1(hi)IL-7R(lo) cells, which appear terminally differentiated and have shorter life spans, were exclusively localized to the red pulp. KLRG1(lo)IL-7R(hi) T cells homed to the T cell zone using pertussis toxin-sensitive chemokine receptors and appeared to contact gp38(+) stromal cells, which produce the chemokines CCL19 and CCL21 and the T cell survival cytokine IL-7. The transcription factors T-bet and B lymphocyte-induced maturation protein-1 controlled effector CD8 T cell splenic migration. Effector CD8 T cells overexpressing T-bet homed to the red pulp, whereas those lacking B lymphocyte-induced maturation protein-1 homed to the T cell zone. Upon memory formation, CD62L(+) memory T cells were predominantly found in the T cell zone, whereas CD62L(-) cells were found in the red pulp. Thus, effector and memory CD8 T cell subset localization within tissues is linked to their differentiation states, and this may identify anatomical niches that regulate their longevity and homeostasis.

Heme oxygenase-1 (HO-1) and its catabolic by-products have potent anti-inflammatory activity in many models of disease. It is not known, however, if HO-1 also plays a role in the homeostatic control of T cell activation and proliferation. We demonstrate here that the HO-1 inhibitor tin mesoporphyrin (SnMP) induces activation, proliferation, and maturation of naive CD4(+) and CD8(+) T cells via interactions with CD14(+) monocytes in vitro. This response is dependent upon interactions of T cells with MHC class I and II on the surface of CD14(+) monocytes. Furthermore, CD4(+)CD25(+)FoxP3(+) regulatory T cells were able to suppress this proliferation, even though their suppressive activity was itself impaired by SnMP. Given the magnitude of the Ag-independent T cell response induced by SnMP, we speculate that HO-1 plays an important role in dampening nonspecific T cell activation. Based on these findings, we propose a potential role for HO-1 in the control of naive T cell homeostatic proliferation.