Background: Enfuvirtide (ENF) is a synthetic peptide that binds to HIV-1 gp41, blocking the fusion of viral and cellular membranes. While its potent antiviral activity against HIV-1 has been demonstrated both in vitro and in vivo, its impact on T cell homeostasis and immune activation is unknown. We report longitudinal immunological analyses of T cells in patients treated for 12 months with ENF as salvage therapy.

Methods: 18 HAART-experienced patients with multidrug resistant virus received ENF (90 mg, SC, twice daily) in combination to at least 3 ARV drugs, according to genotyping testing. Median ENF treatment duration was 6 months (range: 1–12 months). At baseline (BL), median CD4 T cells was 290 cells/ml and median VL 4.40 ± 1.59 log₁₀ copies/mL and decreased to 2.49 ± 0.71 log₁₀ copies/ml, 2.56 ± 1.17 and 2.42 ± 1.33 log₁₀ copies/mL after 4, 12, and 24 weeks of therapy respectively. (VL <50 copies/mL for 27.7% and 30% of the patients at 12W, 24W). Considering all patients, the mean increase in CD4 cells was 97 after 24W and 112cells/mL after 48 W of therapy. For 9 of these patients, blood samples were collected at BL, W4, W12, W24, W48 (5 patients) and phenotyping of naïve (N), central memory (CM), effector memory (EM), and effector (E) CD4 and CD8 T cells, expression of activation markers, and expression of HIV co-receptors was performed on total blood by multicolor FACS analysis (mAbs specific for CD45RA, CD25, CD28, CD45R0, CD38, HLA-DR, CCR5, CXCR4). T cell priming for spontaneous apoptosis was tested in a short-term culture in the absence of stimulus and cell death was quantified with the annexin-V/PI assay.

Results:  Responders to ENF (7/9 patients) (VL reduction >1 log₁₀ copies/ml in 4W of therapy) exhibited a rapid and sustained increase in N and central memory CD4 and CD8 T cells. This was concomitant with a reduction in the priming for apoptosis in these subsets. Moreover, a significant decrease in the activation level was observed, as shown by the diminished expression of the activation markers CD38 and HLA-DR. Interestingly, virological response to ENF was found associated with the decrease in the number of CD4 T cells expressing CCR5, while CXCR4 expression was unchanged.

Conclusions:  Virological response to ENF is associated with a rapid and sustained increase in naïve and central memory CD4 and CD8 T cells, concomitant with a decreased immune activation, and apoptosis. In addition, ENF therapy induces a decreased number of T cells expressing CCR5.