Neutralizing Antibodies Induced by First-Generation gp41-Stabilized HIV-1 Envelope Trimers and Nanoparticles.

The immunogenicity of gp41-stabilized HIV-1 BG505 envelope (Env) trimers and nanoparticles (NPs) was recently assessed in mice and rabbits. Here, we combined Env-specific B-cell sorting and repertoire sequencing to identify neutralizing antibodies (NAbs) from immunized animals. A panel of mouse NAbs was isolated from mice immunized with a 60-meric I3-01 NP presenting 20 stabilized trimers. Three mouse NAbs potently neutralized BG505.T332N by recognizing a glycan epitope centered in the C3/V4 region on BG505 Env, as revealed by electron microscopy (EM), X-ray crystallography, and epitope mapping. A set of rabbit NAbs was isolated from rabbits immunized with a soluble trimer and a 24-meric ferritin NP presenting 8 trimers. Neutralization assays against BG505.T332N variants confirmed that potent rabbit NAbs targeted previously described glycan holes on BG505 Env and accounted for a significant portion of the autologous NAb response in both the trimer and ferritin NP groups. Last, we examined NAb responses that were induced by non-BG505 Env immunogens. We determined a 3.4-Å-resolution crystal structure for the clade C transmitted/founder (T/F) Du172.17 Env with a redesigned heptad repeat 1 (HR1) bend in gp41. This clade C Env, in a soluble trimer form and in a multivalent form with 8 trimers attached to ferritin NP, and the gp41-stabilized clade A Q482-d12 Env trimer elicited distinct NAb responses in rabbits, with notable differences in neutralization breadth. Although eliciting a broad NAb response remains a major challenge, our study provides valuable information on an HIV-1 vaccine design strategy that combines gp41 stabilization and NP display. IMPORTANCE Self-assembling protein nanoparticles (NPs) presenting BG505 envelope (Env) trimers can elicit tier 2 HIV-1-neutralizing antibody (NAb) responses more effectively than soluble trimers. In the present study, monoclonal NAbs were isolated from previously immunized mice and rabbits for structural and functional analyses, which revealed that potent mouse NAbs recognize the C3/V4 region and small NP-elicited rabbit NAbs primarily target known glycan holes on BG505 Env. This study validates the gp41 stabilization strategy for HIV-1 Env vaccine design and highlights the challenge in eliciting a broad NAb response.

Vaccination with the Conserved Caveolin-1 Binding Motif in Human Immunodeficiency Virus Type 1 Glycoprotein gp41 Delays the Onset of Viral Infection and Provides Partial Protection in Simian/Human Immunodeficiency Virus-Challenged Cynomolgus Macaques.

We have previously reported that the CBD1 peptide (SLEQIWNNMTWMQWDK), corresponding to the consensus caveolin-1 binding domain in human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp41, elicits peptide-specific antibodies. Here, we have investigated the cellular immune response and the protective efficacy against a simian/human immunodeficiency virus (SHIV162P3) challenge. In addition to the CBD1 peptide, peptides overlapping the caveolin-binding-motif (CBM) (622IWNNMTWMQW631 or 622IWNNMTW628) were fused to a Gag-p24 T helper epitope for vaccination. All immunized cynomolgus macaques responded to a cocktail peptide immunization by inducing specific T cells and the production of high-titer CBD1/CBM peptide-specific antibodies. Six months after the fourth vaccine boost, six control and five vaccinated animals were challenged weekly by repeated exposure to SHIV162P3 via the mucosal rectal route. All control animals were infected after 1 to 3 challenges with SHIV, while among the five vaccinated monkeys, three became infected after a delay compared to control; one was infected after the eighth viral challenge, and one remained uninfected even after the ninth SHIV challenge. Immunized animals maintained a CD4 T cell count, and their central memory CD4 T cells were less depleted than in the control group. Furthermore, SHIV challenge stimulates antigen-specific memory T cell response in vaccinated macaques. Our results indicate that peptides derived from the CBM region can be immunogenic and provide protection against SHIV infection in cynomolgus monkeys.IMPORTANCE In HIV-1-producing cells, gp41 exists in a complexed form with caveolin-1, an interaction most probably mediated by the caveolin-1 binding motif. This sequence is highly conserved in every single HIV-1 isolate, thus suggesting that there is constant selective pressure to preserve this sequence for a specific function in the HIV infectious cycle. Consequently, the CBM sequence may represent the "Achilles' heel" of HIV-1 in the development of an efficient vaccine. Our results demonstrate that macaques immunized with the CBM-based peptides displayed a delay in the onset of viral infection and CD4 depletion, as well as a significant induction of antigen-specific memory T cell response, which is essential for the control of HIV/SIV infections. Finally, as HIV-infected individuals lack anti-CBM immune responses, CBM-based vaccines could have applications as a therapeutic vaccine in AIDS patients.

A heterologous prime-boosting strategy with replicating Vaccinia virus vectors and plant-produced HIV-1 Gag/dgp41 virus-like particles.

Showing modest efficacy, the RV144 HIV-1 vaccine clinical trial utilized a non-replicating canarypox viral vector and a soluble gp120 protein boost. Here we built upon the RV144 strategy by developing a novel combination of a replicating, but highly-attenuated Vaccinia virus vector, NYVAC-KC, and plant-produced HIV-1 virus-like particles (VLPs). Both components contained the full-length Gag and a membrane anchored truncated gp41 presenting the membrane proximal external region with its conserved broadly neutralizing epitopes in the pre-fusion conformation. We tested different prime/boost combinations of these components in mice and showed that the group primed with NYVAC-KC and boosted with both the viral vectors and plant-produced VLPs have the most robust Gag-specific CD8 T cell responses, at 12.7% of CD8 T cells expressing IFN-γ in response to stimulation with five Gag epitopes. The same immunization group elicited the best systemic and mucosal antibody responses to Gag and dgp41 with a bias towards IgG1.

Protective Effect of an Antibody against Specific Extracellular Domain of TLR2 on Agonists-Driven Inflammatory and Allergic Response.

Specific blocking strategies of TLR2-mediated inflammatory signaling and hypersensitivity reactions may offer novel therapeutic strategies to prevent a variety of diseases. In this study, we investigated the blocking effects of a new anti-TLR2 antibody anti-T20 against a 20 mer peptide T20 located in the extracellular specific domain of mouse TLR2. In addition, the effects of the anti-T20 in vitro, measuring the inhibition of the IL-6 and TNF-α production in response to PGN, LTA, and Pam3CSK4-stimulated RAW264.7 cells, were determined. In vivo, the effects of anti-T20 on a lethal anaphylaxis model using PGN-challenged OVA allergic mice, including the rectal temperature and mortality, and serum levels of TNF-α, IL-6, and LTC4 were assayed. The results showed that anti-T20 specifically bound to TLR2 and significantly inhibited PGN, LTA, and Pam3CSK4-driven TNF-α and IL-6 production by RAW264.7 cells. Also, anti-T20 protected OVA allergic mice from PGN-induced lethal anaphylaxis, and the serum levels of TNF-α, IL-6, and LTC4 of anti-T20 treated PGN-challenged OVA allergic mice were decreased as compared to isotype control of anti-T20 treated mice. In summary, this study produced a new antibody against the specific extracellular domain of TLR2 which has protective effect on TLR2 agonists-driven inflammatory and allergic response.

Continuous intravenous infusion of enfuvirtide in a patient with a multidrug-resistant HIV strain.

Case description To evaluate whether continuous intravenous (i.v.) administration of enfuvirtide (T20) could be a suitable alternative to subcutaneous (s.c.) administration of T20 in a patient with extensively drug-resistant HIV experiencing difficulties administering T20 subcutaneously. T20 was administered to a patient through 100 mL cassettes once daily via a CADD. Plasma samples were drawn and the pharmacokinetic profile compared to that of s.c. twice daily administration of T20. Also, viral replication and CD4+ count were monitored over a period of 9 months for this study. Continuous i.v. administration of T20 resulted in significantly higher T20 plasma levels compared to s.c. administration, continued viral suppression, a rise in CD4+ count and strong patient preference over s.c. administration. Conclusion This method of T20 administration may be a suitable alternative for selected patients who are not able to tolerate it when given subcutaneously. It may even be considered a priori in selected patients with extensive viral resistance who are unable or unwilling to inject T20 subcutaneously.

Five Antiretroviral Drug Class-Resistant HIV-1 in a Treatment-Naïve Patient Successfully Suppressed with Optimized Antiretroviral Drug Selection.

Transmitted HIV-1 exhibiting reduced susceptibility to protease and reverse transcriptase inhibitors is well documented but limited for integrase inhibitors and enfuvirtide. We describe here a case of transmitted 5 drug class-resistance in an antiretroviral (ARV)-naïve patient who was successfully treated based on the optimized selection of an active ARV drug regimen. The value of baseline resistance testing to determine an optimal ARV treatment regimen is highlighted in this case report.

Half-life extension of the HIV-fusion inhibitor peptide TRI-1144 using a novel linker technology.

We have previously developed a linker technology for half-life extension of peptides, proteins and small molecule drugs (1). The linkers undergo ß-elimination reactions with predictable cleavage rates to release the native drug. Here we utilize this technology for half-life extension of the 38 amino acid HIV-1 fusion inhibitor TRI-1144. Conjugation of TRI-1144 to 40 kDa PEG by an appropriate ß-eliminative linker and i.v. administration of the conjugate increased the in vivo half-life of the released peptide from 4 to 34 h in the rat, and the pharmacokinetic parameters were in excellent accord with a one-compartment model. From these data we simulated the pharmacokinetics of the PEG-TRI-1144 conjugate in humans, predicting a t1/2,ß of 70 h for the released peptide, and that a serum concentration of 25 nM could be maintained by weekly doses of 8 µmol of the conjugate. Using a non-circulating carrier (2) similar simulations indicated a t1/2,ß of 150 h for the peptide released from the conjugate and that dosing of only 1.8 µmol/week could maintain serum concentrations of TRI-1144 above 25 nM. Hence, releasable ß-eliminative linkers provide significant half-life extension to TRI-1144 and would be expected to do likewise for related peptides.

A Plant-Derived Multi-HIV Antigen Induces Broad Immune Responses in Orally Immunized Mice.

Multi-HIV, a multiepitopic protein derived from both gp120 and gp41 envelope proteins of the human immunodeficiency virus (HIV), has been proposed as a vaccine prototype capable of inducing broad immune responses, as it carries various B and T cell epitopes from several HIV strains. In this study, the immunogenic properties of a Multi-HIV expressed in tobacco chloroplasts are evaluated in test mice. BALB/c mice orally immunized with tobacco-derived Multi-HIV have elicited antibody responses, including both the V3 loop of gp120 and the ELDKWA epitope of gp41. Based on splenocyte proliferation assays, stimulation with epitopes of the C4, V3 domain of gp120, and the ELDKWA domain of gp41 elicits positive cellular responses. Furthermore, specific interferon gamma production is observed in both CD4+ and CD8+ T cells stimulated with HIV peptides. These results demonstrate that plant-derived Multi-HIV induces T helper-specific responses. Altogether, these findings illustrate the immunogenic potential of plant-derived Multi-HIV in an oral immunization scheme. The potential of this low-cost immunization approach and its implications on HIV/AIDS vaccine development are discussed.

Nasal delivery of PLG microparticle encapsulated defensin peptides adjuvanted gp41 antigen confers strong and long-lasting immunoprotective response against HIV-1.

Defensins display immunostimulatory activities including a chemotactic effect for T lymphocytes/immature dendritic cells and secretion of pro-inflammatory cytokines suggest their role in bridging innate and adaptive immunity. We hypothesized whether defensins with separately emulsified HIV-1 immunogen would elicit peptide-specific systemic and mucosal antibody response in mice. The HIV-1 peptide alone in microsphere showed low peptide-specific antibody response in sera and different washes, while the presence of defensins markedly increased the antibody peak titre both in sera (102,400-409,600) (p < 0.05) and in washes (800-25,600) (p < 0.001). Defensins with HIV-1 peptide were showing 43.0-83.2% and 38.7-72.3% in vitro neutralization against laboratory isolates in serum and lavage samples, respectively, higher than HIV-1 peptide alone. Our findings may have implications in the development of new mucosal adjuvant for AIDS vaccination.

In vitro characterization of a sustained-release formulation for enfuvirtide.

Although approved by the U.S. Food and Drug Administration, enfuvirtide is rarely used in combination antiretroviral therapies (cART) to treat HIV-1 infection, primarily because of its intense dosing schedule that requires twice-daily subcutaneous injection. Here, we describe the development of enfuvirtide-loaded, degradable poly(lactic-co-glycolic) acid microparticles that provide linear in vitro release of the drug over an 18-day period. This sustained-release formulation could make enfuvirtide more attractive for use in cART.

Achieving rapid reduction of HIV-1 viral load in HIV-positive pregnant women close to term - an obstetric/medical emergency: a review of three cases.

Mother-to-child transmission (MTCT) of HIV infection is now uncommon in the UK and the management of HIV-positive pregnant women is usually relatively straightforward. However, HIV viral load suppression may be difficult to achieve peripartum for women who book very late in pregnancy and those with a poor adherence to antiretroviral therapy (ART). These pregnancies are at a higher risk of MTCT due to high viral load (VL). Therefore, the development of interventions to achieve a rapid reduction of HIV VL is essential. We describe three relevant cases that presented to our unit over a 12-month period and discuss the strategies employed to manage these challenging cases. All babies were born healthy and were HIV proviral DNA-negative at 12 weeks postpartum. No serious adverse events were reported for the mothers or their babies.

Role and evolution of viral tropism in patients with advanced HIV disease receiving intensified initial regimen in the ANRS 130 APOLLO trial.

OBJECTIVES: The aims of the study were to assess in patients with advanced HIV disease receiving antiretroviral therapy (ART) intensification with enfuvirtide (i) resistance at virological failure (VF), (ii) impact of baseline tropism on immunovirological response, and (iii) HIV-1 DNA tropism evolution during ART. METHODS: The ANRS 130 APOLLO randomized trial evaluated in naive patients the immunovirological impact of standard ART without (control arm) or with enfuvirtide. Tropism was determined on RNA and DNA by V3-loop sequencing interpreted using the Geno2Pheno algorithm. RESULTS: At baseline the median CD4 cell count was 30 cells/mm(3). Among the 170 patients assessable in this virological substudy, HIV-1 RNA tropism was as follows: 60% of viruses were R5 and 40% were R5X4/X4. HIV-1 DNA tropism was as follows: 54% were R5 and 46% were R5X4/X4. At week 24, 39% and 49% of patients experienced VF in the enfuvirtide and control arms, respectively. In the enfuvirtide arm, only resistance-associated mutations to enfuvirtide were detected. In the control arm, two patients displayed drug-resistant viruses at the time of VF. No impact of baseline tropism was observed on immunovirological response, regardless of the study arm. Among the 25 patients experiencing DNA tropism switch between baseline and week 24, 16 (64%) switched from R5 to R5X4/X4. These latter were mostly successfully suppressed patients receiving enfuvirtide and exhibiting poorer immunological response. CONCLUSIONS: Baseline RNA tropism had no impact on the immunovirological response. Drug resistance mutations were only detected for the fusion inhibitor. Finally, the mechanism of replenishment of the viral cellular reservoir with X4 viruses observed needs to be further analysed.

[Characterization of the HIV-1 subunit vaccine containing the gp41 NHR domain of the HIV-1 CRF01_AE recombinant subtype in China].

AIM: To design and construct an HIV-1 subunit vaccine containing the N-terminal heptad repeat (NHR) domain N51 in gp41 of the HIV-1 CRF01_AE recombinant subtype in China and study its immunogenicity. METHODS: Two pairs of primers were designed to amplify DNA fragment encoding N51Fd gene, which was then subcloned into pFUSE-hIgG1-Fc2 vector. The recombinant plasmid pFUSE/N51Fd was confirmed by DNA sequencing. Western blotting was used to measure the correct expression of the recombinant protein N51FdFc-AE. The N51FdFc-AE protein was used to immunize BALB/c mice, and the specific antibody response was measured by ELISA. RESULTS: A recombinant plasmid pFUSE/N51Fd was successfully constructed and the N51FdFc-AE recombinant protein was expressed effectively in 293T cells. The purified N51FdFc-AE recombinant protein (35 kD) was detected by Western blotting with rabbit anti-gp41 N/C peptide antibodies. The mouse anti-sera could specifically recognize the antigens derived from gp41 NHR. The titers of the specific antibodies were up to 1:102 400 with an average titer of 1:51 200. CONCLUSION: The recombinant N51FdFc-AE protein can effectively induce the gp41 NHR-specific immune responses in BALB/c mice and could be used as an immunogen for design of HIV-1 subunit vaccine.

Lack of benefit of 3-month intensification with enfuvirtide plus optimized background regimen (OBR) versus OBR alone in patients with multiple therapeutic failures: the INNOVE study.

The objective of the present study was to evaluate the virological efficacy of a 3-month short-course intensification with enfuvirtide (ENF) associated with an optimized background regimen (OBR) in treatment-experienced patients infected with HIV-1 with multiple therapeutic failures. This was a prospective, randomized, open-label multicenter trial including patients infected with HIV-1 and harboring a multi-resistant virus that was still susceptible to at least 2 active compounds. Patients were randomized (1:1) to receive OBR + ENF or OBR alone. ENF was discontinued at Week 12. The primary endpoint was the proportion of patients with plasma viral load <50 copies/ml at Week 24. Fifteen patients were randomized into the OBR group and 14 into the OBR + ENF group with a median viral load of 4.1 log(10) copies/ml and a median CD4+ cell count of 346 cells/mm(3) . The primary endpoint was achieved in 93% (14/15) and 79% (11/14) of patients, respectively. Eighty-seven percent (13/15) of patients had a viral load <50 copies/ml as soon as Week 12 in the OBR group and 79% (11/14) in the OBR + ENF group. At Week 12, the median CD4+ cell count was 327 in the OBR and 437 in the OBR + ENF groups and at Week 24 they were comparable. Intensification with ENF had no significant impact on PBMCs HIV-DNA levels. A 3-month short-course intensified treatment with ENF did not improve Week-24 virological response in treatment-experienced patients infected with HIV-1 harboring resistant viruses that were still susceptible to two antiretroviral drugs.

A simple, rapid, and sensitive system for the evaluation of anti-viral drugs in rats.

The lack of small animal models for the evaluation of anti-human immunodeficiency virus type 1 (HIV-1) agents hampers drug development. Here, we describe the establishment of a simple and rapid evaluation system in a rat model without animal infection facilities. After intraperitoneal administration of test drugs to rats, antiviral activity in the sera was examined by the MAGI assay. Recently developed inhibitors for HIV-1 entry, two CXCR4 antagonists, TF14016 and FC131, and four fusion inhibitors, T-20, T-20EK, SC29EK, and TRI-1144, were evaluated using HIV-1(IIIB) and HIV-1(BaL) as representative CXCR4- and CCR5-tropic HIV-1 strains, respectively. CXCR4 antagonists were shown to only possess anti-HIV-1(IIIB) activity, whereas fusion inhibitors showed both anti-HIV-1(IIIB) and anti-HIV-1(BaL) activities in rat sera. These results indicate that test drugs were successfully processed into the rat sera and could be detected by the MAGI assay. In this system, TRI-1144 showed the most potent and sustained antiviral activity. Sera from animals not administered drugs showed substantial anti-HIV-1 activity, indicating that relatively high dose or activity of the test drugs might be needed. In conclusion, the novel rat system established here, "phenotypic drug evaluation", may be applicable for the evaluation of various antiviral drugs in vivo.

The HR2 polymorphism N140I in the HIV-1 gp41 combined with the HR1 V38A mutation is associated with a less cytopathic phenotype.

BACKGROUND: Resistance to the fusion inhibitor enfuvirtide (ENF) is achieved by changes in the gp41 subunit of the HIV envelope glycoprotein (Env). Specific ENF-associated mutational pathways correlate with immunological recovery, even after virological failure, suggesting that the acquisition of ENF resistance alters gp41 pathogenicity. To test this hypothesis, we have characterized the expression, fusion capability, induction of CD4+ T cell loss and single CD4+ T cell death of 48 gp41 proteins derived from three patients displaying different amino acids (N, T or I) at position 140 that developed a V38A mutation after ENF-based treatment. RESULTS: In all cases, intra-patient comparison of Env isolated pre- or post-treatment showed comparable values of expression and fusogenic capacity. Furthermore, Env with either N or T at position 140 induced comparable losses of CD4+ T-cells, irrespective of the residue present at position 38. Conversely, Env acquiring the V38A mutation in a 140I background induced a significantly reduced loss of CD4+ T cells and lower single-cell death than did their baseline controls. No altered ability to induce single-cell death was observed in the other clones. CONCLUSIONS: Overall, primary gp41 proteins with both V38A and N140I changes showed a reduced ability to induce single cell death and deplete CD4+ T cells, despite maintaining fusion activity. The specificity of this phenotype highlights the relevance of the genetic context to the cytopathic capacity of Env and the role of ENF-resistance mutations in modulating viral pathogenicity in vivo, further supporting the hypothesis that gp41 is a critical mediator of HIV pathogenesis.

Diversification of specificity after maturation of the antibody response to the HIV gp41 epitope ELDKWA.

During maturing antibody responses the increase in affinity for target antigens is achieved by genetic diversification of antibody genes followed by selection for improved binding. The effect this process has on the specificity of antibody for variants of the antigen is not well-defined, despite the potential role of antibody diversification in generating enhanced protection against pathogen escape mutants, or novel specificities after vaccination. To investigate this, a library of single amino-acid substitution epitope variants has been screened with serum obtained at different time-points after immunization of mice with the HIV gp41 peptide epitope ELDKWA. The serum IgG response is shown to mature and increase affinity for ELDKWA, and the titre and affinity of IgG against most epitope variants tested increases. Furthermore there is a bias towards high affinity serum IgG binding to variant epitopes with conservative substitutions, although underlying this trend there is also significant binding to many epitopes with non-conservative substitutions. Thus, maturation of the antibody response to a single epitope results in a broadening of the high-affinity response toward variant epitopes. This implies that many pathogen epitope escape variants that could manifest as single amino-acid substitutions would not emerge by escaping immune surveillance.

In situ forming implant for controlled delivery of an anti-HIV fusion inhibitor.

An injectable, phase sensitive, in situ forming, implantable delivery system was developed for enfuvirtide, a therapeutic peptide used in the treatment of HIV infection. The development studies were carried out using poly (D,L-lactide-co-glycolide), a smart, biodegradable polymer. Different formulations were designed, prepared and evaluated by employing response surface, optimal design of experiment technique. The optimized formulation was identified and validated for its performance by using numerical optimization technique. The in vitro evaluation parameters included rheology, compatibility studies, drug release as well as conformational and physicochemical stability studies. In vivo pharmacokinetic parameters and biocompatibility studies were determined in rat models and were statistically analyzed. It was found that the optimized formulation extended the enfuvirtide release and maintained the drug plasma concentration within therapeutically effective range up to 48 h. The optimized formulation maintained physicochemical and conformational stability for at least 6 months and was biocompatible with the animal tissue.

Short-term additional enfuvirtide therapy is associated with a greater immunological recovery in HIV very late presenters: a controlled pilot study.

OBJECTIVES: To evaluate whether the addition of enfuvirtide to standard highly active antiretroviral therapy (HAART) could confer immunovirological benefits in human immunodeficiency virus (HIV)-infected very late presenters. The current study is an open comparative therapeutic trial of standard protease inhibitor (PI)-based HAART ± additional enfuvirtide in treatment-naïve deeply immunologically impaired HIV-positive patients. METHODS: Very late presenters (CD4 <50/mm(3)), without tuberculosis and neoplasms, were alternatively allocated to two nucleoside reverse transcriptase inhibitors (NRTIs) and lopinavir/ritonavir without (control arm, CO) or with (ENF arm) enfuvirtide 90 mg bid. Enfuvirtide was administered until the achievement of viral load <50 copies/ml and for at least 24 weeks. The primary objective was the magnitude of CD4+ cell recovery at 6 months. HIV RNA was intensively monitored in the first month, and, thereafter, monthly, as for CD4+ cell count and percentage, clinical data, and plasma drug concentrations. RESULTS: Of 22 enrolled patients (11 per arm), 19 completed the study (10 in the ENF arm). Baseline CD4+ cell counts and % were comparable, with 20 CD4+/mm(3) (12-37) and a percentage of 3.3 (1.7-7.1) in the ENF arm, and 16 CD4+/mm(3) (9-29) and a percentage of 3.1 (2.3-3.8) in the CO arm, respectively. The baseline viral load was also comparable between the two arms, with 5.77 log10 (5.42-6) and 5.39 log10 (5.06-6) in the ENF and CO arms, respectively. Enfuvirtide recipients had higher CD4+ percentage at week 8 (7.6 vs. 3.6%, p = 0.02) and at week 24 (10.7 vs. 5.9%, p = 0.02), and a greater CD4+ increase at week 24 (207 vs. 134 cells/mm(3), p = 0.04), with 70% of enfuvirtide intakers versus 12.5% of controls who achieved a CD4+ cell count >200/mm(3) (p = 0.01). At 48 weeks, patients in the ENF arm had CD4+ cell counts higher than controls (251 vs. 153cells/mm(3), p = 0.04) and were also found to be faster in reaching a CD4 cell count over 200/mm(3): 18 (8-24) versus 48 (36-108) weeks (p = 0.01). Viral load decay at week 4 was greater in the ENF arm (-3 vs. -2.2 log, p = 0.04), while the proportion of patients with viral load <50 copies/ml at week 24 was comparable. CONCLUSIONS: In this pilot study, the addition of enfuvirtide to a lopinavir-based HAART was shown to be associated with a significantly faster and greater immunological recovery in newly discovered HIV-positive patients with very low CD4+ cell counts. Induction strategies using an enfuvirtide-based approach in such subjects warrant further investigation.