Plasma HIV Viral Load Research Articles

Suppression of HIV-1 plasma viral load below detection preserves IL-17 producing T cells in HIV-1 infection

IL-17 is proinflammatory cytokine secreted by a unique CD4+ T (Th17) cell subset and proposed to play a role in host defense. We hypothesized that Th17 cells are lost in HIV-1 infection. HIV-1-infected children with plasma viremia below 50 copies/ml had IL-17 production, whereas those with detectable viremia had minimal secretion. These results imply viral-mediated destruction or impairment of Th17 cells and argue for complete suppression of viremia for reconstitution of Th17 cells.

Immunologic recovery in survivors following chemotherapy for AIDS-related non-Hodgkin lymphoma

AbstractThe late effects of chemotherapy on immunologic parameters in AIDS-related non-Hodgkin lymphoma (NHL) have not been described. From a cohort of 105 consecutive patients treated with infusional chemotherapy and highly active antiretroviral therapy (HAART), 68 survived more than 3 months following the end of chemotherapy. Their lymphocyte subsets and plasma HIV viral loads were measured at regular intervals for 2 years and values compared with baseline. During chemotherapy, there were statistically significant falls in CD4 (helper T), CD8 (cytotoxic T), and CD19 (B) cell populations but no changes in the CD56 (natural killer [NK]) cell population. Among the 68 survivors, there were statistically significant increases in CD4, CD8, CD19, and CD56 cell populations during the first year of follow up, compared with the values at the start of chemotherapy. During the second year of follow up, there were further statistically significant rises in CD4 and CD19 cell populations, compared with the values at 12 months after chemotherapy. During 244 years of follow-up since chemotherapy in these 68 survivors, 7 second primary tumors and 8 opportunistic infections were diagnosed. Chemotherapy and concomitant HAART for AIDS-related NHL does not cause prolonged suppression of lymphocyte subsets. These data should provide reassurance regarding the long-term consequences of chemotherapy in these individuals.

Photopheresis in HIV-1 Infected Patients Utilizing Benzoporphyrin Derivative (BPD) Verteporfin and Light

An ex vivo trial utilizing photopheresis with Benzoporphyrin Derivative as the photoactive compound, identified the minimum energy levels of light and concentrations of BPD that eradicated both cell-free and cell-associated HIV-1 infectivity without destroying the virus particles or infected leukocytes. Leukocytes remained viable with altered chemokine/cytokine expression. Apoptosis was induced in a minority of CD4 but not CD8 positive cells with a statistically significant increase in cytolytic T-cell activity. In the 24 week clinical trial in 7 HIV-1 infected patients, three who had rapidly rising viral loads prior to initiating therapy stabilized. Two had a sustained greater than 0.5 log decrement and 5 had stable plasma viral loads (less than a 0.5 log increment or decrement) with varied effects on absolute CD4 and CD8 positive lymphocytes counts. One achieved a greater than 1 log decrement in HIV-1 plasma viral load and undetectable in vivo cell-free and cell-associated HIV-1 infectivity with an increased in vitro lymphocyte mitogen stimulation index. Under amended protocol, 5 additional 12 month courses were administered to three additional patients and two of the previous enrollees. Area under the curve for viral load showed a significant decrease from pre- to post-therapy (p 0.007). No associated toxicities were observed.

Virologic Response Using Directly Observed Therapy in Adolescents With HIV: An Adherence Tool

Virologic response to highly active antiretroviral therapy (HAART) treatment of HIV infection depends on viral sensitivity to antiretrovirals and excellent medication adherence. Adolescents with vertically acquired HIV may require complicated regimens because of significant treatment experience and often have poor medication adherence. A retrospective chart review identified five adolescents with vertically acquired HIV and plasma HIV viral load rebound or nonresponse on a stable HAART regimen followed by a period of directly observed therapy (DOT) in a clinic or hospital setting with serial viral load measurements. Four subjects had a virologic response (mean decline, 1.15 log10) after DOT. A response to HAART can be seen despite antiretrovirals resistance using DOT and treatment-experienced patients seemingly unresponsive to HAART may be nonadherent even with reassuring adherence measures. A period of clinic-monitored DOT may allow diagnosis of nonadherence, discussion of medication barriers, and avoidance of unnecessary medication changes.

A case of acute renal failure associated with diffuse infiltrative lymphocytosis syndrome

A 58-year-old African American man with an uncontrolled HIV infection presented to hospital with nephrotic syndrome and diffuse lymphadenopathy. The patient had been taking highly active antiretroviral therapy (HAART; lamivudine, abacavir, fosamprenavir and ritonavir) for 10 years. A renal biopsy showed acute granulomatous interstitial nephritis. Despite a negative tuberculin skin test, he was treated with antituberculosis drugs for 12 months without improvement of his renal profile. Two months after antituberculosis treatment was discontinued, the patient was readmitted to hospital because of acute renal failure. Corticosteroid therapy (prednisone) was started and resulted in a marked improvement in renal function. However, 18 months after steroids were discontinued, renal function declined dramatically. Furthermore, the patient had CD8+ lymphocytosis as well as interstitial tissue infiltration by CD8+ T lymphocytes. Physical examination, plasma HIV viral load, lymphocyte counts, urinalysis, tuberculin skin test, liver function tests, renal ultrasonography, human leukocyte antigen (HLA) typing, renal and minor salivary gland biopsies, ophthalmological examination, chest radiography and culture of bronchoalveolar lavage fluid. Acute granulomatous interstitial nephritis secondary to diffuse infiltrative lymphocytosis syndrome. HAART and prednisone.

Reduced bone mineral density in HIV-infected patients: prevalence and associated factors

There is a high prevalence of bone demineralization among HIV-infected patients but mechanisms of alteration of bone turnover are still unclear and it is thought to be multifactorial. A cross-sectional survey of 492 HIV-infected patients within the Aquitaine cohort estimated the prevalence of osteoporosis/osteopenia and investigated associated factors. Bone mineral density of total body, lumbar spine and femoral neck was measured by dual-energy X-ray absorptiometry. Multivariable analyses of the association with HIV disease status, treatment and anthropometric parameters were stratified according to gender. Median age was 43 years (interquartile range, 38-50); 73% were male; 19.7% patients had reached AIDS, 93.1% were treated with HAART; and 28.5% had lipodystrophy. Based on World Health Organization criteria, osteopenia was diagnosed in 54.6% of men [95% confidence interval (CI), 49.4-59.7) and 51.1% of women (95% CI, 42.6-59.6) and osteoporosis in 33.7% of men (95% CI, 28.8-38.6) and 8.3% of women (95% CI, 3.6-13.9). Using a polytomous logistic regression, older age, homosexual transmission group, low body mass index and low HIV plasma viral load were associated with the diagnosis of bone abnormalities in men, whereas older age and low CD4 lymphocyte count nadir were independently associated with osteoporosis/osteopenia in women. The use of HAART was not related to osteoporosis after adjustment (P = 0.58). This cohort-based survey showed a high prevalence of osteopenia and osteoporosis of multifactorial origin. Mechanisms and consequences of these bone disorders need to be investigated.

A Sudden Rise in Viral Load Is Infrequently Associated With HIV-1 Superinfection

To investigate the association between an unexpected increase in the blood plasma HIV-1 viral load in chronically untreated HIV-infected patients and the occurrence of an HIV superinfection, we analyzed the HIV-1 quasispecies in plasma samples before and at peak level in 14 patients. Phylogenetic analysis of HIV-1 env-V3 fragments showed that in 2 patients a superinfection had occurred: their dominant V3 population at the peak level clustered separately from the V3 sequences in a sample predating the peak level. The rapid rise in viral load could be attributed to upper respiratory tract infections or a vaccination in 4 patients, suggesting that even minor health problems can result in significantly increased HIV-1 replication. In most other patients, no minor or major medical condition accompanied the rise in HIV-1 viral load, implying that in these patients the viral load increase was probably associated with disease progression. This study suggests that an unexpected rapid rise in the plasma HIV-1 viral load of untreated patients can infrequently be ascribed to an HIV-1 superinfection.

Plasma HIV Load and Proviral DNA Decreases After Two Standard Antiretroviral Regimens in HIV-Positive Patients Naive to Antiretrovirals

(i) To compare early decrease of HIV plasma viral load (pVL) after two standard combinations of highly active antiretroviral therapy (HAART). (ii) To evaluate variations of proviral HIV-DNA load on conditions of sustained pVL undetectability. Two different sub-studies of a multicentre prospective randomized controlled trial which compared two first-line HAART (i.e., zidovudine+lamivudine+lopinavir/ritonavir versus tenofovir+lamivudine+ efavirenz). Only patients enrolled at the coordinating centre (University of Brescia) were included in the two sub-studies. In the first sub-study, we calculated pVL decrease with respect to baseline at any of the following time-points: days 1, 3, 7, 14 and 28. Decreases of the pVL were compared between the two treatment groups. In the second sub-study, we analyzed variation of proviral HIV-DNA load in CD4+ T-cells from baseline to week 52 only in patients who maintained the same treatment regimen and had sustained undetectable pVL. In either studies, linear regression analysis was used to investigate what factors could influence variations of pVL and of proviral HIV-DNA load. (i) 64 patients were studied. A significant decrease of pVL was found from day 3 on, without statistically significant differences between the two study groups. However, after adjusting for possible confounders, tenofovir+lamivudine+efavirenz resulted to be associated with greater pVL decreases. (ii) 45 patients were studied. Mean proviral HIV-DNA load decreased from 1,610 (95%CI: 879-2,341) to 896 (95% CI 499-1,293) copies/10(6) cells (P=0.05). Linear regression analysis showed that the decrease of proviral DNA load during follow-up was independently and inversely correlated with age. Further studies are needed to compare pVL decay between antiretroviral regimens and assess whether proviral HIV-DNA load is a surrogate marker of treatment effectiveness.

Genital herpes and HSV transmission in HIV patients

There is a bidirectional relationship between HSV-2 and HIV-1, both at the cellular level, as well as regarding transmission and even progression of HIV-1 infection. There is clear evidence that anti-herpetic therapy reduces the plasma and mucosal HIV-1 viral load, as well as transmission. Serologic testing for HSV-2 in patients with an increased HIV-1 risk, coupled with a better understanding of the interaction between the viruses and appropriate anti-herpetic suppression therapy could both reduce the HIV-1 transmission rate and help the individual with an HIV infection.

Antibody microarray analysis of cell surface antigens on CD4+ and CD8+ T cells from HIV+ individuals correlates with disease stages

BackgroundExpression levels of cell surface antigens such as CD38 and HLA-DR are related to HIV disease stages. To date, the immunophenotyping of cell surface antigens relies on flow cytometry, allowing estimation of 3–6 markers at a time. The recently described DotScan antibody microarray technology enables the simultaneous analysis of a large number of cell surface antigens. This new technology provides new opportunities to identify novel differential markers expressed or co-expressed on CD4+ and CD8+ T cells, which could aid in defining the stage of evolution of HIV infection and the immune status of the patient.ResultsUsing this new technology, we compared cell surface antigen expression on purified CD4+ and CD8+ T cells between 3 HIV disease groups (long-term non-progressors controlling viremia naturally; HIV+ patients on highly active antiretroviral therapy (HAART) with HIV plasma viral loads <50 copies/ml; and HIV+ patients with viremia during HAART) and uninfected controls. Pairwise comparisons identified 17 statistically differential cell surface antigens including 5 novel ones (CD212b1, CD218a, CD183, CD3 epsilon and CD9), not previously reported. Notably, changes in activation marker expression were more pronounced in CD8+ T cells, whereas changes in the expression of cell membrane receptors for cytokines and chemokines were more pronounced in CD4+ T cells.ConclusionOur study not only confirmed cell surface antigens previously reported to be related to HIV disease stages, but also identified 5 novel ones. Of these five, three markers point to major changes in responsiveness to certain cytokines, which are involved in Th1 responses. For the first time our study shows how density of cell surface antigens could be efficiently exploited in an array manner in relation to HIV disease stages. This new platform of identifying disease markers can be further extended to study other diseases.

Photopheresis in HIV-1 Infected Patients Utilizing (Benzoporphyrin Derivative Verteporfin/BPD-MA) and Light.

An ex vivo trial utilizing photopheresis with Benzoporphyrin Derivative as the photoactive compound, identified the minimum energy levels of light and concentrations of BPD that eradicated both cell-free and cell-associated HIV-1 infectivity without destroying the virus particles or infected leukocytes. Leukocytes remained viable with altered chemokine/cytokine expression. Apoptosis was induced in a minority of CD4 but not CD8 positive cells with a statistically significant increase in cytolytic T-cell activity. In the 24 week clinical trial in seven HIV-1 infected patients. Three who had rapidly rising viral loads prior to initiating therapy stabilized. Two had a (sustained) greater than .5 log decrement and 5 had stable plasma viral loads (less than a .5 log increment or decrement) with varied effects on absolute CD4 and CD8 positive lymphocytes counts. One achieved a greater than 1 log decrement in HIV-1 plasma viral load and undetectable in vivo cell-free and cell-associated HIV-1 infectivity with an increased in vitro lymphocyte mitogen stimulation index. Under amended protocol 5 additional 12 month courses were administered to three additional patients and two of the previous enrollees. Area under the curve for viral load showed a significant decrease from pre to post therapy (p 0.007). No associated toxicities observed.

T Cell Responses to Human Endogenous Retroviruses in HIV-1 Infection

Human endogenous retroviruses (HERVs) are remnants of ancient infectious agents that have integrated into the human genome. Under normal circumstances, HERVs are functionally defective or controlled by host factors. In HIV-1-infected individuals, intracellular defense mechanisms are compromised. We hypothesized that HIV-1 infection would remove or alter controls on HERV activity. Expression of HERV could potentially stimulate a T cell response to HERV antigens, and in regions of HIV-1/HERV similarity, these T cells could be cross-reactive. We determined that the levels of HERV production in HIV-1-positive individuals exceed those of HIV-1-negative controls. To investigate the impact of HERV activity on specific immunity, we examined T cell responses to HERV peptides in 29 HIV-1-positive and 13 HIV-1-negative study participants. We report T cell responses to peptides derived from regions of HERV detected by ELISPOT analysis in the HIV-1-positive study participants. We show an inverse correlation between anti-HERV T cell responses and HIV-1 plasma viral load. In HIV-1-positive individuals, we demonstrate that HERV-specific T cells are capable of killing cells presenting their cognate peptide. These data indicate that HIV-1 infection leads to HERV expression and stimulation of a HERV-specific CD8+ T cell response. HERV-specific CD8+ T cells have characteristics consistent with an important role in the response to HIV-1 infection: a phenotype similar to that of T cells responding to an effectively controlled virus (cytomegalovirus), an inverse correlation with HIV-1 plasma viral load, and the ability to lyse cells presenting their target peptide. These characteristics suggest that elicitation of anti-HERV-specific immune responses is a novel approach to immunotherapeutic vaccination. As endogenous retroviral sequences are fixed in the human genome, they provide a stable target, and HERV-specific T cells could recognize a cell infected by any HIV-1 viral variant. HERV-specific immunity is an important new avenue for investigation in HIV-1 pathogenesis and vaccine design.

Transmission of Drug-Resistant HIV-1 from an Infected Individual to a Caregiver

To describe a suspected case of intrafamilial transmission of drug-resistant HIV-1 from an infected individual to his caregiver. HIV-1 protease, reverse transcriptase, nef and gp41 DNA sequences were determined from plasma samples after RNA extraction and nested RT-PCR. Phylogenetic trees were generated using neighbour-joining methods. HIV-1 infection was diagnosed in an individual (index) following the death of her HIV-infected adopted son (source). The index case cared for her son in the 9 months prior to his death. No obvious instances of contact with bodily secretions or other traditional risk factors for HIV transmission were identified, although the index case had mild eczema. At time of death, the source case's HIV plasma viral load was > 1,000,000 HIV copies/ml. Genotyping of the protease and reverse transcriptase of both the source and index samples revealed similar drug-resistance mutations despite the index case being antiretroviral-naive. Both source and index V3 genotypes were consistent with syncytium-inducing virus. The mean pairwise amino acid identity between the source and index samples was 97.0%, 99.2%, 92.6% and 94.6% in protease, reverse transcriptase, nef and gp41, respectively. The source and index sequences clustered together on phylogenetic trees when compared with 50 randomly selected sequences from British Columbia. Although exceptionally rare, our case demonstrates transmission of drug-resistant HIV-1 from an infected individual to his caregiver in the absence of traditional risk factors. It should be noted that the source had a very high viral load during the terminal phase of his illness.

Fever, nephrotic syndrome, and rapidly progressive renal failure

CASE PRESENTATION A 52-year-old African woman, living in France since 5 years, presented with dyspnea and pyrexia. She had a 1-month history of sore throat treated with amoxicillin, migratory polyarthralgia, drenching night sweats, and an evanescent, maculo-papular, non-pruritic rash mainly on her limbs lasting less than 1 week at a time. She denied smoking, alcohol abuse, and illicit drugs use. She had no risk factors for HIV. Examination on admission revealed a temperature of 39.51C, tachycardia, a blood pressure of 120/70 mm Hg, pallor, jaundice, splenomegaly, and bilateral inflammation of knee and ankle joints with synovitis, and severe tenderness of the wrist with signs of fluid overload. There was no sign of meningeal irritation, no focal neurological deficit and normal fundus examination. There were fine crepitations involving the left lung base. Heart sounds were normal on auscultation with no murmur. She was admitted for analgesia and antibiotics pending the results of infective screens and blood tests. Peripheral smear showed no malarial parasite. Her coagulation profile was normal and there was no biochemical evidence of hemolysis. Biochemistry values are summarized in Table 1. Human Immunodeficiency Virus serology, plasma HIV viral load, and p24 determination were negative. Serologies for, hepatitis B and C, Parvovirus B19, cytomegalovirus, Epstein–Barr virus, leptospira, bartonella, rickettsia, chlamydia,

Frequent detection of cell‐associated HIV‐1 RNA in patients with plasma viral load &lt;50 copies/ml

Despite prolonged undetectable plasma viral load some HIV-1 infected patients have been reported to develop resistance-associated mutations leading to treatment failure. The mechanisms for this phenomenon and the point of origin for residual viral evolution are still not elucidated. In order to quantify cell-associated HIV-1 RNA in patients with different levels of plasma viremia paired cell-associated HIV-1 RNA loads and plasma viral loads were determined. Weak inverse correlation between these parameters and the amounts of CD4(+) T cells was observed, whereas there was no correlation between viral loads and CD8(+) T cells or CD14(+) monocytes, respectively. In a subset of patients, cell-associated and plasma HIV-1 env V3 sequences were analyzed. Plasma viral load and the amount of cell-associated HIV-RNA correlated strongly. However, in 62.3% of patients with undetectable plasma viral load cell-associated HIV-RNA could be detected. Analyses of HIV-RNA in plasma and blood cells showed identical sequences in 4/19 patients, whereas the majority of patients had differing HIV-1 RNA sequences in plasma and cells, respectively. In summary, this study shows that residual viral replication in peripheral blood still occurs in the majority of patients with undetectable plasma viral load. Since these replication events could lead to ongoing viral evolution it should be considered to optimize antiretroviral therapy in order to minimize the development of drug resistance.

CD4+ T-Cell Count Increase in HIV-1-Infected Patients with Suppressed Viral Load Within 1 year after start of antiretroviral therapy

Background CD4+ T-cell recovery in patients with continuous suppression of plasma HIV-1 viral load (VL) is highly variable. This study aimed to identify predictive factors for long-term CD4+ T-cell increase in treatment-naive patients starting combination antiretroviral therapy (cART). Methods Treatment-naive patients in the Swiss HIV Cohort Study reaching two VL measurements &lt;50 copies/ml &gt;3 months apart during the 1st year of cART were included ( n=1,816 patients). We studied CD4+ T-cell dynamics until the end of suppression or up to 5 years, subdivided into three periods: 1st year, years 2–3 and years 4–5 of suppression. Multiple median regression adjusted for repeated CD4+T-cell measurements was used to study the dependence of CD4+ T-cell slopes on clinical covariates and drug classes. Results Median CD4+ T-cell increases following VL suppression were 87, 52 and 19 cells/μl per year in the three periods. In the multiple regression model, median CD4+ T-cell increases over all three periods were significantly higher for female gender, lower age, higher VL at cART start, CD4+ T-cell &lt;650 cells/μ l at start of the period and low CD4+ T-cell increase in the previous period. Patients on tenofovir showed significantly lower CD4+T-cell increases compared with stavudine. Conclusions In our observational study, long-term CD4+ T-cell increase in drug-naive patients with suppressed VL was higher in regimens without tenofovir. The clinical relevance of these findings must be confirmed in, ideally, clinical trials or large, collaborative cohort projects but could influence treatment of older patients and those starting cART at low CD4+ T-cell levels.

Rituximab induces long-term remissions in patients with HIV-associated multicentric Castleman's disease

8049 Background: HIV associated multicentric Castlemans (MCD) is rare lympohproliferative disorder and most treatment options to date, have proved largely unsuccessful. This study investigated the efficacy of the anti CD20 monoclonal antibody rituximab in patients with this disease. Methods: Between 2003 and 2006, patients with histological proven HIV related MCD received a course of 4 infusions of rituximab 375mg/m2 at weekly intervals. Results: Twenty one consecutive patients (18 male) were recruited into this study and the median follow-up is 12 months (range 1–49). The median age was 37 years and all patients were either on highly active antiretroviral therapy (HAART) (62%) or started HAART at the time of MCD diagnosis (38%). The median CD4 cell count at MCD diagnosis was 275/mm3 (range 77–725). One died within 2 weeks of starting rituximab (not evaluable); 20 evaluable patients all achieved clinical remission of symptoms and 71% achieved a radiological response according to RECIST criteria. Rituximab lead to a significant fall in anaemia, thrombocytopenia, CRP, ESR, serum HHV8 viral load and IL-10. Rituximab caused transitory fall in the CD19 count, but had no effect on the CD4, CD8 and NK cell counts or plasma HIV viral load. The disease free survival at 2 years is 79% (95%CI: 49–100%) and overall survival is 95% (95%CI: 86–100%). Two patients have relapsed after 1.6 &amp; 2.8 years and were successfully retreated with rituximab therapy. Conclusions: Rituximab therapy results in a sustained clinical, radiological and biochemical remission in patients with HIV related MCD. No significant financial relationships to disclose.

Correlates of epidermal nerve fiber densities in HIV-associated distal sensory polyneuropathy

To demonstrate the relationship between epidermal nerve fiber density (ENFD) in the leg and the phenotype of HIV-associated distal sensory polyneuropathy (HIV-DSP) in a multicenter prospective study (ACTG A5117). A total of 101 HIV-infected adults, with CD4 cell count <300 cells/mm(3) and who had received antiretroviral therapy (ART) for at least 15 consecutive weeks, underwent standardized clinical and electrophysiologic assessment. All 101 subjects were biopsied at the distal leg (DL) and 99 at the proximal thigh (PT) at baseline. ENFD was assessed by skin biopsy using PGP9.5 immunostaining. Associations of ENFD with demographics, ART treatment, Total Neuropathy Score (TNS), sural sensory nerve action potential (SNAP) amplitude and conduction velocity, quantitative sensory testing (QST) measures, and neuropathic pain were explored. ENFD at the DL site correlated with neuropathy severity as gauged by TNS (p < 0.01), the level of neuropathic pain quantified by the Gracely Pain Scale (GPS) (p = 0.01) and Visual Analogue Scale (VAS) (p = 0.01), sural SNAP amplitude (p < 0.01), and toe cooling (p < 0.01) and vibration (p = 0.02) detection thresholds. ENFD did not correlate with neurotoxic ART exposure, CD4 cell count, or plasma HIV-1 viral load. In subjects with advanced HIV-1 infection, epidermal nerve fiber density (ENFD) assessment correlates with the clinical and electrophysiologic severity of distal sensory polyneuropathy (DSP). ENFD did not correlate with previously established risk factors for HIV-DSP, including CD4 cell count, plasma HIV-1 viral load, and neurotoxic antiretroviral therapy exposure.

Successful long-course after failure of short-course desensitization in a patient with severe hypersensitivity reaction to enfuvirtide

Successful long-course after failure of short-course desensitization in a patient with severe hypersensitivity reaction to enfuvirtide

CD4+ T cell evolution and predictors of its trend before and after tenofovir/didanosine backbone in the presence of sustained undetectable HIV plasma viral load

Tenofovir with full-dose didanosine has been associated with paradoxical CD4 + T cell decrease despite virological suppression. We investigated whether tenofovir plus didanosine at a weight-adjusted dosage could be responsible for such an effect, and factors associated with CD4 + T cell count evolution under this combination. This was a prospective observational multicohort study (Italian MASTER and Spanish Hospital Carlos III HIV cohorts). Patients with HIV plasma viral load suppression for >/= 6 months who switched to an antiretroviral combination including tenofovir plus didanosine were studied, as long as virological success was maintained. CD4 + T cell count variations over time (slopes) were compared before and after switching to tenofovir plus didanosine using linear mixed models and segmented regression analysis. Annual time-weighted CD4 + T cell count slope did not change significantly after the prescription of tenofovir plus didanosine: it was 14 cells/mm(3) [95% confidence interval (CI) - 7 to 35] from month - 24 to month - 12, 12 cells/mm(3) (95% CI - 14 to 38) from month - 12 to the time of switching, 30 cells/mm(3) (95% CI 5-55) from switching to month + 12 and 15 cells/mm(3) (95% CI - 8 to 39) from month + 12 to month + 24 after switching to tenofovir plus didanosine. No significant change in the slope of the segment after the switch to tenofovir plus didanosine-containing regimens when compared with the segment preceding the intervention was found (CD4 + T cell count slope change: 24 cells/mm(3); 95% CI - 10 to 58). Similar results were obtained using CD4 + T cell percentage over total lymphocytes. The significant independent predictors of lower CD4 + T cell count slope were older age (P = 0.006), lower nadir CD4 + T cell count (P < 0.001) and positive hepatitis C virus antibody (P = 0.03). Moreover, reduced estimated creatinine clearance was an additional independent predictor of lower CD4 + T cell count slope (P = 0.02), but only after excluding nadir CD4 + T cell count. Tenofovir plus didanosine (weight-adjusted dosage) was not associated with paradoxical CD4 + T cell decrease in our patients maintaining undetectable HIV plasma viral load for a maximum of 24 months after switching. Several factors could explain variability in CD4 + T cell count evolution in these patients.