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Persistent HIV Despite Full Suppression by HAART
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HIV replication persists despite suppression by HAART to <50 copies/ml. This ongoing HIV replication may play a role in the fact that immune restoration is partial. Here are 3 studies presented at the Retrovirus Conference 2003 that discuss these issues. It's important to bear in mind that despite the existence of ongoing low level viral replication patients are able to maintain full suppression of HIV in the blood below 50 copies/ml. A computer simulation study has found that with full adherence and if patients remain undetectable for the first 1-2 years after starting therapy full suppression can be maintained for 10 years or more. I do not think this precludes full suppression for longer than 10 years.
"Persistence of Stable, Quantifiable Viremia in Patients on Antiretroviral Therapy Despite Suppression of Plasma HIV-1 RNA to less than 50 Copies/ml"
Potent antiretroviral therapy is effective in suppressing but not eradicating HIV-1 infection. Antiretroviral drug resistance leading to treatment failure can evolve despite initial suppression of HIV-1 RNA to below the limit of detection of current assays. HIV-1 RNA assays of greater sensitivity and precision are needed to detect and quantify persistent viremia in patients (pts) on therapy. (edit note: the presence of drug resistance when viral load is below 50 copies/ml has not been found to necessarily lead to viral load rebound when adherence is good). This study finds the presence of HIV in blood using a very sensitive viral load test despite viral load <50 copies/ml using a standard viral load test. The study authors suggest this persistent HIV may be due to ongoing replication of HIV.
The study investigators developed a more sensitive and precise assay than has previously existed to quantify HIV-1 RNA in plasma. HIV-1 is pelleted from plasma by ultracentrifugation and RNA is extracted using guanidinium isothiocyanate. Recovery of HIV-1 is monitored using an avian retrovirus as internal standard spiked into the plasma samples. Reverse transcription and real time PCR are used to amplify and quantify a specific, conserved HIV gag sequence. This single copy assay has a dynamic range of 106 to 1 copy of HIV RNA/ml.
Study investigators applied this assay to detect and quantify persistent viremia in 15 pts with HIV-1 RNA suppressed to < 50 copies/ml (as determined by standard methods) for at least 131 days. The single copy assay detected HIV-1 RNA in plasma from 14 of the 15 pts. In one pt, no HIV-1 RNA could be
detected in the assay (< 0.25 copies/ml). HIV-1 RNA levels ranged from 1-40 copies/ml with a mean of 9.3 and a median of 3.9 copies/ml. No HIV-1 RNA
was detected in plasma from 10 seronegative controls. To investigate whether persistent viremia represented a therapeutic steady-state, we analyzed longitudinal samples from 5 of the pts. HIV-1 RNA levels remained stable (mean cv for pts = 0.34) over the period of observation (up to 7 months). They investigated baseline and on treatment factors for associations with the level of persistent viremia. Higher levels of persistent viremia were associated with higher pre-treatment HIV-1 RNA levels. The lowest levels of persistent viremia were present in patients on > 3 antiretroviral agents. No obvious association was found between the level of persistent viremia and the duration of antiretroviral therapy, baseline CD4 cell count, or change in CD4 cell count in response to therapy.
The study authors concluded that in 14 of 15 pts, the single copy HIV-1 RNA assay revealed stable, persistent viremia in pts on suppressive antiretroviral therapy (< 50 copies/ml by standard assays). The apparent relation between regimen potency and the level of viremia suggests that viremia may be sustained by ongoing HIV-1 replication. (edit note: more potent therapy may further suppress viral replication. But it remains uncertain if that would add clinical benefit for patients, particularly in the face of the potential for tolerability or adherence issues related to a regimen of more than 3 drugs).
abst. 466. Retrovirus Conference 2003. F. Maldarelli et al. HIV Drug Resistance Program, NCI, NIH, Frederick, MD; Lab of Immunoregulation, NIAID, NIH, Bethesda, MD; Natl Inst of Allergy and Infectious Diseases/CCMD Clin NIH, Bethesda, MD; and Univ of Pittsburgh, PA
"The Persistence of Morphological and T-lymphocyte Subsets Abnormalities in Lymphoid Tissue in HIV-1 Infected Patients Successfully Treated with HAART Correlate with Lymphoid Tissue Viral Replication"
Patients (pts) successfully treated with HAART still have abnormalities in lymphoid tissue (LT). A complete lymph node recovery may not be possible or may be linked to a persistence of viral replication. This study found ongoing HIV replication in lymph tissue and only partial resoration of the immune system in the lymph tissue.
Fourteen (14) HIV-infected persons in early stages (baseline lymphocytes T CD4+ > 500) treated with HAART for 1 yr and with sustained PVL below 20 c/ml. Tonsil biopsies were performed before and after 1 yr of HAART. Lymphoid tissue viral load (LTVL) was determined, and histological analyses and immunohistochemical procedures were performed using the antibodies HIV-1 p24, CD20, CD21 (FDC, follicular dendritic cells), CD4, CD8, Cytotoxic T-lymphocytes (CTL, granzyme B). The mean cell count per HPF was calculated. The LT morphology was graded: I: follicular hyperplasia; II: follicular regression; III: absence of follicles. The expression of HIV-1 p24 protein was graded, 0: negative; 1: scattered and scarce positive cells; 2: small groups of positive cells with mild intensity; 3: extensive and intense positive cells. Five (5) tonsils of non HIV-infected persons were controls.
Before treatment, 8 cases (57%) were in histological stage III and the immunoexpression of p24 antigen was extense and intense (grade 3) in 12 cases (86%). The CD4 and CD8 T-cell counts were 286 and 276 x HPF, respectively. The mean percentage of CTL was 73%. After treatment, 8 cases were in histological stage II (57%) and 6 in stage I (43%), and the immunoexpression of p24 antigen was positive in 8 cases (57%) (6 cases in grade 2 and 2 in grade 1), mainly in FDC. After treatment, a significant increase of CD4 T-cells and decrease of CD8 T-cells and CTL (463 and 148 x HPF and 39%, respectively) was evidenced. The tonsil LT of non-HIV persons had a higher count of CD4 (638 x HPF), and a lower count of CD8 (96 x HPF) and CTL (28%), than the LT of HIV-infected persons, even after treatment. The morphological parameters and lymph tissue T-cell subsets in HIV-1 infected pts after 1 yr of HAART were significantly correlated with LTVL and the immunoexpression of p24 protein.
The authors concluded that the lack of complete suppression of viral replication in LT may be the cause of the persistence of abnormalities in LT.
Abst. 465. Retrovirus Conference 2003. L. Alos et al. Inst d'Investigacions Biomediques August Pi i Sunyer, Hosp Cl’n, Univ of Barcelona, Spain
"Longitudinal Study of Replication Competent HIV from CD4 T-cell "Latent" Reservoirs in HIV-infected Children on HAART"
CD4 T-cells have been shown to harbor replication competent HIV (RCV) in both children and adults on HAART with prolonged undetectable plasma viremia. This study found HIV capable of replication in latent CD4 cells in 9 of 11 children on HAART with durable suppression of HIV (<50 copies) over a 4-year period.
This study prospectively evaluated 11 HIV-infected infants and children (35 days to 9-yrs-old) and 1 teenager (16 yrs) with durable plasma viremia suppression (< 50 cp/ml) at 0.5-1 yr intervals for 4 yrs post-HAART. Peripheral blood mononuclear cells (PBMC) were separated into purified CD4 T-cells alone, CD45RA or CD45RO T-cells using magnetic beads and/or FACS. CD4 T-cells were activated with monoclonal antibody CD3, CD28 for 48 hours then co-cultured with PHA stimulated HIV-1 (-) donor's CD4 T-cells for up to 48 days. Samples with 1x106 CD4 T-cells were considered adequate. Supernatants were then assayed for P24 Antigen (Ag) as previously described.
RCV was obtained from 9/11 (82%) patients (pts) post-HAART. We were unable to obtain RCV from CD4 T-cells on 4/4 attempts in 1 infant and 1 teenager.
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Pts on HAART < 2 yrs had RCV detected in vitro at day 7-14 as compared to day 21-45, 3-4 yrs post-HAART. We isolated RCV from CD45RA only in 1 young infant (3 mo) and from both CD45RA and RO in 3 older children (2.5-8 years). All CD4 T-cell RCVs were R5 tropic in HOS cell lines. Comparison of in vitro replication kinetics of pre-HAART PBMC virus isolates in pooled 3 donor PBMC to later CD4 T-cell RCV showed a decrease in peak P24Ag production (mean peak P24Ag 20,000 vs10,000 pg/ml).
The study authors concluded that they have isolated RCV in the majority of children (82%) with durable viral suppression on HAART over a 4-yr period. At later time points, virus recovery from latent CD4 T-cells in vitro was delayed. It is of interest that one infant treated early with HAART (< 3 mos) had no RCV detected on multiple attempts and virus was isolated only from CD45RA 62L naive cells in another infant. In addition, RCV isolates from CD4 T-cells have lower replication kinetics in vitro and may be less fit. Further studies of the establishment, persistence, and factors influencing these reservoirs will be important for future therapeutic intervention.
abst. 464. Retrovirus Conference 2003. N Ching et al. of California at Los Angeles and 2Northwestern Univ, Chicago, IL
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