Abstract Body

Background:

The intact proviral DNA assay is a measure of the replication-competent HIV reservoir. Little is known about the decay patterns of intact proviral DNA (IPD) in people with HIV (PWH) during very long-term (15-20 yr) suppressive antiretroviral therapy (ART).

Methods:

Participants in ACTG A5321 with chronic HIV and documented suppression of viremia (HIV RNA < 50 copies/mL) for >15 yr of ART had measurements on blood samples of IPD, 5’ or 3’ defective proviral DNA, and total proviral DNA (sum of defective, hypermutated, intact proviruses). A biexponential model for intact proviral DNA was estimated using non-linear regression.

Results:

Fourteen participants (5 female) were evaluated longitudinally from ART yr 1 to ART yr 17-23 (median 20 yr of ART; 8-10 timepoints). Median pre-ART plasma HIV RNA 4.2 log10 c/mL; median pre-ART CD4 cell count 377/mm3. At yr 1 of ART, median intact proviruses were 204 copies/million CD4 cells; median (Q1, Q3) intact provirus percentage (intact/total) was 66% (41, 83). By the last time point (median 20 yr on ART), intact provirus percentage had fallen to 7% (4, 10), reflecting selective decay of intact proviruses (decay of intact proviruses was 13-fold compared with 3-fold for total proviruses). Over the two decades on ART, 5 participants had biphasic decay in IPD levels, 3 participants had biphasic decay with a second phase plateau (slope effectively zero), and 2 participants showed evidence of increased IPD levels during the second decade of ART (see Figure). The inflection or transition of decay occurred at a median of 5 yr after ART initiation (range 2-13 yr). The median IPD first phase half-life was 1 yr (n=10), whereas the median IPD second phase half-life was >25 yr (n=8). (For the 2 participants with late IPD increases, second phase half-life was undefined.) In the 4 other participants, there was a variable pattern of IPD decay, perhaps in part due to fewer cells assayed or low IPD levels.

Conclusions:

In PWH on very long-term ART, three patterns of IPD decay were revealed despite continual suppression of viremia: 1) biphasic decline with markedly slower second phase decline; 2) initial decline that transitions to a zero slope plateau; and 3) initial decline followed by late increases in IPD. The mechanisms of markedly slower second phase decay or reversal are uncertain but may include the inability to clear cells with intact but transcriptionally silent proviruses and clonal expansion of cells with intact proviruses.

Examples of decay patterns in intact proviral DNA levels for participants on long-term ART. Five participants had a similar pattern as shown on left (A), with slowing decay of intact proviruses during the second decade of ART. Three participants showed plateauing of decay (slope effectively zero) (B) and two participants had patterns of late increases (C).