In total, 942 publications were identified and screened under the search terms (Fig. 1). Of these studies 164 were ATI studies, and out of these 24 studies (14,17,24,26–44) were included in this individual data-based meta-analysis, and 142 ATI studies were excluded due to different reason (Fig. 1). Table 1 summarises the studies included in this analysis.
Characteristics of included studies
Of the 24 studies included in our analysis, 22 were published in peer reviewed journals between 2000–2024 (14,17,24,26–44) and 2 studies have yet to be published (AELIX-003 [NCT04364035] and BNC03 [NCT05208125]). Fourteen were RCTs (17,26,27,29,32,33,36,38,40–42,45 + AELIX-003 and BNC03) and ten were single-arm ATI studies (14,24,30,31,34,35,37,39,43,44). Thirteen studies were undertaken in Northern Europe (14,17,32–35,39–41,43,44 + AELIX-003 and BNC03) and eleven studies in North America (24,26–31,36–38,42). Most studies had only small “placebo” participant numbers with the smallest involving 4 individuals (40) and the largest being 69 individuals (30). Restart criteria for ART between the studies were based upon pVL levels and CD4 + T cell counts, but differed on the exact threshold (Supplementary Table S2).
Study participant demographics
The characteristics of the analysed ATI study participants are shown in Table 1. From the 382 participants of the 24 studies, 91% were male and 75% white. The median age was 42 (interquartile range [IQR] 35–49) years. The median CD4 + T cell count at ART initiation was 422 (330–558) per mm3 and median pre-ART pVL was 48,400 (14,000–150,000) copies/mL. Forty-five and 51 percent of participants were categorized as early-ART and late-ART, respectively, while 4% were categorized as ‘unknown’. At the start of ATI, the median CD4 + T cell count was 781 (IQR 611–1,007) per mm3. Forty-eight percent were on an integrase-strand inhibitor regimen, while 17% were on a NNRTI-containing ART regimen at the time of ATI.
NNRTI impacts time to viremia
NNRTI has been shown to be associated with longer time to viral rebound likely reflecting an antiretroviral drug ‘tail’ into the ATI due to the long half-life of NNRTIs. In agreement with previous analyses, univariable analysis, non-NNRTI regimens compared to NNRTI regimens at ATI start were associated with shorter time to viremia (Supplementary Fig. S1a + b). In multivariable analysis, NNRTI regimen at ATI start continued to be associated with longer time to pVL > 50 copies/mL (Supplementary Fig. S1a: HR 0.50, P < 0.01). However, due to the risk of ART drug resistance, current ATI trials no longer recommend NNRTI regimens and to make our observations pertinent to current recommendations individuals entering an ATI on NNRTI regimens were omitted from the analyses of time to viral rebound, although included in the overall analyses of PTC at day 84 of ATI.
Viral kinetics
While viral rebound kinetics following ART interruption differed (Fig. 2a), most individuals followed a similar pattern. Forty-four percent of the participants had a pVL below 50 copies/mL by day 14 after stopping ART but only 4% had a pVL below 50 copies/mL at day 84 (Fig. 2b).The median time to pVL > 50 copies/mL after ART interruption was 16 days (IQR: 13–25), while time to pVL > 400 and > 10,000 copies/mL was 21 (IQR: 15–28) days and 32 (IQR: 20–35) days, respectively (Fig. 2c-e). Time to viremia data for all individuals irrespective of ART regimen is shown in Supplementary Fig. S2.
Collectively, these data demonstrate that in more than 75% of individuals (not on NNRTI regimens), pVL rebounds within 21 days and only 14 (4%) people have suppressed viremia through day 84.
Post-treatment control
Out of the 14 PTCs with pVL below 50 copies/mL at day 84 (Fig. 3a), only 4 (29%) individuals had pVLs < 50 copies/mL at all prior measurements. The other 10 individuals had variable levels of viremia prior to regaining viral control to < 50 copies/mL, with 29% (n = 4) reaching a peak pVL 50–399 copies/mL, 29% (n = 4) with peak pVL between 400–10,000 copies/mL, and 14% (n = 2) reaching peak pVL above 10,000 copies/mL (Fig. 3b + c). Examining the total study cohort of 382 individuals, categorized by levels of peak pVL < 50, 50–399, 400 − 10,000, and > 10,000 copies/mL, the percentage of PTCs at day 84 within each category were 1%, 1%, 1% and 0.5%, respectively.
Among the 14 PTCs, most were male (93%) and white (71%) with an average age of 38 (IQR: 33–45) years (Fig. 3d), similar to the demographics for the overall cohort. A significantly higher proportion (P = 0.008) of individuals who started ART early (n = 11; 6% of 172 early-ART participants) achieved PTC compared to those who started ART late (n = 2; 1% of 195 late-ART participants). One PTC had unknown time of ART initiation relative to HIV acquisition. Among PTCs, the median CD4 + T cell count at ART interruption was 912 (IQR: 827–1219) per mm3. These observations highlight that PTC is very rare, in particular among people who start ART late. In addition, while 1% of ATI participants maintained ART-free suppression for 84 days, only 0.5% regained control to pVL < 50 copies/mL at 84 day when peak viremia post-ATI was higher than 10,000 copies/mL.
Factors associated with time to viremia
As seen in Fig. 4a, some of the variables associated with time to viremia were highly correlated. For instance, nadir CD4 + T cell count prior to ART start correlated with the CD4 + T cell count at ATI start (Fig. 4b; P < 0.0001) but also with time to viremia (Fig. 4c). There were significant positive correlations between initial viral doubling time and time to pVL > 50 c/mL (Fig. 4a), and these correlations became more positive with higher viremia threshold (> 400 and > 10,000 c/mL, Fig. 4d-f).
In our univariable analysis, late-ART (vs early-ART) at ATI start was associated with shorter time to viremia (Supplementary Fig. S1a + b). In our multivariable analysis, late-ART remained a risk factor for shorter time to pVL > 50 copies/mL (Supplementary Fig. S1a: HR 1.25, P = 0.05) and > 10,000 copies/mL (Supplementary Fig. S1b: HR 1.61, P < 0.01). We observed a significantly longer time to viremia of 50 and 10,000 copies/mL for early-ART compared to late-ART initiation (Supplementary Fig. S1c + d). Similar results were found when using a threshold of time to pVL > 400 copies/mL (Supplementary Fig. S3). In summary, multiple mechanistic factors may impact time to viremia after ART interruption, but in our analyses, based on clinical variables, early-ART initiation was consistently associated with both higher chance of PTC at day 84 and longer time to viremia after interrupting ART.
Powering future interventional HIV cure/remission studies
Using the calculated time to viremia and frequencies of PTC from this meta-analysis, we generated power calculations that may help inform the design of future ATI studies. We used our data as reference and calculated the number of participants needed in either a single arm or 2-group randomized controlled trial design with a power of 90% to detect the indicated prolonged time to viremia or proportion of PTC at a 5% significant level (Fig. 5 and Supplementary Fig. S4). If the expected outcome of an intervention is a frequency of 25% PTC among early-ART participants, 36 individuals would need to be included in a single arm design and 128 individuals in a 2-group randomized trial design (Fig. 5a). However, due to the lower observed frequency of PTC among late-ART individuals (1%), only 12 and 64 participants would be needed in a single arm design and 2-group randomized trial design, respectively, if the expected frequency of PTC in the intervention group is 25% (Fig. 5b).
PTC is generally considered the most clinically relevant outcome in HIV cure/remission studies, but if the primary outcome is time to viremia (e.g. 50 copies/mL), 8 and 32 study participants (irrespectively of stage at ART initiation) would be needed to demonstrate a delay of at least 14 days in a single and randomized trial design, respectively (Supplementary Fig. S4a). Similarly, an expected delay in time to viremia of at least 21 days, would only require 4 and 16 individuals (irrespectively of stage at ART initiation) in a single arm and 2-group randomized trial design, respectively (Supplementary Fig. S4a). Approximately twice as many participants would be needed to demonstrate a delay of at least 14 or 21 days in time to viremia of 10,000 copies/mL (Supplementary Fig. S4b). Of note, clinical trials often include slightly more participants than needed according to the power calculations to account for drop outs, typically 10–20% more. In conclusion, adequately powering of future trials is critical for optimizing resources, risk mitigation, and advancing the HIV cure/remission agenda. Our simulated power calculations show that reducing the study population size may be possible using single arm design and our extensive dataset as reference.