Plasma HIV-1 RNA decay kinetics: Average baseline HIV-1 RNA was 3.9 (range 2.6–4.7) log 10 copies/ml in the 11 infants. In the seven suppressed infants, HIV-1 RNA was undetectable (<100 copies/ml for 200-μl input) in three children within 3.4 months, and in one child it was 120 copies at 3.5 months. In the remaining three patients, the first undetectable plasma HIV-1 RNA loads were recorded between 6 and 7 months.
In infants with a rapid plasma HIV-1 RNA load suppression, here defined as HIV-1 RNA less than 100 copies/ml within 3.5 months, who had assay detectable HIV-1 DNA, total HIV-1 DNA became undetectable in three of 11 infants, respectively at 6 days, 3.5 months and 4 months on treatment. The rate of initial HIV-1 DNA decay from treatment initiation to study enrolment could not be accurately assessed since only DBS were available pretreatment. Thereafter total HIV-1 DNA in PBMC cells decayed with a t½ of 65 days during the remainder of the first year of life with all but one of seven suppressed infants reaching a total HIV-1 DNA load of less than 10 copies/million PBMCs within 13 months of birth. Rapid decay of HIV-1 DNA was observed in adults treated in Fiebig stage I and II (t½ of 21 days in the first 2 weeks). Thereafter, the second phase decay was much slower (t½ of 198 days) . In children treated around 2 months of life the total HIV-1 DNA t½ in the first 24 weeks of life was 53 days, where after it was 124 days between 24 and 48 weeks . Another study that defined early treatment as before 3 months of life found a t½ of 107 days in the first year of life .
The mechanism of rapid HIV-1 DNA decline to low or undetectable levels in infants treated shortly after birth is unknown and requires further investigation. Mechanisms could include the following: low numbers of pretreatment infected cells due to maternal ART and infant prophylaxis, possible rapid loss of cells with unintegrated virus ; high CD4+ cell turnover with a large proportion of short-living infected CD4+ cells that decay rapidly  or a large proportion of surviving cells with integrated HIV-1 DNA that may have defective genomes harboring deletions, and as our assay detects HIV-1 integrase, these genomes may not be detectable .
Our study had the following limitations: First, infants diagnosed at birth and who initiated on early ART were recruited from the public health sector and often only enrolled later into our study. Second, having only a DBS sample pre-ART, we could not accurately assess decay up to the first on-treatment visit, as although HIV-1 DBS DNA levels were normalized for amplifiable cell equivalents, it contained multiple cell types and there was a limited recovery of total nucleic acid, precluding a comparison with subsequent HIV-1 DNA levels measured in PBMC. This combined with not having more frequent sampling prevented us from determining whether the earliest HIV-1 DNA decay was log-linear or biphasic. Third, adherence in young infants is challenging, evident from the high number of viremic children and some having had delayed HIV-1 RNA suppression, limiting our ability to study HIV-1 DNA decay under optimal conditions.
Despite the difficulty of treating infants, HIV-1 DNA decayed very rapidly in most infants and reached very low levels in the first year of life. As HIV is rapidly progressive in infants, it requires early diagnosis and treatment . Moreover, very early ART could result in infants with small HIV reservoirs, who may be good candidates for future immunological interventions aimed at remission or cure. Rapid HIV-1 RNA and DNA decay poses a diagnostic challenge. The combined result of maternal ART (effectively intrauterine treatment of infected babies), extensive neonatal prophylaxis and possibly some antiretroviral absorption through breastfeeding , may together contribute to suppression of viral replication and result in undetectable HIV-1 DNA and RNA levels early in life and false negative diagnostic tests. It is therefore crucial that a definitive diagnosis is established as soon as possible after birth before HIV-1 DNA or plasma HIV-1 RNA become undetectable.
We thank the participants, their parents and the clinical Study Team.
Author contributions: G.U.v.Z. and K.A.V. planned the investigation. A.J.v.R., B.L. and M.F.C. oversaw patient recruitment and data collection. J.M. oversaw the DBS extraction method. K.A.V., S.I. and M.G.K. processed samples. K.A.V. and S.I. performed the assays for HIV-1 DNA. J.W.M. and M.F.C. provided scientific and technical advice. G.U.v.Z. drafted the article with input from K.A.V., J.W.M. and M.F.C. All authors approved of the final article.
NIMH: 1R01MH105134-01; NCI: 1U01CA200441-01; Poliomyelitis Research Foundation, University of Pittsburgh: Centre for Global Health; SAMRC Collaborating Centre for HIV Laboratory Research.
There are no conflicts of interest.
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