Background:  HIV-1 replication is influenced by the phase of cell cycle at the time of infection. It has previously been demonstrated that only partial reverse transcripts of HIV-1 DNA could be found in resting lymphocytes (G0-G1a). We postulate that a portion of perinatal HIV transmissions may involve initial entry of the virus into quiescent cells, which predominate in the immune system of the fetus and newborn. Immune activation of the infected quiescent cell is required before complete reverse-transcription occurs; otherwise, the infection will abort after a time.

Methods:  HIV-exposed infants were enrolled at the Atlanta site of the Perinatal AIDS Collaborative Transmission Study (PACTS) from 1991 until 1998. Real-time PCR assays specific for HIV LTR DNA or gag DNA were developed with sensitivity at 5 to 10 copies. They were used on cryopreserved peripheral blood mononuclear cells (PBMC) from HIV-exposed and -unexposed infants shortly after birth. Samples that tested positive for LTR and negative for gag suggest partial reverse-transcription.

Results:  All samples from 24 HIV-unexposed infants tested negative by both assays, confirming specificity.  Of the HIV-exposed uninfected infants, HIV LTR DNA sequence was found in 4 of 22 (18%) infants who did not receive zidovudine (ZDV) prophylaxis, and in 4 of 34 (12%) infants with ZDV prophylaxis to mother and infant.  Of the LTR-positive samples, 5 were available for the gag DNA assay and all tested negative. Sequence analysis demonstrated that the LTR found in different infants were distinct, ruling out cross-contamination. To investigate how long the viral genome remains detectable in the uninfected infants, serial sequential PBMC samples obtained at various times after birth of the LTR positive cases were tested. Our results indicate that the viral genome persists for 1 to 8 weeks, and is undetectable after 2 months of age. 

Conclusions:  HIV LTR can be found in 12  to 18 % of perinatally HIV-exposed infants who did not become infected.  In these individuals, the HIV genome appears to be only partially reverse-transcribed (i.e., LTR+/gag -), characteristic of quiescent cell infection.  The viral intermediate can persist as long as 8 weeks. However, we cannot rule out the possibility that these infected cells may be of maternal rather than infant origin.

Keywords: perinatal; quiescent cells; reverse transcription