The role of transplacental microtransfusions of maternal lymphocytes in HIV transmission to newborns

Background: Perinatal HIV transmission could occur via microtransfused maternal blood during delivery. If so, detecting maternal cells in umbilical cord blood should correlate with infection risk. Objective: To develop sensitive assays for maternal DNA in infant's blood stored as dried blood spots (DBS) and examine the correlation between microtransfusion and perinatal HIV infection risk. Methods: Blood-in-blood serial dilutions were prepared as DBS. Extracted DNA was amplified for unique minor-population sequences using 24 allele-specific polymerase chain reaction assays. Using newborns born to HIV+ mothers, paired mother-infant samples were similarly examined to identify unique maternal sequences targeted by allele-specific polymerase chain reaction of DNA extracted from cord blood DBS. Cord-blood PCR-negative infants were categorized as uninfected or perinatally infected by HIV PCR on samples collected 4-8 weeks after birth. Results: Sequences from added cells were detected at less than 1:1000 dilutions in 19 of 20 aliquots, and less than 1:10 000 dilutions in seven of 20 aliquots; the median limit of detection (probit analysis) was one added genomic sequence in 9500 background sequences of amplifiable DNA. Maternal sequences were detected in cord-blood DBS of 50% of infected infants (N = 18) and 44% of uninfected infants (N = 43). Infection did not correlate with more frequent detection of maternal sequences. Conclusion: This semiquantitative assay reliably detected maternal DNA sequences in DBS at levels of less than 1:1000 cells. Maternal sequences were frequently detected but did not correlate infection risk with detection or level of maternal DNA in umbilical cord blood. Therefore, we could not demonstrate that microtransfusions at parturition were responsible for perinatal HIV transmission.