Maternal blood during pregnancy, cord blood, and placental villous tissues at the time of delivery were obtained from subjects to measure the HTLV-1 proviral load (PVL) using real-time PCR. As shown in Figure 1A, HTLV-1 provirus was detected in the maternal blood of 248 of 254 subjects (97.6%), in the placental villous tissues of 140 of 254 subjects (55.1%), and in the cord blood samples of 6 of 254 subjects (2.4%). Overall, 248 women had PVL in the maternal blood, of whom 140 also had PVL in the placenta. Of these 140 women, 6 had PVL in the cord blood. Significant differences in the PVL were observed between the maternal blood, cord blood, and placental villous tissues (Figure 1A). The 248 pregnant carriers with PVL in the maternal blood were divided into those with PVL (n = 140) and without PVL (n = 108) in the placental tissue, and their clinical backgrounds were compared. Women with PVL in the placental tissue had a significantly higher peripheral blood PVL, higher antibody titers, and more multiparas compared with women with no PVL in the placental tissue (Table 1 and Figure 1B). These 2 groups did not differ in terms of birth weight and pregnancy complications (Table 1). There was no significant difference in the clinical backgrounds of pregnant women with HTLV-1 in the placenta when divided into those who tested positive versus negative for HTLV-1 in the cord blood (Supplemental Table 1). This was at least in part due to the small number of pregnant women testing positive for HTLV-1 in the cord blood. In addition, there were insufficient numbers of follow-up surveys of cases of MTCT by intrauterine transmission to allow statistical analysis. These issues are subjects for future investigation. A weak positive correlation between the PVLs in the maternal blood and in the placental villous tissues was observed (Figure 1C), whereas PVL in HTLV-1-positive cord blood samples did not correlate with PVL in the maternal blood or placental villous tissues of the same subject (Figure 1, D and E). To test the possibility that HTLV-1 provirus detected in cord blood was derived from maternal blood contamination of cord blood, microsatellite analysis was performed using short tandem repeat (STR) markers (25). Differences in the patterns of representative STR markers were observed between maternal blood-derived DNA and fetal placental villous tissue-and cord blood-derived DNA (Figure 1F). Similar results were obtained for all 6 samples that tested positive for HTLV-1 provirus in the cord blood. Furthermore, STR analysis and HTLV-1 PVL assay were used to examine how much maternal blood in the cord blood was required to detect a positive signal. A mixing rate of 20% (maternal/fetal cell ratio = 20:80) was the detection limit in the STR analysis, and a mixing rate of 5% (maternal/fetal cell ratio = 5:95) was the detection limit in the HTLV-1 PVL assay (Supplemental Figure 1). A previous study reported that the median rates of maternal blood contamination in the cord blood were 0.27% and 0.

BackgroundHuman T-cell leukemia virus type-1 (HTLV-1) is transmitted vertically from an infected mother to her child via breastfeeding during infancy or horizontally via sexual contact. However, little information is available on the HTLV-1 seroconversion rate in pregnant mothers and the impact of new HTLV-1 infection on mothers and babies during the perinatal period.MethodsFrom the database of a prefecture-wide antenatal adult T-cell leukemia prevention program in Nagasaki, Japan, we extracted data on 57,323 pregnant women who were screened for anti-HTLV-1 antibody during 2011–2018. Data on the 16,863 subjects whose HTLV-1 proviral load (PVL) was measured more than twice were included in our analyses.ResultsIn total, 133 (0.79%) pregnant women were HTLV-1-positive during their first pregnancy and nine (0.05%) seroconverted before or during subsequent pregnancies (between pregnancies). The median PVL (per 100 peripheral blood mononuclear cells) was significantly lower in the seroconverted mothers (0.10%) than in the initially seropositive mothers (0.15%). A repeated measures correlation analysis for the individual PVLs of the HTLV-1-positive pregnant women showed that PVL increased with parity number (rrm = 0.25) with no perinatal problems.ConclusionThe HTLV-1 seroconversion rate between pregnancies was 0.05%, and their HTLV-1 PVL increased annually but no perinatal problems were noted.