Evolution in the hypervariable region of hepatitis C virus in infants after vertical transmission

To elucidate the clonal evolution of hepatitis C virus (HCV) during mother- to-infant transmission, we prospectively analyzed HCV clones of the hyperva riable region in four HCV RNA-positive infants and compared them with those of the mother. Cord blood samples from three of the four infants were posi tive for the HCV RNA (less than or equal to 10(3) copies/mL), and all of th e four infants had the HCV RNA titer of >10(6) copies/mL within 2 mo after birth. The hypervariable region clones detected in the infants were closely related to those in the respective mothers. The results suggest the perina tal transmission of HCV. The hyper variable region clones transmitted to in fants were not a single selected clone or minor clones in the mother. None of the clones specific to the low-density fraction in the mother was transm itted to the infants. Moreover, the proportion of HCV in the low-density fr action was minimal in the first few months of life, but increased several m onths after birth in association with the elevation of alanine aminotransfe rase. These results suggest that the increase of HCV in the low-density fra ction reflect the evolution of immune response in infants. We also demonstr ated that the emergence of quasispecies in infants precedes the infantile a ntibody response.