Trimming its initial gains, the Sensex at the Bombay Stock Exchange stood 53 points, or 0.3 percent in positive territory, at 21,133 in afternoon trade, a short while ago. Earlier in the morning, the Sensex had gained 105 points, or 0.5 per cent, to 21,185 on fresh buying by funds and retail investors, amid firm regional bourses. Stock markets in China, Hong Kong, South Korea and Singapore had advanced between 0.2 percent and 0.7 percent, today.