Shares of Longeveron Inc. blasted 120.9% higher on very active morning trading Thursday, after the biotechnology company said its Lomecel-B for the treatment of a congenital heart defect in infants (Hypoplastic Left Heart Syndrome) affecting about 1,000 babies a year was granted rare pediatric disease (RPD) designation by the Food and Drug Administration. Trading volume exploded to 112.0 million shares, compared with the full-day average of about 110,000 shares. The stock was both the biggest gainer and most active on major U.S. exchanges. The company said Lomecel-B is currently being evaluated in a Phase 2 trial. Despite…