Citigroup analysts say the U.S. Public-Private Investment Program appears to be helping raise prices on low-rated commercial mortgage-backed securities. According to the analysts, the debt now trades at 83 on the dollar compared 81 cents in January and 38 cents in March 2009, when the government announced the program. They also noted that investment firms prefer the mezzanine AAA class of CMBS, one notch below the top rated class.