The two major players in the jumbo mortgage-backed security market have seen strong demand for their issuance in recent months. But much broader factors are likely to limit issuance, including ongoing uncertainty regarding reform of the government-sponsored enterprises. Marc Simpson, an executive director at JPMorgan Securities, said 50 investors bought into the bank’s latest jumbo MBS, a $1.03 billion issuance. He said it was a “highwater mark,” as 20 to 30 investors typically ...