Fitch Ratings downgraded four classes of JPMorgan Chase (JPM) commercial mortgage-backed securities Tuesday after discovering potential losses tied to specially serviced loans and loans unlikely to refinance at maturity. So far, losses and payoffs on the pool have cut its overall balance by 30.6% to to $696.8 million from $1 billion, according to Fitch. Of the remaining balance, Fitch expects about 2.3% could suffer additional losses. The downgrades are tied to commercial mortgage certificates in the 2002-CIBC 5 series, with 13 loans, classified as a going concern – two of which are specially serviced loans. One of the loans at high risk of substantial losses is a specially serviced loan backed by a vacant grocery store in a retail center in Woodbridge, N.J. The loan previously went to a special servicers due to monetary default. The servicer is currently trying to cure the loan. Another loan secured by a retail strip center in Gilbert, Ariz., also is a concern, according to Fitch. Write to: Kerri Panchuk.