** Shares of Replimune REPL.O plunge 56% to $2.09 premarket

** J.P. Morgan downgrades biotech firm's stock to "underweight" from "neutral", withdraws price target of $10

** JPM says the U.S. Food and Drug Administration's second complete response letter (CRL) highlights concerns over design of REPL's trials for its drug to treat advanced skin cancer

** The CRL creates "greater uncertainty" over the prospects of the therapy and whether data from the trials will be satisfactory for the FDA - brokerage

** Piper Sandler also downgrades stock to "neutral" from "overweight"

** The regulator declined to approve REPL's drug for a second time on Friday, citing insufficient data from studies

** The second consecutive rejection sent the stock down more than 19% in the previous session

** Five analysts rate stock "buy" or higher, two "hold" and one "sell", median PT at $11.50 - data compiled by LSEG

** REPL has lost more than half its value since the beginning of 2026