An announcement was made on AKB48's official blog that one of the research students, Kawakami Marina left the group on December 3rd.

Kawakami was the third member to leave the 11th generation group, and according to the blog, left of her own volition. She was scheduled to attend handshake events in January and February, so naturally her name will be withdrawn from the event headlines.

For those of you who are super confused about what 'research students' are, these are girls who are not yet official additions to AKB48, and in essence, are extras waiting for a promotion.

Source: Sanspo