Mack reportedly entered the portal on Thursday, May 2.
Robinson played for the Nittany Lions from 2011-13, recording 177 receptions for 2,474 yards and 17 touchdowns.
Henderson became the 13th player to join Penn State's Class of 2025.
Meiga has two years of eligibility remaining.
Wylie didn't appear in the Blue-White Game last month and was absent during the last few media availability of spring practice.
Gaines committed to Penn State in 2023 before decommitting in March.