The ornamental design for multilayer cell culture flask, as shown and described.
FIG. 1 is a first end view of a multilayer cell culture flask;
FIG. 2 is a second view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a perspective view thereof with the access port cap on;
FIG. 5 is a perspective view thereof with the access port cap off;
FIG. 6 is a bottom view thereof;
FIG. 7 is a top view thereof;
FIG. 8 is an enlarged perspective view of a portion of the multilayer cell culture flask with the access port cap on; and,
FIG. 9 is an enlarged perspective view of a portion of the multilayer cell culture flask with the access port cap off.
The broken lines in all drawing views are included for the purpose of illustrating portions of the multilayer cell culture flask that form no part of the claimed design.