The ornamental design for a tissuecellblock, as shown and described.
FIG. 1 is a top perspective view of a tissue cell block showing our new design; and,
FIG. 2 is a top plan view thereof, the bottom plan view being a mirror image thereof.
Area depicted in dense stippling represents a color and species different than the area depicted in sparse stippling. Area depicted in sparse stippling represents a color on an opaque background.