Lysosomal Storage Disease
I-cells produce the normal functional lysosomal hydrolases, however they are secreted outside of the lysosome.

The Hurler cells lack a functional lysosomal hydrolase to degrade the certain oligosaccharides.

When the two cell lines are mixed together in the same media, through non-specific endocytosis, the Hurler cells will simply arbitrarily want to endocytose things such as nutrients from the media into the cell, and some of the times, the Hurler cells may endocytose the functional enzymes secreted outside of the extracellular matrix / membrane from the I-cell. 

Thus, the Hurler cell's lysosomal contents can then be degraded to some extend and restore the defect exhibited in normal Hurler Cells.