Refer to the input text as context and select the correct relationship between 'beta cell' and 'insulin' from the available options.
Options: owner of, headquarters location, product/material produced, operator

In contrast, patients receiving a single course of teplizumab demonstrated a relative increase in C-peptide levels, suggesting not only a delay in beta cell destruction, but also the recovery of sick or dying beta cells and the restoration of their functionality and insulin secretion.
product/material produced