In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Immune mechanisms may be involved in the drug ' s hepatotoxicity , as suggested by the T - cell stimulation study reported here .
### Output Text:
Immune mechanisms may be involved in the drug ' s hepatotoxicity , as suggested by the T - cell stimulation study reported here . 