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: This paper reviews the results of clinical trials that have investigated these new approaches to immunosuppression in renal transplant recipients .
### Output Text:
This paper reviews the results of clinical trials that have investigated these new approaches to immunosuppression in renal transplant recipients . 