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: Protocols of conversion from cyclosporin A ( CsA ) to sirolimus ( SRL ) have been widely used in immunotherapy after transplantation to prevent CsA - induced nephropathy , but the molecular mechanisms underlying these protocols remain nuclear .
### Output Text:
Protocols of conversion from <span class="chemical">cyclosporin A</span> ( <span class="chemical">CsA</span> ) to <span class="chemical">sirolimus</span> ( <span class="chemical">SRL</span> ) have been widely used in immunotherapy after transplantation to prevent <span class="chemical">CsA</span> - induced nephropathy , but the molecular mechanisms underlying these protocols remain nuclear . 