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: In the 8 and 6 years since the transplants ( representing 8 and 4 years since cessation of all immunosuppressive therapy , respectively ) , the RA in each case has been completely quiescent .
### Output Text:
In the 8 and 6 years since the transplants ( representing 8 and 4 years since cessation of all immunosuppressive therapy , respectively ) , the RA in each case has been completely quiescent . 