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: Mild PTCR in allografts without TG did not predict renal failure or significant proteinuria after follow - up periods of between 3 months and 1 year .
### Output Text:
Mild PTCR in allografts without TG did not predict renal failure or significant proteinuria after follow - up periods of between 3 months and 1 year . 