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: Exclusion criteria included CNS leukemic infiltration at diagnosis , therapy - related peripheral neuropathy , late - onset encephalopathy , or long - term neurocognitive defects .
### Output Text:
Exclusion criteria included CNS leukemic infiltration at diagnosis , therapy - related peripheral neuropathy , late - onset encephalopathy , or long - term neurocognitive defects . 