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: Patient response was assessed using changes in CD4 + lymphocyte subset count , HIV p24 antigen , weight , and quality of life .
### Output Text:
Patient response was assessed using changes in CD4 + lymphocyte subset count , HIV p24 antigen , weight , and quality of life . 