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: Only minor changes in CD4 + lymphocyte subset count were observed in AIDS patients , although a more significant rise occurred in those with earlier stages of disease .
### Output Text:
Only minor changes in CD4 + lymphocyte subset count were observed in AIDS patients , although a more significant rise occurred in those with earlier stages of disease . 