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: Although interleukin 3 ( IL - 3 ) and erythropoietin ( EPO ) are known to act synergistically on hematopoietic cell proliferation in vitro , injection of IGF - IL - 3 and EPO in AZT - treated mice resulted in a reduction of red cells and an increase of plasma EPO levels as compared to animals treated with IGF - IL - 3 or EPO alone .
### Output Text:
Although interleukin 3 ( IL - 3 ) and erythropoietin ( EPO ) are known to act synergistically on hematopoietic cell proliferation in vitro , injection of IGF - IL - 3 and EPO in <span class="chemical">AZT</span> - treated mice resulted in a reduction of red cells and an increase of plasma EPO levels as compared to animals treated with IGF - IL - 3 or EPO alone . 