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: These findings reveal the differential impact of immune escape variants on the replication and drug susceptibility of complex HBV mutants , supporting the need of close surveillance and treatment adjustment in response to the selection of distinct mutational patterns .
### Output Text:
These findings reveal the differential impact of immune escape variants on the replication and drug susceptibility of complex HBV mutants , supporting the need of close surveillance and treatment adjustment in response to the selection of distinct mutational patterns . 