In the sentence extracted from biomedical literature, identify all the disease entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="disease"> to denote a disease.

### Input Text: The significant concordance that we have observed in the degree of imbalance in the different blood - cell lineages indicates that a selective mechanism is likely to operate at the level of pluripotent blood stem cells .
### Output Text:
The significant concordance that we have observed in the degree of imbalance in the different blood - cell lineages indicates that a selective mechanism is likely to operate at the level of pluripotent blood stem cells . 