Marrow biopsy for immunostaining. Hematoxylin and eosin stain shows slight hypercellularity with compensatory myeloid hyperplasia. CD3 is a pan T-cell marker expressed in all stages of T-cell development. CD8 is a marker for cytotoxic T cells. GzB is a component of cytotoxic granules. CD57 is a marker of terminal differentiation when expressed on CD8⁺ T cells. Adapted with permission from Lamy and Loughran.⁶