MPO and lymphoid leukemia: The myeloid granule marker (myeloperoxidase, MPO) and the B cell cytoplasmic marker CD79a, both widely used to classify acute myeloid and lymphoid leukemia, and the regulatory T cells (Tregs) nuclear marker FoxP3, broadly studied in the context of autoimmunity, were easily detected after 1 month of storage (Figure 2b,c).