CP Unknown Heme-10/19/2011 Kumaran Mudaliar and Girish Venkataraman Loyola University Medical Center, Pathology

What cells are these?- hematogones Plasma cells are bright CD 38 with variable CD 19 expression What cells are the purple population? -Plasma cells

Additional plot of same case

Light chain negative cells colored green Explain the gates in this tube containing CD45, CD19, CD20, kappa and lambda Primary gate CD19/SSC Light chain negative cells colored green and forwarded to show on all plots. Backgating and coloring the cells green

Hematogones Hematogones: physiologic precursors of B-cells 70 years ago, distinct ‘lymphoid appearing cells’ in the bone marrow (BM). ‘Hematogones’ (hematogonia, meaning ‘blood-maker’) 662 patients 8% pts had 5% or more of hematogones 24.6% < 16 YO had hematogones 6.3% > 16 YO had hematogones MC in patients: lymphoma, marrow regenerative states, immuno cytopenias, AIDS Cells of uncertain significance

Problem At 5% level, they are conspicuous on marrow smear and can be confused with neoplastic lymphoblasts

(A) Several hematogones are illustrated in this bone marrow smear from a 3-year-old boy with immune thrombocytopenia. They bear close resemblance to the neoplastic lymphoblasts illustrated in panel B. (B) Numerous lymphoblasts are present in this bone marrow smear from a 5-year-old girl with precursor B-ALL

Mature hematogones

Figure 5. A scatter plot relating percent bone marrow hematogones to patientage for all 662 specimens. There is a significant decease in the percent hematogones with increasing age as shown by the regression line. (Two cases were off thescale of the scattergram and are not shown: a 5-month-old with 51% hematogones and a 23-year-old with 65%.)

Reference Ranges? No accepted reference ranges BM examination is not performed in healthy people

3 stages of Hematogone Maturation Early Usually comprise a small minority, but can become expanded in regenerating marrows No expression of CD 20 /CD34+ Intermediate Majority in most marrows -CD34-/CD20 dim/CD10+ Late In contrast to mature B cells, Cd34-/CD20+/maintain dim CD10 . Light chain surface+

Take out CD 43, CD 22, IgM, and sIg

As hematogones matures, they express CD 20 19 20

20 38

19 34

10 34

Stage 1 Hematogones CD34+/CD10+ Gated on all CD19+ cells Stage 2 hematogones Dimmer CD10, CD20 het Stg 2 (red) and stg 3 (blue) Hematogones lack CD34 Stage 3 hematogones -bright CD20, dim CD10 >90% of B-cells in this case are hematogones

Immunophenotype CD 10+ CD 19+ CD 20+ Variable expression CD 38+ CD 45+ TdT + [subset] CD 34 + [subset] Kappa & Lambda -

Differences between hematogones and lymphoblasts Both present in CD 45 dim gate Hematogones: low side scatter Consistent, highly reproducible, maturational pattern No aberrant or asynchronous antigen expression B-ALL: relatively higher side scatter Phenotypic abnormalities: Myeloid Markers: 13, 33, 15 T-cell: 2, 5, 7 Concurrent expression: TdT and cytoplasmic IgM; 34 and 20 ; 34 and surface light chains Loss of antigen expression on blasts: 45 – ; 10 – [B-ALL with MLL abnlties] ; 34 – [E2A-PBX1 fusion]

Even tho both may express an antigen, difference in expression patterns and levels of specific antigens exist IF TdT: hematogones (coarsely granular / speckled) to blasts (finely granular / even distribution) Also, hematogones have higher #’s of TdT and CD 10 molecules / cell Leads to brighter expression on FC Hematogones have less CD 19 molecules/ cell Hence dimmer expression on FC

BM Core Biopsies Hematogones: dispersed throughout marrow Blasts: small clusters (> 5 cells)

Issues Differentiation can be challenging Left Shifted Hematogones Early stages after BM transplantation Anti-CD20 immunotherapy Majority of B-ALL lack CD20 expression . -Phenotypic change Anti CD 20 - can change the normal pattern of hematogone antigen expression by abolishing or masking the expression of CD20 in hematogones which might create problems Phenotypic Change: (‘antigen shift or drift’) in recurrent B-ALL has been previously characterized by FC, with over 70% of cases showing loss of at least one aberrant antigen at relapse

Sources McKenna RW, et al. Immunophenotypic analysis of hematogones (B-lymphocyte precursors) in 662 consecutive bone marrow specimens by 4-color flow cytometry. Blood. 2001 Oct 15;98(8):2498-507