Issue highlights—July 2012
THE PERFECT COCKTAIL
In this journal issue, two manuscripts describe flow assays for detecting paroxysmal nocturnal hemoglobinuria (PNH). Flow cytometry provides the definitive test for PNH, which is characterized by loss of glycosylphophatidylinositol (GPI)-linked proteins such as CD59, CD71, or CD235. The manuscript by Rob Sutherland and colleagues (this issue, page 195) builds on the International Clinical Cytometry Society guidelines for PNH testing (1) and goes into specific detail about antibody clones and dilutions that comprise the “perfect cocktail” of reagents for high sensitivity PNH testing. The Sutherland approach used expression of CD235 and CD59 on red blood cells, whereas the second paper on PNH testing by Nikolaos Tsagarakis and George Paterakis (this issue, page 259) monitors CD71 and CD59 on immature reticulocytes, thereby avoiding any potential confounding from transfusion or hemolysis that may affect RBC markers. The Sutherland study also describes detection of PNH neutrophils and PNH monocytes making use of the sensitive bacterial fluorescent aerolysin to test for rare PNH clones with high sensitivity (2).
NOVEL LEUKEMIA-ASSOCIATED PHENOTYPES
There remains a need to identify novel leukemia-associated markers, especially in CD34 negative acute myeloid leukemias (AML) that can be poorly lineage-characterized immunophenotypically and difficult to monitor for residual disease. The paper by Agnes Simon in the group of Janos Kappelmayer (this issue, page 209) has identified a coagulation factor, factor XIII subunit A, typically found in platelets and megakaryocytes, that is expressed on CD34 negative acute promyelocytic leukemias. This finding is reminiscent of another novel leukemia-associated marker reported in a recent issue of the journal, human inhibitory C-type lectin-like receptor, expressed on CD34 negative AML (3).
WHAT IS NORMAL?
This question arises when monitoring patterns of neutrophil maturation markers in the diagnosis of myelodysplastic syndrome, a topical issue in the journal recently (4–6). In this issue, Sara Monaghan in the group of Fiona Craig (this issue, page 217) cautions that left shifts in neutrophil maturation patterns (e.g., CD11b, CD16, and hypogranularity) that apparently diverge from the “normal” may in fact be quite common in certain settings, especially on bone marrow samples older than 24 h. A second paper in this issue by Andreu-Ballester et al., (this issue, page 238) investigates what are normal levels for both types of T lymphocyte receptors, αβ versus γδ, and their subsets in healthy subjects. The paper reports diverging reference levels depending on age and gender, with γδ expression broadly decreases on T lymphocyte subsets with age and αβ expression rising.
MULTIDRUG RESISTANCE SCREENING BY FLOW CYTOMETRY
In this issue, Stephen Drain and colleagues have written a methodological paper examining expression of the drug transporter protein P-glycoprotein (P-gp) by flow cytometry in plasma cell myeloma (PCM) patients (this issue, page 229). The methodological approach is reminiscent of a similar study in a previous issue of the journal that linked P-gp expression with multidrug resistance (MDR) and adverse clinical status in chronic myeloid leukemia (7). The present study by Drain et al. did not find the same correlation between P-gp expression and MDR in PCM patients; however, the flow cytometric method for P-gp detection is gaining ground and yielded the same phenotype as a predicate method based on PCR.
IMMUNOPHENOTYPING IN THE REAL WORLD
Access to fresh bone marrow or lymphoid samples is almost always desirable when immunophenotyping hematologic malignancies. However, this is not always possible, depending on geographical or resource limitations. In this issue, Patricia Brincat and colleagues evaluate the effect of cryopreservation on preservation of antigens on lymph node cells (this issue, page 245). They report good results across a range of markers for percent positivity and only minimal variance in mean fluorescent intensity of expression. Cryopreservation is a perennial discussion point in the journal and may ultimately depend on the given antigen, since a recent paper on cryopreserved peripheral blood cells reported poor preservation of antigen expression for Treg markers (8). Another paper in this issue investigated the issue of flow cytometric phenotyping from the viewpoint of a developing country (this issue, page 252). Nikil Patkar and colleagues, writing from India, describe a relatively cost effective minimal residual disease panel applicable to more than 90% of acute lymphoblastic leukemias). This report will be read with interest not only by flow cytometrists facing similar resource constraints but also by regular readers of the journal who will have noted that some of the most innovative approaches to flow cytometry have been driven precisely because of the resource constraints faced by the developing world (9–12).