Is It Relevant to Determine Routinely Levels of Circulating NK and NK Like Cells in Myelodyplastic Syndroms?.

Myelodysplastic syndromes (MDS) are characterized by an ineffective haematopoiesis due to different pathways: Intrinsic factors as cytogenetic and molecular abnormalities and extrinsic factors as disturbance in cellular immunity. An excess or abnormal natural killer (NK) cells cytolytic function have been previously described in MDS. A sub-group of MDS characterized by bone marrow hypoplasia, an excess of NK, HLA-DR15 and trisomy 8 may respond to an immune-suppressive therapy by antithymocyte globuline (ATG) or Cyclosporin. Recent advances in immunophenotyping of hematopoietic dysplastic cells in blood and bone marrow pointed to a useful role for multiparameter flow cytometry (FCM) in the diagnosis of MDS. This prospective study reports the rates of NK and NK like circulating cells in MDS patients (pts) assessed by routine FCM.

This study concern a cohort of pts with MDS, in a university hospital, proved by morphological criteria on blood samples and bone marrow aspirate or trephine biopsy. Pts were classified according to 2001 WHO classification. IPSS score has been determined for pts according to cytopenia, blasts percent and cytogenetic results. We performed between 02/2005 and 09/2008 a prospective analysis of immunophenotyping data using a double platform method that allowed the enumeration of NK cells according to two different antibodies combinations (CD45+, CD3-, CD16 or CD56+, so called “total” NK cells vs CD45+ CD2+ CD3- so called 2+3- NK cells) and NK like cells (CD3+, CD16+ or CD56+). The statistical analysis was made with STATVIEW software.

The cohort counts 58 pts, median age 75 years (50-86), sex ratio 0,93. MDS subtype were distributed as 34.5% RAEB-1 (n=20), 22.4% RAEB-2 (n=13), 15.5 RA (n=9), 13.7% CMML (n=8), 8.6% RARS (n=5), 1.7% RA/RCMD (n=1), 1.7% 5q- syndrome (n=1), 1.7% inclassifiable (n=1). Cytogenetic analysis could be performed in 96.5% of cases (56/58) and revealed 78.5% of favourable prognosis (44/56) with 60.7% normal, 7.1% del (5q), 7.1% -Y, 3.6% del (20q), intermediate prognosis 12.5% (7/56) with 10.7% trisomy 8 and 1.8% inv(9), 5.4% of unfavourable prognosis (3/56) with 3.6% complex and 1.8% del(7q) and 3.6% failure (2/56). IPSS was calculated for 93% of the files (54/58) with 68.5% of low risk (18.5% low IPSS (n=10), 50% int-1 IPSS (n=27)) and 31.5% of high risk (25.9% int-2 IPSS (n=14), 5.6% high IPSS (n=3). Median rate of 2+3- NK cells, obtained on 96.5% of pts, was 79 cells/μl (6.7-798) (normal values : 130-430). This rate is decreased for 69.6% of pts (n=39), normal for 25% (n=14) and increased for 3.4% (n=3). The classification of these 3 pts was RARS, RAEB-2 and CMML. All had a normal cytogenetic profile. Median rate of “total” NK cells (determined on 60% of pts) was 119.7 cells/μl (17.6-473.1) (normal values 130-430). This rate is decreased for 57.1% (n=20), normal 40% (n=14) and increased 2.9% (n=1). This pts was suffering CMML with absence of cytopenia, 11% blast excess, normal cytogenetic and IPSS Int-2. Individually, the two approaches for NK numeration gives, as expected, close values with superior values for “total” NK cells that comprised the subset of CD2- NK cells. Median rate of NK like cells (60% of pts) was 58.5 cell/μl (7-1264) (normal values: 5-95). This rate is normal for 71.4% of pts (n=25) and increased in 28.6% (n=10). The classification of these 10 pts was 10% of RARS (n=1), 40% RAEB-1 (n=4), 20% RAEB-2 (n=2) and 30% CMML (n=3). Cytogenetic was normal 60% (n=6), trisomy 8 20% (n=2), inv 9 10% (n=1) and –Y 10% (n=1). IPSS was low 10% (n=1), Int-1 50% (n=5), Int-2 40% (n=4).

European Leukemia Net recommendation proposes to use FCM for diagnosis and prognostication of MDS, based abnormal phenotype of myeloid lineages. The interest of lymphocytes immunophenotyping is discussed. Our study shows that cases with elevated circulating NK cells are rare, in addition without correlation with IPSS score and cytogenetic data. By contrast, an increase in circulating NK like cells is more frequent, and seems correlated with a blast excess. Such data could be of interest regarding to the potential therapeutic issues using immunosupressors.

No relevant conflicts of interest to declare.