MARROW of Essential Thrombocythemia PATIENTS IS ENRICHED IN Effector Memory CD4+ and CD4+CD25++ Lymphocytes as Compared to BLOOD

Abstract 5058

The role of T cells residing in the marrow is poorly understood. However, some literature data suggest that the presence of CD8+ lymphocytes in the marrow plays a role in keeping the tumor cells in a dormant state. In chronic myeloid leukemia a significant role of lymphocytes in controlling the malignant clones is well documented. The aim of this study was to define whether there is a specific enrichment of some CD4+ lymphocytes subpopulations in the marrows of newly diagnosed patents with essential thrombocythemia (ET).

Seven patients (F/M: 6/1, age 28–72 - median 6 yrs) with ET diagnosed according to the WHO criteria were studied. They had platelets 425–809 ×10∧3/ul (median 676 × 10∧3), NAP 74–138 score (median 112 score), 6 of them were positive for JAK 2 V617F mutation (heterozygotes). Marrow cellularity was from 18 – 64 ×10∧3/ul (median 44 × 10∧3/ul) Cytological evaluation revealed normal differentiation of erythroid and myeloid lineages, in contrast an increased number of megakaryocytes often enlarged, hyperlobulated and in clusters was seen in all patients. Trephine biopsy revealed activation of megakaryopoiesis with enlarged numerous megakaryocytes with normal representation of other lineages and a lack of an increase in the reticulin fibers. Lymphocytes in the marrows were in proportions from 4.5 – 15,7% (median 10,6%) what resulted with lymphocytosis from 2640/ul to 19405/ul (median 5645/ul). The whole populations of marrow and blood cells were labeled for a purpose of this study with the use CD4, CD25, CD45RO and CCR7 MoAb (Becton Dickinson, San Jose, CA, USA) followed by detection and analysis with the use of flow cytometry (FACS Calibur, Becton Dickinson) equipped with PCLysis programe.

We found:

1. Proportions of lymphocytes in the marrows were rather in a normal value range but in numbers they prevailed over blood lymphocytes (2640-19405/ul, median 5645/ul vs 1300–3100/ul, median 1800/ul, p= 0,003 Wilcoxon Test for pairs),

2. Among T cells subpopulations effector/memory CD4+ lymphocytes CD45RO+, CCR7-) were significantly higher in numbers in the marrows of ET patients as compared to blood (744-3241/ul, median 1126/ul vs 406–2437/ul, median 592/ul, p=0,04 Wilcoxon Test for pairs). There was no difference when numbers of naïve (CD45Ro-, CCR7+) and central memory (CD45RO+, CCR7+) CD4+ lymphocytes were analyzed.

3. The marrows of ET patients had higher numbers of CD4+CD25++ lymphocytes as compared to blood (8,1-40,7/ul, median 11,4/ul vs 1,2-14,8/ul, median 7,3/ul; p=0,02 Wilcoxon Test for pairs).

It appeared that in ET patients there was a selective enrichment of marrow lymphocyte populations in CD4+EM cells and CD4+CD25++ lymphocytes what strongly suggests the presence of active immune response in the marrows affected by this myeloproliferative disorder.