Characterization of normal and regenerating bone marrow cells with a panel of monoclonal antibodies

RAGE controls leukocyte adhesion in preterm and term infants

BACKGROUND

Insufficient leukocyte recruitment may be one reason for the high incidence of life-threatening infections in preterm infants. Since the receptor of advanced glycation end products (RAGE) is a known leukocyte adhesion molecule and highly expressed during early development, we asked whether RAGE plays a role for leukocyte recruitment in preterm and term infants.

METHODS

Leukocyte adhesion was analyzed in dynamic flow chamber experiments using isolated leukocytes of cord blood from extremely premature (<30 weeks of gestation), moderately premature (30-35 weeks of gestation) and mature neonates (>35 weeks of gestation) and compared to the results of adults. For fluorescent microscopy leukocytes were labeled with rhodamine 6G. In the respective age groups we also measured the plasma concentration of soluble RAGE (sRAGE) by ELISA and Mac-1 and LFA-1 expression on neutrophils by flow cytometry.

RESULTS

The adhesive functions of fetal leukocytes significantly increase with gestational age. In all age groups, leukocyte adhesion was crucially dependent on RAGE. In particular, RAGE was equally effective to mediate leukocyte adhesion when compared to ICAM-1. The plasma levels of sRAGE were high in extremely premature infants and decreased with increasing gestational age. In contrast, expression of β2-Integrins Mac-1 and LFA-1 which are known ligands for RAGE and ICAM-1 did not change during fetal development.

CONCLUSION

We conclude that RAGE is a crucial leukocyte adhesion molecule in both preterm and term infants.

Minimal residual disease levels in bone marrow and peripheral blood are comparable in children with T cell acute lymphoblastic leukemia (ALL), but not in precursor-B-ALL

Sensitive and quantitative detection of minimal residual disease (MRD) in bone marrow (BM) samples of children with acute lymphoblastic leukemia (ALL) is essential for evaluation of early treatment response. In this study, we evaluated whether the traumatic BM samplings can be replaced by peripheral blood (PB) samplings. MRD levels were analyzed in follow-up samples of 62 children with precursor-B-ALL (532 paired BM-PB samples) and 22 children with T-ALL (149 paired BM-PB samples) using real-time quantitative PCR (RQ-PCR) analysis of immunoglobulin and T cell receptor gene rearrangements with sensitivities of 10(-3) to 10(-5) (one ALL cell in 10(3) to 10(5) normal cells). In 14 of the 22 T-ALL patients, detectable MRD levels were found in 67 paired BM-PB samples: in 47 pairs MRD was detected both in BM and PB, whereas in the remaining pairs very low MRD levels were detected in BM (n = 11) or PB (n = 9) only. The MRD levels in the paired BM-PB samples were very comparable and strongly correlated (r(s) = 0.849). Comparable results were obtained earlier by immunophenotyping in 26 T-ALL patients (321 paired BM-PB samples), which also showed a strong correlation between MRD levels in paired BM and PB samples (r(s) = 0.822). In 39 of the 62 precursor-B-ALL patients, MRD was detected in 107 BM-PB pairs: in 48 pairs MRD was detected in both BM and PB, in 47 pairs MRD was solely detected in BM (at variable levels), and in 12 pairs only the PB sample was MRD-positive at very low levels (</=10(-4)). Furthermore, in the 48 double-positive pairs, MRD levels in BM and PB varied enormously with MRD levels in BM being up to 1000 times higher than in the corresponding PB samples. Consequently, BM samples cannot easily be replaced by PB sampling for MRD analysis in childhood precursor-B-ALL, in line with their BM origin. In T-ALL, which are of thymic origin, BM sampling might be replaced by PB sampling, because the dissemination of T-ALL cells to BM and PB appears to be comparable.

In vitro inhibition of cytidine triphosphate synthetase activity by cyclopentenyl cytosine in paediatric acute lymphocytic leukaemia

Cytidine triphosphate (CTP) synthetase is a key enzyme for the synthesis of cytosine (deoxy)ribonucleotides, catalysing the conversion of uridine triphosphate (UTP) into CTP, and has a high activity in several malignancies. In this preclinical study, the enzyme activity and mRNA expression of the enzyme and (deoxy)ribonucleotide concentrations were analysed in leukaemic cells of 57 children suffering from acute lymphocytic leukaemia (ALL). In addition, in vitro experiments were performed with the CTP synthetase inhibitor cyclopentenyl cytosine (CPEC). A significantly higher activity of CTP synthetase (6.5 +/- 3.9 nmol CTP/mg/h) was detected in ALL cells than in lymphocytes of healthy controls (1.8 +/- 0.9 nmol CTP/mg/h, P < 0.001) that was independent of white blood cell (WBC) count, blast percentage, age, gender or type of ALL. The enzyme activity was not correlated with the CTP synthetase mRNA expression. The activity of CTP synthetase in ALL cells compared with non-malignant CD34+ bone marrow controls (5.6 +/- 2.4 nmol CTP/mg/h) was not statistically different. In vitro treatment of ALL cells with CPEC induced a dose-dependent decrease of the CTP concentration. The lowest concentration of CPEC (0.63 microM) induced a depletion of CTP of 41 +/- 20% and a depletion of dCTP of 27 +/- 21%. The degree of CTP depletion of ALL cells after treatment with CPEC was positively correlated with the activity of CTP synthetase. The inhibition of CTP synthetase in situ was confirmed by flux studies using radiolabelled uridine. From these results, it can be expected that CPEC has a cytostatic effect on lymphoblasts of children with ALL.

Regenerating normal B-cell precursors during and after treatment of acute lymphoblastic leukaemia: implications for monitoring of minimal residual disease

We studied 57 childhood acute lymphoblastic leukaemia (ALL) patients who remained in continuous complete remission after treatment according to the Dutch Childhood Leukaemia Study Group ALL-8 protocols. The patients were monitored at 18 time points during and after treatment [640 bone marrow (BM) and 600 blood samples] by use of cytomorphology and immunophenotyping for the expression of TdT, CD34, CD10 and CD19. Additionally, 60 BM follow-up samples from six patients were subjected to clonality assessment via heteroduplex polymerase chain reaction (PCR) analysis of immunoglobulin VH-JH gene rearrangements. We observed substantial expansions of normal precursor B cells in regenerating BM not only after maintenance therapy but also during treatment. At the end of the 2-week intervals after consolidation and reinduction treatment, B-cell-lineage regeneration was observed in BM with a large fraction of immature CD34+/TdT+ B cells. In contrast, in regenerating BM after cessation of maintenance treatment, the more mature CD19+/CD10+ B cells were significantly increased, but the fraction of immature CD34+/TdT+ B cells was essentially smaller. Blood samples showed a profound B-cell lymphopenia during treatment followed by a rapid normalization of blood B cells after treatment, with a substantial CD10+ fraction (10-30%). Heteroduplex PCR analysis confirmed the polyclonal origin of the expanded precursor B cells in regenerating BM. This information regarding the regeneration of BM is essential for the correct interpretation of minimal residual disease studies.

Regeneration pattern of precursor-B-cells in bone marrow of acute lymphoblastic leukemia patients depends on the type of preceding chemotherapy

Immunofluorescence stainings for the CD10 antigen and terminal deoxynucleotidyl transferase (TdT) can be used for the detection of leukemic blasts in CD10+ precursor-B-acute lymphoblastic leukemia (precursor-B-ALL) patients, but can also provide insight into the regeneration of normal precursor-B-cells in bone marrow (BM). Over a period of 15 years, we studied the regeneration of CD10+, TdT+, and CD10+/TdT+ cells in BM of children with (CD10+) precursor-B-ALL during and after treatment according to three different treatment protocols of the Dutch Childhood Leukemia Study Group (DCLSG) which differed both in medication and time schedule. This study included a total of 634 BM samples from 46 patients who remained in continuous complete remission (CCR) after treatment according to DCLSG protocols VI (1984-1988; n = 8), VII (1988-1991; n = 10) and VIII (1991-1997; n = 28). After the cytomorphologically defined state of complete remission with CD10+ and CD10+/TdT+ frequencies generally below 1% of total BM cells, a 10-fold increase in precursor-B-cells was observed in protocol VII and protocol VIII, but not in protocol VI. At first sight this precursor-B-cell regeneration during treatment resembled the massive regeneration of the precursor-B-cell compartment after maintenance treatment, and appeared to be related to the post-induction or post-central nervous system (CNS) therapy stops in protocols VII and VIII. However, careful evaluation of the distribution between the 'more mature' (CD10+/TdT-) and the 'immature' (CD10+/TdT+) precursor-B-cells revealed major differences between the post-induction/post-re-induction precursor-B-cell regeneration (low 'mature/immature' ratio: generally <1.0), the post-CNS treatment regeneration (moderate 'mature/immature' ratio: 1.2-2.8), and the post-maintenance regeneration (high 'mature/ immature' ratio: 5.7-7.6). We conclude that a therapy stop of approximately 2 weeks is already sufficient to induce significant precursor-B-cell regeneration even from aplastic BM after induction treatment. Moreover, differences in precursor-B-cell regeneration patterns are related to the intensity of the preceding treatment block, with lower 'mature/immature' ratios after the highly intensive treatment blocks. This information is essential for a correct interpretation of flow cytometric immunophenotyping results of BM samples during follow-up of leukemia patients. Particularly in precursor-B-ALL patients, regeneration of normal precursor-B-cells should not be mistaken for a relapse.

Significance of common acute lymphoblastic leukemia antigen (cALLA) positive cells in bone marrow of children off therapy in complete remission

Bone marrows from 21 children with acute lymphoblastic leukemia in complete remission (CR) and off therapy for 14 months to 10 years were examined by flow cytometry with a panel of monoclonal antibodies. Significant percentages of cALLA+ cells of low fluorescence intensity were present up to 9 years after CR. These results emphasize the need to interpret flow cytometry results in light of the findings that low intensity cALLA+ cells represent a normal population of immature, non-malignant lymphoid cells.

Immunological phenotype of lymphoid cells in regenerating bone marrow of children after treatment for acute lymphoblastic leukemia

Bone marrow samples from 8 children treated for acute lymphoblastic leukemia (ALL) were investigated at cessation of cytostatic treatment and during 18 months thereafter. The course of the percentage of lymphoid cells and characterization of these cells by means of monoclonal antibodies, peanut agglutinin (PNA) binding and S-phase determination are shown. The percentage of lymphocytes rises in the first 1.5 months, followed by a non-significant decline. The percentage of cells in S-phase is higher at 0 months than at 6, 15 and 18 months. The percentage of T-cells does not change significantly. In the first 1.5 months a sudden rise in the percentage of common-ALL-antigen (cALLA)-positive lymphocytes occurs. The number of B-cells rises to a peak at 6 months. PNA positively increases to a maximum at 3 months and is correlated with positivity for markers of the B-cell lineage. The percentages of B-cells, cALLA-positive, and PNA-positive lymphocytes do not change significantly after they reach their maximum values and are still high at 18 months. Our results show that after cessation of chemotherapy for ALL a lymphoid cell regeneration occurs in the bone marrow consisting of cells of the B-cell lineage; many of these are cALLA-positive, but are discernible from their malignant counterparts by PNA-positivity.