High CD33-antigen loads in peripheral blood limit the efficacy of gemtuzumab ozogamicin |(Mylotarg®) treatment in acute myeloid leukemia patients

Gemtuzumab ozogamicin (Mylotarg®) induces remission in approximately 30% of relapsed AML patients. We previously demonstrated that gemtuzumab infusion results in near-complete CD33 saturation in peripheral blood, and that saturating gemtuzumab levels result in continuous binding and internalization of gemtuzumab due to renewed CD33 expression. We now demonstrate that a high CD33-antigen load in peripheral blood is an independent adverse prognostic factor, likely due to peripheral consumption of gemtuzumab. Indeed, CD33 saturation in bone marrow is significantly reduced (40-90% saturation) as compared with CD33 saturation in corresponding peripheral blood samples (>90%). In vitro, such reduced CD33 saturation levels were strongly related with reduced cell kill. Apparently, high CD33-antigen loads in blood consume gemtuzumab and thereby limit its penetration into bone marrow. Consequently, CD33 saturation in bone marrow is reduced, which hampers efficient cell kill. Therefore, gemtuzumab should be administered at higher or repeated doses, or, preferably, after reduction of the leukemic cell burden by classical chemotherapy

Flow cytometric immunobead assay for fast and easy detection of PML-RARA fusion proteins for the diagnosis of acute promyelocytic leukemia

The PML-RARA fusion protein is found in approximately 97% of patients with acute promyelocytic leukemia (APL). APL can be associated with life-threatening bleeding complications when undiagnosed and not treated expeditiously. The PML-RARA fusion protein arrests maturation of myeloid cells at the promyelocytic stage, leading to the accumulation of neoplastic promyelocytes. Complete remission can be obtained by treatment with all-trans-retinoic acid (ATRA) in combination with chemotherapy. Diagnosis of APL is based on the detection of t(15;17) by karyotyping, fluorescence in situ hybridization or PCR. These techniques are laborious and demand specialized laboratories. We developed a fast (performed within 4-5 h) and sensitive (detection of at least 10% malignant cells in normal background) flow cytometric immunobead assay for the detection of PML-RARA fusion proteins in cell lysates using a bead-bound anti-RARA capture antibody and a phycoerythrin-conjugated anti-PML detection antibody. Testing of 163 newly diagnosed patients (including 46 APL cases) with the PML-RARA immunobead assay showed full concordance with the PML-RARA PCR results. As the applied antibodies recognize outer domains of the fusion protein, the assay appeared to work independently of the PML gene break point region. Importantly, the assay can be used in parallel with routine immunophenotyping for fast and easy diagnosis of APL

Vdelta2-Jalpha rearrangements are frequent in precursor-B-acute lymphoblastic leukemia but rare in normal lymphoid cells

The frequently occurring T-cell receptor delta (TCRD) deletions in precursor-B-acute lymphoblastic leukemia (precursor-B-ALL) are assumed to be mainly caused by Vdelta2-Jalpha rearrangements. We designed a multiplex polymerase chain reaction tified clonal Vdelta2-Jalpha rearrangements in 141 of 339 (41%) childhood and 8 of 22 (36%) adult precursor-B-ALL. A significant proportion (44%) of Vdelta2-Jalpha rearrangements in childhood precursor-B-ALL were oligoclonal. Sequence analysis showed preferential usage of the Jalpha29 gene segment in 54% of rearrangements. The remaining Vdelta2-Jalpha rearrangements used 26 other Jalpha segments, which included 2 additional clusters, one involving the most upstream Jalpha segments (ie, Jalpha48 to Jalpha61; 23%) and the second cluster located around the Jalpha9 gene segment (7%). Real-time quantitative PCR studies of normal lymphoid cells showed that Vdelta2 rearrangements to upstream Jalpha segments occurred at low levels in the thymus (10(-2) to 10(-3)) and were rare (generally below 10(-3)) in B-cell precursors and mature T cells. Vdelta2-Jalpha29 rearrangements were virtually absent in normal lymphoid cells. The monoclonal Vdelta2-Jalpha rearrangements in precursor-B-ALL may serve as patient-specific targets for detection of minimal residual disease, because they show high sensitivity (10(-4) or less in most cases) and good stability (88% of rearrangements preserved at relapse)

Minimal residual disease (MRD) detection in acute lymphoblastic leukaemia based on fusion genes and genomic deletions

Minimal residual disease (MRD) diagnostics are implemented in most clinical protocols for patients with acute lymphoblastic leukaemia (ALL) and are mostly performed using rearranged immunoglobulin (IG) and/or T-cell receptor (TR) gene rearrangements as molecular polymerase chain reaction targets. Unfortunately, in 5–10% of patients no or no sensitive IG/TR targets are available, and patients therefore cannot be stratified appropriately. In the present study, we used fusion genes and genomic deletions as alternative MRD targets in these patients, which retrospectively revealed appropriate MDR stratification in 79% of patients with no (sensitive) IG/TR target, and a different risk group stratification in more than half of the cases.</p