Antigen receptor gene rearrangements reflect on the heterogeneity of adult Acute Lymphoblastic Leukaemia (ALL) with implications of cell-origin of ALL subgroups – a UKALLXII study

Comparison of Two Quantitative PCR-Based Assays for Detection of Minimal Residual Disease in B-Precursor Acute Lymphoblastic Leukemia Harboring Three Major Fusion Transcripts

Two quantitative PCR (qPCR)-based methods, for clonal Ig or T-cell receptor gene (Ig/TCR) rearrangements and for fusion transcripts, are widely used for the measurement of minimal residual disease (MRD) in patients with B-precursor acute lymphoblastic leukemia (ALL). MRD of bone marrow samples from 165 patients carrying the three major fusion transcripts, including 74 BCR-ABL1, 54 ETV6-RUNX1, and 37 TCF3-PBX1, was analyzed by using the two qPCR-based methods. The coefficient correlation of both methods was good for TCF3-PBX1 (R² = 0.8088) and BCR-ABL1 (R² = 0.8094) ALL and moderate for ETV6-RUNX1 (R² = 0.5972). The concordance was perfect for TCF3-PBX1 ALL (97.2%), substantially concordant for ETV6-RUNX1 ALL (87.1%), and only moderate for BCR-ABL1 ALL (70.6%). The discordant MRD, positive for only one method with a difference greater than one log, was found in 4 of 93 samples (4.3%) with ETV6-RUNX1, 31 of 245 samples (12.7%) with BCR-ABL1, and 0 of TCF3-PBX1 ALL. None of the eight nontransplanted patients with BCR-ABL1-MRD (+)/Ig/TCR-MRD (-) with a median follow-up time of 73.5 months had hematologic relapses. Our study showed an excellent MRD concordance between the two qPCR-based methods in TCF3-PBX1 ALL, whereas qPCR for Ig/TCR is more reliable in BCR-ABL1 ALL.

Immune Gene Rearrangements: Unique Signatures for Tracing Physiological Lymphocytes and Leukemic Cells

The tremendous diversity of the human immune repertoire, fundamental for the defense against highly heterogeneous pathogens, is based on the ingenious mechanism of immune gene rearrangements. Rearranged immune genes encoding the immunoglobulins and T-cell receptors and thus determining each lymphocyte's antigen specificity are very valuable molecular markers for tracing malignant or physiological lymphocytes. One of their most significant applications is tracking residual leukemic cells in patients with lymphoid malignancies. This so called 'minimal residual disease' (MRD) has been shown to be the most important prognostic factor across various leukemia subtypes and has therefore been given enormous attention. Despite the current rapid development of the molecular methods, the classical real-time PCR based approach is still being regarded as the standard method for molecular MRD detection due to the cumbersome standardization of the novel approaches currently in progress within the EuroMRD and EuroClonality NGS Consortia. Each of the molecular methods, however, poses certain benefits and it is therefore expectable that none of the methods for MRD detection will clearly prevail over the others in the near future.

Mouse xenograft modeling of human adult acute lymphoblastic leukemia provides mechanistic insights into adult LIC biology

The distinct nature of acute lymphoblastic leukemia (ALL) in adults, evidenced by inferior treatment outcome and different genetic landscape, mandates specific studies of disease-initiating mechanisms. In this study, we used NOD/LtSz-scid IL2Rγ null(c) (NSG) mouse xenotransplantation approaches to elucidate leukemia-initiating cell (LIC) biology in primary adult precursor B (pre-B) ALL to optimize disease modeling. In contrast with xenografting studies of pediatric ALL, we found that modification of the NSG host environment using preconditioning total body irradiation (TBI) was indispensable for efficient engraftment of adult non-t(4;11) pre-B ALL, whereas t(4;11) pre-B ALL was successfully reconstituted without this adaptation. Furthermore, TBI-based xenotransplantation of non-t(4;11) pre-B ALL enabled detection of a high frequency of LICs (<1:6900) and permitted frank leukemic engraftment from a remission sample containing drug-resistant minimal residual disease. Investigation of TBI-sensitive stromal-derived factor-1/chemokine receptor type 4 signaling revealed greater functional dependence of non-t(4;11) pre-B ALL on this niche-based interaction, providing a possible basis for the differential engraftment behavior. Thus, our studies establish the optimal conditions for experimental modeling of human adult pre-B ALL and demonstrate the critical protumorogenic role of microenvironment-derived SDF-1 in regulating adult pre-B LIC activity that may present a therapeutic opportunity.

The clinical characteristics, therapy and outcome of 85 adults with acute lymphoblastic leukemia and t(4;11)(q21;q23)/MLL-AFF1 prospectively treated in the UKALLXII/ECOG2993 trial

The biology and outcome of adult t(4;11)(q21;q23)/MLL-AFF1 acute lymphoblastic leukemia are poorly understood. We describe the outcome and delineate prognostic factors and optimal post-remission therapy in 85 consecutive patients (median age 38 years) treated uniformly in the prospective trial UKALLXII/ECOG2993. The immunophenotype of this leukemia was pro-B (CD10(NEG)). Immaturity was further suggested by high expression of the stem-cell antigens, CD133 and CD135, although CD34 expression was significantly lower than in t(4;11)-negative patients. Complete remission was achieved in 77 (93%) patients but only 35% survived 5 years (95% CI: 25-45%); the relapse rate was 45% (95% CI: 33-58%). Thirty-one patients underwent allogeneic transplantation in first remission (15 sibling donors and 16 unrelated donors): with 5-year survival rates of 56% and 67% respectively, only 2/31 patients relapsed. This compares with a 24% survival rate and 59% relapse rate in 46 patients who received post-remission chemotherapy. A major determinant of outcome was age with 71% of patients aged <25 years surviving. Younger patients had lower relapse rates (19%) but most received allografts in first complete remission. In conclusion, multivariate analysis did not demonstrate an advantage of allografting over chemotherapy but only five younger patients received chemotherapy. Prospective trials are required to determine whether poor outcomes in older patients can be improved by reduced-intensity conditioning allografts. NCT00002514 www.clinicaltrials.gov.

Hypersensitivity to mosquito bites associated with natural killer cell-derived large granular lymphocyte lymphocytosis: a case report in Korea

Hypersensitivity to mosquito bites (HMB) is characterized by intense skin reactions at bite sites. The pathogenesis of HMB might be related to clonal lymphoproliferation of Epstein-Barr virus DNA-positive natural killer (NK) cells. We report the first case of HMB possibly associated with NK cell-derived large granular lymphocyte (NK-LGL) lymphocytosis in Korea.