Key Points: Standardized flow cytometry allows highly sensitive MRD measurements in virtually all BCP-ALL patients. If sufficient cells are measured (>4 million), flow cytometric MRD analysis is at least as sensitive as current PCR-based MRD methods.

Multiple myeloma remains largely incurable. However, a few patients experience more than 10 years of relapse-free survival and can be considered as operationally cured. Interestingly, long-term disease control in multiple myeloma is not restricted to patients with a complete response, since some patients revert to having a profile of monoclonal gammopathy of undetermined significance. We compared the distribution of multiple compartments of lymphocytes and dendritic cells in the bone marrow and peripheral blood of multiple myeloma patients with long-term disease control (n=28), patients with newly diagnosed monoclonal gammopathy of undetermined significance (n=23), patients with symptomatic multiple myeloma (n=23), and age-matched healthy adults (n=10). Similarly to the patients with monoclonal gammopathy of undetermined significance and symptomatic multiple myeloma, patients with long-term disease control showed an expansion of cytotoxic CD8⁺ T cells and natural killer cells. However, the numbers of bone marrow T-regulatory cells were lower in patients with long-term disease control than in those with symptomatic multiple myeloma. It is noteworthy that B cells were depleted in patients with monoclonal gammopathy of undetermined significance and in those with symptomatic multiple myeloma, but recovered in both the bone marrow and peripheral blood of patients with long-term disease control, due to an increase in normal bone marrow B-cell precursors and plasma cells, as well as pre-germinal center peripheral blood B cells. The number of bone marrow dendritic cells and tissue macrophages differed significantly between patients with long-term disease control and those with symptomatic multiple myeloma, with a trend to cell count recovering in the former group of patients towards levels similar to those found in healthy adults. In summary, our results indicate that multiple myeloma patients with long-term disease control have a constellation of unique immune changes favoring both immune cytotoxicity and recovery of B-cell production and homing, suggesting improved immune surveillance.

Despite attempts to improve the definitions of ambiguous leukemia (ALAL) during the last two decades, general therapy recommendations are missing. Herein, we report a large cohort of children with ALAL and propose a treatment strategy. A retrospective multinational study iBFM-AMBI2012 on 233 cases of pediatric ALAL patients is presented. Survival statistics were used to compare the prognosis of subsets and types of treatment. Five-year event-free survival (5yEFS) of patients with acute lymphoblastic leukemia (ALL)-type primary therapy (80±4%) was superior to that of children who received acute myeloid leukemia (AML)-type or combined-type treatments (36±7.2% and 50±12%, respectively). When ALL- or AML-specific gene fusions were excluded, 5yEFS of CD19^pos leukemia was 83±5.3% on ALL-type primary treatment compared to 0±0% and 28±14% on AML-type and combined-type primary treatment, respectively. Superiority of ALL-type treatment was documented in single-population mixed phenotype ALAL (using WHO and/or EGIL definitions), and in the bilineal ALAL. Treatment with ALL-type protocols is recommended for the majority of pediatric patients with ALAL, including cases with CD19^pos ALAL. AML-type of treatment is preferred in a minority of ALAL cases with CD19^neg and no other lymphoid features ALALs. No overall benefit of transplantation was documented and it could be introduced in some patients with a poor response to treatment. As no clear indicator was found for a change to the treatment type, this is to be considered only in cases with 5% blast or greater after remission induction. The results provide a basis for a prospective trial. Key points The largest cohort of ambiguous leukemias to date reveals a better prognosis of children who started on lymphoid-directed treatment. Myeloid type of primary treatment correlated with dismal outcomes in CD19pos leukemias.

CD4⁺ T cells produce hematopoietic-related cytokines and are essential for hematopoiesis stimulation during infection and hematologic recovery after bone marrow transplantation. However, it remains unclear if T cells are necessary to maintain normal hematopoiesis. We report here that, in T-cell–deficient mice, terminal differentiation of myeloid progenitors is defective, resulting in very low levels of granulocytes in the periphery. Hematopoiesis is restored after thymus graft or reconstitution with CD4⁺ T cells but not CD8⁺ T cells. Bone marrow CD4⁺ T cells have an activated phenotype and produce cytokines, apparently, in the absence of exogenous stimulation. Transgenic mice carrying T-cell receptor specific for an ovalbumin peptide presented in the context of a specific class II molecule (I-A^d) (DO11.10 RAG^–/–) show the same hematopoietic deficiency as athymic mice. Their bone marrow CD4⁺ T cells are not activated, suggesting that hematopoiesis maintenance requires the presence of cognate antigen in order to activate bone marrow T-helper cells. In fact, priming of transgenic mice with ovalbumin restores normal hematopoiesis. The data show that the current concept of “normal hematopoiesis” does not reflect a basal bone marrow activity, but it is an antigen-induced state maintained by constant activation of bone marrow CD4⁺ T cells.