The human body contains over 500 individual lymph nodes, yet the biology of their formation is poorly understood. Here we identify human lymphoid tissue-inducer cells (LTi cells) as lineage-negative RORC+ CD127+ cells with the functional ability to interact with mesenchymal cells through lymphotoxin and tumor necrosis factor. Human LTi cells were committed natural killer (NK) cell precursors that produced interleukin 17 (IL-17) and IL-22. In vitro, LTi cells gave rise to RORC+ CD127+ NK cells that retained the ability to produce IL-17 and IL-22. Postnatally, similar populations of LTi cell-like cells and RORC+ CD127+ NK cells were present in tonsils, and both secreted IL-17 and IL-22 but no interferon-gamma. Our data indicate that lymph node organogenesis is controlled by an NK cell precursor population with adaptive immune features and demonstrate a previously unappreciated link between the innate and adaptive immune systems.

Chromosomal rearrangements without gene fusions have been implicated in leukemogenesis by causing deregulation of proto-oncogenes via relocation of cryptic regulatory DNA elements. AML with inv(3)/t(3;3) is associated with aberrant expression of the stem-cell regulator EVI1. Applying functional genomics and genome-engineering, we demonstrate that both 3q rearrangements reposition a distal GATA2 enhancer to ectopically activate EVI1 and simultaneously confer GATA2 functional haploinsufficiency, previously identified as the cause of sporadic familial AML/MDS and MonoMac/Emberger syndromes. Genomic excision of the ectopic enhancer restored EVI1 silencing and led to growth inhibition and differentiation of AML cells, which could be replicated by pharmacologic BET inhibition. Our data show that structural rearrangements involving the chromosomal repositioning of a single enhancer can cause deregulation of two unrelated distal genes, with cancer as the outcome.

In CD34 ؉ acute myeloid leukemia (AML), the malignant stem cells reside in the CD38 ؊ compartment. We have shown before that the frequency of such CD34 ؉ CD38 ؊ cells at diagnosis correlates with minimal residual disease (MRD) frequency after chemotherapy and with survival.Specific targeting of CD34 ؉ CD38 ؊ cells might thus offer therapeutic options. Previously, we found that C-type lectin-like molecule-1 (CLL-1) has high expression on the whole blast compartment in the majority of AML cases. We now show that CLL-1 expression is also present on the CD34 ؉ CD38 ؊ stemcell compartment in AML (77/89 patients). The CD34 ؉ CLL-1 ؉ population, containing the CD34 ؉ CD38 ؊ CLL-1 ؉ cells, does engraft in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with outgrowth to CLL-1 ؉ blasts. CLL-1 expression was not different between diagnosis and relapse (n ‫؍‬ 9). In remission, both CLL-1 ؊ normal and CLL-1 ؉ malignant CD34 ؉ CD38 ؊ cells were present. A high CLL-1 ؉ fraction was associated with quick relapse. CLL-1 expression is completely absent both on CD34 ؉ CD38 ؊ cells in normal (n ‫؍‬ 11) and in regenerating bone marrow controls (n ‫؍‬ 6). This IntroductionDespite high-dose chemotherapy, only 30% to 40% of patients with acute myeloid leukemia (AML) survive, which is due mainly to relapse of the disease. 1 AML is generally regarded as a stem-cell disease. However, there is debate whether normal stem cells undergoing leukemogenic mutations is the explanation for leukemogenesis. Alternatively, leukemogenic mutations occurring at a later developmental stage, resulting in stem cell-like behavior, might be an alternative or additional option. [2][3][4] For CD34 ϩ AML, several authors have shown that leukemic stem cells are present in the CD34 ϩ CD38 Ϫ compartment. 5,6 It has been proven in vitro that these stem cells are more resistant to chemotherapy, compared with the progenitor CD34 ϩ CD38 ϩ cells. 7 In vivo, after chemotherapy, the residual malignant CD34 ϩ CD38 Ϫ cells are thought to differentiate to a limited extent, producing leukemic cells with an immunophenotype, which usually reflects that at diagnosis. Sensitive techniques allow early detection of small numbers of these differentiated leukemic cells, called minimal residual disease (MRD), which eventually causes relapse of the disease. 8 Since in this concept the stem cell is the origin of MRD and relapse, stem cell-targeted therapy would be of potentially high benefit for AML patients. Moreover, early detection of leukemic stem cells after chemotherapeutic treatment might offer prognostic value in predicting relapse of the disease. Different options for stem-cell identification and/or targeted therapy have been described such as anti-CD123, anti-CD44, and anti-CD33, but all have some (potential) disadvantages, including expression on normal stem cells and/or nonhematologic tissues. [9][10][11] Since the bone marrow of a (chemotherapy-) treated patient cannot be considered normal, it is extremely important to study whether after treatment nor...

Purpose: In CD34-positive acute myeloid leukemia (AML), the leukemia-initiating event originates from the CD34 + CD38À stem cell compartment. Survival of these cells after chemotherapy may lead to minimal residual disease (MRD) and subsequently to relapse.Therefore, the prognostic impact of stem cell frequency in CD34-positive AML was investigated. Experimental Design: First, the leukemogenic potential of unpurified CD34 + CD38 À cells, present among other cells, was investigated in vivo using nonobese diabetic/severe combined immunodeficient mice transplantation experiments. Second, we analyzed whether the CD34 + CD38À compartment at diagnosis correlates with MRD frequency after chemotherapy and clinical outcome in 92 AML patients. Results: In vivo data showed that engraftment of AML blasts in nonobese diabetic/severe combined immunodeficient mice directly correlated with stem cell frequency of the graft. In patients, a high percentage of CD34 + CD38À stem cells at diagnosis significantly correlated with a high MRD frequency, especially after the third course of chemotherapy. Also, it directly correlated with poor survival. In contrast, total CD34 + percentage showed no such correlations. Conclusions: Both in vivo data, as well as the correlation studies, show that AML stem cell frequency at diagnosis offers a new prognostic factor. From our data, it is tempting to hypothesize that a large CD34 + CD38À population at diagnosis reflects a higher percentage of chemotherapyresistant cells that will lead to the outgrowth of MRD, thereby affecting clinical outcome. Ultimately, future therapies should be directed toward malignant stem cells.

Recently it was shown that, analogous to normal hematopoietic cells, the level of CXC chemokine receptor 4 (CXCR-4) expression on acute myeloid leukemia (AML) cells correlates with stromal cell derived factor-1 alpha (SDF-1)-induced chemotaxis. As we speculated that an anomalous organ distribution of AML cells could affect cell survival and thus result in an altered fraction surviving chemotherapy, we examined a possible correlation between patient prognosis and CXCR-4 expression in AML patients. We found that patients with a high CXCR-4 expression in the CD34 ؉ subset had a significantly reduced survival and a higher probability of relapse, resulting in a median relapsefree survival (