Requirement for cyclin D3 in lymphocyte development and T cell leukemias.

The D-type cyclins (cyclins D1, D2, and D3) are components of the core cell cycle machinery in mammalian cells. Cyclin D3 gene is rearranged and the protein is overexpressed in several human lymphoid malignancies. In order to determine the function of cyclin D3 in development and oncogenesis, we generated and analyzed cyclin D3-deficient mice. We found that cyclin D3(-/-) animals fail to undergo normal expansion of immature T lymphocytes and show greatly reduced susceptibility to T cell malignancies triggered by specific oncogenic pathways. The requirement for cyclin D3 also operates in human malignancies, as knock-down of cyclin D3 inhibited proliferation of acute lymphoblastic leukemias deriving from immature T lymphocytes. These studies point to cyclin D3 as a potential target for therapeutic intervention in specific human malignancies.

Signaling for NKT cell development: the SAP-FynT connection.

New studies demonstrate a critical role for the adaptor protein SAP (SLAM-associated protein) during NKT cell development. By connecting homotypic SLAM family receptor interactions with the FynT Src kinase, SAP may integrate a set of long-standing yet seemingly disparate observations characterizing NKT cell development. In fact, SAP-dependent signaling may underlie the development of multiple unconventional T cell lineages whose thymic selection relies on homotypic interactions between hematopoietic cells.

The BCL2A1 gene as a pre-T cell receptor-induced regulator of thymocyte survival.

The pre-T cell receptor (TCR) is expressed early during T cell development and imposes a tight selection for differentiating T cell progenitors. Pre-TCR-expressing cells are selected to survive and differentiate further, whereas pre-TCR(-) cells are "negatively" selected to die. The mechanisms of pre-TCR-mediated survival are poorly understood. Here, we describe the induction of the antiapoptotic gene BCL2A1 (A1) as a potential mechanism regulating inhibition of pre-T cell death. We characterize in detail the signaling pathway involved in A1 induction and show that A1 expression can induce pre-T cell survival by inhibiting activation of caspase-3. Moreover, we show that in vitro "knockdown" of A1 expression can compromise survival even in the presence of a functional pre-TCR. Finally, we suggest that pre-TCR-induced A1 overexpression can contribute to T cell leukemia in both mice and humans.

Multidisciplinary Responses to the Sexual Victimization of Children: Use of Control Phone Calls.

This descriptive study addresses the question of the value of one-party consent phone calls regarding the sexual victimization of children. The authors reviewed 4 years of experience with children between the ages of 3 and 18 years selected for the control phone calls after a forensic interview by the New York State Police forensic interviewer. The forensic interviewer identified appropriate cases for control phone calls considering New York State law, the child's capacity to make the call, the presence of another person to make the call and a supportive residence. The control phone call process has been extremely effective forensically. Offenders choose to avoid trial by taking a plea bargain thereby dramatically speeding up the criminal judicial and family court processes. An additional outcome of the control phone call is the alleged offender's own words saved the child from the trauma of testifying in court. The control phone call reduced the need for children to repeat their stories to various interviewers. A successful control phone call gives the child a sense of vindication. This technique is the only technique that preserves the actual communication pattern between the alleged victim and the alleged offender. This can be of great value to the mental health professionals working with both the child and the alleged offender. Cautions must be considered regarding potential serious adverse effects on the child. The multidisciplinary team members must work together in the control phone call. The descriptive nature of this study did not allow the authors adequate demographic data, a subject that should be addressed in future prospective study.

Pre-TCRalpha and TCRalpha are not interchangeable partners of TCRbeta during T lymphocyte development.

In contrast with the alphabeta T cell receptor (TCR), the pre-TCR spontaneously segregates to membrane rafts from where it signals in a cell-autonomous fashion. The disparate behaviors of these two receptors may stem either from differences inherent to the distinct developmental stages during which they are expressed, or from features intrinsic and unique to the receptor components themselves. Here, we express TCRalpha precisely at the pre-TCR checkpoint, at levels resembling those of endogenous pre-TCRalpha (pTalpha), and in the absence of endogenous pTalpha. Both in isolation and more dramatically when in competition with pTalpha, TCRalpha induced defective proliferation, survival, and differentiation of alphabeta T lymphocyte precursors, as well as impaired commitment to the alphabeta T lymphocyte lineage. Substitution of TCRalpha transmembrane and cytoplasmic domains with those of pTalpha generated a hybrid molecule possessing enhanced competitive abilities. We conclude that features intrinsic to the pre-TCR, which are absent in TCRalpha, are essential for its unique function.

S1P1 receptor expression regulates emergence of NKT cells in peripheral tissues.

The S1P1 receptor, on the surface of lymphocytes and endothelial cells, regulates the unique trafficking behavior of certain lymphocyte populations. We have examined whether the S1P1 receptor also dictates the distinctive tissue distribution of V alpha14-J alpha18 natural killer T (NKT) cells, whose trafficking pattern is not well understood. Mice (TCS1P1 KO) were established with a conditional deletion of the S1P1 receptor in thymocytes that included precursors of NKT cells. Within the thymus, NKT cells were found at normal or increased levels, indicating that S1P1 receptor expression was dispensable for NKT cell development. However, substantially reduced numbers of NKT cells were detected in the peripheral tissues of the TCS1P1 KO mice. Short-term S1P1 deletion after NKT cells had established residence in the periphery did not substantially alter their distribution in tissues, except for a partial decrease in the spleen. FTY720, a S1P1 receptor ligand that has potent effects on the trafficking of conventional T cells, did not alter the preexisting distribution of NKT cells within peripheral tissues of wild-type mice. Our results indicate that the S1P1 receptor expression on NKT cells is dispensable for development within thymus but is essential for the establishment of their tissue residency in the periphery.

Efficiency of RNA interference in the mouse hematopoietic system varies between cell types and developmental stages.

RNA interference (RNAi) is a naturally occurring posttranscriptional gene-silencing mechanism that has been adapted as a genetic tool for loss-of-function studies of a variety of organisms. It is more widely applicable than classical gene targeting and allows for the simultaneous inactivation of several homologous genes with a single transgene. Recently, RNAi has been used for conditional and conventional gene inactivation in mice. Unlike gene targeting, RNAi is a dynamic process, and its efficiency may vary both between cell types and throughout development. Here we demonstrate that RNAi can be used to target three separately encoded isoforms of the bcl-2 family gene bfl-1/A1 in a conditional manner in mice. The extent of gene inactivation varies between different cell types and is least efficient in mature lymphocytes. Our data suggest that RNAi is affected by factors beyond small interfering RNA-mRNA stoichiometry.

On the brink of becoming a T cell.

Recent studies provide fresh insight into the mechanisms by which precursor cells are committed to and develop within the T-lymphocyte lineage. Precursor/product studies have identified developmental stages between that of the pluripotent hematopoietic stem cell and thymocytes committed to the T lineage. Specific ligands and signaling pathways interacting with the Notch-1 receptor and its ability to influence commitment within the lymphoid lineage have been described. Although the structural features or putative ligands endowing the pre-TCR with constitutive signaling capacity remain elusive, numerous distal mediators of pre-TCR signaling have been identified. It remains for the future to determine what roles they may have in survival, proliferation, lineage commitment and allelic exclusion of TCR genes. Receptor editing and lineage commitment of alphabeta T cells still represent controversial topics that need further study.

Toward understanding and exploiting tumor heterogeneity.

The extent of tumor heterogeneity is an emerging theme that researchers are only beginning to understand. How genetic and epigenetic heterogeneity affects tumor evolution and clinical progression is unknown. The precise nature of the environmental factors that influence this heterogeneity is also yet to be characterized. Nature Medicine, Nature Biotechnology and the Volkswagen Foundation organized a meeting focused on identifying the obstacles that need to be overcome to advance translational research in and tumor heterogeneity. Once these key questions were established, the attendees devised potential solutions. Their ideas are presented here.

Homotypic interactions mediated by Slamf1 and Slamf6 receptors control NKT cell lineage development.

Commitment to the T and natural killer T (NKT) cell lineages is determined during alphabeta T cell receptor (TCR)-mediated interactions of common precursors with ligand-expressing cells in the thymus. Whereas mainstream thymocyte precursors recognize major histocompatibility complex (MHC) ligands expressed by stromal cells, NKT cell precursors interact with CD1d ligands expressed by cortical thymocytes. Here, we demonstrated that such homotypic T-T interactions generated "second signals" mediated by the cooperative engagement of the homophilic receptors Slamf1 (SLAM) and Slamf6 (Ly108) and the downstream recruitment of the adaptor SLAM-associated protein (SAP) and the Src kinase Fyn, which are essential for the lineage expansion and differentiation of the NKT cell lineage. These receptor interactions were required during TCR engagement and therefore only occurred when selecting ligands were presented by thymocytes rather than epithelial cells, which do not express Slamf6 or Slamf1. Thus, the topography of NKT cell ligand recognition determines the availability of a cosignaling pathway that is essential for NKT cell lineage development.

A critical role for the cytoplasmic tail of pTalpha in T lymphocyte development.

Signals that emanate from the pre-T cell receptor (pre-TCR) regulate multiple processes required for the development of the alphabeta T cell lineage. In contrast to the gammadelta TCR, the pre-TCR localizes cell-autonomously to membrane rafts, where it appears to signal in a constitutive and ligand-independent manner. We addressed here the role played by structural features specific to the cytoplasmic domain of the pre-TCRalpha chain (pTalpha). More specifically, we examined a COOH-terminal proline-rich sequence that might play a role in signal transduction and a juxtamembrane cysteine residue that could be a target for palmitoylation, thus allowing spontaneous raft localization. Expression of pTalpha mutants in transgenic mice, retrovirally transduced T cell precursors and cell lines showed that the pTalpha cytoplasmic tail, in particular the proline-rich domain, plays a crucial role in pre-TCR signaling and T cell development. In contrast, the pTalpha juxtamembrane cysteine appeared to be dispensable for pre-TCR function.