A human postnatal lymphoid progenitor capable of circulating and seeding the thymus

Identification of a thymus-seeding progenitor originating from human bone marrow (BM) constitutes a key milestone in understanding the mechanisms of T cell development and provides new potential for correcting T cell deficiencies. We report the characterization of a novel lymphoid-restricted subset, which is part of the lineage-negative CD34⁺CD10⁺ progenitor population and which is distinct from B cell–committed precursors (in view of the absence of CD24 expression). We demonstrate that these Lin⁻CD34⁺CD10⁺CD24⁻ progenitors have a very low myeloid potential but can generate B, T, and natural killer lymphocytes and coexpress recombination activating gene 1, terminal deoxynucleotide transferase, PAX5, interleukin 7 receptor α, and CD3ε. These progenitors are present in the cord blood and in the BM but can also be found in the blood throughout life. Moreover, they belong to the most immature thymocyte population. Collectively, these findings unravel the existence of a postnatal lymphoid-polarized population that is capable of migrating from the BM to the thymus.     

Backward masking during rapid serial visual presentation affects the amplitude but not the latency of the P3 event‐related potential

Masking of the first target in the attentional blink (AB) paradigm increases the magnitude of the AB relative to when the first target is not masked. We examined the underlying causes of this effect in an experiment in which a single target was presented in a rapid visual serial presentation stream. The P3 to the target was isolated by subtracting infrequent target category trials from frequent target category trials. The item immediately trailing the target (i.e., the mask) was present in the masked condition and replaced by a blank screen in the not‐masked condition, reproducing conditions known to modulate the AB. Masking the target significantly reduced the amplitude of the target‐locked P3 but had no effect on P3 latency. Results are discussed in relation to previous findings in the AB literature.     

Cytokines and culture medium have a major impact on human in vitro T-cell differentiation

An important proof of principle has been achieved with the development of an in vitro T-cell differentiation assay based on the coculture of hematopoietic progenitors with the OP9-Delta1 stromal cell line. The original murine T cell differentiation assay has since been adapted for human T-cell differentiation, however with lower efficiency. The choice of both medium and cytokines is crucial in this assay, therefore our work has been focused on these two factors. The use of freshly reconstituted medium, the optimization of interleukine-7 (IL-7) concentration, and the addition of stem cell factor (SCF) have allowed to improve the proliferation of progenitors and T-cell precursors as well as the yield of double positive CD4+CD8+ T cells, and mature γδ and αβ T cells. These optimizations make the OP9-Delta1 system sensitive enough to perform both quantitative and qualitative assays with various type of progenitors, including those transduced by a retroviral vector. The improved OP9-Delta1 assay therefore constitutes an extremely useful test for basic research purposes and for translational medicine.     

Insertional oncogenesis in 4 patients after retrovirus-mediated gene therapy of SCID-X1

Previously, several individuals with X-linked SCID (SCID-X1) were treated by gene therapy to restore the missing IL-2 receptor gamma (IL2RG) gene to CD34+ BM precursor cells using gammaretroviral vectors. While 9 of 10 patients were successfully treated, 4 of the 9 developed T cell leukemia 31-68 months after gene therapy. In 2 of these cases, blast cells contained activating vector insertions near the LIM domain-only 2 (LMO2) proto-oncogene. Here, we report data on the 2 most recent adverse events, which occurred in patients 7 and 10. In patient 10, blast cells contained an integrated vector near LMO2 and a second integrated vector near the proto-oncogene BMI1. In patient 7, blast cells contained an integrated vector near a third proto-oncogene,CCND2. Additional genetic abnormalities in the patients' blast cells included chromosomal translocations, gain-of-function mutations activating NOTCH1, and copy number changes, including deletion of tumor suppressor gene CDKN2A, 6q interstitial losses, and SIL-TAL1 rearrangement. These findings functionally specify a genetic network that controls growth in T cell progenitors. Chemotherapy led to sustained remission in 3 of the 4 cases of T cell leukemia, but failed in the fourth. Successful chemotherapy was associated with restoration of polyclonal transduced T cell populations. As a result, the treated patients continued to benefit from therapeutic gene transfer.