Supraphysiological FOXP3 expression in human CAR-Tregs results in improved stability, efficacy, and safety of CAR-Treg products for clinical application.

The forkhead family transcription factor (FOXP3) is an essential regulator for the development of regulatory T cells (Tregs) and orchestrates both suppressive function and Treg lineage identity. Stable expression of FOXP3 enables Tregs to maintain immune homeostasis and prevent autoimmunity. However, under pro-inflammatory conditions, FOXP3 expression in Tregs can become unstable, leading to loss of suppressive function and conversion into pathogenic T effector cells. Therefore, the success of adoptive cell therapy with chimeric antigen receptor (CAR) Tregs is highly dependent on the stability of FOXP3 expression to ensure the safety of the cell product. To warrant the stable expression of FOXP3 in CAR-Treg products, we have developed an HLA-A2-specific CAR vector that co-expresses FOXP3. The transduction of isolated human Tregs with the FOXP3-CAR led to an increase in the safety and efficacy of the CAR-Treg product. In a hostile microenvironment, under pro-inflammatory and IL-2-deficient conditions, FOXP3-CAR-Tregs showed a stable expression of FOXP3 compared to Control-CAR-Tregs. Furthermore, additional exogenous expression of FOXP3 did not induce phenotypic alterations and dysfunctions such as cell exhaustion, loss of functional Treg characteristics or abnormal cytokine secretion. In a humanized mouse model, FOXP3-CAR-Tregs displayed an excellent ability to prevent allograft rejection. Furthermore, FOXP3-CAR-Tregs revealed coherent Treg niche-filling capabilities. Overexpression of FOXP3 in CAR-Tregs has thereby the potential to increase the efficacy and reliability of cellular products, promoting their clinical use in organ transplantation and autoimmune diseases.

Unbalanced translocation der(5;17) resulting in a TP53 loss as recurrent aberration in myelodysplastic syndrome and acute myeloid leukemia with complex karyotype.

A complex karyotype, detected in myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML), is associated with a reduced median survival. The most frequent chromosomal aberrations in complex karyotypes are deletions of 5q and 17p harboring the tumor suppressor gene TP53. The unbalanced translocation der(5;17) involving chromosome 5q and 17p is a recurrent aberration in MDS/AML, resulting in TP53 loss. We analyzed the karyotypes of 178 patients with an unbalanced translocation der(5;17) using fluorescence R-/G-banding analysis. Whenever possible, fluorescence in situ hybridization (FISH) (n = 138/141), multicolor FISH (n = 8), telomere length measurement (n = 9), targeted DNA sequencing (n = 13), array-CGH (n = 7) and targeted RNA sequencing (n = 2) were conducted. The der(5;17) aberration was accompanied with loss of genetic material in 7q (53%), -7 (27%), gain of 21q (29%), +8 (17%) and - 18 (16%) and all analyzed patients (n = 13) showed a (likely) pathogenic variant inTP53. The der(5;17) cohort showed significantly shortened telomeres in comparison to the healthy age-matched controls (P < .05), but there was no significant telomere shortening in comparison to MDS/AML patients with a complex karyotype without der(5;17). No fusion genes resulted from the unbalanced translocation. This study demonstrates that the unbalanced translocation der(5;17) is associated with a biallelic inactivation of TP53 due to a deletion of TP53 in one allele and a pathogenic variant of the second TP53 allele. Since the breakpoints are located within (near-) heterochromatic regions, alterations of DNA methylation or histone modifications may be involved in the generation of der(5;17).

Cdkn1a deletion improves stem cell function and lifespan of mice with dysfunctional telomeres without accelerating cancer formation.

Telomere shortening limits the proliferative lifespan of human cells by activation of DNA damage pathways, including upregulation of the cell cycle inhibitor p21 (encoded by Cdkn1a, also known as Cip1 and Waf1)) (refs. 1-5). Telomere shortening in response to mutation of the gene encoding telomerase is associated with impaired organ maintenance and shortened lifespan in humans and in mice. The in vivo function of p21 in the context of telomere dysfunction is unknown. Here we show that deletion of p21 prolongs the lifespan of telomerase-deficient mice with dysfunctional telomeres. p21 deletion improved hematolymphopoiesis and the maintenance of intestinal epithelia without rescuing telomere function. Moreover, deletion of p21 rescued proliferation of intestinal progenitor cells and improved the repopulation capacity and self-renewal of hematopoietic stem cells from mice with dysfunctional telomeres. In these mice, apoptotic responses remained intact, and p21 deletion did not accelerate chromosomal instability or cancer formation. This study provides experimental evidence that telomere dysfunction induces p21-dependent checkpoints in vivo that can limit longevity at the organismal level.

Histone methyltransferase Suv39h1 deficiency prevents Myc-induced chromosomal instability in murine myeloid leukemias.

Suv39h1 mediates heterochromatin formation in pericentric and telomeric regions by trimethylation of lysine 9 of histone 3 (H3K9me3). Yet, its role in the induction of chromosomal instability is poorly understood. We established a leukemia model by retrovirally expressing Myc in wild-type and histone methyltransferase Suv39h1-deficient hematopoietic cells and characterized the resulting leukemias for chromosomal instability. All mice that received cells overexpressing Myc developed myeloid leukemia with a median survival of 44 days posttransplantation. Myc-overexpressing wild-type leukemias demonstrated clones with numerical chromosomal aberrations (5/16). In secondary transplantations of these leukemic cells, structural changes, mostly end-to-end fusions of chromosomes, appeared (10/12). In contrast, leukemic cells overexpressing Myc with reduced or no Suv39h1 expression had a normal karyotype in primary, secondary, and tertiary transplantations (16/16). Myc-transduced Suv39h1-deficient cells showed less critically short telomeres (P < 0.05) compared with Myc-transduced wild-type bone marrow cells. Gene expression analysis showed upregulation of genes involved in the alternative lengthening of telomeres (ALT) mechanism. Thus, we hypothesize that loss of Suv39h1 implies activation of the ALT mechanism, in turn ensuring telomere length and stability. Our data show for the first time that Suv39h1 deficiency may prevent chromosomal instability by more efficient telomere stabilization in hematopoietic bone marrow cells overexpressing Myc.

Development of Beta-Amyloid-Specific CAR-Tregs for the Treatment of Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative disease that remains uncured. Its pathogenesis is characterized by the formation of ß-amyloid (Aß) plaques. The use of antigen-specific regulatory T cells (Tregs) through adoptive transfer has shown promise for the treatment of many inflammatory diseases, although the effectiveness of polyspecific Tregs is limited. Obtaining a sufficient number of antigen-specific Tregs from patients remains challenging. AIMS AND METHODS: To address this problem, we used an antibody-like single-chain variable fragment from a phage library and subsequently generated a chimeric antigen receptor (CAR) targeting ß-amyloid. RESULTS: The ß-amyloid-specific CARs obtained were stimulated by both recombinant and membrane-bound Aß isolated from the murine brain. The generated CAR-Tregs showed a normal Treg phenotype, were antigen-specific activatable, and had suppressive capacity. CONCLUSION: This study highlights the potential of CAR technology to generate antigen-specific Tregs and presents novel approaches for developing functional CARs.

BCR-ABL1 positive AML or CML in blast crisis? A pediatric case report with inv(3) and t(9;22) in the initial clone.

The co-occurrence of an inversion inv(3)(q21q26)/GATA2-MECOM and a Philadelphia translocation t(9;22)(q34;q11)/BCR-ABL1 in the context of chronic myeloid leukemia (CML) in blast crisis or acute myeloid leukemia (AML) has only rarely been described. To our knowledge, this co-occurrence has been reported in six pediatric patients with CML but not in pediatric patients with AML. Here, we report on a 7-year-old girl, who, presented with a t(9;22) and inv(3) in 14 of 15 metaphases and an additional monosomy 7 was detected in 5 of these metaphases (ISCN: 46,​XX,​inv(3)(q21q26),​t(9;22)(q34q11)[9]/45,​idem,​-7[5]/46,​XX[1]). The p190 BCR-ABL1 fusion transcript was detected by multiplex PCR and targeted RNA sequencing. Due to these results, a clear distinction between a CML in blast crisis and a BCR-ABL1 positive AML was not possible. The patient was treated according to the treatment recommendations of the AML-BFM study group and additionally received tyrosine kinase inhibitor therapy (Dasatinib). The treatment with Dasatinib was successful in eliminating the inv(3)/t(9;22) clone, but the ancestral inv(3) clone persisted. Based upon these findings we diagnosed an AML with inv(3) and a secondary acquisition of t(9;22). This treatment as well as an allogenic transplantation has led to a complete remission of the disease up to this date (21 months post diagnosis).

Author Correction: Cdkn1a deletion improves stem cell function and lifespan of mice with dysfunctional telomeres without accelerating cancer formation.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Establishing a murine xenograft-model for long-term analysis of factors inducing chromosomal instability in myelodysplastic syndrome: Pitfalls and successes.

Myelodysplastic syndromes (MDS) are difficult to culture long-term showing the need of a model to study the fate of cells with MDS-abnormalities associated with chromosomal instability (CIN). This approach to establish a xenograft model transplanting human hematopoietic stem cells (HSC) with different independent lentivirally-mediated MDS-related modifications into immunodeficient mice is a long-lasting and tedious experiment with many parameters and every positive as well as non-functioning intermediate step will help the research community. As the establishment of appropriate xenograft models is increasing worldwide we aim to share our experiences to contribute toward minimizing loss of mice and following the "right" approach. Here, modified HSCs were intrafemorally transplanted into NSG and/or NSGS mice: (1) RPS14-haploinsufficiency, (2) TP53-deficiency, (3) TP53 hotspot mutations (R248W, R175H, R273H, R249S). Engraftment was achieved and cytogenetic analyses showed human cells with normal karyotypes. However, in all experiments with NSG mice, mainly control cells or GFP-negative cells were engrafted, not allowing observation of modified HSCs. In NSGS mice, engraftment rate was higher, but mice developed graft-versus-host disease. In summary, engraftment of HSCs is promising and could be used to analyze the induction of CIN. However, the analysis of modified HSCs is limited and further experiments are required to improve this model.

Telomerase deletion limits progression of p53-mutant hepatocellular carcinoma with short telomeres in chronic liver disease.

BACKGROUND & AIMS: During early stages of carcinogenesis most human epithelial cancers including hepatocellular carcinoma (HCC) have been observed to transit through a "crisis" stage characterized by telomere shortening, loss of p53 checkpoint function, and a sharp increase in aneuploidy. The function of telomerase during in vivo hepatocarcinogenesis has not been studied in this genetic context. METHODS: Here we generated a mouse model in which HCC was induced by chronic organ damage (HBs-AG transgene) in the presence of telomere shortening and p53 deletion. Tumor development was analyzed in late-generation telomerase knockout mice (mTERC(-/-)) and littermates, genetically rescued for telomerase gene expression (mTERC(+/-)). RESULTS: The formation of HCCs was strongly suppressed in mTERC(-/-) mice compared to mTERC(+/-) siblings correlating with reduced rates of tumor cell proliferation and elevated rates of tumor cell apoptosis. Although the prevalence of short telomeres was similar in chronically damaged liver of both cohorts, mTERC(-/-) HCC developed increased levels of DNA damage and aneuploidy compared to mTERC(+/-) HCC. CONCLUSIONS: This study provides direct evidence that telomerase is a critical component for in vivo progression of p53 mutant HCC with short telomeres in the chronically damaged liver. In this molecular context, telomerase limits the accumulation of telomere dysfunction, the evolution of excessive aneuploidy, and the activation of p53-independent checkpoints suppressing hepatocarcinogenesis.