The clinical dilemma of JAK inhibitor failure in myelofibrosis: Predictive characteristics and outcomes

Two Janus-associated kinase inhibitors (JAKi) (initially ruxolitinib and, more recently, fedratinib) have been approved as treatment options for patients who have intermediate-risk and high-risk myelofibrosis (MF), with pivotal trials demonstrating improvements in spleen volume, disease symptoms, and quality of life. At the same time, however, clinical trial experiences with JAKi agents in MF have demonstrated a high frequency of discontinuations because of adverse events or progressive disease. In addition, overall survival benefits and clinical and molecular predictors of response have not been established in this population, for which the disease burden is high and treatment options are limited. Consistently poor outcomes have been documented after JAKi discontinuation, with survival durations after ruxolitinib ranging from 11 to 16 months across several studies. To address such a high unmet therapeutic need, various non-JAKi agents are being actively explored (in combination with ruxolitinib in first-line or salvage settings and/or as monotherapy in JAKi-pretreated patients) in phase 3 clinical trials, including pelabresib (a bromodomain and extraterminal domain inhibitor), navitoclax (a B-cell lymphoma 2/B-cell lymphoma 2-xL inhibitor), parsaclisib (a phosphoinositide 3-kinase inhibitor), navtemadlin (formerly KRT-232; a murine double-minute chromosome 2 inhibitor), and imetelstat (a telomerase inhibitor). The breadth of data expected from these trials will provide insight into the ability of non-JAKi treatments to modify the natural history of MF.     

Gene Delivery to Human B-Precursor Acute Lymphoblastic Leukemia Cells

Autologous leukemia cells engineered to express immune-stimulatingmolecules may be used to elicit antileukemia immune responses. Genedelivery to human B-precursor acute lymphoblastic leukemia (ALL) cellswas investigated using the enhanced green fluorescent protein (EGFP) asa reporter gene, measured by flow cytometry. Transfection of the Nalm-6and Reh B-precursor ALL leukemia cell lines with an expression plasmidwas investigated using lipofection, electroporation, and a polycationiccompound. Only the liposomal compound Cellfectin showed significantgene transfer (3.9% to 12% for Nalm-6 cells and 3.1% to 5% for Rehcells). Transduction with gibbon-ape leukemia virus pseudotyped Moloneymurine leukemia virus (MoMuLV)-based retrovirus vectors wasinvestigated in various settings. Cocultivation of ALL cell lines withpackaging cell lines showed the highest transduction efficiency forretroviral gene transfer (40.1% to 87.5% for Nalm-6 cells and 0.3%to 9% for Reh cells), followed by transduction with viral supernatant on the recombinant fibronectin fragment CH-296 (13% to 35.5% for Nalm-6 cells and 0.4% to 6% Reh cells), transduction on human bonemarrow stroma monolayers (3.2% to 13.3% for Nalm-6 cells and 0% to0.2% Reh cells), and in suspension with protamine sulfate (0.7% to3.1% for Nalm-6 cells and 0% for Reh cells). Transduction of bothNalm-6 and Reh cells with human immunodeficiency virus-type 1 (HIV-1)-based lentiviral vectors pseudotyped with the vesicular stomatitis virus-G envelope produced the best gene transfer efficiency, transducing greater than 90% of both cell lines. Gene delivery intoprimary human B-precursor ALL cells from patients was then investigatedusing MoMuLV-based retrovirus vectors and HIV-1-based lentivirusvectors. Both vectors transduced the primary B-precursor ALL cells withhigh efficiencies. These studies may be applied for investigating genedelivery into primary human B-precursor ALL cells to be used forimmunotherapy.     

Competitive control of the self-renewing T cell repertoire

We develop a mathematical model for the self-renewing part of the T cell repertoire. Assuming that self-renewing T cells have to be stimulated by immunogenic MHC-peptide complexes presented on the surfaces of antigen-presenting cells, we derive a model of T cell growth in which competition for MHC-peptide complexes limits T cell clone sizes and regulates the total number of self-renewing T cells in the animal. We show that for a sufficient diversity and/or degree of cross-reactivity, the total T cell number hardly depends upon the diversity of the T cell repertoire or the diversity of the set of presented peptides. Conversely, for repertoires of lower diversity and/or cross-reactivity, steady-state total T cell numbers may be limited by the diversity of the T cells. This provides a possible explanation for the limited repertoire expansion in some, but not all, mouse T cell re-constitution experiments. We suggest that the competitive interactions described by our model underlie the normal T cells numbers observed in transgenic mice, germ-free mice and various knockout mice.      

Localization of a gene for otosclerosis to chromosome 15q25-q26

Among white adults otosclerosis is the single most common cause of hearing impairment. Although the genetics of this disease are controversial, the majority of studies indicate autosomal dominant inheritance with reduced penetrance. We studied a large multi- generational family in which otosclerosis has been inherited in an autosomal dominant pattern. Five of16 affected persons have surgically confirmed otosclerosis; the remaining nine have a conductive hearing loss but have not undergone corrective surgery. To locate the disease- causing gene we completed genetic linkage analysis using short tandem repeat polymorphisms (STRPs) distributed over the entire genome. Multipoint linkage analysis showed that only one genomic region, on chromosome 15q, generated a lod score >2.0. Additional STRPs were typed in this area, resulting in a lod score of 3.4. STRPs FES (centromeric) and D15S657 (telomeric) flank the 14. 5 cM region that contains an otosclerosis gene.      

IMPT1, an imprinted gene similar to polyspecific transporter and multi- drug resistance genes

Human chromosome 11p15.5 and distal mouse chromosome 7 include a megabase-scale chromosomal domain with multiple genes subject to parental imprinting. Here we describe mouse and human versions of a novel imprinted gene, IMPT1 , which lies between IPL and p57 KIP2 and which encodes a predicted multi-membrane-spanning protein similar to bacterial and eukaryotic polyspecific metabolite transporter and multi- drug resistance pumps. Mouse Impt1 and human IMPT1 mRNAs are highly expressed in tissues with metabolite transport functions, including liver, kidney, intestine, extra-embryonic membranes and placenta, and there is strongly preferential expression of the maternal allele in various mouse tissues at fetal stages. In post-natal tissues there is persistent expression, but the allelic bias attenuates. An allelic expression bias is also observed in human fetal and post-natal tissues, but there is significant interindividual variation and rare somatic allele switching. The fact that Impt1 is relatively repressed on the paternal allele, together with data from other imprinted genes, allows a statistical conclusion that the primary effect of human chromosome 11p15.5/mouse distal chromosome 7 imprinting is domain-wide relative repression of genes on the paternal homolog. Dosage regulation of the metabolite transporter gene(s) by imprinting might regulate placental and fetal growth.