Purpose: The application of induced pluripotent stem cell-derived retinal pigmented epithelium (iPSC-RPE) in patients with retinal degenerative disease is making headway toward the clinic, with clinical trials already underway. Multiple groups have developed methods for RPE differentiation from pluripotent cells, but previous studies have shown variability in iPSC propensity to differentiate into RPE. Methods: This study provides a comparison between 2 different methods for RPE differentiation: (1) a commonly used spontaneous continuously adherent culture (SCAC) protocol and (2) a more rapid, directed differentiation using growth factors. Integration-free iPSC lines were differentiated to RPE, which were characterized with respect to global gene expression, expression of RPE markers, and cellular function. Results: We found that all 5 iPSC lines (iPSC-1, iPSC-2, iPSC-3, iPSC-4, and iPSC-12) generated RPE using the directed differentiation protocol; however, 2 of the 5 iPSC lines (iPSC-4 and iPSC-12) did not yield RPE using the SCAC method. Both methods can yield bona fide RPE that expresses signature RPE genes and carry out RPE functions, and are similar, but not identical to fetal RPE. No differences between methods were detected in transcript levels, protein localization, or functional analyses between iPSC-1-RPE, iPSC-2-RPE, and iPSC-3-RPE. Directed iPSC-3-RPE showed enhanced transcript levels of RPE65 compared to directed iPSC-2-RPE and increased BEST1 expression and pigment epithelium-derived factor (PEDF) secretion compared to directed iPSC-1-RPE. In addition, SCAC iPSC-3-RPE secreted more PEDF than SCAC iPSC-1-RPE. Conclusions: The directed protocol is a more reliable method for differentiating RPE from various pluripotent sources and some iPSC lines are more amenable to RPE differentiation.

Soft tissue defects are relatively common, yet currently used reconstructive treatments have varying success rates, and serious potential complications such as unpredictable volume loss and reabsorption. Human adipose-derived stem cells (ASCs), isolated from liposuction aspirate have great potential for use in soft tissue regeneration, especially when combined with a supportive scaffold. To design scaffolds that promote differentiation of these cells down an adipogenic lineage, we characterized changes in the surrounding extracellular environment during adipogenic differentiation. We found expression changes in both extracellular matrix proteins, including increases in expression of collagen-IV and vitronectin, as well as changes in the integrin expression profile, with an increase in expression of integrins such as aVb5 and a1b1. These integrins are known to specifically interact with vitronectin and collagen-IV, respectively, through binding to an Arg-Gly-Asp (RGD) sequence. When three different short RGD-containing peptides were incorporated into three-dimensional (3D) hydrogel cultures, it was found that an RGD-containing peptide derived from vitronectin provided strong initial attachment, maintained the desired morphology, and created optimal conditions for in vitro 3D adipogenic differentiation of ASCs. These results describe a simple, nontoxic encapsulating scaffold, capable of supporting the survival and desired differentiation of ASCs for the treatment of soft tissue defects.

Whole blood fibrin clots capture platelets and release growth factors, and the addition of ASCs increases VEGF release for up to 2 weeks after clot formation. This suggests that whole blood fibrin clots may be a viable scaffold and delivery vehicle for future stem cell treatments.

One of the most common regenerative therapies is autologous fat grafting, which frequently suffers from unexpected volume loss. One approach is to deliver adipose stem cells encapsulated in the engineered hydrogels supportive of cell survival, differentiation, and integration after transplant. We describe an encapsulating, biomimetic poly(ethylene)-glycol hydrogel, with embedded peptides for attachment and biodegradation. Poly(ethylene)-glycol hydrogels containing an Arg–Gly–Asp attachment sequence and a matrix metalloprotease 3/10 cleavage site supported adipose stem cell survival and showed remodeling initiated by adipogenic differentiation. Arg–Gly–Asp–matrix metalloprotease 3/10 cleavage site hydrogels showed an increased number and area of lacunae or holes after adipose stem cell differentiation. Image analysis of adipose stem cells in Arg–Gly–Asp–matrix metalloprotease 3/10 cleavage site hydrogels showed larger Voronoi domains, while cell density remained unchanged. The differentiated adipocytes residing within these newly remodeled spaces express proteins and messenger RNAs indicative of adipocytic differentiation. These engineered scaffolds may provide niches for stem cell differentiation and could prove useful in soft tissue regeneration.

In a phase 1b study of acalabrutinib (a covalent Bruton tyrosine kinase (BTK) inhibitor) in combination with vistusertib (a dual mTORC1/2 inhibitor) in patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL), multiple ascending doses of the combination as intermittent or continuous schedules of vistusertib were evaluated. The overall response rate was 12% (3/25). The pharmacodynamic (PD) profile for acalabrutinib showed that BTK occupancy in all patients was >95%. In contrast, PD analysis for vistusertib showed variable inhibition of phosphorylated 4EBP1 (p4EBP1) without modulation of AKT phosphorylation (pAKT). The pharmacokinetic (PK)/ PD relationship of vistusertib was direct for TORC1 inhibition (p4EBP1) but did not correlate with TORC2 inhibition (pAKT). Cell-of-origin subtyping or next-generation sequencing did not identify a subset of DLBCL patients with clinical benefit; however, circulating tumor DNA dynamics correlated with radiographic response. These data suggest that vistusertib does not modulate targets sufficiently to add to the clinical activity of acalabrutinib monotherapy. Clinicaltrials.gov identifier: NCT03205046.

Regenerative medicine possesses the potential to ameliorate damage to tissue that results from a vast range of conditions, including traumatic injury, tumor resection and inherited tissue defects. Adult stem cells, while more limited in their potential than pluripotent stem cells, are still capable of differentiating into numerous lineages and provide feasible allogeneic and autologous treatment options for many conditions. Adipose stem cells are one of the most abundant types of stem cell in the adult human. Here, we review recent advances in the development of synthetic scaffolding systems used in concert with adipose stem cells and assess their potential use for clinical applications.

Background: Acalabrutinib (ACP-196) is a highly selective, potent Bruton tyrosine kinase (BTK) inhibitor developed to minimize off-target activity. Acalabrutinib monotherapy shows promising safety and efficacy in CLL (Ghia et al 2019). However, a few patients (pts) develop resistance to acalabrutinib. A known mechanism of covalent BTK inhibitor resistance is acquired mutations in BTK (particularly Cys481) and its downstream target PLCg2. Alternate mechanisms and the contribution of the CLL microenvironment to acquired resistance remain to be elucidated. In this study, we performed cell surface phenotyping, intracellular signaling, and RNA-seq analyses on samples from 39 pts with relapsed/refractory or treatment-naive CLL from the ACE-CL-001 clinical trial (NCT02029443) to identify novel mechanisms of acalabrutinib resistance with focus on the CLL microenvironment. Methods : Pts were divided into 2 groups: those who continued to respond to treatment (non-progressed, NP, n=23) and those who developed progressive disease (progressed, PD, n=16) within 36 months of starting acalabrutinib. Blood mononuclear cells (PBMCs) were analyzed after 6 months of acalabrutinib therapy (100 mg twice a day) for the first (NP) group of patients, or at the time of progression for the second (PD) group of patients and compared with pre-treatment baseline. Expression of cell surface markers, including CD49d, CD38, and CD79b, was evaluated by flow cytometry. A 30% positive cut-off was used to identify pts that express high levels of CD49d, an α-chain of the VLA-4 integrin (Tissino, et al 2018), CD38, and CD79b. Intracellular flow cytometry was used to measure cell proliferation via Ki-67 staining. RNA-seq was used to measure changes in gene expression. Results: Cell surface phenotyping showed higher expression of CD49d (p<0.001) and CD79b (p<0.01) at baseline and after treatment (p<0.0001; p=0.017) in pts who progressed compared with pts who continued responding to treatment (Fig 1). CD49d levels decreased in NP pts 6 months after treatment (p=0.016) but remained high in pts who progressed. Increased surface expression of CD49d was associated with increased surface expression of CD38 (p<0.001). There was strong correlation between cell surface expression of CD49d and its transcript ITGA4 by RNA-seq (R=0.78, p<0.0001). Gene expression of CD38 and CD79B also correlated with their protein expression (R=0.8, p<0.0001 and R=0.42, p<0.001). CD49d high pts showed decreased lymphocytosis with lower % change in median absolute lymphocyte count from baseline to 5 months post-treatment, compared with CD49d low pts (Fig 2). CD49d high pts also showed a trend of inferior nodal response with less tumor reduction compared with CD49d low pts. Additionally, high CD49d expression was associated with increased risk of progressive disease in relapsed/refractory pts compared with low CD49d expression (HR=3.66, p=0.045). Previous studies with another BTK inhibitor, ibrutinib, also identified a correlation between expression of CD49d and reduced lymphocytosis, nodal response, and progression-free survival in pts with CLL (Tissino, et al 2018). High CD49d cell surface expression was correlated with increased Ki-67 at baseline and after acalabrutinib treatment (p=0.012, p<0.001). Ki-67 levels decreased in CD49d low pts (p<0.0001), but not in CD49d high pts, after acalabrutinib treatment. CD49d may contribute to acalabrutinib resistance in CLL by enhancing cell survival through adhesion to the tumor microenvironment and may serve as a predictive marker to identify pts at high risk of developing resistance to acalabrutinib. Conclusions: High surface expression of CD49d (VLA-4) and CD79b prior to and after therapy correlates with acalabrutinib resistance in pts with CLL. Targeting CD49d may prove an effective strategy to overcome acalabrutinib resistance in CD49d high pts. Disclosures Bibikova: Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Law:Acerta Pharma: Employment; AstraZeneca: Equity Ownership. Clevenger:Acerta Pharma: Employment; AstraZeneca: Equity Ownership. Cheung:AstraZeneca: Equity Ownership; Acerta Pharma: Employment, Equity Ownership. De Jesus:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Gulrajani:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Yamaguchi:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Do:Acerta Pharma: Employment, Equity Ownership; AstraZeneca: Equity Ownership. Burke:AstraZeneca: Employment, Equity Ownership. Brock:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Munugalavadla:Gilead Sciences: Equity Ownership; AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Frigault:Acerta Pharma: Employment; AstraZeneca: Employment, Equity Ownership. Byrd:Acerta: Research Funding; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Genentech: Research Funding; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Genentech: Research Funding; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; BeiGene: Research Funding; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; BeiGene: Research Funding; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Genentech: Research Funding; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S; Novartis: Other: Travel Expenses, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S. Furman:Acerta Pharma: Consultancy; AstraZeneca: Consultancy; Incyte: Consultancy; Janssen: Consultancy; Beigene: Consultancy; Oncotracker: Consultancy; Pharmacyclics: Consultancy; Sunesis: Consultancy; TG Therapeutics: Consultancy; Verastem: Consultancy; Genentech: Consultancy; Abbvie: Consultancy. Brown:Catapult Therapeutics: Consultancy; AbbVie: Consultancy; Genentech/Roche: Consultancy; Acerta Pharma: Consultancy; Pharmacyclics: Consultancy; Pfizer: Consultancy; Janssen: Honoraria; Teva: Honoraria; AstraZeneca: Consultancy; Octapharma: Consultancy; Invectys: Other: Data safety monitoring board; Morphosys: Other: Data safety monitoring board; Dynamo Therapeutics: Consultancy; BeiGene: Consultancy; TG Therapeutics: Consultancy; Sunesis: Consultancy; Loxo: Consultancy, Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Juno/Celgene: Consultancy; Gilead: Consultancy, Research Funding; Verastem: Consultancy, Research Funding; Sun Pharmaceuticals: Research Funding; Novartis: Consultancy. Covey:AstraZeneca: Equity Ownership; Acerta Pharma: Employment, Equity Ownership.

Background:BTK, a key component of B-cell receptor (BCR) signaling, promotes the interaction of CLL cells with the tumor microenvironment contributing to disease-related lymphadenopathy, splenomegaly, hepatic infiltration, and elevated lymphocyte counts (Montresor 2018). In MF, activated JAK2 increases BTK and NFκ B signaling leading to aberrant CD34 + cell trafficking and dysregulated cytokines (Nimmagadda 2019; Fisher 2019). Novel and improved BTK inhibitors may induce deeper and more durable responses in CLL and offer the potential to improve clinical outcomes in MF. TL-895 is a highly potent, selective, orally available, covalent, small molecule inhibitor of BTK and bone marrow tyrosine kinase X-linked (BMX). TL-895 is being studied in patients (pts) with CLL (NCT02825836) and is the first BTKi being investigated in pts with MF (NCT04655118).