A new biodegradable, photocrosslinkable and multifunctional macromer, poly(6-aminohexyl propylene phosphate) (PPE-HA)-ACRL, was synthesized by conjugation of acrylate groups to the side chains of PPE-HA. By controlling the synthetic conditions, different weight fractions of acrylate in the macromers were achieved as confirmed by 1 H NMR. The hydrogels obtained from PPE-HA-ACRL through photocrosslinking were dominantly elastic. With increasing acrylate contents in the macromers, the hydrogels exhibited a lower swelling ratio and higher mechanical strength. The hydrogels with different crosslinking densities lost between 4.3% and 37.4% of their mass in 84 days when incubated in phosphate-buffered saline at 37 °C. No significant cytotoxicity of the macromers against bone marrow-derived mesenchymal stem cells from goat (GMSC) was observed at a concentration up to 10 mg/ml. Finally, GMSCs encapsulated in the photopolymerized gel maintained their viability when cultured in osteogenic medium for three weeks. Clear mineralization in the hydrogel scaffold was revealed by Von Kossa staining. This study suggests the potential of these biodegradable and photocrosslinkable as injectable tissue engineering scaffolds.

BackgroundGlioblastoma (GBM) is refractory to immune checkpoint inhibitor (ICI) therapy. We sought to determine to what extent this immune evasion is due to intrinsic properties of the tumor cells versus the specialized immune context of the brain, and if it can be reversed.MethodsWe used CyTOF mass cytometry to compare the tumor immune microenvironments (TIME) of human tumors that are generally ICI-refractory (GBM and sarcoma) or ICI-responsive (renal cell carcinoma), as well as mouse models of GBM that are ICI-responsive (GL261) or ICI-refractory (SB28). We further compared SB28 tumors grown intracerebrally versus subcutaneously to determine how tumor site affects TIME and responsiveness to dual CTLA-4/PD-1 blockade. Informed by these data, we explored rational immunotherapeutic combinations.ResultsICI-sensitivity in human and mouse tumors was associated with increased T cells and dendritic cells (DCs), and fewer myeloid cells, in particular PD-L1+ tumor-associated macrophages. The SB28 mouse model of GBM responded to ICI when grown subcutaneously but not intracerebrally, providing a system to explore mechanisms underlying ICI resistance in GBM. The response to ICI in the subcutaneous SB28 model required CD4 T cells and NK cells, but not CD8 T cells. Recombinant FLT3L expanded DCs, improved antigen-specific T cell priming, and prolonged survival of mice with intracerebral SB28 tumors, but at the cost of increased Tregs. Targeting PD-L1 also prolonged survival, especially when combined with stereotactic radiation.ConclusionsOur data suggest that a major obstacle for effective immunotherapy of GBM is poor antigen presentation in the brain, rather than intrinsic immunosuppressive properties of GBM tumor cells. Deep immune profiling identified DCs and PD-L1+ tumor-associated macrophages as promising targetable cell populations, which was confirmed using therapeutic interventions in vivo.

Remission durability following single-antigen targeted chimeric antigen receptor (CAR) T-cells is limited by antigen modulation, which may be overcome with combinatorial targeting. Building upon our experiences targeting CD19 and CD22 in B-cell acute lymphoblastic leukemia (B-ALL), we report on the experiences and limitations of a novel MSCV-CD19/CD22-4-1BB bivalent CAR T-cell (CD19.22.BBz). This phase I dose-escalation trial enrolled children and young adults (CAYA) with B-cell malignancies. Primary objectives included toxicity and dose-finding. Secondary objectives included response rates and relapse-free survival (RFS). Biologic correlatives, including CAR T-cell expansion and cytokine profiling, and laboratory investigations, were also analyzed. Twenty patients, ages 5.4-34.6 years, with B-ALL received CD19.22.BBz. The complete response (CR) rate was 60% (12/20) in the full cohort and 71.4% (10/14) in CAR-naïve patients. Ten (50%) developed cytokine release syndrome (CRS), with 3 (15%) having grade 3 CRS and only 1 experiencing any neurotoxicity (grade 3). The 6- and 12-month RFS in those achieving CR was 80.8% (95% CI: 42.4-94.9%) and 57.7% (95% CI: 22.1-81.9%), respectively. Limited CAR T-cell expansion and persistence of MSCV-CD19.22.BBz compared to EF1a-CD22.BBz prompted laboratory investigations comparing EF1a versus MSCV promoters, which did not reveal major differences. Limited CD22 targeting with CD19.22.BBz, as evaluated by ex vivo cytokine secretion and leukemia eradication in humanized mice, led to development of a novel bicistronic CD19.28z/CD22.BBz construct with enhanced cytokine production against CD22. With demonstrated safety and efficacy of CD19.22.BBz in a heavily pre-treated CAYA B-ALL cohort, further optimization of combinatorial antigen targeting serves to overcome identified limitations. (Clinicaltrials.gov NCT03448393)

By increasing disease‐free survival and offering the potential for long‐term cure, chimeric antigen receptor (CAR) T‐cell therapy has dramatically expanded therapeutic options among those with high‐risk B‐cell malignancies. As CAR T‐cell utilization evolves however, novel challenges are generated. These include determining how to optimally integrate CAR T cells into standard of care and overcoming mechanisms of resistance to CAR T‐cell therapy, such as evolutionary stress induced on cancer cells leading to immunophenotypic changes that allow leukemia to evade this targeted therapy. Compounding these challenges are the limited ability to determine differences between various CAR T‐cell constructs, understanding the generalizability of trial outcomes from multiple sites utilizing unique CAR manufacturing strategies, and comparing distinct criteria for toxicity grading while defining optimal management. Additionally, as understanding of CAR behavior in humans has developed, strategies have appropriately evolved to proactively mitigate toxicities. These challenges offer complimentary insights and guide next steps to enhance the efficacy of this novel therapeutic modality. With a focus on B‐cell malignancies as the paradigm for effective CAR T‐cell therapy, this review describes advances in the field as well as current challenges and future directions.