Switching on the green light for chimeric antigen receptor T-cell therapy

Scalable intracellular delivery via microfluidic vortex shedding enhances the function of chimeric antigen receptor T-cells

Adoptive chimeric antigen receptor T-cell (CAR-T) therapy is transformative and approved for hematologic malignancies. It is also being developed for the treatment of solid tumors, autoimmune disorders, heart disease, and aging. Despite unprecedented clinical outcomes, CAR-T and other engineered cell therapies face a variety of manufacturing and safety challenges. Traditional methods, such as lentivirus transduction and electroporation, result in random integration or cause significant cellular damage, which can limit the safety and efficacy of engineered cell therapies. We present hydroporation as a gentle and effective alternative for intracellular delivery. Hydroporation resulted in 1.7- to 2-fold higher CAR-T yields compared to electroporation with superior cell viability and recovery. Hydroporated cells exhibited rapid proliferation, robust target cell lysis, and increased pro-inflammatory and regulatory cytokine secretion in addition to improved CAR-T yield by day 5 post-transfection. We demonstrate that scaled-up hydroporation can process 5 x 108 cells in less than 10 s, showcasing the platform as a viable solution for high-yield CAR-T manufacturing with the potential for improved therapeutic outcomes.

Targeting the Tumor Microenvironment in Acute Myeloid Leukemia: The Future of Immunotherapy and Natural Products

The tumor microenvironment (TME) plays an essential role in the development, proliferation, and survival of leukemic blasts in acute myeloid leukemia (AML). Within the bone marrow and peripheral blood, various phenotypically and functionally altered cells in the TME provide critical signals to suppress the anti-tumor immune response, allowing tumor cells to evade elimination. Thus, unraveling the complex interplay between AML and its microenvironment may have important clinical implications and are essential to directing the development of novel targeted therapies. This review summarizes recent advancements in our understanding of the AML TME and its ramifications on current immunotherapeutic strategies. We further review the role of natural products in modulating the TME to enhance response to immunotherapy.

Toward precision immunotherapy using multiplex immunohistochemistry and in silico methods to define the tumor immune microenvironment

Recent developments in cancer immunotherapy promise better outcomes for cancer patients, although clinical trials for difficult to treat cancers such as malignant brain cancer present special challenges, showing little response to first generation immunotherapies. Reasons for differences in immunotherapy response in some cancer types are likely due to the nature of tumor microenvironment, which harbors multiple cell types which interact with tumor cells to establish immunosuppression. The cell types which appear to hold the key in regulating tumor immunosuppression are the tumor-infiltrating immune cells. The current standard treatment for difficult to treat cancer, including the most malignant brain cancer, glioblastoma, continues to offer a bleak outlook for patients. Immune-profiling and correlation with pathological and clinical data will lead to a deeper understanding of the tumor immune microenvironment and contribute toward the selection, optimization and development of novel precision immunotherapies. Here, we review the current understanding of the tumor microenvironmental landscape in glioblastoma with a focus on next-generation technologies including multiplex immunofluorescence and computational approaches to map the brain tumor microenvironment to decipher the role of the immune system in this lethal malignancy.

CRISPR/Cas9 mediated deletion of the adenosine A2A receptor enhances CAR T cell efficacy

Adenosine is an immunosuppressive factor that limits anti-tumor immunity through the suppression of multiple immune subsets including T cells via activation of the adenosine A_2A receptor (A_2AR). Using both murine and human chimeric antigen receptor (CAR) T cells, here we show that targeting A_2AR with a clinically relevant CRISPR/Cas9 strategy significantly enhances their in vivo efficacy, leading to improved survival of mice. Effects evoked by CRISPR/Cas9 mediated gene deletion of A_2AR are superior to shRNA mediated knockdown or pharmacological blockade of A_2AR. Mechanistically, human A_2AR-edited CAR T cells are significantly resistant to adenosine-mediated transcriptional changes, resulting in enhanced production of cytokines including IFNγ and TNF, and increased expression of JAK-STAT signaling pathway associated genes. A_2AR deficient CAR T cells are well tolerated and do not induce overt pathologies in mice, supporting the use of CRISPR/Cas9 to target A_2AR for the improvement of CAR T cell function in the clinic.

IL-15 Preconditioning Augments CAR T Cell Responses to Checkpoint Blockade for Improved Treatment of Solid Tumors

Chimeric antigen receptor (CAR) T cell therapy has been highly successful in hematological malignancies leading to their US Food and Drug Administration (FDA) approval. However, the efficacy of CAR T cells in solid tumors is limited by tumor-induced immunosuppression, leading to the development of combination approaches, such as adjuvant programmed cell death 1 (PD-1) blockade. Current FDA-approved methods for generating CAR T cells utilize either anti-CD3 and interleukin (IL)-2 or anti-CD3/CD28 beads, which can generate a T cell product with an effector/exhausted phenotype. Whereas different cytokine preconditioning milieu, such as IL-7/IL-15, have been shown to promote T cell engraftment, the impact of this approach on CAR T cell responses to adjuvant immune-checkpoint blockade has not been assessed. In the current study, we reveal that the preconditioning of CAR T cells with IL-7/IL-15 increased CAR T cell responses to anti-PD-1 adjuvant therapy. This was associated with the emergence of an intratumoral CD8⁺CD62L⁺TCF7⁺IRF4^- population that was highly responsive to anti-PD-1 therapy and mediated the vast majority of transcriptional and epigenetic changes in vivo following PD-1 blockade. Our data indicate that preservation of CAR T cells in a TCF7⁺ phenotype is crucial for their responsiveness to adjuvant immunotherapy approaches and should be a key consideration when designing clinical protocols.

Adoptive cellular therapy with T cells expressing the dendritic cell growth factor Flt3L drives epitope spreading and antitumor immunity

Adoptive cell therapies using genetically engineered T cell receptor or chimeric antigen receptor T cells are emerging forms of immunotherapy that redirect T cells to specifically target cancer. However, tumor antigen heterogeneity remains a key challenge limiting their efficacy against solid cancers. Here, we engineered T cells to secrete the dendritic cell (DC) growth factor Fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L-secreting T cells expanded intratumoral conventional type 1 DCs and substantially increased host DC and T cell activation when combined with immune agonists poly (I:C) and anti-4-1BB. Importantly, combination therapy led to enhanced inhibition of tumor growth and the induction of epitope spreading towards antigens beyond those recognized by adoptively transferred T cells in solid tumor models of T cell receptor and chimeric antigen receptor T cell therapy. Our data suggest that augmenting endogenous DCs is a promising strategy to overcome the clinical problem of antigen-negative tumor escape following adoptive cell therapy.

CAR T Cells for Acute Myeloid Leukemia: State of the Art and Future Directions

Relapse after conventional chemotherapy remains a major problem in patients with myeloid malignancies such as acute myeloid leukemia (AML), and the major cause of death after diagnosis of AML is from relapsed disease. The only potentially curative treatment option currently available is allogeneic hematopoietic stem cell transplantation (allo-HSCT), which through its graft-vs.-leukemia effects has the ability to eliminate residual leukemia cells. Despite its long history of success however, relapse following allo-HSCT is still a major challenge and is associated with poor prognosis. In the field of adoptive therapy, CD19-targeted chimeric antigen receptor (CAR) T cells have yielded remarkable clinical success in certain types of B-cell malignancies, and substantial efforts aimed at translating this success to myeloid malignancies are currently underway. While complete ablation of CD19-expressing B cells, both cancerous and healthy, is clinically tolerated, the primary challenge limiting the use of CAR T cells in myeloid malignancies is the absence of a dispensable antigen, as myeloid antigens are often co-expressed on normal hematopoietic stem/progenitor cells (HSPCs), depletion of which would lead to intolerable myeloablation. This review provides a discussion on the current state of CAR T cell therapy in myeloid malignancies, limitations for clinical translation, as well as the most recent approaches to overcome these barriers, through various genetic modification and combinatorial strategies in an attempt to make CAR T cell therapy a safe and viable option for patients with myeloid malignancies.

The Immuno-Modulatory Effects of Inhibitor of Apoptosis Protein Antagonists in Cancer Immunotherapy

One of the hallmarks of cancer cells is their ability to evade cell death via apoptosis. The inhibitor of apoptosis proteins (IAPs) are a family of proteins that act to promote cell survival. For this reason, upregulation of IAPs is associated with a number of cancer types as a mechanism of resistance to cell death and chemotherapy. As such, IAPs are considered a promising therapeutic target for cancer treatment, based on the role of IAPs in resistance to apoptosis, tumour progression and poor patient prognosis. The mitochondrial protein smac (second mitochondrial activator of caspases), is an endogenous inhibitor of IAPs, and several small molecule mimetics of smac (smac-mimetics) have been developed in order to antagonise IAPs in cancer cells and restore sensitivity to apoptotic stimuli. However, recent studies have revealed that smac-mimetics have broader effects than was first attributed. It is now understood that they are key regulators of innate immune signalling and have wide reaching immuno-modulatory properties. As such, they are ideal candidates for immunotherapy combinations. Pre-clinically, successful combination therapies incorporating smac-mimetics and oncolytic viruses, as with chimeric antigen receptor (CAR) T cell therapy, have been reported, and clinical trials incorporating smac-mimetics and immune checkpoint blockade are ongoing. Here, the potential of IAP antagonism to enhance immunotherapy strategies for the treatment of cancer will be discussed.

PD-1 disrupted CAR-T cells in the treatment of solid tumors: Promises and challenges

Unprecedented efficacy of chimeric antigen receptor (CAR) T cell therapy in the treatment of hematologic malignancies brings new hope for patients with many cancer types including solid tumors. However, the challenges for CAR-T cell therapy in eradicating solid tumors are immense. To overcome these seemingly intractable hurdles, more "powerful" CAR-T cells with enhanced antitumor efficacy are required. Emerging data support that the anti-tumor activity of CAR-T cells can be enhanced significantly without evident toxicity through simultaneous PD-1 disruption by genome editing. This review focuses on the current progress of PD-1 gene disrupted CAR-T cells in cancer therapy. Here we discuss key rationales for this new combination strategy and summarize the available pre-clinical studies. An update is provided on human clinical studies and available registered cancer clinical trials using CAR-T cells with PD-1 disruption. Future prospects and challenges are also discussed.

Tuning the performance of CAR T cell immunotherapies

BACKGROUND

Simultaneous advances in gene editing, T cell engineering and biotechnology currently provide an opportunity for rapid progress in medicine. The approval of chimeric antigen receptor (CAR) T cell therapies by the US Food and Drug Administration (FDA) and the European Commission have generated substantial momentum for these first-in-class therapies to be used in patients with B cell malignancies.

MAIN BODY

Considerable efforts focus on improved outcomes and reduced side effects of the newly approved therapies. Using innovative strategies, researchers aim to extend CAR T cell use to tackle difficulties inherent in solid tumors. Efforts are underway to broaden the applications of CAR T cells, and the strategy has been successful in chronic viral infections and preclinical models of autoimmunity. Research is in progress to generate "off-the-shelf" CAR T cells, an advance, which would greatly increase patient availability and reduce treatment cost.

CONCLUSIONS

In this thematic review, we highlight advances that may help develop genetically engineered cells into a new category of medical therapies.

Targeting STAT3 and STAT5 in Tumor-Associated Immune Cells to Improve Immunotherapy

Oncogene-induced STAT3-activation is central to tumor progression by promoting cancer cell expression of pro-angiogenic and immunosuppressive factors. STAT3 is also activated in infiltrating immune cells including tumor-associated macrophages (TAM) amplifying immune suppression. Consequently, STAT3 is considered as a target for cancer therapy. However, its interplay with other STAT-family members or transcription factors such as NF-κB has to be considered in light of their concerted regulation of immune-related genes. Here, we discuss new attempts at re-educating immune suppressive tumor-associated macrophages towards a CD8 T cell supporting profile, with an emphasis on the role of STAT transcription factors on TAM functional programs. Recent clinical trials using JAK/STAT inhibitors highlighted the negative effects of these molecules on the maintenance and function of effector/memory T cells. Concerted regulation of STAT3 and STAT5 activation in CD8 T effector and memory cells has been shown to impact their tumor-specific responses including intra-tumor accumulation, long-term survival, cytotoxic activity and resistance toward tumor-derived immune suppression. Interestingly, as an escape mechanism, melanoma cells were reported to impede STAT5 nuclear translocation in both CD8 T cells and NK cells. Ours and others results will be discussed in the perspective of new developments in engineered T cell-based adoptive therapies to treat cancer patients.