Toward the realization of cell therapy: the advent of MAIT cells from iPSCs

Advancing cell-based cancer immunotherapy through stem cell engineering

Advances in cell-based therapy, particularly CAR-T cell therapy, have transformed the treatment of hematological malignancies. Although an important step forward for the field, autologous CAR-T therapies are hindered by high costs, manufacturing challenges, and limited efficacy against solid tumors. With ongoing progress in gene editing and culture techniques, engineered stem cells and their application in cell therapy are poised to address some of these challenges. Here, we review stem cell-based immunotherapy approaches, stem cell sources, gene engineering and manufacturing strategies, therapeutic platforms, and clinical trials, as well as challenges and future directions for the field.

Development of Stem Cell-Derived Immune Cells for Off-the-Shelf Cancer Immunotherapies

Cell-based cancer immunotherapy has revolutionized the treatment of hematological malignancies. Specifically, autologous chimeric antigen receptor-engineered T (CAR-T) cell therapies have received approvals for treating leukemias, lymphomas, and multiple myeloma following unprecedented clinical response rates. A critical barrier to the widespread usage of current CAR-T cell products is their autologous nature, which renders these cellular products patient-selective, costly, and challenging to manufacture. Allogeneic cell products can be scalable and readily administrable but face critical concerns of graft-versus-host disease (GvHD), a life-threatening adverse event in which therapeutic cells attack host tissues, and allorejection, in which host immune cells eliminate therapeutic cells, thereby limiting their antitumor efficacy. In this review, we discuss recent advances in developing stem cell-engineered allogeneic cell therapies that aim to overcome the limitations of current autologous and allogeneic cell therapies, with a special focus on stem cell-engineered conventional αβ T cells, unconventional T (iNKT, MAIT, and γδ T) cells, and natural killer (NK) cells.

Viral Persistence and Chronicity in Hepatitis C Virus Infection: Role of T-Cell Apoptosis, Senescence and Exhaustion

Hepatitis C virus (HCV) represents a challenging global health threat to ~200 million infected individuals. Clinical data suggest that only ~10–15% of acutely HCV-infected individuals will achieve spontaneous viral clearance despite exuberant virus-specific immune responses, which is largely attributed to difficulties in recognizing the pathognomonic symptoms during the initial stages of exposure to the virus. Given the paucity of a suitable small animal model, it is also equally challenging to study the early phases of viral establishment. Further, the host factors contributing to HCV chronicity in a vast majority of acutely HCV-infected individuals largely remain unexplored. The last few years have witnessed a surge in studies showing that HCV adopts myriad mechanisms to disconcert virus-specific immune responses in the host to establish persistence, which includes, but is not limited to viral escape mutations, viral growth at privileged sites, and antagonism. Here we discuss a few hitherto poorly explained mechanisms employed by HCV that are believed to lead to chronicity in infected individuals. A better understanding of these mechanisms would aid the design of improved therapeutic targets against viral establishment in susceptible individuals.

The role of mucosal-associated invariant T cells in infectious diseases

Mucosal-associated invariant T (MAIT) cells are donor-unrestricted lymphocytes that are surprisingly abundant in humans, representing 1-10% of circulating T cells and further enriched in mucosal tissues. MAIT cells recognize and are activated by small molecule ligands produced by microbes and presented by MR1, a highly conserved MHC-related antigen-presenting protein that is ubiquitously expressed in human cells. Increasing evidence suggests that MAIT cells play a protective role in anti-bacterial immunity at mucosal interfaces. Some fungi are known to produce MAIT-activating ligands, but the role of MAIT cells in fungal infections has not yet been investigated. In viral infections, specifically HIV, which has received the most study, MAIT cell biology is clearly altered, but the mechanisms explaining these alterations and their clinical significance are not yet understood. Many questions remain unanswered about the potential of MAIT cells for protection or pathogenesis in infectious diseases. Because they interact with the universal, donor-unrestricted ligand-presenting MR1 molecule, MAIT cells may be attractive immunotherapy or vaccine targets. New tools, including the development of MR1-ligand tetramers and next-generation T-cell receptor sequencing, have the potential to accelerate MAIT cell research and lead to new insights into the role of this unique set of lymphocytes in infectious diseases.

CD161+ MAIT cells are severely reduced in peripheral blood and lymph nodes of HIV-infected individuals independently of disease progression

Mucosal-associated invariant T (MAIT) cells are characterized by the combined expression of the semi-invariant T cell receptor (TCR) Vα7.2, the lectin receptor CD161, as well as IL-18R, and play an important role in antibacterial host defense of the gut. The current study characterized CD161⁺ MAIT and CD161^–TCRVα7.2⁺ T cell subsets within a large cohort of HIV patients with emphasis on patients with slow disease progression and elite controllers. Mononuclear cells from blood and lymph node samples as well as plasma from 63 patients and 26 healthy donors were analyzed by multicolor flow cytometry and ELISA for IL-18, sCD14 and sCD163. Additionally, MAIT cells were analyzed after in vitro stimulation with different cytokines and/or fixed E.coli. Reduced numbers of CD161⁺ MAIT cells during HIV infection were detectable in the blood and lymph nodes of all patient groups, including elite controllers. CD161⁺ MAIT cell numbers did not recover even after successful antiretroviral treatment. The loss of CD161⁺ MAIT cells was correlated with higher levels of MAIT cell activation; an increased frequency of the CD161^–TCRVα7.2⁺T cell subset in HIV infection was observed. In vitro stimulation of MAIT cells with IL-18 and IL-12, IL-7 and fixed E.coli also resulted in a rapid and additive reduction of the MAIT cell frequency defined by CD161, IL-18R and CCR6. In summary, the irreversible reduction of the CD161⁺ MAIT cell subset seems to be an early event in HIV infection that is independent of later stages of the disease. This loss appears to be at least partially due to the distinctive vulnerability of MAIT cells to the pronounced stimulation by microbial products and cytokines during HIV-infection.

Check MAIT

The evolutionary conservation of T lymphocyte subsets bearing αβ TCRs using invariant α-chains is indicative of unique and important functions. Among these T lymphocytes, NKT cells that express an invariant TCRα-chain and recognize lipid Ags presented by the nonclassical MHC class I molecule CD1d are probably the most studied. However, a new population of evolutionarily conserved T cells with another invariant TCRα rearrangement was recently characterized. These cells, which are very abundant in humans, tend to reside in mucosal tissues and, therefore, were named mucosal-associated invariant T (MAIT) cells. Until recently, little was known about MAIT cells; however, several recent advances in our understanding of MAIT cell characteristics and functions secure their upcoming rise to fame in the immunology field and in clinical practice.