HLA-Fatal attraction

Targeting MHC-I inhibitory pathways for cancer immunotherapy

The MHC-I antigen presentation (AP) pathway is key to shaping mammalian CD8+ T cell immunity, with its aberrant expression closely linked to low tumor immunogenicity and immunotherapy resistance. While significant attention has been given to genetic mutations and downregulation of positive regulators that are essential for MHC-I AP, there is a growing interest in understanding how tumors actively evade MHC-I expression and/or AP through the induction of MHC-I inhibitory pathways. This emerging field of study may offer more viable therapeutic targets for future cancer immunotherapy. Here, we explore potential mechanisms by which cancer cells evade MHC-I AP and function and propose therapeutic strategies that might target these MHC-I inhibitors to restore impaired T cell immunity within the tumor microenvironment (TME).

Clinical Relevance of CD4 Cytotoxic T Cells in High-Risk Neuroblastoma

Neuroblastoma is the most common extracranial childhood solid tumor. The majority of high-risk neuroblastoma is resistant/refractory to the current high intensity therapy, and the survival of these patients remains poor for the last three decades. To effectively treat these extremely unfavorable neuroblastomas, innovative immunotherapy approaches would be the most promising. In this article, we discuss the identity of tumor-infiltrating effector cells and immunosuppressive cells in high-risk neuroblastoma. Neuroblastoma is unique in that it expresses little or no classical HLA Class I and II. In contrast, high-risk neuroblastomas express the stress-responsive non-classical Class I, HLA-E molecule. HLA-E is the ligand of activating receptors NKG2C/E that are expressed on memory NK cells, CD8+T cells and CD4 CTLs. By examining a comprehensive RNA-seq gene expression dataset, we detected relatively high levels of CD4 expression in high-risk neuroblastoma tissues. The majority of CD4+ cells were CD3+, and thus they were likely tumor-associated CD4+T cells. In addition, high-level of both CD4 and NKG2C/E expression was associated with prolonged survival of the high-risk neuroblastoma patients, but CD8 levels were not, further suggesting that the CD4+ NKG2C/E+ T cells or CD4 CTL conferred cytotoxicity against the neuroblastoma cells. However, this T cell mediated- "protective effect" declined over time, in part due to the progressive formation of immunosuppressive tumor microenvironment. These observations suggest that to improve survival of high-risk neuroblastoma patients, it is essential to gain insights into how to enhance CD4 CTL cytotoxicity and control the immunosuppressive tumor microenvironment during the course of the disease.

The Emerging Roles of Human Leukocyte Antigen-F in Immune Modulation and Viral Infection

Human leukocyte antigens (HLAs) play various critical roles in both innate and adaptive immunity through processes such as presenting antigens to T cells and serving as ligands for receptors expressed on natural killer (NK) cells. Among the HLA class I family, the clinical significance and biological function of HLA-F have been the least investigated and have remained elusive for a long period of time. Previous studies have revealed that HLA-F expression might be involved in various physiological and pathological processes, such as pregnancy, viral infection, cancer, transplantation, and autoimmune diseases. However, recent data have shown that, akin to other HLA family members, HLA-F molecules can interact with both activating and inhibitory receptors on immune cells, such as NK cells, and can present a diverse panel of peptides. These important findings pave new avenues for investigations regarding the functions of HLA-F as an important immune regulatory molecule. In the present review, we summarize the studies on the role of HLA-F in immune modulation, with a special emphasis placed on the roles of HLA-F and KIR3DS1 interactions in viral infection.