Memory inflation: Beyond the acute phase of viral infection

Memory inflation is confirmed as the most commonly dysregulation of host immunity with antigen-independent manner in mammals after viral infection. By generating large numbers of effector/memory and terminal differentiated effector memory CD8+ T cells with diminished naïve subsets, memory inflation is believed to play critical roles in connecting the viral infection and the onset of multiple diseases. Here, we reviewed the current understanding of memory inflated CD8+ T cells in their distinct phenotypic features that different from exhausted subsets; the intrinsic and extrinsic roles in regulating the formation of memory inflation; and the key proteins in maintaining the expansion and proliferation of inflationary populations. More importantly, based on the evidences from both clinic and animal models, we summarized the potential mechanisms of memory inflation to trigger autoimmune neuropathies, such as Guillain-Barré syndrome and multiple sclerosis; the correlations of memory inflation between tumorigenesis and resistance of tumour immunotherapies; as well as the effects of memory inflation to facilitate vascular disease progression. To sum up, better understanding of memory inflation could provide us an opportunity to beyond the acute phase of viral infection, and shed a light on the long-term influences of CD8+ T cell heterogeneity in dampen host immune homeostasis.

Restoring, releasing or replacing adaptive immunity in chronic hepatitis B

Multiple new therapeutic approaches are currently being developed to achieve sustained, off-treatment suppression of HBV, a persistent hepatotropic infection that kills ~2,000 people a day. A fundamental therapeutic goal is the restoration of robust HBV-specific adaptive immune responses that are able to maintain prolonged immunosurveillance of residual infection. Here, we provide insight into key components of successful T cell and B cell responses to HBV, discussing the importance of different specificities and effector functions, local intrahepatic immunity and pathogenic potential. We focus on the parallels and interactions between T cell and B cell responses, highlighting emerging areas for future investigation. We review the potential for different immunotherapies in development to restore or release endogenous adaptive immunity by direct or indirect approaches, including limitations and risks. Finally, we consider an alternative HBV treatment strategy of replacing failed endogenous immunity with infusions of highly targeted T cells or antibodies.

Precursor exhausted T cells: key to successful immunotherapy?

Cytotoxic T cell immunity in response to chronic infections and tumours is maintained by a specialized population of CD8⁺ T cells that exhibit hallmarks of both exhausted and memory cells and give rise to terminally differentiated exhausted effector cells that contribute to viral or tumour control. Importantly, recent work suggests these cells, which we refer to as 'precursor exhausted' T (T_PEX) cells, are responsible for the proliferative burst that generates effector T cells in response to immune checkpoint blockade targeting programmed cell death 1 (PD1), and increased T_PEX cell frequencies have recently been linked to increased patient survival. We believe the recent discovery of T_PEX cells not only represents a paradigm shift in our understanding of the mechanisms that maintain CD8⁺ T cell responses in chronic infections and tumours but also opens up unexpected avenues for the development of new and innovative therapeutic approaches. In this Opinion article, we discuss the differentiation and function of T_PEX cells and suggest that targeting these cells may be key for successful immunotherapy.

A non-pathogenic Leishmania tarentolae vector based- HCV polytope DNA vaccine elicits potent and long lasting Th1 and CTL responses in BALB/c mice model

Despite successful anti-viral (DAAs) treatment of Hepatitis C virus (HCV) infection, recent data indicated the need for an effective vaccine. Preexisting anti-vector immunity is an obstacle for application of live vectors for antigen delivery and development of effective T-cell based HCV vaccines. Herein, we report construction of recombinant Leishmania tarentolae, a lizard (non-human) parasite, expressing an HCV polytope DNA, PT-NT(gp96), encoding for several immunogenic HCV epitopes and evaluation of its immunogenicity in three different prime/boost immunization groups (G) of BALB/c mice. Homologous prime/boost immunization by L.tarentolae-PT-NT(gp96) either with or without CpG (G1 and G2 respectively) and heterologous immunization with a PT-NT(gp96) encoding-pCDNA plasmid followed by L.tarentolae-PT-NT (G3) was undertaken. Immune responses were measured three and nine weeks (W) post immunization. Splenocytes (cultured with antigen-stimulant) of mice in G1 showed the highest percentage of specific CTL-cytolytic activity compared to G2 and G3 at both short (W3:70.98% versus 41.29% and 13.12%) and long (W9: 50% versus 24.5% and 20%) term periods, accompanied with high levels of secreted IFN-γ. Comparison of IFN-γ, IL-4, IL-17 and TNF-α cytokines levels obtained from the supernatant of antigen-stimulated splenocytes as well as antibodies level (as IgG1/IgG2a ratio; obtained from sera of immunized mice) indicated higher Th1 oriented responses for G1, G2 groups and balanced Th1-Th17 for G3. Results indicated the potential of L.tarentolae (+CpG), as a non-pathogenic live vaccine vector, for delivery and enhancement of immune responses against HCV-polytope antigens.