抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Regulatory T Cells and Immune Tolerance

With few exceptions biological tissues strongly scatter light, making high-resolution deep imaging impossible for traditional⎯including confocal⎯fluorescence microscopy. Nonlinear optical microscopy, in particular two photon–excited fluorescence microscopy, has overcome this limitation, providing large depth penetration mainly because even multiply scattered signal photons can be assigned to their origin as the result of localized nonlinear signal generation. Two-photon microscopy thus allows cellular imaging several hundred microns deep in various organs of living animals. Here we review fundamental concepts of nonlinear microscopy and discuss conditions relevant for achieving large imaging depths in intact tissue.

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Deep tissue two-photon microscopy

We have previously shown correction of X-linked severe combined immunodeficiency [SCID-X1, also known as gamma chain (gamma(c)) deficiency] in 9 out of 10 patients by retrovirus-mediated gamma(c) gene transfer into autologous CD34 bone marrow cells. However, almost 3 years after gene therapy, uncontrolled exponential clonal proliferation of mature T cells (with gammadelta+ or alphabeta+ T cell receptors) has occurred in the two youngest patients. Both patients' clones showed retrovirus vector integration in proximity to the LMO2 proto-oncogene promoter, leading to aberrant transcription and expression of LMO2. Thus, retrovirus vector insertion can trigger deregulated premalignant cell proliferation with unexpected frequency, most likely driven by retrovirus enhancer activity on the LMO2 gene promoter.

https://science.sciencemag.org/content/sci/302/5644/415.full.pdf

LMO2-associated clonal T cell proliferation in two patients after gene therapy for SCID-X1.

Immunotherapy is proving to be an effective therapeutic approach in a variety of cancers. But despite the clinical success of antibodies against the immune regulators CTLA4 and PD-L1/PD-1, only a subset of people exhibit durable responses, suggesting that a broader view of cancer immunity is required. Immunity is influenced by a complex set of tumour, host and environmental factors that govern the strength and timing of the anticancer response. Clinical studies are beginning to define these factors as immune profiles that can predict responses to immunotherapy. In the context of the cancer-immunity cycle, such factors combine to represent the inherent immunological status - or 'cancer-immune set point' - of an individual.

Elements of cancer immunity and the cancer–immune set point

Severe combined immunodeficiency-X1 (SCID-X1) is an X-linked inherited disorder characterized by an early block in T and natural killer (NK) lymphocyte differentiation. This block is caused by mutations of the gene encoding the gammac cytokine receptor subunit of interleukin-2, -4, -7, -9, and -15 receptors, which participates in the delivery of growth, survival, and differentiation signals to early lymphoid progenitors. After preclinical studies, a gene therapy trial for SCID-X1 was initiated, based on the use of complementary DNA containing a defective gammac Moloney retrovirus-derived vector and ex vivo infection of CD34+ cells. After a 10-month follow-up period, gammac transgene-expressing T and NK cells were detected in two patients. T, B, and NK cell counts and function, including antigen-specific responses, were comparable to those of age-matched controls. Thus, gene therapy was able to provide full correction of disease phenotype and, hence, clinical benefit.

https://science.sciencemag.org/content/sci/288/5466/669.full.pdf

Gene therapy of human severe combined immunodeficiency (SCID)-X1 disease

The cellular dynamics underlying activation of CD8+ T cells by dendritic cells (DCs) in the lymph node are not known. Here we have tracked the behavior of T cells and DCs by subjecting intact lymph nodes to real-time two-photon microscopy. We show that DCs scan at least 500 different T cells per hour in the absence of antigen. Antigen-bearing DCs are highly efficient in recruiting peptide-specific T cells and can engage more than ten T cells simultaneously. The duration of these interactions is of the order of hours, not minutes. The overall avidity of the interaction influences the probability that T cells will be stably captured by DCs, providing a possible basis for T cell competition. Taken together, our results identify the cellular behaviors that promote an efficient CD8+ T cell response in the lymph node.

Dynamics of CD8+ T cell priming by dendritic cells in intact lymph nodes

https://www.cell.com/immunity/pdf/S1074-7613(00)00080-7.pdf

Impact of Negative Selection on the T Cell Repertoire Reactive to a Self-Peptide: A Large Fraction of T Cell Clones Escapes Clonal Deletion

Recent advances in imaging techniques have allowed researchers to 'spy' on T cells and dendritic cells (DCs) as they interact in intact lymph nodes. In this Review, Philippe Bousso discusses how these studies have provided new insights into the processes that underlie T-cell activation by DCs.

T-cell activation by dendritic cells in the lymph node: lessons from the movies

Thymocytes are selected to mature according to their ability to interact with self major histocompatibility complex (MHC)-peptide complexes displayed on the thymic stroma. Using two-photon microscopy, we performed real-time analysis of the cellular contacts made by developing thymocytes undergoing positive selection in a three-dimensional thymic organ culture. A large fraction of thymocytes within these cultures were highly motile. MHC recognition was found to increase the duration of thymocyte-stromal cell interactions and occurred as both long-lived cellular associations displaying stable cell-cell contacts and as shorter, highly dynamic contacts. Our results identify the diversity and dynamics of thymocyte interactions during positive selection.

https://science.sciencemag.org/content/sci/296/5574/1876.full.pdf

Philippe Bousso

Papers

Gene therapy of human severe combined immunodeficiency (SCID)-X1 disease

Dynamics of CD8+ T cell priming by dendritic cells in intact lymph nodes

Impact of Negative Selection on the T Cell Repertoire Reactive to a Self-Peptide: A Large Fraction of T Cell Clones Escapes Clonal Deletion

T-cell activation by dendritic cells in the lymph node: lessons from the movies

Dynamics of Thymocyte-Stromal Cell Interactions Visualized by Two-Photon Microscopy