RESUMEN
Malignant transformation of cells depends on accumulation of DNA damage. Over the past years we have learned that the T cell-based immune system frequently responds to the neoantigens that arise as a consequence of this DNA damage. Furthermore, recognition of neoantigens appears an important driver of the clinical activity of both T cell checkpoint blockade and adoptive T cell therapy as cancer immunotherapies. Here we review the evidence for the relevance of cancer neoantigens in tumor control and the biological properties of these antigens. We discuss recent technological advances utilized to identify neoantigens, and the T cells that recognize them, in individual patients. Finally, we discuss strategies that can be employed to exploit cancer neoantigens in clinical interventions.
Asunto(s)
Antígenos de Neoplasias/inmunología , Autoantígenos/inmunología , Vacunas contra el Cáncer/inmunología , Epítopos de Linfocito T/inmunología , Inmunoterapia Adoptiva/métodos , Neoplasias/inmunología , Linfocitos T/inmunología , Animales , Antígenos de Neoplasias/genética , Autoantígenos/genética , Epítopos de Linfocito T/genética , Humanos , Inmunidad Celular , Activación de Linfocitos , Medicina de Precisión , Linfocitos T/trasplanteRESUMEN
T cell responses display two key characteristics. First, a small population of epitope-specific naive T cells expands by several orders of magnitude. Second, the T cells within this proliferating population take on diverse functional and phenotypic properties that determine their ability to exert effector functions and contribute to T cell memory. Recent technological advances in lineage tracing allow us for the first time to study these processes in vivo at single-cell resolution. Here, we summarize resulting data demonstrating that although epitope-specific T cell responses are reproducibly similar at the population level, expansion potential and diversification patterns of the offspring derived from individual T cells are highly variable during both primary and recall immune responses. In spite of this stochastic response variation, individual memory T cells can serve as adult stem cells that provide robust regeneration of an epitope-specific tissue through population averaging. We discuss the relevance of these findings for T cell memory formation and clinical immunotherapy.
Asunto(s)
Células Madre Adultas/inmunología , Diferenciación Celular , Inmunoterapia/métodos , Análisis de la Célula Individual/métodos , Linfocitos T/inmunología , Animales , Biodiversidad , Linaje de la Célula , Proliferación Celular , Diversidad Cultural , Epítopos de Linfocito T/inmunología , Epítopos de Linfocito T/metabolismo , Humanos , Memoria Inmunológica , Activación de LinfocitosRESUMEN
Many approaches to identify therapeutically relevant neoantigens couple tumor sequencing with bioinformatic algorithms and inferred rules of tumor epitope immunogenicity. However, there are no reference data to compare these approaches, and the parameters governing tumor epitope immunogenicity remain unclear. Here, we assembled a global consortium wherein each participant predicted immunogenic epitopes from shared tumor sequencing data. 608 epitopes were subsequently assessed for T cell binding in patient-matched samples. By integrating peptide features associated with presentation and recognition, we developed a model of tumor epitope immunogenicity that filtered out 98% of non-immunogenic peptides with a precision above 0.70. Pipelines prioritizing model features had superior performance, and pipeline alterations leveraging them improved prediction performance. These findings were validated in an independent cohort of 310 epitopes prioritized from tumor sequencing data and assessed for T cell binding. This data resource enables identification of parameters underlying effective anti-tumor immunity and is available to the research community.
Asunto(s)
Antígenos de Neoplasias/inmunología , Epítopos/inmunología , Neoplasias/inmunología , Alelos , Presentación de Antígeno/inmunología , Estudios de Cohortes , Humanos , Péptidos/inmunología , Receptor de Muerte Celular Programada 1 , Reproducibilidad de los ResultadosRESUMEN
Clonal expansion is a core aspect of T cell immunity. However, little is known with respect to the relationship between replicative history and the formation of distinct CD8+ memory T cell subgroups. To address this issue, we developed a genetic-tracing approach, termed the DivisionRecorder, that reports the extent of past proliferation of cell pools in vivo. Using this system to genetically 'record' the replicative history of different CD8+ T cell populations throughout a pathogen-specific immune response, we demonstrate that the central memory T (TCM) cell pool is marked by a higher number of prior divisions than the effector memory T cell pool, owing to the combination of strong proliferative activity during the acute immune response and selective proliferative activity after pathogen clearance. Furthermore, by combining DivisionRecorder analysis with single-cell transcriptomics and functional experiments, we show that replicative history identifies distinct cell pools within the TCM compartment. Specifically, we demonstrate that lowly divided TCM cells display enriched expression of stem-cell-associated genes, exist in a relatively quiescent state, and are superior in eliciting a proliferative recall response upon activation. These data provide the first evidence that a stem-cell-like memory T cell pool that reconstitutes the CD8+ T cell effector pool upon reinfection is marked by prior quiescence.
Asunto(s)
Linfocitos T CD8-positivos , Memoria InmunológicaRESUMEN
New opportunities are needed to increase immune checkpoint blockade (ICB) benefit. Whereas the interferon (IFN)γ pathway harbors both ICB resistance factors and therapeutic opportunities, this has not been systematically investigated for IFNγ-independent signaling routes. A genome-wide CRISPR/Cas9 screen to sensitize IFNγ receptor-deficient tumor cells to CD8 T cell elimination uncovered several hits mapping to the tumor necrosis factor (TNF) pathway. Clinically, we show that TNF antitumor activity is only limited in tumors at baseline and in ICB non-responders, correlating with its low abundance. Taking advantage of the genetic screen, we demonstrate that ablation of the top hit, TRAF2, lowers the TNF cytotoxicity threshold in tumors by redirecting TNF signaling to favor RIPK1-dependent apoptosis. TRAF2 loss greatly enhanced the therapeutic potential of pharmacologic inhibition of its interaction partner cIAP, another screen hit, thereby cooperating with ICB. Our results suggest that selective reduction of the TNF cytotoxicity threshold increases the susceptibility of tumors to immunotherapy.
Asunto(s)
Linfocitos T CD8-positivos/inmunología , Inmunoterapia , Factor de Necrosis Tumoral alfa/metabolismo , Animales , Apoptosis/efectos de los fármacos , Linfocitos T CD8-positivos/citología , Linfocitos T CD8-positivos/metabolismo , Línea Celular Tumoral , Humanos , Proteínas Inhibidoras de la Apoptosis/metabolismo , Interferón gamma/metabolismo , Estimación de Kaplan-Meier , Masculino , Ratones , Ratones Endogámicos C57BL , Neoplasias/mortalidad , Neoplasias/terapia , ARN Guía de Kinetoplastida/metabolismo , Proteína Serina-Treonina Quinasas de Interacción con Receptores/metabolismo , Receptores de Interferón/deficiencia , Receptores de Interferón/genética , Transducción de Señal/efectos de los fármacos , Factor 2 Asociado a Receptor de TNF/deficiencia , Factor 2 Asociado a Receptor de TNF/genética , Factor de Necrosis Tumoral alfa/farmacología , Receptor de Interferón gammaRESUMEN
Tumor immune cell compositions play a major role in response to immunotherapy, but the heterogeneity and dynamics of immune infiltrates in human cancer lesions remain poorly characterized. Here, we identify conserved intratumoral CD4 and CD8 T cell behaviors in scRNA-seq data from 25 melanoma patients. We discover a large population of CD8 T cells showing continuous progression from an early effector "transitional" into a dysfunctional T cell state. CD8 T cells that express a complete cytotoxic gene set are rare, and TCR sharing data suggest their independence from the transitional and dysfunctional cell states. Notably, we demonstrate that dysfunctional T cells are the major intratumoral proliferating immune cell compartment and that the intensity of the dysfunctional signature is associated with tumor reactivity. Our data demonstrate that CD8 T cells previously defined as exhausted are in fact a highly proliferating, clonal, and dynamically differentiating cell population within the human tumor microenvironment.
Asunto(s)
Linfocitos T CD8-positivos/inmunología , Linfocitos T CD8-positivos/metabolismo , Melanoma/inmunología , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD4-Positivos/metabolismo , Humanos , Inmunoterapia , Linfocitos Infiltrantes de Tumor/inmunología , Receptor de Muerte Celular Programada 1/inmunología , Microambiente Tumoral/inmunologíaRESUMEN
Cancer immunotherapies have shown substantial clinical activity for a subset of patients with epithelial cancers. Still, technological platforms to study cancer T-cell interactions for individual patients and understand determinants of responsiveness are presently lacking. Here, we establish and validate a platform to induce and analyze tumor-specific T cell responses to epithelial cancers in a personalized manner. We demonstrate that co-cultures of autologous tumor organoids and peripheral blood lymphocytes can be used to enrich tumor-reactive T cells from peripheral blood of patients with mismatch repair-deficient colorectal cancer and non-small-cell lung cancer. Furthermore, we demonstrate that these T cells can be used to assess the efficiency of killing of matched tumor organoids. This platform provides an unbiased strategy for the isolation of tumor-reactive T cells and provides a means by which to assess the sensitivity of tumor cells to T cell-mediated attack at the level of the individual patient.
Asunto(s)
Leucocitos Mononucleares/citología , Linfocitos T/inmunología , Anciano , Carcinoma de Pulmón de Células no Pequeñas/metabolismo , Carcinoma de Pulmón de Células no Pequeñas/patología , Técnicas de Cultivo de Célula , Técnicas de Cocultivo , Neoplasias Colorrectales/metabolismo , Neoplasias Colorrectales/patología , Femenino , Humanos , Técnicas In Vitro , Interferón gamma/farmacología , Leucocitos Mononucleares/metabolismo , Neoplasias Pulmonares/metabolismo , Neoplasias Pulmonares/patología , Activación de Linfocitos/efectos de los fármacos , Masculino , Persona de Mediana Edad , Linfocitos T/citología , Linfocitos T/efectos de los fármacos , Células Tumorales CultivadasRESUMEN
The immune system can mount T cell responses against tumors; however, the antigen specificities of tumor-infiltrating lymphocytes (TILs) are not well understood. We used yeast-display libraries of peptide-human leukocyte antigen (pHLA) to screen for antigens of "orphan" T cell receptors (TCRs) expressed on TILs from human colorectal adenocarcinoma. Four TIL-derived TCRs exhibited strong selection for peptides presented in a highly diverse pHLA-A∗02:01 library. Three of the TIL TCRs were specific for non-mutated self-antigens, two of which were present in separate patient tumors, and shared specificity for a non-mutated self-antigen derived from U2AF2. These results show that the exposed recognition surface of MHC-bound peptides accessible to the TCR contains sufficient structural information to enable the reconstruction of sequences of peptide targets for pathogenic TCRs of unknown specificity. This finding underscores the surprising specificity of TCRs for their cognate antigens and enables the facile indentification of tumor antigens through unbiased screening.
Asunto(s)
Adenocarcinoma/inmunología , Antígenos de Neoplasias/inmunología , Neoplasias Colorrectales/inmunología , Linfocitos Infiltrantes de Tumor/inmunología , Receptores de Antígenos de Linfocitos T/inmunología , Anciano , Animales , Antígenos de Neoplasias/química , Línea Celular Tumoral , Células Cultivadas , Células HEK293 , Antígenos HLA-A/química , Antígenos HLA-A/inmunología , Humanos , Masculino , Persona de Mediana Edad , Biblioteca de Péptidos , Células Sf9 , SpodopteraRESUMEN
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
RESUMEN
Emerging data show that tissue-resident memory T (TRM) cells play an important protective role at murine and human barrier sites. TRM cells in the epidermis of mouse skin patrol their surroundings and rapidly respond when antigens are encountered. However, whether a similar migratory behavior is performed by human TRM cells is unclear, as technology to longitudinally follow them in situ has been lacking. To address this issue, we developed an ex vivo culture system to label and track T cells in fresh skin samples. We validated this system by comparing in vivo and ex vivo properties of murine TRM cells. Using nanobody labeling, we subsequently demonstrated in human ex vivo skin that CD8+ TRM cells migrated through the papillary dermis and the epidermis, below sessile Langerhans cells. Collectively, this work allows the dynamic study of resident immune cells in human skin and provides evidence of tissue patrol by human CD8+ TRM cells.
Asunto(s)
Linfocitos T CD8-positivos/inmunología , Linfocitos T CD8-positivos/metabolismo , Memoria Inmunológica , Piel/inmunología , Animales , Antígenos/inmunología , Línea Celular Tumoral , Movimiento Celular/inmunología , Epidermis/inmunología , Epidermis/metabolismo , Técnica del Anticuerpo Fluorescente , Humanos , Ratones , Especificidad de Órganos/inmunología , Anticuerpos de Dominio Único/inmunología , Piel/metabolismo , Vacunas de ADN/genética , Vacunas de ADN/inmunologíaRESUMEN
Development of mature blood cell progenies from hematopoietic stem cells involves the transition through lineage-restricted progenitors. The first branching point along this developmental process is thought to separate the erythro-myeloid and lymphoid lineage fate by yielding two intermediate progenitors, the common myeloid and the common lymphoid progenitors (CMPs and CLPs). Here, we use single-cell lineage tracing to demonstrate that so-called CMPs are highly heterogeneous with respect to cellular output, with most individual CMPs yielding either only erythrocytes or only myeloid cells after transplantation. Furthermore, based on the labeling of earlier progenitors, we show that the divergence between the myeloid and erythroid lineage develops within multipotent progenitors (MPP). These data provide evidence for a model of hematopoietic branching in which multiple distinct lineage commitments occur in parallel within the MPP pool.
Asunto(s)
Linaje de la Célula , Hematopoyesis , Células Progenitoras Mieloides/citología , Animales , Eritrocitos/citología , Linfocitos/citología , Ratones , Ratones Endogámicos C57BLRESUMEN
CD4+ T cells can either enhance or inhibit tumour immunity. Although regulatory T cells have long been known to impede antitumour responses1-5, other CD4+ T cells have recently been implicated in inhibiting this response6,7. Yet, the nature and function of the latter remain unclear. Here, using vaccines containing MHC class I (MHC-I) neoantigens (neoAgs) and different doses of tumour-derived MHC-II neoAgs, we discovered that whereas the inclusion of vaccines with low doses of MHC-II-restricted peptides (LDVax) promoted tumour rejection, vaccines containing high doses of the same MHC-II neoAgs (HDVax) inhibited rejection. Characterization of the inhibitory cells induced by HDVax identified them as type 1 regulatory T (Tr1) cells expressing IL-10, granzyme B, perforin, CCL5 and LILRB4. Tumour-specific Tr1 cells suppressed tumour rejection induced by anti-PD1, LDVax or adoptively transferred tumour-specific effector T cells. Mechanistically, HDVax-induced Tr1 cells selectively killed MHC-II tumour antigen-presenting type 1 conventional dendritic cells (cDC1s), leading to low numbers of cDC1s in tumours. We then documented modalities to overcome this inhibition, specifically via anti-LILRB4 blockade, using a CD8-directed IL-2 mutein, or targeted loss of cDC2/monocytes. Collectively, these data show that cytotoxic Tr1 cells, which maintain peripheral tolerance, also inhibit antitumour responses and thereby function to impede immune control of cancer.
Asunto(s)
Antígenos de Neoplasias , Linfocitos T CD4-Positivos , Citotoxicidad Inmunológica , Inmunoterapia , Neoplasias , Linfocitos T Reguladores , Animales , Femenino , Humanos , Masculino , Ratones , Antígenos de Neoplasias/inmunología , Vacunas contra el Cáncer/inmunología , Vacunas contra el Cáncer/uso terapéutico , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD4-Positivos/metabolismo , Línea Celular Tumoral , Quimiocina CCL5/metabolismo , Células Dendríticas/inmunología , Granzimas/metabolismo , Antígenos de Histocompatibilidad Clase I/inmunología , Antígenos de Histocompatibilidad Clase II/inmunología , Interleucina-10/metabolismo , Interleucina-10/inmunología , Ratones Endogámicos C57BL , Neoplasias/inmunología , Neoplasias/terapia , Linfocitos T Reguladores/inmunología , Receptores Inmunológicos/antagonistas & inhibidores , Glicoproteínas de Membrana/antagonistas & inhibidores , Tolerancia Inmunológica , Linfocitos T CD8-positivos/inmunologíaRESUMEN
The cytotoxic activity of myeloid cells is regulated by a balance of signals that are transmitted through inhibitory and activating receptors. The Cluster of Differentiation 47 (CD47) protein, expressed on both healthy and cancer cells, plays a pivotal role in this balance by delivering a "don't eat me signal" upon binding to the Signal-regulatory protein alpha (SIRPα) receptor on myeloid cells. Here, we review the current understanding of the role of the CD47-SIRPα axis in physiological tissue homeostasis and as a promising therapeutic target in, among others, oncology, fibrotic diseases, atherosclerosis, and stem cell therapies. We discuss gaps in understanding and highlight where additional insight will be beneficial to allow optimal exploitation of this myeloid cell checkpoint as a target in human disease.
Asunto(s)
Antígenos de Diferenciación/inmunología , Antígeno CD47/inmunología , Homeostasis/inmunología , Receptores Inmunológicos/inmunología , Transducción de Señal/inmunología , Animales , Antígenos de Diferenciación/metabolismo , Antígeno CD47/metabolismo , Humanos , Inmunoterapia , Células Mieloides/inmunología , Células Mieloides/metabolismo , Neoplasias/inmunología , Neoplasias/metabolismo , Neoplasias/terapia , Unión Proteica/inmunología , Receptores Inmunológicos/metabolismoRESUMEN
T cell responses upon infection display a remarkably reproducible pattern of expansion, contraction, and memory formation. If the robustness of this pattern builds entirely on signals derived from other cell types or if activated T cells themselves contribute to the orchestration of these population dynamics-akin to bacterial quorum regulation-is unclear. Here, we examined this question using time-lapse microscopy, genetic perturbation, bioinformatic predictions, and mathematical modeling. We found that ICAM-1-mediated cell clustering enabled CD8+ T cells to collectively regulate the balance between proliferation and apoptosis. Mechanistically, T cell expressed CD80 and CD86 interacted with the receptors CD28 and CTLA-4 on neighboring T cells; these interactions fed two nested antagonistic feedback circuits that regulated interleukin 2 production in a manner dependent on T cell density as confirmed by in vivo modulation of this network. Thus, CD8+ T cell-population-intrinsic mechanisms regulate cellular behavior, thereby promoting robustness of population dynamics.
Asunto(s)
Antígenos CD28/metabolismo , Linfocitos T CD8-positivos/citología , Linfocitos T CD8-positivos/inmunología , Antígeno CTLA-4/metabolismo , Animales , Antígeno B7-1/metabolismo , Antígeno B7-2/metabolismo , Linfocitos T CD8-positivos/metabolismo , Comunicación Celular , Recuento de Células , Línea Celular , Supervivencia Celular , Rastreo Celular , Células Dendríticas/inmunología , Molécula 1 de Adhesión Intercelular/metabolismo , Interleucina-2/metabolismo , Activación de Linfocitos , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Modelos TeóricosRESUMEN
DNA mismatch repair-deficient (MMR-d) cancers present an abundance of neoantigens that is thought to explain their exceptional responsiveness to immune checkpoint blockade (ICB)1,2. Here, in contrast to other cancer types3-5, we observed that 20 out of 21 (95%) MMR-d cancers with genomic inactivation of ß2-microglobulin (encoded by B2M) retained responsiveness to ICB, suggesting the involvement of immune effector cells other than CD8+ T cells in this context. We next identified a strong association between B2M inactivation and increased infiltration by γδ T cells in MMR-d cancers. These γδ T cells mainly comprised the Vδ1 and Vδ3 subsets, and expressed high levels of PD-1, other activation markers, including cytotoxic molecules, and a broad repertoire of killer-cell immunoglobulin-like receptors. In vitro, PD-1+ γδ T cells that were isolated from MMR-d colon cancers exhibited enhanced reactivity to human leukocyte antigen (HLA)-class-I-negative MMR-d colon cancer cell lines and B2M-knockout patient-derived tumour organoids compared with antigen-presentation-proficient cells. By comparing paired tumour samples from patients with MMR-d colon cancer that were obtained before and after dual PD-1 and CTLA-4 blockade, we found that immune checkpoint blockade substantially increased the frequency of γδ T cells in B2M-deficient cancers. Taken together, these data indicate that γδ T cells contribute to the response to immune checkpoint blockade in patients with HLA-class-I-negative MMR-d colon cancers, and underline the potential of γδ T cells in cancer immunotherapy.
Asunto(s)
Neoplasias del Colon , Genes MHC Clase I , Antígenos de Histocompatibilidad Clase I , Inhibidores de Puntos de Control Inmunológico , Inmunoterapia , Receptores de Antígenos de Linfocitos T gamma-delta , Linfocitos T , Humanos , Neoplasias del Colon/tratamiento farmacológico , Neoplasias del Colon/genética , Neoplasias del Colon/inmunología , Neoplasias del Colon/terapia , Antígenos de Histocompatibilidad Clase I/genética , Antígenos de Histocompatibilidad Clase I/inmunología , Inhibidores de Puntos de Control Inmunológico/farmacología , Inhibidores de Puntos de Control Inmunológico/uso terapéutico , Receptores de Antígenos de Linfocitos T gamma-delta/inmunología , Linfocitos T/inmunología , Microglobulina beta-2/deficiencia , Microglobulina beta-2/genética , Reparación de la Incompatibilidad de ADN/genética , Receptores KIR , Línea Celular Tumoral , Organoides , Presentación de Antígeno , Genes MHC Clase I/genéticaRESUMEN
BACKGROUND: Mismatch repair-deficient (dMMR) tumors can be found in 10 to 15% of patients with nonmetastatic colon cancer. In these patients, the efficacy of chemotherapy is limited. The use of neoadjuvant immunotherapy has shown promising results, but data from studies of this approach are limited. METHODS: We conducted a phase 2 study in which patients with nonmetastatic, locally advanced, previously untreated dMMR colon cancer were treated with neoadjuvant nivolumab plus ipilimumab. The two primary end points were safety, defined by timely surgery (i.e., ≤2-week delay of planned surgery owing to treatment-related toxic events), and 3-year disease-free survival. Secondary end points included pathological response and results of genomic analyses. RESULTS: Of 115 enrolled patients, 113 (98%; 97.5% confidence interval [CI], 93 to 100) underwent timely surgery; 2 patients had surgery delayed by more than 2 weeks. Grade 3 or 4 immune-related adverse events occurred in 5 patients (4%), and none of the patients discontinued treatment because of adverse events. Among the 111 patients included in the efficacy analysis, a pathological response was observed in 109 (98%; 95% CI, 94 to 100), including 105 (95%) with a major pathological response (defined as ≤10% residual viable tumor) and 75 (68%) with a pathological complete response (0% residual viable tumor). With a median follow-up of 26 months (range, 9 to 65), no patients have had recurrence of disease. CONCLUSIONS: In patients with locally advanced dMMR colon cancer, neoadjuvant nivolumab plus ipilimumab had an acceptable safety profile and led to a pathological response in a high proportion of patients. (Funded by Bristol Myers Squibb; NICHE-2 ClinicalTrials.gov number, NCT03026140.).
Asunto(s)
Antineoplásicos Inmunológicos , Protocolos de Quimioterapia Combinada Antineoplásica , Neoplasias del Colon , Reparación de la Incompatibilidad de ADN , Ipilimumab , Terapia Neoadyuvante , Nivolumab , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Humanos , Masculino , Persona de Mediana Edad , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Protocolos de Quimioterapia Combinada Antineoplásica/efectos adversos , Neoplasias del Colon/tratamiento farmacológico , Neoplasias del Colon/genética , Neoplasias del Colon/patología , Neoplasias del Colon/cirugía , Supervivencia sin Enfermedad , Ipilimumab/administración & dosificación , Ipilimumab/efectos adversos , Ipilimumab/uso terapéutico , Nivolumab/administración & dosificación , Nivolumab/efectos adversos , Nivolumab/uso terapéutico , Tiempo de Tratamiento , Antineoplásicos Inmunológicos/administración & dosificación , Antineoplásicos Inmunológicos/efectos adversos , Antineoplásicos Inmunológicos/uso terapéutico , Países Bajos , Adulto JovenRESUMEN
Expression of programmed death-ligand 1 (PD-L1) is frequently observed in human cancers. Binding of PD-L1 to its receptor PD-1 on activated T cells inhibits anti-tumor immunity by counteracting T cell-activating signals. Antibody-based PD-1-PD-L1 inhibitors can induce durable tumor remissions in patients with diverse advanced cancers, and thus expression of PD-L1 on tumor cells and other cells in the tumor microenviroment is of major clinical relevance. Here we review the roles of the PD-1-PD-L1 axis in cancer, focusing on recent findings on the mechanisms that regulate PD-L1 expression at the transcriptional, posttranscriptional, and protein level. We place this knowledge in the context of observations in the clinic and discuss how it may inform the design of more precise and effective cancer immune checkpoint therapies.