TIGIT blockade enhances functionality of peritoneal NK cells with altered expression of DNAM-1/TIGIT/CD96 checkpoint molecules in ovarian cancer.

Advanced ovarian cancer (OC) patients have a poor 5-year survival of only 28%, emphasizing the medical need for improved therapies. Adjuvant immunotherapy could be an attractive approach since OC is an immunogenic disease and the presence of tumor-infiltrating lymphocytes has shown to positively correlate with patient survival. Among these infiltrating lymphocytes are natural killer (NK) cells, key players involved in tumor targeting, initiated by signaling via activating and inhibitory receptors. Here, we investigated the role of the DNAM-1/TIGIT/CD96 axis in the anti-tumor response of NK cells toward OC. Ascites-derived NK cells from advanced OC patients showed lower expression of activating receptor DNAM-1 compared to healthy donor peripheral blood NK cells, while inhibitory receptor TIGIT and CD96 expression was equal or higher, respectively. This shift to a more inhibitory phenotype could also be induced in vitro by co-culturing healthy donor NK cells with OC tumor spheroids, and in vivo on intraperitoneally infused NK cells in SKOV-3 OC bearing NOD/SCID-IL2Rγnull (NSG) mice. Interestingly, TIGIT blockade enhanced degranulation and interferon gamma (IFNγ) production of healthy donor CD56dim NK cells in response to OC tumor cells, especially when DNAM-1/CD155 interactions were in place. Importantly, TIGIT blockade boosted functional responsiveness of CD56dim NK cells of OC patients with a baseline reactivity against SKOV-3 cells. Overall, our data show for the first time that checkpoint molecules TIGIT/DNAM-1/CD96 play an important role in NK cell responsiveness against OC, and provides rationale for incorporating TIGIT interference in NK cell-based immunotherapy in OC patients.

PD-L1 siRNA-mediated silencing in acute myeloid leukemia enhances anti-leukemic T cell reactivity.

Acute myeloid leukemia (AML) is an immune-susceptible malignancy, as demonstrated by its responsiveness to allogeneic stem cell transplantation (alloSCT). However, by employing inhibitory signaling pathways, including PD-1/PD-L1, leukemia cells suppress T cell-mediated immune attack. Notably, impressive clinical efficacy has been obtained with PD-1/PD-L1 blocking antibodies in cancer patients. Yet, these systemic treatments are often accompanied by severe toxicity, especially after alloSCT. Here, we investigated RNA interference technology as an alternative strategy to locally interfere with PD-1/PD-L1 signaling in AML. We demonstrated efficient siRNA-mediated PD-L1 silencing in HL-60 and patients' AML cells. Importantly, WT1-antigen T cell receptor+ PD-1+ 2D3 cells showed increased activation toward PD-L1 silenced WT1+ AML. Moreover, PD-L1 silenced AML cells significantly enhanced the activation, degranulation, and IFN-γ production of minor histocompatibility antigen-specific CD8+ T cells. Notably, PD-L1 silencing was equally effective as PD-1 antibody blockade. Together, our study demonstrates that PD-L1 silencing may be an effective strategy to augment AML immune-susceptibility. This provides rationale for further development of targeted approaches to locally interfere with immune escape mechanisms in AML, thereby minimizing severe toxicity. In combination with alloSCT and/or adoptive T cell transfer, this strategy could be very appealing to boost graft-versus-leukemia immunity and improve outcome in AML patients.

Comprehensive Phenotyping of T Cells Using Flow Cytometry.

The T cell compartment can form a powerful defense against extrinsic (e.g., pathogens) and intrinsic danger (e.g., malignant cells). At the same time, specific subsets of T cells control this process to keep the immune system in check and prevent autoimmunity. A wide variety in T cell functionalities exists, which is dependent on the differentiation and maturation state of the T cells. In this review, we report an overview for the identification of CD4+ T-αß cells (T-helper (Th)1, Th2, Th9, Th17, Th22, and CD4+ regulatory T cells), CD8+ T-αß cells (cytotoxic T lymphocyte (Tc)1, Tc2, Tc9, Tc17, and CD8+ regulatory T cells), and their additional effector memory status (naïve, stem cell memory, central memory, effector memory, and effector) using flow cytometry. These different subsets can be discriminated based on selective extracellular markers, in combination with intracellular transcription factor and/or cytokine stainings. Additionally, identification of very small subsets, including antigen-specific T cells, and important technical considerations of flow cytometry are discussed. Together, this overview can be used for comprehensive phenotyping of a T cell subset of interest. © 2019 International Society for Advancement of Cytometry.

Single-cell analysis reveals that stochasticity and paracrine signaling control interferon-alpha production by plasmacytoid dendritic cells.

Type I interferon (IFN) is a key driver of immunity to infections and cancer. Plasmacytoid dendritic cells (pDCs) are uniquely equipped to produce large quantities of type I IFN but the mechanisms that control this process are poorly understood. Here we report on a droplet-based microfluidic platform to investigate type I IFN production in human pDCs at the single-cell level. We show that type I IFN but not TNFα production is limited to a small subpopulation of individually stimulated pDCs and controlled by stochastic gene regulation. Combining single-cell cytokine analysis with single-cell RNA-seq profiling reveals no evidence for a pre-existing subset of type I IFN-producing pDCs. By modulating the droplet microenvironment, we demonstrate that vigorous pDC population responses are driven by a type I IFN amplification loop. Our study highlights the significance of stochastic gene regulation and suggests strategies to dissect the characteristics of immune responses at the single-cell level.

Increased Coexpression of PD-1, TIGIT, and KLRG-1 on Tumor-Reactive CD8+ T Cells During Relapse after Allogeneic Stem Cell Transplantation.

Allogeneic stem cell transplantation (allo-SCT) can be a curative treatment for patients with a hematologic malignancy due to alloreactive T cell responses recognizing minor histocompatibility antigens (MiHA). Yet tumor immune escape mechanisms can cause failure of T cell immunity, leading to relapse. Tumor cells display low expression of costimulatory molecules and can up-regulate coinhibitory molecules that inhibit T cell functionality on ligation with their counter-receptors on the tumor-reactive T cells. The aim of this explorative study was to evaluate immune checkpoint expression profiles on T cell subsets and on cytomegalovirus (CMV)- and/or MiHA-reactive CD8+ T cells of allo-SCT recipients using a 13-color flow cytometry panel, and to correlate these expression patterns to clinical outcomes. MiHA-reactive CD8+ T cells exhibited an early differentiated CD27++/CD28++ phenotype with low KLRG-1 and CD57 expression. These T cells also displayed increased expression of PD-1, TIM-3, and TIGIT compared with total effector memory T cells and CMV-specific CD8+ T cells in healthy donors and allo-SCT recipients. Remarkably, high coexpression of PD-1, TIGIT, and KLRG-1 on MiHA-reactive CD8+ T cells was associated with relapse after allo-SCT. Taken together, these findings indicate that MiHA-specific CD8+ T cells of relapsed patients have a distinctive coinhibitory expression signature compared with patients who stay in remission. This phenotype may serve as a potential monitoring tool in patients. Moreover, these findings suggest that PD-1 and TIGIT play important roles in regulating T cell-mediated tumor control, providing a rationale for immunotherapy with blocking antibodies to treat relapse after allo-SCT.

Apoptosis-Related Gene Expression Profiling in Hematopoietic Cell Fractions of MDS Patients.

Although the vast majority of patients with a myelodysplastic syndrome (MDS) suffer from cytopenias, the bone marrow is usually normocellular or hypercellular. Apoptosis of hematopoietic cells in the bone marrow has been implicated in this phenomenon. However, in MDS it remains only partially elucidated which genes are involved in this process and which hematopoietic cells are mainly affected. We employed sensitive real-time PCR technology to study 93 apoptosis-related genes and gene families in sorted immature CD34+ and the differentiating erythroid (CD71+) and monomyeloid (CD13/33+) bone marrow cells. Unsupervised cluster analysis of the expression signature readily distinguished the different cellular bone marrow fractions (CD34+, CD71+ and CD13/33+) from each other, but did not discriminate patients from healthy controls. When individual genes were regarded, several were found to be differentially expressed between patients and controls. Particularly, strong over-expression of BIK (BCL2-interacting killer) was observed in erythroid progenitor cells of low- and high-risk MDS patients (both p = 0.001) and TNFRSF4 (tumor necrosis factor receptor superfamily 4) was down-regulated in immature hematopoietic cells (p = 0.0023) of low-risk MDS patients compared to healthy bone marrow.

Chromosomal abnormalities in hepatic cysts point to novel polycystic liver disease genes.

Autosomal dominant polycystic liver disease (ADPLD) is caused by variants in PRKCSH, SEC63, and LRP5, whereas autosomal dominant polycystic kidney disease is caused by variants in PKD1 and PKD2. Liver cyst development in these disorders is explained by somatic loss-of-heterozygosity (LOH) of the wild-type allele in the developing cyst. We hypothesize that we can use this mechanism to identify novel disease genes that reside in LOH regions. In this study, we aim to map abnormal genomic regions using high-density SNP microarrays to find novel PLD genes. We collected 46 cysts from 23 patients with polycystic or sporadic hepatic cysts, and analyzed DNA from those cysts using high-resolution microarray (n=24) or Sanger sequencing (n=22). We here focused on regions of homozygosity on the autosomes (>3.0 Mb) and large CNVs (>1.0 Mb). We found frequent LOH in PRKCSH (22/29) and PKD1/PKD2 (2/3) cysts of patients with known heterozygous germline variants in the respective genes. In the total cohort, 12/23 patients harbored abnormalities outside of familiar areas. In individual ADPLD cases, we identified germline events: a 2q13 complex rearrangement resulting in BUB1 haploinsufficiency, a 47XXX karyotype, chromosome 9q copy-number loss, and LOH on chromosome 3p. The latter region was overlapping with an LOH region identified in two other cysts. Unique germline and somatic abnormalities occur frequently in and outside of known genes underlying cysts. Each liver cyst has a unique genetic makeup. LOH driver gene BUB1 may imply germline causes of genetic instability in PLD.

CLEC12A-Mediated Antigen Uptake and Cross-Presentation by Human Dendritic Cell Subsets Efficiently Boost Tumor-Reactive T Cell Responses.

Potent immunotherapies are urgently needed to boost antitumor immunity and control disease in cancer patients. As dendritic cells (DCs) are the most powerful APCs, they are an attractive means to reinvigorate T cell responses. An appealing strategy to use the effective Ag processing and presentation machinery, T cell stimulation and cross-talk capacity of natural DC subsets is in vivo tumor Ag delivery. In this context, endocytic C-type lectin receptors are attractive targeting molecules. In this study, we investigated whether CLEC12A efficiently delivers tumor Ags into human DC subsets, facilitating effective induction of CD4(+) and CD8(+) T cell responses. We confirmed that CLEC12A is selectively expressed by myeloid cells, including the myeloid DC subset (mDCs) and the plasmacytoid DC subset (pDCs). Moreover, we demonstrated that these DC subsets efficiently internalize CLEC12A, whereupon it quickly translocates to the early endosomes and subsequently routes to the lysosomes. Notably, CLEC12A Ab targeting did not negatively affect DC maturation or function. Furthermore, CLEC12A-mediated delivery of keyhole limpet hemocyanin resulted in enhanced proliferation and cytokine secretion by keyhole limpet hemocyanin-experienced CD4(+) T cells. Most importantly, CLEC12A-targeted delivery of HA-1 long peptide resulted in efficient Ag cross-presentation by mDCs and pDCs, leading to strong ex vivo activation of HA-1-specific CD8(+) T cells of patients after allogeneic stem cell transplantation. Collectively, these data indicate that CLEC12A is an effective new candidate with great potential for in vivo Ag delivery into mDCs and pDCs, thereby using the specialized functions and cross-talk capacity of these DC subsets to boost tumor-reactive T cell immunity in cancer patients.

Addition of 10-Day Decitabine to Fludarabine/Total Body Irradiation Conditioning is Feasible and Induces Tumor-Associated Antigen-Specific T Cell Responses.

Allogeneic hematopoietic cell transplantation (HCT) offers the possibility of curative therapy for patients with myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML), and acute myelogenous leukemia (AML). However, post-HCT relapse remains a major problem, particularly in patients with high-risk cytogenetics and in patients who cannot tolerate consolidation chemotherapy (eg, due to previous toxicity). We assessed the toxicity and efficacy of 10-day decitabine (Dec), fludarabine (Flu), and 2 Gy total body irradiation (TBI) as a new conditioning regimen for allogeneic HCT in patients with MDS, CMML, or AML. Thirty patients were enrolled, including 11 with MDS, 2 with CMML, and 17 with AML. Patients received 20 mg/m(2)/day Dec on days -11 to -2, 30 mg/m(2)/day Flu on days -4 to -2, and 2 Gy TBI on day -1, followed by infusion of a donor stem cell graft on day 0. Postgrafting immunosuppression consisted of cyclosporin A and mycophenolate mofetil. At a median follow-up of 443 days, the overall survival was 53%, relapse incidence was 27%, and nonrelapse mortality was 27%. The incidence of severe acute (grade III/IV) graft-versus-host disease (GVHD) was 27%, and that of (predominantly mild) chronic GVHD was 60%. Immunomonitoring studies revealed that specific CD8(+) T cell responses against epigenetically silenced tumor-associated antigens (TAAs), including cancer-testis antigens (MAGE-A1/A2/A3 and PRAME) and RHAMM, occurred more frequently in patients who had received Dec/Flu/TBI conditioning (8 of 11 patients) compared with a control group of patients who had received only Flu/TBI conditioning (2 of 9 patients). In summary, Dec/Flu/TBI conditioning proved feasible and effective and enhanced the induction of TAA-reactive CD8(+) T cell responses in vivo, which may contribute to disease control post-transplantation.

Enhanced cellular uptake of albumin-based lyophilisomes when functionalized with cell-penetrating peptide TAT in HeLa cells.

Lyophilisomes are a novel class of biodegradable proteinaceous nano/micrometer capsules with potential use as drug delivery carrier. Cell-penetrating peptides (CPPs) including the TAT peptide have been successfully implemented for intracellular delivery of a broad variety of cargos including various nanoparticulate pharmaceutical carriers. In the present study, lyophilisomes were modified using CPPs in order to achieve enhanced cellular uptake. Lyophilisomes were prepared by a freezing, annealing, and lyophilization method and a cystein-elongated TAT peptide was conjugated to the lyophilisomes using a heterobifunctional linker. Fluorescent-activated cell sorting (FACS) was utilized to acquire a lyophilisome population with a particle diameter smaller than 1000 nm. Cultured HeLa, OVCAR-3, Caco-2 and SKOV-3 cells were exposed to unmodified lyophilisomes and TAT-conjugated lyophilisomes and examined with FACS. HeLa cells were investigated in more detail using a trypan blue quenching assay, confocal microscopy, and transmission electron microscopy. TAT-conjugation strongly increased binding and cellular uptake of lyophilisomes in a time-dependent manner in vitro, as assessed by FACS. These results were confirmed by confocal microscopy. Transmission electron microscopy indicated rapid cellular uptake of TAT-conjugated lyophilisomes via phagocytosis and/or macropinocytosis. In conclusion, TAT-peptides conjugated to albumin-based lyophilisomes are able to enhance cellular uptake of lyophilisomes in HeLa cells.

Concurrent detection of circulating minor histocompatibility antigen-specific CD8+ T cells in SCT recipients by combinatorial encoding MHC multimers.

Allogeneic stem cell transplantation (SCT) is a potentially curative treatment for patients with hematologic malignancies. Its therapeutic effect is largely dependent on recognition of minor histocompatibility antigens (MiHA) by donor-derived CD8⁺ T cells. Therefore, monitoring of multiple MiHA-specific CD8⁺ T cell responses may prove to be valuable for evaluating the efficacy of allogeneic SCT. In this study, we investigated the use of the combinatorial encoding MHC multimer technique to simultaneously detect MiHA-specific CD8⁺ T cells in peripheral blood of SCT recipients. Feasibility of this approach was demonstrated by applying dual-color encoding MHC multimers for a set of 10 known MiHA. Interestingly, single staining using a fluorochrome- and Qdot-based five-color combination showed comparable results to dual-color staining for most MiHA-specific CD8⁺ T cell responses. In addition, we determined the potential value of combinatorial encoding MHC multimers in MiHA identification. Therefore, a set of 75 candidate MiHA peptides was predicted from polymorphic genes with a hematopoietic expression profile and further selected for high and intermediate binding affinity for HLA-A2. Screening of a large cohort of SCT recipients resulted in the detection of dual-color encoded CD8⁺ T cells following MHC multimer-based T cell enrichment and short ex vivo expansion. Interestingly, candidate MiHA-specific CD8⁺ T cell responses for LAG3 and TLR10 derived polymorphic peptides could be confirmed by genotyping of the respective SNPs. These findings demonstrate the potency of the combinatorial MHC multimer approach in the monitoring of CD8⁺ T cell responses to known and potential MiHA in limited amounts of peripheral blood from allogeneic SCT recipients.

Foxp3+ regulatory T cells of psoriasis patients easily differentiate into IL-17A-producing cells and are found in lesional skin.

Psoriasis is an autoimmune-related chronic inflammatory skin disease that is strongly associated with IL-23 and T helper-17 (Th17) effector cytokines. In addition, CD4+CD25(high) regulatory T-cell (Treg) function appeared to be impaired in psoriasis. CD4+CD25(high)Foxp3+ Tregs are typically considered inhibitors of autoimmune responses. However, under proinflammatory conditions, Tregs can differentiate into inflammation-associated Th17 cells--a paradigm shift, with as yet largely unknown consequences for human disease initiation or progression. Th17 cells are highly proinflammatory T cells that are characterized by IL-17A and IL-22 production and expression of the transcription factor retinoic acid-related orphan receptor γt (RORγt). We here show that Tregs of patients with severe psoriasis, as compared with those of healthy controls, have an enhanced propensity to differentiate into IL-17A-producing cells on ex vivo stimulation. This enhanced Treg differentiation was linked to unexpectedly high RORγt levels and enhanced loss of Foxp3. Notably, IL-23 boosted this Treg differentiation process particularly in patients with psoriasis but less so in controls. IL-23 further reduced Foxp3 expression while leaving the high RORγt levels unaffected. The histone/protein deacetylase inhibitor, Trichostatin-A, prevented Th17 differentiation of Tregs in psoriasis patients. Importantly, IL-17A+/Foxp3+/CD4+ triple-positive cells were present in skin lesions of patients with severe psoriasis. These data stress the clinical relevance of Treg differentiation for the perpetuation of chronic inflammatory disease and may pave novel ways for immunotherapy.

Deficiency of either P-glycoprotein or breast cancer resistance protein protect against acute kidney injury.

The kidney has a high capacity to regenerate after ischemic injury via several mechanisms, one of which involves bone marrow-derived (stem) cells. The ATP binding cassette transporters, P-glycoprotein and breast cancer resistance protein, are determinants for the enriched stem and progenitor cell fraction in bone marrow. Because they are upregulated after acute kidney injury, we hypothesized that both efflux pumps may play a role in protecting against renal injury. Surprisingly, transporter-deficient mice were protected against ischemia-induced renal injury. To further study this, bone marrow from irradiated wild-type mice was reconstituted by bone marrow from wild-type, P-glycoprotein- or breast cancer resistance protein-deficient mice. Four weeks later, kidney injury was induced and its function evaluated. Significantly more bone marrow-derived cells were detected in kidneys grafted with transporter-deficient bone marrow. A gender mismatch study suggested that cell fusion of resident tubular cells with bone marrow cells was unlikely. Renal function analyses indicated an absence of renal damage following ischemia-reperfusion in animals transplanted with transporter-deficient bone marrow. When wild-type bone marrow was transplanted in breast cancer resistance protein-deficient mice this protection is lost. Furthermore, we demonstrate that transporter-deficient bone marrow contained significantly more monocytes, granulocytes, and early outgrowth endothelial progenitor cells.

A frameshift polymorphism in P2X5 elicits an allogeneic cytotoxic T lymphocyte response associated with remission of chronic myeloid leukemia.

Minor histocompatibility antigens (mHAgs) constitute the targets of the graft-versus-leukemia response after HLA-identical allogeneic stem cell transplantation. Here, we have used genetic linkage analysis to identify a novel mHAg, designated lymphoid-restricted histocompatibility antigen-1 (LRH-1), which is encoded by the P2X5 gene and elicited an allogeneic CTL response in a patient with chronic myeloid leukemia after donor lymphocyte infusion. We demonstrate that immunogenicity for LRH-1 is due to differential protein expression in recipient and donor cells as a consequence of a homozygous frameshift polymorphism in the donor. Tetramer analysis showed that emergence of LRH-1-specific CD8+ cytotoxic T cells in peripheral blood and bone marrow correlated with complete remission of chronic myeloid leukemia. Furthermore, the restricted expression of LRH-1 in hematopoietic cells including leukemic CD34+ progenitor cells provides evidence of a role for LRH-1-specific CD8+ cytotoxic T cells in selective graft-versus-leukemia reactivity in the absence of severe graft-versus-host disease. These findings illustrate that the P2X5-encoded mHAg LRH-1 could be an attractive target for specific immunotherapy to treat hematological malignancies recurring after allogeneic stem cell transplantation.