Multi-omic approach identifies hypoxic tumor-associated myeloid cells that drive immunobiology of high-risk pediatric ependymoma.

Ependymoma (EPN) is a devastating childhood brain tumor. Single-cell analyses have illustrated the cellular heterogeneity of EPN tumors, identifying multiple neoplastic cell states including a mesenchymal-differentiated subpopulation which characterizes the PFA1 subtype. Here, we characterize the EPN immune environment, in the context of both tumor subtypes and tumor cell subpopulations using single-cell sequencing (scRNAseq, n = 27), deconvolution of bulk tumor gene expression (n = 299), spatial proteomics (n = 54), and single-cell cytokine release assays (n = 12). We identify eight distinct myeloid-derived subpopulations from which a group of cells, termed hypoxia myeloid cells, demonstrate features of myeloid-derived suppressor cells, including IL6/STAT3 pathway activation and wound healing ontologies. In PFA tumors, hypoxia myeloid cells colocalize with mesenchymal-differentiated cells in necrotic and perivascular niches and secrete IL-8, which we hypothesize amplifies the EPN immunosuppressive microenvironment. This myeloid cell-driven immunosuppression will need to be targeted for immunotherapy to be effective in this difficult-to-cure childhood brain tumor.

Activated tissue resident memory T-cells (CD8+CD103+CD39+) uniquely predict survival in left sided "immune-hot" colorectal cancers.

Introduction: Characterization of the tumour immune infiltrate (notably CD8+ T-cells) has strong predictive survival value for cancer patients. Quantification of CD8 T-cells alone cannot determine antigenic experience, as not all infiltrating T-cells recognize tumour antigens. Activated tumour-specific tissue resident memory CD8 T-cells (TRM) can be defined by the co-express of CD103, CD39 and CD8. We investigated the hypothesis that the abundance and localization of TRM provides a higher-resolution route to patient stratification. Methods: A comprehensive series of 1000 colorectal cancer (CRC) were arrayed on a tissue microarray, with representative cores from three tumour locations and the adjacent normal mucosa. Using multiplex immunohistochemistry we quantified and determined the localization of TRM. Results: Across all patients, activated TRM were an independent predictor of survival, and superior to CD8 alone. Patients with the best survival had immune-hot tumours heavily infiltrated throughout with activated TRM. Interestingly, differences between right- and left-sided tumours were apparent. In left-sided CRC, only the presence of activated TRM (and not CD8 alone) was prognostically significant. Patients with low numbers of activated TRM cells had a poor prognosis even with high CD8 T-cell infiltration. In contrast, in right-sided CRC, high CD8 T-cell infiltration with low numbers of activated TRM was a good prognosis. Conclusion: The presence of high intra-tumoural CD8 T-cells alone is not a predictor of survival in left-sided CRC and potentially risks under treatment of patients. Measuring both high tumour-associated TRM and total CD8 T-cells in left-sided disease has the potential to minimize current under-treatment of patients. The challenge will be to design immunotherapies, for left-sided CRC patients with high CD8 T-cells and low activate TRM,that result in effective immune responses and thereby improve patient survival.

Engineering the Human Fc Region Enables Direct Cell Killing by Cancer Glycan-Targeting Antibodies without the Need for Immune Effector Cells or Complement.

Murine IgG3 glycan-targeting mAb often induces direct cell killing in the absence of immune effector cells or complement via a proinflammatory mechanism resembling oncotic necrosis. This cancer cell killing is due to noncovalent association between Fc regions of neighboring antibodies, resulting in enhanced avidity. Human isotypes do not contain the residues underlying this cooperative binding mode; consequently, the direct cell killing of mouse IgG3 mAb is lost upon chimerization or humanization. Using the Lewisa/c/x -targeting 88mAb, we identified the murine IgG3 residues underlying the direct cell killing and increased avidity via a series of constant region shuffling and subdomain swapping approaches to create improved ("i") chimeric mAb with enhanced tumor killing in vitro and in vivo. Constant region shuffling identified a major CH3 and a minor CH2 contribution, which was further mapped to discontinuous regions among residues 286-306 and 339-378 that, when introduced in 88hIgG1, recapitulated the direct cell killing and avidity of 88mIgG3. Of greater interest was the creation of a sialyl-di-Lewisa-targeting i129G1 mAb via introduction of these selected residues into 129hIgG1, converting it into a direct cell killing mAb with enhanced avidity and significant in vivo tumor control. The human iG1 mAb, termed Avidimabs, retained effector functions, paving the way for the proinflammatory direct cell killing to promote antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity through relief of immunosuppression. Ultimately, Fc engineering of human glycan-targeting IgG1 mAb confers proinflammatory direct cell killing and enhanced avidity, an approach that could be used to improve the avidity of other mAb with therapeutic potential. SIGNIFICANCE: Fc engineering enhances avidity and direct cell killing of cancer-targeting anti-glycan antibodies to create superior clinical candidates for cancer immunotherapy.

Connexin 43 is an independent predictor of patient outcome in breast cancer patients.

PURPOSE: Gap junctions are specialized membrane structures that form channels between adjacent cells allowing cell communication. Gap junctions and specifically Connexin 43 (Cx43) are down-regulated in cancer; however, there are contrasting reports on how this effects breast cancer patient survival. This paper is the first large-scale tissue microarray analysis of Cx43 expression in breast cancer patients with an associated clinical long-term follow-up. METHODS: Using a validated TMA of 1118 primary breast cancers, coupled to a comprehensive database of clinicopathological variables, the expression levels and subcellular localisation of Cx43 was assessed by immunohistochemistry. Its impact in terms of survival, distant metastasis-free survival, and clinicopathological variables was determined. RESULTS: Patients whose tumors expressed high levels of Cx43 had significantly better survival (p < 0.001) than patients with low levels. High Cx43 expression within tumors was associated with an 18-month survival advantage. Loss of Cx43 expression was associated with markers of poor prognosis, namely large tumor size, high grade, high proliferation status, high pleomorphism, high mitosis, poor Nottingham Prognostic Index (NPI), and triple negative tumors. Cx43 expression was independent of tumor size, grade, stage and ER-status in predicting poor survival on multivariate analysis (p = 0.004). CONCLUSION: Connexin 43 (Cx43) is an independent predictor of breast cancer survival and distant metastasis-free survival. High expression of Cx43 was seen in only 13% of tumors, suggesting that drugs to increase Cx43 expression may result in prolonged patients survival.

High mobility group protein B1 is a predictor of poor survival in ovarian cancer.

High-mobility group protein B1 (HMGB1) has been implicated in numerous tumour types where expression regulates tumour cell growth and survival. We hypothesised that high HMGB1 expression in ovarian tumours would predict poor patient survival. Using tissue microarrays of primary ovarian cancers combined with a comprehensive database of clinicopathological variables, the expression of HMGB1 was assessed by immunohistochemistry in two independent cohorts (n=194 and n=360) using a monoclonal antibody specific for HMGB1. Kaplan-Meier analysis showed an association of HMGB1 expression with progression free survival in the primary cohort (p=0.023). In the validation cohort, expression was associated with overall survival (p=0.002). Low expression of HMGB1 was protective and in a multivariate model HMGB1 expression was shown to be an independent predictor of poor survival in ovarian cancer (p=0.006). The role of HMGB1 in cancer is complex. As high levels of HMGB1 expression are likely to render ovarian cancer cells resistant to chemotherapy, therapies targeting the HMGB1 axis may be appropriate in the treatment of ovarian cancer patients.

SCIB2, an antibody DNA vaccine encoding NY-ESO-1 epitopes, induces potent antitumor immunity which is further enhanced by checkpoint blockade.

Checkpoint blockade has demonstrated promising antitumor responses in approximately 10-40% of patients. However, the majority of patients do not make a productive immune response to their tumors and do not respond to checkpoint blockade. These patients may benefit from an effective vaccine that stimulates high-avidity T cell responses in combination with checkpoint blockade. We have previously shown that incorporating TRP-2 and gp100 epitopes into the CDR regions of a human IgG1 DNA (ImmunoBody®: IB) results in significant tumor regression both in animal models and patients. This vaccination strategy is superior to others as it targets antigen to antigen-presenting cells and stimulates high-avidity T cell responses. To broaden the application of this vaccination strategy, 16 NY-ESO-1 epitopes, covering over 80% of HLA phenotypes, were incorporated into the IB (SCIB2). They produced higher frequency and avidity T cell responses than peptide vaccination. These T cells were of sufficient avidity to kill NY-ESO-1-expressing tumor cells, and in vivo controlled the growth of established B16-NY-ESO-1 tumors, resulting in long-term survival (35%). When SCIB2 was given in combination with Treg depletion, CTLA-4 blockade or PD-1 blockade, long-term survival from established tumors was significantly enhanced to 56, 67 and 100%, respectively. Translating these responses into the clinic by using a combination of SCIB2 vaccination and checkpoint blockade can only further improve clinical responses.

Stromal fibroblasts support dendritic cells to maintain IL-23/Th17 responses after exposure to ionizing radiation.

Dendritic cell function is modulated by stromal cells, including fibroblasts. Although poorly understood, the signals delivered through this crosstalk substantially alter dendritic cell biology. This is well illustrated with release of TNF-α/IL-1ß from activated dendritic cells, promoting PGE2 secretion from stromal fibroblasts. This instructs dendritic cells to up-regulate IL-23, a key Th17-polarizing cytokine. We previously showed that ionizing radiation inhibited IL-23 production by human dendritic cells in vitro. In the present study, we investigated the hypothesis that dendritic cell-fibroblast crosstalk overcomes the suppressive effect of ionizing radiation to support appropriately polarized Th17 responses. Radiation (1-6 Gy) markedly suppressed IL-23 secretion by activated dendritic cells (P < 0.0001) without adversely impacting their viability and consequently, inhibited the generation of Th17 responses. Cytokine suppression by ionizing radiation was selective, as there was no effect on IL-1ß, -6, -10, and -27 or TNF-α and only a modest (11%) decrease in IL-12p70 secretion. Coculture with fibroblasts augmented IL-23 secretion by irradiated dendritic cells and increased Th17 responses. Importantly, in contrast to dendritic cells, irradiated fibroblasts maintained their capacity to respond to TNF-α/IL-1ß and produce PGE2, thus providing the key intermediary signals for successful dendritic cell-fibroblasts crosstalk. In summary, stromal fibroblasts support Th17-polarizing cytokine production by dendritic cells that would otherwise be suppressed in an irradiated microenvironment. This has potential ramifications for understanding the immune response to local radiotherapy. These findings underscore the need to account for the impact of microenvironmental factors, including stromal cells, in understanding the control of immunity.

CD55 costimulation induces differentiation of a discrete T regulatory type 1 cell population with a stable phenotype.

Unlike other helper T cells, the costimulatory ligands responsible for T regulatory type 1 (Tr1) cell differentiation remain undefined. Understanding the molecular interactions driving peripheral Tr1 differentiation is important because Tr1s potently regulate immune responses by IL-10 production. In this study, we show that costimulation of human naive CD4(+) cells through CD97/CD55 interaction drives Tr1 activation, expansion, and function. T cell activation and expansion was equipotent with CD55 or CD28 costimulation; however, CD55 costimulation resulted in two IL-10-secreting populations. Most IL-10 was secreted by the minor Tr1 population (IL-10(high)IFN-γ(-)IL-4(-), <5% cells) that expresses Tr1 markers CD49b, LAG-3, and CD226. This Tr1 phenotype was not restimulated by CD28. However, on CD55 restimulation, Tr1s proliferated and maintained their differentiated IL-10(high) phenotype. The Tr1s significantly suppressed effector T cell function in an IL-10-dependent manner. The remaining (>95%) cells adopted a Th1-like IFN-γ(+) phenotype. However, in contrast to CD28-derived Th1s, CD55-derived Th1s demonstrated increased plasticity with the ability to coexpress IL-10 when restimulated through CD55 or CD28. These data identify CD55 as a novel costimulator of human Tr1s and support a role for alternative costimulatory pathways in determining the fate of the growing number of T helper populations. This study demonstrates that CD55 acts as a potent costimulator and activator of human naive CD4(+) cells, resulting in the differentiation of a discrete Tr1 population that inhibits T cell function in an IL-10-dependent manner and maintains the Tr1 phenotype upon restimulation.

DNA vaccination with T-cell epitopes encoded within Ab molecules induces high-avidity anti-tumor CD8+ T cells.

Stimulation of high-avidity CTL responses is essential for effective anti-tumor and anti-viral vaccines. In this study we have demonstrated that a DNA vaccine incorporating CTL epitopes within an Ab molecule results in high-avidity T-cell responses to both foreign and self epitopes. The avidity and frequency was superior to peptide, peptide-pulsed DC vaccines or a DNA vaccine incorporating the epitope within the native Ag. The DNA Ab vaccine was superior to an identical protein vaccine that can only cross-present, indicating a role for direct presentation by the DNA vaccine. However, the avidity of CTL responses was significantly reduced in Fc receptor gamma knockout mice or if the Fc region was removed suggesting that cross presentation of Ag via Fc receptor was also important in the induction of high-avidity CTL. These results suggest that generation of high-avidity CTL responses by the DNA vaccine is related to its ability to both directly present and cross-present the epitope. High-avidity responses were capable of efficient anti-tumor activity in vitro and in vivo. This study demonstrates a vaccine strategy to generate high-avidity CTL responses that can be used in anti-tumor and anti-viral vaccine settings.

Costimulation via CD55 on human CD4+ T cells mediated by CD97.

Decay-accelerating factor (CD55) is a complement regulatory protein, which is expressed by most cells to protect them from complement-mediated attack. CD55 also binds CD97, an EGF-TM7 receptor constitutively expressed on granulocytes and monocytes and rapidly up-regulated on T and B cells upon activation. Early results suggested that CD55 could further enhance T cell proliferation induced by phorbol ester treatment. The present study demonstrates that coengagement of CD55, using either cross-linking mAbs or its natural ligand CD97, and CD3 results in enhanced proliferation of human peripheral blood CD4(+) T cells, expression of the activation markers CD69 and CD25, and secretion of IL-10 and GM-CSF. Recently, an increase in T cell responsiveness in CD55(-/-) mice was shown to be mediated by a lack of complement regulation. In this study, we show that direct stimulation of CD55 on CD4(+) T cells with CD97 can modulate T cell activation but does not interfere with CD55-mediated complement regulation. Our results support a multifaceted role for CD55 in human T cell activation, constituting a further link between innate and adaptive immunity.

Complement decay accelerating factor (DAF)/CD55 in cancer.

The complement system is a powerful innate mechanism involved in protection of the host against pathogens. It also has a role in the clearance of apoptotic cells and has been implicated in a range of pathologies including autoimmunity and graft rejection. The control of complement is mediated through the complement regulatory proteins (CRPs). These are present on most cells and protect normal cells from complement-mediated attack during innate activation. However, in a range of pathologies and cancer, these molecules are up or down regulated, sometimes secreted and even lost. We will review the expression of CRPs in cancer, focussing on CD55 and highlight other roles of the CRPs and their involvement in leukocyte function. We will also provide some data providing a potential mechanism by which soluble CD55 can inhibit T-cell function and discuss some of the implications of this data.

The use of reverse immunology to identify HLA-A2 binding epitopes in Tie-2.

A potential target for a cancer vaccine would be receptors, such as Tie-2 which are over expressed on tumour endothelium. Using computer aided motif predictions for possible HLA class I epitopes, we have identified peptides from Tie-2 that should bind with a range of affinities to HLA-A*0201. No direct correlation between predicted values and actual binding affinities was observed. Although, the programs did produce a number of false positives, two epitopes were predicted that bound with relatively high affinity when compared with an influenza peptide. We have previously identified a Tie-2 epitope and shown that it was only immunogenic when we substituted preferred amino acids at key anchor residues to increase binding affinity. In this study we used a similar approach to generate modified epitopes. When HLA-A2 transgenic mice were immunised with peptides, CTL killing of the target cells was only achieved when the wild type epitope was presented at moderate levels. Moreover, the efficiency of immunisation was increased when we linked CD4 epitopes to CD8 epitopes. Caution should therefore be employed in the use of both reverse immunology and anchor modification of CTL epitopes in the identification of CTL epitopes for cancer vaccines.

Immunosurveillance is active in colorectal cancer as downregulation but not complete loss of MHC class I expression correlates with a poor prognosis.

Many colorectal tumors lose or downregulate cell surface expression of MHC class I molecules conferring resistance to T-cell-mediated attack. It has been suggested that this phenomenon is due to in vivo immune-tumor interactions. However, evidence of the impact of MHC class I loss on outcomes from colorectal cancer is scarce. In our study of more than 450 colorectal cancers in tissue microarray format, we have shown that both high levels of MHC class I expression and absent MHC class I expression are associated with similar disease-specific survival times, possibly due to natural killer cell-mediated clearance of MHC class I-negative tumor cells. However, tumors with low level expression of MHC class I were found to confer a significantly poorer prognosis, retaining independent significance on multivariate analysis. The existence of these poor prognosis tumors, which may avoid both NK- and T-cell-mediated immune surveillance, has important implications for the design of immunotherapeutic strategies in colorectal cancer.

Comparison of the immune response to a self antigen after DNA immunisation of HLA*A201/H-2Kb and HHD transgenic mice.

HHD mice which express human HLA-A2 but no mouse class I, have been shown to have improved cytotoxic lymphocyte (CTL) responses to foreign antigens compared to HLA*A201/Kb transgenic mice. We have previously designed a DNA vaccine to a self antigen. Vaccination of A2.1/H-2Kb mice with this vaccine resulted in CTL in one third of the mice, but the frequency of antigen-specific cells was low. An increased frequency was observed in HHD mice, moreover CTL were obtained from all immunised mice. HHD mice are therefore useful for studying immunisation strategies for inducing and maintaining CD8 responses to over-expressed self antigens.

Identification of an HLA-A*0201 cytotoxic T lymphocyte epitope specific to the endothelial antigen Tie-2.

Tie-2 stabilises pericyte-endothelial interactions during angiogenesis and is highly expressed on endothelium during several diseases, including arthritis, age-related macular degeneration and cancer. A vaccine that targets endothelium overexpressing Tie-2 may result in vessel damage and stimulate an inflammatory cascade resulting in disease regression. We have identified a region unique to Tie-2 (amino acids 1-196) that is homologous in humans and mice. Using computer algorithms, several HLA-A*0201 epitopes that are identical in mice and humans were predicted within this region; however, binding assays showed that the majority of these epitopes were of low affinity. Modification of the anchor residues of 4 epitopes enhanced HLA binding. These epitopes were incorporated by site-directed mutagenesis into a Tie-2 DNA construct. Immunisation of HLA*0201 transgenic mice with one of the modified Tie-2 constructs stimulated CTLs that recognised both wild-type and modified peptide-pulsed target cells. In contrast, no CTLs were generated in mice immunised with wild-type Tie-2 construct, demonstrating that the modified epitope was necessary in the generation of CTLs. Moreover, CTLs from mice immunised with the modified construct killed HLA-A*0201 endothelial cells overexpressing Tie-2. Our study demonstrates that it is possible to break tolerance to the endothelial antigen Tie-2, suggesting that it may be feasible to design a vaccine to activate CTLs to kill endothelial cells overexpressing Tie-2.