Alison M. McDonnell

Tumor Antigen Cross-Presentation and the Dendritic Cell: Where it All Begins?

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that are critical for the generation of effective cytotoxic T lymphocyte (CTL) responses; however, their function and phenotype are often defective or altered in tumor-bearing hosts, which may limit their capacity to mount an effective tumor-specific CTL response. In particular, the manner in which exogenous tumor antigens are acquired, processed, and cross-presented to CD8 T cells by DCs in tumor-bearing hosts is not well understood, but may have a profound effect on antitumor immunity. In this paper, we have examined the role of DCs in the cross-presentation of tumor antigen in terms of their subset, function, migration, and location with the intention of examining the early processes that contribute to the development of an ineffective anti-tumor immune response.

Dual control of antitumor CD8 T cells through the programmed death-1/programmed death-ligand 1 pathway and immunosuppressive CD4 T cells: regulation and counterregulation

Tumors have evolved multiple mechanisms to evade immune destruction. One of these is expression of T cell inhibitory ligands such as programmed death-ligand 1 (PD-L1; B7-H1). In this study, we show that PD-L1 is highly expressed on mesothelioma tumor cells and within the tumor stroma. However, PD-L1 blockade only marginally affected tumor growth and was associated with the emergence of activated programmed death-1+ ICOS+ CD4 T cells in tumor-draining lymph nodes, whereas few activated CD8 T cells were present. Full activation of antitumor CD8 T cells, characterized as programmed death-1+ ICOS+ Ki-67+ and displaying CTL activity, was only observed when CD4 T cells were depleted, suggesting that a population of suppressive CD4 T cells exists. ICOS+ foxp3+ regulatory T cells were found to be regulated through PD-L1, identifying one potentially suppressive CD4 T cell population. Thus, PD-L1 blockade activates antitumor CD8 T cell most potently in the absence of CD4 T cells. These findings have implications for the development of PD-L1-based therapies.

CD8α+ DC are not the sole subset cross-presenting cell-associated tumor antigens from a solid tumor

One of the clear paradoxes in tumor immunology is the fact that cross‐presentation of cell‐associated tumor antigens to CD8+ T cells is efficient, yet CTL generation is weak, and tumors continue to grow. We examined, for the first time whether this may be due to alterations in the phenotype or function of cross‐presenting DC using a solid tumor model expressing a membrane bound neo‐antigen (hemagglutinin, HA). Tumor antigen was constitutively cross‐presented in the tumor‐draining LN throughout tumor progression by CD11c+ DC. Further analysis revealed that both CD8α+ and CD8α− DC subsets, but not plasmacytoid DC, were effective at cross‐presenting HA tumor antigen. The proportions of DC subsets in the tumor‐draining LN were equivalent to those seen in the LN of naïve mice; however, a significant increase in the expression of the potential inhibitory B7 molecule, B7‐DC, was noted and appeared to be restricted to the CD8α– DC subset. Therefore LN resident CD8α+ DC are not the sole DC subset capable of cross‐presenting cell‐associated tumor antigens. Migratory tumor DC subsets with altered co‐stimulatory receptor expression may contribute to induction and regulation of tumor‐specific responses.

A phase 1b clinical trial of the CD40-activating antibody CP-870,893 in combination with cisplatin and pemetrexed in malignant pleural mesothelioma

BACKGROUND Data from murine models suggest that CD40 activation may synergize with cytotoxic chemotherapy. We aimed to determine the maximum tolerated dose (MTD) and toxicity profile and to explore immunological biomarkers of the CD40-activating antibody CP-870,893 with cisplatin and pemetrexed in patients with malignant pleural mesothelioma (MPM). PATIENTS AND METHODS Eligible patients had confirmed MPM, ECOG performance status 0-1, and measurable disease. Patients received cisplatin 75 mg/m(2) and pemetrexed 500 mg/m(2) on day 1 and CP-870,893 on day 8 of a 21-day cycle for maximum 6 cycles with up to 6 subsequent cycles single-agent CP-870,893. Immune cell subset changes were examined weekly by flow cytometry. RESULTS Fifteen patients were treated at three dose levels. The MTD of CP-870,893 was 0.15 mg/kg, and was exceeded at 0.2 mg/kg with one grade 4 splenic infarction and one grade 3 confusion and hyponatraemia. Cytokine release syndrome (CRS) occurred in most patients (80%) following CP-870,893. Haematological toxicities were consistent with cisplatin and pemetrexed chemotherapy. Six partial responses (40%) and 9 stable disease (53%) as best response were observed. The median overall survival was 16.5 months; the median progression-free survival was 6.3 months. Three patients survived beyond 30 months. CD19+ B cells decreased over 6 cycles of chemoimmunotherapy (P < 0.001) with a concomitant increase in the proportion of CD27+ memory B cells (P < 0.001) and activated CD86+CD27+ memory B cells (P < 0.001), as an immunopharmacodynamic marker of CD40 activation. CONCLUSIONS CP-870,893 with cisplatin and pemetrexed is safe and tolerable at 0.15 mg/kg, although most patients experience CRS. While objective response rates are similar to chemotherapy alone, three patients achieved long-term survival. AUSTRALIA NEW ZEALAND CLINICAL TRIALS REGISTRY NUMBER ACTRN12609000294257.

Contribution of the immune system to the chemotherapeutic response

The immune system plays an important role in the surveillance of neoplastic cells by eliminating them before they manifest as full-blown cancer. Despite this, tumors do develop in the presence of a functioning immune system. Conventional chemotherapy and its ability to directly kill tumor cells is one of the most effective weapons in the fight against cancer, however, increasing evidence suggests that the therapeutic efficacy of some cytotoxic drugs relies on their capacity to interact with the immune system. Killing of tumor cells in a manner that favors their capture by immune cells or selective targeting of immunosuppressive pathways by specific chemotherapies promotes the generation of an effective anti-cancer response; however, this alone is rarely sufficient to cause elimination of advanced disease. An understanding of the immunological events occurring in both animal models and patients undergoing chemotherapy will guide decisions for the development of appropriate combinations and scheduling for the integration of chemotherapy with immunotherapy.

Tumor-infiltrating dendritic cells exhibit defective cross-presentation of tumor antigens, but is reversed by chemotherapy

Cross‐presentation defines the unique capacity of an APC to present exogenous Ag via MHC class I molecules to CD8+ T cells. DCs are specialized cross‐presenting cells and as such have a critical role in antitumor immunity. DCs are routinely found within the tumor microenvironment, but their capacity for endogenous or therapeutically enhanced cross‐presentation is not well characterized. In this study, we examined the tumor and lymph node DC cross‐presentation of a nominal marker tumor Ag, HA, expressed by the murine mesothelioma tumor AB1‐HA. We found that tumors were infiltrated by predominantly CD11b+ DCs with a semimature phenotype that could not cross‐present tumor Ag, and therefore, were unable to induce tumor‐specific T‐cell activation or proliferation. Although tumor‐infiltrating DCs were able to take up, process, and cross‐present exogenous cell‐bound and soluble Ags, this was significantly impaired relative to lymph node DCs. Importantly, however, systemic chemotherapy using gemcitabine reversed the defect in Ag cross‐presentation of tumor DCs. These data demonstrate that DC cross‐presentation within the tumor microenvironment is defective, but can be reversed by chemotherapy. These results have important implications for anticancer therapy, particularly regarding the use of immunotherapy in conjunction with cytotoxic chemotherapy.

Tumor cells, rather than dendritic cells, deliver antigen to the lymph node for cross-presentation

It is widely accepted that generation of tumor specific CD8+ T-cell responses occur via cross-priming; however the source of tumor antigen for this event is unknown. We examined the source and form of tumor antigen required for cross-presentation in the local lymph node (LN) using a syngeneic mouse tumor model expressing a marker antigen. We found that cross-presentation of this model tumor antigen in the LN is dependent on continuous traffic of antigen from the tumor site, but without any detectable migration of tumor resident dendritic cells (DCs). Instead, small numbers of tumor cells metastasize to local LNs where they are exposed to a localized CTL attack, resulting in delivery of tumor antigen into the cross-presentation pathway.

Dexamethasone co-medication in cancer patients undergoing chemotherapy causes substantial immunomodulatory effects with implications for chemo-immunotherapy strategies

ABSTRACT The glucocorticoid (GC) steroid dexamethasone (Dex) is used as a supportive care co-medication for cancer patients undergoing standard care pemetrexed/platinum doublet chemotherapy. As trials for new cancer immunotherapy treatments increase in prevalence, it is important to track the immunological changes induced by co-medications commonly used in the clinic, but not specifically included in trial design or in pre-clinical models. Here, we document a number of Dex -induced immunological effects, including a large-scale lymphodepletive effect particularly affecting CD4+ T cells but also CD8+ T cells. The proportion of regulatory T cells within the CD4+ compartment did not change after Dex was administered, however a significant increase in proliferation and activation of regulatory T cells was observed. We also noted Dex -induced proportional changes in dendritic cell (DC) subtypes. We discuss these immunological effects in the context of chemoimmunotherapy strategies, and suggest a number of considerations to be taken into account when designing future studies where Dex and other GCs may be in use.

Restoration of defective cross-presentation in tumors by gemcitabine

Tumor antigen cross-presentation by dendritic cells (DCs) to specific CD8+ T cells is central to antitumor immunity. Although highly efficient in draining lymph nodes, it is defective within the tumor site itself. Importantly, an immunogenic chemotherapy, gemcitabine, reverses this defect, allowing the potential re-stimulation of cytotoxic T lymphocytes within tumor sites.

PD-L1 on peripheral blood T lymphocytes is prognostic in patients with non-small cell lung cancer (NSCLC) treated with EGFR inhibitors

OBJECTIVES The immune effects of EGFR tyrosine kinase inhibitors (EGFR-TKIs) are poorly understood. Identifying immune biomarkers could guide patient selection and optimisation of EGFR-TKI-immunotherapy combinations. MATERIALS AND METHODS 33 patients with NSCLC treated with an EGFR-TKI were prospectively enrolled. Peripheral blood mononuclear cells were collected pre-treatment, and after 1, 3 and 8 weeks. Flow cytometry was used to identify immune cell subsets, including PD-1 and PD-L1 expressing T cells. Immune parameters were correlated with clinical outcomes. RESULTS Compared to healthy donors (n=10), patients had higher pre-treatment proportions of proliferating and PD-L1(+)CD3(+) T cells (p<0.001). Compared to patients with an EGFR mutation (n=12), patients without a known mutation (n=21) had higher proportions of proliferating CD4(+) and PD-L1(+)CD3(+) T cells (p=0.03). There was a significant increase in PD-L1(+) T cells after 1 week of EGFR-TKI in patients whose disease progressed compared to non-progressors. Patients with higher PD-L1(+)CD3(+) T cells at 1-week were more likely to progress (OR 30.3, p<0.01) and had shorter PFS (1.6 vs. 8.8m; p<0.01) and OS (3.8 vs 23.2m; p<0.001) than those with fewer PD-L1(+)CD3(+) T cells. On multivariate analysis, high PD-L1(+)CD3(+) T cells was the only independent predictor for PFS (HR 3.7, p=0.01), while for OS independent predictors were high PD-L1(+)CD3(+) T cells (HR 6.5, p<0.01) and EGFR-negative status (HR 3.3, p=0.04). CONCLUSIONS There was a significant correlation between PD-L1 expression on peripheral T cells and clinical outcomes in EGFR-TKI-treated NSCLC. This warrants further validation as a blood-based biomarker that may identify candidates for PD-1 inhibitors or immunotherapy-EGFR-TKI combinations.