Andrew J. Rech

Radiation and dual checkpoint blockade activate non-redundant immune mechanisms in cancer

Immune checkpoint inhibitors result in impressive clinical responses, but optimal results will require combination with each other and other therapies. This raises fundamental questions about mechanisms of non-redundancy and resistance. Here we report major tumour regressions in a subset of patients with metastatic melanoma treated with an anti-CTLA4 antibody (anti-CTLA4) and radiation, and reproduced this effect in mouse models. Although combined treatment improved responses in irradiated and unirradiated tumours, resistance was common. Unbiased analyses of mice revealed that resistance was due to upregulation of PD-L1 on melanoma cells and associated with T-cell exhaustion. Accordingly, optimal response in melanoma and other cancer types requires radiation, anti-CTLA4 and anti-PD-L1/PD-1. Anti-CTLA4 predominantly inhibits T-regulatory cells (Treg cells), thereby increasing the CD8 T-cell to Treg (CD8/Treg) ratio. Radiation enhances the diversity of the T-cell receptor (TCR) repertoire of intratumoral T cells. Together, anti-CTLA4 promotes expansion of T cells, while radiation shapes the TCR repertoire of the expanded peripheral clones. Addition of PD-L1 blockade reverses T-cell exhaustion to mitigate depression in the CD8/Treg ratio and further encourages oligoclonal T-cell expansion. Similarly to results from mice, patients on our clinical trial with melanoma showing high PD-L1 did not respond to radiation plus anti-CTLA4, demonstrated persistent T-cell exhaustion, and rapidly progressed. Thus, PD-L1 on melanoma cells allows tumours to escape anti-CTLA4-based therapy, and the combination of radiation, anti-CTLA4 and anti-PD-L1 promotes response and immunity through distinct mechanisms.

Clinical Use of Anti‐CD25 Antibody Daclizumab to Enhance Immune Responses to Tumor Antigen Vaccination by Targeting Regulatory T cells

CD4+ regulatory T cells frustrate productive tumor immune surveillance and represent an obstacle for cancer immunotherapy. In mice, anti‐CD25 antibody is an effective method of depleting CD25+ FOXP3+ T regulatory cells (Tregs) in vivo and enhancing cancer immunity. Here, we propose the use of the anti‐CD25 monoclonal antibody daclizumab for the depletion of Tregs in cancer patients. In early results from an ongoing clinical trial, a single intravenous infusion of daclizumab in patients with metastatic breast cancer is associated with a marked and prolonged elimination of CD25+ FOXP3+ Tregs in peripheral blood. When a cancer antigen peptide vaccine is administered during the daclizumab‐induced Treg nadir, effective generation of cytotoxic T lymphocytes has been observed, including those specific for neo‐antigens, such as cytomegalovirus peptide used as an immunological control. If confirmed in additional patients, these observations suggest that daclizumab may be an effective and available therapeutic agent for Treg modulation in patients with cancer.

CD25 Blockade Depletes and Selectively Reprograms Regulatory T Cells in Concert with Immunotherapy in Cancer Patients

CD25 monoclonal antibody therapy rapidly and durably depletes Tregs in cancer patients through a mechanism consistent with reprogramming. Rehabilitating Tregs In A Clockwork Orange, a young criminal undergoes a controversial rehabilitation therapy that reprograms him to become sick at even the thought of violence. Indeed, rehabilitation, although carried out with much less extreme measures, is a critical strategy for reforming many types of bad apples. Rech et al. now extend this concept to the delinquent regulatory T cells (Tregs) that suppress antitumor immune responses. Tregs perform a critical role in healthy individuals—they prevent immune cells from the attacks on their host that causes autoimmunity. However, in the tumor microenvironment, Tregs are insidious—inhibiting immune responses against the tumor itself. Rech et al. hypothesized that daclizumab, a Food and Drug Administration–approved antibody to CD25, which is expressed on Tregs, could deplete Tregs and restore the antitumor immune response. They found in vitro that Tregs treated with daclizumab lost their suppressive function and secreted interferon-γ, which is consistent with reprogramming to effector T cells. They then treated patients with daclizumab in conjunction with an experimental vaccine for metastatic breast cancer. These patients had fewer Tregs and increased levels of vaccine antigen-specific effector T cell responses. Despite the loss of Tregs, these patients did not develop autoimmunity. Although these are still early studies, they provide hope that daclizumab may help to restore antitumor immunity without inducing autoimmunity. Regulatory T cells (Tregs) are key mediators of immune tolerance and feature prominently in cancer. Depletion of CD25+ FoxP3+ Tregs in vivo may promote T cell cancer immunosurveillance, but no strategy to do so in humans while preserving immunity and preventing autoimmunity has been validated. We evaluated the Food and Drug Administration–approved CD25-blocking monoclonal antibody daclizumab with regard to human Treg survival and function. In vitro, daclizumab did not mediate antibody-dependent or complement-mediated cytotoxicity but rather resulted in the down-regulation of FoxP3 selectively among CD25high CD45RAneg Tregs. Moreover, daclizumab-treated CD45RAneg Tregs lost suppressive function and regained the ability to produce interferon-γ, consistent with reprogramming. To understand the impact of daclizumab on Tregs in vivo, we performed a clinical trial of daclizumab in combination with an experimental cancer vaccine in patients with metastatic breast cancer. Daclizumab administration led to a marked and prolonged decrease in Tregs in patients. Robust CD8 and CD4 T cell priming and boosting to all vaccine antigens were observed in the absence of autoimmunity. We conclude that CD25 blockade depletes and selectively reprograms Tregs in concert with active immune therapy in cancer patients. These results suggest a mechanism to target cancer-associated Tregs while avoiding autoimmunity.

Collapse of the CD27+ B-Cell Compartment Associated with Systemic Plasmacytosis in Patients with Advanced Melanoma and Other Cancers

Purpose: Disturbed peripheral blood B-cell homeostasis complicates certain infections and autoimmune diseases, such as HIV and systemic lupus erythematosus, but has not been reported in cancer. This study aimed to investigate whether B-cell physiology was altered in the presence of melanoma and other cancers. Experimental Design: Flow cytometry was used to identify phenotypic differences in B cells from patients with melanoma and normal donors. In vitro stimulated B cells were assessed for responsiveness and also used as stimulators of allogeneic T cells in mixed lymphocyte reactions. Results: We show B-cell dysregulation in patients with advanced melanoma (n = 26) and other solid tumors (n = 13), marked by a relative and absolute loss of CD27+ (memory) B cells and associated with an aberrant systemic plasmacytosis. Functionally, B cells from patients with melanoma inefficiently up-regulated immunoregulatory molecules and weakly secreted cytokines in response to CD40 and toll-like receptor 9 agonists. Stimulated B cells from patients induced proliferation of alloreactive CD4+ T cells, but these T cells poorly secreted IFNγ and interleukin-2. These effects were recapitulated by using purified normal donor CD27neg B cells in these same assays, linking the predominance of CD27neg B cells in patients with the observed functional hyporesponsiveness. Indeed, B-cell dysfunction in patients strongly correlated with the extent of loss of CD27+ B cells in peripheral blood. Conclusions: Disturbed B-cell homeostasis is a previously unrecognized feature of patients with advanced melanoma and other cancers and may represent an unanticipated mechanism of immune incompetence in cancer.

Homeostasis of peripheral FoxP3+ CD4+ regulatory T cells in patients with early and late stage breast cancer

FoxP3+ CD4+ regulatory T cells (Tregs) are important mediators of peripheral immune tolerance, acting via multiple mechanisms to suppress cellular immunity including antitumor responses. Although therapeutic strategies have been proposed to deplete Tregs in patients with breast cancer and other malignancies, dynamic changes in the Treg compartment as a function of stage and treatment of breast cancer remain poorly understood. Here, we evaluated peripheral blood CD4+ T cells and FoxP3+ CD4+ T cells from 45 patients with early or late stage breast cancer and compared percentages, absolute counts, and Treg function to those from healthy volunteers (HV) of comparable age. Patients having completed adjuvant chemotherapy and patients with metastatic cancer exhibited significantly lower absolute CD4 counts and significantly higher percentages of FoxP3+ CD4+ T cells. In contrast, the absolute counts of circulating FoxP3+ CD4+ T cells did not differ significantly among early stage patients, late stage patients, or HV. Functionally, FoxP3+ CD4+ T cells from all donor groups similarly expressed CTLA-4 and failed to secrete IFN-γ in response to stimulation. Thus, although Tregs comprise an increased percentage of circulating CD4+ T cells in patients with metastatic breast cancer and patients in remission after completing the adjuvant chemotherapy, the systemic Treg pool, as measured by absolute counts, appears relatively constant regardless of disease stage or treatment status. Total CD4+ T cell counts are not constant, however, suggesting that homeostatic mechanisms, or susceptibility to cytotoxic or malignant insults, fundamentally differ for regulatory and non-regulatory CD4+ T cells.

Immune cytolytic activity stratifies molecular subsets of human pancreatic cancer

Purpose: Immunotherapy has the potential to improve the dismal prognosis in pancreatic ductal adenocarcinoma (PDA), but clinical trials, including those with single-agent PD-1 or PD-L1 inhibition, have been disappointing. Our aim was to examine the immune landscape of PDA as it relates to aspects of tumor biology, including neoepitope burden. Experimental Design: We used publicly available expression data from 134 primary resection PDA samples from The Cancer Genome Atlas to stratify patients according to a cytolytic T-cell activity expression index. We correlated cytolytic immune activity with mutational, structural, and neoepitope features of the tumor. Results: Human PDA displays a range of intratumoral cytolytic T-cell activity. PDA tumors with low cytolytic activity exhibited significantly increased copy number alterations, including recurrent amplifications of MYC and NOTCH2 and recurrent deletions and mutations of CDKN2A/B. In sharp contrast to other tumor types, high cytolytic activity in PDA did not correlate with increased mutational burden or neoepitope load (MHC class I and class II). Cytolytic-high tumors exhibited increased expression of multiple immune checkpoint genes compared to cytolytic-low tumors, except for PD-L1 expression, which was uniformly low. Conclusions: These data identify a subset of human PDA with high cytolytic T-cell activity. Rather than being linked to mutation burden or neoepitope load, immune activation indices in PDA were inversely linked to genomic alterations, suggesting that intrinsic oncogenic processes drive immune inactivity in human PDA. Furthermore, these data highlight the potential importance of immune checkpoints other than PD-L1/PD-1 as therapeutic targets in this lethal disease. Clin Cancer Res; 23(12); 3129–38. ©2016 AACR.

Dynamic Interplay of Oncogenes and T Cells Induces PD-L1 in the Tumor Microenvironment

Tumor-infiltrating T cells have recently been found to upregulate immunosuppressive pathways, such as programmed cell death protein 1 ligand 1 (PD-L1), in a paracrine fashion on tumor cells, but tumor cell-intrinsic regulation of PD-L1 is another potential mechanism. In this issue of Cancer Discovery, Akbay and colleagues show that signaling via mutant EGF receptor (EGFR) in murine lung tumor cells directly upregulates tumor PD-L1 and that therapeutic blockade of this pathway improves survival in EGFR-driven preclinical models-highlighting the dynamic interplay and therapeutic opportunities of cancer cell biology and immune biology.

Class I-restricted T-cell responses to a polymorphic peptide in a gene therapy clinical trial for .ALPHA.-1-antitrypsin deficiency

Significance The use of adeno-associated virus (AAV)-mediated gene therapy to treat monogenic disorders is currently being tested in phase I, II, and III clinical trials. An immune response to the newly introduced gene product remains a potential problem because of the patient’s lack of central and peripheral tolerance to foreign epitopes. In this study, we show the induction of a T-cell response to the therapeutic product in a α-1-antitrypsin (AAT)-deficient subject receiving AAV1-AAT treatment. The response was directed to an AAT epitope upstream of the mutation and was associated with a polymorphism present in the subject but not in the wild-type AAT therapeutic product. Our study highlights the importance of considering polymorphisms in the targeted population when designing a transgene. Adeno-associated virus (AAV)-mediated gene therapy is currently being pursued as a treatment for the monogenic disorder α-1-antitrypsin (AAT) deficiency. Results from phase I and II studies have shown relatively stable and dose-dependent increases in transgene-derived wild-type AAT after local intramuscular vector administration. In this report we describe the appearance of transgene-specific T-cell responses in two subjects that were part of the phase II trial. The patient with the more robust T-cell response, which was associated with a reduction in transgene expression, was characterized more thoroughly in this study. We learned that the AAT-specific T cells in this patient were cytolytic in phenotype, mapped to a peptide in the endogenous mutant AAT protein that contained a common polymorphism not incorporated into the transgene, and were restricted by a rare HLA class I C alleles present only in this patient. These human studies illustrate the genetic influence of the endogenous gene and HLA haplotype on the outcome of gene therapy.

Tumor Cell-Intrinsic Factors Underlie Heterogeneity of Immune Cell Infiltration and Response to Immunotherapy

Summary The biological and functional heterogeneity between tumors—both across and within cancer types—poses a challenge for immunotherapy. To understand the factors underlying tumor immune heterogeneity and immunotherapy sensitivity, we established a library of congenic tumor cell clones from an autochthonous mouse model of pancreatic adenocarcinoma. These clones generated tumors that recapitulated T cell‐inflamed and non‐T‐cell‐inflamed tumor microenvironments upon implantation in immunocompetent mice, with distinct patterns of infiltration by immune cell subsets. Co‐injecting tumor cell clones revealed the non‐T‐cell‐inflamed phenotype is dominant and that both quantitative and qualitative features of intratumoral CD8+ T cells determine response to therapy. Transcriptomic and epigenetic analyses revealed tumor‐cell‐intrinsic production of the chemokine CXCL1 as a determinant of the non‐T‐cell‐inflamed microenvironment, and ablation of CXCL1 promoted T cell infiltration and sensitivity to a combination immunotherapy regimen. Thus, tumor cell‐intrinsic factors shape the tumor immune microenvironment and influence the outcome of immunotherapy. Graphical Abstract Figure. No caption available. HighlightsGenerated a library of congenic pancreatic cancer cell clones derived from KPC miceEach tumor elicited unique immune infiltration correlating with therapeutic responseTumors lacking T cells exhibit different epigenetic and transcriptomic statusCXCL1 was increased in therapy‐resistant tumors that lacked T cell infiltration &NA; Using a library of pancreatic cancer cell clones, Li et al. identify heterogeneous and multifactorial pathways regulating tumor‐cell‐intrinsic mechanisms that dictate the immune microenvironment and thereby responses to immunotherapy. This tumor clone library provides a tool for identifying new targets responsible for thwarting responses to immunotherapy in resistant tumors.

Tumor Immunity and Survival as a Function of Alternative Neopeptides in Human Cancer

Analysis of neopeptides across multiple tumor types revealed that “alternatively defined neopeptides,” derived from tumor-associated mutations, exhibited higher peptide affinity for MHC compared with nonmutant counterparts. These neopeptides were strong predictors of immune phenotype and patient survival. The immune system exerts antitumor activity via T cell–dependent recognition of tumor-specific antigens. Although the number of tumor neopeptides—peptides derived from somatic mutations—often correlates with immune activity and survival, most classically defined high-affinity neopeptides (CDNs) are not immunogenic, and only rare CDNs have been linked to tumor rejection. Thus, the rules of tumor antigen recognition remain incompletely understood. Here, we analyzed neopeptides, immune activity, and clinical outcome from 6,324 patients across 27 tumor types. We characterized a class of “alternatively defined neopeptides” (ADNs), which are mutant peptides predicted to bind MHC (class I or II) with improved affinity relative to their nonmutated counterpart. ADNs are abundant and molecularly distinct from CDNs. The load of ADNs correlated with intratumoral T-cell responses and immune suppression, and ADNs were also strong predictors of patient survival across tumor types. These results expand the spectrum of mutation-derived tumor antigens with potential clinical relevance. Cancer Immunol Res; 6(3); 276–87. ©2018 AACR.