Tumor stromal barriers to the success of adoptive T cell therapy

Colorectal Cancer-Infiltrating Regulatory T Cells: Functional Heterogeneity, Metabolic Adaptation, and Therapeutic Targeting

Colorectal cancer (CRC) is a heterogeneous disease with one of the highest rates of incidence and mortality among cancers worldwide. Understanding the CRC tumor microenvironment (TME) is essential to improve diagnosis and treatment. Within the CRC TME, tumor-infiltrating lymphocytes (TILs) consist of a heterogeneous mixture of adaptive immune cells composed of mainly anti-tumor effector T cells (CD4+ and CD8+ subpopulations), and suppressive regulatory CD4+ T (Treg) cells. The balance between these two populations is critical in anti-tumor immunity. In general, while tumor antigen-specific T cell responses are observed, tumor clearance frequently does not occur. Treg cells are considered to play an important role in tumor immune escape by hampering effective anti-tumor immune responses. Therefore, CRC-tumors with increased numbers of Treg cells have been associated with promoting tumor development, immunotherapy failure, and a poorer prognosis. Enrichment of Treg cells in CRC can have multiple causes including their differentiation, recruitment, and preferential transcriptional and metabolic adaptation to the TME. Targeting tumor-associated Treg cell may be an effective addition to current immunotherapy approaches. Strategies for depleting Treg cells, such as low-dose cyclophosphamide treatment, or targeting one or more checkpoint receptors such as CTLA-4 with PD-1 with monoclonal antibodies, have been explored. These have resulted in activation of anti-tumor immune responses in CRC-patients. Overall, it seems likely that CRC-associated Treg cells play an important role in determining the success of such therapeutic approaches. Here, we review our understanding of the role of Treg cells in CRC, the possible mechanisms that support their homeostasis in the tumor microenvironment, and current approaches for manipulating Treg cells function in cancer.

Identification of an immune gene expression signature associated with favorable clinical features in Treg-enriched patient tumor samples

Immune heterogeneity within the tumor microenvironment undoubtedly adds several layers of complexity to our understanding of drug sensitivity and patient prognosis across various cancer types. Within the tumor microenvironment, immunogenicity is a favorable clinical feature in part driven by the antitumor activity of CD8+ T cells. However, tumors often inhibit this antitumor activity by exploiting the suppressive function of regulatory T cells (Tregs), thus suppressing the adaptive immune response. Despite the seemingly intuitive immunosuppressive biology of Tregs, prognostic studies have produced contradictory results regarding the relationship between Treg enrichment and survival. We therefore analyzed RNA-seq data of Treg-enriched tumor samples to derive a pan-cancer gene signature able to help reconcile the inconsistent results of Treg studies, by better understanding the variable clinical association of Tregs across alternative tumor contexts. We show that increased expression of a 32-gene signature in Treg-enriched tumor samples (n = 135) is able to distinguish a cohort of patients associated with chemosensitivity and overall survival. This cohort is also enriched for CD8+ T cell abundance, as well as the antitumor M1 macrophage subtype. With a subsequent validation in a larger TCGA pool of Treg-enriched patients (n = 626), our results reveal a gene signature able to produce unsupervised clusters of Treg-enriched patients, with one cluster of patients uniquely representative of an immunogenic tumor microenvironment. Ultimately, these results support the proposed gene signature as a putative biomarker to identify certain Treg-enriched patients with immunogenic tumors that are more likely to be associated with features of favorable clinical outcome.

A new genetic test could help predict responses to therapy and survival outcomes among cancer patients with tumors that are infiltrated with large numbers of regulatory T cells (Tregs). Kevin B. Givechian of NantOmics in Los Angeles, California, USA, and colleagues measured gene activity levels in tumor samples taken from 135 patients with Treg-enriched cancers of all kinds. They singled out genes with particularly variable expression levels to create a 32-gene signature that revealed two distinct clusters of patients: those who responded to their prescribed drugs and lived longer, and those who were treatment-resistant and died sooner. The researchers also validated the gene panel in a larger, independent cohort of 626 tumor samples, showing that it could identify patients with immunogenic tumors who are more likely have favorable clinical outcomes.

Systemic Analysis of Predictive Biomarkers for Recurrence in Colorectal Cancer Patients Treated with Curative Surgery

BACKGROUND

Preoperative serum systemic inflammatory response (SIR) in patients with colorectal cancer (CRC) has been reported to be a predictive biomarker of early recurrence. The molecular status of CRC, including microsatellite instability (MSI), BRAF and KRAS mutations, and tumor-infiltrating lymphocytes (TILs), has also been associated with recurrence in CRC patients treated with curative surgery.

AIM

We investigated the impacts of SIR status, TILs, and MSI on recurrence in curative CRC patients.

METHODS

In this retrospective study, we enrolled 157 patients with stage I-III CRC undergoing curative surgery, for whom preoperative neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), and C-reactive protein (CRP) data were available as indicators of SIR status. Molecular status was evaluated by counting TILs as the numbers of intratumoral Foxp3- and CD8-positive T cells by immunohistochemistry. MSI status was determined using five mononucleotide repeat microsatellite markers.

RESULTS

Kaplan-Meier analysis of SIR indicators revealed that higher CRP, NLR, and PLR were associated with significantly poorer disease-free survival (DFS). Low levels of infiltrating CD8-positive T cells in CRC tissue was a significant predictor of poor DFS. Multivariate analysis showed that few infiltrating CD8-positive T cells and high serum CRP levels were independent predictive factors for recurrence. Furthermore, the combination of high CRP and few infiltrating CD8-positive T cells increased the predictive accuracy in these patients.

CONCLUSIONS

The results of this study suggest that both CRP levels in preoperative serum and CD8 T cells in CRC tissue are useful biomarkers for predicting early relapse in CRC patients treated with curative surgery.

CCL21 and IFNγ recruit and activate tumor specific T cells in 3D scaffold model of breast cancer

Effective elicitation of endogenous immunity is associated with improved prognosis for cancer patients. Clinical evidence in hematological and solid cancers shows that intratumoral injection of immunostimulatory genes primes and augments endogenous T cell responses. The ability of pro-inflammatory chemokines/cytokines to facilitate migration/activation of antigen-presenting cells (APC) and lymphocytes prompted our modeling of intratumoral delivery of a chemokine/cytokine combination for breast cancer treatment. Here, we demonstrate that expression of chemokine ligand 21 (CCL21) and interferon gamma (IFNγ) in tumors improves tumor specific T cell recruitment to tumor and activation in the tumor milieu. IFNγ and CCL21 were delivered into tumor cells via plasmids, and transfected cells were seeded to form spheroids on three-dimensional (3D) chitosan-alginate (CA) scaffolds. Co-expression of CCL21 and IFNγ, as evidenced by qRT-PCR and ELISA, induced increased recruitment, binding, and infiltration of anti-neu (p98) peptide specific T cells into the breast tumors as determined by SEM and immunofluorescence assays. The co-expression promoted recruitment of only p98 T cells, but not naïve T cells, demonstrating an antigen-restricted activation. Furthermore, the co-expression impacted T helper (Th) cell immunity, promoting an increase in secretion of pro-inflammatory Th-associated cytokine, tumor necrosis factor alpha (TNFα), and cytotoxic T lymphocyte (CTL)-associated protease, Granzyme B (GzB). Therefore, 3D CA scaffolds may be a useful breast cancer tumor microenvironment model to evaluate T cell function. Further characterization of CCL21-IFNγ mediated anti-tumor immunity will potentially benefit the development of chemokine/cytokine combination platforms as anti-cancer agents.

Three-dimensional scaffolds to evaluate tumor associated fibroblast-mediated suppression of breast tumor specific T cells

In the tumor microenvironment, the signals from tumor-associated fibroblasts (TAF) that suppress antitumor immunity remain unclear. Here, we develop and investigate an in vitro three-dimensional (3D) scaffold model for the novel evaluation of TAF interaction with breast tumor cells and breast specific, neu antigen (p98) reactive T cells. Breast cancer cells seeded on 3D chitosan-alginate (CA) scaffolds showed productive growth and formed distinct tumor spheroids. Antigen specific p98 T cells, but not naïve T cells, bound significantly better to tumor cells on scaffolds. The p98 T cells induced potent tumor cell killing but T helper cell cytokine function was impaired in the presence of TAF coseeding on scaffolds. We found that the immunosuppression was mediated, in part, by transforming growth factor beta (TGF-b) and interleukin-10 (IL-10). Therefore, TAF appear capable of inducing potent T cell suppression. CA scaffolds can provide clinically relevant findings prior to preclinical testing of novel immunotherapies.

Prognostic impact of FoxP3+ regulatory T cells in relation to CD8+ T lymphocyte density in human colon carcinomas

BACKGROUND

T-lymphocyte infiltration into colon carcinomas can influence clinical outcome, and interactions among T cell subsets may be more informative than either subset alone. Our objective was to examine the prognostic impact of tumor-infiltrating FoxP3(+) regulatory T cells (Tregs) in relation to cytotoxic CD8(+) T lymphocytes in patients with colon carcinomas characterized by DNA mismatch repair (MMR) status who participated in adjuvant chemotherapy trials.

METHODS

FoxP3(+) and CD8(+) densities in tumor epithelial and stromal compartments were analyzed by immunohistochemistry and quantified in resected, stage II and III colonic carcinomas (N = 216). Immune marker density was dichotomized at the median and categorized as high vs low. MMR status was classified as MMR deficient (dMMR) or proficient (pMMR). Cox models were adjusted for age, stage, and tumor grade.

RESULTS

The density of FoxP3+ infiltration was similar in tumor stroma and epithelia, whereas CD8+ was higher in stroma. The prognostic impact of FoxP3+ and CD8+ T cell infiltration was stronger in stroma vs epithelia, and the density of each marker in stroma was independently associated with improved overall survival (OS). However, the impact of FoxP3+ on survival was dependent upon CD8+ density (P interaction = 040). Among CD8+(low) tumors, FoxP3+(high) cases had significantly improved OS compared to FoxP3+(low) cases after adjustment for covariates (hazard ratio 0.43; 95% confidence interval 0.19 to 0.95; P = .030). In contrast, FoxP3+ was not prognostic among CD8+(high) tumors. FoxP3+ remained prognostic in CD8+(low) tumors after further adjustment for MMR or BRAF(V600E) mutation status. Additionally, these immune markers identified a pMMR subgroup with a similarly favorable OS as for dMMR tumors.

CONCLUSIONS

The prognostic impact of FoxP3+ and CD8+ T cell density are inter-dependent, whereby FoxP3+ exerts a favorable influence on survival only in colon cancers with low CD8+ infiltration.

Controlled extracellular matrix degradation in breast cancer tumors improves therapy by trastuzumab

Extracellular matrix (ECM) in solid tumors affects the effectiveness of therapeutics through blocking of intratumoral diffusion and/or physical masking of target receptors on malignant cells. In immunohistochemical studies of tumor sections from breast cancer patients and xenografts, we observed colocalization of ECM proteins and Her2/neu, a tumor-associated antigen that is the target for the widely used monoclonal antibody trastuzumab (Herceptin). We tested whether intratumoral expression of the peptide hormone relaxin (Rlx) would result in ECM degradation and the improvement of trastuzumab therapy. As viral gene delivery into epithelial tumors with extensive tumor ECM is inefficient, we used a hematopoietic stem cell (HSC)-based approach to deliver the Rlx gene to the tumor. In mouse models with syngeneic breast cancer tumors, HSC-mediated intratumoral Rlx expression resulted in a decrease of ECM proteins and enabled control of tumor growth. Moreover, in a model with Her2/neu-positive BT474-M1 tumors and more treatment-refractory tumors derived from HCC1954 cells, we observed a significant delay of tumor growth when trastuzumab therapy was combined with Rlx expression. Our results have implications for antibody therapy of cancer as well as for other anticancer treatment approaches that are based on T-cells or encapsulated chemotherapy drugs.

Density of tumour stroma is correlated to outcome after adoptive transfer of CD4+ and CD8+ T cells in a murine mammary carcinoma model

Adoptive immunotherapy shows promise for the treatment of cancer; however, partial or mixed responses remain common outcomes due to the heterogeneity of tumours. We studied three murine mammary tumour lines that express an ovalbumin-tagged version of HER-2/neu and reproducibly undergo complete regression (CR), partial regression (PR), or progressive disease (PD) after adoptive transfer of ovalbumin-specific CD8(+) (OT-I) and CD4(+) (OT-II) T cells. The three tumour lines were implanted in immunocompetent C57Bl/6 host mice, and established tumours were treated by adoptive transfer of naive OT-I and OT-II T cells. Tumours of the CR and PR classes triggered almost indistinguishable T cell responses in terms of activation, proliferation, trafficking to the tumour site, infiltration of tumour stroma, and intratumoural T cell proliferation; however, tumours of the PR class showed reduced infiltration of tumour epithelium by donor T cells. PD responses were associated with early impairment of T cell activation and proliferation in draining lymph node, followed by negligible infiltration of tumour tissue by donor T cells. Histopathological determinants of outcome were investigated through an unsupervised analysis of 64 untreated tumours representing the three response classes. Tumours of the CR class had proportionately more stroma, which had a looser, more collagen-rich histological appearance. Thus, the amount and composition of tumour stroma distinguished successfully (CR) from unsuccessful (PR or PD) outcomes after adoptive T cell transfer, a finding that might facilitate the design of immunotherapy trials for human breast cancer.