A Synthetic CD8α:MyD88 Coreceptor Enhances CD8+ T-cell Responses to Weakly Immunogenic and Lowly Expressed Tumor Antigens.

T cell-based immunotherapies are a promising approach for patients with advanced cancers. However, various obstacles limit T-cell efficacy, including suboptimal T-cell receptor (TCR) activation and an immunosuppressive tumor environment. Here, we developed a fusion protein by linking CD8α and MyD88 (CD8α:MyD88) to enhance CD8+ T-cell responses to weakly immunogenic and poorly expressed tumor antigens. CD8α:MyD88-engineered T cells exhibited increased proliferation and expression of effector and costimulatory molecules in a tumor antigen-dependent manner. These effects were accompanied by elevated activation of TCR and Toll-like receptor signaling-related proteins. CD8α:MyD88-expressing T cells improved antitumor responses in mice. Enhanced antitumor activity was associated with a unique tumor cytokine/chemokine signature, improved T-cell infiltration, reduced markers of T-cell exhaustion, elevated levels of proteins associated with antigen presentation, and fewer macrophages with an immunosuppressive phenotype in tumors. Given these observations, CD8α:MyD88 represents a unique and versatile approach to help overcome immunosuppression and enhance T-cell responses to tumor antigens. Cancer Res; 77(24); 7049-58. ©2017 AACR.

TLR5 Ligand-Secreting T Cells Reshape the Tumor Microenvironment and Enhance Antitumor Activity.

The tumor microenvironment counters antitumor T-cell responses, in part, by blunting their activation and infiltration. Ligands that engage Toll-like receptors (TLR) on T cells and antigen-presenting cells can act as potent immune adjuvants. In this study, we show how tumor-reactive T cells engineered to secrete bacterial flagellin, a TLR5 ligand (TLR5L), can engender a costimulatory signal that augments antitumor activity. Human T cells engineered to express TLR5L along with DMF5, a T-cell receptor that recognizes the melanoma antigen MART-127-35 (DMF5(TLR5L) T cells), displayed increased proliferation, cytokine production, and cytolytic activity against melanoma cells. In a xenogenetic model, adoptive transfer of DMF5(TLR5L) T cells reduced tumor growth kinetics and prolonged mouse survival. In a syngeneic model, similarly engineered melanoma-reactive T cells (pmel(TLR5L)) displayed a relative increase in antitumor activity against established tumors, compared with unmodified T cells. In this model, we documented increased T-cell infiltration associated with increased levels of CCR1 and CXCR3 levels on T cells, a reduction in PD-1(+)Lag3(+) T cells and CD11(+)Gr1(+) myeloid-derived suppressor cells, and changes in the chemokine/cytokine profile of tumors. Our findings show how T cell-mediated delivery of a TLR agonist to the tumor site can contribute to antitumor efficacy, in the context of adoptive T-cell immunotherapy.

Inhibition of IRAK1/4 sensitizes T cell acute lymphoblastic leukemia to chemotherapies.

Signaling via the MyD88/IRAK pathway in T cells is indispensable for cell survival; however, it is not known whether this pathway functions in the progression of T acute lymphoblastic leukemia (T-ALL). Here, we determined that compared with thymic and peripheral T cells, T-ALL cells from patients have elevated levels of IRAK1 and IRAK4 mRNA as well as increased total and phosphorylated protein. Targeted inhibition of IRAK1 and IRAK4, either with shRNA or with a pharmacological IRAK1/4 inhibitor, dramatically impeded proliferation of T-ALL cells isolated from patients and T-ALL cells in a murine leukemia model; however, IRAK1/4 inhibition had little effect on cell death. We screened several hundred FDA-approved compounds and identified a set of drugs that had enhanced cytotoxic activity when combined with IRAK inhibition. Administration of an IRAK1/4 inhibitor or IRAK knockdown in combination with either ABT-737 or vincristine markedly reduced leukemia burden in mice and prolonged survival. IRAK1/4 signaling activated the E3 ubiquitin ligase TRAF6, increasing K63-linked ubiquitination and enhancing stability of the antiapoptotic protein MCL1; therefore, IRAK inhibition reduced MCL1 stability and sensitized T-ALL to combination therapy. These studies demonstrate that IRAK1/4 signaling promotes T-ALL progression through stabilization of MCL1 and suggest that impeding this pathway has potential as a therapeutic strategy to enhance chemotherapeutic efficacy.

NKT Cell Responses to B Cell Lymphoma.

Natural killer T (NKT) cells are a unique subset of CD1d-restricted T lymphocytes that express characteristics of both T cells and natural killer cells. NKT cells mediate tumor immune-surveillance; however, NKT cells are numerically reduced and functionally impaired in lymphoma patients. Many hematologic malignancies express CD1d molecules and co-stimulatory proteins needed to induce anti-tumor immunity by NKT cells, yet most tumors are poorly immunogenic. In this study, we sought to investigate NKT cell responses to B cell lymphoma. In the presence of exogenous antigen, both mouse and human NKT cell lines produce cytokines following stimulation by B cell lymphoma lines. NKT cell populations were examined ex vivo in mouse models of spontaneous B cell lymphoma, and it was found that during early stages, NKT cell responses were enhanced in lymphoma-bearing animals compared to disease-free animals. In contrast, in lymphoma-bearing animals with splenomegaly and lymphadenopathy, NKT cells were functionally impaired. In a mouse model of blastoid variant mantle cell lymphoma, treatment of tumor-bearing mice with a potent NKT cell agonist, α-galactosylceramide (α-GalCer), resulted in a significant decrease in disease pathology. Ex vivo studies demonstrated that NKT cells from α-GalCer treated mice produced IFN-γ following α-GalCer restimulation, unlike NKT cells from vehicle-control treated mice. These data demonstrate an important role for NKT cells in the immune response to an aggressive hematologic malignancy like mantle cell lymphoma.