B Cells Are Critical to T-cell—Mediated Antitumor Immunity Induced by a Combined Immune-Stimulatory/Conditionally Cytotoxic Therapy for Glioblastoma

Abstract

We have demonstrated that modifying the tumor microenvironment through intratumoral administration of adenoviral vectors (Ad) encoding the conditional cytotoxic molecule, i.e., HSV1-TK and the immune-stimulatory cytokine, i.e., fms-like tyrosine kinase 3 ligand (Flt3L) leads to T-cell-dependent tumor regression in rodent models of glioblastoma. We investigated the role of B cells during immune-mediated glioblastoma multiforme regression. Although treatment with Ad-TK+Ad-Flt3L induced tumor regression in 60% of wild-type (WT) mice, it completely failed in B-cell-deficient Igh6(-/-) mice. Tumor-specific T-cell precursors were detected in Ad-TK+Ad-Flt3L-treated WT mice but not in Igh6(-/-) mice. The treatment also failed in WT mice depleted of total B cells or marginal zone B cells. Because we could not detect circulating antibodies against tumor cells and the treatment was equally efficient in WT mice and in mice with B-cell-specific deletion of Prdm 1 (encoding Blimp-1), in which B cells are present but unable to fully differentiate into antibody-secreting plasma cells, tumor regression in this model is not dependent on B cells' production of tumor antigen-specific immunoglobulins. Instead, B cells seem to play a role as antigen-presenting cells (APCs). Treatment with Ad-TK+Ad-Flt3L led to an increase in the number of B cells in the cervical lymph nodes, which stimulated the proliferation of syngeneic T cells and induced clonal expansion of antitumor T cells. Our data show that B cells act as APCs, playing a critical role in clonal expansion of tumor antigen-specific T cells and brain tumor regression.

Immunosuppressive Myeloid Cells’ Blockade in the Glioma Microenvironment Enhances the Efficacy of Immune-Stimulatory Gene Therapy

“…Therefore, to ensure the maintenance of TK/Flt3L-induced tumor-specific T cell proliferation, we administered the antibody so that MDSCs would be eliminated from the GBM TME around the peak of the T cell response, which occurs 7 days after the administration of gene therapy. 18,20,64 In agreement with our hypothesis, we saw that combining MDSC depletion with the TK/Flt3L gene therapy increased the frequency of tumor-specific CD8 T cells in the TME and increased cytotoxicity as indicated by enhanced granzyme B production. Although the increased frequency of tumor-specific CD8 T cells could result from either increased proliferation or decreased apoptosis of the CD8 T cells, our in vitro data regarding the impact of MDSCs on antigenspecific CD8 T cell proliferation do suggest that depleting immunosuppressive MDSCs allows for amplified tumor-specific CD8 T cell proliferation in the TME (Figure 7).…”

“…17,19,64,69 All cell suspensions obtained from tissues were resuspended in PBS containing 2% fetal calf serum (FCS) (flow buffer) for antibody staining for flow cytometry. All flow data were acquired on a FACSAria flow cytometer (BD Biosciences) and analyzed using Flow Jo version 10 (Treestar).…”

Complement C3-dependent uptake of targeted liposomes into human macrophages, B cells, dendritic cells, neutrophils, and MDSCs

“…The first step in creating a robust adaptive immune response against cancer cells requires efficient presentation of tumor antigen by APCs to the effector cells of the immune system. 1,3 APCs present 26,27 Techniques to improve antigen presentation include ex vivo strategies such as adoptive T-cell transfer and in vivo strategies such as nanoparticle antigen delivery. 8,9,19,28 Drawbacks of ex vivo techniques include high cost and lack of a memory T-cell population after inoculation into the patient.…”

Preclinical Efficacy and Safety Profile of Allometrically Scaled Doses of Doxycycline Used to Turn “On” Therapeutic Transgene Expression from High-Capacity Adenoviral Vectors in a Glioma Model

“…[7][8][9][10][11][12] To address GBM recurrence, we developed a novel combined gene therapy strategy utilizing the HC-Ads encoding the herpes simplex type 1-thymidine kinase (TK) transgene, which induces apoptosis in dividing cells in the presence of the prodrug, ganciclovir (GCV), and the FMS-like tyrosine kinase 3 ligand (Flt3L) transgene under tight regulation by the Tet-On transactivation system. [13][14][15][16][17][18][19][20][21][22][23][24] Flt3L has been shown to recruit dendritic cells (DCs) to the site of TK-mediated tumor killing where they bind to the high-mobility-group box 1 (HMGB1) protein, an alarmin released by dying GBM cells within the tumor microenvironment, acting as an endogenous ligand for Toll-like receptor 2 (TLR2) on DCs. 21,22 Once bound to HMGB1, these DCs migrate to the draining lymph nodes to prime CD4…”