Cure of established GL261 mouse gliomas after combined immunotherapy with GM‐CSF and IFNγ is mediated by both CD8⁺ and CD4⁺ T‐cells

Abstract

We were the first to demonstrate that combined immunotherapy with GM-CSF producing GL261 cells and recombinant IFNc of preestablished GL261 gliomas could cure 90% of immunized mice. To extend these findings and to uncover the underlying mechanisms, the ensuing experiments were undertaken. We hypothesized that immunizations combining both GM-CSF and IFNc systemically would increase the number of immature myeloid cells, which then would mature and differentiate into dendritic cells (DCs) and macrophages, thereby augmenting tumor antigen presentation and T-cell activation. Indeed, the combined therapy induced a systemic increase of both immature and mature myeloid cells but also an increase in T regulatory cells (T-regs). Cytotoxic anti-tumor responses, mirrored by an increase in Granzyme B-positive cells as well as IFNc-producing T-cells, were augmented after immunizations with GM-CSF and IFNc. We also show that the combined therapy induced a long-term memory with rejection of intracerebral (i.c.) rechallenges. Depletion of Tcells showed that both CD4 1 and CD8 1 T-cells were essential for the combined GM-CSF and IFNc effect. Finally, when immunizations were delayed until day 5 after tumor inoculation, only mice receiving immunotherapy with both GM-CSF and IFNc survived. We conclude that the addition of recombinant IFNc to immunizations with GM-CSF producing tumor cells increased the number of activated tumoricidal T-cells, which could eradicate established intracerebral tumors. These results clearly demonstrate that the combination of cytokines in immunotherapy of brain tumors have synergistic effects that have implications for clinical immunotherapy of human malignant brain tumors.

Anti-PD-1 Blockade and Stereotactic Radiation Produce Long-Term Survival in Mice With Intracranial Gliomas

“…Other studies examining immunotherapy in murine CNS tumor models have also found a similar dependence on the CD8 population (19). Smith et al (19) found that both CD4 and CD8 cells were essential for the combined immunologic effect of GM-CSF and IFN-γ against intracranial GL261 mouse gliomas.…”

“…Other studies examining immunotherapy in murine CNS tumor models have also found a similar dependence on the CD8 population (19). Smith et al (19) found that both CD4 and CD8 cells were essential for the combined immunologic effect of GM-CSF and IFN-γ against intracranial GL261 mouse gliomas. However, in our study, CD4-depleted mice still derived a survival benefit with the addition of PD-1 blockade to radiation, but the survival improvement was not as robust as in wild-type mice.…”

Immunizations With IFNγ Secreting Tumor Cells can Eliminate Fully Established and Invasive Rat Gliomas

“…However, the downregulation of IFNg secretion in both cell lines after irradiation implies that the major effect of IFNg transfected tumor cells is intrinsic. 19 Apoptosis occurs in a variety of cell types, including tumor cells, after radiation. 20,21 An irradiation dose of 20 Gy was necessary to fully prevent the formation of new tumor cell clones in the standard clonogenic assay but the cells were irradiated with 80 Gy before immunizations, as the cell numbers were much higher than in the clonogenic assays.…”

Glioblastomas: are individual therapies required for individual tumors?

“…Thus, an even much more individualized, targeted approach was developed which is immunotherapy by vaccination with dendritic cells after ex vivo stimulation and pulsing with autologous tumor antigens [53,54]. This is, indeed, by itself a completely individualized therapy: for each patient, a completely different vaccine is produced [53].…”

“…This is, indeed, by itself a completely individualized therapy: for each patient, a completely different vaccine is produced [53]. Being robust and simple, on the one hand, it has proven to be quite successful on the other, and might thus give an indication in which way to develop future strategies in the difficult field of glioblastoma therapy.…”