Reprogramming of myeloid cells of the tumor microenvironment increases the efficiency of CTLA-4 and PD-1 blockade in experimental malignant melanoma immunotherapy

Abstract

Introduction. Blockade of immune checkpoints (immune checkpoint blockade) for the treatment of patients with malignant neoplasms is successfully and widely implemented in practical oncology. In essence, this direction of immunotherapy is the removal of suppression from T cells using antibodies to the inhibitory receptors CTLA-4 or PD-1 (PD-L1), allowing to reactivate antitumor T-cell immune responses and leading to significant clinical effects. Such immunotherapy saves patients even in the 4th stage of the oncological process. Even though the effectiveness of the checkpoint blockade is not high enough. Complete regression of the disease and complete recovery occur only in a small percentage of patients. The majority of patients with solid tumors who received checkpoint blockade either had no clinical effect or had a partial, relatively short-term effect.

One of the most common reasons preventing effective tumor elimination during checkpoint blockade therapy is that the myeloid cells of the tumor microenvironment create an immunosuppressive microenvironment inside the tumor, thus protecting malignant cells from antitumor immune responses, in particular, from the attack of cytotoxic T and NK cells.

Aim of the work – investigation the possibility of increasing the effectiveness of checkpoint blockade therapy with antibodies to CTLA-4 and PD-1 by simultaneously reprogramming myeloid cells of the tumor microenvironment from their protumor to an antitumor state using a TLR4 agonist.

Material and methods. An experimental model of B16F0 melanoma in C57BL/6J mice was used. Checkpoint blockade was performed simultaneously with two antibodies specific for CTLA-4 and PD-1. Reprogramming of myeloid cells of the tumor microenvironment was induced by intratumoral administration of acidic peptidoglycan (APG, TLR4 agonist). The effectiveness of immunotherapy was assessed by the growth rate of a solid tumor, the tumor mass on day 16 after inoculation of B16F0 cells, the cellular composition of the tumor infiltrate, and also by the intensity of transcription of key genes that determine the polarization and functional activity of myeloid and T cells, purified by sorting from tumor tissue.

Results. It has been shown that combined immunotherapy with both checkpoint blocking antibodies to CTLA-4/PD-1 and a TLR4 agonist significantly suppresses the growth of B16F0 melanoma, reduces the mass of tumors by 3 times by day 16, and induces a powerful infiltration of tumor tissue by CD8+-T cells and NK cells with increased expression of granzyme A and interferon-γ genes, as well as by monocytes and neutrophils polarized into an antitumor state, as evidenced by increased expression of the iNOS gene and the absence of active expression of the arginase-1 gene.

Conclusion. Combination therapy of malignant melanoma in an experimental model with immune checkpoint blockers together with a TLR4 agonist is significantly more effective than monotherapy with the same therapeutic agents used alone.

Keywords:cancer immunotherapy; checkpoint blockade; tumor microenvironment; transcriptional reprogramming of myeloid cells; TLR agonist

For citation: Pichugin A.V., Podsvirova S.A., Ushakova E.I., Spirin D.M., Lebedeva E.S., Ataullakhanov R.I. Reprogramming of myeloid cells of the tumor microenvironment increases the efficiency of CTLA-4 and PD-1 blockade in experimental malignant melanoma immunotherapy. Immunologiya. 2022; 43 (6): 673–90. DOI: https://doi.org/10.33029/0206-4952-2022-43-6-673-690 (in Russian)

Funding. The study was supported with the Russian Science Foundation grant (project No. 20-15-00391).

Conflict of interests. The authors declare no conflict of interests.

Authors’ contribution. Planning and conducting experiments, data analysis, editing the article – Pichugin A.V.; conducting experiments – Podsvirova S.A.; statistical processing, editing the article – Ushakova E.I.; data analysis, article editing – Spirin D.M., Lebedeva E.S.; concept of the study, design of experiments, data analysis, article writing – Ataullakhanov R.I.

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