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Abstract

Effectively activating protective CD8+ T cell immunity specifically against cancer antigens is an important pathway to prevent the growth of various types of cancers. A major obstacle in this approach is variations in cancer antigens among patients. A valuable material to overcome the antigen variation among cancer patients is the use of each individual’s own cancer cells for immunization. In colorectal cancer (CRC), approximately one-third of the patients who receive curative surgical resection have a recurrence of cancer. Therefore, the use of surgically resected CRC for immunotherapy to specifically activate the protective CD8+ T cells against their own cancer cells is a valuable approach to prevent the recurrence of cancer. However, since cancer-specific antigens are often not strongly immunogenic, a potent immunostimulant is required as an adjuvant for efficiently facilitating the activation of cancer-specific protective CD8+ T cells. We recently identified that a protein molecule, the amino-terminus region of the dense granule protein 6 (GRA6Nt) of Toxoplasma gondii, selectively activates innate expressions of IFN-γ and IL-18 and functions as a powerful adjuvant when used in immunization with nonreplicable (treated with mitomycin C or irradiated) MC38 CRC cells to potently activate the cytotoxic activity and IFN-γ production of CD8+ T cells against cancer cells. In addition, immunization using the GRA6Nt protein adjuvant effectively inhibits the growth of identical CRC cells after its challenge implantation, which mimics a recurrence of the surgically resected CRC used for the immunizations. In contrast to the two nucleotide- or deoxynucleotide-based Toll-like receptor agonists currently being used as adjuvants in cancer immunotherapy in clinical settings, GRA6Nt is a protein molecule. Thus, the rGRA6Nt protein adjuvant provides a new pathway in cancer immunotherapy to effectively activate the protective CD8+ T cells specific for the individual’s cancer cells to prevent the recurrence of surgically resected CRC in patients.

Document Type

Article

Publication Date

2026

Notes/Citation Information

© 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.

Digital Object Identifier (DOI)

https://doi.org/10.3390/cancers18061003

Funding Information

The study is supported in part by bridge funding from the University of Kentucky College of Medicine and AI095032, AI181567, and AI187757 from NIAID. Markey Cancer Center Shared Resources Facilities are supported by P30CA177558.

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