Background Even when tumors are infiltrated by T cells, progressive growth eventually kills the host. The use of immune checkpoint inhibitors (ICI) or adoptive transfer of tumor-infiltrating lymphocytes (TILs) have led to advanced immunotherapies which can be successful in some patients with certain types of cancers. Even though these immunotherapies have revolutionized modern cancer treatments, achieving tumor eradication remains a major challenge.^{1 2} When ICI and TIL therapies are effective, cancer-specific neoantigens seem to be the important immunological targets.^{3 4} An alternative approach isolates T cell receptors (TCRs) from neoantigen-specific T cells for adoptive transfer of TCR-engineered peripheral blood T cells (TCR-T cell therapy).^{5 6} We wanted to determine the requirements needed for TCR-T cell therapy to eradicate established solid tumors.

Methods We used the UV-induced, primary and autochthonous cancer cell line 6132A and its well-studied neoantigen mL9.⁷ We isolated a TCR from mL9-specific CD4⁺ T cells (CD4TCR) and another TCR from 6132A-specific CD8⁺ T cells (CD8TCR) generated from the spleen of 6132A–immune mice. We cloned the CD4TCR and the CD8TCR into retroviral vectors and evaluated in vitro and in vivo responses of TCR-engineered CD4⁺ and CD8⁺ T cells.

Results The CD4TCR recognized the immunosuppressive tumor stroma and caused destruction followed by long-term growth arrest of tumors formed by the MHC class II negative 6132A cancer cells. However, the CD4TCR failed to eradicate the tumors completely. Remarkably, the CD8TCR was ineffective on its own, yet large unmanipulated solid tumors were eradicated when the CD8TCR was combined with the CD4TCR. Thus, direct cancer cell recognition by the CD8TCR together with stromal recognition by the CD4TCR was needed for effective therapy. As underlying mechanism, in vitro analyses suggest a four-cell type interaction between CD4⁺ and CD8⁺ T cells together with stromal APCs and cancer cells leading to effective elimination of cancer cells.⁸

Conclusions CD8TCRs eradicated long-established solid tumors expressing unmanipulated mutant neoantigens only when combined with a CD4TCR. In vitro experiments suggest a four-cell interaction being essential for cancer cell eradication.

References

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