Novel Fab-peptide-HLA-I fusion proteins for redirecting pre-existing anti-CMV T cell immunity to selectively eliminate carcinoma cells

• Published in: Oncoimmunology Vol. 12; no. 1
• Main Authors: Britsch, Isabel, van Wijngaarden, Anne P., Ke, Xiurong, Hendriks, Mark. A.J.M., Samplonius, Douwe F., Ploeg, Emily M., Helfrich, Wijnand
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 31.12.2023; Taylor & Francis Group
• Subjects: anti-CMV T cells; Cancer immunotherapy; carcinoma; EpCAM; T cell-induced cytotoxicity
• ISSN: 2162-402X; 2162-402X
• DOI: 10.1080/2162402X.2023.2207868

Typically, anticancer CD8 pos T cells occur at low frequencies and become increasingly impaired in the tumor micro environment. In contrast, antiviral CD8 pos T cells display a much higher polyclonality, frequency, and functionality. In particular, cytomegalovirus (CMV) infection induces high numbers of 'inflationary' CD8 pos T cells that remain lifelong abundantly present in CMV-seropositive subjects. Importantly, these so-called inflationary anti-CMV T cells increase with age, maintain a ready-to-go state, populate tumors, and do not become exhausted or senescent. Given these favorable attributes, we devised a novel series of recombinant Fab-peptide-HLA-I fusion proteins and coined them 'ReTARGs'. A ReTARG fusion protein consists of a high-affinity Fab antibody fragment directed to carcinoma-associated cell surface antigen EpCAM (or EGFR), fused in tandem with soluble HLA-I molecule/β2-microglobulin, genetically equipped with an immunodominant peptide derived from CMV proteins pp65 (or IE-1). Decoration with EpCAM-ReTARG pp65 rendered EpCAM-expressing primary patient-derived carcinoma cells highly sensitive to selective elimination by cognate anti-CMV CD8 pos T cells. Importantly, this treatment did not induce excessive levels of proinflammatory T cell-secreted IFNγ. In contrast, analogous treatment with equimolar amounts of EpCAM/CD3-directed bispecific T-cell engager solitomab resulted in a massive release of IFNγ, a feature commonly associated with adverse cytokine-release syndrome. Combinatorial treatment with EpCAM-ReTARG pp65 and EGFR-ReTARG IE-1 strongly potentiated selective cancer cell elimination owing to the concerted action of the corresponding cognate anti-CMV CD8 pos T cell clones. In conclusion, ReTARG fusion proteins may be useful as an alternative or complementary form of targeted cancer immunotherapy for 'cold' solid cancers.