Adoptive Transfer of T-Cell-Receptor Engineered Human T Cells Specifically Reduces Viral Titers in HLA-Transgenic NSG Mice Infected with a Humanized Cytomegalovirus

Reactivation of latent human cytomegalovirus (HCMV) infection is a frequent complication in patients after allogeneic hematopoietic stem cell transplantation (HSCT). Preclinical research in murine models as well as clinical phase I/II trials have shown that the adoptive transfer of virus-specific CD8⁺ T cells is a therapeutic option for preventing HCMV disease. However, the feasibility of HCMV-specific immunotherapy is currently limited in clinical routine due to technical restrictions. It has also limitations, if the donor is HCMV-seronegative or carries only low numbers of HCMV-specific memory T cells. In this situation, grafting non-reactive T cells by virus-antigen specific T-cell receptors (TCR) may be an alternative means to transfer HCMV-specific T-cell function into HSCT recipients. Nevertheless, improvement of clinical protocols is needed before HCMV-specific cell therapy can be implemented in general clinical practice.

Here we describe a novel preclinical mouse model that will help to evaluate new HCMV-immunotherapy options. Due to the strict species specificity of CMV, we constructed a recombinant murine CMV (mCMV) coding for the HLA-A2 restricted pp65_495-503 (NLV) peptide epitope of HCMV. This peptide is expressed with flanking amino acids within the mCMV-IE2-protein in the context of experimental infection with mCMV-IE2/NLV. The NLV peptide was found to be presented by infected murine fibroblasts from NOD/SCID/IL-2Rγc^-/--HLA-A2-transgenic (NSG-A2) mice as shown by T cell specific recognition in ELISPOT and cytotoxicity assays. Interestingly, this presentation proved to be susceptible to the inhibitory function of mCMV immune evasion proteins. NSG-A2 mice were then used to evaluate antiviral control by HCMV-NLV-specific TCR (TCR_NLV)-engineered human T cells. After infection with mCMV-IE2-NLV, the NSG-A2 mice showed high viral titers in liver, spleen, lungs, and salivary glands as well as a dramatic virus-induced morbidity and mortality. In contrast, after intravenous injection of TCR_NLV-transduced human CD4⁺/CD8⁺ T cells, viral infection was reduced in all tested organs, and mice showed improved survival. These findings suggest that the NLV peptide is processed and presented by stromal and parenchymal cells of the NSG-A2 mice and promise validity of the model for preclinical evaluation of adoptive transfer protocols, for instance cell therapy with TCR-engineered T cells alone or in combination with therapeutic vaccination.