Engineered FVIII-Specific Human T-Effector Cells: Can the T-Cell Receptor Modulate CD4+ T-Helper Phenotypes or Is It Just a “Switch”?
Authors: Adair Patrick , Kim Yong Chan , Pratt Kathleen P. , Scott David W 
Published: October 2019

Abstract
Engineered T cells are a vital component in the armamentarium of cellular therapies. In this presentation, we examine how human CD4+ T cells, genetically engineered to express a T-cell receptor (TCR) specific for a C2 domain epitope of the coagulation protein cofactor FVIII, can be skewed or polarized to different T-helper subsets. Two TCRs were cloned from Th2 and Th17/Th1 phenotyped CD4+ T cells isolated via a tetramer guided epitope mapping (TGEM) technique from a hemophilia A subject after clinical diagnosis of an inhibitor (neutralizing antibody) to FVIII given as replacement therapy. The two TCRs were cloned using a 5’ RACE with semi-nested PCR and transduced via a retroviral vector into healthy non-hemophilia A human donor CD4+ T cells. Based on proliferation and HLA class II tetramer staining data, engineered CD4+ T cells expressing the different cloned TCRs exhibited different avidities for the same C2 peptide (containing the epitope) over a dose titration curve, despite similar levels of TCR expression on the CD4 T-cell surface. IFN-γ, TNF-α, IL-6, and IL-10 cytokine production levels following stimulation with C2 peptide and DR1 antigen presenting cells, as measured by cytokine bead analysis, were significantly greater for the higher avidity TCR, which was cloned from a “Th2” phenotyped CD4+ T-cell clone. Interestingly, neither the engineered CD4+ T cells expressing the Th2 TCR nor the cells expressing the Th17/Th1 TCR produced cytokines characteristic of their respective original parental clones. Rather, they reflected the cytokine profiles of the donor populations used for transduction. These preliminary data led us to investigate how the different avidities of the two cloned TCRs can modulate the T-helper subset skewing/differentiation potential of engineered CD4+T cells. We hypothesized that the TCR is merely a switch that can activate or direct engineered CD4+ T cells to an antigen-specific response that would be skewed to the T-helper phenotypes of the cells prior to TCR transduction. We further hypothesized that this response could be modulated after TCR transduction according to the apparent tetramer avidity of the engineered cells. We successfully skewed the engineered human T-helper cells to Th1, Th2 and Th17 lineages, based on T-helper signature cytokine expression and the transcription factors T-bet, Gata3 and RORγt. Moreover, we observed that TCR transduction into naïve human CD4+ T cells did not itself affect the T-helper subset skewing of the cells. Preliminary experiments showed a trend toward Th2 skewing for the high avidity Th2 CD4+ T cells having an engineered TCR when they were cultured under either Th1 or Th2 polarizing conditions and stimulated with the C2 peptide, compared to the phenotypes obtained following stimulation of polyclonal CD4 T cells with anti-CD3. These studies will improve our designing of engineered TCRs for CD4+T-cell therapy, especially when concerns of T-helper effector function and plasticity are important to clinical outcomes.
Supported by NIH RO1-HL061883 (DWS), funding from Bayer and CSL Behring (KPP) and intramural support from NIAID (EMS). We thank Dr. Arthur Thompson (Puget Sound Blood Center) for enrolling patients and we thank all blood donors.

Disclosures
No relevant conflicts of interest to declare.