A rapid method to assess the in vivo multi-functionality of adoptively transferred engineered TCR T cells

The clinical efficacy of chimeric antigen and T cell receptor (TCR) T cell immunotherapies is attributed to their ability to proliferate and persist in vivo. Since the interaction of the engineered T cells with the targeted tumour or its environment might suppress their function, their functionality should be characterized not only before but also after adoptive transfer.

We sought to achieve this by adapting a recently developed Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapid whole blood T cell assay to stimulate engineered TCR T cells in small volumes of whole blood (<1 ml) without in vitro cellular purification. As a proof-of-concept, we used this method to longitudinally study two patients with primary Hepatitis B Virus (HBV)-related hepatocellular carcinoma who received multiple dose-escalating infusions of transiently functional mRNA-engineered HBV-TCR T cells.

We demonstrated that a simple pulsing of whole blood with a peptide corresponding to the epitope recognized by the specific HBV-TCR elicited Th1 cytokine secretion in both patients only after HBV-TCR T cell treatment and not before. The amount of cytokines secreted also showed an infusion-dose-dependent association.

These findings support the utility of the whole blood cytokine release assay in monitoring the in vivo function and quantity of engineered T cell products following adoptive transfer.