Augmenting TCR signal strength and ICOS costimulation results in metabolically fit and therapeutically potent human CAR Th17 cells

IL-17-producing antigen-specific human T cells elicit potent antitumor activity in mice. Yet, refinement of this approach is needed to position it for clinical use. While activation signal strength regulates IL-17 production by CD4+ T cells, the degree to which T cell antigen receptor (TCR) and costimulation signal strength influences Th17 immunity remains unknown. We discovered that decreasing TCR/costimulation signal strength by incremental reduction of αCD3/costimulation beads progressively altered Th17 phenotype. Moreover, Th17 cells stimulated with αCD3/inducible costimulator (ICOS) beads produced more IL-17A, IFNγ, IL-2, and IL-22 than those stimulated with αCD3/CD28 beads. Compared with Th17 cells stimulated with the standard, strong signal strength (three beads per T cell), Th17 cells propagated with 30-fold fewer αCD3/ICOS beads were less reliant on glucose and favored the central carbon pathway for bioenergetics, marked by abundant intracellular phosphoenolpyruvate (PEP). Importantly, Th17 cells stimulated with weak αCD3/ICOS beads and redirected with a chimeric antigen receptor that recognizes mesothelin were more effective at clearing human mesothelioma. Less effective CAR Th17 cells generated with high αCD3/ICOS beads were rescued by overexpressing phosphoenolpyruvate carboxykinase 1 (PCK1), a PEP regulator. Thus, Th17 therapy can be improved by using fewer activation beads during manufacturing, a finding that is cost effective and directly translatable to patients.

T cells exhibit prolonged immunity against melanoma tumors expressing high, but not low affinity antigens

We seek to identify the intrinsic properties in T cells from patients responsive or not to immunotherapy. Therapeutic efficacy is seen in patients where the immune system attacks ‘hot’ tumors due to their high mutation burden. ‘Cold’ tumors, in contrast, are not effectively recognized by T cells due to low mutation burden or expression of self-antigen. To simulate this clinical scenario, we used two different melanoma models: 1) B16F10 expressing a low affinity peptide (mgp100 = i.e. self-antigen), which represents a cold tumor or 2) B16F10 expressing a high affinity peptide (hgp100 = i.e. neoantigen), which represents a hot tumor. In these tumor-bearing mice, we infused pmel-1 CD8+ T cells expressing a TCR that recognizes gp100 peptide on B16F10 melanoma. We hypothesized that the function and persistence of adoptively transferred (ACT) cells would be increased in responsive tumors compared to unresponsive. Our findings show that pmel-1 were less exhausted and persisted more in mice bearing responsive tumors. In these mice, efficiency was observed as shrinkage of large subcutaneous tumors post ACT treatment and enhanced long-term survival. Interestingly, mice bearing hot tumors had metabolically improved pmel-1 cells, demonstrated by their ability to take up glucose and mitochondrial health. Mice that were cured from bearing responsive tumors were protected when rechallenged with both cold and hot tumors simultaneously, implicating a memory response. Herein, we underscore how tumor antigen affinity can drastically change the fate and memory of T cells.