One of the main goals in T cell biology has been to investigate how TCR recognition of peptide:MHC (pMHC) determines T cell phenotype and fate. Ag recognition is required to facilitate survival, expansion, and effector function of T cells. Historically, TCR affinity for pMHC has been used as a predictor for T cell fate and responsiveness, but there have now been several examples of nonfunctional high-affinity clones and low-affinity highly functional clones. Recently, more attention has been paid to the TCR being a mechanoreceptor where the key biophysical determinant is TCR bond lifetime under force. As outlined in this review, the fundamental parameters between the TCR and pMHC that control Ag recognition and T cell triggering are affinity, bond lifetime, and the amount of force at which the peak lifetime occurs.

Immunotherapies relying on type 1 immunity have shown robust clinical responses in some cancers yet remain relatively ineffective in solid breast tumors. Polarization toward type 2 immunity and expansion of myeloid-derived suppressor cells (MDSC) confer resistance to therapy, though it remains unclear whether polarization toward type 3 immunity occurs or has a similar effect. Therefore, we investigated the involvement of type 3 T_h17 and T_h22 cells and their association with expanding MDSC populations in the 4T1 mouse mammary carcinoma model. T_h17 and T_h22 were detected in the earliest measurable mass at d 14 and remained present until the final sampling on d 28. In peripheral organs, T_h17 populations were significantly higher than the non-tumor bearing control and peaked early at d 7, before a palpable tumor had formed. Peripheral T_h22 proportions were also significantly increased, though at later times when tumors were established. To further address the mechanism underlying type 3 immune cell and MDSC recruitment, we used CRISPR-Cas9 to knock out 4T1 tumor production of interleukin-6 (4T1-IL-6-KO), which functions in myelopoiesis, MDSC recruitment, and T_h maturation. While 4T1-IL-6-KO tumor growth was similar to the control, the reduced IL-6 significantly expanded the total CD4⁺ T_h population and T_h17 in tumors, while T_h22 and MDSC were reduced in all tissues; this suggests that clinical IL-6 depletion combined with immunotherapy could improve outcomes. In sum, 4T1 mammary carcinomas secrete IL-6 and other factors, to polarize and reshape T_h populations and expand distinct T_h17 and T_h22 populations, which may facilitate tumor growth and confer immunotherapy resistance.

Mast cell (MC) contributions to solid cancer microenvironments are controversial and seem tissue dependent. TGFβ is a potent MC chemokine abundantly expressed by high-grade cancers. Previous work reported that TGFβ alone induces biologically relevant expression of IL-6 from MC, which is potentially important for reciprocal paracrine interactions with cancer cells and other leukocytes. Therefore, the objective of the present study was to examine MC in an immunocompetent, high-grade model of breast cancer. Using the 4T1 system in BALB/c mice, we compared mast cell infiltration into primary tumors of wild-type versus 4T1 cell-specific knockouts of IL-6. We also hypothesized that TGFβ institutes a training effect on MC like other metabolically driven mechanisms involving the NLRP3 inflammasome. Using a mixture of flow cytometric and qPCR assays we explored potential MC training in the context of TGFβ. Results: Contrary to our prediction, MC infiltration into IL-6KO tumors was significantly increased compared to WT. Studies of classic intracellular training mechanisms in response to TGFβ were mixed. Glucose uptake, glycolytic capacity, mitochondrial potential, and ASC speck formation were unaffected by TGFβ, but IL-6 expression increased as previously seen. Additionally, we were unable to detect substantive NLRP3 expression in MC regardless of condition. Despite these results, we were surprised to observe robust increases in expression of IL-1β, IL-18, and caspase-1 with TGFβ stimulus. We conclude that MC are actively recruited to 4T1 tumors dependent on IL-6 (and TGFβ), MC produce select cytokines in response to TGFβ, yet the mechanism explaining this does not involve the NLRP3 inflammasome and remains unresolved.