The T cell antigen receptor (TCR) contains ten immunoreceptor tyrosine-based activation motif (ITAM) signaling sequences distributed within six CD3 subunits; however, the reason for such structural complexity and multiplicity is unclear. Here we evaluated the effect of inactivating the three CD3ζ chain ITAMs on TCR signaling and T cell effector responses using a conditional 'switch' mouse model. Unexpectedly, we found that T cells expressing TCRs containing inactivated (non-signaling) CD3ζ ITAMs (6F-CD3ζ) exhibited reduced ability to discriminate between low- and high-affinity ligands, resulting in enhanced signaling and cytokine responses to low-affinity ligands because of a previously undetected inhibitory function of CD3ζ ITAMs. Also, 6F-CD3ζ TCRs were refractory to antagonism, as predicted by a new in silico adaptive kinetic proofreading model that revises the role of ITAM multiplicity in TCR signaling. Finally, T cells expressing 6F-CD3ζ displayed enhanced cytolytic activity against solid tumors expressing low-affinity ligands, identifying a new counterintuitive approach to TCR-mediated cancer immunotherapy.
© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.

B cell-targeted therapies, such as CD20-targeting mAbs, deplete B cells but do not target the autoantibody-producing plasma cells (PCs). PC-targeting therapies such as daratumumab (anti-CD38) form an attractive approach to treat PC-mediated diseases. CD38 possesses enzymatic and receptor capabilities, which may impact a range of cellular processes including proliferation and differentiation. However, very little is known whether and how CD38 targeting affects B-cell differentiation, in particular for humans beyond cancer settings. Using in-depth in vitro B-cell differentiation assays and signaling pathway analysis, we show that CD38 targeting with daratumumab demonstrated a significant decrease in proliferation, differentiation, and IgG production upon T cell-dependent B-cell stimulation. We found no effect on T-cell activation or proliferation. Furthermore, we demonstrate that daratumumab attenuated the activation of NF-κB in B cells and the transcription of NF-κB-targeted genes. When culturing sorted B-cell subsets with daratumumab, the switched memory B-cell subset was primarily affected. Overall, these in vitro data elucidate novel non-depleting mechanisms by which daratumumab can disturb humoral immune responses. Affecting memory B cells, daratumumab may be used as a therapeutic approach in B cell-mediated diseases other than the currently targeted malignancies.
© 2023 Verhoeven et al.

Lymph nodes (LNs) are a common site of metastasis in solid cancers, and cutaneous melanomas show inherent properties of LN colonization. However, interactions between LN stroma and pioneer metastatic cells during metastatic colonization remain largely uncharacterized. Here we studied mice implanted with GFP-expressing melanoma cells to decipher early LN colonization events. We show that Siglec1-expressing subcapsular sinus (SCS) macrophages provide anchorage to pioneer metastatic cells. We performed in vitro co-culture to demonstrate that interactions between hypersialylated cancer cells and Siglec1 drive the proliferation of cancer cells. When comparing the transcriptome profile of Siglec1-interacting cancer cells against non-Siglec1-interacting cancer cells, we detected enrichment in positive regulators of cell cycle progression. Further, knockout of St3gal3 sialyltransferase compromised the metastatic efficiency of tumor cells by reducing α-2,3-linked sialylation. Thus, the interaction between Siglec1-expressing SCS macrophages and pioneer metastatic cells drives cell cycle progression and enables efficient metastatic colonization.
© 2019, Singh and Choi.