Two subsets of stem-like CD8+ memory T cell progenitors with distinct fate commitments in humans.

T cell memory relies on the generation of antigen-specific progenitors with stem-like properties. However, the identity of these progenitors has remained unclear, precluding a full understanding of the differentiation trajectories that underpin the heterogeneity of antigen-experienced T cells. We used a systematic approach guided by single-cell RNA-sequencing data to map the organizational structure of the human CD8+ memory T cell pool under physiological conditions. We identified two previously unrecognized subsets of clonally, epigenetically, functionally, phenotypically and transcriptionally distinct stem-like CD8+ memory T cells. Progenitors lacking the inhibitory receptors programmed death-1 (PD-1) and T cell immunoreceptor with Ig and ITIM domains (TIGIT) were committed to a functional lineage, whereas progenitors expressing PD-1 and TIGIT were committed to a dysfunctional, exhausted-like lineage. Collectively, these data reveal the existence of parallel differentiation programs in the human CD8+ memory T cell pool, with potentially broad implications for the development of immunotherapies and vaccines.

α-Sheet secondary structure in amyloid ß-peptide drives aggregation and toxicity in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the deposition of ß-sheet-rich, insoluble amyloid ß-peptide (Aß) plaques; however, plaque burden is not correlated with cognitive impairment in AD patients; instead, it is correlated with the presence of toxic soluble oligomers. Here, we show, by a variety of different techniques, that these Aß oligomers adopt a nonstandard secondary structure, termed "α-sheet." These oligomers form in the lag phase of aggregation, when Aß-associated cytotoxicity peaks, en route to forming nontoxic ß-sheet fibrils. De novo-designed α-sheet peptides specifically and tightly bind the toxic oligomers over monomeric and fibrillar forms of Aß, leading to inhibition of aggregation in vitro and neurotoxicity in neuroblastoma cells. Based on this specific binding, a soluble oligomer-binding assay (SOBA) was developed as an indirect probe of α-sheet content. Combined SOBA and toxicity experiments demonstrate a strong correlation between α-sheet content and toxicity. The designed α-sheet peptides are also active in vivo where they inhibit Aß-induced paralysis in a transgenic Aß Caenorhabditis elegans model and specifically target and clear soluble, toxic oligomers in a transgenic APPsw mouse model. The α-sheet hypothesis has profound implications for further understanding the mechanism behind AD pathogenesis.

The Role of α-sheet in Amyloid Oligomer Aggregation and Toxicity.

A major barrier to developing effective treatments and diagnostics for amyloid diseases is the inability of traditional protein structure characterization methods to elucidate the structure of the toxic oligomers that form during amyloidogenesis. Some years ago, our lab "discovered" a novel protein secondary structure in molecular dynamics simulations of multiple unrelated amyloid proteins, which we call α-sheet. We hypothesize that α-sheet plays an important role in amyloid aggregation and oligomer toxicity. De novo monomeric α-sheet peptides designed to be complementary to the structure observed in simulations inhibit amyloid aggregation and toxicity and specifically bind to the toxic oligomeric species in a variety of unrelated mammalian and bacterial amyloid systems associated with a range of diseases. Furthermore, spectroscopic analysis of α-sheet structure, including nuclear magnetic resonance (NMR), circular dichroism (CD), and Fourier-transform infrared spectroscopy (FTIR), correspond well to values predicted for α-sheet. These α-sheet designs are now being tested for their ability to detect and neutralize toxic oligomers in animals and in patient samples, demonstrating the potential of this nonstandard secondary structure as a target for therapeutic and diagnostic agents for amyloid diseases.

Merkel cell polyomavirus-specific and CD39+CLA+ CD8 T cells as blood-based predictive biomarkers for PD-1 blockade in Merkel cell carcinoma.

Merkel cell carcinoma is a skin cancer often driven by Merkel cell polyomavirus (MCPyV) with high rates of response to anti-PD-1 therapy despite low mutational burden. MCPyV-specific CD8 T cells are implicated in anti-PD-1-associated immune responses and provide a means to directly study tumor-specific T cell responses to treatment. Using mass cytometry and combinatorial tetramer staining, we find that baseline frequencies of blood MCPyV-specific cells correlated with response and survival. Frequencies of these cells decrease markedly during response to therapy. Phenotypes of MCPyV-specific CD8 T cells have distinct expression patterns of CD39, cutaneous lymphocyte-associated antigen (CLA), and CD103. Correspondingly, overall bulk CD39+CLA+ CD8 T cell frequencies in blood correlate with MCPyV-specific cell frequencies and similarly predicted favorable clinical outcomes. Conversely, frequencies of CD39+CD103+ CD8 T cells are associated with tumor burden and worse outcomes. These cell subsets can be useful as biomarkers and to isolate blood-derived tumor-specific T cells.