In-depth analysis of human virus-specific CD8+ T cells delineates unique phenotypic signatures for T cell specificity prediction

Following viral infection, the human immune system generates CD8+ T cell responses to virus antigens that differ in specificity, abundance, and phenotype. A characterization of virus-specific T cell responses allows one to assess infection history and to understand its contribution to protective immunity. Here, we perform in-depth profiling of CD8+ T cells binding to CMV-, EBV-, influenza-, and SARS-CoV-2-derived antigens in peripheral blood samples from 114 healthy donors and 55 cancer patients using high-dimensional mass cytometry and single-cell RNA sequencing. We analyze over 500 antigen-specific T cell responses across six different HLA alleles and observed unique phenotypes of T cells specific for antigens from different virus categories. Using machine learning, we extract phenotypic signatures of antigen-specific T cells, predict virus specificity for bulk CD8+ T cells, and validate these predictions, suggesting that machine learning can be used to accurately predict antigen specificity from T cell phenotypes.

Abstract 1894: Immunophenotypic and functional characterization of higher-risk MDS patient moDCs

Background: Myelodysplastic syndromes (MDS) are the most common acquired cause of bone marrow failure. Baseline immunity among MDS patients varies significantly with limited ability to mount a clinically significant immune response, affecting treatment and survival outcomes. Dendritic cells (DCs) can be derived from the malignant MDS clones and have compromised immune function. Here we examine the immunophenotypes and endocytic capacity of monocyte-derived DCs (moDCs) from higher-risk MDS patients.

Methods: Purified CD14+ cells were magnetically isolated from peripheral blood mononuclear cells from patients with IPSS-R Intermediate/High/Very High-risk MDS (collectively referred as higher-risk MDS) and age-matched healthy donors (n=8 and n=3, respectively). CD14+ cells were cultured in complete medium with IL-4 and GM-CSF for 6 days. Immature moDCs were then incubated with Ovalbumin-Alexa Fluor 488 conjugate (OVA), and cells from higher-risk MDS patients were also incubated with autologous tumor cell lines (TCLs) stained with a pH-sensitive red fluorescent dye (TCL-pHrodo). Phenotypic analysis was performed prior to transformation, pre- and post-incubation with OVA. Phenotypic parameters and endocytosis assays were measured by flow cytometry.

Results: Comparing CD14-CD209+ immature moDCs from higher-risk MDS patients to healthy donors, there was no significant difference in CD86 (p=0.476) and CD80 expression (p=0.190), but significantly lower CCR7 expression (p=0.010). Higher-risk MDS moDCs post-incubation with OVA also had significantly lower CCR7 expression (p=0.013) compared to donor moDCs post-incubation. Uptake of OVA was comparable in higher-risk MDS and healthy donor immature moDCs (p=0.322). However, higher-risk MDS immature moDCs had significantly decreased internalization when incubated with TCL-pHrodo compared to OVA (p<0.001). TCL-pHrodo uptake varied significantly across patients (range 5-34%). When TCL-pHrodo uptake was correlated with marker expression, CD80, CD209, and CCR7 were largely uncorrelated (r<0.300), and CD86 was moderately correlated (r=0.579). Multiple correlation analysis found that two-marker combinations of CD80 with CD86 and CD86 with CCR7 correlated moderately well with TCL-pHrodo uptake (r=0.698 and r=0.592, respectively).

Conclusions: Lower CCR7 expression among higher-risk MDS immature moDCs and post-incubation with OVA suggests dysfunction in the chemotactic ability of moDCs. Endocytic capacity of the autologous TCLs varies widely across MDS patients and is significantly lower than endocytic capacity for OVA, suggesting that DC and tumor micro-interactions are more complex than with an ovalbumin bead. Further studies, including whole exome and transcriptome sequencing of moDCs, may help elucidate mechanisms underlying differential endocytic capacity across MDS patients that could predict tumor sensitivity to immunotherapy.

Citation Format: Randy G. Tsai, Hannah F. Fields, Xinlian Zhang, Valentina Ferrari, Soo J. Park, Rafael Bejar, Tiffany N. Tanaka. Immunophenotypic and functional characterization of higher-risk MDS patient moDCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1894.

The effects of nitroxyl (HNO) on H₂O₂ metabolism and possible mechanisms of HNO signaling

Nitroxyl (HNO) possesses unique and potentially important biological/physiological activity that is currently mechanistically ill-defined. Previous work has shown that the likely biological targets for HNO are thiol proteins, oxidized metalloproteins (i.e. ferric heme proteins) and, most likely, selenoproteins. Interestingly, these are the same classes of proteins that interact with H2O2. In fact, these classes of proteins not only react with H2O2, and thus potentially responsible for the signaling actions of H2O2, but are also responsible for the degradation of H2O2. Therefore, it is not unreasonable to speculate that HNO can affect H2O2 degradation by interacting with H2O2-degrading proteins possibly leading to an increase in H2O2-mediated signaling. Moreover, considering the commonality between HNO and H2O2 biological targets, it also seems likely that HNO-mediated signaling can also be due to reactivity at otherwise H2O2-reactive sites. Herein, it is found that HNO does indeed inhibit H2O2 degradation via inhibition of H2O2-metaboilizing proteins. Also, it is found that in a system known to be regulated by H2O2 (T cell activation), HNO behaves similarly to H2O2, indicating that HNO- and H2O2-signaling may be similar and/or intimately related.

An ounce of prevention is worth a pound of cure-shoring up the public health infrastructure to respond to bioterrorist attacks

US public health departments must be prepared for the possibility of a biological terrorist event. Readiness means not only making sure our national security systems are adequate and vigilant, but that public health has the ability and resources to rapidly identify, investigate, and control the consequences of a terrorist event. Preparing for a bioterrorist attack will also improve public health's ability to address infectious disease outbreaks, food safety concerns, and environmental hazards.