Summary Little is known on the functional differences of the human skin myeloid DC subsets, epidermal CD207+ Langerhans cells (LCs) and dermal CD14+ DCs. We show that CD14+ DCs prime CD4+ T cells into cells that induce naïve B cells to switch isotype and become plasma cells. LCs preferentially induce the differentiation of CD4+ T cells secreting Th2 cytokines and are remarkably efficient at priming and crosspriming naïve CD8+ T cells. A third DC population, CD14-CD207-CD1a+ DC population, which resides in the dermis can activate CD8+ T cells better than CD14+ DCs but less efficiently than LCs. Thus, human skin display three DC subsets, two of them i.e. CD14+ DCs and LCs, display functional specializations; the preferential activation of humoral or cellular immunity respectively.

CD1d-restricted lymphocytes recognize a broad lipid range. However, how CD1d-restricted lymphocytes translate T cell receptor (TCR) recognition of lipids with similar group heads into distinct biological responses remains unclear. Using a soluble invariant NKT (iNKT) TCR and a newly engineered antibody specific for α-galactosylceramide (α-GalCer)–human CD1d (hCD1d) complexes, we measured the affinity of binding of iNKT TCR to hCD1d molecules loaded with a panel of α-GalCer analogues and assessed the rate of dissociation of α-GalCer and α-GalCer analogues from hCD1d molecules. We extended this analysis by studying iNKT cell synapse formation and iNKT cell activation by the same panel of α-GalCer analogues. Our results indicate the unique role of the lipid chain occupying the hCD1d F′ channel in modulating TCR binding affinity to hCD1d–lipid complexes, the formation of stable immunological synapse, and cell activation. These data are consistent with previously described conformational changes between empty and loaded hCD1d molecules (Koch, M., V.S. Stronge, D. Shepherd, S.D. Gadola, B. Mathew, G. Ritter, A.R. Fersht, G.S. Besra, R.R. Schmidt, E.Y. Jones, and V. Cerundolo. 2005. Nat. Immunol 6:819–826), suggesting that incomplete occupation of the hCD1d F′ channel results in conformational differences at the TCR recognition surface. This indirect effect provides a general mechanism by which lipid-specific lymphocytes are capable of recognizing both the group head and the length of lipid antigens, ensuring greater specificity of antigen recognition.

We evaluated human CD8 ؉ T-cell responses generated by targeting antigens to dendritic cells (DCs) through various lectin receptors. We found the immunoreceptor tyrosine-based inhibitory motifcontaining DC immunoreceptor (DCIR) to mediate potent cross-presentation. A single exposure to a low dose of anti-DCIR-antigen conjugate initiated antigenspecific CD8 ؉ T-cell immunity by all human DC subsets including ex vivogenerated DCs, skin-isolated Langerhans cells, and blood myeloid DCs and plasma-

Background: An Israeli national taskforce performed a multi-center clinical and analytical validation of seven serology assays to determine their utility and limitations for SARS-CoV-2 diagnosis. Methods: Serology assays from Roche, Abbott, Diasorin, BioMerieux, Beckman-Coulter, Siemens, and Mt.-Sinai ELISA were included. Negative samples from 2391 individuals representative of the Israeli population, and 698 SARS-CoV-2 PCR positive patients, collected between March and May 2020, were analyzed Findings: Immunoassays sensitivities between 81.5%-89.4% and specificities between 97.7%-100% resulted in a profound impact on the expected Positive Predictive Value (PPV) in low (<15%) prevalence scenarios. No meaningful increase was detected in the false positive rate in children compared to adults. A positive correlation between disease severity and antibody titers, and no decrease in antibody titers in the first 8 weeks after PCR positivity was observed. We identified a subgroup of symptomatic SARS-CoV-2 positive patients (~5% of patients), who remained seronegative across a wide range of antigens, isotypes, and technologies. Interpretation: wThe commercially available automated immunoassays exhibit significant differences in performance and expected PPV in low prevalence scenarios. The low false-positivity rate in under 20 0 s suggests that cross-reactive immunity from previous CoV strains is unlikely to explain the milder disease course in children. Finding no decrease in antibody titers in the first 8 weeks is in contrast to some reports of short half-life for SARS-CoV-2 antibodies. The~5% who were seronegative non-responders, using multiple

Bacterial and viral infections are often clinically indistinguishable, leading to inappropriate patient management and antibiotic misuse. Bacterial-induced host proteins such as procalcitonin, C-reactive protein (CRP), and Interleukin-6, are routinely used to support diagnosis of infection. However, their performance is negatively affected by inter-patient variability, including time from symptom onset, clinical syndrome, and pathogens. Our aim was to identify novel viral-induced host proteins that can complement bacterial-induced proteins to increase diagnostic accuracy. Initially, we conducted a bioinformatic screen to identify putative circulating host immune response proteins. The resulting 600 candidates were then quantitatively screened for diagnostic potential using blood samples from 1002 prospectively recruited patients with suspected acute infectious disease and controls with no apparent infection. For each patient, three independent physicians assigned a diagnosis based on comprehensive clinical and laboratory investigation including PCR for 21 pathogens yielding 319 bacterial, 334 viral, 112 control and 98 indeterminate diagnoses; 139 patients were excluded based on predetermined criteria. The best performing host-protein was TNF-related apoptosis-inducing ligand (TRAIL) (area under the curve [AUC] of 0.89; 95% confidence interval [CI], 0.86 to 0.91), which was consistently up-regulated in viral infected patients. We further developed a multi-protein signature using logistic-regression on half of the patients and validated it on the remaining half. The signature with the highest precision included both viral- and bacterial-induced proteins: TRAIL, Interferon gamma-induced protein-10, and CRP (AUC of 0.94; 95% CI, 0.92 to 0.96). The signature was superior to any of the individual proteins (P<0.001), as well as routinely used clinical parameters and their combinations (P<0.001). It remained robust across different physiological systems, times from symptom onset, and pathogens (AUCs 0.87-1.0). The accurate differential diagnosis provided by this novel combination of viral- and bacterial-induced proteins has the potential to improve management of patients with acute infections and reduce antibiotic misuse.

IMPORTANCEThe efficacy and safety profile of SARS-CoV-2 vaccines have been acquired from phase 3 studies; however, patients with cancer were not represented in these trials. Owing to the recommendation to prioritize high-risk populations for vaccination, further data are warranted.OBJECTIVE To evaluate the use and safety of the BNT162b2 vaccine in patients undergoing treatment for cancer. DESIGN, SETTING, AND PARTICIPANTSIn January 2021, mass SARS-CoV-2 vaccination of high-risk populations, including patients with cancer, was initiated in Israel. This cohort study prospectively enrolled and followed up patients with cancer and healthy participants between January 15 and March 14, 2021. The study was conducted at the Division of Oncology of Rambam Health Care Campus, the major tertiary (referral) medical center of northern Israel. Participants included 232 patients with cancer who were receiving active treatment after the first and second doses of the BNT162b2 vaccine and 261 healthy, age-matched health care workers who served as controls.EXPOSURES Serum samples were collected after each vaccine dose and in cases of seronegativity. Questionnaires regarding sociodemographic characteristics and adverse reactions were administered at serum collection. A regulatory agencies-approved assay was used to assess IgG at all time points. Patients' electronic medical records were reviewed for documentation of COVID-19 infection and results of blood cell counts, liver enzyme levels, and imaging studies. MAIN OUTCOMES AND MEASURESSeroconversion rate after the first and second doses of the BNT162b2 vaccine and documented COVID-19 infection. RESULTSOf the 232 patients undergoing treatment for cancer, 132 were men (57%); mean (SD) age was 66 (12.09) years. After the first dose of BNT162b2 vaccine, 29% (n = 25) patients were seropositive compared with 84% (n = 220) of the controls (P < .001). After the second dose, the seropositive rate reached 86% (n = 187) in the patients. Testing rate ratios per 1000 person-days after the first dose were 12.5 (95% CI, 3.4-45.7) for the patients and 48.5 (95% CI, 37.2-63.2) for the controls. Patients undergoing chemotherapy showed reduced immunogenicity (odds ratio, 0.41; 95% CI, 0.17-0.98). In seronegative patients, the rate of documented absolute leukopenia reached 39%. No COVID-19 cases were documented throughout the study period; however, 2 cases in the patient cohort were noted immediately after the first dose. Reported adverse events were similar to data in former trials comprising mostly healthy individuals. CONCLUSIONS AND RELEVANCEIn this cohort study, the SARS-CoV-2 BNT162b2 vaccine appeared to be safe and achieve satisfactory serologic status in patients with cancer. There was a pronounced lag in antibody production compared with the rate in noncancer controls; however, seroconversion occurred in most patients after the second dose. Future real-world data are warranted to determine the long-term efficacy of the vaccine with regard to type of anticancer treatment.

Specificity in the cellular immune system is controlled and regulated by the T cell antigen receptor (TCR), which specifically recognizes peptide͞major histocompatibility complex (MHC) molecules. In recent years many cancer-associated MHC-restricted peptides have been isolated and because of their highly restricted fine specificity, they are desirable targets for novel approaches in immunotherapy. Antibodies that would recognize tumor-associated MHC-peptide complexes with the same specificity as the TCR would be valuable reagents for studying antigen presentation by tumor cells, for visualizing MHCpeptide complexes on cells, and eventually for monitoring the expression of specific complexes during immunotherapy. To generate molecules with such a unique fine specificity, we selected a large nonimmune repertoire of phage Fab antibodies on recombinant HLA-A2 complexed with three common antigenic T cell, HLA-A2-restricted epitopes derived from the melanoma differentiation antigen gp100. We were able to isolate a surprisingly large panel of human recombinant Fab antibodies that exhibit a characteristic TCRlike binding specificity to each of the three gp100-derived epitopes, yet unlike TCRs, they did so with an affinity in the nanomolar range. These TCR-like antibodies recognize the native MHC-peptide complex expressed on the surface of antigen-presenting cells. Moreover, they can detect the specific MHC-peptide complexes on the surface of melanoma tumor cells. These results demonstrate the ability to isolate high-affinity human recombinant antibodies with the antigenspecific, MHC-restricted specificity of T cells, and this ability was demonstrated for three different epitopes of the same melanomaderived antigen.

(10,11). Another way to stabilize Fvs would be to connect VH and VL by a disulfide bond. One previous study (9) indicated that this is possible. But in that approach "custom disulfides" were placed in complementaritydetermining regions (CDRs) of an antibody whose structure was known (12)