The Identity of Human Tissue-Emigrant CD8+ T Cells.

Lymphocyte migration is essential for adaptive immune surveillance. However, our current understanding of this process is rudimentary, because most human studies have been restricted to immunological analyses of blood and various tissues. To address this knowledge gap, we used an integrated approach to characterize tissue-emigrant lineages in thoracic duct lymph (TDL). The most prevalent immune cells in human and non-human primate efferent lymph were T cells. Cytolytic CD8+ T cell subsets with effector-like epigenetic and transcriptional signatures were clonotypically skewed and selectively confined to the intravascular circulation, whereas non-cytolytic CD8+ T cell subsets with stem-like epigenetic and transcriptional signatures predominated in tissues and TDL. Moreover, these anatomically distinct gene expression profiles were recapitulated within individual clonotypes, suggesting parallel differentiation programs independent of the expressed antigen receptor. Our collective dataset provides an atlas of the migratory immune system and defines the nature of tissue-emigrant CD8+ T cells that recirculate via TDL.

The Transcription Factor T-bet Resolves Memory B Cell Subsets with Distinct Tissue Distributions and Antibody Specificities in Mice and Humans.

B cell subsets expressing the transcription factor T-bet are associated with humoral immune responses and autoimmunity. Here, we examined the anatomic distribution, clonal relationships, and functional properties of T-bet+ and T-bet- memory B cells (MBCs) in the context of the influenza-specific immune response. In mice, both T-bet- and T-bet+ hemagglutinin (HA)-specific B cells arose in germinal centers, acquired memory B cell markers, and persisted indefinitely. Lineage tracing and IgH repertoire analyses revealed minimal interconversion between T-bet- and T-bet+ MBCs, and parabionts showed differential tissue residency and recirculation properties. T-bet+ MBCs could be subdivided into recirculating T-betlo MBCs and spleen-resident T-bethi MBCs. Human MBCs displayed similar features. Conditional gene deletion studies revealed that T-bet expression in B cells was required for nearly all HA stalk-specific IgG2c antibodies and for durable neutralizing titers to influenza. Thus, T-bet expression distinguishes MBC subsets that have profoundly different homing, residency, and functional properties, and mediate distinct aspects of humoral immune memory.

Longitudinal analysis of nursing home residents' T cell responses after SARS-CoV-2 mRNA vaccinations shows influence of biological sex and SARS-CoV-2 infection history.

BACKGROUND: Vaccines and vaccine boosting have blunted excess morbidity and mortality from SARS-CoV-2 infection suffered by older nursing home residents (NHR). However, the impact of repeated vaccination on the T cell response based on biological sex and prior infection of NHR remain understudied. METHODS: We examined T cell responses to mRNA vaccines to SARS-CoV-2 in a cohort of NHR and healthcare workers (HCW) over 2 years. We used IFN-γ ELIspot and flow cytometry to assess T cell response before, two weeks and 6 months after the initial series and each of two booster vaccines. We analyzed these data longitudinally with mixed-effect modeling and also examined subsets of our cohorts for additional changes in T cell effector function. RESULTS: We show that prior SARS-CoV-2 infection and female sex contribute to higher T cell response in NHR but not HCW. When looking across time points, NHR but not HCW with prior infection had significantly higher T cell responses than infection-naive subjects. These patterns of response were maintained across multiple booster vaccinations and suggest that the age, multimorbidity, and/or frailty of the NHR cohort may accentuate sex and infection status differences in T cell response to mRNA vaccination.

Humoral and Cellular Immunity Induced by Adjuvanted and Standard Trivalent Influenza Vaccine in Older Nursing Home Residents.

BACKGROUND: Despite wide use of adjuvanted influenza vaccine in nursing home residents (NHR), little immunogenicity data exist for this population. METHODS: We collected blood from NHR (n = 85) living in nursing homes participating in a cluster randomized clinical trial comparing MF59-adjuvanted trivalent inactivated influenza vaccine (aTIV) with nonadjuvanted vaccine (TIV) (parent trial, NCT02882100). NHR received either vaccine during the 2016-2017 influenza season. We assessed cellular and humoral immunity using flow cytometry and hemagglutinin inhibition, antineuraminidase (enzyme-linked lectin assay), and microneutralization assays. RESULTS: Both vaccines were similarly immunogenic and induced antigen-specific antibodies and T cells, but aTIV specifically induced significantly larger 28 days after vaccination (D28) titers against A/H3N2 neuraminidase than TIV. CONCLUSIONS: NHRs respond immunologically to TIV and aTIV. From these data, the larger aTIV-induced antineuraminidase response at D28 may help explain the increased clinical protection observed in the parent clinical trial for aTIV over TIV in NHR during the A/H3N2-dominant 2016-2017 influenza season. Additionally, a decline back to prevaccination titers at 6 months after vaccination emphasizes the importance of annual vaccination against influenza. CLINICAL TRIALS REGISTRATION: NCT02882100.

SARS-CoV-2 Antibody Responses to the Ancestral SARS-CoV-2 Strain and Omicron BA.1 and BA.4/BA.5 Variants in Nursing Home Residents After Receipt of Bivalent COVID-19 Vaccine - Ohio and Rhode Island, September-November 2022.

Introduction of monovalent COVID-19 mRNA vaccines in late 2020 helped to mitigate disproportionate COVID-19-related morbidity and mortality in U.S. nursing homes (1); however, reduced effectiveness of monovalent vaccines during the period of Omicron variant predominance led to recommendations for booster doses with bivalent COVID-19 mRNA vaccines that include an Omicron BA.4/BA.5 spike protein component to broaden immune response and improve vaccine effectiveness against circulating Omicron variants (2). Recent studies suggest that bivalent booster doses provide substantial additional protection against SARS-CoV-2 infection and severe COVID-19-associated disease among immunocompetent adults who previously received only monovalent vaccines (3).* The immunologic response after receipt of bivalent boosters among nursing home residents, who often mount poor immunologic responses to vaccines, remains unknown. Serial testing of anti-spike protein antibody binding and neutralizing antibody titers in serum collected from 233 long-stay nursing home residents from the time of their primary vaccination series and including any subsequent booster doses, including the bivalent vaccine, was performed. The bivalent COVID-19 mRNA vaccine substantially increased anti-spike and neutralizing antibody titers against Omicron sublineages, including BA.1 and BA.4/BA.5, irrespective of previous SARS-CoV-2 infection or previous receipt of 1 or 2 booster doses. These data, in combination with evidence of low uptake of bivalent booster vaccination among residents and staff members in nursing homes (4), support the recommendation that nursing home residents and staff members receive a bivalent COVID-19 booster dose to reduce associated morbidity and mortality (2).

Significant Reduction in Vaccine-Induced Antibody Levels and Neutralization Activity Among Healthcare Workers and Nursing Home Residents 6 Months Following Coronavirus Disease 2019 BNT162b2 mRNA Vaccination.

Antibody decline occurred from 2 weeks to 6 months post-BNT162b2 mRNA vaccination in nursing home (NH) residents and healthcare workers. Antispike, receptor-binding domain, and neutralization levels dropped >81% irrespective of prior infection. Notably, 69% of infection-naive NH residents had neutralizing antibodies at or below the assay's limit of detection.

Effectiveness of a Second COVID-19 Vaccine Booster Dose Against Infection, Hospitalization, or Death Among Nursing Home Residents - 19 States, March 29-July 25, 2022.

Nursing home residents continue to experience significant COVID-19 morbidity and mortality (1). On March 29, 2022, the Advisory Committee on Immunization Practices (ACIP) recommended a second mRNA COVID-19 vaccine booster dose for adults aged ≥50 years and all immunocompromised persons who had received a first booster ≥4 months earlier.* On September 1, 2022, ACIP voted to recommend bivalent mRNA COVID-19 vaccine boosters for all persons aged ≥12 years who had completed the primary series using monovalent vaccines ≥2 months earlier (2). Data on COVID-19 booster dose vaccine effectiveness (VE) in the nursing home population are limited (3). For this analysis, academic, federal, and private partners evaluated routine care data collected from 196 U.S. community nursing homes to estimate VE of a second mRNA COVID-19 vaccine booster dose among nursing home residents who had received 3 previous COVID-19 vaccine doses (2 primary series doses and 1 booster dose). Residents who received second mRNA COVID-19 vaccine booster doses during March 29-June 15, 2022, with follow-up through July 25, 2022, were found to have 60-day VE of 25.8% against SARS-CoV-2 (the virus that causes COVID-19 infection), 73.9% against severe COVID-19 outcomes (a combined endpoint of COVID-19-associated hospitalizations or deaths), and 89.6% against COVID-19-associated deaths alone. During this period, subvariants BA.2 and BA.2.12.1 (March-June 2022), and BA.4 and BA.5 (July 2022) of the B.1.1.529 and BA.2 (Omicron) variant were predominant. These findings suggest that among nursing home residents, second mRNA COVID-19 vaccine booster doses provided additional protection over first booster doses against severe COVID-19 outcomes during a time of emerging Omicron variants. Facilities should continue to ensure that nursing home residents remain up to date with COVID-19 vaccination, including bivalent vaccine booster doses, to prevent severe COVID-19 outcomes.

On Setting Expectations for a Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine.

The global coronavirus pandemic is unlike any other since 1918. A century of dramatic medical advances has produced a public expectation that the medical field will rapidly provide solutions to restore normalcy. In less than 6 months, since severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified, the massive international effort to develop a SARS-CoV-2 vaccine has generated more than 140 vaccines in different stages of development, with 9 already recruiting into clinical trials posted on ClinicalTrials.gov. The long-term strategy to handle coronavirus disease 2019 (COVID-19) will almost certainly rely on vaccines. But what type of protection can we realistically expect to achieve from vaccines and when?

Cluster-randomized Trial of Adjuvanted Versus Nonadjuvanted Trivalent Influenza Vaccine in 823 US Nursing Homes.

BACKGROUND: Influenza leads in preventable infection-related hospitalization in nursing home (NH) residents. The adjuvanted trivalent influenza vaccine (aTIV) is more immunogenic than similarly dosed nonadjuvanted trivalent influenza vaccine (TIV), and observational studies suggest aTIV better prevents hospitalizations in older adults. We prospectively tested this in an NH setting. METHODS: NHs with ≥50 long-stay residents aged ≥65 years were randomized to offer aTIV or TIV for residents for the 2016-2017 influenza season. Using intent-to-treat resident-level analysis with Cox proportional hazards regression models adjusted for clustering by facility and a priori baseline covariates (eg, age, heart failure, and facility-level characteristics), we assessed relative aTIV:TIV effectiveness for hospitalization (ie, all-cause, respiratory, and pneumonia and influenza [P&I]). RESULTS: We randomized 823 NHs, housing 50 012 eligible residents, to aTIV or TIV. Residents were similar between groups by age (mean, ~79 years), heart failure, lung disease, and influenza and pneumococcal vaccine uptake, except aTIV homes housed fewer Black residents (14.5 vs 18.9%). Staff vaccine uptake was similar (~55%). P&I and all-cause resident hospitalization rates were lower (adjusted HR [aHR], .80 [95% CI, .66-.98; P = .03] and .94 [.89-.99; P = .02], respectively) for aTIV versus TIV, while the respiratory hospitalization rate was similar, in a season where vaccine effectiveness was considered poor. CONCLUSIONS: aTIV was more effective than TIV in preventing all-cause and P&I hospitalization from NHs during an A/H3N2-predominant season when TIV was relatively ineffective. CLINICAL TRIALS REGISTRATION: NCT02882100.

Adjuvanted Influenza Vaccine and Influenza Outbreaks in US Nursing Homes: Results From a Pragmatic Cluster-Randomized Clinical Trial.

BACKGROUND: Influenza outbreaks in nursing homes pose a threat to frail residents and occur even in vaccinated populations. We conducted a pragmatic cluster-randomized trial comparing adjuvanted trivalent influenza vaccine (aTIV) versus trivalent influenza vaccine (TIV). We report an exploratory analysis to compare the effect of aTIV versus TIV on facility-reported influenza outbreaks. METHODS: We evaluated the impact of the intent-to-treat vaccine assignment on outbreaks reported from November 2016 to March 2017. We collected data according to standard CDC definitions for both suspected outbreaks and those with a laboratory-confirmed case and adjusted for facility-level vaccination rates and resident characteristics in nursing homes. RESULTS: Of 823 randomized nursing homes, 777 (aTIV, n = 387; TIV, n = 390) reported information on influenza outbreaks. Treatment groups had similar characteristics at baseline except for race/ethnicity: homes assigned to TIV had a higher percentage of African-American residents (18.0% vs 13.7%). There were 133 versus 162 facility-reported suspected influenza outbreaks in aTIV versus TIV facilities, respectively; of these, 115 versus 140 were laboratory confirmed. The aTIV group experienced a 17% reduction in suspected (rate ratio, .83; 95% confidence interval, .65-1.05) and laboratory-confirmed (.83; .63-1.06) influenza outbreaks. Covariate adjustment increased the estimated reduction for suspected outbreaks to 21% (.79; .61-.99) and 22% for laboratory-confirmed outbreaks (.78; .60-1.02). CONCLUSIONS: In an exploratory analysis of a cluster-randomized trial we observed 17-21% fewer outbreaks with aTIV than TIV. Clinical Trials Registration. (NCT02882100).

Reduced BNT162b2 Messenger RNA Vaccine Response in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)-Naive Nursing Home Residents.

After BNT162b2 messenger RNA vaccination, antibody levels to spike, receptor-binding domain, and virus neutralization were examined in 149 nursing home residents and 110 healthcare worker controls. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-naive nursing home residents' median post-second vaccine dose antibody neutralization titers are one-quarter that of SARS-CoV-2-naive healthcare workers.

Mycobacterium tuberculosis-Induced Bronchoalveolar Lavage Gene Expression Signature in Latent Tuberculosis Infection Is Dominated by Pleiotropic Effects of CD4+ T Cell-Dependent IFN-γ Production despite the Presence of Polyfunctional T Cells within the Airways.

Tuberculosis (TB) remains a worldwide public health threat. Development of a more effective vaccination strategy to prevent pulmonary TB, the most common and contagious form of the disease, is a research priority for international TB control. A key to reaching this goal is improved understanding of the mechanisms of local immunity to Mycobacterium tuberculosis, the causative organism of TB. In this study, we evaluated global M. tuberculosis-induced gene expression in airway immune cells obtained by bronchoalveolar lavage (BAL) of individuals with latent TB infection (LTBI) and M. tuberculosis-naive controls. In prior studies, we demonstrated that BAL cells from LTBI individuals display substantial enrichment for M. tuberculosis-responsive CD4+ T cells compared with matched peripheral blood samples. We therefore specifically assessed the impact of the depletion of CD4+ and CD8+ T cells on M. tuberculosis-induced BAL cell gene expression in LTBI. Our studies identified 12 canonical pathways and a 47-gene signature that was both sensitive and specific for the contribution of CD4+ T cells to local recall responses to M. tuberculosis In contrast, depletion of CD8+ cells did not identify any genes that fit our strict criteria for inclusion in this signature. Although BAL CD4+ T cells in LTBI displayed polyfunctionality, the observed gene signature predominantly reflected the impact of IFN-γ production on a wide range of host immune responses. These findings provide a standard for comparison of the efficacy of standard bacillus Calmette-Guérin vaccination as well as novel TB vaccines now in development at impacting the initial response to re-exposure to M. tuberculosis in the human lung.

Does a lack of vaccine side effects correlate with reduced BNT162b2 mRNA vaccine response among healthcare workers and nursing home residents?

BACKGROUND: The BNT162b2 SARS-CoV-2 mRNA vaccination has mitigated the burden of COVID-19 among residents of long-term care facilities considerably, despite being excluded from the vaccine trials. Data on reactogenicity (vaccine side effects) in this population are limited. AIMS: To assess reactogenicity among nursing home (NH) residents. To provide a plausible proxy for predicting vaccine response among this population. METHODS: We enrolled and sampled NH residents and community-dwelling healthcare workers who received the BNT162b2 mRNA vaccine, to assess local or systemic reactogenicity and antibody levels (immunogenicity). RESULTS: NH residents reported reactions at a much lower frequency and lesser severity than the community-dwelling healthcare workers. These reactions were mild and transient with all subjects experiencing more local than systemic reactions. Based on our reactogenicity and immunogenicity data, we developed a linear regression model predicting log-transformed anti-spike, anti-receptor-binding domain (RBD), and neutralizing titers, with a dichotomous variable indicating the presence or absence of reported reactions which revealed a statistically significant effect, with estimated shifts in log-transformed titers ranging from 0.32 to 0.37 (all p < 0.01) indicating greater immunogenicity in subjects with one or more reported reactions of varying severity. DISCUSSION: With a significantly lower incidence of post-vaccination reactions among NH residents as reported in this study, the BNT162b2 mRNA vaccine appears to be well-tolerated among this vulnerable population. If validated in larger populations, absence of reactogenicity could help guide clinicians in prioritizing vaccine boosters. CONCLUSIONS: Reactogenicity is significantly mild among nursing home residents and overall, subjects who reported post-vaccination reactions developed higher antibody titers.

Limited immune surveillance in lymphoid tissue by cytolytic CD4+ T cells during health and HIV disease.

CD4+ T cells subsets have a wide range of important helper and regulatory functions in the immune system. Several studies have specifically suggested that circulating effector CD4+ T cells may play a direct role in control of HIV replication through cytolytic activity or autocrine ß-chemokine production. However, it remains unclear whether effector CD4+ T cells expressing cytolytic molecules and ß-chemokines are present within lymph nodes (LNs), a major site of HIV replication. Here, we report that expression of ß-chemokines and cytolytic molecules are enriched within a CD4+ T cell population with high levels of the T-box transcription factors T-bet and eomesodermin (Eomes). This effector population is predominately found in peripheral blood and is limited in LNs regardless of HIV infection or treatment status. As a result, CD4+ T cells generally lack effector functions in LNs, including cytolytic capacity and IFNγ and ß-chemokine expression, even in HIV elite controllers and during acute/early HIV infection. While we do find the presence of degranulating CD4+ T cells in LNs, these cells do not bear functional or transcriptional effector T cell properties and are inherently poor to form stable immunological synapses compared to their peripheral blood counterparts. We demonstrate that CD4+ T cell cytolytic function, phenotype, and programming in the peripheral blood is dissociated from those characteristics found in lymphoid tissues. Together, these data challenge our current models based on blood and suggest spatially and temporally dissociated mechanisms of viral control in lymphoid tissues.

Immune activation and regulatory T cells in Mycobacterium tuberculosis infected lymph nodes.

BACKGROUND: Lymph node tuberculosis (LNTB) is the most frequent extrapulmonary form of tuberculosis (TB). Studies of human tuberculosis at sites of disease are limited. LNTB provides a unique opportunity to compare local in situ and peripheral blood immune response in active Mycobacterium tuberculosis (Mtb) disease. The present study analysed T regulatory cells (Treg) frequency and activation along with CD4+ T cell function in lymph nodes from LNTB patients. RESULTS: Lymph node mononuclear cells (LNMC) were compared to autologous peripheral blood mononuclear cells (PBMC). LNMC were enriched for CD4+ T cells with a late differentiated effector memory phenotype. No differences were noted in the frequency and mutifunctional profile of memory CD4+ T cells specific for Mtb. The proportion of activated CD4+ and Tregs in LNMC was increased compared to PBMC. The correlation between Tregs and activated CD4+ T cells was stronger in LNMC than PBMC. Tregs in LNMC showed a strong positive correlation with Th1 cytokine production (IL2, IFNγ and TNFα) as well as MIP-1α after Mtb antigen stimulation. A subset of Tregs in LNMC co-expressed HLA-DR and CD38, markers of activation. CONCLUSION: Further research will determine the functional relationship between Treg and activated CD4+ T cells at lymph node sites of Mtb infection.

Diminished antibody response to influenza vaccination is characterized by expansion of an age-associated B-cell population with low PAX5.

Individuals over the age of 65 comprise a substantial portion of the world population and become more susceptible to vaccine-preventable infections with age as vaccination response diminishes. The underlying reason for this impaired vaccine response in older individuals is not entirely clear. We evaluated potential differences in phenotypic and functional responses of B cells from healthy younger (22-45years) and older (64-95years) individuals that may associate with a diminished antibody response to influenza vaccination. We report that age is associated with expansion of atypical memory B cells (CD10-CD20+CD21-CD27-) and an age-associated B cell (ABC, CD21-T-bet+CD11c+) phenotype. Reduced expression of PAX5 was also seen in older individuals. Poor influenza-specific antibody production following vaccination was associated with low PAX5 expression and a distinct composition of the ABC compartment. Collectively, these findings demonstrate that the characteristics of the ABC populations of older individuals are associated with antibody production following influenza vaccination.

Productive HIV-1 infection is enriched in CD4(-)CD8(-) double negative (DN) T cells at pleural sites of dual infection with HIV and Mycobacterium tuberculosis.

A higher human immunodeficiency virus 1 (HIV-1) viral load at pleural sites infected with Mycobacterium tuberculosis (MTB) than in peripheral blood has been documented. However, the cellular source of productive HIV infection in HIV-1/MTB-coinfected pleural fluid mononuclear cells (PFMCs) remains unclear. In this study, we observed significant quantities of HIV-1 p24(+) lymphocytes in PFMCs, but not in peripheral blood mononuclear cells (PBMCs). HIV-1 p24(+) lymphocytes were mostly enriched in DN T cells. Intracellular CD4 expression was detectable in HIV-1 p24(+) DN T cells. HIV-1 p24(+) DN T cells showed lower surface expression of human leukocyte antigen (HLA)-ABC and tetherin than did HIV-1 p24(+) CD4 T cells. Upon in vitro infection of PFMC CD4 T cells from TB mono-infected subjects, Nef- and/or Vpu-deleted HIV mutants showed lower generation of HIV-1 p24(+) DN T cells than the wild-type virus. These data indicate that productively HIV-1-infected DN T cells, generated through down-modulation of surface CD4, likely by HIV-1 Nef and Vpu, are the predominant source of HIV-1 at pleural sites of HIV/MTB coinfection.

Circulating CXCR5+PD-1+ response predicts influenza vaccine antibody responses in young adults but not elderly adults.

Although influenza vaccination is recommended for all adults annually, the incidence of vaccine failure, defined as weak or absent increase in neutralizing Ab titers, is increased in the elderly compared with young adults. The T follicular helper cell (Tfh) subset of CD4 T cells provides B cell help in germinal centers and is necessary for class-switched Ab responses. Previous studies suggested a role for circulating Tfh cells (cTfh) following influenza vaccination in adults, but cTfh have not been studied in elderly adults in whom weak vaccine responses are often observed. In this study, we studied cTfh expressing CXCR5 and programmed death-1 (PD-1). cTfh from elderly adults were present at reduced frequency, had decreased in vitro B cell help ability, and had greater expression of ICOS compared with young adults. At 7 d after inactivated influenza vaccination, cTfh correlated with influenza vaccine-specific IgM and IgG responses in young adults but not in elderly adults. In sum, we have identified aging-related changes in cTfh that correlated with reduced influenza vaccine responses. Future rational vaccine design efforts should incorporate Tfh measurement as an immune correlate of protection, particularly in the setting of aging.

Herpes Zoster Vaccination: Controversies and Common Clinical Questions.

Herpes zoster, clinically referred to as shingles, is an acute, cutaneous viral infection caused by reactivation of the varicella zoster virus, the same virus that causes chickenpox. The incidence of herpes zoster and its complications increase with decline in cell-mediated immunity, including age-associated decline. The most effective management strategy for herpes zoster is prevention of the disease through vaccination in those who are most vulnerable. Despite the demonstrated efficacy in reducing the incidence and severity of herpes zoster, the uptake of vaccine remains low. Here, we will discuss the controversies that surround the live herpes zoster vaccine and address the common clinical questions that arise. We will also discuss the new adjuvanted herpes zoster vaccine currently under investigation.

Type I IFN drives a distinctive dendritic cell maturation phenotype that allows continued class II MHC synthesis and antigen processing.

Microbial molecules or cytokines can stimulate dendritic cell (DC) maturation, which involves DC migration to lymph nodes and enhanced presentation of Ag to launch T cell responses. Microbial TLR agonists are the most studied inducers of DC maturation, but type I IFN (IFN-I) also promotes DC maturation. In response to TLR stimulation, DC maturation involves a burst of Ag processing with enhanced expression of peptide-class II MHC complexes and costimulator molecules. Subsequently, class II MHC (MHC-II) synthesis and expression in intracellular vacuolar compartments is inhibited, decreasing Ag processing function. This limits presentation to a cohort of Ags kinetically associated with the maturation stimulus and excludes presentation of Ags subsequently experienced by the DC. In contrast, our studies show that IFN-I enhances DC expression of MHC-II and costimulatory molecules without a concomitant inhibition of subsequent MHC-II synthesis and Ag processing. Expression of mRNA for MHC-II and the transcription factor CIITA is inhibited in DCs treated with TLR agonists but maintained in cells treated with IFN-I. After stimulation with IFN-I, MHC-II expression is increased on the plasma membrane but is also maintained in intracellular vacuolar compartments, consistent with sustained Ag processing function. These findings suggest that IFN-I drives a distinctive DC maturation program that enhances Ag presentation to T cells without a shutdown of Ag processing, allowing continued sampling of Ags for presentation.