scholarly journals Comparative analysis of human immune responses following SARS-CoV-2 vaccination with BNT162b2, mRNA-1273, or Ad26.COV2.S

2021 ◽  
Author(s):  
Dominique J. Barbeau ◽  
Judith M. Martin ◽  
Emily Carney ◽  
Emily Dougherty ◽  
Joshua D. Doyle ◽  
...  
Keyword(s):  
T Cell ◽  
Immune Responses ◽  
Cell Response ◽  
T Cell Responses ◽  
Neutralizing Antibody ◽  
T Cell Response ◽  
Virus Neutralization ◽  
Cell Responses ◽  
Humoral Responses ◽  
Prospective Longitudinal

AbstractBackgroundThree SARS-CoV-2 vaccines, two based on mRNA, BNT162b2 and mRNA-1273, and one based on an adenovirus platform, Ad26.COV2.S, received emergency use authorization by the U.S. Food and Drug Administration in 2020/2021. These vaccines displayed clinical efficacy in initial studies against confirmed COVID-19 of 95.0%, 94.1%, and 66.9%, respectively.MethodsIndividuals receiving one of these vaccines were invited to participate in a prospective longitudinal comparative study of immune responses elicited by the three vaccines. In this observational cohort study, humoral responses were evaluated using a SARS-CoV-2 receptor-binding domain (RBD) ELISA and a SARS-CoV-2 virus neutralization assay at mean of 21-31 days and 45-63 days following each initial vaccination. IFN-γ ELISPOT assays were conducted with peripheral blood mononuclear cells obtained at a median of 45-63 days after each initial vaccination.ResultsThe two mRNA-based platforms elicited similar RBD ELISA responses and neutralizing antibody responses. The adenovirus-based vaccine elicited significantly lower RBD ELISA and SARS-CoV-2 virus neutralization activity. The mRNA-1273 vaccine elicited significantly higher spike glycoprotein-specific T cell responses than either the BNT162b2 or the Ad26.COV2.S vaccines.ConclusionsBoth mRNA based vaccines elicited higher magnitude humoral responses than Ad26.COV2.S and mRNA1273 elicited the highest magnitude of T cell response. Neutralizing antibody titers correlated with reported estimates of vaccine efficacy.Summary of key pointsWe compared antigen specific humoral and T cell responses following vaccination with BNT162b2, mRNA-1273, or Ad26.COV2.S. Both mRNA based vaccines elicited higher magnitude humoral responses than Ad26.COV2.S and mRNA1273 elicited the highest magnitude of T cell response.

scholarly journals Sustained Specific and Cross-Reactive T Cell Responses to Zika and Dengue Virus NS3 in West Africa

2018 ◽  
Vol 92 (7) ◽  
Author(s):  
Bobby Brooke Herrera ◽  
Wen-Yang Tsai ◽  
Charlotte A. Chang ◽  
Donald J. Hamel ◽  
Wei-Kung Wang ◽  
...  
Keyword(s):  
T Cell ◽  
Immune Responses ◽  
Dengue Virus ◽  
Zika Virus ◽  
Cell Response ◽  
Vaccine Development ◽  
T Cell Responses ◽  
T Cell Response ◽  
Zikv Infection ◽  
Cell Responses

ABSTRACT Recent studies on the role of T cells in Zika virus (ZIKV) infection have shown that T cell responses to Asian ZIKV infection are important for protection, and that previous dengue virus (DENV) exposure amplifies the protective T cell response to Asian ZIKV. Human T cell responses to African ZIKV infection, however, remain unexplored. Here, we utilized the modified anthrax toxin delivery system to develop a flavivirus enzyme-linked immunosorbent spot (ELISPOT) assay. Using human ZIKV and DENV samples from Senegal, West Africa, our results demonstrate specific and cross-reactive T cell responses to nonstructural protein 3 (NS3). Specifically, we found that T cell responses to NS3 protease are ZIKV and DENV specific, but responses to NS3 helicase are cross-reactive. Sequential sample analyses revealed immune responses sustained many years after infection. These results have important implications for African ZIKV/DENV vaccine development, as well as for potential flavivirus diagnostics based on T cell responses. IMPORTANCE The recent Zika virus (ZIKV) epidemic in Latin America and the associated congenital microcephaly and Guillain-Barré syndrome have raised questions as to why we have not recognized these distinct clinical diseases in Africa. The human immunologic response to ZIKV and related flaviviruses in Africa represents a research gap that may shed light on the mechanisms contributing to protection. The goal of our study was to develop an inexpensive assay to detect and characterize the T cell response to African ZIKV and DENV. Our data show long-term specific and cross-reactive human immune responses against African ZIKV and DENV, suggesting the usefulness of a diagnostic based on the T cell response. Additionally, we show that prior flavivirus exposure influences the magnitude of the T cell response. The identification of immune responses to African ZIKV and DENV is of relevance to vaccine development.

EBV-positive lymphoma patients have a selective deficiency in EBV immunity

2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 21032-21032
Author(s):  
K. N. Heller ◽  
P. G. Steinherz ◽  
C. S. Portlock ◽  
C. Münz
Keyword(s):  
Immune Response ◽  
T Cells ◽  
T Cell ◽  
Immune Responses ◽  
Healthy Volunteers ◽  
Cell Response ◽  
T Cell Responses ◽  
T Cell Response ◽  
Specific Immune Response ◽  
Cell Responses

21032 Background: Epstein-Barr virus (EBV) asymptomatically establishes persistent infections in more than 90% of the adult population. However, due to effective immune control, only a minority of infected carriers develops spontaneous EBV-associated lymphomas. Since EBV nuclear antigen-1 (EBNA1) is the only protein expressed in all proliferating EBV infected cells we hypothesize that EBNA1 specific immune response is critical in preventing EBV-positive lymphomas. Methods: After informed consent, peripheral blood from healthy volunteers and lymphoma patients (prior to therapy- no evidence of cytopenia) were stimulated (ex vivo) with overlapping peptides covering the immunogenic EBNA1 (aa400–641) sequence. Frequency of EBNA1-specific T-cells were assessed by intracellular cytokine staining and flow cytometric proliferation assays. Cytokine pattern, surface marker phenotype and functional reactivity against EBV specific and control antigens were analyzed. Results: Patient and volunteer immune responses to control antigens and other viruses were assessed and statistically indistinguishable. EBNA1 specific CD4+ T cell responses were detected among 18 of 20 healthy carriers, and among 10 of 16 patients with EBV-negative lymphoma (relative to healthy volunteers p=0.145 via paired student T test). None of the patients with EBV-positive lymphomas (n=8) had a detectable EBNA1-specific CD4+ T-cell response (p<0.003 relative to healthy volunteers and patients with EBV-negative lymphomas). Conclusions: Healthy volunteers and patients with EBV-negative lymphoma have statistically similar EBNA1-specific CD4+ T cell responses. Although patients with EBV-positive lymphoma have intact immune responses to common viruses and antigens, they selectively lack an EBNA1-specific CD4+ T cell response. An intact EBNA1 specific immune response among patients with EBV-negaitve lymphoma implies that lymphoma is not a cause of a selective immune deficiency. On the contrary, these findings suggest that EBNA1-specific CD4+ T cells are critical in the prevention of EBV mediated lymphomas, and a defect in EBNA1 specific immunity may leave EBV carriers suseptible to EBV-positive lymphomas. EBNA1- specific CD4+ T cell function may be a new target for therapies of EBV-associated malignancies. No significant financial relationships to disclose.

scholarly journals AAV Vector Dose Determines TLR9 Dependence of CD8+ T Cell Response to Transgene Product

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 3-3
Author(s):  
Ning Li ◽  
Thais Bertolini ◽  
Roland W Herzog
Keyword(s):  
T Cells ◽  
T Cell ◽  
Gene Transfer ◽  
Immune Responses ◽  
Cell Response ◽  
T Cell Responses ◽  
Cd8 T Cell ◽  
T Cell Response ◽  
Innate Immune ◽  
Cell Responses

Adeno-associated viral (AAV) vectors are currently evaluated in multiple Phase III clinical trial for the treatment of hemophilia and neuromuscular disorders. A major concern is the potential for immune responses. Viral vectors are initially sensed by the innate immune system, which shapes subsequent adaptive immune responses. Particularly, toll-like receptors (TLRs) have been reported as major sensors of pathogens during innate immune response. TLRs recognize pathogen-associated molecular patterns (PAMPs). Our previous studies found that cross-priming of AAV capsid-specific CD8+ T cells depended on TLR9-MyD88 pathway. TLR9 is an endosomal DNA receptor that responds most potently to unmethylated CpG motifs as found in bacterial and viral DNA. Similarly, others documented TLR9-dependent CD8+ T cell responses against non-secreted transgene products such as LacZ and hemagglutinin upon muscle-directed AAV gene transfer. Similarly, we published that CD8+ T cell responses to a secreted ovalbumin (ova) transgene product were substantially reduced (although not entirely eliminated) upon muscle gene transfer in TLR9-deficient mice [J Innate Immun. 7:302-14]. For those studies, we had used a self-complementary scAAV genomes, which we found to more strongly activate TLR9 than conventional single-stranded ssAAV vectors. Here, we performed intramuscular injections of 3 doses of ssAAV1-CMV-ova vector (2X1010, 2X1011 and1X1012 vg) in wild-type (WT), TLR9-/-, or MYD88-/- C57BL/6 mice. Using MHC tetramer (H2-Kb -SIINFEKL), ova-specific CD8+ T cell frequencies were monitored in peripheral blood for up to 6 weeks. As expected from prior studies, TLR9-/- mice showed a substantially reduced response (1.2% tetramer+ of CD8) at the low dose when compared to WT (12% tetramer+ of CD8) animals (p&lt;0.0001, n=5/group). To our surprise, CD8+ T cell responses were similar in TLR9-/- and WT mice at the 2 higher doses. TLR9-/- mice displayed 16% and 3.3% tetramer+ of CD8 frequencies at the median and the high doses, respectively; which was comparable to WT mice, where 15% and 4.8% tetramer+ of CD8 frequencies were observed (n=5/group). Therefore, sensing of the AAV genome by TLR9 is more critical for the CD8+ T cell response to the secreted transgene product at lower vector doses (possibly related to the lower levels of transgene expression). Interestingly, transgene product-specific CD8+ T cell responses were much reduced in MyD88-/- mice, in which 0.2% and 1.7% tetramer+ of CD8 frequencies were found for low and median doses. Therefore, an alternative signaling pathway that includes the MyD88 adaptor molecule likely exists that is more critical than TLR9 above a certain level of expression. The reduced strength of the CD8+ T cell response seen at the highest vector dose compared to the medium dose may be explained by a transient increase in FoxP3+ Treg and in PD-1+ T cells that we observed 1 week after gene transfer and that was significantly greater at the highest vector dose. In related experiments, we performed intramuscular gene transfer using a ssAAV1-EF1a-FIX vector in hemophilia B mice (C3H/HeJ F9-/-, 1x1011 vg/mouse). Here, we used either a vector with native sequences or with an expression cassette that was entirely devoid of CpG motifs (and there stimulates TLR9 less effectively). CpG depletion did not have substantial effects on antibody formation against human FIX or the viral capsid. However, CD8+ T cell infiltrates in skeletal muscle were markedly reduced but not entirely eliminated when tissue sections were examined 1 month after gene transfer. In conclusion, TLR9 signaling is one important factor in the activation of transgene product-specific CD8+ T cells in AAV gene transfer, but other pathways exist that may be more critical depending on vector dose or levels of expression. Disclosures Herzog: Takeda Pharmaceuticals: Patents & Royalties.

scholarly journals Discordant humoral and T cell immune responses to SARS-CoV-2 vaccination in people with multiple sclerosis on anti-CD20 therapy

2021 ◽  
Author(s):  
Sachin P Gadani ◽  
Maria Reyes-Mantilla ◽  
Larissa Jank ◽  
Samantha Harris ◽  
Morgan Douglas ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
T Cell ◽  
Immune Responses ◽  
T Cell Responses ◽  
T Cell Response ◽  
Cell Immune Response ◽  
Ifn Gamma ◽  
Cell Responses ◽  
Anti Cd20 ◽  
Humoral Responses

Background: Sphingosine-1-phosphate receptor (S1P) modulators and antiCD20 therapies impair humoral responses to SARS-CoV-2 mRNA vaccines. Whether disease modifying therapies (DMTs) for multiple sclerosis (MS) also impact T cell immune response to vaccination is unknown. Methods: In 101 people with MS, we measured humoral responses via an immunoassay to measure IgG against the COVID-19 spike S1 glycoprotein in serum. We also measured T cell responses using FluoroSpot assay for interferon gamma (IFN-gamma; Mabtech,Sweden) using cryopreserved rested PBMCs and then incubated in cRPMI with 1microg/ml of pooled peptides spanning the entire spike glycoprotein (Genscript, 2 pools; 158 peptides each). Plates were read on an AID iSpot Spectrum to determine number of spot forming cells (SFC)/10 6 PBMCs. We tested for differences in immune responses across DMTs using linear models. Findings: Humoral responses were detected in 22/39 (56.4%) participants on anti-CD20 and in 59/63 (93.6%) participants on no or other DMTs. In a subset with immune cell phenotyping (n=88; 87%), T cell responses were detected in 76/88 (86%), including 32/33 (96.9%) participants on anti-CD20 therapies. AntiCD20 therapies were associated with an increase in IFN-gamma; SFC counts relative to those on no DMT or other DMTs (for antiCD20 vs. no DMT: 425.9% higher [95%CI: 109.6%, 1206.6%] higher; p<0.001; for antiCD20 vs. other DMTs: 289.6% [95%CI: 85.9%, 716.6%] higher; p<0.001). Interpretation: We identified a robust T cell response in individuals on anti-CD20 therapies despite a reduced humoral response to SARS-CoV-2 vaccination. Follow up studies are needed to determine if this translates to protection against COVID-19 infection.

scholarly journals Single dose of BNT162b2 mRNA vaccine against SARS-CoV2 induces neutralizing antibody and polyfunctional T-cell responses in patients with CML

2021 ◽  
Author(s):  
Patrick Harrington ◽  
Katie Doores ◽  
Deepti Radia ◽  
Amy O'Reilly ◽  
Ho Pui Jeff Lam ◽  
...  
Keyword(s):  
Immune Response ◽  
Single Dose ◽  
T Cell ◽  
Cell Response ◽  
T Cell Responses ◽  
Neutralizing Antibody ◽  
T Cell Response ◽  
Haematological Malignancies ◽  
Cell Responses ◽  
Cellular Immune

Patients receiving targeted cancer treatments such as tyrosine kinase inhibitors (TKIs) have been classified in the clinically extremely vulnerable group to develop severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), including patients with Chronic Myeloid Leukaemia (CML) taking TKIs. In addition, concerns that immunocompromised individuals with solid and haematological malignancies may not mount an adequate immune response to a single dose of SARS-CoV-2 BNT162b2 (Pfizer- BioNTech) vaccine have been raised. We evaluated humoral and cellular immune responses after a first injection of BNT162b2 vaccine in 16 CML patients. Seroconversion and cellular immune response prior and after vaccination were assessed. By day 21 post-vaccination, anti-Spike IgG were detected in 14/16 (87.5%) of CML patients and all developed a neutralizing antibody response (ID50>50), including medium (ID50 of 200-500) or high (501-2000) neutralising antibodies titres in 9/16 (56.25%) patients. T cell response was seen in 14/15 (93.3%) evaluable patients, with polyfunctional responses seen in 12/15 (80%) patients (polyfunctional CD4+ response 9/15, polyfunctional CD8+ T cell response 9/15). These data demonstrate the immunogenicity of a single dose of SARS-CoV-2 BNT162b2 vaccine in most CML patients with both neutralizing antibodies and polyfunctional T-cell responses seen, in contrast to patients with solid tumour or lymphoid haematological malignancies.

scholarly journals Targeting cancer-associated fibroblast-secreted WNT2 restores dendritic cell-mediated antitumour immunity

Gut ◽  
2021 ◽  
pp. gutjnl-2020-322924
Author(s):  
Tuxiong Huang ◽  
Xiang-Yu Tan ◽  
Hui-Si Huang ◽  
Yu-Ting Li ◽  
Bei-Lei Liu ◽  
...  
Keyword(s):  
T Cell ◽  
Dendritic Cell ◽  
Cell Response ◽  
T Cell Responses ◽  
Tumour Microenvironment ◽  
T Cell Response ◽  
Cell Responses ◽  
Cancer Associated Fibroblast ◽  
Anticancer Immunotherapy ◽  
Novel Therapeutic Strategies

ObjectiveSolid tumours respond poorly to immune checkpoint inhibitor (ICI) therapies. One major therapeutic obstacle is the immunosuppressive tumour microenvironment (TME). Cancer-associated fibroblasts (CAFs) are a key component of the TME and negatively regulate antitumour T-cell response. Here, we aimed to uncover the mechanism underlying CAFs-mediated tumour immune evasion and to develop novel therapeutic strategies targeting CAFs for enhancing ICI efficacy in oesophageal squamous cell carcinoma (OSCC) and colorectal cancer (CRC).DesignAnti-WNT2 monoclonal antibody (mAb) was used to treat immunocompetent C57BL/6 mice bearing subcutaneously grafted mEC25 or CMT93 alone or combined with anti-programmed cell death protein 1 (PD-1), and the antitumour efficiency and immune response were assessed. CAFs-induced suppression of dendritic cell (DC)-differentiation and DC-mediated antitumour immunity were analysed by interfering with CAFs-derived WNT2, either by anti-WNT2 mAb or with short hairpin RNA-mediated knockdown. The molecular mechanism underlying CAFs-induced DC suppression was further explored by RNA-sequencing and western blot analyses.ResultsA negative correlation between WNT2+ CAFs and active CD8+ T cells was detected in primary OSCC tumours. Anti-WNT2 mAb significantly restored antitumour T-cell responses within tumours and enhanced the efficacy of anti-PD-1 by increasing active DC in both mouse OSCC and CRC syngeneic tumour models. Directly interfering with CAFs-derived WNT2 restored DC differentiation and DC-mediated antitumour T-cell responses. Mechanistic analyses further demonstrated that CAFs-secreted WNT2 suppresses the DC-mediated antitumour T-cell response via the SOCS3/p-JAK2/p-STAT3 signalling cascades.ConclusionsCAFs could suppress antitumour immunity through WNT2 secretion. Targeting WNT2 might enhance the ICI efficacy and represent a new anticancer immunotherapy.

scholarly journals Role of Thymic Output in Regulating CD8 T-Cell Homeostasis during Acute and Chronic Viral Infection

2005 ◽  
Vol 79 (15) ◽  
pp. 9419-9429 ◽  
Author(s):  
Nicole E. Miller ◽  
Jennifer R. Bonczyk ◽  
Yumi Nakayama ◽  
M. Suresh
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Cell Response ◽  
Viral Infections ◽  
T Cell Responses ◽  
Cd8 T Cell ◽  
T Cell Response ◽  
Cell Responses ◽  
Lcmv Infection

ABSTRACT Although it is well documented that CD8 T cells play a critical role in controlling chronic viral infections, the mechanisms underlying the regulation of CD8 T-cell responses are not well understood. Using the mouse model of an acute and chronic lymphocytic choriomeningitis virus (LCMV) infection, we have examined the relative importance of peripheral T cells and thymic emigrants in the elicitation and maintenance of CD8 T-cell responses. Virus-specific CD8 T-cell responses were compared between mice that were either sham thymectomized or thymectomized (Thx) at ∼6 weeks of age. In an acute LCMV infection, thymic deficiency did not affect either the primary expansion of CD8 T cells or the proliferative renewal and maintenance of virus-specific lymphoid and nonlymphoid memory CD8 T cells. Following a chronic LCMV infection, in Thx mice, although the initial expansion of CD8 T cells was normal, the contraction phase of the CD8 T-cell response was exaggerated, which led to a transient but striking CD8 T-cell deficit on day 30 postinfection. However, the virus-specific CD8 T-cell response in Thx mice rebounded quickly and was maintained at normal levels thereafter, which indicated that the peripheral T-cell repertoire is quite robust and capable of sustaining an effective CD8 T-cell response in the absence of thymic output during a chronic LCMV infection. Taken together, these findings should further our understanding of the regulation of CD8 T-cell homeostasis in acute and chronic viral infections and might have implications in the development of immunotherapy.

scholarly journals Marburg virus survivor immune responses are Th1 skewed with limited neutralizing antibody responses

2017 ◽  
Vol 214 (9) ◽  
pp. 2563-2572 ◽  
Author(s):  
Spencer W. Stonier ◽  
Andrew S. Herbert ◽  
Ana I. Kuehne ◽  
Ariel Sobarzo ◽  
Polina Habibulin ◽  
...  
Keyword(s):  
T Cell ◽  
Immune Responses ◽  
Ebola Virus ◽  
T Cell Responses ◽  
Neutralizing Antibody ◽  
Cd8 T Cell ◽  
Marburg Virus ◽  
Antibody Responses ◽  
Cd4 T Cell ◽  
Cell Responses

Until recently, immune responses in filovirus survivors remained poorly understood. Early studies revealed IgM and IgG responses to infection with various filoviruses, but recent outbreaks have greatly expanded our understanding of filovirus immune responses. Immune responses in survivors of Ebola virus (EBOV) and Sudan virus (SUDV) infections have provided the most insight, with T cell responses as well as detailed antibody responses having been characterized. Immune responses to Marburg virus (MARV), however, remain almost entirely uncharacterized. We report that immune responses in MARV survivors share characteristics with EBOV and SUDV infections but have some distinct differences. MARV survivors developed multivariate CD4+ T cell responses but limited CD8+ T cell responses, more in keeping with SUDV survivors than EBOV survivors. In stark contrast to SUDV survivors, rare neutralizing antibody responses in MARV survivors diminished rapidly after the outbreak. These results warrant serious consideration for any vaccine or therapeutic that seeks to be broadly protective, as different filoviruses may require different immune responses to achieve immunity.

scholarly journals Listeria Monocytogenes: A Model Pathogen Continues to Refine Our Knowledge of the CD8 T Cell Response

Pathogens ◽  
2018 ◽  
Vol 7 (2) ◽  
pp. 55 ◽  
Author(s):  
Zhijuan Qiu ◽  
Camille Khairallah ◽  
Brian Sheridan
Keyword(s):  
Listeria Monocytogenes ◽  
T Cell ◽  
Cell Response ◽  
Protective Immunity ◽  
T Cell Responses ◽  
Cd8 T Cell ◽  
Oral Infection ◽  
T Cell Response ◽  
Infection Model ◽  
Cell Responses

Listeria monocytogenes (Lm) infection induces robust CD8 T cell responses, which play a critical role in resolving Lm during primary infection and provide protective immunity to re-infections. Comprehensive studies have been conducted to delineate the CD8 T cell response after Lm infection. In this review, the generation of the CD8 T cell response to Lm infection will be discussed. The role of dendritic cell subsets in acquiring and presenting Lm antigens to CD8 T cells and the events that occur during T cell priming and activation will be addressed. CD8 T cell expansion, differentiation and contraction as well as the signals that regulate these processes during Lm infection will be explored. Finally, the formation of memory CD8 T cell subsets in the circulation and in the intestine will be analyzed. Recently, the study of CD8 T cell responses to Lm infection has begun to shift focus from the intravenous infection model to a natural oral infection model as the humanized mouse and murinized Lm have become readily available. Recent findings in the generation of CD8 T cell responses to oral infection using murinized Lm will be explored throughout the review. Finally, CD8 T cell-mediated protective immunity against Lm infection and the use of Lm as a vaccine vector for cancer immunotherapy will be highlighted. Overall, this review will provide detailed knowledge on the biology of CD8 T cell responses after Lm infection that may shed light on improving rational vaccine design.

scholarly journals Public T-cell epitopes shared among SARS-CoV-2 variants are presented on prevalent HLA class I alleles

2021 ◽  
Author(s):  
Saskia Meyer ◽  
Isaac Blaas ◽  
Ravi Chand Bollineni ◽  
Marina Delic-Sarac ◽  
Trung T Tran ◽  
...  
Keyword(s):  
T Cell ◽  
Cell Response ◽  
T Cell Responses ◽  
Hla Class I ◽  
Cd8 T Cell ◽  
T Cell Response ◽  
Class I ◽  
T Cell Epitopes ◽  
Low Frequencies ◽  
Cell Responses

T-cell epitopes with broad population coverage may form the basis for a new generation of SARS-CoV-2 vaccines. However, published studies on immunoprevalence are limited by small test cohorts, low frequencies of antigen-specific cells and lack of data correlating eluted HLA ligands with T-cell responsiveness. Here, we investigate CD8 T-cell responses to 48 peptides eluted from prevalent HLA alleles, and an additional 84 predicted binders, in a large cohort of convalescents (n=83) and pre-pandemic control samples (n=19). We identify nine conserved SARS-CoV-2 specific epitopes restricted by four of the most prevalent HLA class I alleles in Caucasians, to which responding CD8 T cells are detected in 70-100% of convalescents expressing the relevant HLA allele, including two novel epitopes. We find a strong correlation between immunoprevalence and immunodominance. Using a new algorithm, we predict that a vaccine including these epitopes would induce a T cell response in 83% of Caucasians. Significance Statement: Vaccines that induce broad T-cell responses may boost immunity as protection from current vaccines against SARS-CoV-2 is waning. From a manufacturing standpoint, and to deliver the highest possible dose of the most immunogenic antigens, it is rational to limit the number of epitopes to those inducing the strongest immune responses in the highest proportion of individuals in a population. Our data show that the CD8 T cell response to SARS-CoV-2 is more focused than previously believed. We identify nine conserved SARS-CoV-2 specific CD8 T cell epitopes restricted by four of the most prevalent HLA class I alleles in Caucasians and demonstrate that seven of these are endogenously presented.

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