There is a pressing need for an in-depth understanding of immunity to SARS-CoV-2. In this study, we investigated human T cell recall responses to fully glycosylated spike trimer, recombinant N protein, as well as to S, N, M, and E peptide pools in the early convalescent phase and compared them with influenza-specific memory responses from the same donors. All subjects showed SARS-CoV-2–specific T cell responses to at least one Ag. Both SARS-CoV-2–specific and influenza-specific CD4+ T cell responses were predominantly of the central memory phenotype; however SARS-CoV-2–specific CD4+ T cells exhibited a lower IFN-γ to TNF ratio compared with influenza-specific memory responses from the same donors, independent of disease severity. SARS-CoV-2–specific T cells were less multifunctional than influenza-specific T cells, particularly in severe cases, potentially suggesting exhaustion. Most SARS-CoV-2–convalescent subjects also produced IFN-γ in response to seasonal OC43 S protein. We observed granzyme B+/IFN-γ+, CD4+, and CD8+ proliferative responses to peptide pools in most individuals, with CD4+ T cell responses predominating over CD8+ T cell responses. Peripheral T follicular helper (pTfh) responses to S or N strongly correlated with serum neutralization assays as well as receptor binding domain–specific IgA; however, the frequency of pTfh responses to SARS-CoV-2 was lower than the frequency of pTfh responses to influenza virus. Overall, T cell responses to SARS-CoV-2 are robust; however, CD4+ Th1 responses predominate over CD8+ T cell responses, have a more inflammatory profile, and have a weaker pTfh response than the response to influenza virus within the same donors, potentially contributing to COVID-19 disease.

Our findings highlight the relative importance of SARS-CoV-2-specific GzmB-producing T cell responses in SARS-CoV-2 control and shared CD4 and CD8 immunodominant epitopes in seasonal coronaviruses or SARS-CoV-1, and they indicate robust persistence of T cell memory at least 1 year after infection. Our findings should inform future strategies to induce T cell vaccines against SARS-CoV-2 and other coronaviruses.

Aims: Dedifferentiated chondrosarcoma (DDCHS) is an aggressive type of chondrosarcoma that results from high-grade transformation of a low-grade chondrosarcoma. Mutations in the isocitrate dehydrogenase (IDH) 1 gene and the IDH2 gene that lead to increased D-2-hydroxyglutarate (2HG) oncometabolite production, promoting tumorigenesis, have been recently described in low-grade cartilaginous neoplasms. The aims of this study were to examine the prevalence of IDH mutations in a single-institution cohort of DDCHS cases and correlate 2HG levels with mutation status. Methods and results: We examined a series of 21 primary DDCHS cases by using Sanger sequencing and quantitative polymerase chain reaction genotyping to look for IDH1/IDH2 mutations, and evaluated the 2HG levels in formalin-fixed paraffin-embedded tumour and matched normal tissue samples by using a fluorometric assay. Seventy-six per cent of DDCHS cases (16/21) harboured a heterozygous IDH1 or IDH2 mutation. Six of 14 IDH-mutated DDCHS cases showed elevated 2HG levels in tumour tissue relative to matched normal tissue. There were no consistent histological or diseasespecific survival differences between IDH-mutated tumours and wild-type tumours. Conclusions: Our study confirms the frequent presence of a variety of IDH1 and IDH2 mutation variants, indicating that a sequencing-based approach is required for DDCHS if IDH is to be used as a diagnostic marker. Similarly to other IDH-mutated tumour types, IDH-mutated DDCHS cases show elevated 2HG levels, indicating that the oncometabolite activity of 2HG may contribute to DDCHS oncogenesis and progression.

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Cellular-mediated immunity is critical for long-term protection against most viral infections, including coronaviruses. We studied 23 SARS-CoV-2-infected survivors over a one year post symptom onset (PSO) interval by ex vivo cytokine ELISpot assay. All subjects demonstrated SARS-CoV-2-specific IFN-γ, IL-2, and Granzyme B (GzmB) T cell responses at presentation, with greater frequencies in severe disease. Cytokines, mainly produced by CD4+ T cells, targeted all structural proteins (Nucleocapsid, Membrane, Spike) except Envelope, with GzmB > IL-2 > IFN-γ. Mathematical modeling predicted that: 1) cytokine responses peaked at 6 days for IFN-γ, 36 days for IL-2, and 7 days for GzmB, 2) severe illness was associated with reduced IFN-γ and GzmB, but increased IL-2 production rates, 3) males displayed greater production of IFN-γ, whereas females produced more GzmB. Ex vivo responses declined over time with persistence of IL-2 in 86% and of IFN-γ and GzmB in 70% of subjects at a median of 336 days PSO. The average half-life of SARS-CoV-2-specific cytokine-producing cells was modelled to be 139 days (~4.6 months). Potent T cell proliferative responses persisted throughout observation, were CD4 dominant, and were capable of producing all 3 cytokines. Several immunodominant CD4 and CD8 epitopes identified in this study were shared by seasonal coronaviruses or SARS-CoV-1 in the Nucleocapsid and Membrane regions. Both SARS-CoV-2-specific CD4+ and CD8+ T cell clones were able to kill target cells, though CD8 tended to be more potent.