Abstract While there is accumulating evidence on the antibody response against SARS-CoV-2, we are only beginning to acquire knowledge regarding the SARS-CoV-2 specific CD8 T-cell response. Therefore, it is an urgent matter to gain a deeper insight into the virus specific CD8 T-cell response to both assist vaccine design and provide tools to evaluate the vaccine-induced T-cell responses. To address this issue, we have analyzed samples from 20 COVID-19 patients for CD8 T-cell recognition of 500 predicted SARS-CoV-2-derived epitopes restricted to 10 of the most common HLA-A and HLA-B alleles. For each HLA allele, the top 50 epitopes were selected based on predicted binding affinity and likelihood of successful proteasomal processing. In addition, SARS-CoV-2 epitope predictions shared by the science community were considered. To probe for CD8 T-cell recognition of the selected epitopes, we made use of our in-house technology based on multiplexing of peptide HLA (pHLA) multimers conjugated to fluorescent dyes. Our data demonstrated that CD8 T-cell reactivity against SARS-CoV-2 was common. Remarkably, a substantial fraction of the observed CD8 T-cell responses were directed towards the ORF1ab polyprotein 1ab. These CD8 T-cell responses were frequently of a profound magnitude. In particular, a CD8 T-cell response towards a potentially immunodominant epitope (TTDPSFLGRY) restricted to the HLA-A*01:01 allele was found in all patients positive for this allele. Interestingly, the fraction of SARS-CoV-2 specific CD8 T cells expressing the inhibitory receptor NKG2A was higher as compared to bulk CD8 T cells. In conclusion, the fact that a major part of the identified SARS-CoV-2 specific CD8 T-cell response is directed against a part of the viral genome that is not included in the majority of vaccine candidates currently in development may potentially influence their clinical activity and toxicity profile. Citation Format: Anastasia Gangaev, Steven L. Ketelaars, Sanne Patiwael, Anna Dopler, Olga I. Isaeva, Kelly Hoefakker, Sara De Biasi, Cristina Mussini, Giovanni Guaraldi, Massimo Girardis, Cami M.P. Talavera Ormeno, Paul J.M. Hekking, Neubury M. Lardy, Mireille Toebes, Robert Balderas, Ton N. Schumacher, Huib Ovaa, Andrea Cossarizza, Pia Kvistborg. Profound CD8 T-cell responses towards SARS-CoV-2 OFR1ab in COVID-19 patients [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2020 Jul 20-22. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(18_Suppl):Abstract nr S05-01.