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Objective Vaccinated patients with cancer in follow-up studies showed a high seropositivity rate but impaired antibody titres and T cell responses following mRNA vaccine against COVID-19. Besides clinical characteristics and the type of anticancer treatment before vaccination, the identification of patients susceptible to non-response following vaccination using immunological markers is worth to be investigated.Methods and analysis All patients (n=138, solid cancers) were included in the CACOV-VAC Study comprising three cohorts ((neo)-adjuvant, metastatic and surveillance). Immune responses were assessed using, respectively, anti-receptor-binding domain (RBD) SARS-CoV-S-IgG assay and interferon-γ ELISpot assay 3 months following the prime vaccination dose. Immunophenotyping of T cells and immunosuppressive cells from peripheral blood was performed before the prime dose. The serological threshold 3563 AU/mL was used to discriminate non-responders or suboptimal responders versus responders.Results Most patients achieved seroconversion after receiving the two doses of vaccine (97.6%). The median serological level of anti-RBD SARS-CoV-S-IgG was equal to 3029 for patients at the metastatic stage. The patient’s age was the main demographic characteristic that influenced vaccine efficacy. Among the immunological parameters measured at baseline, lower TIGIT (T cell immunoreceptor with Ig and ITIM domains) expression on CD8 T cells was associated with a better vaccine immunogenicity both in terms of humoral and cellular immune responses.Conclusion Despite a high seroconversion rate, median serological levels of patients with cancer, particularly elderly patients, were below the threshold equal to 3563 AU/mL considered as a humoral correlate of protection against SARS-CoV-2. Our findings suggest that the inhibitory receptor TIGIT might be an interesting predictive biomarker of COVID-19 vaccine immunogenicity and beyond in an anticancer vaccine context.Trial registration number ClinicalTrials.gov Registry (NCT04836793).