Immunogenicity after Two and Three Doses of Mrna Vaccine in Patients with Cancer Treated with Exclusive Radiotherapy.

Background and Purpose: Data on immunoresponse after SARS-CoV-2 vaccines for patients treated with exclusive radiotherapy (RT) are scarce. Since RT may affect the immune system, we conducted the MORA trial (Antibody response and cell-mediated immunity of MOderna mRNA-1273 vaccine in patients treated with RAdiotherapy). Materials and Methods: Data regarding humoral and cellular immune response of patients treated with RT were prospectively collected after the second and third dose of mRNA vaccines. Results: Ninety-two patients were enrolled. With a median of 147 days after the second dose, the median SARS-CoV-2 IgG titer was 300 BAU/mL: six patients were seronegative (Spike IgG titer & LE; 40 BAU/mL), whereas 24, 46 and 16 were poor responders (Spike IgG titer:41-200 BAU/mL), responders (Spike IgG titer:201-800 BAU/mL) and ultraresponders (Spike IgG titer > 800 BAU/mL), respectively. Among seronegative patients, two patients were negative also for cell mediated response, as tested with IFN-& gamma; release Assay (IGRA) test. With a median of 85 days after the third dose, the median SARS-CoV-2 IgG titer was 1632 BAU/mL in 81 patients: only two pa-tients were seronegative, whereas 16 and 63 patients were responders and ultraresponders, respectively. Among the 2 persistently seronegative patients, IGRA test was negative in one who had previously received anti-CD20 therapy. Documented paucisymptomatic (n = 3) or asymptomatic (n = 4) infection occurred after the third dose, during the Omicron wave. Conclusion: In patients treated with exclusive RT, even during the Omicron breakthrough, robust humoral response and clinical protection from severe SARS-CoV-2 disease were achievable with three doses of mRNA vaccine.