We describe three cases of critical acute myositis with myocarditis occurring within 22 days of each other at a single institution, all within 1 month of receiving the initial cycle of the anti-PD-1 drug pembrolizumab. Analysis of T cell receptor repertoires from peripheral blood and tissues revealed a high degree of clonal expansion and public clones between cases, with several T cell clones expanded within the skeletal muscle putatively recognizing viral epitopes. All patients had recently received a COVID-19 mRNA booster vaccine prior to treatment and were positive for SARS-CoV2 Spike antibody. In conclusion, we report a series of unusually severe myositis and myocarditis following PD-1 blockade and the COVID-19 mRNA vaccination.
Competing Interests: Competing interests: RAW, WY, CAT, EJ, RC, OT, TJ, BS, MH, DJ, RP, EI, SJ, DM-P, NC and MP: no competing interests. MRM reports grants from Roche, grants from Astrazeneca, grants from GSK, other from Novartis, grants and other from Immunocore, other from BMS, other from Pfizer, other from Merck/MSD, other from Regeneron, other from BiolineRx, other from Replimune, grants from GRAIL; all outside the submitted work; ISDR reports consultancy for Novartis, Travere Therapeutics, Q32Bio and is an unpaid Director of Oxford Pathology Education Limited, Oramis Digital Autopsy, UK Renal Pathology; all outside submitted work. BF has received speaker fees from GSK, Immunocore, BMS and reports consultancy for Roche, Pathios Therapeutics, NICE advisory, UCB; NC has received honoraria Pierre Fabre, BMS.
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