We conducted a prospective, three-center, observational study in Japan to evaluate the prevalence of seropositivity and clinically protective titer after coronavirus disease 2019 vaccination in patients with plasma cell dyscrasia(PCD). Two-hundred sixty-nine patients with PCD [206 symptomatic multiple myeloma (MM)] were evaluated. Seropositivity was observed in 88.7% and a clinically protective titer in 38.3% of MM patients, both of which were significantly lower than those of healthy controls. Patients receiving anti-CD38 antibodies had much lower antibody titers, but antibody titers recovered in those who underwent a wash-out period before vaccine administration. Older age (≥65), anti-CD38 antibody administration, immunomodulatory drugs use, lymphopenia (<1000/μL), and lower polyclonal IgG (<550 mg/dL) had a negative impact for the sufficient antibody production according to multivariate analysis. Patients with clinically protective titer had a significantly higher number of CD19+ lymphocytes than those with lower antibody responses (114 vs. 35/μL, p = 0.016). Our results suggested that patients with PCD should be vaccinated, and that the ideal protocol is to temporarily interrupt anti-CD38 antibody therapy for a “wash-out” period of a few months, followed by a (booster) vaccine after the B-cells have recovery. Supplementary Information The online version contains supplementary material available at 10.1007/s12185-022-03300-4.

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Summary This study reports the relationship between CD38+ regulatory T cells (Tregs) and messenger RNA coronavirus disease 2019 (mRNA‐COVID‐19) vaccination in 60 patients with plasma cell dyscrasia. Patients treated with anti‐CD38 monoclonal antibodies (mAbs) had significantly lower CD38+ Tregs than those not treated (0.9 vs. 13.2/μl). Late‐responders, whose antibody titres increased from weeks 4–12 after the second vaccination, had significantly lower CD38+ Treg counts than non‐late‐responders (2.5 vs. 10.3/μl). Antibody titres in patients with lower CD38+ Treg levels were maintained from weeks 4–12 but decreased in those with higher CD38+ Treg levels. Therefore, depletion of CD38+ Tregs by anti‐CD38 mAbs may induce a durable response to mRNA‐COVID‐19 vaccination.

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