Correspondence on ‘SARS-CoV-2 vaccination in rituximab-treated patients: evidence for impaired humoral but inducible cellular immune response’

We read with a great interest the article published by Bonelli et al suggesting an inducible cellular immune response in rituximab (Rtx) treated patients. The CD20antibody Rtx is one of the most widespread biologicals worldwide with a broad spectrum of oncological and rheumatological indications. Due to its depleting effect on circulating B cells, the generation of antibodies against novel pathogens is impaired in Rtxtreated patients. 3 Accordingly, the last EULAR recommendations on vaccination advised that ‘vaccination should be provided at least 6 months after the last administration and 4 weeks before the next course of B celldepleting therapy’. To ensure appropriate SARSCoV-2 vaccination, the last EULAR advise was to refer to a rheumatologist. The American College of Rheumatology (ACR) has recommended to vaccinate Rtxtreated patients not earlier than 5 months after the last administration with the next cycle given not earlier than 2–4 weeks thereafter. In any case, the combination of B celldepleting therapy with vaccination has been quite a challenge for patients and physicians—especially since it became clear that Rtx therapy may be associated with unfavourable outcomes in B celldepleted patients. Fortunately, very recent data by Bonelli et al have now suggested that a cellular response is mounted after SARSCoV-2 vaccination in Rtxtreated patients despite a failed humoral immune response. The authors demonstrated that peripheral blood cells of vaccinated patients do produce Interferon γ (IFNγ) after stimulation with SARSCoV-2 spike (S) proteinderived overlapping peptides. These results increase the scientific interest into a more detailed characterisation of vaccinereactive Tcell immunity, which has recently been in the focus of our group as well due to a frequent Rtx application in our settings. Applying multiparameter flow cytometry, we explored the efficacy of SARSCoV-2 vaccination as defined by quantification and indepth characterisation of T cell immunity in nine Rtxtreated patients diagnosed with autoantibodies against myeloperoxidase (MPO), proteinase 3 (PR3), MPO/PR overlap and immunoglobulin A (IgA) vasculitis or membranous glomerulopathy (table 1). Their mean age was 65 years, 33.3% were women, and the mean time after the last application of Rtx was 4.5 months (2–7 months). The vaccination by two doses of BNT162b2 was performed within 3 weeks. SARSCoV-2reactive immunity was analysed before the first dose, and 3 weeks after the first and the second dose, respectively. Vaccinated healthcare workers (n=14) served as controls. All but two Rtxtreated patients had neglectable levels of CD19 B cells (figure 1D). Consequently, the development of antibodies to the SARSCoV-2 Sprotein was substantially impaired in Rtx group excluding two of the patients with detectable CD19 B cells, who showed seroconversion. In contrast, virus specific IgG antibodies were detected in all healthy controls. Importantly, vaccinereactive T cells were found in the majority of Rtxtreated patients. Due to preexisting SARSCoV-2crossreactive T cells known to be detectable in unexposed patients as demonstrated by other and our groups, 9 vaccinedirected T cell response was defined by a >twofold increase of SARSCoV-2 Sproteinreactive T cell frequencies compared with the prevaccination (TP0) state. Accordingly, CD4 T cell vaccination response was observed in 78% of Rtxtreated patients 3 weeks after the first vaccination and 86% after the second vaccination (figure 1A), while CD8 T cell responses were only found in 22% and 43% of the patients after the first and second vaccinations, respectively. Of note, there were no statistically significant differences in the frequencies of vaccinereactive CD4 and CD8 T cells between patients and controls (figure 1B). The substantial number of activated T cells produced GranzymeB, interleukin (IL)-2, interferon γ (IFNγ) or tumour necrosis factor α (TNFα) as monofunctional or polyfunctional T cells suggesting their protective function (figure 1C). Again, there were no statistically significant differences between patients and controls. T cell reactivity against SARSCoV-2 variants of concern (VOC), including B1.1. 7 and B1.351 strains, after vaccination with the Wuhan wild type Sprotein are of special interest. Importantly, 75% of Rtxtreated patients had T cells directed against the Sprotein derived from both mutant strains after the second vaccination, respectively (figure 1B). These T cells were able to produce several cytokines simultaneously suggesting antiviral potential of these polyfunctional T cells (figure 1C). Again, the magnitude and functionality of B1.1. 7 and B1.351 Sreactive T cells were not significantly different between patients and controls (figure 1B), with a tendency towards lower frequencies in the former. In conclusion, despite the lack of seroconversion in most patients, Rtxtreated patients are able to raise T cells reactive not only to SARSCoV-2 wild type strain but also to B1.1. 7 and B1.351 VOC. Although not a confirmation of antiviral protection of vaccinereactive T cells, their polyfunctional properties suggest an antiviral potential. Correspondence