Immune response after SARS-CoV-2 vaccination in patients with inflammatory immune-mediated diseases receiving immunosuppressive treatment

The SARS-CoV-2 pandemic resulted in high morbidity and mortality due to COVID-19. The risk factors associated with worse COVID-19 outcomes among the general population include older age, sex, and chronic diseases [1‐3]. Evidence for the severity of SARS-CoV-2 infections in patients with immune-mediated diseases (IMIDs) is controversial [1, 4‐6]. Unadjusted analyses from a recent meta-analysis demonstrated that SARS-CoV-2 infection and death are more frequent in patients with IMIDs [1]. EULAR recommendations clarify that patients with IMIDs do not face a higher risk of SARS-CoV-2 infection than individuals without IMIDs and that prognosis is no poorer when they contract it [7]. Although they do emphasize the importance of vaccination prior to starting immunosuppressants or schedule it in patients treated with anti-CD20, in a way to optimize vaccine immunogenicity [7].

Vaccination strategies protect against infections through stimulation of the humoral and cellular immune responses. The relative importance of humoral and cellular immunity in conferring protection from infection varies with the individual microorganism [8]. Antibody responses (seroconversion) are mediated by a B-cell response and are better represented in the literature than T cell-driven responses. The immunogenicity of the SARS-CoV-2 vaccine can be measured based on specific-antibodies to spike protein or T-cell reactivity via the interferon (IFN)-γ response to SARS-CoV-2 peptides [8]. While the role of T-cell responses to SARS-CoV-2 vaccines is not fully understood, emerging evidence suggests that T-cell responses may confer protection [9, 10], even in the absence of a humoral response [11, 12]. However, it is not yet completely known how antibody titers influence the efficacy of these vaccines and how titers decline over time. In addition, the response to a vaccine may be affected by characteristics inherent to the individual, such as age, sex, obesity, and smoking [13].

Vaccination against SARS-CoV-2 has been the largest vaccination program in the history of the Spanish National Health System, and immunocompromised patients have been prioritized in vaccination schedules. The vaccines approved for prevention of SARS-CoV-2 infections include mRNA vaccines (e.g., BNT162b2 and mRNA-1273), non-replicating viral vector vaccines (e.g., Janssen Ad26.COV2.S and AZD1222), and traditional inactivated whole virus vaccines (e.g., CoronaVac). All currently available vaccines against SARS-CoV-2 have proven to be effective in clinical trials. However, their efficacy has not been tested in immunocompromised patients [14]. A recent meta-analysis showed that seroconversion rates and antibody titers after SARS-CoV-2 vaccination are significantly lower in immunocompromised patients than in immunocompetent individuals [14]. Notwithstanding, there is no global consensus on how vaccination strategies should be both in immunocompromised and immunocompetent patients.

Immunosuppressive therapy plays a leading role in the impaired response in patients with IMIDs. Conventional, biologic, and targeted synthetic disease-modifying antirheumatic drugs (c/b/ts-DMARDs) and corticosteroids are widely used in monotherapy or in combination to treat affected patients. Some of these drugs have been shown to impair the response to vaccines [15]. Data on this topic focus largely on influenza, pneumococcal, and tetanus vaccines [8]. In addition, most studies have evaluated the humoral immune response to the above-mentioned vaccines. Whether these data can be extrapolated to provide guidance for vaccination strategies in COVID-19 remains uncertain. Recent data suggest that rituximab, corticosteroids, methotrexate, abatacept, mycophenolate mofetil, and JAK-inhibitors (JAKi) [17] impair SARS-CoV-2 vaccine responses in many patients [8, 16]. The focus has mainly been on patients treated with corticosteroids and anti-CD20 therapy such as rituximab, since this agent has been associated with an increased risk of serious infections and mortality [3, 17, 18].

Although there is increasing evidence on how the response to the SARS-CoV-2 vaccine may be impaired in patients with rheumatic diseases, many areas remain to be clarified. There is an urgent need for real-world data on the immune response to the SARS-CoV-2 vaccine in patients with IMIDs treated with immunosuppressants and on the incidence and severity of SARS-CoV-2 infection in adequately vaccinated patients.

This study provides insight into the clinical relevance of immune response to SARS-COV-2 vaccination in patients with IMIDs treated with immunosupressants. In our cohort, most of patients (86%) with IMIDs treated with b/tsDMARDs had detectable humoral responses. However, anti-SARS-COV-2 Ab levels were lower in patients than in controls, with rituximab being associated with a higher risk of an absent humoral response (OR: 18.5), as expected. On the other hand, we found that up to 37% of patients with a poor humoral response may have a cellular response to the vaccine, being more frequently detected in patients treated with rituximab (91%). Another important issue is that the presence of CD19+ B cells in peripheral blood is associated with the time since the last rituximab infusion. The study of the pre-GC B cell compartment showed that the B cell regeneration pattern in patients is mainly at the expense of immature cells.

There is substantial variation in the immune response to vaccination between individuals. Factors that influence humoral and cellular vaccine responses include intrinsic host factors such as age, sex, genetics, and comorbidities, perinatal factors such as gestational age, birth weight, feeding method, and maternal factors, as well as extrinsic factors like preexisting immunity, microbiota, infections, and antibiotics [13]. Additionally, environmental factors including geographic location, season, family size, and toxins, behavioral factors such as smoking, alcohol consumption, exercise, and sleep, and nutritional factors such as body mass index, micronutrients, and enteropathy can also influence how individuals respond to vaccines [13]. Sex differences in the response to vaccination have been reported [22, 23]. Females generate overall higher antibody levels, experience more adverse events, have higher B cell frequencies and exhibit elevated innate immune cell phagocytic activity [22]. In contrast, males have increased NK cell numbers, enhanced type-1 immune responses, and so on [22]. However, in our study we have observed that women are associated with lower levels of antibodies. These discrepancies are due to the fact that most of the patients are female and the lowest levels were found in patients with RA treated with rituximab. The impact of the BMI on the response to vaccines is more controversial [24‐26]. Bates et al. found no association between antibody titers and BMI at 50 and 200 days after vaccination against SARS-COV-2 in 127 people [24]. In our cohort, RA patients had a higher BMI but this was not independently associated with lack of humoral response.

Moreover, factors related with vaccine (such as vaccine type, product, adjuvant, and dose) and administration (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important [13, 27]. An understanding of all these factors and their impacts on the design of vaccine studies and decisions on vaccination schedules can help to improve vaccine immunogenicity and efficacy. In fact, in a study carried out in the Swiss cohort (SCQM) including 565 patients, two-dose vaccination with mRNA1273 (Moderna) versus BNT162b2 (Pfizer) resulted in a higher anti-SARS-CoV-2 Ab levels [27]. In our study most patients (50) received the vaccination scheme with BNT162b2 (Pfizer) and only 8 patients were vaccinated with mRNA1273 (Moderna) as the first 2 doses. Thus, statistical significance analyses regarding vaccine type could not be performed in our study.

The seroconversion rate in our cohort of patients with IMIDs was very high (86%). However, anti-SARS-CoV-2 Ab levels were lower in patients with IMIDs treated with b/tsDMARDs than in controls. These data are consistent with previous publications [8]. In an observational multicenter study, researchers observed that BNT162b2 (Pfizer) was immunogenic in most patients with IMIDs with a good safety profile. In parallel, they found that drugs such as rituximab, mycophenolate, glucocorticoids, and abatacept were associated with a lower humoral response to the vaccine [8, 15]. These findings coincide with our data, which show that the lowest levels of antibodies were detected in patients with rituximab. Furthermore, all patients with undetectable levels of anti-SARS-CoV-2 Ab in our cohort were treated with this drug. A recent review found that patients with SLE have lower rate of seroconversion than healthy controls and patients with RA [28]. In the present study, we only included 6 patients with connective tissue disorders, so statistical analysis comparing with other pathologies are not able to be performed. However, it is worth emphasizing that anti-SARS-CoV-2 Ab levels were lower in patients with CTD than in the other pathologies (see Additional file 1: Fig. S2).

Another interesting point to describe in detail is the cellular response that patients with IMIDs can generate against the SARS-COV-2 vaccine. Lledó et al. found that cellular immune response against SARS-CoV-2 was similar between patients with IMIDs (53) and controls (61) [29]. They also observed that this response was not affected by the different pathologies or by immunosuppressive treatments. Another recent study by Bock et al. evaluated the humoral and cellular response to the SARS-CoV-2 vaccine in patients with multiple sclerosis treated with immunosuppressant [30]. First, they found that patients treated with anti-CD20 therapy had a poor humoral response but an intact cellular response. In contrast, an impaired cellular and humoral response was seen in patients treated with sphingosine 1 phosphate inhibitors [30]. This may be due to the direct action of this drug on T lymphocytes, secondarily affecting the T-cell dependent B-cell activation. Our results are in agreement with findings observed in this last study. We found that the cellular response was more frequent in patients with anti-CD20 therapy than in those with anti-TNF therapy and with JAK inhibitors. These differences could be due to the type of assay used to evaluate the cellular response. Whereas Lledó et al. used the ELISpot assay to evaluate the cellular response, Bock et al. and our study used the QTF-SARS-COV-2 assay. Both assays evaluated the same immune response but have different nuances. ELISpot is performed with PBMC and measures interferon-producing cells after a stimulus, while the QTF-SARS-COV-2 measures serum interferon production after a stimulus [31]. Another aspect to consider is that Lledó et al. included a small number of patients treated with TNFi and rituximab (10 and 4 patients, respectively). A possible hypothesis that supports our findings in TNFi group lies in the influence of these drugs on the homeostasis of T lymphocytes regulating their response in many ways [32]. Hence, it is logical that in patients treated with TNFi, the cellular response to vaccines may be impaired.

Delving into the mechanism of rituximab, CD20 is expressed on circulating peripheral blood B cells, but not on bone marrow stem cells or plasma cells [33]. Therefore, anti-CD20 drugs would not be expected to deplete the total B-cell pool, and theoretically, should not compromise humoral immunity as B-cell regeneration from bone marrow precursors is not directly inhibited. B-cell recovery upon treatment discontinuation is quite heterogeneous, and mild to profound impact on the peripheral B-cell compartment can be observed, together with partial or severe impairment of the antibody response. Here, in fact we observed RA patients with almost normal absolute counts of total B-cells whereas others presented reduced B-cells or undetectable B-cell counts. In general, B-cell numbers remains reduced or undetectable in peripheral blood up to 2–6 months post-rituximab [34]. B-cell reconstitution may take longer to reach pretreatment levels, depending on underlying clinical context, medication dosing, and treatment duration, concomitant administration of immunosuppressive medications, age and patient comorbidities [35]. Here, RA patients presented increased absolute numbers of the three immature/transitional B-cell subsets that are the first populations of maturation that appear in peripheral blood during reconstitution after rituximab as previously observed [36] (Fig. 3B and Additional file 1: Fig. S3). In addition, the expansion of CD21⁻ B-cells have been described in the naïve B-cell compartment and in the memory B cell (MBC) compartment [37]. Here, the MBC is severely reduced, but within the naïve B-cell compartment we also detected in some patients the expansion of CD21⁻ CD24⁻ mature naïve B cells. Although we have not evaluated the B-cell phenotype prior to the rituximab treatment, it could be presumed that the regeneration of B-cell compartment, with accumulation of CD21⁻ B-cells, is similar to the preexisting one which is the result of the chronic stimulation occurred in the pathogenesis of RA.

In concordance with delayed MBC compartment reconstitution, seven patients with RA presented severely reduced unswitched IgMD⁺ MBC and switched IgMD⁺ MBC, as also previously reported in systemic lupus erythematous (SLE) patients treated with rituximab [38]. Considering all, a message that we take from the basic to the clinic, is that delaying the infusion of rituximab prior to vaccination enables the regeneration of B cell compartment thus favoring a better vaccination response.

A very reassuring fact is that in our cohort there is no difference in the frequency of infections between patients and controls after vaccination and they were mostly mild cases. The infections requiring hospitalization after vaccination were scarce and they only occurred in patients who were treated with rituximab. These results support the importance of promoting an adequate vaccination strategy as stated in the EULAR recommendations for vaccination in patients with IMIDs [7]. However, many unanswered questions remain. In this work we have observed that the majority of patients with IMIDs treated with b/tsDMARD had detectable anti-SARS-COV-2 antibodies and infections in vaccinated patients were mostly mild.

Following the recommendations from the Ministry of Health, all patients received additional COVID-19 vaccine boosters (third, fourth and fifth doses). It is evident that vaccination against SARS-COV-2 has decreased the frequency and severity of infections. In fact, our data show that the majority of patients presented mild infections after vaccination like those observed in the general population. However, an interesting point observed in this work is that the antibody titers were significantly lower after the 3rd dose than after the initial regimen that included the 1st and 2nd doses. This fact reflects how the antibody response diminishes over time and may be related to the dose used and/or the timing of the booster. Therefore, the frequency and number of boosters needed for these patients are unclear. In this sense, efforts should be made to move towards more personalized strategies, establishing profiles of patients at higher risk based on scientific evidence.” In this sense, efforts should be made to move towards more personalized strategies, establishing profiles of patients at higher risk based on scientific evidence.

Some limitations were observed in the present study. First, the limited number of patients in the groups of patients treated with anti-IL6R and JAKi. Second, some differences in age and BMI between controls and patients. However, these age differences were only observed in patients with RA. Regarding BMI, recent data do not seem to find a relationship between BMI and response to the SARS-COV-2 vaccine. Another aspect to consider is that the cellular response was only studied in patients with a poor humoral response, so we cannot compare the cellular response between patients with a good humoral response or not.

On brief, the humoral immune response to the SARS-COV-2 vaccine is poorer in patients than in healthy controls, especially in those treated with rituximab. However, in patients with rituximab, a cellular-mediated immune response can be detected despite having a poor humoral response. Finally, severe infections in vaccinated patients with IMIDs are rare, mainly observed in patients treated with rituximab.

In conclusion, a scheduled delay of the rituximab infusion to ensure a better humoral response to the vaccine would be recommended in patients with IMID.