BackgroundHumoral and cellular immune responses are known to be crucial for patients to recover from COVID-19 and to protect them against SARS-CoV-2 reinfection once infected or vaccinated.ObjectivesThis study aimed to investigate humoral and T cell responses to SARS-CoV-2 vaccination in patients with autoimmune diseases after the second and third vaccine doses while on rituximab and their potential protective role against reinfection.MethodsTen COVID-19-naïve patients were included. Three time points were used for monitoring cellular and humoral responses: pre-vaccine to exclude virus exposure (time point 1) and post-second and post-third vaccine (time points 2 and 3). Specific IgG antibodies were monitored by Luminex and T cells against SARS-CoV-2 spike-protein by ELISpot and CoVITEST. All episodes of symptomatic COVID-19 were recorded.ResultsNine patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis and one with an undifferentiated autoimmune disease were included. Nine patients received mRNA vaccines. The last rituximab infusion was administered for a mean (SD) of 15 (10) weeks before the first vaccine and six patients were CD19-B cell-depleted. After a mean (SD) of 19 (10) and 16 (2) days from the second and third vaccine dose, IgG anti-SARS-CoV-2 antibodies were detected in six (60%) and eight (80%) patients, respectively. All patients developed specific T cell responses by ELISpot and CoVITEST in time points 2 and 3. Previous B cell depletion correlated with anti-SARS-CoV-2 IgG levels. Nine (90%) patients developed mild COVID-19 after a median of 7 months of the third dose.ConclusionRituximab in patients with autoimmune diseases reduces humoral responses but does not avoid the development of T cell responses to SARS-CoV-2 vaccination, which remain present after a booster dose. A steady cellular immunity appears to be protective against subsequent reinfections.

Cellular and humoral immune responses are essential for COVID-19 recovery and protection against SARS-CoV-2 reinfection. To date, the evaluation of SARS-CoV-2 immune protection has mainly focused on antibody detection, generally disregarding the cellular response, or placing it in a secondary position. This phenomenon may be explained by the complex nature of the assays needed to analyze cellular immunity compared with the technically simple and automated detection of antibodies. Nevertheless, a large body of evidence supports the relevance of the T cell’s role in protection against SARS-CoV-2, especially in vulnerable individuals with a weakened immune system (such as the population over 65 and patients with immunodeficiencies). Here we propose to use CoVITEST (Covid19 anti-Viral Immunity based on T cells for Evaluation in a Simple Test), a fast, affordable and accessible in-house assay that, together with a diagnostic matrix, allows us to determine those patients who might be protected with SARS-CoV-2-reactive T cells. The method was established using healthy SARS-CoV-2-naïve donors pre- and post-vaccination (n=30), and further validated with convalescent COVID-19 donors (n=51) in a side-by-side comparison with the gold standard IFN-γ ELISpot. We demonstrated that our CoVITEST presented reliable and comparable results to those obtained with the ELISpot technique in a considerably shorter time (less than 8 hours). In conclusion, we present a simple but reliable assay to determine cellular immunity against SARS-CoV-2 that can be used routinely during this pandemic to monitor the immune status in vulnerable patients and thereby adjust their therapeutic approaches. This method might indeed help to optimize and improve decision-making protocols for re-vaccination against SARS-CoV-2, at least for some population subsets.