Single-cell transcriptional profiling reveals a persistent type I IFN signature in COVID-19 CVID patients
We isolated paired samples of peripheral blood mononuclear cells (PBMCs) from five CVID patients at three distinct stages of the SARS-CoV-2 infection: 1) baseline, before viral infection, 2) progression, during viral infection, and 3) convalescence, once the viral infection had been resolved and the patient was PCR negative (Figure 1a). All collected CVID patients were under regular immunoglobulin replacement therapy and displayed only mild symptoms during SARS-CoV-2 infection (for detailed patient description see Supplementary Table 1). We profiled a total of 116,958 single-cell transcriptomes of isolated immune cells from the CVID cohort (Supplementary Table 2).
In addition, we processed and integrated publicly available single-cell RNA sequencing (scRNA-seq) datasets of PBMCs from a cohort of individuals without any known primary or secondary immunodeficiency (control cohort), who were either negative or positive for SARS-CoV-2 27. This control cohort included both non-CVID COVID-19 patients with mild symptoms (similar to patients in the CVID cohort) or severe symptoms (as a reference of a higher COVID-19-associated immune dysregulation). As in our CVID cohort, samples were classified in three stages: 1) baseline (48,517 cells), 2) progression (46,102 cells), and 3) convalescence (48,187 cells). Samples from the control cohort were selected to match in sex, age and time of sample collection after symptoms onset with our cohort of CVID patients (Supplementary Table 1). In addition, we integrated our data with 95,548 cells from 24 control individuals obtained from an additional publicly available scRNA-seq dataset of PBMCs to contextualize our analyses with previous work in that area that processed samples in a similar way to ours 28.
Our single-cell analysis transcriptomics census allowed us to identify several immune cell compartments at high resolution (Figure 1b): B cells, including naïve B cells, un-switched memory B cells, switched memory B cells, CD21low B cells and plasma cells (PCs); T cells, including naïve CD4+ T cells, effector memory CD4+ T (CD4+ TEM) cells, central memory CD4+ T (CD4+ TCM) cells, effector CD4+ T cells (CD4+ TEff), naïve CD8+ T cells, effector memory CD8+ T (CD8+ TEM) cells, effector CD8+ T (CD8+ TEff) cells and cycling T (Tcycling) cells among others; Natural killer (NK) cells, including CD56high NK cells and CD16high NK cells; Myeloid cells, including classical, intermediate and non-classical monocytes, as well as conventional dendritic cells (cDC) and plasmacytoid dendritic cells (pDCs). All subsets have a good representation of the patients (Suppl. Table 3).
After immune cell subsets annotation, we analyzed the general response mediated by the interferon (IFN) proteins, which play a crucial role in the immune activity against viruses and other pathogens 29–31. The inspection of well represented cell populations showed an increased type I IFN response during SARS-CoV-2 infection in all populations of both controls and CVID patients when compared to baseline (Figure 1c). However, in contrast to COVID-19 controls, type I IFN response was maintained at the convalescence stage in CVID patients in most cell subsets with the exception of monocytes.
Dysfunctional B cell receptor and NF-κB signaling pathways in COVID-19 CVID patients
The second line of defense against SARS-CoV-2 that we investigated addresses the humoral response. CVID patients are characterized by profound defects in humoral and B-cell-mediated immune responses. Consistent with this knowledge, only one patient had detectable SARS-CoV-2 specific IgG antibodies and none of the patients produced specific IgA after COVID-19 (Supp. Table 1). Our scRNA-seq analysis allowed us to identify several B cell subsets in the three CVID patients with B cells (Figure 2a and Supp. Figure 1a). As expected for CVID patient samples 32, both switched memory B cells and PCs are underrepresented (Supplementary Table 3). For this reason, we focused our analyses on the transcriptional alterations of naïve B cells upon SARS-CoV2 infection, whose activation and differentiation gives rise to the aforementioned B cell subsets altered in CVID patients. Importantly, given that only a minor fraction of B cells might generate SARS-CoV-2 specific responses, we investigated global alterations in B cells which reflect not only a virus antigen specific response but also general immune stimulation of B cells via TLR and cytokines. Interestingly, our results showed that the naïve B cell compartment of the inspected COVID-19 CVID patients presented a dysregulated expression of several target genes of the canonical nuclear factor of κ light chain (NF-κB) pathway, including CCL3, IL6, TNF, CD69, CD83, NFKBIA and EGR1 among others at progression and convalescence (Figure 2b). In this regard, we observed that the canonical NF-κB pathway displayed a significant activation upon SARS-CoV-2 infection only in control individuals and not in CVID patients (Figure 2c). Specifically, the p50 and p65 subunits displayed a significantly higher activity in both mild and severe COVID-19 controls at convalescence, which was only observed in severe COVID-19 controls at the progression stage. Interestingly, no significant activity of any of these subunits was detected at progression nor convalescence in CVID patients (Figure 2c). Conversely, we observed a significantly higher activity of the NF-κB inhibitor IκBα (NFKBIA) in COVID-19 CVID patients (Figure 2c), which is in line with the impaired activation of the NF-κB pathway observed in the immunodeficient patients. CD21low B cells have been previously described to display profound dysregulation of the canonical NF-κB pathway in CVID patients 33. In our data, CD21low B cells constitute a separate cluster from naïve B cells (Figure 2a and Supp. Figures 1b and 1c), suggesting that the defective activation of the NF-κB pathway observed in the naïve B cell compartment is not a consequence of the presence of expanded CD21low B cells within the naïve B cell cluster.
In addition, we observed that the hypoxia-inducible factor 1-alpha (HIF-1α) transcription factor (TF), which might affect B cell function and induce B cell abnormalities in COVID-19 patients 34,35, showed a significantly higher activity at both progression and convalescence in naïve B cells of COVID-19 CVID patients (Figure 2c), despite the previously described impaired HIF-1α upregulation in CVID patients upon BCR in vitro stimulation 36. Moreover, inflammation-related genes, such as IL1B, IL6, LTA and TNF, showed an impaired upregulation in naïve B cells of CVID individuals during SARS-CoV-2 infection compared with COVID-19 controls (Supp. Figure 1e).
Furthermore, we performed gene ontology (GO) analysis on naïve B cells and observed a higher enrichment in GO categories related to B cell activation and regulation of the B cell receptor (BCR) signaling pathway in COVID-19 CVID patients compared with COVID-19 controls (Figure 2d). Hence, we inspected the expression of BCR-related genes along the viral infection. We found a higher and persistent transcriptional upregulation of several genes encoding members of the BCR signaling pathway, both activators and repressors, in the naïve B cell compartment of COVID-19 CVID patients compared with COVID-19 controls (Figure 2e and Supp. Figure 1d). This upregulation included BCR signaling pathway activator genes such as CD19, CD81, CD79B, BTK and BLNK, and also BCR inhibitory genes such as PTPN6 (which encodes the tyrosine phosphatase SHP-1), CD22 and CD72 (Figure 2e).
Following the observation of a dysregulated BCR signaling, we analyzed the BCR repertoires of naïve B cells in our dataset. The inspection of the dynamics of the VDJ usage upon SARS-CoV-2 infection indicates that the proportion of B cells expressing the IGHV3-53 gene, which has been described as the most frequently used IGHV gene among SARS-CoV-2 neutralizing antibodies 37,38, was increased in COVID-19 controls in contrast to COVID-19 CVID patients at both progression and convalescence stages (Figure 2f). Similar profiles were observed for the IGHV gene usage of other SARS-CoV-2 spike-targeting antibodies 27,37, such as IGHV1-46, IGHV3-23 or IGHV5-51 (Figure 2f).
Altogether, we show that during SARS-CoV-2 infection, naïve B cells from CVID patients show a dysregulated expression of several components of the BCR signaling pathway, as well as a sustained impairment of NF-κB pathway activation, which might have a negative impact on the proper expression of relevant molecules involved in B cell responses.
Preserved and enhanced cytotoxicity but reduced cytokine responses in COVID-19 CVID NK and T cells
We next focused on the NK and T cell compartments (Figure 3a and Supp. Figure 2a) which also play key roles during SARS-CoV-2 infection 39–41. CD16high NK cells, the most abundant subset of NK cells in our data, showed a significant enrichment in several GO categories related to NK cell cytotoxicity in CVID patients at the progression stage (Figure 3b). In line with this result, GZMB, PRF1, GZMA and NKG7 - all of them relevant genes for cytotoxic activity - were upregulated in the CD16high NK cells of CVID patients during the infection and, to a lesser extent, in mild but not in severe COVID-19 individuals (Supp. Figure 2b). Interestingly, unlike in control individuals, the expression of these cytotoxic genes was maintained in CVID patients at the convalescence stage. Similarly, the minor CD56high NK cluster also showed that those cytotoxic genes were mainly upregulated in CVID patients compared with controls upon SARS-CoV-2 infection (Supp. Figure 2b).This higher and persistent cytotoxic activity in the NK compartment of COVID-19 CVID patient was also confirmed when we expanded the analysis to a higher number of cytotoxicity-related genes (see Methods) and calculated a cytotoxic score (Figure 3c). Additionally, both NK subsets presented an upregulation of IFN-γ and tumor necrosis factor alpha (TNF-α) coding genes in control individuals during infection, and even at a higher extent at the convalescence stage, but this upregulation was not observed in CVID patients (Figure 3d).
In addition, the aforementioned lytic-associated genes GZMB, PRF1, GZMA and NKG7 were also upregulated in CD8+ TEff cells and CD8+ TEM cells especially in of CVID patients during viral infection, whereas such upregulation was not so evident in COVID-19 controls (Supp. Figure 2b). Similarly to NK cells, we found a more persistent cytotoxic activity in the CD8+ T cell compartment of COVID-19 CVID patients that was not observed in COVID-19 controls (Figure 3c). In addition, we found a pronounced upregulation of IFN-γ and TNF-α coding genes in CD8+ TEff and CD8+ TEM cells of control individuals upon SARS-CoV-2 infection, especially remarked in the convalescence stage, which was not detected in CVID patients at the same stages (Figure 3d).
Multiple CD4+ T cell subsets, including naïve CD4+ T cells, CD4+ TEM cells, CD4+ TCM cells and CD4+ TEff cells, showed upregulation of the TNF-α coding gene at the convalescence stage in control individuals (Figure 3e). In contrast, this upregulation was impaired in the distinct CD4+ T cell subsets of COVID-19 CVID patients (Figure 3e). The defective activation of CD4+ T cells in COVID-19 CVID patients was also observed for CD40L, whose transcriptional upregulation took place in CD4+ TCM cells of COVID-19 control individuals upon SARS-CoV-2 infection but not in COVID-19 CVID patients (Figure 3e).
All these results indicate that the NK and T cell compartments of COVID-19 CVID patients show incomplete antiviral immune responses with impaired gene expression of IFN-γ and TNF-α, as well as CD40L in the case of CD4+ TCM cells. On the contrary, NK and cytotoxic T cells from COVID-19 CVID patients display a higher activation state, expressing high levels of cytotoxic genes during SARS-CoV-2 infection, that are also maintained at convalescence.
Next, we performed TCR analysis. The highest level of T cell clonal expansion was observed in CD8+ TEM cells, CD8+ TEff cells, CD4+ CTL cells and Tcycling cells (Supp. Figure 2c). The inspection of CD4+ CTL cells showed that most of the expanded clones were already present in CVID patients prior to viral infection, whereas CD8+ TEM cells and specially CD8+ TEff cells and Tprolif. cells showed strong clonal expansion during progression and convalescence stages (Supp. Figure 2c). In contrast, MAIT cells, TDN cells, as well as the different subsets of CD4 T cells, including naïve CD4+ T cells, CD4+ TEM, CD4+ TCM, CD4+ TEff and Treg cells, showed only a modest clonal expansion at progression and convalescence stages (Supp. Figure 2c). As expected, within the NK and Tγδ cell clusters, only a small fraction of cells displayed a productive TCR chain, which may derive from cytotoxic T cells co-clustering with NK and Tγδ cells.
Persistent activation of inflammasome genes in COVID-19 CVID monocytes
COVID-19 patients display functional and phenotypic alterations in monocytes 42–44. Hence, we analyzed the three main subsets of monocytes (classical, intermediate and non-classical monocytes) during SARS-CoV-2 infection and recovery (Figure 4a and Supp. Figure 3a). Baseline vs progression or convalescence comparisons indicated that GO categories related to inflammasome complex assembly, pyroptosis and IL-1β production were more enriched in monocytes from COVID-19 CVID patients compared with those from COVID-19 control individuals (Figure 4b and Supp. Figure 3b). Interestingly, the three monocyte subsets displayed significant upregulation of genes that encode members of distinct inflammasome complexes in COVID-19 CVID patients. The inspection of several inflammasome sensor genes showed that the AIM2 gene was upregulated upon SARS-CoV-2 infection in both CVID patients and control individuals regardless of disease severity. In contrast, we detected a specific and significant upregulation of the NLRC4 gene (NLRC4 inflammasome) and the MEFV gene (pyrin inflammasome) during infection in COVID-19 CVID patients that was not observed in control individuals (Figure 4c and Supp. Figure 3c). In line with this, the expression of many inflammasome-related genes was increased upon SARS-CoV-2 infection and was also maintained during convalescence in CVID patients unlike control individuals. For instance, CASP1, CARD8, CARD16, PYCARD and GSDMD genes were highly expressed at both progression and convalescence stages in COVID-19 CVID patients, whereas such persistent upregulation was not observed in mild or severe COVID-19 control individuals (Fig 4c and Supp. Figure 3c).
Next, we analyzed the gene expression of the toll-like receptors TLR7 and TLR8, which are sensors of single stranded RNAs, as the SARS-CoV-2 genome. We observed that these two receptors were significantly upregulated in COVID-19 CVID patients upon SARS-CoV-2 infection in the three subsets of monocytes, in contrast to COVID-19 controls (mild or severe) where the upregulation occurs only in intermediate monocytes (Figure 4d). Furthermore, we observed that TLR7 and TLR8 gene upregulation persisted only in COVID-19 CVID patients at the convalescence stage in comparison with COVID-19 controls (Figure 4d).
Finally, we analyzed the expression of several anti-inflammatory genes in the three monocyte subsets upon SARS-CoV-2 infection. IL10, ARG1, SOCS3, PPARG, ADM and CD63 genes were upregulated upon SARS-CoV-2 infection and their expression decreased later at convalescence in the three subsets of monocytes in COVID-19 controls (Figure 4e). In contrast, we did not detect upregulation of these anti-inflammatory genes in COVID-19 CVID patients (Figure 4e).
All these results indicate that upregulation and persistent activation of specific inflammasome genes in the monocytic compartment upon SARS-CoV-2 infection are features of CVID patients. In addition, COVID-19 CVID monocytes show a defective expression of anti-inflammatory genes that might explain the sustained upregulation of inflammasome-related genes observed in COVID-19 CVID patients.