SARS-CoV-2 Vaccine-Elicited Immunity after B Cell Depletion in Multiple Sclerosis

The impact of B cell deficiency on the humoral and cellular responses to SARS-CoV2 mRNA vaccination remains a challenging and significant clinical management question. We evaluated vaccine-elicited serological and cellular responses in 1) healthy individuals who were pre-exposed to SARS-CoV-2 (n = 21), 2) healthy individuals who received a homologous booster (mRNA, n = 19; or Novavax, n = 19), and 3) persons with multiple sclerosis on B cell depletion therapy (MS-αCD20) receiving mRNA homologous boosting (n = 36). Pre-exposure increased humoral and CD4 T cellular responses in immunocompetent individuals. Novavax homologous boosting induced a significantly more robust serological response than mRNA boosting. MS-α CD20 had an intact IgA mucosal response and an enhanced CD8 T cell response to mRNA boosting compared with immunocompetent individuals. This enhanced cellular response was characterized by the expansion of only effector, not memory, T cells. The enhancement of CD8 T cells in the setting of B cell depletion suggests a regulatory mechanism between B and CD8 T cell vaccine responses.

A partial human LCK defect causes a T cell immunodeficiency with intestinal inflammation

Lymphocyte-specific protein tyrosine kinase (LCK) is essential for T cell antigen receptor (TCR)-mediated signal transduction. Here, we report two siblings homozygous for a novel LCK variant (c.1318C>T; P440S) characterized by T cell lymphopenia with skewed memory phenotype, infant-onset recurrent infections, failure to thrive, and protracted diarrhea. The patients' T cells show residual TCR signal transduction and proliferation following anti-CD3/CD28 and phytohemagglutinin (PHA) stimulation. We demonstrate in mouse models that complete (Lck-/-) versus partial (LckP440S/P440S) loss-of-function LCK causes disease with differing phenotypes. While both Lck-/- and LckP440S/P440S mice exhibit arrested thymic T cell development and profound T cell lymphopenia, only LckP440S/P440S mice show residual T cell proliferation, cytokine production, and intestinal inflammation. Furthermore, the intestinal disease in the LckP440S/P440S mice is prevented by CD4+ T cell depletion or regulatory T cell transfer. These findings demonstrate that P440S LCK spares sufficient T cell function to allow the maturation of some conventional T cells but not regulatory T cells-leading to intestinal inflammation.

Innate and Adaptive Cell-Mediated Immune Responses to a COVID-19 mRNA Vaccine in Young Children

Background

There is little information on cell-mediated immunity (CMI) to COVID-19 mRNA vaccines in children. We studied adaptive and innate CMI in vaccinated children aged 6 to 60 months.

Methods

Blood obtained from participants in a randomized placebo-controlled trial of an mRNA vaccine before and 1 month after the first dose was used for antibody measurements and CMI (flow cytometry).

Results

We enrolled 29 children with a mean age of 28.5 months (SD, 15.7). Antibody studies revealed that 10 participants were infected with SARS-CoV-2 prevaccination. Ex vivo stimulation of peripheral blood mononuclear cells with SARS-CoV-2 spike peptides showed significant increases pre- to postimmunization of activated conventional CD4+ and γδ T cells, natural killer cells, monocytes, and conventional dendritic cells but not mucosa-associated innate T cells. Conventional T-cell, monocyte, and conventional dendritic cell responses in children were higher immediately after vaccination than after SARS-CoV-2 infection. The fold increase in CMI pre- to postvaccination did not differ between children previously infected with SARS-CoV-2 and those uninfected.

Conclusions

Children aged 6 to 60 months who were vaccinated with a COVID-19 mRNA vaccine developed robust CMI responses, including adaptive and innate immunity.

SARS-CoV-2 mRNA vaccination induces an antigen-specific T cell response correlating with plasma interferon-gamma in B cell depleted patients

Emerging evidence is encouraging and suggests that a substantial proportion of patients without antibody responses (due to anti-CD20 therapy or other etiologies) to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccines develop T cell responses. However, antigen-specific T cellular responses are notoriously difficult to assess clinically, given the lack of such assays under satisfactory CAP/CLIA regulation, and the laborious nature of the flow cytometric assessment. To evaluate the ability to apply a clinically feasible assay to measure T cellular responses to SARS-CoV-2 mRNA vaccination, we compared flow cytometric and enzyme-linked immunosorbent assay (ELISA) based assays in 24 participants treated with anti-CD20 therapy. T cellular activation (CD69 + CD137+ surface expression, i.e., activation induced markers [AIM]) and intracellular interferon gamma (INFγ) production via flow cytometry was compared to plasma Interferon Gamma Release Assay (IGRA) via ELISA. Plasma INFγ production measured by IGRA correlated with the percent of INFγ-producing AIM positive T cells, supporting the use of IGRA assay as a robust assessment of T cellular response to the SARS-CoV-2 vaccine for B-cell depleted patients that is clinically feasible, time efficient, and cost effective.

An Observational Study on the Humoral and Cellular Immune Response to SARS-CoV-2 mRNA Vaccination in Multiple Sclerosis and Other Autoimmune Neurological Disorders Treated With Anti-CD20 Therapies

Objective

To assess adaptive immunity to SARS-CoV-2 in anti-CD20 treated individuals with mRNA vaccination.

Background

Anti-CD20 therapies attenuate humoral responses to vaccines. However, their effect on T cell responses is less clear. We examined B and T cell responses following COVID-19 vaccination in patients receiving anti-CD20 therapy for multiple sclerosis (MS) and other autoimmune inflammatory neurologic diseases (AINDs, e.g., autoimmune encephalitis, stiff person syndrome, etc.).

Design/Methods

MS and AIND patients on anti-CD20 therapies were prospectively enrolled for longitudinal analysis of antibody and T cell responses after a 3rd COVID-19 vaccination. Serum antibodies against the receptor-binding domain of the S1 spike protein (RBD-S1 IgG), neutralizing antibodies, and SARS-CoV-2 CD8 T cell responses, using activation-induced markers (AIM) and INF-γ release assays (EUROIMMUN, Germany), were measured at various time points including pre-vaccination, post initial vaccination series, and 4 and 12 weeks after 3rd dose.

Results

Thirty-four MS and AIND participants are enrolled. Results for these patients (mean age 52 years-old, 79% female, 21 Pfizer, 13 Moderna) demonstrated attenuated RBD IgG antibody responses. However, a robust CD8 T cell response was observed, following a two-dose series, compared to non-immunosuppressed, age-matched vaccinated controls or unvaccinated with severe SARS-CoV-2 infection (p = 0.01). T cell response was sustained long-term (>12 weeks post 3rd dose) in all 11 anti-CD20 patients analyzed thus far. Collections are completed for all participants at 12 weeks and analysis to be completed by 05/15/22. Further analysis includes correlation of the INF- γ release assay compared to RBD-CD8 T cell response detected by AIM assay.

Conclusions

Results suggest that patients treated with anti-CD20 therapy generate a robust CD8 T cell response to SARS-CoV-2 mRNA after three doses but remain with attenuated humoral immune responses. Our observational study will provide important data to guide vaccine management in patients on or anticipating anti-CD20 therapy.

Dissecting the effect of a novel hypomorphic IL2RB mutation on immune dysregulation

Human inborn errors of immunity (IEIs) are a class of genetic disorders caused by monogenic germline mutations that impair the function of the encoded protein. We recently described a novel IEI due to an IL2RB homozygous mutation (p.Pro222_Gln225Del) in two siblings who suffered from multi-organ autoimmunity and CMV susceptibility. This mutation resulted in decreased cell surface protein expression and increased serum IL-2/15 levels, with concomitant increased baseline STAT5 phosphorylation (pSTAT5) but poor pSTAT5 response to IL-2 and IL-15 stimulation. Counterintuitively, this IL-2Rβ hypomorphic mutation led to an expansion of memory CD8+ T and immature CD56bright NK cells, which express the highest levels of IL-2Rβ and require IL-2/15 signaling for survival and differentiation. Yet, their maturation and function appeared impaired, suggesting that both intrinsic (hypomorphic receptor) and extrinsic (serum cytokine milieu) mechanisms were at play. To further interrogate these receptor instrinsic/extrinsic mechanisms we developed a mouse model that harbors the homolog mutation (Il2rbMut/Mut). When mutant bone marrow cells reconstituted a WT host, serum IL-2/15 levels and IL-2Rβ protein surface expression partially normalized, though IL-2/15-induced signaling remained hypofunctional. Additionally, the dysregulated mutant IL-2Rβ-driven CD8+ T cell immunophenotype normalized but the NK phenotype did not. These data highlight the asymmetrical effect that a partial IL-2Rβ defect has on CD8 T and NK cell IL-2/15-dependent signaling and downstream cellular processes. These results imply that strategies to modify serum IL-2/15 levels may serve as a therapeutic approach to treating IL-2/15 signaling defects.

 Supported by grants from NIH (T32 AI074491, K23 AR070897)

Adenosine receptor 2a agonists target mouse CD11c+T-bet+ B cells in infection and autoimmunity

CD11c+T-bet+ B cells are recognized as an important component of humoral immunity and autoimmunity. These cells can be distinguished from other B cells by their higher expression of the adenosine receptor 2a. Here we address whether A2A receptor activation can affect CD11c+T-bet+ B cells. We show that administration of the A2A receptor agonist CGS-21680 depletes established CD11c+T-bet+ B cells in ehrlichial-infected mice, in a B cell-intrinsic manner. Agonist treatment similarly depletes CD11c+T-bet+ B cells and CD138+ B cells and reduces anti-nuclear antibodies in lupus-prone mice. Agonist treatment is also associated with reduced kidney pathology and lymphadenopathy. Moreover, A2A receptor stimulation depletes pathogenic lymphocytes and ameliorates disease even after disease onset, highlighting the therapeutic potential of this treatment. This study suggests that targeting the adenosine signaling pathway may provide a method for the treatment of lupus and other autoimmune diseases mediated by T-bet+ B cells.

CD11c+ T-bet+ B Cells Require IL-21 and IFN-γ from Type 1 T Follicular Helper Cells and Intrinsic Bcl-6 Expression but Develop Normally in the Absence of T-bet

CD11c⁺ T-bet⁺ B cells generated during ehrlichial infection require CD4⁺ T cell help and IL-21 signaling for their development, but the exact T cell subset required had not been known. In this study, we show in a mouse model of Ehrlichia muris that type 1 T follicular helper (T_FH1) cells provide help to CD11c⁺ T-bet⁺ B cells via the dual secretion of IL-21 and IFN-γ in a CD40/CD40L-dependent manner. T_FH1 cell help was delivered in two phases: IFN-γ signals were provided early in infection, whereas CD40/CD40L help was provided late in infection. In contrast to T-bet⁺ T cells, T-bet⁺ B cells did not develop in the absence of B cell-intrinsic Bcl-6 but were generated in the absence of T-bet. T-bet-deficient memory B cells were largely indistinguishable from their wild-type counterparts, although they no longer underwent switching to IgG2c. These data suggest that a primary function of T-bet in B cells during ehrlichial infection is to promote appropriate class switching, not lineage specification. Thus, CD11c⁺ memory B cells develop normally without T-bet but require Bcl-6 and specialized help from dual cytokine-producing T_FH1 cells.

T-bet regulates T cell-independent plasmablast responses during intracellular bacterial infection

T-bet+ B cells have emerged as a major B cell subset associated with both protective immunity and autoimmunity. T-bet is considered to be a master transcription factor in type I adaptive immune responses to intracellular pathogens, a response characterized by the production of interferon gamma. Our studies have shown that infection with the intracellular bacterium, E. muris, generates both extrafollicular T cell-independent T-bet+ CD11c+ IgM-secreting plasmablasts (PB), as well as T-bet+ CD11c+ IgM memory cells. Both of these B cell populations play key roles in antigen-specific humoral immunity, although the role of T-bet in their development had not been resolved. Although T-bet is often considered to define lineage in Type I B cells, we found that T-bet was dispensable for memory B cell development. Memory B cells from mice with B cell-specific T-bet deficiency exhibited nearly identical surface marker expression as those of wild-type mice, including CD11c, CD73, PD-L2, CD80, CD38, CD95, and CXCR3. In contrast, T-bet-deficient early CD11c+ splenic PB were significantly reduced in frequency, suggesting that T-bet regulates PB, but not memory cell development or differentiation. As has been reported, antigen-specific IgG2c was no longer the dominant serum antibody isotype in mice lacking B cell T-bet expression. Our data suggest that a critical function of T-bet in B cells is to promote the differentiation of short-lived antibody-secreting PB, and to restrict class switching to protective IgG2c antibodies. Our findings are relevant to how T-bet+ B cells function not only in pathogen-specific immunity, but also in autoimmune diseases, wherein the quality of the humoral response is of critical importance.

T-Bet+ IgM Memory Cells Generate Multi-lineage Effector B Cells

Immunoglobulin M (IgM) memory cells undergo differentiation in germinal centers following antigen challenge, but the full effector cell potential of these cells is unknown. We monitored the differentiation of enhanced yellow fluorescent protein (eYFP)- labeled CD11c⁺ and CD11c^neg T-bet⁺ IgM memory cells after their transfer into naive recipient mice. Following challenge infection, many memory cells differentiated into IgM-producing plasmablasts. Other donor B cells entered germinal centers, down- regulated CD11c, underwent class switch recombination, and became switched memory cells. Yet other donor cells were maintained as IgM memory cells, and these IgM memory cells retained their multi-lineage potential following serial transfer. These findings were corroborated at the molecular level using immune repertoire analyses. Thus, IgM memory cells can differentiate into all effector B cell lineages and undergo self-renewal, properties that are characteristic of stem cells. We propose that these memory cells exist to provide long-term multi-functional immunity and act primarily to maintain the production of protective antibodies.

T-bet⁺ B cells have now been identified in a wide range of immunological contexts. Using a model bacterial infection, Kenderes et al. show that single T-bet⁺ IgM memory cells exhibit multi-lineage potential and can undergo self-renewal, both properties of stem cells.

TNF-α Contributes to Lymphoid Tissue Disorganization and Germinal Center B Cell Suppression during Intracellular Bacterial Infection

Bacterial, parasitic, and viral infections are well-known causes of lymphoid tissue disorganization, although the factors, both host and/or pathogen derived, that mediate these changes are largely unknown. Ehrlichia muris infection in mice causes a loss of germinal center (GC) B cells that is accompanied by the generation of extrafollicular T-bet⁺ CD11c⁺ plasmablasts and IgM memory B cells. We addressed a possible role for TNF-α in this process because this cytokine has been shown to regulate GC development. Ablation of TNF-α during infection resulted in an 8-fold expansion of GL7⁺ CD38^lo CD95⁺ GC B cells, and a 2.5- and 5-fold expansion of CD138⁺ plasmablasts and T-bet⁺ memory cells, respectively. These changes were accompanied by a reduction in splenomegaly, more organized T and B cell zones, and an improved response to Ag challenge. CXCL13, the ligand for CXCR5, was detected at 6-fold higher levels following infection but was much reduced following TNF-α ablation, suggesting that CXCL13 dysregulation also contributes to loss of lymphoid tissue organization. T follicular helper cells, which also underwent expansion in infected TNF-α--deficient mice, may also have contributed to the expansion of T-bet⁺ B cells, as the latter are known to require T cell help. Our findings contrast with previously described roles for TNF-α in GCs and reveal how host-pathogen interactions can induce profound changes in cytokine and chemokine production that can alter lymphoid tissue organization, GC B cell development, and extrafollicular T-bet⁺ B cell generation.

Stem cell-like T-bet+ IgM memory cells generate multi-lineage effector B cells

Our laboratory has been studying the differentiation of CD11c+ T-bet+ IgM memory B cells during secondary ehrlichial infection.

These cells are closely related to B cells that have been described in a range of other contexts, including hepatitis, AIDs, malaria, SLE, and age-related autoimmunity.

Following secondary infection, IgM memory cells, as a population, undergo self-renewal, and differentiate into effector cells, including splenic and bone marrow antibody secreting cells (ASC).

Moreover, IgM memory cells enter germinal centers, where they undergo class-switch recombination and give rise to class-switched memory and effector cells.

Although these data suggest that a single memory cell has multi-lineage potential, we sought to formally address this question by searching for shared clones among IgM memory cell-derived effector cells.

Among the IgM memory cell-derived subsets, we identified several clones common to all effector cell populations. The number of common clones varied for each pairwise comparison of effector cells and suggested lineal relationships.

IgM memory cells accumulated mutations following rechallenge; although all memory cell-derived subsets displayed similar numbers of V region mutations.

Lineage analysis demonstrated that the effector cell subsets underwent varying degrees of clonal diversification, although this was clone-dependent.

These studies reveal that a single IgM memory cell clone can give rise to different memory and effector cell subsets, that is, they exhibit stem cell properties. This property distinguishes these T-bet+ IgM memory cells as a unique memory cell subset.

Regulation of CD11c+ T-bet+ IgM+ Memory B-cells by TNFα

Our studies of ehrlichial infection have identified a population of CD11c+ T-bet+ IgM memory B-cells that arise within 30 days post-infection. We and others have shown that CD11c+ T-bet+B cells require for their development or function a number of factors, including T-bet, IFNγ, CD4 T-cells, IL-21, and TLRs. Here, we addressed a possible role for TNFα in the generation of CD11c+ T-bet+IgM memory B-cells, because aside from being a major inflammatory cytokine, it can regulate germinal center development, and mediate apoptosis. We observed an 8-fold increase in the number of CD11c+IgM memory B-cells (also CD73+) in TNFα-deficient mice, relative to wild-type mice, on day 16 post-infection. The B cell population persisted at much higher frequency and number on day 30 post-infection. The changes in the IgM memory cell population were associated with a concomitant 10-fold relative increase in the frequency of GL7+ CD38lo CD95+germinal center B cells in TNFα-deficient mice. These latter data contrast with published studies that have reported that TNFα is required for GC development, suggesting that the requirement we have observed for TNFα is context-dependent. These data suggest that there may be a positive relationship between GC development and generation of CD11c+ IgM memory cells, and that TNFα may act to mediate IgM memory cell homeostasis by regulating apoptosis. Ongoing studies will address mechanisms whereby TNFα contributes to the genesis and maintenance of CD11c+ T-bet+IgM memory B-cells.

CD11c+ T-bet+ IgM memory B cells provide multi-lineage reconstitution of effector and memory B cells following challenge infection

IgM memory B cells are now recognized as an important component of immunological memory. These cells have been proposed to act as a reservoir of broadly-reactive B cells that differentiate, in germinal centers, into high affinity class-switched effector B cells following antigen encounter. However, we propose IgM memory cells can differentiate into more than just germinal center and class-switched cells. To address this, we monitored the secondary response of CD11c+ T-bet+ IgM memory cells generated by Ehrlichia muris infection, by monitoring eYFP-labeled, flow cytometrically-purified, IgM memory cells following their transfer to naïve recipient mice and subsequent challenge infection. The IgM memory B cells differentiated into IgM-producing plasmablasts early following infection; this resulted in a 4-fold increase in IgM production, relative to control mice that did not receive memory cells. Other donor memory B cells entered germinal centers, down-regulated CD11c, and underwent class switching, generating switched memory B cells. Finally, some donor B cells were maintained as IgM memory cells. Upon secondary transfer and challenge, purified IgM memory cells underwent the same pattern of self-renewal and differentiation. Additionally, when IgM memory cell recipient mice were challenged with a virulent Ehrlichia strain, a reduction in bacterial burden was observed, indicating that IgM memory cells can provide immunity to challenge infection. Our findings also suggest that T-bet+ IgM memory cells act as a self-renewing population capable of repopulating the entire spectrum of effector and memory B cells during secondary infection, and demonstrate an important role for IgM memory cells in maintaining long-term immunity.