Analysis of the humoral and cellular response after the third COVID-19 vaccination in patients with autoimmune hepatitis.

BACKGROUND & AIMS: To explore the humoral and T-cell response to the third COVID-19 vaccination in autoimmune hepatitis (AIH). METHODS: Anti-SARS-CoV-2 antibody titers were prospectively determined in 81 AIH patients and 53 healthy age- and sex-matched controls >7 days (median 35) after the first COVID-19 booster vaccination. The spike-specific T-cell response was assessed using an activation-induced marker assay (AIM) in a subset of patients. RESULTS: Median antibody levels were significantly lower in AIH compared to controls (10 908 vs. 25 000 AU/ml, p < .001), especially in AIH patients treated with MMF (N = 14, 4542 AU/ml, p = .004) or steroids (N = 27, 7326 AU/ml, p = .020). Also, 48% of AIH patients had antibody titers below the 10% percentile of the healthy controls (9194 AU/ml, p < .001). AIH patients had a high risk of failing to develop a spike-specific T-cell response (15/34 (44%) vs. 2/16 (12%), p = .05) and showed overall lower frequencies of spike-specific CD4 + T cells (median: 0.074% vs 0.283; p = .01) after the booster vaccination compared to healthy individuals. In 34/81 patients, antibody titers before and after booster vaccination were available. In this subgroup, all patients but especially those without detectable/low antibodies titers (<100 AU/ml) after the second vaccination (N = 11/34) showed a strong, 148-fold increase. CONCLUSION: A third COVID-19 vaccination efficiently boosts antibody levels and T-cell responses in AIH patients and even seroconversion in patients with the absent immune response after two vaccinations, but to a lower level compared to controls. Therefore, we suggest routinely assessing antibody levels in AIH patients and offering additional booster vaccinations to those with suboptimal responses.

Humoral and Cellular Immune Response After Third and Fourth SARS-CoV-2 mRNA Vaccination in Liver Transplant Recipients.

BACKGROUND & AIMS: Liver transplant recipients (LTRs) show a decreased immune response after 2 severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) vaccinations compared with healthy controls (HCs). Here, we investigated the immunogenicity of additional vaccinations. METHODS: In this prospective study, humoral (anti-SARS-CoV-2 receptor-binding domain [anti-S RBD]) and cellular (interferon-gamma release assay) immune responses were determined after mRNA-based SARS-CoV-2 vaccination in 106 LTRs after a third vaccination and in 36 LTRs after a fourth vaccination. Patients with anti-S RBD antibody levels >0.8 arbitrary unit (AU)/mL after vaccination were defined as responders. RESULTS: After 3 vaccinations, 92% (97/106) of LTRs compared with 100% (28/28) of HCs were responders. However, the antibody titer of LTRs was lower compared with HCs (1891.0 vs 21,857.0 AU/mL; P < .001). Between a second and third vaccination (n = 75), the median antibody level increased 67-fold in LTRs. In patients seronegative after 2 vaccinations, a third dose induced seroconversion in 76% (19/25), whereas all HCs were already seropositive after 2 vaccinations. A spike-specific T-cell response was detected in 72% (28/39) after a third vaccination compared with 32% (11/34) after a second vaccination. Independent risk factors for a low antibody response (anti-S RBD <100 AU/mL) were first vaccination within the first year after liver transplant (odds ratio [OR], 8.00; P = .023), estimated glomular filtration rate <45 mL/min (OR, 4.72; P = .006), and low lymphocyte counts (OR, 5.02; P = .008). A fourth vaccination induced a 9-fold increase in the median antibody level and seroconversion in 60% (3/5) of previous non-responders. CONCLUSIONS: A third and fourth SARS-CoV-2 vaccination effectively increases the humoral and cellular immune response of LTRs, but to a lesser extent than in HCs. A fourth vaccination should be generally considered in LTRs.

SARS-CoV2-specific Humoral and T-cell Immune Response After Second Vaccination in Liver Cirrhosis and Transplant Patients.

BACKGROUND & AIMS: Detailed information on the immune response after second vaccination of cirrhotic patients and liver transplant (LT) recipients against severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is largely missing. We aimed at comparing the vaccine-induced humoral and T-cell responses of these vulnerable patient groups. METHODS: In this prospective cohort study, anti-SARS-CoV-2 spike-protein titers were determined using the DiaSorin LIAISON (anti-S trimer) and Roche Elecsys (anti-S RBD) immunoassays in 194 patients (141 LT, 53 cirrhosis Child-Pugh A-C) and 56 healthy controls before and 10 to 84 days after second vaccination. The spike-specific T-cell response was assessed using an interferon-gamma release assay (EUROIMMUN). A logistic regression analysis was performed to identify predictors of low response. RESULTS: After the second vaccination, seroconversion was achieved in 63% of LT recipients and 100% of cirrhotic patients and controls using the anti-S trimer assay. Median anti-SARS-CoV-2 titers of responding LT recipients were lower compared with cirrhotic patients and controls (P < .001). Spike-specific T-cell response rates were 36.6%, 65.4%, and 100% in LT, cirrhosis, and controls, respectively. Altogether, 28% of LT recipients did neither develop a humoral nor a T-cell response after second vaccination. In LT recipients, significant predictors of absent or low humoral response were age >65 years (odds ratio [OR], 4.57; 95% confidence interval [CI], 1.48-14.05) and arterial hypertension (OR, 2.50; 95% CI, 1.10-5.68), whereas vaccination failure was less likely with calcineurin inhibitor monotherapy than with other immunosuppressive regimens (OR, 0.36; 95% CI, 0.13-0.99). CONCLUSION: Routine serological testing of the vaccination response and a third vaccination in patients with low or absent response seem advisable. These vulnerable cohorts need further research on the effects of heterologous vaccination and intermittent reduction of immunosuppression before booster vaccinations.

Human dental pulp cells modulate CD8+ T cell proliferation and efficiently degrade extracellular ATP to adenosine in vitro.

The pulp of human teeth contains a population of self-renewing stem cells that can regulate the functions of immune cells. When applied to patients, these cells can protect tissues from damage by excessive inflammation. We confirm that dental pulp cells effectively inhibit the proliferation and activation of cytotoxic T cells in vitro, and show that they carry high levels of CD73, a key enzyme in the conversion of pro-inflammatory extracellular ATP to immunosuppressive adenosine. Given their accessibility and abundance, as well as their potential for allogeneic administration, dental pulp cells provide a valuable source for immunomodulatory therapy.

Sustained Response After Remdesivir and Convalescent Plasma Therapy in a B-Cell-Depleted Patient With Protracted Coronavirus Disease 2019 (COVID-19).

We provide detailed clinical, virological, and immunological data of a B-cell-depleted patient treated with obinutuzumab for follicular lymphoma with protracted coronavirus disease 2019 (COVID-19) and viremia. A sustained response was achieved after 2 courses of remdesivir and subsequent convalescent plasma therapy. Immunocompromised patients might require combined and prolonged antiviral treatment regimens.

Update of the simplified criteria for autoimmune hepatitis: Evaluation of the methodology for immunoserological testing.

BACKGROUND & AIMS: The simplified criteria for the diagnosis of autoimmune hepatitis (AIH) include immunofluorescence testing (IFT) of antinuclear and smooth muscle autoantibodies (ANA and SMA) on rodent tissue sections. We aimed to establish scoring criteria for the implementation of ANA IFT on human epithelioma-2 (HEp-2) cells and ELISA-based testing. METHODS: ANA and SMA reactivity of 61 AIH sera and 72 non-alcoholic fatty liver disease controls were separately assessed on tissue sections and HEp-2 cells to compare the diagnostic value at increasing titers. A total of 113 patients with AIH at diagnosis and 202 controls from 3 European centers were assessed by IFT as well as 3 different commercially available ANA ELISA and 1 anti-F-actin ELISA. RESULTS: ANA assessment by IFT on liver sections had 83.6% sensitivity and 69.4% specificity for AIH at a titer of 1:40. On HEp-2 cells, sensitivity and specificity were 75.4% and 73.6%, respectively, at an adjusted titer of 1:160. Area under the curve (AUC) values of ANA ELISA ranged from 0.70-0.87, with ELISA coated with HEp-2 extracts in addition to selected antigens performing significantly better. SMA assessment by IFT had the highest specificity for the SMA-VG/T pattern and anti-microfilament reactivity on HEp-2 cells. ELISA-based anti-F-actin evaluation was a strong predictor of AIH (AUC 0.88) and performed better than SMA assessment by IFT (AUC 0.77-0.87). CONCLUSION: At adjusted cut-offs, both ANA IFT using HEp-2 cells and ELISA-based autoantibody evaluation for ANA and SMA are potential alternatives to tissue-based IFT for the diagnosis of AIH. LAY SUMMARY: Autoantibodies are a hallmark of autoimmune hepatitis and are traditionally tested for by immunofluorescence assays on rodent tissue sections. Herein, we demonstrate that human epithelioma cells can be used as a reliable substrate for immunofluorescence testing. ELISA-based testing is also a potentially reliable alternative for autoantibody assessment in autoimmune hepatitis. We propose the implementation of these testing methods into the simplified criteria for the diagnosis of autoimmune hepatitis.

P2X7-mediated ATP secretion is accompanied by depletion of cytosolic ATP.

ATP and its metabolites are important extracellular signal transmitters acting on purinergic P2 and P1 receptors. Most cells can actively secrete ATP in response to a variety of external stimuli such as gating of the P2X7 receptor. We used Yac-1 murine lymphoma cells to study P2X7-mediated ATP release. These cells co-express P2X7 and ADP-ribosyltransferase ARTC2, permitting gating of P2X7 by NAD+-dependent ADP-ribosylation without the need to add exogenous ATP. Yac-1 cells released ATP into the extracellular space within minutes after stimulation with NAD+. This was blocked by pre-incubation with the inhibitory P2X7-specific nanobody 13A7. Gating of P2X7 for 3 h significantly decreased intracellular ATP levels in living cells, but these had returned to normal by 20 h. P2X7-mediated ATP release was dependent on a rise in cytosolic calcium and the depletion of intracellular potassium, but was not blocked by inhibitors of pannexins or connexins. We used genetically encoded FRET-based ATP sensors targeted to the cytosol to image P2X7-mediated changes in the distribution of ATP in 3T3 fibroblasts co-expressing P2X7 and ARTC2 and in Yac-1 cells. In response to NAD+, we observed a marked depletion of ATP in the cytosol. This study demonstrates the potential of ATP sensors as tools to study regulated ATP release by other cell types under other conditions.

A transplant "immunome" screening platform defines a targetable epitope fingerprint of multiple myeloma.

Multiple myeloma (MM) is a hematological cancer for which immune-based treatments are currently in development. Many of these rely on the identification of highly disease-specific, strongly and stably expressed antigens. Here, we profiled the myeloma B-cell immunome both to explore its predictive role in the context of autologous and allogeneic hematopoietic stem cell transplantation (HSCT) and to identify novel immunotherapeutic targets. We used random peptide phage display, reverse immunization, and next-generation sequencing-assisted antibody phage display to establish a highly myeloma-specific epitope fingerprint targeted by B-cell responses of 18 patients in clinical remission. We found that allogeneic HSCT more efficiently allowed production of myeloma-specific antibodies compared with autologous HSCT and that a highly reactive epitope recognition signature correlated with superior response to treatment. Next, we performed myeloma cell surface screenings of phage-displayed patient transplant immunomes. Although some of the screenings yielded clear-cut surface binders, the majority of screenings did not, suggesting that many of the targeted antigens may in fact not be accessible to the B-cell immune system in untreated myeloma cells. This fit well with the identification of heat-shock proteins as a class of antigens that showed overall the broadest reactivity with myeloma patient sera after allogeneic HSCT and that may be significantly translocated to the cell surface upon treatment as a result of immunogenic cell death. Our data reveal a disease-specific epitope signature of MM that is predictive for response to treatment. Mining of transplant immunomes for strong myeloma surface binders may open up avenues for myeloma immunotherapy.

Nucleotide-Induced Membrane-Proximal Proteolysis Controls the Substrate Specificity of T Cell Ecto-ADP-Ribosyltransferase ARTC2.2.

ARTC2.2 is a toxin-related, GPI-anchored ADP-ribosyltransferase expressed by murine T cells. In response to NAD(+) released from damaged cells during inflammation, ARTC2.2 ADP-ribosylates and thereby gates the P2X7 ion channel. This induces ectodomain shedding of metalloprotease-sensitive cell surface proteins. In this study, we show that ARTC2.2 itself is a target for P2X7-triggered ectodomain shedding. We identify the metalloprotease cleavage site 3 aa upstream of the predicted GPI anchor attachment site of ARTC2.2. Intravenous injection of NAD(+) increased the level of enzymatically active ARTC2.2 in serum, indicating that this mechanism is operative also under inflammatory conditions in vivo. Radio-ADP-ribosylation assays reveal that shedding refocuses the target specificity of ARTC2.2 from membrane proteins to secretory proteins. Our results uncover nucleotide-induced membrane-proximal proteolysis as a regulatory mechanism to control the substrate specificity of ARTC2.2.

Identification and analysis of ADP-ribosylated proteins.

The analysis of ADP-ribosylated proteins is a challenging task, on the one hand because of the diversity of the target proteins and the modification sites, on the other hand because of the particular problems posed by the analysis of ADP-ribosylated peptides. ADP-ribosylated proteins can be detected in in vitro experiments after the incorporation of radioactively labeled or chemically modified ADP-ribose. Endogenously ADP-ribosylated proteins may be detected and enriched by antibodies directed against the ADP-ribosyl moiety or by ADP-ribosyl binding macro domains. The determination of the exact attachment site of the modification, which is a prerequisite for the understanding of the specificity of the various ADP-ribosyl transferases and the structural consequences of ADP-ribosylation, necessitates the proteolytic cleavage of the proteins. The resulting peptides can afterwards be enriched either by IMAC (using the affinity of the pyrophosphate group for heavy metal ions) or by immobilized boronic acid beads (using the affinity of the vicinal ribose hydroxy groups for boronic acid). The identification of the modified peptides usually requires tandem mass spectrometric measurements. Problems that hamper the mass spectrometric analysis by collision-induced decay (CID) can be circumvented either by the application of different fragmentation techniques (electron transfer or electron capture dissociation; ETD or ECD) or by enzymatic cleavage of the ADP-ribosyl group to ribosyl-phosphate.

ADP-ribosylation of P2X7: a matter of life and death for regulatory T cells and natural killer T cells.

ADP-ribosyltransferases comprise a family of enzymes originally discovered as bacterial toxins and later characterised also in mammals. In mice, the ADP-ribosyltransferase ARTC2.2 is expressed at the surface of T lymphocytes and has been studied extensively. In the presence of extracellular NAD(+), ARTC2.2 ADP-ribosylates several cell surface target proteins and thereby regulates their function. P2X7, an ATP-gated cation channel, has been discovered as a prominent ARTC2.2 target at the surface of mouse T cells. ADP-ribosylation of P2X7 in the presence of low micromolar extracellular NAD(+) induces long-lasting P2X7 activation and triggers cell death. Regulatory T cell subsets (Tregs and NKT cells) are remarkably sensitive to NAD(+)-induced cell death (NICD). Thus, liberation of endogenous NAD(+) by stressed cells is now viewed as a danger signal promoting immune responses by hindering regulatory T cells. This review will highlight the recent discoveries on the in vivo role of the ARTC2.2/P2X7 pathway triggered by the endogenous release of extracellular NAD(+), the relative sensitivity of lymphocytes subsets to this regulatory pathway and its pharmacological manipulation using camelid-derived ARTC2.2-blocking nanobodies.

The expression of CD39 on regulatory T cells is genetically driven and further upregulated at sites of inflammation.

Regulatory T cells (Tregs) use different mechanisms to exert their suppressive function, among them the conversion of ATP to adenosine initiated by the ectonucleotidase CD39. In humans, the expression of CD39 on Tregs shows a high interindividual variation, and is especially high at sites of inflammation, like the synovia of patients with arthritis. How CD39 expression is regulated, and the functional consequences of different levels of CD39 expression is not known. We show here that stimulation of CD39(-) Tregs results in a modest upregulation of CD39, which cannot explain the high levels observed in many donors. Moreover, CD39(+) Tregs are present in naïve compartments such as cord blood and thymus, and the individual frequency of CD39(+) Tregs remains stable over time, suggesting inherent regulation of CD39 expression. Indeed, we show that a single nucleotide polymorphism in the CD39 gene determines expression levels in Tregs. CD39(+) Tregs suppress T cell proliferation and inflammatory cytokine production more efficiently than CD39(-) Tregs. Accordingly, Tregs from donors with the GG (high CD39) genotype have a higher capacity to suppress IFN-γ and IL-17 production by effector cells than Tregs from AA (low CD39) donors. Our study demonstrates that the expression of CD39 in Tregs is primarily genetically driven, and this may determine interindividual differences in the control of inflammatory responses.

Mucolipidosis II-related mutations inhibit the exit from the endoplasmic reticulum and proteolytic cleavage of GlcNAc-1-phosphotransferase precursor protein (GNPTAB).

Mucolipidosis (ML) II and MLIII alpha/beta are two pediatric lysosomal storage disorders caused by mutations in the GNPTAB gene, which encodes an α/ß-subunit precursor protein of GlcNAc-1-phosphotransferase. Considerable variations in the onset and severity of the clinical phenotype in these diseases are observed. We report here on expression studies of two missense mutations c.242G>T (p.Trp81Leu) and c.2956C>T (p.Arg986Cys) and two frameshift mutations c.3503_3504delTC (p.Leu1168GlnfsX5) and c.3145insC (p.Gly1049ArgfsX16) present in severely affected MLII patients, as well as two missense mutations c.1196C>T (p.Ser399Phe) and c.3707A>T (p.Lys1236Met) reported in more mild affected individuals. We generated a novel α-subunit-specific monoclonal antibody, allowing the analysis of the expression, subcellular localization, and proteolytic activation of wild-type and mutant α/ß-subunit precursor proteins by Western blotting and immunofluorescence microscopy. In general, we found that both missense and frameshift mutations that are associated with a severe clinical phenotype cause retention of the encoded protein in the endoplasmic reticulum and failure to cleave the α/ß-subunit precursor protein are associated with a severe clinical phenotype with the exception of p.Ser399Phe found in MLIII alpha/beta. Our data provide new insights into structural requirements for localization and activity of GlcNAc-1-phosphotransferase that may help to explain the clinical phenotype of MLII patients.

Multidimensional scaling analysis identifies pathological and prognostically relevant profiles of circulating T-cells in chronic lymphocytic leukemia.

Antitumor immunity in chronic lymphocytic leukemia (CLL) is hampered by highly dysfunctional T-cells. Although certain T-cell subsets have been reported to be of prognostic significance in this disease, their interplay is complex and it remains incompletely understood which of these subsets significantly drive CLL progression. Here, we determined immunological profiles of 24 circulating T-cell subsets from 79 untreated individuals by multiparametric flow cytometry. This screening cohort included healthy donors, patients with monoclonal B-cell lymphocytosis (MBL), Rai 0 CLL and advanced CLL. We applied multidimensional scaling analysis as rigorous and unbiased statistical tool to globally assess the composition of the circulating T-cell environment and to generate T-cell scores reflecting its integrity. These scores allowed clear distinction between advanced CLL and healthy controls, whereas both MBL and Rai 0 CLL showed intermediate scores mirroring the biological continuum of CLL and its precursor stages. T-cell stimulation and suppression assays as well as longitudinal T-cell profiling showed an increasingly suppressive regulatory function initiating at the MBL stage. Effector function was impaired only after transition to CLL and partially recovered after chemoimmunotherapy. In an independent validation cohort of 52 untreated CLL cases, aberrant T-cell profiles were significantly associated with shorter time to treatment independently of other prognostic parameters. Random forest modeling predicted regulatory T-cell, gamma/delta and NKT-cells, as well as exhaustion of the CD8+ subset as potential drivers of progression. Our data illustrate a pathological T-cell environment in MBL that evolves toward a more and more suppressive and prognostically relevant profile across the disease stages.

CD8-ß ADP-ribosylation affects CD8(+) T-cell function.

The CD8αß coreceptor is crucial for effective peptide: MHC-I recognition by the TCR of CD8(+) T cells. Adenosine diphosphate ribosyl transferase 2.2 (ART2.2) utilizes extracellular NAD(+) to transfer ADP-ribose to arginine residues of extracellular domains of surface proteins. Here, we show that in the presence of extracellular NAD(+) , ART2.2 caused ADP-ribosylation of CD8-ß on murine CD8(+) T cells in vitro and in vivo. Treatment with NAD(+) prevented binding of anti-CD8-ß mAb YTS156.7.7 but not of mAb H35-17.2, indicating that NAD(+) caused modification of certain epitopes and not a general loss of CD8-ß. Loss of antibody binding was strictly dependent on ART2.2, because it was not observed on ART2-deficient T cells or in the presence of inhibitory anti-ART2.2 single-domain antibodies. ADP-ribosylation of CD8-ß occurred during cell isolation, particularly when cells were isolated from CD38-deficient mice. Incubation of ART2-expressing, but not of ART2-deficient, OVA-specific CD8(+) T cells with NAD(+) interfered with binding of OVA257-264 :MHC-I tetramers. In line with this result, treatment of WT mice with NAD(+) resulted in reduced CD8(+) T-cell mediated cytotoxicity in vivo. We propose that ADP-ribosylation of CD8-ß can regulate the coreceptor function of CD8 in the presence of elevated levels of extracellular NAD(+) .

Functional autoantibodies against SSX-2 and NY-ESO-1 in multiple myeloma patients after allogeneic stem cell transplantation.

BACKGROUND: Multiple myeloma (MM) is the malignancy with the most frequent expression of the highly immunogenic cancer-testis antigens (CTA), and we have performed the first analysis of longitudinal expression, immunological properties, and fine specificity of CTA-specific antibody responses in MM. METHODS: Frequency and characteristics of antibody responses against cancer-testis antigens MAGE-A3, NY-ESO-1, PRAME, and SSX-2 were analyzed using peripheral blood (N = 1094) and bone marrow (N = 200) plasma samples from 194 MM patients. RESULTS: We found that antibody responses against CTA were surprisingly rare, only 2.6 and 3.1 % of patients evidenced NY-ESO-1- and SSX-2-specific antibodies, respectively. NY-ESO-1-specific responses were observed during disease progression, while anti-SSX-2 antibodies appeared after allogeneic stem cell transplantation and persisted during clinical remission. We found that NY-ESO-1- and SSX-2-specific antibodies were both capable of activating complement and increasing CTA uptake by antigen-presenting cells. SSX-2-specific antibodies were restricted to IgG3, NY-ESO-1 responses to IgG1 and IgG3. Remarkably, NY-ESO-1-positive sera recognized various non-contiguous regions, while SSX-2-specific responses were directed against a single 6mer epitope, SSX-2(85-90). CONCLUSIONS: We conclude that primary autoantibodies against intracellular MM-specific tumor antigens SSX-2 and NY-ESO-1 are rare but functional. While their contribution to disease control still remains unclear, our data demonstrate their theoretic ability to affect cellular anti-tumor immunity by formation and uptake of mono- and polyvalent immune complexes.

Generation and characterization of antagonistic anti-human CD39 nanobodies.

CD39 is the major enzyme controlling the levels of extracellular adenosine triphosphate (ATP) via the stepwise hydrolysis of ATP to adenosine diphosphate (ADP) and adenosine monophosphate (AMP). As extracellular ATP is a strong promoter of inflammation, monoclonal antibodies (mAbs) blocking CD39 are utilized therapeutically in the field of immune-oncology. Though anti-CD39 mAbs are highly specific for their target, they lack deep penetration into the dense tissue of solid tumors, due to their large size. To overcome this limitation, we generated and characterized nanobodies that targeted and blocked human CD39. From cDNA-immunized alpacas we selected 16 clones from seven nanobody families that bind to two distinct epitopes of human CD39. Among these, clone SB24 inhibited the enzymatic activity of CD39. Of note, SB24 blocked ATP degradation by both soluble and cell surface CD39 as a 15kD monomeric nanobody. Dimerization via fusion to an immunoglobulin Fc portion further increased the blocking potency of SB24 on CD39-transfected HEK cells. Finally, we confirmed the CD39 blocking properties of SB24 on human PBMCs. In summary, SB24 provides a new small biological antagonist of human CD39 with potential application in cancer therapy.

Generation of nanobodies from transgenic 'LamaMice' lacking an endogenous immunoglobulin repertoire.

Due to their exceptional solubility and stability, nanobodies have emerged as powerful building blocks for research tools and therapeutics. However, their generation in llamas is cumbersome and costly. Here, by inserting an engineered llama immunoglobulin heavy chain (IgH) locus into IgH-deficient mice, we generate a transgenic mouse line, which we refer to as 'LamaMouse'. We demonstrate that LamaMice solely express llama IgH molecules without association to Igκ or λ light chains. Immunization of LamaMice with AAV8, the receptor-binding domain of the SARS-CoV-2 spike protein, IgE, IgG2c, and CLEC9A enabled us to readily select respective target-specific nanobodies using classical hybridoma and phage display technologies, single B cell screening, and direct cloning of the nanobody-repertoire into a mammalian expression vector. Our work shows that the LamaMouse represents a flexible and broadly applicable platform for a facilitated selection of target-specific nanobodies.

CD38 controls the innate immune response against Listeria monocytogenes.

CD38, adenosine-5'-diphosphate-ribosyl cyclase 1, is a multifunctional enzyme, expressed on a wide variety of cell types. CD38 has been assigned diverse functions, including generation of calcium-mobilizing metabolites, cell activation, and chemotaxis. Using a murine Listeria monocytogenes infection model, we found that CD38 knockout (KO) mice were highly susceptible to infection. Enhanced susceptibility was already evident within 3 days of infection, suggesting a function of CD38 in the innate immune response. CD38 was expressed on neutrophils and inflammatory monocytes, and especially inflammatory monocytes further upregulated CD38 during infection. Absence of CD38 caused alterations of the migration pattern of both cell types to sites of infection. We observed impaired accumulation of cells in the spleen but surprisingly similar or even higher accumulation of cells in the liver. CD38 KO and wild-type mice showed similar changes in the composition of neutrophils and inflammatory monocytes in blood and bone marrow, indicating that mobilization of these cells from the bone marrow was CD38 independent. In vitro, macrophages of CD38 KO mice were less efficient in uptake of listeria but still able to kill the bacteria. Dendritic cells also displayed enhanced CD38 expression following infection. However, absence of CD38 did not impair the capacity of mice to prime CD8(+) T cells against L. monocytogenes, and CD38 KO mice could efficiently control secondary listeria infection. In conclusion, our results demonstrate an essential role for CD38 in the innate immune response against L. monocytogenes.