Transcriptome analysis of primary adult B-cell lineage acute lymphoblastic leukemia identifies pathogenic variants and gene fusions, and predicts subtypes for in depth molecular diagnosis

BACKGROUND

B-cell acute lymphoblastic leukemia (B-ALL) is classified into subgroups based on known driver oncogenes and molecular lesions, including translocations and recurrent mutations. However, the current diagnostic tests do not identify subtypes or oncogenic lesions for all B-ALL samples, creating a heterogeneous B-ALL group of unknown subtypes.

METHODS

We sorted primary adult B-ALL cells and performed transcriptome analysis by bulk RNA sequencing (RNA-seq).

RESULTS

Transcriptomic analysis of an adult B-ALL cohort allowed the classification of four patient samples with subtypes that were not previously revealed by standard gene panels. The leukemia of two patients were of the DUX4 subtype and two were CRLF2+ Ph-like B-ALL. Furthermore, single nucleotide variant analysis detected the oncogenic NRAS-G12D, KRAS-G12D, and KRAS-G13D mutations in three of the patient samples, presenting targetable mutations. Additional oncogenic variants and gene fusions were uncovered, as well as multiple variants in the PDE4DIP gene across five of the patient samples.

CONCLUSION

We demonstrate that RNA-seq is an effective tool for precision medicine in B-ALL by providing comprehensive molecular profiling of leukemia cells, identifying subtype and oncogenic lesions, and stratifying patients for appropriate therapy.

Incidence and outcome of COVID-19 following vaccine and hybrid immunity in patients on immunosuppressive therapy: identification of protective post-immunisation anti-RBD antibody levels in a prospective cohort study

OBJECTIVES

To assess incidence, severity and predictors of COVID-19, including protective post-vaccination levels of antibodies to the receptor-binding domain of SARS-CoV-2 spike protein (anti-RBD), informing further vaccine strategies for patients with immune-mediated inflammatory diseases (IMIDs) on immunosuppressive medication.

METHODS

IMIDs on immunosuppressives and healthy controls (HC) receiving SARS-CoV-2 vaccines were included in this prospective observational study. COVID-19 and outcome were registered and anti-RBD antibodies measured 2-5 weeks post-immunisation.

RESULTS

Between 15 February 2021 and 15 February 2023, 1729 IMIDs and 350 HC provided blood samples and self-reported COVID-19. The incidence of COVID-19 was 66% in patients and 67% in HC, with re-infection occurring in 12% of patients. Severe COVID-19 was recorded in 22 (2%) patients and no HC. No COVID-19-related deaths occurred. Vaccine-induced immunity gave higher risk of COVID-19 (HR 5.89 (95% CI 4.45 to 7.80)) than hybrid immunity. Post-immunisation anti-RBD levels <6000 binding antibody units/mL were associated with an increased risk of COVID-19 following three (HR 1.37 (95% CI 1.08 to 1.74)) and four doses (HR 1.28 (95% CI 1.02 to 1.62)), and of COVID-19 re-infection (HR 4.47 (95% CI 1.87 to 10.67)).

CONCLUSION

Vaccinated patients with IMID have a low risk of severe COVID-19. Hybrid immunity lowers the risk of infection. High post-immunisation anti-RBD levels protect against COVID-19. These results suggest that knowledge on COVID-19 history, and assessment of antibody levels post-immunisation can help individualise vaccination programme series in high-risk individuals.

TRIAL REGISTRATION NUMBER

NCT04798625.

Gene expression analysis revealed downregulation of complement receptor 1 in clonal B cells in cold agglutinin disease

Cold agglutinin disease (CAD) is a rare B-cell lymphoproliferative disorder of the bone marrow, manifested by autoimmune hemolytic anemia caused by binding of monoclonal IgM autoantibodies to the I antigen. Underlying genetic changes have previously been reported, but their impact on gene expression profile has been unknown. Here, we define differentially expressed genes in CAD B cells. To unravel downstream alteration in cellular pathways, gene expression by RNA sequencing was undertaken. Clonal B-cell samples from 12 CAD patients and IgM-expressing memory B cells from 4 healthy individuals were analyzed. Differential expression analysis and filtering resulted in 93 genes with significant differential expression. Top upregulated genes included SLC4A1, SPTA1, YBX3, TESC, HBD, AHSP, TRAF1, HBA2, RHAG, CA1, SPTB, IL10, UBASH3B, ALAS2, HBA1, CRYM, RGCC, KANK2, and IGHV4-34. They were upregulated at least 8-fold, while complement receptor 1 (CR1/CD35) was downregulated 11-fold in clonal CAD B cells compared to control B cells. Flow cytometry analyses further confirmed reduced CR1 (CD35) protein expression by clonal CAD IgM+ B cells compared to IgM+ memory B cells in controls. CR1 (CD35) is an important negative regulator of B-cell activation and differentiation. Therefore, reduced CR1 (CD35) expression may increase activation, proliferation, and antibody production in CAD-associated clonal B cells.

Dynamics of SARS-CoV-2 immunity after vaccination and breakthrough infection in rituximab-treated rheumatoid arthritis patients: a prospective cohort study

Background

SARS-CoV-2 vaccination in rheumatoid arthritis (RA) patients treated with B cell-depleting drugs induced limited seroconversion but robust cellular response. We aimed to document specific T and B cell immunity in response to vaccine booster doses and breakthrough infection (BTI).

Methods

We included 76 RA patients treated with rituximab who received up to four SARS-CoV-2 vaccine doses or three doses plus BTI, in addition to vaccinated healthy donors (HD) and control patients treated with tumor necrosis factor inhibitor (TNFi). We quantified anti-SARS-CoV-2 receptor-binding domain (RBD) Spike IgG, anti-nucleocapsid (NC) IgG, 92 circulating inflammatory proteins, Spike-binding B cells, and Spike-specific T cells along with comprehensive high-dimensional phenotyping and functional assays.

Findings

The time since the last rituximab infusion, persistent inflammation, and age were associated with the anti-SARS-CoV-2 RBD IgG seroconversion. The vaccine-elicited serological response was accompanied by an incomplete induction of peripheral Spike-specific memory B cells but occurred independently of T cell responses. Vaccine- and BTI-elicited cellular immunity was similar between RA and HD ex vivo in terms of frequency or phenotype of Spike-specific cytotoxic T cells and in vitro in terms of the functionality and differentiation profile of Spike-specific T cells.

Interpretation

SARS-CoV-2 vaccination in RA can induce persistent effector T-cell responses that are reactivated by BTI. Paused rituximab medication allowed serological responses after a booster dose (D4), especially in RA with lower inflammation, enabling efficient humoral and cellular immunity after BTI, and contributed overall to the development of potential durable immunity.

People who use drugs show no increase in pre-existing T-cell cross-reactivity toward SARS-CoV-2 but develop a normal polyfunctional T-cell response after standard mRNA vaccination

People who use drugs (PWUD) are at a high risk of contracting and developing severe coronavirus disease 2019 (COVID-19) and other infectious diseases due to their lifestyle, comorbidities, and the detrimental effects of opioids on cellular immunity. However, there is limited research on vaccine responses in PWUD, particularly regarding the role that T cells play in the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we show that before vaccination, PWUD did not exhibit an increased frequency of preexisting cross-reactive T cells to SARS-CoV-2 and that, despite the inhibitory effects that opioids have on T-cell immunity, standard vaccination can elicit robust polyfunctional CD4+ and CD8+ T-cell responses that were similar to those found in controls. Our findings indicate that vaccination stimulates an effective immune response in PWUD and highlight targeted vaccination as an essential public health instrument for the control of COVID-19 and other infectious diseases in this group of high-risk patients.

Hybrid and SARS-CoV-2-vaccine immunity in kidney transplant recipients

BACKGROUND

Kidney transplant recipients (KTR) are at high risk for severe COVID-19 and have demonstrated poor response to vaccination, making it unclear whether successive vaccinations offer immunity and protection.

METHODS

We conducted a serologically guided interventional study where KTR patients that failed to seroconvert were revaccinated and also monitored seroconversion of KTR following the Norwegian vaccination program. We analysed IgG anti-RBD Spike responses from dose 2 (n = 432) up to after the 6th (n = 37) mRNA vaccine dose. The frequency and phenotype of Spike-specific T and B cell responses were assessed in the interventional cohort after 3-4 vaccine doses (n = 30). Additionally, we evaluated the Specific T and B cell response to breakthrough infection (n = 32), measured inflammatory cytokines and broadly cross-neutralizing antibodies, and defined the incidence of COVID-19-related hospitalizations and deaths. The Norwegian KTR cohort has a male dominance (2323 males, 1297 females), PBMC were collected from 114 male and 78 female donors.

FINDINGS

After vaccine dose 3, most KTR developed Spike-specific T cell responses but had significantly reduced Spike-binding B cells and few memory cells. The B cell response included a cross-reactive subset that could bind Omicron VOC, which expanded after breakthrough infection (BTI) and gave rise to a memory IgG+ B cell response. After BTI, KTR had increased Spike-specific T cells, emergent non-Spike T and B cell responses, and a systemic inflammatory signature. Late seroconversion occurred after doses 5-6, but 38% (14/37) of KTR had no detectable immunity even after multiple vaccine doses.

INTERPRETATION

Boosting vaccination can induce Spike-specific immunity that may expand in breakthrough infections highlighting the benefit of vaccination to protect this vulnerable population.

FUNDING

CEPI and internal funds.

Humoral vaccine response and breakthrough infections in kidney transplant recipients during the COVID-19 pandemic: a nationwide cohort study

Background

Kidney transplant recipients (KTRs) experienced reduced SARS-CoV-2 vaccine response and were at increased risk of severe COVID-19. It is unknown if level of vaccine induced anti-receptor binding domain IgG (anti-RBD IgG) correlates with protection from and survival following COVID-19. We aimed to evaluate the effect of vaccine response on risk of breakthrough infections (BTI) and COVID-19 death in KTRs.

Methods

We performed a nationwide study, examining the competing risk of SARS-CoV-2 infection, COVID-19 related/unrelated death, and vaccine efficacy as assessed by level of anti-RBD IgG response 4-10 weeks after each vaccination. The study included all KTR in Norway alive and with a functioning graft on February 20th, 2020, and events after November 11th, 2022 were right-censored. A pre-pandemic reference-cohort from January 1st 2019 to January 1st 2020 was included to evaluate excess mortality. The study was conducted at Oslo University Hospital, Rikshospitalet, Norway.

Findings

The study included 3607 KTRs (59 [48-70] years) with a functioning graft at February 20th, 2020, who received (median [IQR]) 4 [3-4] vaccines (range 2-6, 99% mRNA). Anti-RBD IgG was measured in 12 701 serum samples provided by 3213 KTRs. Vaccine response was assessed 41 [31-57] days after vaccination. A total of 1090 KTRs were infected with SARS-CoV-2, 1005 (92%) were BTI, and vaccine response did not protect against BTI. The hazard ratio for COVID-19 related death 40 days post-infection was 1.71 (95% CI: 1.14, 2.56) comparing vaccine response levels (≥5 vs. ≥5000 BAU/mL). No excess non-COVID-19 mortality was registered in KTRs surviving SARS-CoV-2 infection compared to a 2019 pre-pandemic reference.

Interpretation

Our findings suggested that SARS-CoV-2 mRNA vaccine response did not predict protection against infection, but prevention of fatal disease progression in KTRs and greater vaccine response further reduced the risk of COVID-19 death. No excess non-COVID-19 mortality was seen during the pandemic.

Funding

CEPI and internal funds.

T cell responses to SARS-CoV-2 vaccination differ by disease-modifying therapy for multiple sclerosis

Immune responses in people with multiple sclerosis (pwMS) on disease-modifying therapies (DMTs) have been of significant interest throughout the COVID-19 pandemic. Lymphocyte-targeting immunotherapies including anti-CD20 treatments and sphingosine-1-phosphate receptor (S1PR) modulators attenuate antibody responses after vaccination. Evaluation of cellular responses after vaccination is therefore of particular importance in these populations. In this study, we analysed CD4 and CD8 T cell functional responses to SARS-CoV-2 spike peptides in healthy controls and pwMS on five different DMTs by flow cytometry. Although pwMS on rituximab and fingolimod therapies had low antibody responses after both two and three vaccine doses, T cell responses in pwMS on rituximab were preserved after a third vaccination, even when an additional dose of rituximab was administered between vaccine doses two and three. PwMS taking fingolimod had low detectable T cell responses in peripheral blood. CD4 and CD8 T cell responses to SARS-CoV-2 variants of concern Delta and Omicron were lower than to the ancestral Wuhan-Hu-1 variant. Our results indicate the importance of assessing both cellular and humoral responses after vaccination and suggest that even in the absence of robust antibody responses vaccination can generate immune responses in pwMS.

Determinants of humoral and cellular immune responses to three doses of mRNA SARS-CoV-2 vaccines in older adults: a longitudinal cohort study

BACKGROUND

Older age is associated with poorer outcomes to COVID-19 infection. The Norwegian Institute of Public Health established a longitudinal cohort of adults aged 65-80 years to study the effects of the COVID-19 pandemic. Here we describe the characteristics of the cohort in general, and specifically the immune responses at baseline and after primary and booster vaccination in a subset of longitudinal blood samples, and the epidemiological factors affecting these responses.

METHODS

4551 participants were recruited, with humoral (n=299) and cellular (n=90) responses measured before vaccination and after two and three vaccine doses. Information on general health, infections, and vaccinations were obtained from questionnaires and national health registries.

FINDINGS

Half of the participants had a chronic condition. 849 (18·7%) of 4551 were prefrail and 184 (4%) of 4551 were frail. 483 (10·6%) of 4551 had general activity limitations (scored with the Global Activity Limitation Index). After dose two, 295 (98·7%) of 299 participants were seropositive for anti-receptor binding domain IgG, and 210 (100%) of 210 participants after dose three. Spike-specific CD4 and CD8 T cell responses showed high heterogeneity after vaccination and responded to the alpha (B.1.1.7), delta (B.1.617.2), and omicron (B.1.1.529 or BA.1) variants of concern. Cellular responses to seasonal coronaviruses increased after SARS-CoV-2 vaccination. Heterologous prime boosting with mRNA vaccines was associated with the highest antibody (p=0·019) and CD4 T cell responses (p=0·003), and hypertension with lower antibody levels after three doses (p=0·04).

INTERPRETATION

Most older adults, including those with comorbidities, generated good serological and cellular responses after two vaccine doses. Responses further improved after three doses, particularly after heterologous boosting. Vaccination also generated cross-reactive T cells against variants of concern and seasonal coronaviruses. Frailty was not associated with impaired immune responses, but hypertension might indicate reduced responsiveness to vaccines even after three doses. Individual differences identified through longitudinal sampling enables better prediction of the variability of vaccine responses, which can help guide future policy on the need for subsequent doses and their timing.

FUNDING

Norwegian Institute of Public Health, Norwegian Ministry of Health, Research Council of Norway, and Coalition for Epidemic Preparedness Innovations.

A tumor microenvironment model of chronic lymphocytic leukemia enables drug sensitivity testing to guide precision medicine

The microenvironment of chronic lymphocytic leukemia (CLL) cells in lymph nodes, spleen, and bone marrow provides survival, proliferation, and drug resistance signals. Therapies need to be effective in these compartments, and pre-clinical models of CLL that are used to test drug sensitivity must mimic the tumor microenvironment to reflect clinical responses. Ex vivo models have been developed that capture individual or multiple aspects of the CLL microenvironment, but they are not necessarily compatible with high-throughput drug screens. Here, we report on a model that has reasonable associated costs, can be handled in a regularly equipped cell lab, and is compatible with ex vivo functional assays including drug sensitivity screens. The CLL cells are cultured with fibroblasts that express the ligands APRIL, BAFF and CD40L for 24 h. The transient co-culture was shown to support survival of primary CLL cells for at least 13 days, and mimic in vivo drug resistance signals. Ex vivo sensitivity and resistance to the Bcl-2 antagonist venetoclax correlated with in vivo responses. The assay was used to identify treatment vulnerabilities and guide precision medicine for a patient with relapsed CLL. Taken together, the presented CLL microenvironment model enables clinical implementation of functional precision medicine in CLL.

Four SARS-CoV-2 vaccine doses or hybrid immunity in patients on immunosuppressive therapies: a Norwegian cohort study

Background

Data on response and safety of repeated vaccinations and hybrid immunity in patients with immune-mediated inflammatory diseases on immunosuppressive therapy is needed to further develop vaccination strategies in this vulnerable population. This study aimed to evaluate hybrid immunity and humoral immune response and safety of four SARS-CoV-2 vaccine doses in patients with immune-mediated inflammatory diseases on immunosuppressive therapy.

Methods

This prospective observational Norwegian study of vaccine response to COVID-19 (Nor-vaC) included adult patients aged 18 years and older with immune-mediated inflammatory diseases (rheumatoid arthritis, spondyloarthritis, psoriatic arthritis, Crohn's disease, or ulcerative colitis) on immunosuppressive therapy, who had received four SARS-CoV-2 vaccine doses (vaccine group) or three vaccine doses followed by COVID-19 (hybrid group), and healthy controls receiving three vaccine doses (control group). Patients were recruited from the Division of Rheumatology at Diakonhjemmet Hospital, Oslo, and the Department of Gastroenterology at Akershus University Hospital, Lørenskog. Patients who had COVID-19 before the third vaccine dose, and patients with allergies or intolerances to elements of the vaccine were excluded. Antibodies to the receptor-binding domain of SARS-CoV-2 spike protein (anti-RBD antibodies) were assessed 2-4 weeks following vaccination or COVID-19. This study is registered at Clinialtrials.gov, NCT04798625.

Findings

Between Nov 12, 2021, and April 19, 2022, 1458 participants with immune-mediated inflammatory diseases provided post-vaccination samples at 2-4 weeks following a third vaccine dose. After 544 participants were excluded, 715 (78%) of the remaining 914 participants received the fourth dose of the vaccine, and of these, 536 (75%) provided post-vaccination samples 2-4 weeks after their fourth vaccination (vaccine group). 199 (22%) of the 914 had COVID-19 after their third dose of the vaccine and of these, 167 (84%) provided samples (hybrid group). 256 of the eligible 703 patients had rheumatoid arthritis, 107 had spondyloarthritis, 115 had psoriatic arthritis, 130 had Crohn's disease, and 95 had ulcerative colitis). Median age was 56 years [IQR 45-65], 398 (57%) were women, and 305 (43%) were men. Patients in the vaccine group had higher anti-RBD antibody concentrations following the fourth vaccine dose (median 6192 BAU/ml [IQR 2878-11 243]) than after the third dose (median 5087 BAU/ml [1250-9081]; p< 0·0001), but lower antibody concentrations than the control group following the third dose (median 7595 BAU/ml [5916-12 001]; p< 0·0001). Antibody concentrations were higher in the patients in the hybrid group (23 548 BAU/ml [IQR 11 440-35 935]) than in the vaccine group (p<0·0001). No difference was found in antibody concentrations between the fourth dose of BNT162b2 (full-dose) and mRNA-1273 (half-dose). Patients and controls had a comparable safety profile after both three and four vaccine doses.

Interpretation

Vaccine boosters improve humoral immune responses and are safe in patients with immune-mediated inflammatory diseases on immunosuppressive therapy, and administration should be considered regularly in this patient group. Hybrid immunity with omicron induces a strong humoral response suggesting longer intervals between booster doses in this patient group.

Funding

The South-Eastern Norway Regional Health Authority, The Coalition for Epidemic Preparedness Innovations, Akershus University Hospital.

Mechanism of CD79A and CD79B Support for IgM+ B Cell Fitness through B Cell Receptor Surface Expression

The BCR consists of surface-bound Ig and a heterodimeric signaling unit comprised of CD79A and CD79B. Upon cognate Ag recognition, the receptor initiates important signals for B cell development and function. The receptor also conveys Ag-independent survival signals termed tonic signaling. Although the requirement of a CD79A/CD79B heterodimer for BCR complex assembly and surface expression is well established based on mice models, few studies have investigated this in human mature B cells. In this study, we found that human tonsillar B cells with high surface expression of IgM or IgG had potentiated BCR signaling compared with BCRlow cells, and high IgM expression in germinal center B cells was associated with reduced apoptosis. We explored the mechanism for IgM surface expression by CRISPR/Cas9-induced deletion of CD79A or CD79B in four B lymphoma cell lines. Deletion of either CD79 protein caused loss of surface IgM in all cell lines and reduced fitness in three. From two cell lines, we generated stable CD79A or CD79B knockout clones and demonstrated that loss of CD79A or CD79B caused a block in N-glycan maturation and accumulation of immature proteins, compatible with retention of BCR components in the endoplasmic reticulum. Rescue experiments with CD79B wild-type restored surface expression of CD79A and IgM with mature glycosylation, whereas a naturally occurring CD79B G137S mutant disrupting CD79A/CD79B heterodimerization did not. Our study highlights that CD79A and CD79B are required for surface IgM expression in human B cells and illuminates the importance of the IgM expression level for signaling and fitness.

Immunogenicity and safety of a three-dose SARS-CoV-2 vaccination strategy in patients with immune-mediated inflammatory diseases on immunosuppressive therapy

Objectives

Humoral vaccine responses to SARS-CoV-2 vaccines are impaired and short lasting in patients with immune-mediated inflammatory diseases (IMID) following two vaccine doses. To protect these vulnerable patients against severe COVID-19 disease, a three-dose primary vaccination strategy has been implemented in many countries. The aim of this study was to evaluate humoral response and safety of primary vaccination with three doses in patients with IMID.

Methods

Patients with IMID on immunosuppressive therapy and healthy controls receiving three-dose and two-dose primary SARS-CoV-2 vaccination, respectively, were included in this prospective observational cohort study. Anti-Spike antibodies were assessed 2–4 weeks, and 12 weeks following each dose. The main outcome was anti-Spike antibody levels 2–4 weeks following three doses in patients with IMID and two doses in controls. Additional outcomes were the antibody decline rate and adverse events.

Results

1100 patients and 303 controls were included. Following three-dose vaccination, patients achieved median (IQR) antibody levels of 5720 BAU/mL (2138–8732) compared with 4495 (1591–6639) in controls receiving two doses, p=0.27. Anti-Spike antibody levels increased with median 1932 BAU/mL (IQR 150–4978) after the third dose. The interval between the vaccine doses and vaccination with mRNA-1273 or a combination of vaccines were associated with antibody levels following the third dose. Antibody levels had a slower decline-rate following the third than the second vaccine dose, p<0.001. Adverse events were reported by 464 (47%) patients and by 196 (78%) controls. Disease flares were reported by 70 (7%) patients.

Conclusions

This study shows that additional vaccine doses to patients with IMID contribute to strong and sustained immune-responses comparable to healthy persons vaccinated twice, and supports repeated vaccination of patients with IMID.

Trial registration number

NCT04798625.

Immune responses in Omicron SARS-CoV-2 breakthrough infection in vaccinated adults

The SARS-CoV-2 Omicron variant has more than 15 mutations in the receptor binding domain of the Spike protein enabling increased transmissibility and viral escape from antibodies in vaccinated individuals. It is unclear how vaccine immunity protects against Omicron infection. Here we show that vaccinated participants at a super-spreader event have robust recall response of humoral and pre-existing cellular immunity induced by the vaccines, and an emergent de novo T cell response to non-Spike antigens. Individuals with Omicron SARS-CoV-2 breakthrough infections have significantly increased activated SARS-CoV-2 wild type Spike-specific cytotoxic T cells, activated follicular helper (T_FH) cells, functional T cell responses, boosted humoral responses, and rapid release of Spike and RBD-specific IgG⁺ B cell plasmablasts and memory B cells into circulation. Omicron breakthrough infection affords significantly increased de novo memory T cell responses to non-Spike viral antigens. Concerted T and B cell responses may provide durable and broad immunity.

The SARS-CoV-2 Omicron variant possess many mutations within the receptor binding domain of the Spike protein, which confer increased transmissibility and higher antibody escape. Here, the authors carry out analysis of the serological and cellular immune responses of individuals with Omicron breakthrough infection.

T‐helper cell regulation of CD45 phosphatase activity by galectin‐1 and CD43 governs chronic lymphocytic leukaemia proliferation

Chronic lymphocytic leukaemia (CLL) is characterised by malignant mature‐like B cells. Supportive to CLL cell survival is chronic B‐cell receptor (BCR) signalling; however, emerging evidence demonstrates CLL cells proliferate in response to T‐helper (Th) cells in a CD40L‐dependent manner. We showed provision of Th stimulation via CD40L upregulated CD45 phosphatase activity and BCR signalling in non‐malignant B cells. Consequently, we hypothesised Th cell upregulation of CLL cell CD45 activity may be an important regulator of CLL BCR signalling and proliferation. Using patient‐derived CLL cells in a culture system with activated autologous Th cells, results revealed increases in both Th and CLL cell CD45 activity, which correlated with enhanced downstream antigen receptor signalling and proliferation. Concomitantly increased was the surface expression of Galectin‐1, a CD45 ligand, and CD43, a CLL immunophenotypic marker. Galectin‐1/CD43 double expression defined a proliferative CLL cell population with enhanced CD45 activity. Targeting either Galectin‐1 or CD43 using silencing, pharmacology, or monoclonal antibody strategies dampened CD45 activity and CLL cell proliferation. These results highlight a mechanism where activated Th cells drive CLL cell BCR signalling and proliferation via Galectin‐1 and CD43‐mediated regulation of CD45 activity, identifying modulation of CD45 phosphatase activity as a potential therapeutic target in CLL.

Immunogenicity and Safety of Standard and Third Dose SARS-CoV-2 Vaccination in Patients on Immunosuppressive Therapy

Objective

Immunogenicity and safety following receipt of the standard SARS–CoV‐2 vaccination regimen in patients with immune‐mediated inflammatory diseases (IMIDs) are poorly characterized, and data after receipt of the third vaccine dose are lacking. The aim of the study was to evaluate serologic responses and adverse events following the standard 2‐dose regimen and a third dose of SARS–CoV‐2 vaccine in IMID patients receiving immunosuppressive therapy.

Methods

Adult patients receiving immunosuppressive therapy for rheumatoid arthritis, spondyloarthritis, psoriatic arthritis, Crohn's disease, or ulcerative colitis, as well as healthy adult controls, who received the standard 2‐dose SARS–CoV‐2 vaccination regimen were included in this prospective observational study. Analyses of antibodies to the receptor‐binding domain (RBD) of the SARS–CoV‐2 spike protein were performed prior to and 2–4 weeks after vaccination. Patients with a weak serologic response, defined as an IgG antibody titer of ≤100 arbitrary units per milliliter (AU/ml) against the receptor‐binding domain of the full‐length SARS–Cov‐2 spike protein, were allotted a third vaccine dose.

Results

A total of 1,505 patients (91%) and 1,096 healthy controls (98%) had a serologic response to the standard regimen (P < 0.001). Anti‐RBD antibody levels were lower in patients (median 619 AU/ml interquartile range [IQR] 192–4,191) than in controls (median 3,355 AU/ml [IQR 896–7,849]) (P < 0.001). The proportion of responders was lowest among patients receiving tumor necrosis factor inhibitor combination therapy, JAK inhibitors, or abatacept. Younger age and receipt of messenger RNA–1273 vaccine were predictors of serologic response. Of 153 patients who had a weak response to the standard regimen and received a third dose, 129 (84%) became responders. The vaccine safety profile among patients and controls was comparable.

Conclusion

IMID patients had an attenuated response to the standard vaccination regimen as compared to healthy controls. A third vaccine dose was safe and resulted in serologic response in most patients. These data facilitate identification of patient groups at risk of an attenuated vaccine response, and they support administering a third vaccine dose to IMID patients with a weak serologic response to the standard regimen.

Functional testing of relapsed chronic lymphocytic leukemia guides precision medicine and maps response and resistance mechanisms. An index case

Not available.

Humoral and cellular immune responses to two and three doses of SARS-CoV-2 vaccines in rituximab-treated patients with rheumatoid arthritis: a prospective, cohort study

BACKGROUND

In rituximab-treated patients with rheumatoid arthritis, humoral and cellular immune responses after two or three doses of SARS-CoV-2 vaccines are not well characterised. We aimed to address this knowledge gap.

METHODS

This prospective, cohort study (Nor-vaC) was done at two hospitals in Norway. For this sub-study, we enrolled patients with rheumatoid arthritis on rituximab treatment and healthy controls who received SARS-CoV-2 vaccines according to the Norwegian national vaccination programme. Patients with insufficient serological responses to two doses (antibody to the receptor-binding domain [RBD] of the SARS-CoV-2 spike protein concentration <100 arbitrary units [AU]/mL) were allotted a third vaccine dose. Antibodies to the RBD of the SARS-CoV-2 spike protein were measured in serum 2-4 weeks after the second and third doses. Vaccine-elicited T-cell responses were assessed in vitro using blood samples taken before and 7-10 days after the second dose and 3 weeks after the third dose from a subset of patients by stimulating cryopreserved peripheral blood mononuclear cells with spike protein peptides. The main outcomes were the proportions of participants with serological responses (anti-RBD antibody concentrations of ≥70 AU/mL) and T-cell responses to spike peptides following two and three doses of SARS-CoV-2 vaccines. The study is registered at ClinicalTrials.gov, NCT04798625, and is ongoing.

FINDINGS

Between Feb 9, 2021, and May 27, 2021, 90 patients were enrolled, 87 of whom donated serum and were included in our analyses (69 [79·3%] women and 18 [20·7%] men). 1114 healthy controls were included (854 [76·7%] women and 260 [23·3%] men). 49 patients were allotted a third vaccine dose. 19 (21·8%) of 87 patients, compared with 1096 (98·4%) of 1114 healthy controls, had a serological response after two doses (p<0·0001). Time since last rituximab infusion (median 267 days [IQR 222-324] in responders vs 107 days [80-152] in non-responders) and vaccine type (mRNA-1273 vs BNT162b2) were significantly associated with serological response (adjusting for age and sex). After two doses, 10 (53%) of 19 patients had CD4+ T-cell responses and 14 (74%) had CD8+ T-cell responses. A third vaccine dose induced serological responses in eight (16·3%) of 49 patients, but induced CD4+ and CD8+ T-cell responses in all patients assessed (n=12), including responses to the SARS-CoV-2 delta variant (B.1.617.2). Adverse events were reported in 32 (48%) of 67 patients and in 191 (78%) of 244 healthy controls after two doses, with the frequency not increasing after the third dose. There were no serious adverse events or deaths.

INTERPRETATION

This study provides important insight into the divergent humoral and cellular responses to two and three doses of SARS-CoV-2 vaccines in rituximab-treated patients with rheumatoid arthritis. A third vaccine dose given 6-9 months after a rituximab infusion might not induce a serological response, but could be considered to boost the cellular immune response.

FUNDING

The Coalition for Epidemic Preparedness Innovations, Research Council of Norway Covid, the KG Jebsen Foundation, Oslo University Hospital, the University of Oslo, the South-Eastern Norway Regional Health Authority, Dr Trygve Gythfeldt og frues forskningsfond, the Karin Fossum Foundation, and the Research Foundation at Diakonhjemmet Hospital.

B-cell receptor dependent phagocytosis and presentation of particulate antigen by chronic lymphocytic leukemia cells

Aim

T-helper cells could play an important role in the pathogenesis of chronic lymphocytic leukemia (CLL), a common B-cell neoplasm. Although CLL cells can present soluble antigens targeted from the B-cell receptor to T-helper cells via major histocompatibility complex (MHC) class II, antigens recognized by some CLL cells may be encountered in a particulate form. Here the ability of CLL cells to internalize and present anti-immunoglobulin M (IgM) beads as a model for the interaction of CLL cells with particulate antigens was investigated.

Methods

The effect of anti-IgM beads on antigen presentation pathways was analyzed using RNA-seq and internalization of anti-IgM beads by primary CLL cells was investigated using confocal microscopy and flow cytometry. Antigen presentation was investigated by analyzing activation of a T-cell line expressing a T-cell receptor specific for a peptide derived from mouse κ light chains after incubating CLL cells with a mouse κ light chain-containing anti-IgM monoclonal antibody. Kinase inhibitors were used to characterize the pathways mediating internalization and antigen presentation.

Results

Stimulation of surface IgM of CLL cells increased expression of the antigen presentation machinery and CLL cells were able to phagocytose anti-IgM beads. Internalization of anti-IgM beads was associated with MHC class II-restricted activation of cognate T-helper cells. Antigen presentation by CLL cells was dependent on activity of spleen tyrosine kinase (SYK) and phosphatidylinositol 3-kinase delta (PI3Kδ) but was unaffected by inhibitors of Bruton's tyrosine kinase (BTK).

Conclusions

CLL cells can internalize and present antigen from anti-IgM beads. This capacity of CLL cells may be particularly important for recruitment of T-cell help in vivo in response to particulate antigens.

Ex vivo drug sensitivity screening in multiple myeloma identifies drug combinations that act synergistically

The management of multiple myeloma (MM) is challenging: an assortment of available drug combinations adds complexity to treatment selection, and treatment resistance frequently develops. Given the heterogeneous nature of MM, personalized testing tools are required to identify drug sensitivities. To identify drug sensitivities in MM cells, we established a drug testing pipeline to examine ex vivo drug responses. MM cells from 44 patients were screened against 30 clinically relevant single agents and 44 double and triple drug combinations. We observed variability in responses across samples. The presence of gain(1q21) was associated with low sensitivity to venetoclax, and decreased ex vivo responses to dexamethasone reflected the drug resistance observed in patients. Less heterogeneity and higher efficacy was detected with many combinations compared to the corresponding single agents. We identified new synergistic effects of melflufen plus panobinostat using low concentrations (0.1-10 nM and 8 nM, respectively). In agreement with clinical studies, clinically approved combinations, such as triple combination of selinexor plus bortezomib plus dexamethasone, acted synergistically, and synergies required low drug concentrations (0.1 nM bortezomib, 10 nM selinexor and 4 nM dexamethasone). In summary, our drug screening provided results within a clinically actionable 5-day time frame and identified synergistic drug efficacies in patient-derived MM cells that may aid future therapy choices.

Immune complexes, innate immunity, and NETosis in ChAdOx1 vaccine-induced thrombocytopenia

Aims

We recently reported five cases of vaccine-induced immune thrombotic thrombocytopenia (VITT) 7–10 days after receiving the first dose of the ChAdOx1 nCoV-19 adenoviral vector vaccine against corona virus disease 2019 (COVID-19). We aimed to investigate the pathogenic immunological responses operating in these patients.

Methods and results

We assessed circulating inflammatory markers by immune assays and immune cell phenotyping by flow cytometry analyses and performed immunoprecipitation with anti-platelet factor (PF)4 antibody in plasma samples followed by mass spectrometry from all five patients. A thrombus was retrieved from the sinus sagittal superior of one patient and analysed by immunohistochemistry and flow cytometry. Precipitated immune complexes revealed multiple innate immune pathway triggers for platelet and leucocyte activation. Plasma contained increased levels of innate immune response cytokines and markers of systemic inflammation, extensive degranulation of neutrophils, and tissue and endothelial damage. Blood analyses showed activation of neutrophils and increased levels of circulating H3Cit, dsDNA, and myeloperoxidase–DNA complex. The thrombus had extensive infiltration of neutrophils, formation of neutrophil extracellular traps (NETs), and IgG deposits.

Conclusions

The results show that anti-PF4/polyanion IgG-mediated thrombus formation in VITT patients is accompanied by a massive innate immune activation and particularly the fulminant activation of neutrophils including NETosis. These results provide novel data on the immune response in this rare adenoviral vector-induced VITT.

Integration of T helper and BCR signals governs enhanced plasma cell differentiation of memory B cells by regulation of CD45 phosphatase activity

Humoral immunity relies on the efficient differentiation of memory B cells (MBCs) into antibody-secreting cells (ASCs). T helper (Th) signals upregulate B cell receptor (BCR) signaling by potentiating Src family kinases through increasing CD45 phosphatase activity (CD45 PA). In this study, we show that high CD45 PA in MBCs enhances BCR signaling and is essential for their effective ASC differentiation. Mechanistically, Th signals upregulate CD45 PA through intensifying the surface binding of a CD45 ligand, Galectin-1. CD45 PA works as a sensor of T cell help and defines high-affinity germinal center (GC) plasma cell (PC) precursors characterized by IRF4 expression in vivo. Increasing T cell help in vitro results in an incremental CD45 PA increase and enhances ASC differentiation by facilitating effective induction of the transcription factors IRF4 and BLIMP1. This study connects Th signals with BCR signaling through Galectin-1-dependent regulation of CD45 PA and provides a mechanism for efficient ASC differentiation of MBCs.

Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination

We report findings in five patients who presented with venous thrombosis and thrombocytopenia 7 to 10 days after receiving the first dose of the ChAdOx1 nCoV-19 adenoviral vector vaccine against coronavirus disease 2019 (Covid-19). The patients were health care workers who were 32 to 54 years of age. All the patients had high levels of antibodies to platelet factor 4-polyanion complexes; however, they had had no previous exposure to heparin. Because the five cases occurred in a population of more than 130,000 vaccinated persons, we propose that they represent a rare vaccine-related variant of spontaneous heparin-induced thrombocytopenia that we refer to as vaccine-induced immune thrombotic thrombocytopenia.

The PI3K p110δ Isoform Inhibitor Idelalisib Preferentially Inhibits Human Regulatory T Cell Function

In chronic lymphocytic leukemia (CLL), signaling through several prosurvival B cell surface receptors activates the PI3K signaling pathway. Idelalisib is a highly selective PI3K (PI3Kδ) isoform-specific inhibitor effective in relapsed/refractory CLL and follicular lymphoma. However, severe autoimmune adverse effects in association with the use of idelalisib in the treatment of CLL, particularly as a first-line therapy, gave indications that idelalisib may preferentially target the suppressive function of regulatory T cells (Tregs). On this background, we examined the effect of idelalisib on the function of human Tregs ex vivo with respect to proliferation, TCR signaling, phenotype, and suppressive function. Our results show that human Tregs are highly susceptible to PI3Kδ inactivation using idelalisib compared with CD4⁺ and CD8⁺ effector T cells (Teffs) as evident from effects on anti-CD3/CD28/CD2-induced proliferation (order of susceptibility [IC₅₀]: Treg [.5 μM] > CD4⁺ Teff [2.0 μM] > CD8⁺ Teff [6.5 μM]) and acting at the level of AKT and NF-κB phosphorylation. Moreover, idelalisib treatment of Tregs altered their phenotype and reduced their suppressive function against CD4⁺ and CD8⁺ Teffs. Phenotyping Tregs from CLL patients treated with idelalisib supported our in vitro findings. Collectively, our data show that human Tregs are more dependent on PI3Kδ-mediated signaling compared with CD4⁺ and CD8⁺ Teffs. This Treg-preferential effect could explain why idelalisib produces adverse autoimmune effects by breaking Treg-mediated tolerance. However, balancing effects on Treg sensitivity versus CD8⁺ Teff insensitivity to idelalisib could still potentially be exploited to enhance inherent antitumor immune responses in patients.

Bone marrow T helper cells with a Th1 phenotype induce activation and proliferation of leukemic cells in precursor B acute lymphoblastic leukemia patients

Precursor B cell acute lymphoblastic leukemia (BCP-ALL) constitutes the leading cause of cancer-related death in children. While chromosomal alterations contribute to BCP-ALL pathogenesis, they are insufficient for leukemia development. Epidemiological data and evidence from a mouse model suggest that immune responses to infections may trigger the emergence of leukemia, but the mechanisms remain unclear. Here, we show that T helper (Th) cells from bone marrow of pediatric BCP-ALL patients can be attracted and activated by autologous BCP-ALL cells. Bone-marrow Th cells supportively interacted with BCP-ALL cells, inducing upregulation of important surface molecules and BCP-ALL cell proliferation. These Th cells displayed a Th1-like phenotype and produced high levels of IFN-γ. IFN-γ was responsible for the upregulation of CD38 in BCP-ALL cells, a molecule which we found to be associated with early relapse, and accountable for the production of IP-10, a chemokine involved in BCP-ALL migration and drug resistance. Thus, our data provide mechanistic support for an involvement of Th cell immune responses in the propagation of BCP-ALL and suggest that BCP-ALL cell-supportive Th cells may serve as therapeutic target.

Cryopreservation of primary B cells minimally influences their signaling responses

Phospho flow is a powerful approach to detect cell signaling aberrations, identify biomarkers and assess pharmacodynamics, and can be performed using cryopreserved samples. The effects of cryopreservation on signaling responses and the reproducibility of phospho flow measurements are however unknown in many cell systems. Here, B lymphocytes were isolated from healthy donors and patients with the B cell malignancy chronic lymphocytic leukemia and analyzed by phospho flow using phospho-specific antibodies targeting 20 different protein epitopes. Cells were analyzed both at basal conditions and after activation of cluster of differentiation 40 (CD40) or the B cell receptor. Pharmacodynamics of the novel pathway inhibitor ibrutinib was also assessed. At all conditions, fresh cells were compared to cryopreserved cells. Minimal variation between fresh and frozen samples was detected. Reproducibility was tested by running samples from the same donors in different experiments. The results demonstrate reproducibility across different phospho flow runs and support the use of cryopreserved samples in future phospho flow studies of B lymphocytes.

Single cell profiling of phospho-protein levels in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) has a high incidence and a steeply growing prevalence in the Western world. The heterogeneity of the disease necessitates individual mapping of biology and predicted drug response in each patient as basis for administration of tailored treatments. Cell signaling aberrations may serve as biological indicators for suitable therapy. By applying phospho-specific flow cytometry, we mapped basal and induced phosphorylation levels of 20 phospho-epitopes on proteins relevant to B-cell signaling in B cells from 22 CLL patients and 25 normal controls. The signaling response of the cytostatic drugs fludarabine, doxorubicin and vincristine was also investigated. CLL cells exerted similar or lower basal phosphorylation levels compared to normal B cells, with the exception of STAT3 (pY705) which was increased. Interestingly, STAT3 inhibitors normalized the STAT3 (pY705) level and reduced cell viability. Vincristine treatment significantly modulated phosphorylation levels in CLL cells, while no effect was observed in controls or after fludarabine or doxorubicin treatment. After BCR stimulation, CLL cells showed a tendency towards impaired phosphorylation levels, significant for several of the analyzed proteins. However, the level of Akt (pS473) was more potently induced in IgHV unmutated CLL (UM-CLL) patient samples and was significantly higher than in M-CLL samples. Importantly, the PI3Kδ inhibitor idelalisib potently reversed the effect of anti-IgM on Akt (pS473). Thus, signaling aberrations could be identified by phosphoflow cytometry and aberrant signaling could be normalized by small molecule drugs. This approach can identify relevant drug targets as well as drug effects in the individual patient.

Autologous bone marrow Th cells can support multiple myeloma cell proliferation in vitro and in xenografted mice

Multiple myeloma (MM) is a plasma cell malignancy where MM cell growth is supported by the bone marrow (BM) microenvironment with poorly defined cellular and molecular mechanisms. MM cells express CD40, a receptor known to activate autocrine secretion of cytokines and elicit proliferation. Activated T helper (Th) cells express CD40 ligand (CD40L) and BM Th cells are significantly increased in MM patients. We hypothesized that activated BM Th cells could support MM cell growth. We here found that activated autologous BM Th cells supported MM cell growth in a contact- and CD40L-dependent manner in vitro. MM cells had retained the ability to activate Th cells that reciprocated and stimulated MM cell proliferation. Autologous BM Th cells supported MM cell growth in xenografted mice and were found in close contact with MM cells. MM cells secreted chemokines that attracted Th cells, secretion was augmented by CD40-stimulation. Within 14 days of culture of whole BM aspirates in autologous serum, MM cells and Th cells mutually stimulated each other, and MM cells required Th cells for further expansion in vitro and in mice. The results suggest that Th cells may support the expansion of MM cells in patients.

Systemic Lupus Erythematosus: Molecular Mimicry between Anti-dsDNA CDR3 Idiotype, Microbial and Self Peptides-As Antigens for Th Cells

Systemic lupus erythematosus (SLE) is marked by a T helper (Th) cell-dependent B cell hyperresponsiveness, with frequent germinal center reactions, and gammaglobulinemia. A feature of SLE is the finding of IgG autoantibodies specific for dsDNA. The specificity of the Th cells that drive the expansion of anti-dsDNA B cells is unresolved. However, anti-microbial, anti-histone, and anti-idiotype Th cell responses have been hypothesized to play a role. It has been entirely unclear if these seemingly disparate Th cell responses and hypotheses could be related or unified. Here, we describe that H chain CDR3 idiotypes from IgG⁺ B cells of lupus mice have sequence similarities with both microbial and self peptides. Matched sequences were more frequent within the mutated CDR3 repertoire and when sequences were derived from lupus mice with expanded anti-dsDNA B cells. Analyses of histone sequences showed that particular histone peptides were similar to VDJ junctions. Moreover, lupus mice had Th cell responses toward histone peptides similar to anti-dsDNA CDR3 sequences. The results suggest that Th cells in lupus may have multiple cross-reactive specificities linked to the IgVH CDR3 Id-peptide sequences as well as similar DNA-associated protein motifs.

Chronic lymphocytic leukemia cells express CD38 in response to Th1 cell-derived IFN-γ by a T-bet-dependent mechanism

Chronic lymphocytic leukemia (CLL) is a B cell malignancy associated with increased levels of inflammatory cytokines. Similarly, expression of CD38 on CLL cells correlates with CLL cell survival and proliferation, but the mechanisms that regulate CD38 expression and inflammatory cytokines remain unclear. We have recently demonstrated that patients have CLL-specific Th cells that support CLL proliferation. In this article, we show that CLL cells attract such Th cells, thereby establishing an Ag-dependent collaboration. Blocking experiments performed in vitro as wells as in vivo, using a xenograft model, revealed that secretion of IFN-γ was a major mechanism by which CLL-specific Th cells increased CD38 on CLL cells. The expression of the transcription factor T-bet in peripheral blood CLL cells significantly correlated with CD38 expression, and transient transfection of CLL cells with T-bet resulted in T-bet(hi)CD38(hi) cells. Finally, chromatin immunoprecipitation experiments revealed that T-bet can bind to regulatory regions of the CD38 gene. These data suggest that CLL cells attract CLL-specific Th cells and initiate a positive feedback loop with upregulation of T-bet, CD38, and type 1 chemokines allowing further recruitment of Th cells and increased type 1 cytokine secretion. This insight provides a cellular and molecular mechanism that links the inflammatory signature observed in CLL pathogenesis with CD38 expression and aggressive disease and suggests that targeting the IFN-γ/IFN-γR/JAK/STAT/T-bet/CD38 pathway could play a role in the therapy of CLL.

Idiotype-specific Th cells support oligoclonal expansion of anti-dsDNA B cells in mice with lupus

Systemic lupus erythematosus (SLE) is marked by a Th cell-dependent B cell hyperresponsiveness, with frequent germinal center reactions and hypergammaglobulinemia. The specificity of Th cells in lupus remains unclear, but B cell Ids have been suggested. A hallmark is the presence of anti-dsDNA, mutated IgG autoantibodies with a preponderance of arginines in CDR3 of the Ig variable H chain (IgVH). B cells can present V region-derived Id peptides on their MHC class II molecules to Id-specific Th cells. We show that Id-specific Th cells support the proliferation of anti-dsDNA Id(+) B cells in mice suffering from systemic autoimmune disease with SLE-like features. Mice developed marked clonal expansions of B cells; half of the IgVH sequences were clonally related. Anti-dsDNA B cells made up 40% of B cells in end-stage disease. The B cells expressed mutated IgVH with multiple arginines in CDR3. Hence, Id-driven T cell-B cell collaboration supported the production of classical anti-dsDNA Abs, recapitulating the characteristics of such Abs in SLE. The results support the concept that Id-specific Th cells may trigger the development of SLE and suggest that manipulation of the Id-specific T cell repertoire could play a role in treatment.

How Do CD4(+) T Cells Detect and Eliminate Tumor Cells That Either Lack or Express MHC Class II Molecules?

CD4⁺ T cells contribute to tumor eradication, even in the absence of CD8⁺ T cells. Cytotoxic CD4⁺ T cells can directly kill MHC class II positive tumor cells. More surprisingly, CD4⁺ T cells can indirectly eliminate tumor cells that lack MHC class II expression. Here, we review the mechanisms of direct and indirect CD4⁺ T cell-mediated elimination of tumor cells. An emphasis is put on T cell receptor (TCR) transgenic models, where anti-tumor responses of naïve CD4⁺ T cells of defined specificity can be tracked. Some generalizations can tentatively be made. For both MHCII^POS and MHCII^NEG tumors, presentation of tumor-specific antigen by host antigen-presenting cells (APCs) appears to be required for CD4⁺ T cell priming. This has been extensively studied in a myeloma model (MOPC315), where host APCs in tumor-draining lymph nodes are primed with secreted tumor antigen. Upon antigen recognition, naïve CD4⁺ T cells differentiate into Th1 cells and migrate to the tumor. At the tumor site, the mechanisms for elimination of MHCII^POS and MHCII^NEG tumor cells differ. In a TCR-transgenic B16 melanoma model, MHCII^POS melanoma cells are directly killed by cytotoxic CD4⁺ T cells in a perforin/granzyme B-dependent manner. By contrast, MHCII^NEG myeloma cells are killed by IFN-γ stimulated M1-like macrophages. In summary, while the priming phase of CD4⁺ T cells appears similar for MHCII^POS and MHCII^NEG tumors, the killing mechanisms are different. Unresolved issues and directions for future research are addressed.

Naive idiotope-specific B and T cells collaborate efficiently in the absence of dendritic cells

Anti-idiotope (anti-Id) Abs have a role in therapy against B cell lymphomas, as inhibitors of pathogenic autoantibodies, and as surrogate Ags for immunization. Despite these observations, the mechanism by which Id(+) Ig generates anti-Id Abs is essentially unknown. To address this issue, we generated a double knock-in mouse that expresses V regions of a somatically mutated anti-Id mAb with intermediate affinity (affinity constant [Ka] = 0.77 × 10(7) M(-1)) for the myeloma protein M315. The anti-Id mice have normal peripheral B cell populations, and allelic exclusion is efficient. Anti-Id B cells from BCR knock-in mice, together with Id-specific CD4(+) T cells from previously established TCR-transgenic mice, enabled us to study Id-specific T cell-B cell collaboration by dilution of transferred cells into syngeneic BALB/c recipients. We show that previously unstimulated (naive) Id-specific B and T cells collaborate efficiently in vivo, even at low frequencies and in the presence of low amounts of Id(+) Ig, resulting in germinal center formation, plasma cell development, and secretion of isotype-switched anti-Id Abs. We further demonstrate that Id-specific T cell-B cell collaboration occurs readily in the absence of adjuvant and is not dependent on Id-presentation by dendritic cells. The results underscore the potency of anti-Id B cells in MHC class II-restricted presentation of Id(+) Ig and suggest that Id-specific T cell-B cell collaboration is of physiological relevance.

NF-κB activity in perinatal brain during infectious and hypoxic-ischemic insults revealed by a reporter mouse

Infants suffering from infection or hypoxia-ischemia around the time of birth can develop brain damage resulting in life-long impairment such as cerebral palsy, epilepsy and cognitive disability. Inflammation appears to be an important contributor irrespective of whether the primary event is infection or hypoxia-ischemia. Activation of the transcription factor NF-κB is a hallmark of inflammation. To study perinatal brain inflammation, we developed a transgenic reporter mouse for imaging NF-κB activity in live animals and tissue samples. The reporter genes firefly luciferase and a destabilized version of enhanced GFP (dEGFP) were regulated by common NF-κB sites using a bidirectional promoter. Luciferase activity was imaged in vivo, while dEGFP was detected at cellular level in tissue sections. In newborn mice subjected to experimental models of infections or hypoxia-ischemia; luciferase signal increased in brains of live animals. In brain sections dEGFP expression, revealing NF-κB activation was observed in the endothelial cells of the blood-brain barrier in all disease models. In meningitis and hypoxia-ischemia expression of dEGFP was also induced in perivascular astrocytes. In conclusion, by using this transgenic reporter mouse in experimental models of perinatal complications, we could assess NF-κB activity in vivo and subsequently determine the cellular origin in the tissues.

A mild form of Mucopolysaccharidosis IIIB diagnosed with targeted next-generation sequencing of linked genomic regions

Next-generation sequencing (NGS) techniques have already shown their potential in the identification of mutations underlying rare inherited disorders. We report here the application of linkage analysis in combination with targeted DNA capture and NGS to a Norwegian family affected by an undiagnosed mental retardation disorder with an autosomal recessive inheritance pattern. Linkage analysis identified two loci on chromosomes 9 and 17 which were subject to target enrichment by hybridization to a custom microarray. NGS achieved 20-fold or greater sequence coverage of 83% of all protein-coding exons in the target regions. This led to the identification of compound heterozygous mutations in NAGLU, compatible with the diagnosis of Mucopolysaccharidosis IIIB (MPS IIIB or Sanfilippo Syndrome type B). This diagnosis was confirmed by demonstrating elevated levels of heparan sulphate in urine and low activity of α-N-acetyl-glucosaminidase in cultured fibroblasts. Our findings describe a mild form of MPS IIIB and illustrate the diagnostic potential of targeted NGS in Mendelian disease with unknown aetiology.

Tracking early autoimmune disease by bioluminescent imaging of NF-kappaB activation reveals pathology in multiple organ systems

It is desirable to have an early and sensitive detection marker of autoimmune disease in intact animals. Nuclear factor (NF)-kappaB is a transcription factor that is associated with inflammatory responses and immune disorders. Previously, we demonstrated that so-called idiotypic-driven T-B cell collaboration in mice doubly transgenic for paired immunoglobulin and T cell receptor transgenes resulted in a systemic autoimmune disease with systemic lupus erythematosus-like features. Here, we investigated NF-kappaB activation by including an NF-kappaB-responsive luciferase reporter transgene in this animal model. Triply transgenic mice developed bioluminescence signals from diseased organs before onset of clinical symptoms and autoantibody production, and light emissions correlated with disease progression. Signals were obtained from secondary lymphoid organs, inflamed intestines, skin lesions, and arthritic joints. Moreover, bioluminescence imaging and immunohistochemistry demonstrated that a minority of mice suffered from an autoimmune disease of the small intestine, in which light emissions correlated with antibodies against tissue transglutaminase and gliadin. Detection of luciferase by immunohistochemistry revealed NF-kappaB activation in collaborating B and T cells, as well as in macrophages. These results demonstrate that bioluminescent in vivo imaging of NF-kappaB activation can be used for early and sensitive detection of autoimmune disease in an experimental mouse model, offering new possibilities for the evaluation of anti-inflammatory drugs.

Isoform-specific regulation of immune cell reactivity by the catalytic subunit of protein kinase A (PKA)

There are two major genes encoding the catalytic subunits of protein kinase A, Calpha and Cbeta. The functional significance of these isoforms is enigmatic. Lymphoid cells of the immune system express both Calpha and Cbeta. In this study we tested the role of Calpha and Cbeta in regulating immune cell reactivity to antigens using mice carrying a targeted disruption of the Calpha and Cbeta gene respectively. Calpha and Cbeta ablation both resulted in a 50% reduction in PKA-specific kinase activity and the level of PKA type I but not PKA type II. Moreover, despite that C subunit ablation did not affect immune cell development and homeostasis, Calpha but not Cbeta ablation augmented expression of the activation marker CD69 on lymphocytes. CD69 induction coincided with immune cell hyperresponsiveness and was associated with reduced sensitivity to cAMP-mediated inhibition of anti-CD3 induced T cell proliferation. Our results imply that Calpha is required for normal immune cell reactivity and demonstrates isoform-specific effects and non-redundant functions of C subunit isoforms expressed in the same cell.

Lymphomas can develop from B cells chronically helped by idiotype-specific T cells

B cell lymphomas have been associated with chronic infections and autoimmunity. However, most lymphomas develop in the absence of any known chronic antigenic stimulation. B cells process their highly diversified endogenous immunoglobulin and present clonally unique variable-region idiotypic (Id) peptides on their major histocompatibility complex (MHC) class II molecules to Id-specific T cells. We show that B cells chronically helped by Id-specific Th2 cells developed into large B cell lymphomas with cytogenetic DNA aberrations. The lymphomas expressed high amounts of Id, MHC class II, CD80/86, and CD40 and bidirectionally collaborated with Th2 cells. Thus, MHC class II–presented Id peptides may represent a chronic self-antigenic stimulus for T cell–dependent lymphomagenesis. Eventually, B lymphomas grew independent of T cells. Thus, T cells do not only eliminate cancers as currently believed. In fact, Id-specific Th2 cells can induce B lymphomas.

MHC-restricted Ig V region-driven T-B lymphocyte collaboration: B cell receptor ligation facilitates switch to IgG production

B cells spontaneously process their endogenous Ig and present V region peptides on their MHC class II molecules. We have here investigated whether B cells collaborate with V region-specific CD4+ T cells in vivo. By use of paired Ig L chain-transgenic and TCR-transgenic mice and cell transfer into normal hosts, we demonstrate that B cell presentation of a V(L) region peptide to CD4+ T cells results in germinal centers, plasma cells, and Ab secretion. Because the transgenic B cells have a fixed L chain but polyclonal H chains, their B cell receptor (BCR) repertoire is diverse and may bind a multitude of ligands. In a hapten-based system, BCR ligation concomitant with V region-driven T-B collaboration induced germinal center formation and an IgM --> IgG isotype switch. In the absence of BCR ligation, mainly IgM was produced. Consistent with this, prolonged V region-driven T-B collaboration resulted in high titers of IgG autoantibodies against ubiquitous self-Ags, while natural-type Abs against exotic bacteria remained IgM. Taken together, V region-driven T-B collaboration may explain induction of natural IgM Abs (absence of BCR ligation) and IgG autoantibodies (BCR ligation by autoantigen) and may be involved in the development of autoimmunity.

Immunotherapy in multiple myeloma: Id-specific strategies suggested by studies in animal models

Multiple myeloma (MM) cells produce monoclonal immunoglobulin (Ig) which serves as a truly tumor-specific antigen. The tumor-specific antigenic determinants are localized in the variable (V)-regions of the monoclonal Ig and are called idiotopes (Id). We review here the evidence obtained in a T-cell receptor (TCR) transgenic mouse model that Id-specific, MHC class II-restricted CD4+ T cells play a pivotal role in immunosurveillance and eradication of MHC class II-negative MM cells. In brief, monoclonal Ig secreted by MM cells is endocytosed and processed by antigen-presenting cells (APCs) in the tumor. Such tumor-resident dendritic cell APCs in turn present Id peptide on their class II molecules to Id-specific CD4+ T cells which become activated and indirectly kill the MHC class II-negative myeloma cells. However, if the Id-specific CD4+ cells fail to eliminate the MM cells during their initial encounter, the increasing number of tumor cells secretes so much monoclonal Ig that T-cell tolerance to Id is induced. Extending these findings to MM patients, Id-specific immunotherapy should be applied at a time of minimal residual disease and when new Id-specific T cells have been educated in the thymus, like after high-dose chemotherapy and autologous stem cell transplantation.

Therapeutic effect of idiotype-specific CD4+ T cells against B-cell lymphoma in the absence of anti-idiotypic antibodies

Immunoglobulin (Ig) variable (V) region idiotypes (Id's) are highly tumor-specific antigens produced by B-lymphoma cells and are promising targets for immunotherapy. Id vaccination has proven effective in experimental mouse models and may possibly prevent recurrence of B lymphomas in humans. It has previously been shown that anti-Id antibodies protect against B-cell lymphoma in the absence of T cells. We here demonstrate in a T-cell-receptor transgenic mouse model that the contrary is also true: Id-specific CD4+ T cells can protect against Id+ B-lymphoma cells in the absence of B cells, antibodies, and CD8+ T cells. Moreover, Id-specific CD4+ T cells have a curative potential since they could be transferred as late as 17 days after subcutaneous tumor cell injection of severe combined immunodeficiency (SCID) mice and still abrogate tumor development in about 50% of mice. Such mice undergo an acute inflammatory swelling with infiltration of neutrophils at the site of tumor injection, which subsides over weeks, with some mice cured and delayed emergence of lymphomas in other mice. Adoptively transferred CD4+ T cells accumulated in the tumor and were activated (CD69+). In vitro experiments demonstrated that memory, but not naive, Id-specific CD4+ T cells kill Id+ B-lymphoma cells. The results show that Id-specific CD4+ T cells, in the absence of antibodies home to subcutaneous Id+ B lymphoma, become activated, induce inflammation, and prevent tumor development.

Deletion of idiotype (Id)-specific T cells in multiple myeloma

Mycloma cells secrete monoclonal immunoglobulin (Ig), called myeloma protein. The variable (V) regions of myeloma proteins are unique to each plasma cell tumor, and therefore contain highly tumor-specific antigenic determinants called idiotopes (Id). T cells with specificity for Id are thought to be of importance in eradication of multiple myeloma. In ongoing clinical trials, myeloma patients are vaccinated against the Id of their own myeloma protein, with the aim of inducing Id-specific T cells. However, this strategy will only succeed if Id-specific T cells are present in patients, and are able to respond. In an experimental animal model, we have shown that [d-specific T cells become progressively deleted as the myeloma protein serum concentration exceeds 50 microg/ml. This indicates that the ability of multiple myeloma patients to respond to Id-vaccination might be seriously handicapped. We suggest that Id-vaccination should be reserved for eradication of minimal residual disease, e.g. after high-dose chemotherapy and stem-cell transplantation.

Resting small B cells present endogenous immunoglobulin variable-region determinants to idiotope-specific CD4(+) T cells in vivo

Antigenic determinants localized within the highly diversified V-regions of Ig are called idiotopes (Id). Processed Id-peptides can be presented on MHC class II molecules to CD4(+) T cells. If B cells present their endogenous Id-peptides, T cell activation could occur in the absence of nominal antigen, a potentially important process in T-B cooperation and immune regulation. To test this idea, we used mice made transgenic for a lambda2 L-chain (Id(+) mice). Another transgenic mouse strain expresses TCR transgenes with specificity for the Id (lambda2), presented on MHC class II molecules. When highly purified sorted Id(+) B cells and Id-specific T cells were sequentially injected into MHC syngeneic SCID host, T cell became blastoid, CD69(+) and proliferated. To exclude any role of host APC, MHC incompatible Rag2(- / -) mice (H-2(b)) were used as recipients for the Id(+) B and Id-specific T cells, with similar results. Exposure to extracellular Id(+) immunoglobulin (Ig) was not sufficient for Id priming of B cells in vivo, highlighting the preferential presentation of Id peptides derived from endogenous Ig, by B cells. The results suggest that B cells presenting Id self-peptides generated by V(D)J recombinations or somatic mutations may directly stimulate T cell in vivo in the absence of conventional antigen.

Antibodies engineered with IgD specificity efficiently deliver integrated T-cell epitopes for antigen presentation by B cells

We have developed a strategy for improving the stimulation of T cells during immune responses by constructing recombinant antibodies that enhance the delivery of antigen to antigen-presenting cells, such as B cells. These antibodies have variable regions specific for surface molecules on B cells, and a constant region with an inserted antigen. In vitro, such antibodies make B cells approximately 1000-fold more efficient at presenting antigen and stimulating specific T cells. In vivo, the antibodies turn B cells of the spleen into potent stimulators of T cells. This approach may be useful for the generation of new vaccines.