Sensitizing breast cancers to immune checkpoint inhibitors through CD27 agonism and vaccination against tumor-associated antigen

Project objective: Despite the recent revolution in immune checkpoint inhibitors (ICIs), only modest improvement in overall survival and likely caused by not enough potent cellular immunity among BC patients. Our lab has been focus on inducing cellular immunity against HER2+ BC through vaccination against the tumor-associated antigen HER2. Approximately 20 years ago, we performed an experimental pilot study by administrating HER2 peptide and recombinant protein pulsed dendritic cells (DC vaccine) to six patients with refractory HER2+ advanced or metastatic (stage II (>= 6 +LN), III, or stage IV) BC. We followed the patients on 2019 found that all of the six patients were still alive, 18 years after vaccination. Their blood sample were analyzed with cytometry by time-offlight (CyTOF) and found there is a significantly increased presence of CD27 expressing memory T cells in response to HER2 peptide stimulation. Recent report on the SARS-CoV2 mRNA vaccine also suggested that CD27 expressing memory T cells plays a critical role in long-lasting cellular immunity against SARS-CoV2 infection. Therefore, we hypothesized that CD27 plays a critical role in cellular immunity against BC, and the stimulation of CD27 expressing T cells with mAb targeting CD27 significantly increase the cellular immunity triggered by vaccination against tumor-associated antigen. Result(s): We recapitulate the rise of CD27+ antigen specific T cells among the vaccinated patients using a transgenic mouse model expressing human CD27. When combined the adenoviral-vector based HER2 (Ad-HER2) vaccination with a single dose of human aCD27 antibody (Varlilumab), we found there is a robust increase in the HER2 specific T cells compared to vaccination alone, especially CD27+CD44+ memory CD4 T cells, even after 120 days post vaccination. Using an ICIinsensitive syngeneic HER2+ BC models, we found 50% of mice in the combination group of aCD27 antibody plus Ad-HER2 showed total tumor regression by the end of study. When combined with anti-PD1 antibody, the combination of AdHER2 and Varlilumab leads to total tumor regression in 90% of tumor bearing mice with syngeneic HER2+ BC, indicating that the vaccination against tumor associated antigen HER2 plus anti-CD27 antibody sensitized ICI-insensitive HER2+ BC toward ICI. Conclusion(s): Our data demonstrates that the administration of anti-CD27 antibody significantly increase the long term presence of CD27+ antigen specific memory T cells after vaccination against tumor associated antigen HER2. As consequence, combination of anti-CD27 with HER2 sensitized the immune unresponsive breast cancer toward anti-PD1 antibody. Our study suggests that the vaccination against tumor-associated antigen with mAb targeting CD27 leads to the robust cellular immunity, which is required for successful ICIs against breast cancer.

Pbmc Immunophenotyping and Plasma Inflammatory Profile of Children with Long Covid

Background: Long COVID can be developed by individuals after an infection with SARS-CoV-2 as described by the WHO. Although this condition is more commonly described in adults, it can occur in children and adolescents with a wide range of estimated prevalence of 1-25%. Little is known about the role of the immune system in long COVID. However, one of the main hypotheses about the underlying mechanism in long COVID is that there is an immune and inflammatory dysregulation that persists after the acute infection. The objective of this study is to compare immune cells populations, and inflammatory biomarkers in paediatric populations with and without long COVID. Method(s): We analyzed 55 blood samples from the pediaCOVID cohort (Hospital Germans Trias i Pujol), which includes more than 130 children diagnosed with long COVID and 23 controls. We measured different immune cell populations using spectral cytometry with a panel of 37 cellular markers, and 42 inflammatory markers using Luminex or ELISA. EdgeR was used for statistical analysis of the spectral data;p-values of inflammatory markers were calculated using the likelihood ratio test and they were corrected for multiple comparisons. Result(s): The study cohort had a median age of 14.3 (IQR, 12.5-15.2) and 69.1% female. Patients had at least 3 symptoms associated with long COVID (median [IQR];10 [7-16]). The most common symptom was asthenia/fatigue (98.2%). Compared to the control cohort, children with long COVID had increased numbers of CD4+CD8+ T cells, IgA+CD21+CD27+ memory B cells, and IgA+CD21-CD27- memory B cells, while CD4+ TEMRA cells (CD45RA+, CCR7-), intermediate monocytes (CD14+, CD16+) and classical monocytes (CD14+, CD16-) were decreased (all p< 0.05;q=n.s.). None of the 42 inflammatory biomarkers showed significant differences between children with and without long COVID. Conclusion(s): The results of this study suggest that specific populations of peripheral blood immune cells might be involved in the mechanisms underlying prolonged COVID in children and adolescents. The increase in both IgA+CD21-CD27- and IgA+CD21+CD27+ memory B cells could be associated with the persistence of viral antigen in the gut and/or gut dysbiosis. Moreover, the decrease in CD4+ TEMRA cells could be related to autoantibodies against G-protein coupled receptors (GPCRs), since this cell population can express GPR56, and autoantibodies against GPCRs were previously reported to be elevated in adults with long COVID.

FEATURES OF POST-VACCINATION HUMORAL IMMUNE RESPONSE IN THE PERSONS WHO UNDERWENT COVID-19 OF VARIOUS SEVERITY.

The studies on humoral immune response in the individuals who have undergone COVID-19 and vaccinated with anti-COVID vaccines allows us to assess the development of "hybrid" immunity, which contributes to understanding the mechanisms of its formation from the effector phase to the step of immunological memory. We assessed the relative and absolute contents of B cell populations and subpopulations, development of humoral immunity in the patients who suffered with COVID-19 of varying severity being thereafter vaccinated with "KoviVak" and "Sputnik V". The study involved volunteers (age 47.3+/-14.5 years) who beared COVID-19 asymptomatically (n = 32), at moderate severity (n = 21), or had severe form of the disease (n = 12), then being vaccinated with "KoviVak" and "Sputnik V" 6-9 months after their recovery. The groups of vaccinated persons consisted of those who beared severe disease being vaccinated with "KoviVak" (n = 6) or "Sputnik V" (n = 6);moderate cases, vaccinated with "KoviVak" (n = 10) and "Sputnik V" (n = 11);asymptomatic cases vaccinated with "KoviVak" (n = 10) and "Sputnik V" (n = 22). We have determined relative and absolute numbers of B lymphocytes (CD45+CD19+), B1 lymphocytes (CD45+CD5+CD19-CD27-), B2 lymphocytes (CD45+CD19+CD5-CD27-), total population of memory B cells (CD45+CD19+CD5-CD27+), non-switched (CD45+CD19+IgD+CD27+), and switched (CD45+CD19+IgD-CD27+) memory B cells;mature naive B lymphocytes (CD45+CD19+CD27-IgD+), plasmoblasts (CD45+CD19+ CD38+++IgD-CD27+), as well as presence of IgG to S(RBD)-SARS-CoV-2 protein. We have found that the humoral immunity among survivors of COVID-19 of varying severity is expressed for up to nine months. The largest number of volunteers who raised antibodies to SARS-CoV-2 S-protein was registered in the group of seriously ill patients. As soon as 1 month after "Sputnik V" vaccination and until the end of the observation, all the examined subjects in this group became seropositive. 4-5 months after injection of this vaccine, specific immunoglobulins were present in all patients who had asymptomatic or average-severity infection. All volunteers who received "KoviVak" had antibodies to the COVID-19 viral S protein from the beginning to the end of the study. Vaccination, especially with "KoviVak", contributed to the highest increase, both in relative and absolute numbers of memory B lymphocytes in asymptomatic patients. Less pronounced changes in the content of B lymphocytes in COVID-19 patients who had severe and moderate clinical course may be associated with higher levels of these cells prior to injection of the vaccines. A positive correlation was found between the number of memory B cells and presence of immunoglobulins to the S protein SARS-CoV-2 in all examined patients.Copyright © 2023 Russian Association of Allergologists and Clinical Immunologists, St. Petersburg Regional Branch (SPb RAACI). All rights reserved.

CD27-IgD- B cells might portray an exhausted B cell phenotype resulting in lack of response to checkpoint inhibitor treatment in NSCLC

Background Checkpoint inhibitor (CI) therapy has revolutionized the therapy landscape of NSCLC. However, why some patients do not respond to CI therapy remains unknown. The correlation between intra-tumoral B cell follicles and response to CI therapy has been established. B cell follicles within the lymph node become more dispersed with age and CD27-IgD- B cells (DNBc) are described to be age-associated. Moreover, DNBc are abundant in chronic infection, elderly, long COVID and auto-immunity and are described to be anergic and exhausted and often lack expression of CD21. DNBc are expanded in NSCLC tumors compared to healthy lung tissue and inversely correlate to switched memory B cells in the tumor. In this study we explored if there is a correlation between this B cell subtype in peripheral blood of NSCLC patients and response to CI therapy. Methods Patients treated with CIs within the Erasmus Medical Center were included in a prospective observational immunomonitoring study. Nineteen NSCLC patients treated with either Pembrolizumab (Pem) or Nivolumab and 5 healthy controls (HC) were selected. Pem was given in 6/11 responding patients (R) and 5/8 non-responding patients (NR). Peripheral blood mononuclear cells (PBMC) were collected before start of treatment and characterized by multicolor flow cytometry. Results HC and R showed a similar pattern in most B cell subsets. NR had significantly lower proportion of B cells within the PBMC fraction than Rand HC (R: 7.14%, NR: 2.91%, HC: 10.60%). In addition, NR had a significantly higher frequency of DNBc than R and HC (R: 9.43%, NR: 23.78%, HC: 7.19%) and there was no correlation between age and DNBc. The frequency of DNBc correlated positively with lack of CD21 expression (r2: 0.83) and expression of Ki67 (r2: 0.54) both in NR, Rand HC. The frequency of Ki67+CD21-DNBc within the B cell fraction was higher in NR than in R and HC (NR: 18.34%, R: 3.51%, HC: 0.67%). Conclusions We are the first to describe that frequencies of DNBc are higher in NR compared to R and HC. Specifically, Ki67+CD21-DNBc are increased in NR and might reflect an anergic, exhausted B cell phenotype. The absence of a correlation between age and DNBc could suggest that the increase in DNBc is induced by the tumor. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure D. Dumoulin: Financial Interests, Personal, Other: Roche, BMS, MSD, AstraZeneca, Novartis. J.G. Aerts: Financial Interests, Personal, Research Grant: Amphera, Roche, Eli Lilly;Financial Interests, Personal, Advisory Board: Amphera, Bristol-Myers Squibb, Eli Lilly, MSD, Roche;Financial Interests, Personal, Ownership Interest: Amphera;Financial Interests, Personal, Other: Takeda. All other authors have declared no conflicts of interest.Copyright © 2023 International Association for the Study of Lung Cancer. Published by Elsevier Inc.

FEATURES OF POST-VACCINATION HUMORAL IMMUNE RESPONSE IN THE PERSONS WHO UNDERWENT COVID-19 OF VARIOUS SEVERITY.

The studies on humoral immune response in the individuals who have undergone COVID-19 and vaccinated with anti-COVID vaccines allows us to assess the development of "hybrid" immunity, which contributes to understanding the mechanisms of its formation from the effector phase to the step of immunological memory. We assessed the relative and absolute contents of B cell populations and subpopulations, development of humoral immunity in the patients who suffered with COVID-19 of varying severity being thereafter vaccinated with "KoviVak" and "Sputnik V". The study involved volunteers (age 47.3+/-14.5 years) who beared COVID-19 asymptomatically (n = 32), at moderate severity (n = 21), or had severe form of the disease (n = 12), then being vaccinated with "KoviVak" and "Sputnik V" 6-9 months after their recovery. The groups of vaccinated persons consisted of those who beared severe disease being vaccinated with "KoviVak" (n = 6) or "Sputnik V" (n = 6);moderate cases, vaccinated with "KoviVak" (n = 10) and "Sputnik V" (n = 11);asymptomatic cases vaccinated with "KoviVak" (n = 10) and "Sputnik V" (n = 22). We have determined relative and absolute numbers of B lymphocytes (CD45+CD19+), B1 lymphocytes (CD45+CD5+CD19-CD27-), B2 lymphocytes (CD45+CD19+CD5-CD27-), total population of memory B cells (CD45+CD19+CD5-CD27+), non-switched (CD45+CD19+IgD+CD27+), and switched (CD45+CD19+IgD-CD27+) memory B cells;mature naive B lymphocytes (CD45+CD19+CD27-IgD+), plasmoblasts (CD45+CD19+ CD38+++IgD-CD27+), as well as presence of IgG to S(RBD)-SARS-CoV-2 protein. We have found that the humoral immunity among survivors of COVID-19 of varying severity is expressed for up to nine months. The largest number of volunteers who raised antibodies to SARS-CoV-2 S-protein was registered in the group of seriously ill patients. As soon as 1 month after "Sputnik V" vaccination and until the end of the observation, all the examined subjects in this group became seropositive. 4-5 months after injection of this vaccine, specific immunoglobulins were present in all patients who had asymptomatic or average-severity infection. All volunteers who received "KoviVak" had antibodies to the COVID-19 viral S protein from the beginning to the end of the study. Vaccination, especially with "KoviVak", contributed to the highest increase, both in relative and absolute numbers of memory B lymphocytes in asymptomatic patients. Less pronounced changes in the content of B lymphocytes in COVID-19 patients who had severe and moderate clinical course may be associated with higher levels of these cells prior to injection of the vaccines. A positive correlation was found between the number of memory B cells and presence of immunoglobulins to the S protein SARS-CoV-2 in all examined patients.Copyright © 2023 Russian Association of Allergologists and Clinical Immunologists, St. Petersburg Regional Branch (SPb RAACI). All rights reserved.

T HELPER CELL SUBSETS AND RELATED TARGET CELLS IN ACUTE COVID-19.

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 2-4 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells - basophiles and eosinophils - were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased "regulatory" Tfh1 cell and increased "pro-inflammatory" Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of "naive" and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24- plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.Copyright © 2022 Saint Petersburg Pasteur Institute. All rights reserved.

T HELPER CELL SUBSETS AND RELATED TARGET CELLS IN ACUTE COVID-19

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 2–4 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells — basophiles and eosinophils — were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased "regulatory” Tfh1 cell and increased "pro-inflammatory” Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of "naïve” and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24– plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.

Effector memory T cell subset CD45RA−CCR7−CD27−CD28− EM3 increases in direct proportion to the disease severity of COVID‐19

COVID‐19, which emerged in December 2019 and continues to wreak havoc, has led to the death of many people around the world. In this study, we aimed to uncover the variables underlying the exacerbation of the disease by considering the changes in T cell subsets in adults and juveniles with different disease severity of COVID‐19. Peripheral blood samples of 193 patients (128 adults and 65 juveniles) diagnosed with COVID‐19 were evaluated in a flow cytometer, and a broad T cell profile was revealed by examining T cell subsets in terms of exhaustion and senescence. We found remarkable differences in the effector memory (EM;CD45RA−CCR7−) cell subsets of severe pneumonia cases. The frequencies of EM2 CD4+ T, EM3 CD4+ T, EM3 CD8+ T, EM2 DN T and EM3 DN T cells were found to increase in severe pneumonia cases. Consistently, these cells were found in juveniles and uncomplicated adults in similar or lower proportions to healthy controls. The findings of our study provide a view of the T cell profile that may underlie differences in the course of COVID‐19 cases in juveniles and adults and may provide new insights into the development of effective treatment strategies.

DEPLETION AND RECOVERY OF NORMAL B-CELLS DURING AND AFTER TREATMENT WITH CHEMOIMMUNOTHERAPY, IBRUTINIB OR VENETOCLAX

Background: Infectious complications are a major cause of morbidity and mortality in Chronic Lymphocytic Leukaemia (CLL). Therapeutic approaches that deplete CLL cells also affect normal B-cells. Optimal treatment would result in eradication of CLL cells and recovery of normal immune function. FLAIR (ISRCTN01844152) is a phase III trial for previously untreated CLL comparing ibrutinib plus rituximab (IR) with fludarabine, cyclophosphamide and rituximab (FCR) and subsequently amended to also compare ibrutinib plus venetoclax (I+V) and ibrutinib alone (I) with FCR. Measurable residual disease (MRD) and normal B-cell levels were assessed at multiple timepoints. Aims: To assess the depletion of normal B-cells during treatment and recovery after end of treatment. Methods: Participants aged under 75 years with <20% TP53-deleted cells were initially randomised to FCR or IR and subsequently to FCR, IR, I+V or I with the IR arm closed after randomisation of 771 participants to FCR/IR. FCR was given for 6 cycles, while treatment in the IR, I and I+V arms continued for up to 6 years except in participants attaining <0.01% MRD who continued treatment for the time taken to achieved MRD <0.01% and then stopped if MRD remained <0.01%. Month (M) 24 was earliest permitted stopping point. MRD flow cytometry was performed according to ERIC guidelines (panel: CD19/5/20/43/79/81+ROR1, acquisition of 0.5-2.2 million cells, BD Biosciences Lyric). Additional analysis of normal B-cell subsets was performed in a cohort of >500 patients (panel: CD19 to identify B-cells, CD20/5/79b+ROR1 and CD3 to exclude CLL & contaminating cells, with CD27/ 38/IgD/IgM to characterise normal B-cell subsets using a Coulter Cytoflex LX). Results: Normal B-cells were undetectable during FCR treatment and only rarely detectable until 12 months after last FCR cycle. Circulating normal B-cells were reduced in number or undetectable in participants receiving ibrutinibcontaining regimens with greater depletion in the I+V and IR arms relative to I monotherapy. B-progenitors persist through FCR treatment but were depleted during I, I+R or I+V treatment. Normal B-cell levels at 24 and 36 months after randomisation, with time off-treatment if applicable, are shown in Figure 1. In the ibrutinib-containing arms (IR, I, and I+V), there was a trend towards fewer COVID-associated SAE at any time point for participants with detectable B-cells at 24M (4/181, 2.2%) compared to those with no detectable B-cells (14/344, 4.1%) and COVID-associated SAEs were not observed in FCR-treated participants who had recovered any level of normal B-cells by 24M (0/215). However, the data on COVID infections are limited and there was no apparent association between normal B-cell levels at 24M with the proportion of participants experiencing an infectious SAE overall. Assessment of normal B-cell subsets during ibrutinib-based treatment demonstrated a mix of naïve and memory B-cells. Serological response to COVID infection/vaccination in this cohort is currently being performed. Participants stopping I+V treatment at 24-30 months post-randomisation due to MRD eradication showed rapid recovery of normal naive B-cells within 6-12 months after end of treatment in the vast majority (>95%) of evaluable cases. Summary/Conclusion: Normal circulating B-cells are depleted during treatment with rituximab but can persist at a low level during I, IR or I+V treatment. Most patients in remission after treatment with FCR or I+V show recovery of normal B-cells at 12 months of stopping treatment.

B CELL CHARACTERISTICS at BASELINE PREDICT HUMORAL RESPONSE UPON SARS-COV-2 VACCINATION among PATIENTS TREATED with RITUXIMAB

Background: Vaccination is considered efficient in controlling infections incl. SARS-CoV-2. Prior studies showed that patients receiving rituximab (RTX) with low B cell counts are at increased infectious risk (1) and risk of inadequate vaccination responses (2, 3). Thus, the ability to further defne and predict vaccination responses in these patients may guide their optimal protection. Objectives: To assess predictive biomarkers of vaccination responses upon SARS-CoV-2 vaccination in RTX treated patients. Methods: B cell characteristics before vaccination were evaluated to predict responses in 15 patients with autoimmune infammatory rheumatic diseases receiving RTX. 11 patients with rheumatoid arthritis on other therapies (RA), 11 kidney transplant recipients (KTR) and 15 healthy volunteers (HC) served as controls. A multidimensional analysis of B cell subsets and a correlation matrix were performed to identify predictive biomarkers. Results: Signifcant differences regarding absolute B cell counts and specifc subset distribution pattern between the groups were validated at baseline. Here, the majority of B cells from vaccination responders of the RTX group (RTX IgG+) comprised naïve and transitional B cells, whereas vaccination non-responders (RTX IgG-) carried preferentially plasmablasts and double negative (CD27-IgD-) B cells (Figure 1). Moreover, there was a positive correlation between neutralizing antibodies and absolute B cell numbers with B cells expressing HLA-DR and CXCR5 (involved in antigen presentation and germinal center formation) as well as an inverse correlation with CD95 expression and CD21low expression (marker for activation and exhaustion) on B cells. Conclusion: Substantial repopulation of naïve B cells upon RTX therapy appears to be essential for an adequate vaccination response requiring germinal center formation. In contrast, expression of exhaustion markers (CD21low, CXCR5-, CD95+) indicate negative predictors of vaccination responses. These results may guide optimized vaccination strategies in RTX treated patients clearly requiring antigen-inexperienced B cells for appropriate protection.

Updated results of a multicenter first-in-human study of BCMA/CD19 dual-targeting fast CAR-T GC012F for patients with relapsed/refractory multiple myeloma (RRMM)

Background: GC012F is a B cell maturation antigen (BCMA)/CD19 dual-targeting CAR-T developed on the novel FasT CAR-T platform with overnight manufacturing and designed to improve depth of response and efficacy. Data was presented at ASCO and EHA 2021 for initial 19 pts. We present updated data for study (NCT04236011;NCT04182581) with longer follow up and 9 additional pts treated (n = 28) in 3 different dose levels. Methods: From October 2019 to November 2021, 28 heavily pretreated RRMM pts (age 27-76) median of 5 prior lines (range 2-9) were treated on a single-arm, open label, multicenter Investigator Initiated Trial receiving a single infusion of GC012F. 89.3% (25/ 28) were high risk (HR- mSMART), 8 pts had EM disease, 3 had never achieved a CR including after transplant, 1 pts presented with plasma cell leukemia, 24/28 pts were refractory to last therapy, 3 pts primary refractory. 9/28 pts had received prior anti-CD38, 27/28 pts prior IMiDs. 26/28 pts were refractory to PI, 26/28 pts to IMiDs. After lymphodepletion over 2-3 days (30 mg/m2/d, 300mg/ m2/d Flu/Cy) GC012F was administered as single infusion at 3 dose levels: 1x105/kg (DL1) n = 2, 2x105/kg (DL2) n = 10 and 3x105/kg (DL3) n = 16. Results: As of Jan 26th 2022, 28 pts - median follow-up (f/ u) 6.3 mths (1.8-29.9) - had been evaluated for response. Overall response rate (ORR) in DL1 was 100% (2/2)- DL 2 -80% (8/10) DL 3 -93.8% (15/16) with 27 pts MRD negative by flow cytometry (sensitivity 10-4-10-6). 100% of MRD assessable pts (27/27) achieved MRD negativity. One patient out of 28 could not get assessed. At d28, 21/24 assessable patients were MRD negative (81.5%), 4/ 28 pts could not get d28 MRD assessment f/u due to COVID-19 restrictions however were assessed at a later timepoint. To date best response is MRD- sCR in 21/28 patients(75.0%) across all dose levels. Some pts after short f/u show responses that are still deepening. Cytokine Release Syndrome (CRS) was mostly low grade: gr 0 n = 3 (10.7%), gr 1-2 n = 23 (82.1%), gr 3 n = 2 (7.1%) - no gr 4/5 CRS and no ICANs were observed (Graded by ASBMT criteria). Median duration of CRS was 3 d (1-8 d). PK results showed no difference amongst dose levels DL1 to DL3. Overall, CAR-T median Tmax was 10 d (range 8-14 d), median peak copy number (Cmax) was 97009 (16,011-374,346) copies /μg DNA with long duration of persistence of up to d793 (data cut-off). CAR-T geometric mean AUC0-28 for DL1, DL2 and DL3 were 468863, 631540 and 581620 copies/μg DNA×day, respectively. Pts continue to be monitored for safety and efficacy including DOR. Conclusions: BCMA-CD19 dual FasT CAR-T GC012F continues to provide deep and durable responses with a favorable safety profile in additional RRMM pts across all dose levels demonstrating a very high MRD negativity rate including in pts refractory to anti-CD38, PI and IMIDs. GC012F is currently being studied in earlier lines of therapy as well as additional indications.

T HELPER CELL SUBSETS AND RELATED TARGET CELLS IN ACUTE COVID-19

Current review presents a brief overview of the immune system dysregulation during acute COVID-19 and illustrates the main alterations in peripheral blood CD4+ T-cell (Th) subsets as well as related target cells. Effects of dendritic cell dysfunction induced by SARS-CoV-2 exhibited decreased expression of cell-surface HLA-DR, CCR7 as well as co-stimulatory molecules CD80 and CD86, suggesting reduced antigen presentation, migratory and activation capacities of peripheral blood dendritic cells. SARS-CoV-2-specific Th cells could be detected as early as days 2–4 post-symptom onset, whereas the prolonged lack of SARS-CoV-2-specific Th cells was associated with severe and/or poor COVID-19 outcome. Firstly, in acute COVID-19 the frequency of Th1 cell was comparable with control levels, but several studies have reported about upregulated inhibitory immune checkpoint receptors and exhaustion-associated molecules (TIM3, PD-1, BTLA, TIGIT etc.) on circulating CD8+ T-cells and NK-cells, whereas the macrophage count was increased in bronchoalveolar lavage (BAL) samples. Next, type 2 immune responses are mediated mainly by Th2 cells, and several studies have revealed a skewing towards dominance of Th2 cell subset in peripheral blood samples from patients with acute COVID-19. Furthermore, the decrease of circulating main Th2 target cells — basophiles and eosinophils — were associated with severe COVID-19, whereas the lung tissue was enriched with mast cells and relevant mediators released during degranulation. Moreover, the frequency of peripheral blood Th17 cells was closely linked to COVID-19 severity, so that low level of Th17 cells was observed in patients with severe COVID-19, but in BAL the relative number of Th17 cells as well as the concentrations of relevant effector cytokines were dramatically increased. It was shown that severe COVID-19 patients vs. healthy control had higher relative numbers of neutrophils if compared, and the majority of patients with COVID-19 had increased frequency and absolute number of immature neutrophils with altered ROS production. Finally, the frequency of Tfh cells was decreased during acute COVID-19 infection. Elevated count of activated Tfh were found as well as the alterations in Tfh cell subsets characterized by decreased “regulatory” Tfh1 cell and increased “pro-inflammatory” Tfh2 as well as Tfh17 cell subsets were revealed. Descriptions of peripheral blood B cells during an acute SARS-CoV-2 infection werev reported as relative B cell lymphopenia with decreased frequency of “naïve” and memory B cell subsets, as well as increased level of CD27hiCD38hiCD24– plasma cell precursors and atypical CD21low B cells. Thus, the emerging evidence suggests that functional alterations occur in all Th cell subsets being linked with loss-of-functions of main Th cell subsets target cells. Furthermore, recovered individuals could suffer from long-term immune dysregulation and other persistent symptoms lasting for many months even after SARS-CoV-2 elimination, a condition referred to as post-acute COVID-19 syndrome.

ANTIVIRAL RESPONSE OF NATURAL KILLER CELLS IN EARLY STAGE OF COVID-19 PATIENTS

Backgroung: COVID-19 pandemic (SARS-CoV-2) has affected an increasing number of people worldwide, with death rates higher than previous viral epidemics. It is possible that NK cells, known to have great cytokine secreting potential are competent at the onset of the condition and that in some individuals, the viral load is able to exhaust them. Balance between tolerant (CD27- CD11b-), secretory (CD27+ CD11b-/ CD27+ CD11b+) and cytotoxic (CD27- CD11b+) NK cells involved in the inflammatory response and their anti-SARS-CoV-2 activity are still not well established. Strategies that can restore function of NK cells against the virus are worth investigating. Here, we aimed to characterize NK cells frequency, functional subtypes and maturation in early phase of COVID-19 patients, by Multiparametric Flow Cytometry (MFC). Methods: Peripheral blood from 15 COVID-19 patients in early stage of infection (day 1-14, confirmed by RT-PCR), categorized according comorbidities in: G1 (not oncologic;n = 6), G2 (oncologic;n = 3), G3 (hematologic neoplasms;n = 3) and G4 (without comorbidities;n = 3), and 10 healthy samples enrolled the study. Clinical and laboratorial data were collected from electronic medical records. Samples were stained with CD45, CD19, CD3, CD56, CD11b, CD27, acquired on a FACS Canto II (BD Biosciences) and data analyzed with FlowJo V10 software. Results: A lower frequency of lymphocytes was observed in the disease when compared to controls (P < 0.0001) and frequency of NK cells were similar in both groups (P = 0.6605). Although frequency of CD27- CD11b- NK cells was lower in the disease (P = 0.0109), there was a significantly higher frequency of CD27+ CD11b- NK cells in COVID-19 samples when compared to controls (P < 0.0001), featuring a mostly immature profile in the disease. On the other hand, no statistical significance was observed regarding the frequencies of CD27+ CD11b+ (P = 0.1370) and CD27- CD11b+ NK cells with a more mature profile (P = 0.3094). Amongst disease groups, no statistical significance was found regarding frequency of NK cells and G1 showed lower frequency of CD27- CD11b- NK cells (P = 0.0226), while G3 group had an increased frequency of CD27+ CD11b- NK cells (P = 0.0238) when compared to the other groups and controls. Finally, no statistical significance was found in the frequency of CD27+ CD11b+ (P = 0.6691) and CD27- CD11b+ (P = 0.6270) NK cells between disease groups and controls. Conclusion: Although the frequency of NK cells did not show a significant difference between COVID-19 patients and healthy controls, our findings showed a possible change in their maturation profile, which seems to be inversely proportional to normal, with the frequency of CD27+ CD11b- NK cells considerably higher in the disease. This phenotype is directly associated with secretory function of a more immature NK cell and is responsible for triggering inflammatory responses that could lead to severe respiratory failure, what seems to be consistent with COVID-19 profile. A high frequency of cytotoxic cells was observed, which seemed to be similar to what we found in normal heathy samples. Even though unregulated maturation might be associated to a dysfunctional mature NK cell, additional studies of cytotoxicity and activation of NK cells in COVID-19 are required to affirm whether there is functional exhaustion or hyperactivation of the cytotoxic subtypes of these cells.

Safety and Efficacy of Cusatuzumab in Combination with Venetoclax and Azacitidine (CVA) in Patients with Previously Untreated Acute Myeloid Leukemia (AML) Who Are Not Eligible for Intensive Chemotherapy;An Open-Label, Multicenter, Phase 1b Study

Background: Acute myeloid leukemia (AML) is driven by aberrant leukemic stem cells (LSCs) that initiate and sustain malignancy. To circumvent resistance to therapy, combination therapies with additive mechanisms of action are needed. CD70, a tumor necrosis factor receptor ligand, and its receptor CD27 are expressed on LSCs and AML blasts, but not on hematopoietic stem cells. Cusatuzumab, a high-affinity humanized monoclonal anti-CD70 antibody, kills CD70-expressing cells by Fc domain-mediated effector functions and is a potent inhibitor of CD70-CD27 signaling. Here we report initial results of a study of cusatuzumab in combination with the current standard of care therapy, venetoclax plus azacitidine (CVA), in patients with untreated AML (de novo or secondary) ineligible for intensive chemotherapy due to age ≥75 years or medical comorbidities. Methods: The primary objective of this open label, multicenter, phase 1b study was to assess safety and tolerability of CVA. Key secondary objectives included response rate per ELN 2017 criteria and time to response. Patients received cusatuzumab 10 or 20 mg/kg IV on Day 3 and Day 17, a 3-day ramp-up of venetoclax (100, 200, and 400 mg PO) followed by 400 mg daily dosing, and azacitidine 75 mg/m 2 SC or IV on Days 1-7 of each 28-day cycle. Results: Based on data through Jul 9, 2021, 44 patients enrolled with median age 75 years (range 32-89), 36.4% had secondary AML, 40.9% had an ECOG performance status of 2, and ELN risk was favorable, intermediate and adverse in 18.2%, 20.5% and 61.4%, respectively. All patients received 20 mg/kg cusatuzumab except for 3 patients who received a starting dose of 10 mg/kg with the option to escalate to 20 mg/kg. Of these 3 patients, 1 escalated to 20 mg/kg. At a median follow-up of 29.1 weeks, the median number of treatment cycles was 4.0 (range 1.0-11.0). Grade 3 or above TEAEs were reported in 97.7% of patients;the most common (reported in ≥10%) were neutropenia (68.2%), thrombocytopenia (65.9%), febrile neutropenia (36.4%), anemia (34.1%), leukopenia (29.5%), sepsis (27.3%), and lymphopenia (15.9%). Treatment-emergent serious adverse events (SAEs) were reported in 75% of patients;the most common (reported in at least ≥5%) were febrile neutropenia (27.3%), sepsis (22.7%), COVID-19 (6.8%), and thrombocytopenia (6.8%). Treatment-emergent SAEs of grade ≥3 were reported in 72.7% of the patients. Infusion-related reactions (IRRs) were reported for 11.4% of patients with 2.3% at grade ≥3. Six (13.6%) patients discontinued treatment due to AEs, and 5 (11.4%) TEAEs resulted in death. The mortality rate within 30 days from start of treatment was 4.5%. Table 1 summarizes best response to study treatment. In the intent-to-treat analysis set (n=44) complete remission (CR) rate was 45.5%, while CR + CR with partial hematologic recovery (CRh) + CR with incomplete hematologic recovery (CRi) was 77.3%;MLFS was observed in 11.4% of patients. Of 34 responders (defined as CR, CRi or CRh), 47% were MRD negative by flow cytometry at or after achievement of response. Median time to first response for patients who achieved CR, CRh or CRi was 4.21 (3.0-25.0) weeks. Best response rates in the post-hoc response evaluable analysis set (n=42) that excluded two patients who died before the first disease evaluation were: CR in 47.6%, CR + CRh + CRi in 81.0% and MLFS in 11.9% of patients (Table 1). The majority (97.1%) of responders experienced at least one cycle delay in administration of CVA post response. Conclusions: Cusatuzumab administered in combination with venetoclax and azacitidine to elderly patients with untreated AML was generally well tolerated and demonstrated a safety profile consistent with that previously reported with venetoclax-azacitidine, with the addition of generally manageable IRRs. Response rates support an additive effect of cusatuzumab to the standard of care with potential for improved clinical outcomes. However, further clinical trials are needed for validation of these initial results. HK and GB contributed equally to this publ cation. [Formula presented] Disclosures: Roboz: AstraZeneca: Consultancy;Janssen: Research Funding;Bristol Myers Squibb: Consultancy;Jasper Therapeutics: Consultancy;Agios: Consultancy;Novartis: Consultancy;Amgen: Consultancy;Blueprint Medicines: Consultancy;Janssen: Consultancy;Helsinn: Consultancy;Daiichi Sankyo: Consultancy;Glaxo SmithKline: Consultancy;Celgene: Consultancy;Jazz: Consultancy;MEI Pharma - IDMC Chair: Consultancy;Mesoblast: Consultancy;Actinium: Consultancy;AbbVie: Consultancy;Astex: Consultancy;Bayer: Consultancy;Astellas: Consultancy;Roche/Genentech: Consultancy;Pfizer: Consultancy;Otsuka: Consultancy. Aribi: Seagen: Consultancy. Brandwein: Astellas: Honoraria;Jazz: Honoraria;Amgen: Honoraria;Taiho: Honoraria;BMS/Celgene: Honoraria;Pfizer: Honoraria;Abbvie: Honoraria;University of Alberta: Current Employment. Döhner: Astellas: Consultancy, Honoraria, Research Funding;AstraZeneca: Consultancy, Honoraria;Berlin-Chemie: Consultancy, Honoraria;Amgen: Consultancy, Honoraria, Research Funding;Abbvie: Consultancy, Honoraria, Research Funding;Agios: Consultancy, Honoraria, Research Funding;Celgene: Consultancy, Honoraria, Research Funding;GEMoaB: Consultancy, Honoraria;Helsinn: Consultancy, Honoraria;Janssen: Consultancy, Honoraria;Jazz: Consultancy, Honoraria, Research Funding;Novartis: Consultancy, Honoraria, Research Funding;Oxford Biomedicals: Consultancy, Honoraria;Pfizer: Research Funding;Roche: Consultancy, Honoraria;Gilead: Consultancy, Honoraria;Bristol Myers Squibb: Consultancy, Honoraria, Research Funding;Astex: Consultancy, Honoraria;Ulm University Hospital: Current Employment. Fiedler: Jazz Pharmaceuticals: Consultancy, Other: support for meeting attendance;Abbvie: Consultancy, Honoraria;Morphosys: Consultancy;Celgene: Consultancy;Pfizer: Consultancy, Research Funding;Novartis: Consultancy;ARIAD/Incyte: Consultancy;Amgen: Consultancy, Other: support for meeting attendance, Patents & Royalties, Research Funding;Servier: Consultancy, Other: support for meeting attendance;Daiichi Sankyo: Consultancy, Other: support for meeting attendance;Stemline: Consultancy. Gandini: argenx: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. Geddes: University of Calgary: Current Employment;Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees;Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees;Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees;Novartis: Consultancy;BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau;Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees;Amgen: Consultancy;Paladin: Consultancy;Janssen: Research Funding;Geron: Research Funding;Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding. Hou: University of Pittsburgh Medical Center Hillman Cancer Centers: Current Employment;AbbVie: Honoraria;AstraZeneca: Honoraria;Karyopharm: Honoraria;Chinese American Hematology Oncology Network: Membership on an entity's Board of Directors or advisory committees. Howes: Janssen R&D, part of Johnson & Johnson: Current Employment;Johnson & Johnson: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Hultberg: argenx: Current Employment, Patents & Royalties. Huselton: University of Rochester: Current Employment. Jacobs: Argenx BV: Current Employment, Current equity holder in publicly-traded company;University of Antwerp: Ended employment in the past 24 months. Kane: Janssen R&D, part of Johnson & Johnson: Current Employment, Current equity holder in publicly-traded company. Lech-Marańda: Takeda: Membership on an entity's Board of Directors or advisory committees;AbbVie: Membership on an entity's Board of Directors r advisory committees;Novartis: Membership on an entity's Board of Directors or advisory committees;Roche: Membership on an entity's Board of Directors or advisory committees;Janssen-Cilag: Membership on an entity's Board of Directors or advisory committees;Amgen: Membership on an entity's Board of Directors or advisory committees;Sanofi: Membership on an entity's Board of Directors or advisory committees;Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding. Louwers: argenx: Current Employment, Patents & Royalties: Patents (no royalties). Nottage: Janssen R&D, part of Johnson & Johnson: Current Employment;Johnson & Johnson: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Platzbecker: Novartis: Honoraria;AbbVie: Honoraria;Janssen: Honoraria;Celgene/BMS: Honoraria;Geron: Honoraria;Takeda: Honoraria. Rampal: Pharmaessentia: Consultancy;BMS/Celgene: Consultancy;Abbvie: Consultancy;Sierra Oncology: Consultancy;Incyte: Consultancy, Research Funding;Blueprint: Consultancy;Disc Medicine: Consultancy;Jazz Pharmaceuticals: Consultancy;Constellation: Research Funding;Kartos: Consultancy;Stemline: Consultancy, Research Funding;CTI: Consultancy;Novartis: Consultancy;Memorial Sloan Kettering: Current Employment. Salman: Janssen: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Shah: Janssen R&D, part of Johnson & Johnson: Current Employment. Stuart: Clinical Drug Development Consultants LLC: Current Employment;Argenx: Consultancy;Cleave Therapeutics: Consultancy;Triphase Accelerator Corp: Consultancy;IgM Biosciences: Consultancy;Revolution Medicines: Consultancy;Jiya Corp:Consultancy;Geron Corp: Current holder of individual stocks in a privately-held company. Subklewe: Janssen: Consultancy;Pfizer: Consultancy, Speakers Bureau;Takeda: Speakers Bureau;Klinikum der Universität München: Current Employment;MorphoSys: Research Funding;Novartis: Consultancy, Research Funding, Speakers Bureau;Roche: Research Funding;Seattle Genetics: Consultancy, Research Funding;Miltenyi: Research Funding;Gilead: Consultancy, Research Funding, Speakers Bureau;Amgen: Consultancy, Research Funding, Speakers Bureau;BMS/Celgene: Consultancy, Research Funding, Speakers Bureau. Sumbul: argenx: Current Employment. Wang: Takeda: Consultancy, Honoraria, Other: Advisory board;Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board;Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees;Stemline Therapeutics: Consultancy, Honoraria, Other: Advisory board, Speakers Bureau;AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees;Kite Pharmaceuticals: Consultancy, Honoraria, Other: Advisory Board;GlaxoSmithKline: Consultancy, Honoraria, Other: Advisory Board;Genentech: Membership on an entity's Board of Directors or advisory committees;BMS/Celgene: Membership on an entity's Board of Directors or advisory committees;DAVA Oncology: Consultancy, Speakers Bureau;Kura Oncology: Consultancy, Honoraria, Other: Advisory board, steering committee, Speakers Bureau;Novartis: Consultancy, Honoraria, Other: Advisory Board;Mana Therapeutics: Consultancy, Honoraria;Pfizer: Consultancy, Honoraria, Other: Advisory Board, Speakers Bureau;Rafael Pharmaceuticals: Other: Data safety monitoring committee;Gilead: Consultancy, Honoraria, Other: Advisory board;Daiichi Sankyo: Consultancy, Honoraria, Other: Advisory board;PTC Therapeutics: Consultancy, Honoraria, Other: Advisory board;Genentech: Consultancy;MacroGenics: Consultancy. Wierzbowska: Jazz: Research Funding;Pfizer: Honoraria;Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees;Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees;Astellas: Honoraria, Membership on an entity's Board of Directors or advisory comm ttees;Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees;BMS: Honoraria. Yao: Statagize LLC: Current Employment;Puma Biotechnology, Inc.: Ended employment in the past 24 months;Argenx: Consultancy. Yee: Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding;Janssen: Research Funding;TaiHo: Membership on an entity's Board of Directors or advisory committees;Otsuka: Membership on an entity's Board of Directors or advisory committees;Onconova: Research Funding;Pfizer: Membership on an entity's Board of Directors or advisory committees;Tolero: Research Funding;Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding;Paladin: Membership on an entity's Board of Directors or advisory committees;MedImmune: Research Funding;AbbVie: Honoraria;Bristol-Myers Squibb/Celgene: Membership on an entity's Board of Directors or advisory committees;Shattuck Labs: Membership on an entity's Board of Directors or advisory committees;Forma Therapeutics: Research Funding;Takeda: Membership on an entity's Board of Directors or advisory committees;Geron: Research Funding;Genentech: Research Funding;F. Hoffmann La Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding;Jazz: Research Funding. Kantarjian: Immunogen: Research Funding;Astra Zeneca: Honoraria;KAHR Medical Ltd: Honoraria;Astellas Health: Honoraria;Pfizer: Honoraria, Research Funding;NOVA Research: Honoraria;Ascentage: Research Funding;Precision Biosciences: Honoraria;Novartis: Honoraria, Research Funding;Aptitude Health: Honoraria;Ipsen Pharmaceuticals: Honoraria;Jazz: Research Funding;Daiichi-Sankyo: Research Funding;BMS: Research Funding;Amgen: Honoraria, Research Funding;AbbVie: Honoraria, Research Funding;Taiho Pharmaceutical Canada: Honoraria. Borthakur: Protagonist: Consultancy;Ryvu: Research Funding;Astex: Research Funding;GSK: Consultancy;Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees;Takeda: Membership on an entity's Board of Directors or advisory committees;University of Texas MD Anderson Cancer Center: Current Employment;ArgenX: Membership on an entity's Board of Directors or advisory committees.

Whole exome sequencing of MIS-C patients: Analysis of genes involved in inborn errors of type I IFN immunity, hemophagocytic lymphohistiocytosis (HLH), Kawasaki disease (KD) and TLR7 gene

Introduction: After spring 2020, a series of reports from Europe and USA described clusters of children, presenting life-threatening multisystem inflammatory syndrome in children (MIS-C), associated with antecedent exposure to SARS-CoV-2 (1). In patients with life threatening COVID-19 3.5% were found to have inborn errors in type I IFN signalling pathway (2). A case series of 4 young patients with severe COVID-19 reported rare loss-of-function variants in the TLR7 gene associated with impaired type I IFN responses (3). Clinically, MIS-C shares features with secondary hemophagocytic lymphohistiocytosis (HLH) and Kawasaki disease (KD), which were also associated with possible infectious trigger and might share a common genetic cause (4). Objectives: We analysed whether MIS-C patients have an underlying presence of genetic variants in exomes associated with inborn errors of type I IFN immunity, HLH, KD and presence of variants in TLR7 gene. Methods: Blood was drawn from 17 MIS-C patients upon submission into the hospital, DNA from peripheral blood was isolated and whole exome sequencing was performed. Variants in the following genes were investigated: type I IFN immunity (TLR3, UNC93B1, TRAF3, TBK1, IRF3/9, IRF7, IFNAR1/2, STAT1/2, IKBKG, TRIF), HLH (AP3B1, CD27, FADD, FAS, FASLG, HPLH1, ITK, LYST, MAGT1, MYO5A, NLRC4, PRF1, RAB27A, RECQL4, SH2D1A, STX11, STXBP2, UNC13D, XIAP, TNFRSF9, CDC42), KD (ITPKC, CD40, FCGR2A, BLK, CASP3, TRX-CAT1-7, PGBD1, LTA, TSBP1, HLA-DQB1/2, HLA-DOB, IGHV1-69) and TLR7 genes. Analysis was focused on rare (GnomAD<0.01) exonic or splicing variants. Results: No common genetic denominators were found in analysed genes. Five rare variants were observed in four patients (4/17). According to ACMG classification variants of uncertain significance (VUS) were found in LYST (2), IKBKG (1), IRF3 (1) and NLRC4 (1) in heterozygous genotype. No clinical evidence was found in ClinVar database for any of the variants, except for one variant in LYST (c.3931A>G:p.M1311V) with uncertain significance for Chédiak-Higashi syndrome and medium prediction scores. Variants in LYST (c.5990C>G:p.A1997G), NLRC4 (c.772T>C:p.C258R) and IRF3 (c.325G>C: p.G109R) have high CADD, Mutation Taster, Polyphen and SIFT prediction scores. And IKBKG (c.325C>G:p.L109V) variant had medium prediction scores. Conclusion: Our findings suggest that MIS-C patients do not share a rare loss-of-function variant in type I IFN immunity genes, TLR7 gene or genes associated either with HLH or KD. Despite numerous clinical, immunological and genetic research of the MIS-C patients, the syndromes pathogenesis and etiologic cause remain elusive.