Intracellular flow cytometry staining of antibody-secreting cells using phycoerythrin-conjugated antibodies: pitfalls and solutions

Antibody-secreting cells are terminally differentiated B cells that play a critical role in humoral immunity through immunoglobulin secretion along with possessing the potential to be long-lived. It is now appreciated that antibody-secreting cells regulate multiple aspects of biology through the secretion of various cytokines. In this regard, intracellular flow cytometry is a key tool used to assess the presence of intracellular proteins such as cytokines and transcription factors. Here, we showed that the use of phycoerythrin-containing antibody conjugates led to a false interpretation of antibody-secreting cell intracellular protein expression compared to other cell types. This was mainly due to the inappropriate retention of these antibodies specifically within antibody-secreting cells. Furthermore, we demonstrated how to reduce this retention which allowed for a more accurate comparison of intracellular protein expression between antibody-secreting cells and other cell types such as B lymphocytes. Using this methodology, our data revealed that spleen antibody-secreting cells expressed Toll-like receptor 7 as well as the pro-form of the inflammatory cytokine interleukin-1β.

Similar antibody responses against SARS-CoV-2 in HIV uninfected and infected individuals on antiretroviral therapy during the first South African infection wave

Background There is limited understanding of SARS-CoV-2 pathogenesis in African populations with a high burden of infectious disease comorbidities such as HIV. The kinetics, magnitude and duration of virus-specific antibodies and the underlying B cell responses in people living with HIV (PLWH) in sub-Saharan Africa have not been fully characterized. Methods We longitudinally followed SARS-CoV-2 infected individuals in Durban, KwaZulu-Natal, South Africa and characterized SARS-CoV-2 receptor binding domain-specific IgM, IgG and IgA antibodies weekly for a month, and then at 3 months post diagnosis. 7/30 (41.7%) were PLWH, 83% (25/30) of which were on ART and with full HIV suppression. Potency of convalescent plasma neutralization was determined using a live virus neutralization assay and antibody secreting cell population frequencies were determined by flow cytometry. Results Similar seroconversion rates, time to peak antibody titer, peak magnitude and durability of anti-SARS-CoV-2 IgM, IgG, IgA, were observed in HIV uninfected and PLWH with complete HIV suppression on ART. In addition, similar neutralization potency against an isolate of SARS-CoV-2, circulating at the time of sampling in the first wave of SARS-CoV-2 infections in South Africa was observed in both groups. Loss of IgA was significantly associated with age (p=0.023) and a previous diagnosis of TB (p=0.018). Conclusions Similar antibody response kinetics and neutralization potency in HIV negative and PLWH on stable ART in an African setting suggests that COVID-19 natural infections may confer comparable antibody immunity in these groups. This provides hope that COVID-19 vaccines will be effective in PLWH on stable ART.

Spatiotemporal Analysis of B Cell- and Antibody Secreting Cell-Subsets in Human Melanoma Reveals Metastasis-, Tumor Stage-, and Age-Associated Dynamics

Background: The role of tumor-associated B cells in human cancer is only starting to emerge. B cells typically undergo a series of developmental changes in phenotype and function, however, data on the composition of the B cell population in human melanoma are largely absent including changes during tumor progression and their potential clinical significance.Methods: In this study, we compared the number and distribution of six major B cell and antibody secreting cell subpopulations outside tertiary lymphoid structures in whole tumor sections of 154 human cutaneous melanoma samples (53 primary tumors without subsequent metastasis, 44 primary tumors with metastasis, 57 metastatic samples) obtained by seven color multiplex immunohistochemistry and automated tissue imaging and analysis.Results: In primary melanomas, we observed the highest numbers for plasmablast-like, memory-like, and activated B cell subtypes. These cells showed a patchy, predominant paratumoral distribution at the invasive tumor-stroma margin. Plasma cell-like cells were hardly detected, germinal center- and transitional/regulatory-like B cells not at all. Of the major clinicopathologic prognostic factors for primary melanomas, metastasis was associated with decreased memory-like B cell numbers and a higher age associated with higher plasmablast-like cell numbers. When we compared the composition of B cell subpopulations in primary melanomas and metastatic samples, we found a significantly higher proportion of plasma cell-like cells at distant metastatic sites and a higher proportion of memory-like B cells at locoregional than distant metastatic sites. Both cell types were detected mainly in the para- and intratumoral stroma.Conclusion: These data provide a first comprehensive and comparative spatiotemporal analysis of major B cell and antibody secreting cell subpopulations in human melanoma and describe metastasis-, tumor stage-, and age-associated dynamics, an important premise for B cell-related biomarker and therapy studies.

Early Emergence of Adaptive Mechanisms Sustaining Ig Production: Application to Antibody Therapy

Antibody therapy, where artificially-produced immunoglobulins (Ig) are used to treat pathological conditions such as auto-immune diseases and cancers, is a very innovative and competitive field. Although substantial efforts have been made in recent years to obtain specific and efficient antibodies, there is still room for improvement especially when considering a precise tissular targeting or increasing antigen affinity. A better understanding of the cellular and molecular steps of terminal B cell differentiation, in which an antigen-activated B cell becomes an antibody secreting cell, may improve antibody therapy. In this review, we use our recently published data about human B cell differentiation, to show that the mechanisms necessary to adapt a metamorphosing B cell to its new secretory function appear quite early in the differentiation process i.e., at the pre-plasmablast stage. After characterizing the molecular pathways appearing at this stage, we will focus on recent findings about two main processes involved in antibody production: unfolded protein response (UPR) and endoplasmic reticulum (ER) stress. We’ll show that many genes coding for factors involved in UPR and ER stress are induced at the pre-plasmablast stage, sustaining our hypothesis. Finally, we propose to use this recently acquired knowledge to improve productivity of industrialized therapeutic antibodies.

CRTC2 regulates plasma cell metabolism and survival

Antibody secreting cell (ASC) function and longevity determines the strength and durability of a humoral immune response. Previously, we identified the inactivation of the CREB-regulated transcriptional coactivator-2 (CRTC2) in an in vitro B cell differentiation assay that produced functional ASCs. However, the requirement for CRTC2 inactivation in ASC physiology in vivo remains unknown. Using transgenic (TG) mice that express a constitutively active form of CRTC2 (Crtc2-AA) as an experimental tool, we demonstrate that Crtc2 repression in plasma cells (PCs) is an intrinsic requirement for ASC metabolic fitness. Sustained CRTC2 activity shortens the survival of splenic and bone marrow PCs, resulting in reduced numbers of long-lived PCs and antibody deficits against T cell dependent and independent antigens, and an acute viral infection. TG PCs resemble short-lived PCs with reductions in glycolysis, oxidative metabolism, spare respiratory capacity, and antibody secretion. Mechanistically, Crtc2 repression is necessary for the fidelity of PC gene expression and mRNA alternative-splicing programs. Combined, Crtc2 repression in PCs must occur to support PC metabolism and extend ASC survival during a humoral immune response.

Robust immune responses after one dose of BNT162b2 mRNA vaccine dose in SARS-CoV-2 experienced individuals

ABSTRACTThe use of COVID-19 vaccines will play a major role in helping to end the pandemic that has killed millions worldwide. COVID-19 vaccine candidates have resulted in robust humoral responses and protective efficacy in human trials, but efficacy trials excluded individuals with prior diagnosis of COVID-19. As a result, little is known about how immune responses induced by mRNA vaccine candidates differ in individuals who recovered from COVID-19. Here, we evaluated longitudinal immune responses to two-dose BNT162b2 mRNA vaccination in 13 adults who recovered from COVID-19, compared to 19 adults who did not have prior COVID-19 diagnosis. Consistent with prior studies of mRNA vaccines, we observed robust cytotoxic CD8 T cell responses in both cohorts. Furthermore, SARS-CoV-2-naive individuals had progressive increases in humoral and antigen-specific antibody-secreting cell (ASC) responses following each dose of vaccine, whereas SARS-CoV-2-experienced individuals demonstrated strong humoral and antigen-specific ASC responses to the first dose but muted responses to the second dose of the vaccine for the time points studied. Together, these data highlight the relevance of immunological history for understanding vaccine immune responses and may have significant implications for personalizing mRNA vaccination regimens used to prevent COVID-19.One Sentence SummaryPrior history of COVID-19 affects adaptive immune responses to mRNA vaccination.

HIV infection alters SARS-CoV-2 responsive immune parameters but not clinical outcomes in COVID-19 disease

HIV infection alters the immune response and can compromise protective immunity to multiple pathogens following vaccination. We investigated the impact of HIV on the immune response to SARS-CoV-2 using longitudinal samples from 124 participants from KwaZulu-Natal, South Africa, an area of extremely high HIV prevalence. 44% of participants were people living with HIV (PLWH) and commonly had other co-morbidities, including obesity, hypertension, and diabetes. The majority of PLWH but not HIV negative participants showed CD8 T cell expansion above the normal range post-SARS-CoV-2. Yet, in participants with HIV suppressed by antiretroviral therapy (ART), CD8 expansion was associated with milder COVID-19 disease. There were multiple differences in T cell, B cell, and natural killer cell correlations in PLWH compared to HIV negative participants, including lower tissue homing CXCR3+ CD8 T cells in the presence of SARS-CoV-2 RNA in PLWH but not HIV negative and a pronounced early antibody secreting cell (ASC) expansion in HIV negative but not PLWH. These changes were COVID-19 associated: low CXCR3 correlated with increased COVID-19 disease severity across groups, and high ASC correlated with increased disease severity in HIV negative participants and waned when SARS-CoV-2 was cleared. Despite the altered response of immune cell subsets, COVID-19 disease in PLWH was mostly mild and similar to HIV negative participants. This likely reflects the heterogeneity of an effective COVID-19 immune response. Whether the differences in immune cell dynamics in PLWH will lead to different long-term consequences or compromise vaccination is yet to be determined.

Maturation and persistence of the anti-SARS-CoV-2 memory B cell response

Memory B cells play a fundamental role in host defenses against viruses, but to date, their role have been relatively unsettled in the context of SARS-CoV-2. We report here a longitudinal single-cell and repertoire profiling of the B cell response up to 6 months in mild and severe COVID-19 patients. Distinct SARS-CoV-2 Spike-specific activated B cell clones fueled an early antibody-secreting cell burst as well as a durable synchronous germinal center response. While highly mutated memory B cells, including preexisting cross-reactive seasonal Betacoronavirus-specific clones, were recruited early in the response, neutralizing SARS-CoV-2 RBD-specific clones accumulated with time and largely contributed to the late remarkably stable memory B-cell pool. Highlighting germinal center maturation, these cells displayed clear accumulation of somatic mutations in their variable region genes over time. Overall, these findings demonstrate that an antigen-driven activation persisted and matured up to 6 months after SARS-CoV-2 infection and may provide long-term protection.