Naïve and memory B cells in the rhesus macaque can be differentiated by surface expression of CD27 and have differential responses to CD40 ligation

Desensitization and belatacept-based maintenance therapy in pregnancy-sensitized monkeys receiving a kidney transplant

Among sensitized patients awaiting a transplant, females are disproportionately represented, partly because of pregnancy-induced sensitization. Using female NHPs sensitized by pregnancy alone, we examined the efficacy of costimulation blockade and proteasome inhibition for desensitization. Three animals received no desensitization (control), and seven animals received weekly carfilzomib (27 mg/m2) and belatacept (20 mg/kg) before kidney transplantation. All animals received renal allografts from crossmatch-positive/maximally MHC-mismatched donors. Controls and three desensitized animals received tacrolimus-based immunosuppression. Four desensitized animals received additional belatacept with tacrolimus-based immunosuppression. Multiparous females had less circulating donor-specific antibody when compared to skin-sensitized males before transplantation. While females receiving desensitization showed only a marginal survival benefit over control females (MST = 11 days versus 63 days), additional belatacept to posttransplant maintenance significantly prolonged graft survival (MST > 164 days) and suppressed posttransplant DSA and circulating follicular helper T-like cells. This combination of therapies demonstrates great potential to reduce antibody-mediated rejection in sensitized recipients.

Limited access to antigen drives generation of early B cell memory while restraining the plasmablast response

Cell fate decisions during early B cell activation determine the outcome of responses to pathogens and vaccines. We examined the early B cell response to T-dependent antigen in mice by single-cell RNA sequencing. Early after immunization, a homogeneous population of activated precursors (APs) gave rise to a transient wave of plasmablasts (PBs), followed a day later by the emergence of germinal center B cells (GCBCs). Most APs rapidly exited the cell cycle, giving rise to non-GC-derived early memory B cells (eMBCs) that retained an AP-like transcriptional profile. Rapid decline of antigen availability controlled these events; provision of excess antigen precluded cell cycle exit and induced a new wave of PBs. Fate mapping revealed a prominent contribution of eMBCs to the MBC pool. Quiescent cells with an MBC phenotype dominated the early response to immunization in primates. A reservoir of APs/eMBCs may enable rapid readjustment of the immune response when failure to contain a threat is manifested by increased antigen availability.

Long-Term Recovery of the Adaptive Immune System in Rhesus Macaques After Total Body Irradiation

PURPOSE

Ionizing radiation causes acute damage to hematopoietic and immune cells, but the long-term immunologic consequences of irradiation are poorly understood. We therefore performed a prospective study of the delayed immune effects of radiation using a rhesus macaque model.

METHODS AND MATERIALS

Ten macaques received 4 Gy high-energy x-ray total body irradiation (TBI) and 6 control animals received sham irradiation. TBI caused transient lymphopenia that resolved over several weeks. Once white blood cell counts recovered, flow cytometry was used to immunophenotype the circulating adaptive immune cell populations 4, 9, and 21 months after TBI. Data were fit using a mixed-effects model to determine age-dependent, radiation-dependent, and interacting effects. T cell receptor (TCR) sequencing and quantification of TCR Excision Circles were used to determine relative contributions of thymopoiesis and peripheral expansion to T cell repopulation. Two years after TBI, the cohort was vaccinated with a 23-valent pneumococcal polysaccharide vaccine and a tetravalent influenza hemagglutinin vaccine.

RESULTS

Aging, but not TBI, led to significant changes in the frequencies of dendritic cells, CD4 and CD8 T cells, and B cells. However, irradiated animals exhibited increased frequencies of central memory T cells and decreased frequencies of naïve T cells. These consequences of irradiation were time-dependent and more prolonged in the CD8 T cell population. Irradiation led to transient increases in CD8+ T cell TCR Excision Circles and had no significant effect on TCR sequence entropy, indicating T cell recovery was partially mediated by thymopoiesis. Animals that were irradiated and then vaccinated showed normal immunoglobulin G binding and influenza neutralization titers in response to the 4 protein antigens but weaker immunoglobulin G binding titers to 10 of the 23 polysaccharide antigens.

CONCLUSIONS

These findings indicate that TBI causes subtle but long-lasting immune defects that are evident years after recovery from lymphopenia.

TFH Cells Induced by Vaccination and Following SIV Challenge Support Env-Specific Humoral Immunity in the Rectal-Genital Tract and Circulation of Female Rhesus Macaques

T follicular helper (T_FH) cells are pivotal in lymph node (LN) germinal center (GC) B cell affinity maturation. Circulating CXCR5⁺ CD4⁺ T (cT_FH) cells have supported memory B cell activation and broadly neutralizing antibodies in HIV controllers. We investigated the contribution of LN SIV-specific T_FH and cT_FH cells to Env-specific humoral immunity in female rhesus macaques following a mucosal Ad5hr-SIV recombinant priming and SIV gp120 intramuscular boosting vaccine regimen and following SIV vaginal challenge. T_FH and B cells were characterized by flow cytometry. B cell help was evaluated in T_FH-B cell co-cultures and by real-time PCR. Vaccination induced Env-specific T_FH and Env-specific memory (ESM) B cells in LNs. LN Env-specific T_FH cells post-priming and GC ESM B cells post-boosting correlated with rectal Env-specific IgA titers, and GC B cells at the same timepoints correlated with vaginal Env-specific IgG titers. Vaccination expanded cT_FH cell responses, including CD25⁺ Env-specific cT_FH cells that correlated negatively with vaginal Env-specific IgG titers but positively with rectal Env-specific IgA titers. Although cT_FH cells post-2^nd boost positively correlated with viral-loads following SIV challenge, cT_FH cells of SIV-infected and protected macaques supported maturation of circulating B cells into plasma cells and IgA release in co-culture. Additionally, cT_FH cells of naïve macaques promoted upregulation of genes associated with B cell proliferation, BCR engagement, plasma cell maturation, and antibody production, highlighting the role of cT_FH cells in blood B cell maturation. Vaccine-induced LN T_FH and GC B cells supported anti-viral mucosal immunity while cT_FH cells provided B cell help in the periphery during immunization and after SIV challenge. Induction of T_FH responses in blood and secondary lymphoid organs is likely desirable for protective efficacy of HIV vaccines.

TLR7 agonists induce transient viremia and reduce the viral reservoir in SIV-infected rhesus macaques on antiretroviral therapy

Antiretroviral therapy (ART) can halt HIV-1 replication but fails to target the long-lived latent viral reservoir. Several pharmacological compounds have been evaluated for their ability to reverse HIV-1 latency, but none has demonstrably reduced the latent HIV-1 reservoir or affected viral rebound after the interruption of ART. We evaluated orally administered selective Toll-like receptor 7 (TLR7) agonists GS-986 and GS-9620 for their ability to induce transient viremia in rhesus macaques infected with simian immunodeficiency virus (SIV) and treated with suppressive ART. In an initial dose-escalation study, and a subsequent dose-optimization study, we found that TLR7 agonists activated multiple innate and adaptive immune cell populations in addition to inducing expression of SIV RNA. We also observed TLR7 agonist-induced reductions in SIV DNA and measured inducible virus from treated animals in ex vivo cell cultures. In a second study, after stopping ART, two of nine treated animals remained aviremic for more than 2 years, even after in vivo CD8+ T cell depletion. Moreover, adoptive transfer of cells from aviremic animals could not induce de novo infection in naïve recipient macaques. These findings suggest that TLR7 agonists may facilitate reduction of the viral reservoir in a subset of SIV-infected rhesus macaques.

Pilot Study of Delayed ICOS/ICOS-L Blockade With αCD40 to Modulate Pathogenic Alloimmunity in a Primate Cardiac Allograft Model

Supplemental digital content is available in the text.

Background

Inducible costimulator (ICOS) is rapidly upregulated with T-cell stimulation and may represent an escape pathway for T-cell costimulation in the setting of CD40/CD154 costimulation blockade. Induction treatment exhibited no efficacy in a primate renal allograft model, but rodent transplant models suggest that the addition of delayed ICOS/ICOS-L blockade may prolong allograft survival and prevent chronic rejection. Here, we ask whether ICOS-Ig treatment, timed to anticipate ICOS upregulation, prolongs NHP cardiac allograft survival or attenuates pathogenic alloimmunity.

Methods

Cynomolgus monkey heterotopic cardiac allograft recipients were treated with αCD40 (2C10R4, d0-90) either alone or with the addition of delayed ICOS-Ig (d63-110).

Results

Median allograft survival was similar between ICOS-Ig + αCD40 (120 days, 120-125 days) and αCD40 (124 days, 89-178 days) treated animals, and delayed ICOS-Ig treatment did not prevent allograft rejection in animals with complete CD40 receptor coverage. Although CD4⁺ T_EM cells were decreased in peripheral blood (115 ± 24) and mLNs (49 ± 1.9%) during ICOS-Ig treatment compared with monotherapy (214 ± 27%, P = 0.01; 72 ± 9.9%, P = 0.01, respectively), acute and chronic rejection scores and kinetics of alloAb elaboration were similar between groups.

Conclusions

Delayed ICOS-Ig treatment with the reagent tested is probably ineffective in modulating pathogenic primate alloimmunity in this model.

Comparative Evaluation of αCD40 (2C10R4) and αCD154 (5C8H1 and IDEC-131) in a Nonhuman Primate Cardiac Allotransplant Model

BACKGROUND

Specific blockade of T cell costimulation pathway is a promising immunomodulatory approach being developed to replace our current clinical immunosuppression therapies. The goal of this study is to compare results associated with 3 monoclonal antibodies directed against the CD40/CD154 T cell costimulation pathway.

METHODS

Cynomolgus monkey heterotopic cardiac allograft recipients were treated with either IDEC-131 (humanized αCD154, n = 9), 5C8H1 (mouse-human chimeric αCD154, n = 5), or 2C10R4 (mouse-rhesus chimeric αCD40, n = 6) monotherapy using a consistent, comparable dosing regimen for 3 months after transplant.

RESULTS

Relative to the previously reported IDEC-131-treated allografts, median survival time (35 ± 31 days) was significantly prolonged in both 5C8H1-treated (142 ± 26, P < 0.002) and 2C10R4-treated (124 ± 37, P < 0.020) allografts. IDEC-131-treated grafts had higher cardiac allograft vasculopathy severity scores during treatment relative to either 5C8H1 (P = 0.008) or 2C10R4 (P = 0.0002). Both 5C8H1 (5 of 5 animals, P = 0.02) and 2C10R4 (6/6, P = 0.007), but not IDEC-131 (2/9), completely attenuated IgM antidonor alloantibody (alloAb) production during treatment; 5C8H1 (5/5) more consistently attenuated IgG alloAb production compared to 2C10R4 (4/6) and IDEC-131 (0/9). All evaluable explanted grafts experienced antibody-mediated rejection. Only 2C10R4-treated animals exhibited a modest, transient drop in CD20 lymphocytes from baseline at day 14 after transplant (-457 ± 152 cells/μL) compared with 5C8H1-treated animals (16 ± 25, P = 0.037), and the resurgent B cells were primarily of a naive phenotype.

CONCLUSIONS

In this model, CD154/CD40 axis blockade using IDEC-131 is an inferior immunomodulatory treatment than 5C8H1 or 2C10R4, which have similar efficacy to prolong graft survival and to delay cardiac allograft vasculopathy development and antidonor alloAb production during treatment.

Zika viral dynamics and shedding in rhesus and cynomolgus macaques

Infection with Zika virus has been associated with serious neurological complications and fetal abnormalities. However, the dynamics of viral infection, replication and shedding are poorly understood. Here we show that both rhesus and cynomolgus macaques are highly susceptible to infection by lineages of Zika virus that are closely related to, or are currently circulating in, the Americas. After subcutaneous viral inoculation, viral RNA was detected in blood plasma as early as 1 d after infection. Viral RNA was also detected in saliva, urine, cerebrospinal fluid (CSF) and semen, but transiently in vaginal secretions. Although viral RNA during primary infection was cleared from blood plasma and urine within 10 d, viral RNA was detectable in saliva and seminal fluids until the end of the study, 3 weeks after the resolution of viremia in the blood. The control of primary Zika virus infection in the blood was correlated with rapid innate and adaptive immune responses. We also identified Zika RNA in tissues, including the brain and male and female reproductive tissues, during early and late stages of infection. Re-infection of six animals 45 d after primary infection with a heterologous strain resulted in complete protection, which suggests that primary Zika virus infection elicits protective immunity. Early invasion of Zika virus into the nervous system of healthy animals and the extent and duration of shedding in saliva and semen underscore possible concern for additional neurologic complications and nonarthropod-mediated transmission in humans.

Reduced expression of CD27 by collagenase treatment: implications for interpreting b cell data in tissues

Surface markers have been used to identify distinct cell subpopulations and to delineate various stages of maturation or activation of lymphocytes. In particular CD27 is used for delineation of naïve and memory B cell populations, and is readily detected by flow cytometry. We here used flow cytometry to examine the expression of CD27 on lymphocytes isolated from various tissues of rhesus macaques, and found its expression was consistently low to absent on intestinal cell suspensions. However, immunohistochemistry revealed abundant CD27+ cells in intestinal tissue sections. Further investigation showed the marked loss of CD27 expression on processed intestinal cells was due to collagenase digestion of intestinal tissues, yet CD27 expression was recoverable within hours of cell isolation. By combining confocal microscopy, we confirmed that only a fraction of B cells express CD27, in contrast to expression on all T cells from tissues examined including the gut. Taken together, our results suggest that CD27 may be a memory marker for B cells, but not for T cells, since essentially all CD3 T cells expressed CD27. In summary, it is important to consider the influence of isolation procedures on cell surface expression of phenotypic markers, especially when examining tissue-resident lymphocytes by flow cytometry.

Inhibition of protein geranylgeranylation specifically interferes with CD40-dependent B cell activation, resulting in a reduced capacity to induce T cell immunity

Ab-independent effector functions of B cells, such as Ag presentation and cytokine production, have been shown to play an important role in a variety of immune-mediated conditions such as autoimmune diseases, transplant rejection, and graft-versus-host disease. Most current immunosuppressive treatments target T cells, are relatively unspecific, and result in profound immunosuppression that places patients at an increased risk of developing severe infections and cancer. Therapeutic strategies, which interfere with B cell activation, could therefore be a useful addition to the current immunosuppressive armamentarium. Using a transcriptomic approach, we identified upregulation of genes that belong to the mevalonate pathway as a key molecular event following CD40-mediated activation of B cells. Inhibition of 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme of the mevalonate pathway, by lipophilic statins such as simvastatin and atorvastatin resulted in a specific inhibition of B cell activation via CD40 and impaired their ability to act as stimulatory APCs for allospecific T cells. Mechanistically, the inhibitory effect resulted from the inhibition of protein geranylgeranylation subsequent to the depletion of mevalonate, the metabolic precursor for geranylgeranyl. Thus, inhibition of geranylgeranylation either directly through geranylgeranyl transferase inhibitors or indirectly through statins represents a promising therapeutic approach for the treatment of diseases in which Ag presentation by B cells plays a role.

Primate B-1 cells generate antigen-specific B cell responses to T cell-independent type 2 antigens

Ab responses to T cell-independent type 2 (TI-2) Ags, such as bacterial capsular polysaccharides, are critical for host defense. In mice, B-1b cells expressing a CD11b(+)FSC(hi)CD21(lo/-)CD19(hi) phenotype play a key role in producing Abs against TI-2 Ags. In primates, a distinct IgM(+)CD27(+) "memory" B cell population is thought to generate TI-2 Ab responses, and evidence for a B-1b-like cell population participating in these responses is lacking. In this article, we demonstrate that nonhuman primates (NHPs; African green monkeys and cynomolgus macaques) harbor serosal B cells expressing a CD11b(+)FSC(hi)CD21(lo/-)CD80(+/-)CD19(hi) phenotype, constitutively active Stat3, and increased reactivity with phosphorylcholine, similar to murine peritoneal B-1a and B-1b cell populations. Like what is observed for murine B-1b cells, NHP CD11b(+)FSC(hi)CD21(lo/-)CD19(hi) B cells dominate the Ag-specific B cell response and Ab production against the TI-2 Ag trinitrophenyl-Ficoll. Although Ag-specific IgM(+) B cells expressing CD27 were not detected prior to immunization, Ag-specific CD11b(+)CD19(hi) B cells expressed and maintained an IgM(+)IgD(lo)CD27(+)CD80(+) phenotype following immunization. Thus, the murine and NHP B cell populations responding to trinitrophenyl-Ficoll are highly similar, with the main exception being that Ag-specific NHP B-1-like cells express CD27 following TI-2 Ag encounter. Therefore, murine B-1b and primate IgM(+)CD27(+) "memory" B cell subsets proposed to produce TI-2 Ab responses may be highly related, if not identical. Overall, these data not only support that B-1-like cells are present in NHPs but also provide evidence that these cells perform the same functions attributed to murine B-1b cells.

Flow cytometry: a flexible tool for biomarker research

Flow cytometry is increasingly recognized as an invaluable technology in biomarker research. Owing to its multiparametric nature it can provide highly detailed information on any single cell in a heterogeneous population. Its versatility means it can be conducted in both the preclinical and clinical setting, generating biomarker data that can drive decisions pertaining to dose selection in clinical trials, treatment options for cancer sufferers and even suitability of patients to receive transplants. Most tissue types can be utilized by the flow cytometrist, allowing the technology to be applied to many fields of research, yet consensus still needs to be reached on standardization, regulation and validation of multiparametric flow cytometry assays. In parallel, continual innovation in analysis software to manage the huge datasets that can be generated is also needed. Nevertheless, the flexibility of flow cytometry means that it remains at the forefront of both routine and exploratory biomarker studies.

Isolation of antibody V(D)J sequences from single cell sorted rhesus macaque B cells

Studies in nonhuman primates offer information of high relevance to clinical medicine due to their close genetic relationship with humans. Here, we established an optimized protocol for the isolation of antibody V(D)J sequences from rhesus macaque B cells. Nested PCR primers were designed to align to sequences flanking the V(D)J coding region to enable amplification of highly mutated antibody sequences. The primers were evaluated using cDNA from bulk PBMCs as well as from single-sorted memory and naïve B cells from several macaques to ascertain effective germline coverage. The nested PCR efficiency reached 60.6% positive wells for heavy chain amplification, 39.2% for kappa chain, and 23.7% for lambda chain sequences. Matching heavy and light chain sequences, indicating antibodies that potentially can be cloned, were obtained in 50% of the positive wells. Using these primers, we found that the efficiency and specificity of V(D)J amplifications were markedly improved compared to when primers designed for human Ab isolation were used. In particular, the amplification of recombined light chain VJ sequences was improved. Thus, we describe the design and testing of a new set of rhesus-specific primers that enable efficient and specific amplification of heavy, kappa and lambda V(D)J genes from single sorted B cells. The use of these primers will facilitate future efforts to clone and express rhesus macaque MAbs for genetic, functional and structural analyses.

Human and rhesus plasmacytoid dendritic cell and B-cell responses to Toll-like receptor stimulation

Interferon-α (IFN-α) produced at high levels by human plasmacytoid dendritic cells (pDCs) can specifically regulate B-cell activation to Toll-like receptor (TLR) 7/8 stimulation. To explore the influence of IFN-α and pDCs on B-cell functions in vivo, studies in non-human primates that closely resemble humans in terms of TLR expression on different subsets of immune cells are valuable. Here, we performed a side-by side comparison of the response pattern between human and rhesus macaque B cells and pDCs in vitro to well-defined TLR ligands and tested whether IFN-α enhanced B-cell function comparably. We found that both human and rhesus B cells proliferated while pDCs from both species produced high levels of IFN-α in response to ligands targeting TLR7/8 and TLR9. Both human and rhesus B-cell proliferation to TLR7/8 ligand and CpG class C was significantly increased in the presence of IFN-α. Although both human and rhesus B cells produced IgM upon stimulation, only human B cells acquired high expression of CD27 associated with plasmablast formation. Instead, rhesus B-cell differentiation and IgM levels correlated to down-regulation of CD20. These data suggest that the response pattern of human and rhesus B cells and pDCs to TLR7/8 and TLR9 is similar, although some differences in the cell surface phenotype of the differentiating cells exist. A more thorough understanding of potential similarities and differences between human and rhesus cells and their response to potential vaccine components will provide important information for translating non-human primate studies into human trials.

Alterations in peripheral blood B-cell populations in SHIV89.6P-infected macaques (Macacca fascicularis)

In addition to CD4+ T cell depletion, the B cell compartment of HIV-infected patients exhibits abnormalities, including deficits and diminished responses to ex vivo antigenic stimulation and in vivo vaccination. We used chimeric simian-human immunodeficiency virus (SHIV) infection of cynomolgus macaques to determine the dynamics of peripheral blood B cell alterations in this model of HIV infection. During the course of infection, we observed progressive loss of total and memory (CD27+) B cells, increased percentages of activated (CD95+) B cells, hypergammaglobulinemia, and deficits in the CD21+ B cell population. In addition, we noted declines in subsets of memory B cells, including both IgM+ and class-switched (IgD-IgM- CD27+) cells, with sustained deficits in the IgM+ memory (IgM+CD27+) B cell population. The similarity of the B cell alterations in these studies to those observed in HIV+ subjects supports the utility of the SHIV macaque model for examination of HIV-related B cell dysfunction.

Vaccine-elicited SIV and HIV envelope-specific IgA and IgG memory B cells in rhesus macaque peripheral blood correlate with functional antibody responses and reduced viremia

An effective HIV vaccine requires strong systemic and mucosal, cellular and humoral immunity. Numerous non-human primate studies have investigated memory T cells, but not memory B cells. Humoral immunologic memory is mediated by long-lived antibody-secreting plasma cells and differentiation of memory B cells into short-lived plasma blasts following re-exposure to immunizing antigen. Here we studied memory B cells in vaccinated rhesus macaques. PBMC were stimulated polyclonally using CD40 Ligand, IL-21 and CpG to induce B cell proliferation and differentiation into antibody secreting cells (ASCs). Flow cytometry was used for phenotyping and evaluating proliferation by CFSE dilution. B cell responses were quantified by ELISPOT. Methodology was established using PBMC of vaccinated elite-controller macaques that exhibited strong, multi-functional antibody activities. Subsequently, memory B cells elicited by two replicating Ad-recombinant prime/envelope boost regimens were retrospectively evaluated pre- and post-SIV and SHIV challenges. The vaccine regimens induced SIV and HIV Env-specific IgG and IgA memory B cells. Prior to challenge, IgA memory B cells were more numerous than IgG memory B cells, reflecting the mucosal priming immunizations. Pre- and post-challenge memory B cells were correlated with functional antibody responses including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cell-mediated viral inhibition (ADCVI) and transcytosis inhibition. Post-challenge, Env-specific IgG and IgA memory B cells were correlated with reduced chronic viremia. We conclude that functional antibody responses elicited by our prime/boost regimen were effectively incorporated into the memory B cell pool where they contributed to control of viremia following re-exposure to the immunizing antigen.