The immunogenicity of an HIV-1 Gag conserved element DNA vaccine in people with HIV and receiving antiretroviral therapy

OBJECTIVE

The primary objective of the study was to assess the immunogenicity of an HIV-1 Gag conserved element DNA vaccine (p24CE DNA) in people with HIV (PWH) receiving suppressive antiretroviral therapy (ART).

DESIGN

AIDS Clinical Trials Group A5369 was a phase I/IIa, randomized, double-blind, placebo-controlled study of PWH receiving ART with plasma HIV-1 RNA less than 50 copies/ml, current CD4 + T-cell counts greater than 500 cells/μl, and nadir CD4 + T-cell counts greater than 350 cells/μl.

METHODS

The study enrolled 45 participants randomized 2 : 1 : 1 to receive p24CE DNA vaccine at weeks 0 and 4, followed by p24CE DNA admixed with full-length p55 Gag DNA vaccine at weeks 12 and 24 (arm A); full-length p55 Gag DNA vaccine at weeks 0, 4, 12, and 24 (arm B); or placebo at weeks 0, 4, 12, and 24 (arm C). The active and placebo vaccines were administered by intramuscular electroporation.

RESULTS

There was a modest, but significantly greater increase in the number of conserved elements recognized by CD4 + and/or CD8 + T cells in arm A compared with arm C ( P  = 0.014). The percentage of participants with an increased number of conserved elements recognized by T cells was also highest in arm A (8/18, 44.4%) vs. arm C (0/10, 0.0%) ( P  = 0.025). There were no significant differences between treatment groups in the change in magnitude of responses to total conserved elements.

CONCLUSION

A DNA-delivered HIV-1 Gag conserved element vaccine boosted by a combination of this vaccine with a full-length p55 Gag DNA vaccine induced a new conserved element-directed cellular immune response in approximately half the treated PWH on ART.

Rapid transient and longer-lasting innate cytokine changes associated with adaptive immunity after repeated SARS-CoV-2 BNT162b2 mRNA vaccinations

Introduction

Cytokines and chemokines play an important role in shaping innate and adaptive immunity in response to infection and vaccination. Systems serology identified immunological parameters predictive of beneficial response to the BNT162b2 mRNA vaccine in COVID-19 infection-naïve volunteers, COVID-19 convalescent patients and transplant patients with hematological malignancies. Here, we examined the dynamics of the serum cytokine/chemokine responses after the 3rd BNT162b2 mRNA vaccination in a cohort of COVID-19 infection-naïve volunteers.

Methods

We measured serum cytokine and chemokine responses after the 3rd dose of the BNT162b2 mRNA (Pfizer/BioNtech) vaccine in COVID-19 infection-naïve individuals by a chemiluminescent assay and ELISA. Anti-Spike binding antibodies were measured by ELISA. Anti-Spike neutralizing antibodies were measured by a pseudotype assay.

Results

Comparison to responses found after the 1st and 2nd vaccinations showed persistence of the coordinated responses of several cytokine/chemokines including the previously identified rapid and transient IL-15, IFN-γ, CXCL10/IP-10, TNF-α, IL-6 signature. In contrast to the transient (24hrs) effect of the IL-15 signature, an inflammatory/anti-inflammatory cytokine signature (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β, CXCL8/IL-8, IL-1Ra) remained at higher levels up to one month after the 2nd and 3rd booster vaccinations, indicative of a state of longer-lasting innate immune change. We also identified a systemic transient increase of CXCL13 only after the 3rd vaccination, supporting stronger germinal center activity and the higher anti-Spike antibody responses. Changes of the IL-15 signature, and the inflammatory/anti-inflammatory cytokine profile correlated with neutralizing antibody levels also after the 3rd vaccination supporting their role as immune biomarkers for effective development of vaccine-induced humoral responses.

Conclusion

These data revealed that repeated SARS-Cov-2 BNT162b2 mRNA vaccination induces both rapid transient as well as longer-lasting systemic serum cytokine changes associated with innate and adaptive immune responses.

Clinical trial registration

Clinicaltrials.gov, identifier NCT04743388.

First-in-human phase I/Ib study of NIZ985, a recombinant heterodimer of IL-15 and IL-15Rα, as a single agent and in combination with spartalizumab in patients with advanced and metastatic solid tumors

BACKGROUND

Preclinically, interleukin-15 (IL-15) monotherapy promotes antitumor immune responses, which are enhanced when IL-15 is used in combination with immune checkpoint inhibitors (ICIs). This first-in-human study investigated NIZ985, a recombinant heterodimer comprising physiologically active IL-15 and IL-15 receptor α, as monotherapy and in combination with spartalizumab, an anti-programmed cell death protein-1 (anti-PD-1) monoclonal antibody, in patients with advanced solid tumors.

METHODS

This phase I/Ib study had two dose-escalation arms: single-agent NIZ985 administered subcutaneously thrice weekly (TIW, 2 weeks on/2 weeks off) or once weekly (QW, 3 weeks on/1 week off), and NIZ985 TIW or QW administered subcutaneously plus spartalizumab (400 mg intravenously every 4 weeks (Q4W)). The dose-expansion phase investigated NIZ985 1 µg/kg TIW/spartalizumab 400 mg Q4W in patients with anti-PD-1-sensitive or anti-PD-1-resistant tumor types stratified according to approved indications. The primary objectives were the safety, tolerability, and the maximum tolerated doses (MTDs) and/or recommended dose for expansion (RDE) of NIZ985 for the dose-expansion phase.

RESULTS

As of February 17, 2020, 83 patients (median age: 63 years; range: 28-85) were treated in dose escalation (N=47; single-agent NIZ985: n=27; NIZ985/spartalizumab n=20) and dose expansion (N=36). No dose-limiting toxicities occurred nor was the MTD identified. The most common treatment-related adverse event (TRAE) was injection site reaction (primarily grades 1-2; single-agent NIZ985: 85% (23/27)); NIZ985/spartalizumab: 89% [50/56]). The most common grade 3-4 TRAE was decreased lymphocyte count (single-agent NIZ985: 7% [2/27]; NIZ985/spartalizumab: 5% [3/56]). The best overall response was stable disease in the single-agent arm (30% (8/27)) and partial response in the NIZ985/spartalizumab arm (5% [3/56]; melanoma, pancreatic cancer, gastric cancer). In dose expansion, the disease control rate was 45% (5/11) in the anti-PD-1-sensitive and 20% (5/25) in the anti-PD-1-resistant tumor type cohorts. Pharmacokinetic parameters were similar across arms. The transient increase in CD8+ T cell and natural killer cell proliferation and induction of several cytokines occurred in response to the single-agent and combination treatments.

CONCLUSIONS

NIZ985 was well tolerated in the single-agent and NIZ985/spartalizumab regimens. The RDE was established at 1 µg/kg TIW. Antitumor activity of the combination was observed against tumor types known to have a poor response to ICIs.

TRIAL REGISTRATION NUMBER

NCT02452268.

Tumor eradication by hetIL-15 locoregional therapy correlates with an induced intratumoral CD103intCD11b+ dendritic cell population

Locoregional monotherapy with heterodimeric interleukin (IL)-15 (hetIL-15) in a triple-negative breast cancer (TNBC) orthotopic mouse model resulted in tumor eradication in 40% of treated mice, reduction of metastasis, and induction of immunological memory against breast cancer cells. hetIL-15 re-shaped the tumor microenvironment by promoting the intratumoral accumulation of cytotoxic lymphocytes, conventional type 1 dendritic cells (cDC1s), and a dendritic cell (DC) population expressing both CD103 and CD11b markers. These CD103intCD11b+DCs share phenotypic and gene expression characteristics with both cDC1s and cDC2s, have transcriptomic profiles more similar to monocyte-derived DCs (moDCs), and correlate with tumor regression. Therefore, hetIL-15, a cytokine directly affecting lymphocytes and inducing cytotoxic cells, also has an indirect rapid and significant effect on the recruitment of myeloid cells, initiating a cascade for tumor elimination through innate and adoptive immune mechanisms. The intratumoral CD103intCD11b+DC population induced by hetIL-15 may be targeted for the development of additional cancer immunotherapy approaches.

Efficient ex vivo expansion of conserved element vaccine-specific CD8+ T-cells from SHIV-infected, ART-suppressed nonhuman primates

HIV-specific T cells are necessary for control of HIV-1 replication but are largely insufficient for viral clearance. This is due in part to these cells' recognition of immunodominant but variable regions of the virus, which facilitates viral escape via mutations that do not incur viral fitness costs. HIV-specific T cells targeting conserved viral elements are associated with viral control but are relatively infrequent in people living with HIV (PLWH). The goal of this study was to increase the number of these cells via an ex vivo cell manufacturing approach derived from our clinically-validated HIV-specific expanded T-cell (HXTC) process. Using a nonhuman primate (NHP) model of HIV infection, we sought to determine i) the feasibility of manufacturing ex vivo-expanded virus-specific T cells targeting viral conserved elements (CE, CE-XTCs), ii) the in vivo safety of these products, and iii) the impact of simian/human immunodeficiency virus (SHIV) challenge on their expansion, activity, and function. NHP CE-XTCs expanded up to 10-fold following co-culture with the combination of primary dendritic cells (DCs), PHA blasts pulsed with CE peptides, irradiated GM-K562 feeder cells, and autologous T cells from CE-vaccinated NHP. The resulting CE-XTC products contained high frequencies of CE-specific, polyfunctional T cells. However, consistent with prior studies with human HXTC and these cells' predominant CD8+ effector phenotype, we did not observe significant differences in CE-XTC persistence or SHIV acquisition in two CE-XTC-infused NHP compared to two control NHP. These data support the safety and feasibility of our approach and underscore the need for continued development of CE-XTC and similar cell-based strategies to redirect and increase the potency of cellular virus-specific adaptive immune responses.

Abstract 5082: Heterodimeric IL-15 (hetIL-15) immunotherapy synergizes with Fatty Acid Metabolism Modulator (FAMM) to eradicate TNBC EO771 murine tumors

Introduction: Metabolic fitness and T cell survival are crucial in anti-tumor responses because nutrients are often scarce and other regulatory molecules may be unfavorable in the tumor microenvironment leading to T cell dysfunction, stress, and apoptosis. Tumor-infiltrating cytotoxic CD8+T cells frequently acquire an altered state of differentiation referred to as “exhaustion” and, as a result, they fail to control tumor outgrowth. IL-15 cytokine stimulates the generation, proliferation and cytotoxic function of tumor specific CD8+ T cells and NK cells. The objective of this study was to assess the effects of hetIL-15 immunotherapy in triple negative breast cancer tumors (TNBC), to evaluate the metabolic profile of the tumor-infiltrating T cells and to study any potential synergy using a Fatty Acid Metabolism Modulator (FAMM) to enhance T cell metabolism.

Study design and methods: We used the murine EO771 orthotopic breast cancer model to study the efficacy of locoregional administration of hetIL-15 immunotherapy in combination with a FAMM. We monitored the effect of treatment on number, metabolism and mitochondrial function of the tumor-infiltrating immune cells by flow cytometry, Seahorse flux analysis and Mitotracker, 2-NBDG and/or Bodipy staining.

Results: hetIL-15 locoregional administration, as as single agent, resulted in complete regression in 40% of the treated animals and increased survival. Tumor-infiltrating cytotoxic CD8+T and NK cells increased in hetIL-15 treated tumors and showed enhanced activation and proliferation. Metabolic flux analysis of the tumor-infiltrating cytotoxic CD8+T cells from hetIL-15-treated mice confirmed a rise in oxygen consumption rate (OCR) with substantial increase of spare respiratory capacity, which supports an activated/non exhausted phenotype of these hetIL-15 treated effector cells. Since, further promoting fatty acid (FA) catabolism improves the tumor-infiltrated CD8+T cells’s ability to slow tumor progression, we combined hetIL-15 immunotherapy with a FAMM. Combination therapy resulted in increased mitochondrial function, FA uptake and OCR, revealing a more metabolically active phenotype compared to the tumor-infiltrating CD8+T cells from hetIL-15 monotherapy group. In addition, combined treatment of IL-15 immunotherapy and FAMM resulted in statistically significant EO771 tumor growth delay and complete eradication of the tumors in 85% of mice.

Conclusions: Our results indicate that hetIL-15 synergizes with metabolic reprogramming of T cells to achieve superior antitumor efficacy and complete cures. We suggest that metabolic reprogramming of tumor-specific CD8+Tcells might represent a strategy to promote survival in the metabolically hostile TME as part of an approach to enhance the clinical efficacy of immunotherapy.

Citation Format: Sevasti Karaliota, Dimitris Stellas, Vasiliki Stravokefalou, Breana Myers, Barbara K. Felber, George N. Pavlakis. Heterodimeric IL-15 (hetIL-15) immunotherapy synergizes with Fatty Acid Metabolism Modulator (FAMM) to eradicate TNBC EO771 murine tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5082.

Step-dose IL-7 treatment promotes systemic expansion of T cells and alters immune cell landscape in blood and lymph nodes

We employed a dose-escalation regimen in rhesus macaques to deliver glycosylated IL-7, a cytokine critical for development and maintenance of T lymphocytes. IL-7 increased proliferation and survival of T cells and triggered several chemokines and cytokines. Induction of CXCL13 in lymph nodes (LNs) led to a remarkable increase of B cells in the LNs, proliferation of germinal center follicular T helper cells and elevated IL-21 levels suggesting an increase in follicle activity. Transcriptomics analysis showed induction of IRF-7 and Flt3L, which was linked to increased frequency of circulating plasmacytoid dendritic cells (pDCs) on IL-7 treatment. These pDCs expressed higher levels of CCR7, homed to LNs, and were associated with upregulation of type-1 interferon gene signature and increased production of IFN-α2a on TLR stimulation. Superior effects and dose-sparing advantage was observed by the step-dose regimen. Thus, IL-7 treatment leads to systemic effects involving both lymphoid and myeloid compartments.

Heterodimeric IL-15 (hetIL-15) reduces circulating tumor cells and metastasis formation improving chemotherapy and surgery in 4T1 mouse model of TNBC

Immunotherapy has emerged as a viable approach in cancer therapy, with cytokines being of great interest. Interleukin IL-15 (IL-15), a cytokine that supports cytotoxic immune cells, has been successfully tested as an anti-cancer and anti-metastatic agent, but combinations with conventional chemotherapy and surgery protocols have not been extensively studied. We have produced heterodimeric IL-15 (hetIL-15), which has shown anti-tumor efficacy in several murine cancer models and is being evaluated in clinical trials for metastatic cancers. In this study, we examined the therapeutic effects of hetIL-15 in combination with chemotherapy and surgery in the 4T1 mouse model of metastatic triple negative breast cancer (TNBC). hetIL-15 monotherapy exhibited potent anti-metastatic effects by diminishing the number of circulating tumor cells (CTCs) and by controlling tumor cells colonization of the lungs. hetIL-15 treatment in combination with doxorubicin resulted in enhanced anti-metastatic activity and extended animal survival. Systemic immune phenotype analysis showed that the chemoimmunotherapeutic regimen shifted the tumor-induced imbalance of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in favor of cytotoxic effector cells, by simultaneously decreasing PMN-MDSCs and increasing the frequency and activation of effector (CD8⁺T and NK) cells. Tumor resection supported by neoadjuvant and adjuvant administration of hetIL-15, either alone or in combination with doxorubicin, resulted in the cure of approximately half of the treated animals and the development of anti-4T1 tumor immunity. Our findings demonstrate a significant anti-metastatic potential of hetIL-15 in combination with chemotherapy and surgery and suggest exploring the use of this regimen for the treatment of TNBC.

Comparative immunogenicity of an mRNA/LNP and a DNA vaccine targeting HIV gag conserved elements in macaques

Immunogenicity of HIV-1 mRNA vaccine regimens was analyzed in a non-human primate animal model. Rhesus macaques immunized with mRNA in lipid nanoparticle (mRNA/LNP) formulation expressing HIV-1 Gag and Gag conserved regions (CE) as immunogens developed robust, durable antibody responses but low adaptive T-cell responses. Augmentation of the dose resulted in modest increases in vaccine-induced cellular immunity, with no difference in humoral responses. The gag mRNA/lipid nanoparticle (LNP) vaccine provided suboptimal priming of T cell responses for a heterologous DNA booster vaccination regimen. In contrast, a single immunization with gag mRNA/LNP efficiently boosted both humoral and cellular responses in macaques previously primed by a gag DNA-based vaccine. These anamnestic cellular responses were mediated by activated CD8⁺ T cells with a phenotype of differentiated T-bet⁺ cytotoxic memory T lymphocytes. The heterologous prime/boost regimens combining DNA and mRNA/LNP vaccine modalities maximized vaccine-induced cellular and humoral immune responses. Analysis of cytokine responses revealed a transient systemic signature characterized by the release of type I interferon, IL-15 and IFN-related chemokines. The pro-inflammatory status induced by the mRNA/LNP vaccine was also characterized by IL-23 and IL-6, concomitant with the release of IL-17 family of cytokines. Overall, the strong boost of cellular and humoral immunity induced by the mRNA/LNP vaccine suggests that it could be useful as a prophylactic vaccine in heterologous prime/boost modality and in immune therapeutic interventions against HIV infection or other chronic human diseases.

Abstract 5603: Heterodimeric IL-15 (hetIL-15) immunotherapy reverses CD8+T cell metabolic dysfunction in murine breast tumors

Introduction: Metabolic fitness and T cell survival are crucial in anti-tumor responses because nutrients are often scarce and other regulatory molecules may be unfavorable in the tumor microenvironment leading to T cell dysfunction, stress, and apoptosis. Tumor-infiltrating cytotoxic CD8+T cells often acquire an altered state of differentiation referred to as “exhaustion” and, as a result, they fail to control tumor outgrowth. IL-15 cytokine stimulates the generation, the proliferation and the cytotoxic function of tumor specific CD8+ T cells and NK cells. The objective of this study was to assess the effects of hetIL-15 immunotherapy after locoregional administration in triple negative breast cancer tumors (TNBC) and to evaluate the metabolic profile of the tumor infiltrating T cells.

Study design and methods: We studied the therapeutic efficacy of hetIL-15 immunotherapy in murine EO771 orthotopic breast cancer model. We monitored the effect of the treatment on tumor size and immune infiltration using flow cytometry and immunohistochemistry. We also evaluated hetIL-15 effects on the cell metabolism and the mitochondrial function of the tumor-infiltrating immune cells, using flow cytometry, Seahorse flux analysis, Mitotracker, 2-NBDG and/or Bodipy staining.

Results: hetIL-15 peritumoral administration, as monotherapy resulted in complete regression in 40% of the treated animals and increased survival. We demonstrated that tumor infiltrating cytotoxic CD8+T and NK cells were increased in hetIL-15 treated tumors and showed enhanced activation and proliferation, resulting in enhanced intratumoral immunological killing. Metabolic flux analysis of the tumor-infiltrating CD8+T cells from treated mice confirmed a rise in oxygen consumption rate (OCR) with substantial increase of spare respiratory capacity, which supports an activated/non exhausted phenotype of these hetIL-15 treated effector cells. Consistent with the above finding, tumor infiltrated CD8+T cells from hetIL-15 treated mice showed increased mitochondrial potential and fatty acid uptake, as evidenced by increased Mitotracker and Bodipy staining, respectively. In addition, tumor infiltrating CD8+T cells from hetIL-15 treated mice presented elevated extracellular acidification rate (ECAR) and showed a pronounced shift in the OCR to ECAR ratio in comparison to control, confirming their increased proliferating status.

Conclusions: Our results indicate that hetIL-15 not only increases the infiltration and the cytotoxic properties of the CD8+T cells inside the tumors, but also enhances the metabolic reprogramming of T cells to achieve superior antitumor efficacy. We suggest that metabolic reprogramming of tumor-specific CD8+T cells might represent a strategy to promote survival in the metabolically hostile TME as part of an approach to enhance the clinical efficacy of immunotherapy.

Citation Format: Dimitris Stellas, Sevasti Karaliota, Vasiliki Stravokefalou, Breana Myers, Barbara K. Felber, George N. Pavlakis. Heterodimeric IL-15 (hetIL-15) immunotherapy reverses CD8+T cell metabolic dysfunction in murine breast tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5603.

Abstract 2441: hetIL-15 decreases tumor cell dissemination and colonization and synergizes with chemotherapy and surgery to cure murine 4T1 breast tumors

Introduction: Metastasis is responsible for most of the cancer-related deaths (~ 90%). Metastatic triple negative breast cancer (TNBC) has poor survival and chemotherapy pre- and post-surgery has been the standard treatment for decades. Polymorphonuclear - myeloid derived suppressor cells (PMN-MDSCs) are implicated in the process of metastasis. IL-15 stimulates the proliferation and cytolytic activity of CD8+T cells and Natural Killer cells (NKs) and has been reported to have anti-metastatic activity. We have produced the native heterodimeric form of IL-15 (hetIL-15) which has advanced in clinical trials due to its anticancer activities. Here, we report the anti-metastatic effects of hetIL-15 alone and in combination with doxorubicin and surgery using the 4T1 mouse model of TNBC.

Study design and methods: We studied the efficacy of the chemo-immunotherapeutic regimen with surgery in a neoadjuvant and adjuvant setting or without surgery. The animals were evaluated regarding metastatic disease and survival. The anti-metastatic effect was evaluated by examining the metastatic foci in lungs and the circulating tumor cells (CTCs) in blood by histology and clonogenic assays. Treatment effects in immune populations in blood, spleen and lungs were evaluated by flow cytometry analysis and immunohistochemistry (IHC).

Results: Mice treated with hetIL-15 in combination with doxorubicin had significantly better survival in comparison to monotherapy treatments and control group. H&E histological analysis in the lungs revealed substantially fewer metastatic foci after hetIL-15 monotherapy, and even fewer in the combination group. Furthermore, clonogenic assays from lungs and blood, reinforced these findings showing significantly lower numbers of tumor colonies upon hetIL-15 monotherapy and combination treatment. Immune profiling evaluation of blood, spleen and lungs by flow cytometry and IHC revealed a significant systemic increase of cytotoxic effector cells (CD8+T cells and NKs), combined with reduction of immunosuppressive populations (PMN-MDSCs) especially in the combination group. These findings suggest a synergistic effect of doxorubicin and hetIL-15 in controlling the metastatic disease. Lastly, hetIL-15 monotherapy or co-administration with doxorubicin, together with surgery, led to the cure of approximately 50% of the treated mice.

Conclusions: Our results demonstrate that hetIL-15 reduces metastatic disease and synergizes with doxorubicin and surgery to maximize the effectiveness of the treatment against breast cancer in mice. We suggest that the effect of hetIL-15 on metastatic disease is both at the level of dissemination and also colonization in the metastatic sites. This should be further explored in the clinical setting as a neoadjuvant and adjuvant therapy in combination with chemotherapy and surgery for the treatment of TNBC.

Citation Format: Vasiliki Stravokefalou, Dimitris Stellas, Sevasti Karaliota, Breana Myers, Cristina Bergamaschi, Konstantinos Dimas, Barbara K. Felber, George N. Pavlakis. hetIL-15 decreases tumor cell dissemination and colonization and synergizes with chemotherapy and surgery to cure murine 4T1 breast tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2441.

Reduced Antibodies and Innate Cytokine Changes in SARS-CoV-2 BNT162b2 mRNA Vaccinated Transplant Patients With Hematological Malignancies

Immunocompromised individuals including patients with hematological malignancies constitute a population at high risk of developing severe disease upon SARS-CoV-2 infection. Protection afforded by vaccination is frequently low and the biology leading to altered vaccine efficacy is not fully understood. A patient cohort who had received bone marrow transplantation or CAR-T cells was studied following a 2-dose BNT162b2 mRNA vaccination and compared to healthy vaccine recipients. Anti-Spike antibody and systemic innate responses were compared in the two vaccine cohorts. The patients had significantly lower SARS-CoV-2 Spike antibodies to the Wuhan strain, with proportional lower cross-recognition of Beta, Delta, and Omicron Spike-RBD proteins. Both cohorts neutralized the wildtype WA1 and Delta but not Omicron. Vaccination elicited an innate cytokine signature featuring IFN-γ, IL-15 and IP-10/CXCL10, but most patients showed a diminished systemic cytokine response. In patients who failed to develop antibodies, the innate systemic response was dominated by IL-8 and MIP-1α with significant attenuation in the IFN-γ, IL-15 and IP-10/CXCL10 signature response. Changes in IFN-γ and IP-10/CXCL10 at priming vaccination and IFN-γ, IL-15, IL-7 and IL-10 upon booster vaccination correlated with the Spike antibody magnitude and were predictive of successful antibody development. Overall, the patients showed heterogeneous adaptive and innate responses with lower humoral and reduced innate cytokine responses to vaccination compared to naïve vaccine recipients. The pattern of responses described offer novel prognostic approaches for potentiating the effectiveness of COVID-19 vaccination in transplant patients with hematological malignancies.

Evaluating the effects of second-dose vaccine-delay policies in European countries: A simulation study based on data from Greece

The results of a simulation-based evaluation of several policies for vaccine rollout are reported, particularly focusing on the effects of delaying the second dose of two-dose vaccines. In the presence of limited vaccine supply, the specific policy choice is a pressing issue for several countries worldwide, and the adopted course of action will affect the extension or easing of non-pharmaceutical interventions in the next months. We employ a suitably generalised, age-structure, stochastic SEIR (Susceptible → Exposed → Infectious → Removed) epidemic model that can accommodate quantitative descriptions of the major effects resulting from distinct vaccination strategies. The different rates of social contacts among distinct age-groups (as well as some other model parameters) are informed by a recent survey conducted in Greece, but the conclusions are much more widely applicable. The results are summarised and evaluated in terms of the total number of deaths and infections as well as life years lost. The optimal strategy is found to be one based on fully vaccinating the elderly/at risk as quickly as possible, while extending the time-interval between the two vaccine doses to 12 weeks for all individuals below 75 years old, in agreement with epidemic theory which suggests targeting a combination of susceptibility and infectivity. This policy, which is similar to the approaches adopted in the UK and in Canada, is found to be effective in reducing deaths and life years lost in the period while vaccination is still being carried out.

The benefits, costs and feasibility of a low incidence COVID-19 strategy

In the summer of 2021, European governments removed most NPIs after experiencing prolonged second and third waves of the COVID-19 pandemic. Most countries failed to achieve immunization rates high enough to avoid resurgence of the virus. Public health strategies for autumn and winter 2021 have ranged from countries aiming at low incidence by re-introducing NPIs to accepting high incidence levels. However, such high incidence strategies almost certainly lead to the very consequences that they seek to avoid: restrictions that harm people and economies. At high incidence, the important pandemic containment measure 'test-trace-isolate-support' becomes inefficient. At that point, the spread of SARS-CoV-2 and its numerous harmful consequences can likely only be controlled through restrictions. We argue that all European countries need to pursue a low incidence strategy in a coordinated manner. Such an endeavour can only be successful if it is built on open communication and trust.

Sequential Analysis of Binding and Neutralizing Antibody in COVID-19 Convalescent Patients at 14 Months After SARS-CoV-2 Infection

Durability of SARS-CoV-2 Spike antibody responses after infection provides information relevant to understanding protection against COVID-19 in humans. We report the results of a sequential evaluation of anti-SARS-CoV-2 antibodies in convalescent patients with a median follow-up of 14 months (range 12.4-15.4) post first symptom onset. We report persistence of antibodies for all four specificities tested [Spike, Spike Receptor Binding Domain (Spike-RBD), Nucleocapsid, Nucleocapsid RNA Binding Domain (N-RBD)]. Anti-Spike antibodies persist better than anti-Nucleocapsid antibodies. The durability analysis supports a bi-phasic antibody decay with longer half-lives of antibodies after 6 months and antibody persistence for up to 14 months. Patients infected with the Wuhan (WA1) strain maintained strong cross-reactive recognition of Alpha and Delta Spike-RBD but significantly reduced binding to Beta and Mu Spike-RBD. Sixty percent of convalescent patients with detectable WA1-specific NAb also showed strong neutralization of the Delta variant, the prevalent strain of the present pandemic. These data show that convalescent patients maintain functional antibody responses for more than one year after infection, suggesting a strong long-lasting response after symptomatic disease that may offer a prolonged protection against re-infection. One patient from this cohort showed strong increase of both Spike and Nucleocapsid antibodies at 14 months post-infection indicating SARS-CoV-2 re-exposure. These antibodies showed stronger cross-reactivity to a panel of Spike-RBD including Beta, Delta and Mu and neutralization of a panel of Spike variants including Beta and Gamma. This patient provides an example of strong anti-Spike recall immunity able to control infection at an asymptomatic level. Together, the antibodies from SARS-CoV-2 convalescent patients persist over 14 months and continue to maintain cross-reactivity to the current variants of concern and show strong functional properties.

Phase I study of single agent NIZ985, a recombinant heterodimeric IL-15 agonist, in adult patients with metastatic or unresectable solid tumors

Background

NIZ985 is a recombinant heterodimer of physiologically active interleukin (IL-)15 and IL-15 receptor alpha. In preclinical models, NIZ985 promotes cytotoxic lymphocyte proliferation, killing function, and organ/tumor infiltration, with resultant anticancer effects. In this first-in-human study, we assessed the safety, pharmacokinetics, and immune effects of NIZ985 in patients with metastatic or unresectable solid tumors.

Methods

Single agent NIZ985 dose escalation data are reported from a phase I dose escalation/expansion study of NIZ985 as monotherapy. Adult patients (N=14) received 0.25, 0.5, 1, 2 or 4 µg/kg subcutaneous NIZ985 three times weekly (TIW) for the first 2 weeks of each 28-day cycle, in an accelerated 3+3 dose escalation trial design. IL-15 and endogenous cytokines were monitored by ELISA and multiplexed electrochemiluminescent assays. Multiparameter flow cytometry assessed the frequency, phenotype and proliferation of peripheral blood mononuclear cells. Preliminary antitumor activity was assessed by overall response rate (Response Evaluation Criteria in Solid Tumors V.1.1).

Results

As of March 2, 2020, median treatment duration was 7.5 weeks (range 1.1–77.1). Thirteen patients had discontinued and one (uveal melanoma) remains on treatment with stable disease. Best clinical response was stable disease (3 of 14 patients; 21%). The most frequent adverse events (AEs) were circular erythematous injection site reactions (100%), chills (71%), fatigue (57%), and fever (50%). Treatment-related grade 3/4 AEs occurred in six participants (43%); treatment-related serious AEs (SAEs) in three (21%). The per-protocol maximum tolerated dose was not reached. Pharmacokinetic accumulation of serum IL-15 in the first week was followed by significantly lower levels in week 2, likely due to more rapid cytokine consumption by an expanding lymphocyte pool. NIZ985 treatment was associated with increases in several cytokines, including interferon (IFN)-γ, IL-18, C-X-C motif chemokine ligand 10, and tumor necrosis factor-β, plus significant induction of cytotoxic lymphocyte proliferation (including natural killer and CD8⁺ T cells), increased CD16⁺ monocytes, and increased CD163⁺ macrophages at injection sites.

Conclusions

Subcutaneous NIZ985 TIW was generally well tolerated in patients with advanced cancer and produced immune activation paralleling preclinical observations, with induction of IFN-γ and proliferation of cytotoxic lymphocytes. Due to delayed SAEs at the two highest dose levels, administration is being changed to once-weekly in a revised protocol, as monotherapy and combined with checkpoint inhibitor spartalizumab. These alterations are expected to maximize the potential of NIZ985 as a novel immunotherapy.

Trial registration number

NCT02452268.

Control of SARS-CoV-2 infection after Spike DNA or Spike DNA+Protein co-immunization in rhesus macaques

The speed of development, versatility and efficacy of mRNA-based vaccines have been amply demonstrated in the case of SARS-CoV-2. DNA vaccines represent an important alternative since they induce both humoral and cellular immune responses in animal models and in human trials. We tested the immunogenicity and protective efficacy of DNA-based vaccine regimens expressing different prefusion-stabilized Wuhan-Hu-1 SARS-CoV-2 Spike antigens upon intramuscular injection followed by electroporation in rhesus macaques. Different Spike DNA vaccine regimens induced antibodies that potently neutralized SARS-CoV-2 in vitro and elicited robust T cell responses. The antibodies recognized and potently neutralized a panel of different Spike variants including Alpha, Delta, Epsilon, Eta and A.23.1, but to a lesser extent Beta and Gamma. The DNA-only vaccine regimens were compared to a regimen that included co-immunization of Spike DNA and protein in the same anatomical site, the latter of which showed significant higher antibody responses. All vaccine regimens led to control of SARS-CoV-2 intranasal/intratracheal challenge and absence of virus dissemination to the lower respiratory tract. Vaccine-induced binding and neutralizing antibody titers and antibody-dependent cellular phagocytosis inversely correlated with transient virus levels in the nasal mucosa. Importantly, the Spike DNA+Protein co-immunization regimen induced the highest binding and neutralizing antibodies and showed the strongest control against SARS-CoV-2 challenge in rhesus macaques.

Anti-Spike neutralizing antibodies provide strong protection against SARS-CoV-2 infection in animal models, and correlate with protection in humans, supporting the notion that induction of strong humoral immunity is key to protection. We show induction of robust antibody and T cell responses by different Spike DNA-based vaccine regimens able to effectively mediate protection and to control SARS-CoV-2 infection in the rhesus macaque model. This study provides the opportunity to compare vaccines able to induce different humoral and cellular immune responses in an effort to develop durable immunity against the SARS-CoV-2. A vaccine regimen comprising simultaneous co-immunization of DNA and Protein at the same anatomical site showed best neutralizing abilities and was more effective than DNA alone in inducing protective immune responses and controlling SARS-CoV-2 infection. Thus, an expansion of the DNA vaccine regimen to include co-immunization with Spike protein may be of advantage also for SARS-CoV-2.

Interleukin-15 response signature predicts RhCMV/SIV vaccine efficacy

Simian immunodeficiency virus (SIV) challenge of rhesus macaques (RMs) vaccinated with strain 68–1 Rhesus Cytomegalovirus (RhCMV) vectors expressing SIV proteins (RhCMV/SIV) results in a binary outcome: stringent control and subsequent clearance of highly pathogenic SIV in ~55% of vaccinated RMs with no protection in the remaining 45%. Although previous work indicates that unconventionally restricted, SIV-specific, effector-memory (EM)-biased CD8⁺ T cell responses are necessary for efficacy, the magnitude of these responses does not predict efficacy, and the basis of protection vs. non-protection in 68–1 RhCMV/SIV vector-vaccinated RMs has not been elucidated. Here, we report that 68–1 RhCMV/SIV vector administration strikingly alters the whole blood transcriptome of vaccinated RMs, with the sustained induction of specific immune-related pathways, including immune cell, toll-like receptor (TLR), inflammasome/cell death, and interleukin-15 (IL-15) signaling, significantly correlating with subsequent vaccine efficacy. Treatment of a separate RM cohort with IL-15 confirmed the central involvement of this cytokine in the protection signature, linking the major innate and adaptive immune gene expression networks that correlate with RhCMV/SIV vaccine efficacy. This change-from-baseline IL-15 response signature was also demonstrated to significantly correlate with vaccine efficacy in an independent validation cohort of vaccinated and challenged RMs. The differential IL-15 gene set response to vaccination strongly correlated with the pre-vaccination activity of this pathway, with reduced baseline expression of IL-15 response genes significantly correlating with higher vaccine-induced induction of IL-15 signaling and subsequent vaccine protection, suggesting that a robust de novo vaccine-induced IL-15 signaling response is needed to program vaccine efficacy. Thus, the RhCMV/SIV vaccine imparts a coordinated and persistent induction of innate and adaptive immune pathways featuring IL-15, a known regulator of CD8⁺ T cell function, that support the ability of vaccine-elicited unconventionally restricted CD8⁺ T cells to mediate protection against SIV challenge.

SIV insert-expressing vaccine vectors based on strain 68–1 RhCMV elicit robust, highly effector-memory-biased, unconventionally restricted T cell responses that are associated with an unprecedented level of SIV control after challenge (replication arrest leading to clearance) in slightly over half of vaccinated monkeys. Since efficacy among monkeys vaccinated with the effective 68–1 vaccine is not predicted by standard measures of immunogenicity, we used functional genomics analysis of RhCMV/SIV vaccinated monkeys with known challenge outcomes to identify immune correlates of protection. We found that vaccine efficacy significantly correlates with a vaccine-induced response to IL-15 that includes modulation of immune cell, inflammation, TLR signaling, and cell death programming response pathways. These data suggest that RhCMV/SIV efficacy results from a coordinated and sustained vaccine-mediated induction of innate and adaptive immune pathways featuring IL-15, a known regulator of CD8⁺ effector-memory T cell function, that cooperates with vaccine-elicited CD8⁺ T cells to mediate efficacy.

SARS-CoV-2 antibody kinetics eight months from COVID-19 onset: Persistence of spike antibodies but loss of neutralizing antibodies in 24% of convalescent plasma donors

Elucidating the characteristics of human immune response against SARS-CoV-2 is of high priority and relevant for determining vaccine strategies. We report the results of a follow-up evaluation of anti-SARS-CoV-2 antibodies in 148 convalescent plasma donors who participated in a phase 2 study at a median of 8.3 months (range 6.8-10.5 months) post first symptom onset. Monitoring responses over time, we found contraction of antibody responses for all four antigens tested, with Spike antibodies showing higher persistence than Nucleocapsid antibodies. A piecewise linear random-effects multivariate regression analysis showed a bi-phasic antibody decay with a more pronounced decrease during the first 6 months post symptoms onset by analysis of two intervals. Interestingly, antibodies to Spike showed better longevity whereas their neutralization ability contracted faster. As a result, neutralizing antibodies were detected in only 76% of patients at the last time point. In a multivariate analysis, older age and hospitalization were independently associated with higher Spike, Spike-RBD, Nucleocapsid, N-RBD antibodies and neutralizing antibody levels. Results on persistence and neutralizing ability of anti-SARS-CoV-2 antibodies, especially against Spike and Spike-RBD, should be considered in the design of future vaccination strategies.

Abstract 2727: Heterodimeric IL-15 (hetIL-15) affects conventional dendritic cells and a distinct novel dendritic cell population in different mouse cancer models of breast and pancreatic cancer

Introduction: IL-15 is a cytokine inducing proliferation and cytotoxic function of lymphocytes, including CD8+ T and NKs cells. We have produced the native heterodimeric form of IL-15 (hetIL-15) which has advanced in clinical trials due to its anticancer activities in many different mouse cancer models. The objective of this study was to explore how hetIL-15 affects lymphoid and myeloid cell populations in the tumor microenvironment in different mouse cancer models of breast and pancreatic cancer.

Study Design and Methods: We studied the therapeutic efficacy of intraperitoneal or locoregional administration of hetIL-15 in three different orthotopic mouse cancer models. We employed 4T1 and EO771 breast cancer models, which mimic human triple negative breast cancer and a KPC derived pancreatic cancer model. hetIL-15 effects on tumor infiltrating immune cells were evaluated by flow cytometry and immunohistochemistry.

Results: hetIL-15 treatment showed a profound effect on the EO771 breast cancer model resulting in complete tumor regression in ~40% of the treated mice. Additionally, hetIL-15 caused tumor delay in 4T1 and KPC derived cancer models. Flow cytometry analysis revealed an increase of cytotoxic effector cells, and especially CD8+ T cells, with enhanced cytotoxic activity and proliferation in all cancer models tested. Immunohistochemistry verified the accumulation of cytotoxic effector cells intratumorally upon hetIL-15 treatment. Furthermore, flow analysis showed an increase of infiltrating conventional type 1 dendritic cells (cDC1s) which was found only in EO771 breast tumors. On the contrary, 4T1 breast and KPC derived pancreatic tumors, but not EO771 tumors, displayed an accumulation of infiltrating conventional type 2 dendritic cells (cDC2s). Importantly, the flow cytometry analysis revealed yet additional novel distinct dendritic cell population characterized by CD103intCD11b+ immunophenotype, which was mostly evident in tumor tissues treated with hetIL-15 in all three models. Phenotypic profiling of this novel DC population identified expression of several cDC1 specific markers, including CD103, IRF8 and XCR1. Both cDC1s and the novel DC population were inversely correlated with the tumor size in EO771 breast cancer model.

Conclusions: hetIL-15 affects both T cells and conventional dendritic cells in syngeneic murine cancer models of breast and pancreatic cancer. We report that the treatment with hetIL-15 increases a novel distinct dendritic cell population (CD103intCD11b+) in all three models. Since we have previously reported that hetIL-15 induces long term immunological protection from tumor rechallenge, these findings suggest hetIL-15 as a promising therapeutic agent in treatment of triple negative breast and pancreatic cancer.

Citation Format: Vasiliki Stravokefalou, Dimitris Stellas, Sevasti Karaliota, Bethany Nagy, Theresa Guerin, Serguei Kozlov, Barbara K. Felber, George N. Pavlakis. Heterodimeric IL-15 (hetIL-15) affects conventional dendritic cells and a distinct novel dendritic cell population in different mouse cancer models of breast and pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2727.

Co-immunization of DNA and Protein in the Same Anatomical Sites Induces Superior Protective Immune Responses against SHIV Challenge

We compare immunogenicity and protective efficacy of an HIV vaccine comprised of env and gag DNA and Env (Envelope) proteins by co-administration of the vaccine components in the same muscles or by separate administration of DNA + protein in contralateral sites in female rhesus macaques. The 6-valent vaccine includes gp145 Env DNAs, representing six sequentially isolated Envs from the HIV-infected individual CH505, and matching GLA-SE-adjuvanted gp120 Env proteins. Interestingly, only macaques in the co-administration vaccine group are protected against SHIV CH505 acquisition after repeated low-dose intravaginal challenge and show 67% risk reduction per exposure. Macaques in the co-administration group develop higher Env-specific humoral and cellular immune responses. Non-neutralizing Env antibodies, ADCC, and antibodies binding to FcγRIIIa are associated with decreased transmission risk. These data suggest that simultaneous recognition, processing, and presentation of DNA + Env protein in the same draining lymph nodes play a critical role in the development of protective immunity.

Evaluation of chimeric antigen receptor T cell therapy in non-human primates infected with SHIV or SIV

Achieving a functional cure is an important goal in the development of HIV therapy. Eliciting HIV-specific cellular immune responses has not been sufficient to achieve durable removal of HIV-infected cells due to the restriction on effective immune responses by mutation and establishment of latent reservoirs. Chimeric antigen receptor (CAR) T cells are an avenue to potentially develop more potent redirected cellular responses against infected T cells. We developed and tested a range of HIV- and SIV-specific chimeric antigen receptor (CAR) T cell reagents based on Env-binding proteins. In general, SHIV/SIV CAR T cells showed potent viral suppression in vitro, and adding additional CAR molecules in the same transduction resulted in more potent viral suppression than single CAR transduction. Importantly, the primary determinant of virus suppression potency by CAR was the accessibility to the Env epitope, and not the neutralization potency of the binding moiety. However, upon transduction of autologous T cells followed by infusion in vivo, none of these CAR T cells impacted either acquisition as a test of prevention, or viremia as a test of treatment. Our study illustrates limitations of the CAR T cells as possible antiviral therapeutics.

Heterodimeric IL-15 delays tumor growth and promotes intratumoral CTL and dendritic cell accumulation by a cytokine network involving XCL1, IFN-γ, CXCL9 and CXCL10

BACKGROUND

Interleukin-15 (IL-15) promotes growth and activation of cytotoxic CD8⁺ T and natural killer (NK) cells. Bioactive IL-15 is produced in the body as a heterodimeric cytokine, comprising the IL-15 and IL-15 receptor alpha chains (hetIL-15). Several preclinical models support the antitumor activity of hetIL-15 promoting its application in clinical trials.

METHODS

The antitumor activity of hetIL-15 produced from mammalian cells was tested in mouse tumor models (MC38 colon carcinoma and TC-1 epithelial carcinoma). The functional diversity of the immune infiltrate and the cytokine/chemokine network within the tumor was evaluated by flow cytometry, multicolor immunohistochemistry (IHC), gene expression profiling by Nanostring Technologies, and protein analysis by electrochemiluminescence and ELISA assays.

RESULTS

hetIL-15 treatment resulted in delayed primary tumor growth. Increased NK and CD8⁺ T cell tumoral infiltration with an increased CD8⁺/Treg ratio were found by flow cytometry and IHC in hetIL-15 treated animals. Intratumoral NK and CD8⁺ T cells showed activation features with enhanced interferon-γ (IFN-γ) production, proliferation (Ki67⁺), cytotoxic potential (Granzyme B⁺) and expression of the survival factor Bcl-2. Transcriptomics and proteomics analyses revealed complex effects on the tumor microenvironment triggered by hetIL-15 therapy, including increased levels of IFN-γ and XCL1 with intratumoral accumulation of XCR1⁺IRF8⁺CD103⁺ conventional type 1 dendritic cells (cDC1). Concomitantly, the production of the chemokines CXCL9 and CXCL10 by tumor-localized myeloid cells, including cDC1, was boosted by hetIL-15 in an IFN-γ-dependent manner. An increased frequency of circulating CXCR3⁺ NK and CD8⁺ T cells was found, suggesting their ability to migrate toward the tumors following the CXCL9 and CXCL10 chemokine gradient.

CONCLUSIONS

Our results show that hetIL-15 administration enhances T cell entry into tumors, increasing the success rate of immunotherapy interventions. Our study further supports the incorporation of hetIL-15 in tumor immunotherapy approaches to promote the development of antitumor responses by favoring effector over regulatory cells and by promoting lymphocyte and DC localization into tumors through the modification of the tumor chemokine and cytokine milieu.

Insights to SARS-CoV-2 life cycle, pathophysiology, and rationalized treatments that target COVID-19 clinical complications

BACKGROUND

Gaining further insights into SARS-CoV-2 routes of infection and the underlying pathobiology of COVID-19 will support the design of rational treatments targeting the life cycle of the virus and/or the adverse effects (e.g., multi-organ collapse) that are triggered by COVID-19-mediated adult respiratory distress syndrome (ARDS) and/or other pathologies.

MAIN BODY

COVID-19 is a two-phase disease being marked by (phase 1) increased virus transmission and infection rates due to the wide expression of the main infection-related ACE2, TMPRSS2 and CTSB/L human genes in tissues of the respiratory and gastrointestinal tract, as well as by (phase 2) host- and probably sex- and/or age-specific uncontrolled inflammatory immune responses which drive hyper-cytokinemia, aggressive inflammation and (due to broad organotropism of SARS-CoV-2) collateral tissue damage and systemic failure likely because of imbalanced ACE/ANGII/AT1R and ACE2/ANG(1-7)/MASR axes signaling.

CONCLUSION

Here we discuss SARS-CoV-2 life cycle and a number of approaches aiming to suppress viral infection rates or propagation; increase virus antigen presentation in order to activate a robust and durable adaptive immune response from the host, and/or mitigate the ARDS-related "cytokine storm" and collateral tissue damage that triggers the severe life-threatening complications of COVID-19.

Anti-V2 antibodies virus vulnerability revealed by envelope V1 deletion in HIV vaccine candidates

The efficacy of ALVAC-based HIV and SIV vaccines in humans and macaques correlates with antibodies to envelope variable region 2 (V2). We show here that vaccine-induced antibodies to SIV variable region 1 (V1) inhibit anti-V2 antibody-mediated cytotoxicity and reverse their ability to block V2 peptide interaction with the α₄β₇ integrin. SIV vaccines engineered to delete V1 and favor an α helix, rather than a β sheet V2 conformation, induced V2-specific ADCC correlating with decreased risk of SIV acquisition. Removal of V1 from the HIV-1 clade A/E A244 envelope resulted in decreased binding to antibodies recognizing V2 in the β sheet conformation. Thus, deletion of V1 in HIV envelope immunogens may improve antibody responses to V2 virus vulnerability sites and increase the efficacy of HIV vaccine candidates.

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HIV vaccine candidate protects against SIV_mac251 acquisition

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V1 deleted envelope immunogens with V2 in α-helical conformation are protective

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V2-specific ADCC as correlate of risk

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Anti-V1 antibodies interfere with V2-specific ADCC

Anti-SARS-CoV-2 Antibody Responses in Convalescent Plasma Donors Are Increased in Hospitalized Patients; Subanalyses of a Phase 2 Clinical Study

We evaluated the antibody responses in 259 potential convalescent plasma donors for Covid-19 patients. Different assays were used: a commercial ELISA detecting antibodies against the recombinant spike protein (S1); a multiplex assay detecting total and specific antibody isotypes against three SARS-CoV-2 antigens (S1, basic nucleocapsid (N) protein and receptor-binding domain (RBD)); and an in-house ELISA detecting antibodies to complete spike, RBD and N in 60 of these donors. Neutralizing antibodies (NAb) were also evaluated in these 60 donors. Analyzed samples were collected at a median time of 62 (14-104) days from the day of first symptoms or positive PCR (for asymptomatic patients). Anti-SARS-CoV-2 antibodies were detected in 88% and 87.8% of donors using the ELISA and the multiplex assay, respectively. The multivariate analysis showed that age ≥50 years (p < 0.001) and need for hospitalization (p < 0.001) correlated with higher antibody titers, while asymptomatic status (p < 0.001) and testing >60 days after symptom onset (p = 0.001) correlated with lower titers. Interestingly, pseudotype virus-neutralizing antibodies (PsNAbs) significantly correlated with spike and with RBD antibodies by ELISA. Sera with high PsNAb also showed a strong ability to neutralize active SARS-CoV-2 virus, with hospitalized patients showing higher titers. Therefore, convalescent plasma donors can be selected based on the presence of high RBD antibody titers.

Abstract 5694: Complete regression of murine breast tumors by hetIL-15FC monotherapy correlates with infiltration by T, NK, cDC1 cells and a novel population of dendritic cells

Introduction: IL-15 cytokine stimulates the proliferation and cytotoxic function of CD8+ T and NK cells. Several preclinical models have supported the anti-tumor activity of IL-15. We have produced the native heterodimeric IL-15 (hetIL-15) of human, macaque or mouse and also fusions to the Fc antibody fragments (hetIL-15FC).

Experimental procedures: We studied the therapeutic efficacy of hetIL-15 or hetIL-15FC immunotherapy in the murine EO771 orthotopic breast cancer model in syngeneic C57BL/6 mice. The effects of hetIL-15FC on immune cells were compared in tumors, lymph nodes and spleen by flow cytometry, immunohistochemistry (IHC) and gene expression profiling (Nanostring). We also assessed the metabolic profile of tumor infiltrating T cells.

Results: hetIL-15 therapy delayed the primary tumor growth and increased overall survival. hetIL-15 or hetIL-15FC peritumoral administration resulted in tumor regression in 40% of the treated animals and resistance to tumor re-challenge. Therefore, monotherapy induced long term immunological memory able to block tumor growth. Both CD8+ T and NK cells were increased in hetIL-15FC treated tumors; phenotypic analysis showed they were activated and in an active proliferation state. Transcriptomic analysis confirmed the activated state of the T and NK cells, whereas metabolic flux analysis of the infiltrated CD8+T cells from treated mice confirmed a rise in oxygen consumption rate (OCR) with substantial increase of spare respiratory capacity (as a measure of mitochondrial reserve), which supports an activated/non exhausted phenotype of these hetIL-15 treated effector cells. In addition, peritumoral hetIL-15FC administration resulted in an increase of infiltrating, conventional type 1 dendritic cells (cDC1s), suggesting mechanisms of DC-lymphocyte interactions in the tumor. We also observed a new population of intra-tumoral DCs induced by hetIL-15, CD24+ F4/80high cDC2s (F4/80high DCs). The new DC population was negatively correlated with the tumor size of EO771 tumor bearing mice. Phenotypic profiling of F4/80high DCs identified expression of several cDC1 specific markers, including CD103 and IRF8 and t-SNE analysis clustered F4/80high DCs close to cDC1s and macrophages.

Conclusion: Our results show complete eradication of EO771 tumors by hetIL-15FC treatment, correlating with different tumor infiltrating immune cell types. We propose that the anti-cancer activity of hetIL-15 in primary tumors is orchestrated by the interplay of CD8+T cells, cDC1s and a novel subset of antigen presenting cells with a distinct phenotypic profile. hetIL-15 supported a favorable metabolic profile of intra-tumoral effector lymphocytes, important for their function. Effective hetIL-15 treatment leads to development of long-term anti-tumor memory.

Citation Format: Sevasti Karaliota, Dimitris Stellas, Vasiliki Stravokefalou, Bethany Nagy, Cristina Bergamaschi, Barbara K. Felber, George N. Pavlakis. Complete regression of murine breast tumors by hetIL-15FC monotherapy correlates with infiltration by T, NK, cDC1 cells and a novel population of dendritic cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5694.

The Emerging Role of Convalescent Plasma in the Treatment of COVID-19

Various agents are currently under evaluation as potential treatments in the fight against coronavirus disease 2019 (COVID-19). Plasma from patients that have overcome COVID-19 infection, referred to as convalescent plasma, is a treatment option with considerable background in viral diseases such as Spanish influenza, H1N1, Ebola, Severe Acute Respiratory Syndrome (SARS), and Middle East Respiratory Syndrome (MERS). Although convalescent plasma has historically proven beneficial in the treatment of some viral diseases, its use is still explorative in the context of COVID-19. To date, preliminary evidence from case series is favorable as significant clinical, biochemical improvement and hospital discharge have been reported. A detailed overview of randomized as well non-randomized trials of treatment with convalescent plasma, which have been registered worldwide, is provided in this review. Based on these studies, data from thousands of patients is anticipated in the near future. Convalescent plasma seems to be a safe option, but potential risks such as transfusion-related acute lung injury and antibody-dependent enhancement are discussed. Authorities including the Food and Drug Administration (FDA), and scientific associations such as the International Society of Blood Transfusion (ISBT) and the European Blood Alliance (EBA), have provided guidance into the selection criteria for donors and recipients. A debatable, pivotal issue pertains to the optimal timing of convalescent plasma transfusion. This treatment should be administered as early as possible to maximize efficacy, but at the same time be reserved for severe cases. Emerging risk stratification algorithms integrating clinical and biochemical markers to trace the cases at risk of significant deterioration can prove valuable in this direction.

Mechanism of Heterodimeric IL-15 in tumor reduction: Induction of myeloid-lymphoid cell interactions leads to IFN-γ dependent lymphocyte recruitment by dendritic cells into tumors

Background

hetIL-15 is evaluated in on-going immunotherapy clinical trials. We studied the mechanism of hetIL-15 antitumor function in several mouse models (MC38, TC-1, 4T1 and EO771).

Methods

We evaluated tumor immune infiltrate by flow cytometry, multi-color immunohistochemistry (IHC), transcriptomics and proteomics.

Results

hetIL-15 treatment delayed primary tumor growth, induced tumor regression and reduced metastases. Flow cytometry and IHC showed increased intratumoral NK and CD8+ T cell infiltration. Tumor-resident NK and CD8+ T cells were activated with enhanced IFN-γ production, increased proliferation (Ki67+), expression of survival factors (Bcl-2) and cytotoxic potential (Granzyme B+). hetIL-15 therapy resulted in increased IFN-γ and XCL1 levels and enhanced tumor accumulation of conventional type 1 dendritic cells (cDC1) expressing XCR1, IRF-8 and CD103. Production of CXCL9 and CXCL10 chemokines by tumor infiltrating cDC1 was boosted in an IFN-γ-dependent manner. Increased frequency of circulating NK and CD8+ T cells expressing CXCR3 was found, suggesting their migration toward tumors following the CXCL9/10 chemokine gradient.

Conclusions

hetIL-15 inhibits tumor growth by triggering lymphocyte-myeloid cell interactions modifying the tumor chemokine and cytokine milieu. hetIL-15 causes induction of XCL1 by lymphocytes, inducing DC intratumoral number, subsequent IFN-γ dependent CXCL9/10 production by DC and increased attraction of effector lymphocytes.

Regression of murine breast tumors after hetIL-15 monotherapy correlates with a novel population of intratumoral dendritic cells, in addition to increased infiltration of T, NK and cDC1 cells

Background

We studied mechanisms of therapeutic efficacy of the heterodimeric IL-15 (hetIL-15) of human, macaque or mouse in several mouse tumor models, including the murine EO771 orthotopic breast cancer model in syngeneic C57BL/6 mice.

Methods

The effects of hetIL-15 on immune cells were compared in tumors, lymph nodes and spleen by flow cytometry, immunohistochemistry (IHC), gene expression profiling (Nanostring) and metabolic profiling of tumor infiltrating T cells.

Results

hetIL-15 administration resulted in tumor regression in 40% of the treated animals and resistance to tumor rechallenge, inducing long term immunological memory. Activated NK and CD8+ T cells were increased in hetIL-15 treated tumors. hetIL-15 administration resulted in increased intratumoral infiltration of conventional Dendritic cells (cDC1) and also induced a new population of intratumoral DC, (F4/80high DCs), which were correlated negatively with the tumor size. Phenotypic profiling of F4/80high DCs identified expression of several cDC1 specific markers, including CD103, IRF8 and XCR1. tSNE analysis clustered F4/80high DCs close to cDC1s and macrophages.

Conclusion

Complete eradication of EO771 tumors by hetIL-15 treatment correlates with different tumor infiltrating immune cell types. We propose that the anti-cancer activity of hetIL-15 in primary tumors is orchestrated by the interplay of CD8+T cells, cDC1 and a novel subset of antigen presenting cells with a distinct phenotypic profile. Effective hetIL-15 treatment leads to development of long term anti-tumor memory. hetIL-15 supported a favorable metabolic profile of intratumoral effector lymphocytes, important for their function.

DNA priming vaccination to induce T cell responses to subdominant conserved HIV epitopes

Background

HIV sequence diversity and epitope immunodominance exerted by the variable regions are hurdles in the development of an effective AIDS vaccine. We developed novel DNA vaccine regimens to redirect T cell responses to highly conserved regions (CE) in the HIV proteome.

Methods

Rhesus macaques were primed with DNA expressing CE immunogen and boosted with a combination of DNAs expressing CE and/or full-length (FL) immunogens. Different prime-boost protocols were compared. The CE prime/CE+FL boost vaccination co-delivered in the same anatomical site was compared to delivery of CE and FL DNA in contralateral sites.

Results

CE prime/CE+FL boost regimens induced high and broad CTL responses which cannot be achieved using FL DNAs only. Thus, priming with CE DNA profoundly alters the immunodominance exerted by the variable non-CE regions, promoting responses to subdominant CE. This vaccine regimen is currently tested in clinical trials (HVTN 119, ACTG A5369). Comparison of same site vs contralateral vaccine delivery showed that separating CE and FL DNA resulted in increased breadth of T cell responses to non-CE while maintaining CTL responses to CE. Separating the immunogens at the prime allows for induction of independent primary adaptive responses by targeting the two vaccine components to distinct lymph nodes and preventing interference.

Conclusions

HIV DNA vaccine regimens comprising CE as prime and native immunogens as boost induce responses to subdominant epitopes, maximizing breadth and focusing the immune response against vulnerable regions of the virus. Separating the immunogens results in broader epitope recognition. This has implications for many vaccine protocols promoting induction of protective responses.

Novel HIV DNA vaccine changes the immune hierarchy and elicits broad cytotoxic T cell responses targeting subdominant viral epitopes

HIV sequence diversity and the propensity of eliciting immunodominant responses targeting non-essential variable regions are hurdles in the development of an effective AIDS vaccine. We developed a DNA vaccine comprising conserved elements (CE) of Gag and Env. Macaques (RM) received the CE DNA prime/CE+full-length DNA co-delivery booster vaccine regimen via intramuscular injection followed by electroporation. Priming vaccination with CE DNA is critical to efficiently overcome the dominance imposed by Gag and Env variable regions. CE vaccine induced broad, potent and durable cytotoxic T cell responses targeting conserved segments. Gag CE-specific T cells showed robust anamnestic responses upon infection with SIVmac239 which led to the identification of CE-specific cytotoxic lymphocytes able to recognize several CE epitopes presented on SIV infected cells in vivo. The T cell responses induced by the HIV Env CE immunogen were also recalled upon SIV infection, leading to the identification of two cross-reactive epitopes between HIV and SIV Env. These data demonstrate that the CE DNA vaccines changed the normal immunodominance patterns, eliciting immune responses that included subdominant, highly conserved epitopes. These vaccine regimens augment cytotoxic T cell responses to highly conserved epitopes in the viral proteome and maximize response breadth. The HIV Gag CE vaccine regimen is evaluated for prevention and immunotherapy in clinical trials (HVTN119 and ACTG 5369).

Neutrophil Vaccination Dynamics and Their Capacity To Mediate B Cell Help in Rhesus Macaques

Neutrophils are the most abundant leukocyte and play a critical role in the initial response to an Ag. Recently, their ability to contribute to adaptive immunity has been highlighted. We evaluated the ability of neutrophils from blood to contribute to the adaptive immune response in a preclinical rhesus macaque SIV vaccine trial. Replication-competent adenovirus-SIV recombinants induced neutrophil activation, B cell help markers, and enhanced ability to generate reactive oxygen species. Boosting with SIV vaccines (adjuvant together with ALVAC or DNA plus envelope protein) elicited significant neutrophil responses. Serum cytokine and chemokine levels induced correlated with the frequency of neutrophil subsets expressing IL-21, myeloperoxidase, and CD64. Post-SIV infection, neutrophils exhibited dysfunction, both phenotypically and functionally. B cells from protected and infected macaques cocultured with autologous polymorphonuclear cells, consisting primarily of neutrophils, were activated, underwent class switching, and produced Abs. This B cell help was not aided by addition of IL-10 and was largely contact dependent. Numerous genes associated with inflammation, Ab production, and chemotaxis were upregulated in the cocultured B cells. We conclude that immune stimulation by vaccination or antigenic exposure imparts a greater ability of neutrophils to contribute to the adaptive immune response. Harnessing this granulocytic response has the potential to improve vaccine efficacy.

Gag and env conserved element CE DNA vaccines elicit broad cytotoxic T cell responses targeting subdominant epitopes of HIV and SIV Able to recognize virus-infected cells in macaques

HIV sequence diversity and the propensity of eliciting immunodominant responses targeting inessential variable regions are hurdles in the development of an effective AIDS vaccine. We developed a DNA vaccine comprising conserved elements (CE) of SIV p27^Gag and HIV-1 Env and found that priming vaccination with CE DNA is critical to efficiently overcome the dominance imposed by Gag and Env variable regions. Here, we show that DNA vaccinated macaques receiving the CE prime/CE+full-length DNA co-delivery booster vaccine regimens developed broad, potent and durable cytotoxic T cell responses targeting conserved protein segments of SIV Gag and HIV Env. Gag CE-specific T cells showed robust anamnestic responses upon infection with SIV_mac239 which led to the identification of CE-specific cytotoxic lymphocytes able to recognize epitopes covering distinct CE on the surface of SIV infected cells in vivo. Though not controlling infection overall, we found an inverse correlation between Gag CE-specific CD8⁺ T cell responses and peak viremia. The T cell responses induced by the HIV Env CE immunogen were recalled in some animals upon SIV infection, leading to the identification of two cross-reactive epitopes between HIV and SIV Env based in sequence homology. These data demonstrate that a vaccine combining Gag and Env CE DNA subverted the normal immunodominance patterns, eliciting immune responses that included subdominant, highly conserved epitopes. These vaccine regimens augment cytotoxic T cell responses to highly conserved epitopes in the viral proteome and maximize response breadth. The vaccine-induced CE-specific T cells were expanded upon SIV infection, indicating that the predicted CE epitopes incorporated in the DNA vaccine are processed and exposed by infected cells in their natural context within the viral proteome.

DNA Vaccine-Induced Long-Lasting Cytotoxic T Cells Targeting Conserved Elements of Human Immunodeficiency Virus Gag Are Boosted Upon DNA or Recombinant Modified Vaccinia Ankara Vaccination

DNA-based vaccines able to induce efficient cytotoxic T-cell responses targeting conserved elements (CE) of human immunodeficiency virus type 1 (HIV-1) Gag have been developed. These CE were selected by stringent conservation, the ability to induce T-cell responses with broad human leukocyte antigen coverage, and the association between recognition of CE epitopes and viral control in HIV-infected individuals. Based on homology to HIV, a simian immunodeficiency virus p27^gag CE DNA vaccine has also been developed. This study reports on the durability of the CE-specific T-cell responses induced by HIV and simian immunodeficiency virus CE DNA-based prime/boost vaccine regimens in rhesus macaques, and shows that the initially primed CE-specific T-cell responses were efficiently boosted by a single CE DNA vaccination after the long rest period (up to 2 years). In another cohort of animals, the study shows that a single inoculation with non-replicating recombinant Modified Vaccinia Ankara (rMVA62B) also potently boosted CE-specific responses after around 1.5 years of rest. Both CE DNA and rMVA62B booster vaccinations increased the magnitude and cytotoxicity of the CE-specific responses while maintaining the breadth of CE recognition. Env produced by rMVA62B did not negatively interfere with the recall of the Gag CE responses. rMVA62B could be beneficial to further boosting the immune response to Gag in humans. Vaccine regimens that employ CE DNA as a priming immunogen hold promise for application in HIV prevention and therapy.

HIV vaccine candidate activation of hypoxia and the inflammasome in CD14+ monocytes is associated with a decreased risk of SIVmac251 acquisition

Qualitative differences in the innate and adaptive responses elicited by different HIV vaccine candidates have not been thoroughly investigated. We tested the ability of the Aventis Pasteur live recombinant canarypox vector (ALVAC)-SIV, DNA-SIV and Ad26-SIV vaccine prime modalities together with two ALVAC-SIV + gp120 protein boosts to reduce the risk of SIVmac251 acquisition in rhesus macaques. We found that the DNA and ALVAC prime regimens were effective, but the Ad26 prime was not. The activation of hypoxia and the inflammasome in CD14+CD16- monocytes, gut-homing CCR5-negative CD4+ T helper 2 (TH2) cells and antibodies to variable region 2 correlated with a decreased risk of SIVmac251 acquisition. By contrast, signal transducer and activator of transcription 3 activation in CD16+ monocytes was associated with an increased risk of virus acquisition. The Ad26 prime regimen induced the accumulation of CX3CR1+CD163+ macrophages in lymph nodes and of long-lasting CD4+ TH17 cells in the gut and lungs. Our data indicate that the selective engagement of monocyte subsets following a vaccine prime influences long-term immunity, uncovering an unexpected association of CD14+ innate monocytes with a reduced risk of SIVmac251 acquisition.

Optimized administration of hetIL-15 expands lymphocytes and minimizes toxicity in rhesus macaques

The common γ-chain cytokine interleukin-15 (IL-15) plays a significant role in regulating innate and adaptive lymphocyte homeostasis and can stimulate anti-tumor activity of leukocytes. We have previously shown that the circulating IL-15 in the plasma is the heterodimeric form (hetIL-15), produced upon co-expression of IL-15 and IL-15 Receptor alpha (IL-15Rα) polypeptides in the same cell, heterodimerization of the two chains and secretion. We investigated the pharmacokinetic and pharmacodynamic profile and toxicity of purified human hetIL-15 cytokine upon injection in rhesus macaques. We compared the effects of repeated hetIL-15 administration during a two-week dosing cycle, using different subcutaneous dosing schemata, i.e. fixed doses of 0.5, 5 and 50 μg/kg or a doubling step-dose scheme ranging from 2 to 64 μg/kg. Following a fixed-dose regimen, dose-dependent peak plasma IL-15 levels decreased significantly between the first and last injection. The trough plasma IL-15 levels measured at 48 h after injections were significantly higher after the first dose, compared to subsequent doses. In contrast, following the step-dose regimen, the systemic exposure increased by more than 1 log between the first injection given at 2 μg/kg and the last injection given at 64 μg/kg, and the trough levels were comparable after each injection. Blood lymphocyte cell count, proliferation, and plasma IL-18 levels peaked at day 8 when hetIL-15 was provided at fixed doses, and at the end of the cycle following a step-dose regimen, suggesting that sustained expansion of target cells requires increasing doses of cytokine. Macaques treated with a 50 μg/kg dose showed moderate and transient toxicity, including fever, signs of capillary leak syndrome and renal dysfunction. In contrast, these effects were mild or absent using the step-dose regimen. The results provide a new method of optimal administration of this homeostatic cytokine and may have applications for the delivery of other cytokines.

Immune Competition of HIV Epitopes in Draining Lymph Nodes

Background

Using HIV-derived DNAs encoding only conserved elements (CE) within Gag or Env, we were able to alter the immune hierarchy redirecting to otherwise subdominant viral targets. This hierarchy was preserved after boosting with DNA expressing full-length (FL) Gag or Env proteins. A vaccination strategy including simultaneous delivery of CE and FL molecules in separate anatomical sites was compared to CE prime/co-delivery CE+FL booster vaccination to examine the magnitude and breadth of epitope recognition to variable and conserved regions.

Methods

The DNA vaccine components were administered by IM route followed by in vivo electroporation in macaques. Antigen-specific cellular immune responses in blood were monitored by flow cytometry.

Results

The T cell responses targeting CE were similar in magnitude, function and breadth in both regimens. Separating anatomical sites of vaccination CE resulted in increased levels of cytotoxic T cell responses targeting variable regions. Thus, separating the immunogens allows development of T cell responses with overall increased breadth including conserved and variable epitopes.

Conclusion

The CE prime/CE+FL DNA boost vaccine induces immune responses targeting the CE epitopes. The vaccination strategy that separates CE and FL DNA plasmids to different anatomical sites, thereby targeting different draining lymph nodes, induces responses to both CE and variable regions. This vaccine regimen has the advantage of avoiding interference of the different vaccine components (CE, FL) during the priming of the adaptive immune response, redirecting immune dominance, and eliciting robust cytotoxic T cell responses targeting conserved and variable regions in the viral proteome.

Accumulation of follicular CD8+ T cells in pathogenic SIV infection

LN follicles constitute major reservoir sites for HIV/SIV persistence. Cure strategies could benefit from the characterization of CD8+ T cells able to access and eliminate HIV-infected cells from these areas. In this study, we provide a comprehensive analysis of the phenotype, frequency, localization, and functionality of follicular CD8+ T cells (fCD8+) in SIV-infected nonhuman primates. Although disorganization of follicles was a major factor, significant accumulation of fCD8+ cells during chronic SIV infection was also observed in intact follicles, but only in pathogenic SIV infection. In line with this, tissue inflammatory mediators were strongly associated with the accumulation of fCD8+ cells, pointing to tissue inflammation as a major factor in this process. These fCD8+ cells have cytolytic potential and can be redirected to target and kill HIV-infected cells using bispecific antibodies. Altogether, our data support the use of SIV infection to better understand the dynamics of fCD8+ cells and to develop bispecific antibodies as a strategy for virus eradication.

Therapeutic conserved elements (CE) DNA vaccine induces strong T-cell responses against highly conserved viral sequences during simian-human immunodeficiency virus infection

HIV-specific T-cell responses play a key role in controlling HIV infection, and therapeutic vaccines for HIV that aim to improve viral control will likely need to improve on the T-cell responses induced by infection. However, in the setting of chronic infection, an effective therapeutic vaccine must overcome the enormous viral genetic diversity and the presence of pre-existing T-cell responses that are biased toward immunodominant T-cell epitopes that can readily mutate to evade host immunity and thus potentially provide inferior protection. To address these issues, we investigated a novel, epidermally administered DNA vaccine expressing SIV capsid (p27^Gag) homologues of highly conserved elements (CE) of the HIV proteome in macaques experiencing chronic but controlled SHIV infection. We assessed the ability to boost or induce de novo T-cell responses against the conserved but immunologically subdominant CE epitopes. Two groups of animals were immunized with either the CE DNA vaccine or a full-length SIV p57^gag DNA vaccine. Prior to vaccination, CE responses were similar in both groups. The full-length p57^gag DNA vaccine, which contains the CE, increased overall Gag-specific responses but did not increase CE responses in any animals (0/4). In contrast, the CE DNA vaccine increased CE responses in all (4/4) vaccinated macaques. In SIV infected but unvaccinated macaques, those that developed stronger CE-specific responses during acute infection exhibited lower viral loads. We conclude that CE DNA vaccination can re-direct the immunodominance hierarchy towards CE in the setting of attenuated chronic infection and that induction of these responses by therapeutic vaccination may improve immune control of HIV.

Scalable, cGMP-compatible purification of extracellular vesicles carrying bioactive human heterodimeric IL-15/lactadherin complexes

The development of extracellular vesicles (EV) for therapeutic applications is contingent upon the establishment of reproducible, scalable, and high-throughput methods for the production and purification of clinical grade EV. Methods including ultracentrifugation (U/C), ultrafiltration, immunoprecipitation, and size-exclusion chromatography (SEC) have been employed to isolate EV, each facing limitations such as efficiency, particle purity, lengthy processing time, and/or sample volume. We developed a cGMP-compatible method for the scalable production, concentration, and isolation of EV through a strategy involving bioreactor culture, tangential flow filtration (TFF), and preparative SEC. We applied this purification method for the isolation of engineered EV carrying multiple complexes of a novel human immunostimulatory cytokine-fusion protein, heterodimeric IL-15 (hetIL-15)/lactadherin. HEK293 cells stably expressing the fusion cytokine were cultured in a hollow-fibre bioreactor. Conditioned medium was collected and EV were isolated comparing three procedures: U/C, SEC, or TFF + SEC. SEC demonstrated comparable particle recovery, size distribution, and hetIL-15 density as U/C purification. Relative to U/C, SEC preparations achieved a 100-fold reduction in ferritin concentration, a major protein-complex contaminant. Comparative proteomics suggested that SEC additionally decreased the abundance of cytoplasmic proteins not associated with EV. Combination of TFF and SEC allowed for bulk processing of large starting volumes, and resulted in bioactive EV, without significant loss in particle yield or changes in size, morphology, and hetIL-15/lactadherin density. Taken together, the combination of bioreactor culture with TFF + SEC comprises a scalable, efficient method for the production of highly purified, bioactive EV carrying hetIL-15/lactadherin, which may be useful in targeted cancer immunotherapy approaches.

Treatment with native heterodimeric IL-15 increases cytotoxic lymphocytes and reduces SHIV RNA in lymph nodes

B cell follicles in secondary lymphoid tissues represent an immune privileged sanctuary for AIDS viruses, in part because cytotoxic CD8+ T cells are mostly excluded from entering the follicles that harbor infected T follicular helper (TFH) cells. We studied the effects of native heterodimeric IL-15 (hetIL-15) treatment on uninfected rhesus macaques and on macaques that had spontaneously controlled SHIV infection to low levels of chronic viremia. hetIL-15 increased effector CD8+ T lymphocytes with high granzyme B content in blood, mucosal sites and lymph nodes, including virus-specific MHC-peptide tetramer+ CD8+ cells in LN. Following hetIL-15 treatment, multiplexed quantitative image analysis (histo-cytometry) of LN revealed increased numbers of granzyme B+ T cells in B cell follicles and SHIV RNA was decreased in plasma and in LN. Based on these properties, hetIL-15 shows promise as a potential component in combination immunotherapy regimens to target AIDS virus sanctuaries and reduce long-term viral reservoirs in HIV-1 infected individuals.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02452268.

HIV Env conserved element DNA vaccine alters immunodominance in macaques

Sequence diversity and immunodominance are major obstacles in the design of an effective vaccine against HIV. HIV Env is a highly-glycosylated protein composed of ‘conserved’ and ‘variable’ regions. The latter contains immunodominant epitopes that are frequently targeted by the immune system resulting in the generation of immune escape variants. This work describes 12 regions in HIV Env that are highly conserved throughout the known HIV M Group sequences (Env CE), and are poorly immunogenic in macaques vaccinated with full-length Env expressing DNA vaccines. Two versions of plasmids encoding the 12 Env CE were generated, differing by 0–5 AA per CE to maximize the inclusion of commonly detected variants. In contrast to the full-length env DNA vaccine, vaccination of macaques with a combination of these 2 Env CE DNA induced robust, durable cellular immune responses with a significant fraction of CD8⁺ T cells with cytotoxic phenotype (Granzyme B⁺ and CD107a⁺). Although inefficient in generating primary responses to the CE, boosting of the Env CE DNA primed macaques with the intact env DNA vaccine potently augmented pre-existing immunity, increasing magnitude, breadth and cytotoxicity of the cellular responses. Fine mapping showed that 7 of the 12 CE elicited T cell responses. Env CE DNA also induced humoral responses able to recognize the full-length Env. Env CE plasmids are therefore capable of inducing durable responses to highly conserved regions of Env that are frequently absent after Env vaccination or immunologically subdominant. These modified antigens are candidates for use as prophylactic and therapeutic HIV vaccines.

Labeling Extracellular Vesicles for Nanoscale Flow Cytometry

Extracellular vesicles (EVs), including exosomes and microvesicles, are 30-800 nm vesicles that are released by most cell types, as biological packages for intercellular communication. Their importance in cancer and inflammation makes EVs and their cargo promising biomarkers of disease and cell-free therapeutic agents. Emerging high-resolution cytometric methods have created a pressing need for efficient fluorescent labeling procedures to visualize and detect EVs. Suitable labels must be bright enough for one EV to be detected without the generation of label-associated artifacts. To identify a strategy that robustly labels individual EVs, we used nanoFACS, a high-resolution flow cytometric method that utilizes light scattering and fluorescence parameters along with sample enumeration, to evaluate various labels. Specifically, we compared lipid-, protein-, and RNA-based staining methods and developed a robust EV staining strategy, with the amine-reactive fluorescent label, 5-(and-6)-Carboxyfluorescein Diacetate Succinimidyl Ester, and size exclusion chromatography to remove unconjugated label. By combining nanoFACS measurements of light scattering and fluorescence, we evaluated the sensitivity and specificity of EV labeling assays in a manner that has not been described for other EV detection methods. Efficient characterization of EVs by nanoFACS paves the way towards further study of EVs and their roles in health and disease.

Modulation of DNA/ALVAC/gp120 vaccine immune-response by vaccination with Insulin-Like Growth Factor 1 (IGF-1)

ALVAC-SIV/gp120 vaccine reduced the risk of infection in SIVmac251 model. Protection was associated with antibodies (Abs) to V2 region of gp120 protein, mucosal NKp44+ cells, and the expression of 11 genes in the Ras pathway. IGF-1 hormone is a Ras activator and its plasma level diminishes with aging. We hypothesized that IGF-1 might affect the efficacy of the ALVAC-SIV/gp120 platform by modulating the immune responses, particularly when administered in old macaques. In this study we enrolled 25 young (Group 1, av. 3 years) and 34 old macaques (Group 2, av. 9 years) having significantly different plasma levels of IGF-1, and we immunized them with a DNA-SIV/ALVAC-SIV/gp120 vaccine. During immunizations, half of the animals of each group were also administered IGF-1, as recombinant protein (Increlex, Ipsen) and as DNA vaccine. All the animals, including controls, were challenged intra-vaginally with repeated low-doses of SIVmac251. The estimated vaccine efficacy in young macaques of Group 1 was 69%. IGF-1 administration did not increase the efficacy; although, it determined a significant increase of serum Abs titers against V2 and frequency of mucosal NKp44+ cells. Furthermore, IGF-1 treated macaques showed higher frequencies of circulating classical (CCR2+CD14+CD16−) and intermediate (CCR2+CD14+CD16+) monocytes and lower frequencies of mucosal CD4+ T cells expressing α4β7 or CCR5 compared to the untreated animals. These data suggest that IGF-1 administration might improve protective immune responses and decrease possible SIV target cells in the mucosa. Therefore, IGF-1 administration during vaccination might particularly benefit older animals. Challenge exposure of older animals in Group 2 is ongoing.