First-in-human Study With LIS1, a Next-generation Porcine Low Immunogenicity Antilymphocyte Immunoglobulin in Kidney Transplantation.

BACKGROUND: Polyclonal rabbit antithymocyte globulins (ATGs) are commonly used in organ transplantation as induction. Anti-N-glycolylneuraminic acid carbohydrate antibodies which develop in response to rabbit carbohydrate antigens might lead to unwanted systemic inflammation. LIS1, the first new generation of antilymphocyte globulins (ALGs) derived from double knockout swine, lacking carbohydrate xenoantigens was already tested in nonhuman primates and rodent models. METHODS: This open-label, single-site, dose escalation, first-in-human, phase 1 study evaluated the safety, T cell depletion, pharmacokinetics, and pharmacodynamics of LIS1. In an ascending dose cohort (n = 5), a primary kidney transplant recipient at low immunologic risk (panel reactive antibody [PRA] < 20%), received LIS1 for 5 d at either 0.6, 1, 3, 6, or 8 mg/kg. After each patient completed treatment, the data safety monitoring board approved respective dose escalation. In the therapeutic dose cohort (n = 5) in patients with PRA <50% without donor specific antibodies, 2 patients received 8 mg/kg and 3 patients 10 mg/kg. RESULTS: CD3+ T cell depletion <100/mm3 at day 2 was observed in all patients who received 6, 8, and 10 mg/kg of LIS1. The terminal half-life of LIS1 was 33.7 d with linearity in its disposition. Lymphocyte repopulation was fast and pretransplant lymphocyte subpopulation counts recovered within 2-4 wk. LIS1 was well tolerated, neither cytokine release syndrome nor severe thrombocytopenia or leukopenia were noticed. Antibodies to LIS1 were not detected. CONCLUSIONS: In this first-in-human trial, genome-edited swine-derived polyclonal LIS1 ALG was well tolerated, did not elicit antidrug antibodies, and caused time-limited T cell depletion in low- and medium-risk kidney transplant recipients.

Polyclonal antibodies selectively inhibit tumor growth and invasion and synergize with immune checkpoint inhibitors.

Heterologous polyclonal antibodies (pAb) were shown to possess oncolytic properties a century ago with reported clinical responses. More recent preclinical models confirmed pAb efficacy, though their ability to tackle complex target antigens reduces susceptibility to tumor escape. Owing to the recent availability of glyco-humanized pAb (GH-pAb) with acceptable clinical toxicology profile, we revisited use of pAb in oncology and highlighted their therapeutic potential against multiple cancer types. Murine antitumor pAb were generated after repeated immunization of rabbits with murine tumor cell lines from hepatocarcinoma, melanoma, and colorectal cancers. Antitumor pAb recognized and showed cytotoxicity against their targets without cross-reactivity with healthy tissues. In vivo, pAb are effective alone; moreover, these pAb synergize with immune checkpoint inhibitors like anti-PD-L1 in several cancer models. They elicited an antitumor host immune response and prevented metastases. The anticancer activity of pAb was also confirmed in xenografted NMRI nude mice using GH-pAb produced by repeated immunization of pigs with human tumor cell lines. In conclusion, the availability of bioengineered GH-pAb allows for revisiting of passive immunotherapy with oncolytic pAb to fight against solid tumor and cancer metastasis.

Effect of Swine Glyco-humanized Polyclonal Neutralizing Antibody on Survival and Respiratory Failure in Patients Hospitalized With Severe COVID-19: A Randomized, Placebo-Controlled Trial.

Background: We evaluated the safety and efficacy of XAV-19, an antispike glyco-humanized swine polyclonal neutralizing antibody in patients hospitalized with severe coronavirus disease 2019 (COVID-19). Methods: This phase 2b clinical trial enrolled adult patients from 34 hospitals in France. Eligible patients had a confirmed diagnosis of severe acute respiratory syndrome coronavirus 2 within 14 days of onset of symptoms that required hospitalization for low-flow oxygen therapy (<6 L/min of oxygen). Patients were randomly assigned to receive a single intravenous infusion of 2 mg/kg of XAV-19 or placebo. The primary end point was the occurrence of death or severe respiratory failure between baseline and day 15. Results: Between January 12, 2021, and April 16, 2021, 398 patients were enrolled in the study and randomly assigned to XAV-19 or placebo. The modified intention-to-treat population comprised 388 participants who received full perfusion of XAV-19 (199 patients) or placebo (189 patients). The mean (SD) age was 59.8 (12.4) years, 249 (64.2%) individuals were men, and the median time (interquartile range) from symptom onset to enrollment was 9 (7-10) days. There was no statistically significant decrease in the cumulative incidence of death or severe respiratory failure through day 15 in the XAV-19 group vs the placebo group (53/199 [26.6%] vs 48/189 [25.4%]; adjusted risk difference, 0.6%; 95% CI, -6% to 7%; hazard ratio, 1.03; 95% CI, 0.64-1.66; P = .90). In the safety population, adverse events were reported in 75.4% of 199 patients in the XAV-19 group and in 76.3% of 190 patients in the placebo group through D29. Conclusions: Among patients hospitalized with COVID-19 requiring low-flow oxygen therapy, treatment with a single intravenous dose of XAV-19, compared with placebo, did not show a significant difference in terms of disease progression at day 15.

Corrigendum: XAV-19, a swine glyco-humanized polyclonal antibody against SARS-CoV-2 spike receptor-binding domain, targets multiple epitopes and broadly neutralizes variants.

[This corrects the article DOI: 10.3389/fimmu.2021.761250.].

LIS1, a glyco-humanized swine polyclonal anti-lymphocyte globulin, as a novel induction treatment in solid organ transplantation.

Anti-thymocyte or anti-lymphocyte globulins (ATGs/ALGs) are immunosuppressive drugs used in induction therapies to prevent acute rejection in solid organ transplantation. Because animal-derived, ATGs/ALGs contain highly immunogenic carbohydrate xenoantigens eliciting antibodies that are associated with subclinical inflammatory events, possibly impacting long-term graft survival. Their strong and long-lasting lymphodepleting activity also increases the risk for infections. We investigated here the in vitro and in vivo activity of LIS1, a glyco-humanized ALG (GH-ALG) produced in pigs knocked out for the two major xeno-antigens αGal and Neu5Gc. It differs from other ATGs/ALGs by its mechanism of action excluding antibody-dependent cell-mediated cytotoxicity and being restricted to complement-mediated cytotoxicity, phagocyte-mediated cytotoxicity, apoptosis and antigen masking, resulting in profound inhibition of T-cell alloreactivity in mixed leucocyte reactions. Preclinical evaluation in non-human primates showed that GH-ALG dramatically reduced CD4+ (p=0.0005,***), CD8+ effector T cells (p=0.0002,***) or myeloid cells (p=0.0007,***) but not T-reg (p=0.65, ns) or B cells (p=0.65, ns). Compared with rabbit ATG, GH-ALG induced transient depletion (less than one week) of target T cells in the peripheral blood (<100 lymphocytes/L) but was equivalent in preventing allograft rejection in a skin allograft model. The novel therapeutic modality of GH-ALG might present advantages in induction treatment during organ transplantation by shortening the T-cell depletion period while maintaining adequate immunosuppression and reducing immunogenicity.

Concerted BAG3 and SIRPα blockade impairs pancreatic tumor growth.

The BAG3- and SIRPα- mediated pathways trigger distinct cellular targets and signaling mechanisms in pancreatic cancer microenvironment. To explore their functional connection, we investigated the effects of their combined blockade on cancer growth in orthotopic allografts of pancreatic cancer mt4-2D cells in immunocompetent mice. The anti-BAG3 + anti-SIRPα mAbs treatment inhibited (p = 0.007) tumor growth by about the 70%; also the number of metastatic lesions was decreased, mostly by the effect of the anti-BAG3 mAb. Fibrosis and the expression of the CAF activation marker α-SMA were reduced by about the 30% in animals treated with anti-BAG3 mAb compared to untreated animals, and appeared unaffected by treatment with the anti-SIRPα mAb alone; however, the addition of anti-SIRPα to anti-BAG3 mAb in the combined treatment resulted in a > 60% (p < 0.0001) reduction of the fibrotic area and a 70% (p < 0.0001) inhibition of CAF α-SMA positivity. Dendritic cells (DCs) and CD8+ lymphocytes, hardly detectable in the tumors of untreated animals, were modestly increased by single treatments, while were much more clearly observable (p < 0.0001) in the tumors of the animals subjected to the combined treatment. The effects of BAG3 and SIRPα blockade do not simply reflect the sum of the effects of the single blockades, indicating that the two pathways are connected by regulatory interactions and suggesting, as a proof of principle, the potential therapeutic efficacy of a combined BAG3 and SIRPα blockade in pancreatic cancer.

The proliferation of belatacept-resistant T cells requires early IFNα pathway activation.

Belatacept was developed to replace calcineurin inhibitors in kidney transplantation. Its use is associated with better kidney transplant function, a lower incidence of anti-donor antibodies and higher graft survival. However, it is also associated with a higher risk of cellular rejection. We studied the activation and proliferation mechanisms of belatacept-resistant T lymphocytes (TLs), to identify new pathways for control. We performed a transcriptomic analysis on CD4+ CD57+ PD1- memory TLs, which are responsible for a higher incidence of graft rejection, after allogeneic stimulation with activated dendritic cells (aDCs) in the presence or absence of belatacept. After six hours of contact with aDCs, the (CD4+ CD57+ PD1- ) (CD4+ CD57+ PD1+ ) and (CD4+ CD57- ) lymphocytes had different transcriptional profiles with or without belatacept. In the CD4+ CD57+ PD1- population, the IFNα-dependent activation pathway was positively overrepresented, and IRF7 transcript levels were high. IRF7 was associated with IFNα/ß and IL-6 regulation. The inhibition of both these cytokines in a context of belatacept treatment inhibited the proliferation of CD4+ CD57+ PD1- T cells. Our results show that IRF7 is rapidly upregulated in belatacept-resistant CD4+ CD57+ PD1- TLs. The inhibition of type I IFN or IL-6 in association with belatacept treatment reduces the proliferation of belatacept-resistant TLs, paving the way for new treatments for use in organ transplantation.

XAV-19, a Swine Glyco-Humanized Polyclonal Antibody Against SARS-CoV-2 Spike Receptor-Binding Domain, Targets Multiple Epitopes and Broadly Neutralizes Variants.

Amino acid substitutions and deletions in the Spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants can reduce the effectiveness of monoclonal antibodies (mAbs). In contrast, heterologous polyclonal antibodies raised against S protein, through the recognition of multiple target epitopes, have the potential to maintain neutralization capacities. XAV-19 is a swine glyco-humanized polyclonal neutralizing antibody raised against the receptor binding domain (RBD) of the Wuhan-Hu-1 Spike protein of SARS-CoV-2. XAV-19 target epitopes were found distributed all over the RBD and particularly cover the receptor binding motives (RBMs), in direct contact sites with the angiotensin converting enzyme-2 (ACE-2). Therefore, in Spike/ACE-2 interaction assays, XAV-19 showed potent neutralization capacities of the original Wuhan Spike and of the United Kingdom (Alpha/B.1.1.7) and South African (Beta/B.1.351) variants. These results were confirmed by cytopathogenic assays using Vero E6 and live virus variants including the Brazil (Gamma/P.1) and the Indian (Delta/B.1.617.2) variants. In a selective pressure study on Vero E6 cells conducted over 1 month, no mutation was associated with the addition of increasing doses of XAV-19. The potential to reduce viral load in lungs was confirmed in a human ACE-2 transduced mouse model. XAV-19 is currently evaluated in patients hospitalized for COVID-19-induced moderate pneumonia in phase 2a-2b (NCT04453384) where safety was already demonstrated and in an ongoing 2/3 trial (NCT04928430) to evaluate the efficacy and safety of XAV-19 in patients with moderate-to-severe COVID-19. Owing to its polyclonal nature and its glyco-humanization, XAV-19 may provide a novel safe and effective therapeutic tool to mitigate the severity of coronavirus disease 2019 (COVID-19) including the different variants of concern identified so far.

Pharmacokinetics and Safety of XAV-19, a Swine Glyco-humanized Polyclonal Anti-SARS-CoV-2 Antibody, for COVID-19-Related Moderate Pneumonia: a Randomized, Double-Blind, Placebo-Controlled, Phase IIa Study.

We assessed the pharmacokinetics and safety of XAV-19, a swine glyco-humanized polyclonal antibody against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in coronavirus disease 2019 (COVID-19)-related moderate pneumonia. The objective was to evaluate the optimal dose and safety of XAV-19 during this first administration to patients with COVID-19-related moderate pneumonia. In this phase IIa trial, adults with COVID-19-related moderate pneumonia with a duration of ≤10 days were randomized to receive an infusion of XAV-19 at 0.5 mg/kg of body weight at day 1 and day 5 (group 1), 2 mg/kg at day 1 and day 5 (group 2), or 2 mg/kg at day 1 (group 3) or placebo. Eighteen patients (n = 7 for group 1, n = 1 for group 2, n = 5 for group 3, and n = 5 for placebo) were enrolled. Baseline characteristics were similar across groups; median XAV-19 serum concentrations (ranges) at the time of the maximum serum concentration of the drug (Cmax) and at day 8 were 9.1 (5.2 to 18.1) and 6.4 (2.8 to 11.9) µg/ml, 71.5 and 47.2 µg/ml, and 50.4 (29.1 to 55.0) and 20.3 (12.0 to 22.7) µg/ml for groups 1, 2, and 3, respectively (P = 0.012). The median terminal half-life (range) was estimated at 11.4 (5.5 to 13.9) days for 2 mg/kg of XAV-19 at day 1. Serum XAV-19 concentrations were above the target concentration of 10 µg/ml (2-fold the in vitro 100% inhibitory concentration [IC100]) from the end of perfusion to more than 8 days for XAV-19 at 2 mg/kg at day 1. No hypersensitivity or infusion-related reactions were reported during treatment, and there were no discontinuations for adverse events and no serious adverse events related to the study drug. A single intravenous dose of 2 mg/kg of XAV-19 demonstrated high serum concentrations, predictive of potent durable neutralizing activity with good tolerability. (This study has been registered at ClinicalTrials.gov under identifier NCT04453384.).

Inhibition of acid sphingomyelinase increases regulatory T cells in humans.

Genetic deficiency for acid sphingomyelinase or its pharmacological inhibition has been shown to increase Foxp3+ regulatory T-cell frequencies among CD4+ T cells in mice. We now investigated whether pharmacological targeting of the acid sphingomyelinase, which catalyzes the cleavage of sphingomyelin to ceramide and phosphorylcholine, also allows to manipulate relative CD4+ Foxp3+ regulatory T-cell frequencies in humans. Pharmacological acid sphingomyelinase inhibition with antidepressants like sertraline, but not those without an inhibitory effect on acid sphingomyelinase activity like citalopram, increased the frequency of Foxp3+ regulatory T cell among human CD4+ T cells in vitro. In an observational prospective clinical study with patients suffering from major depression, we observed that acid sphingomyelinase-inhibiting antidepressants induced a stronger relative increase in the frequency of CD4+ Foxp3+ regulatory T cells in peripheral blood than acid sphingomyelinase-non- or weakly inhibiting antidepressants. This was particularly true for CD45RA- CD25high effector CD4+ Foxp3+ regulatory T cells. Mechanistically, our data indicate that the positive effect of acid sphingomyelinase inhibition on CD4+ Foxp3+ regulatory T cells required CD28 co-stimulation, suggesting that enhanced CD28 co-stimulation was the driver of the observed increase in the frequency of Foxp3+ regulatory T cells among human CD4+ T cells. In summary, the widely induced pharmacological inhibition of acid sphingomyelinase activity in patients leads to an increase in Foxp3+ regulatory T-cell frequencies among CD4+ T cells in humans both in vivo and in vitro.

Evaluation of the safety and efficacy of XAV-19 in patients with COVID-19-induced moderate pneumonia: study protocol for a randomized, double-blinded, placebo-controlled phase 2 (2a and 2b) trial.

BACKGROUND: Early inhibition of entry and replication of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a very promising therapeutic approach. Polyclonal neutralizing antibodies offers many advantages such as providing immediate immunity, consequently blunting an early pro-inflammatory pathogenic endogenous antibody response and lack of drug-drug interactions. By providing immediate immunity and inhibiting entry into cells, neutralizing antibody treatment is of interest for patient with COVID-19-induced moderate pneumonia. Convalescent plasma to treat infected patients is therefore a relevant therapeutic option currently under assessment (CORIMUNO-PLASM NCT04324047). However, the difficulties of collecting plasma on the long term are not adapted to a broad use across all populations. New polyclonal humanized anti-SARS-CoV2 antibodies (XAV-19) developed by Xenothera and administered intravenous. XAV-19 is a heterologous swine glyco-humanized polyclonal antibody (GH-pAb) raised against the spike protein of SARS-CoV-2, blocking infection of ACE-2-positive human cells with SARS-CoV-2. METHODS: Pharmacokinetic and pharmacodynamic studies have been performed in preclinical models including primates. A first human study with another fully representative GH-pAb from Xenothera is ongoing in recipients of a kidney graft. These studies indicated that 5 consecutive administrations of GH-pAbs can be safely performed in humans. The objectives of this 2-step phase 2 randomized double-blinded, placebo-controlled study are to define the safety and the optimal XAV-19 dose to administrate to patients with SARS-CoV-2 induced moderate pneumonia, and to assess the clinical benefits of a selected dose of XAV-19 in this population. DISCUSSION: This study will determine the clinical benefits of XAV-19 when administered to patients with SARS-CoV-2-induced moderate pneumonia. As a prerequisite, a first step of the study will define the safety and the dose of XAV-19 to be used. Such treatment might become a new therapeutic option to provide an effective treatment for COVID-19 patients (possibly in combination with anti-viral and immunotherapies). Further studies could later evaluate such passive immunotherapy as a potential post-exposure prophylaxis. TRIAL REGISTRATION: ClinicalTrials.gov NCT04453384 , registered on 1 July 2020, and EUDRACT 2020-002574-27, registered 6 June 2020.

Cystathionine-gamma-lyase overexpression in T cells enhances antitumor effect independently of cysteine autonomy.

T cells could be engineered to overcome the aberrant metabolic milieu of solid tumors and tip the balance in favor of a long-lasting clinical response. Here, we explored the therapeutic potential of stably overexpressing cystathionine-gamma-lyase (CTH, CSE, or cystathionase), a pivotal enzyme of the transsulfuration pathway, in antitumor CD8+ T cells with the initial aim to boost intrinsic cysteine metabolism. Using a mouse model of adoptive cell transfer (ACT), we found that CTH-expressing T cells showed a superior control of tumor growth compared to control T cells. However, contrary to our hypothesis, this effect was not associated with increased T cell expansion in vivo or proliferation rescue in the absence of cysteine/cystine in vitro. Rather than impacting methionine or cysteine, ACT with CTH overexpression unexpectedly reduced glycine, serine, and proline concentration within the tumor interstitial fluid. Interestingly, in vitro tumor cell growth was mostly impacted by the combination of serine/proline or serine/glycine deprivation. These results suggest that metabolic gene engineering of T cells could be further investigated to locally modulate amino acid availability within the tumor environment while avoiding systemic toxicity.

High neutralizing potency of swine glyco-humanized polyclonal antibodies against SARS-CoV-2.

Heterologous polyclonal antibodies might represent an alternative to the use of convalescent plasma or monoclonal antibodies (mAbs) in coronavirus disease (COVID-19) by targeting multiple antigen epitopes. However, heterologous antibodies trigger human natural xenogeneic antibody responses particularly directed against animal-type carbohydrates, mainly the N-glycolyl form of the neuraminic acid (Neu5Gc) and the α1,3-galactose, potentially leading to serum sickness or allergy. Here, we immunized cytidine monophosphate-N-acetylneuraminic acid hydroxylase and α1,3-galactosyl-transferase (GGTA1) double KO pigs with the Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike receptor binding domain to produce glyco-humanized polyclonal neutralizing antibodies lacking Neu5Gc and α1,3-galactose epitopes. Animals rapidly developed a hyperimmune response with anti-SARS-CoV-2 end-titers binding dilutions over one to a million and end-titers neutralizing dilutions of 1:10 000. The IgG fraction purified and formulated following clinical Good Manufacturing Practices, named XAV-19, neutralized spike/angiotensin converting enzyme-2 interaction at a concentration <1 µg/mL, and inhibited infection of human cells by SARS-CoV-2 in cytopathic assays. We also found that pig GH-pAb Fc domains fail to interact with human Fc receptors, thereby avoiding macrophage-dependent exacerbated inflammatory responses and a possible antibody-dependent enhancement. These data and the accumulating safety advantages of using GH-pAbs in humans warrant clinical assessment of XAV-19 against COVID-19.

Selective SIRPα blockade reverses tumor T cell exclusion and overcomes cancer immunotherapy resistance.

T cell exclusion causes resistance to cancer immunotherapies via immune checkpoint blockade (ICB). Myeloid cells contribute to resistance by expressing signal regulatory protein-α (SIRPα), an inhibitory membrane receptor that interacts with ubiquitous receptor CD47 to control macrophage phagocytosis in the tumor microenvironment. Although CD47/SIRPα-targeting drugs have been assessed in preclinical models, the therapeutic benefit of selectively blocking SIRPα, and not SIRPγ/CD47, in humans remains unknown. We report a potent synergy between selective SIRPα blockade and ICB in increasing memory T cell responses and reverting exclusion in syngeneic and orthotopic tumor models. Selective SIRPα blockade stimulated tumor nest T cell recruitment by restoring murine and human macrophage chemokine secretion and increased anti-tumor T cell responses by promoting tumor-antigen crosspresentation by dendritic cells. However, nonselective SIRPα/SIRPγ blockade targeting CD47 impaired human T cell activation, proliferation, and endothelial transmigration. Selective SIRPα inhibition opens an attractive avenue to overcoming ICB resistance in patients with elevated myeloid cell infiltration in solid tumors.

Corneal Xenotransplantation: Anterior Lamellar Keratoplasty.

Corneal transplantation for the treatment of corneal blindness is challenging in many countries due to the shortage of graft procurement. Xenocorneal transplantation is an interesting alternative to explore despite immunologic rejection, which mainly involves endothelial cells. As anterior lamellar keratoplasty, when indicated, shows less immunologic reaction, we developed and describe below a pig-to-non-human-primate model of anterior lamellar corneal xenograft. This model can be used to assess the efficacy of corneas from genetically modified pigs.

Interleukin-7 receptor blockade by an anti-CD127 monoclonal antibody in nonhuman primate kidney transplantation.

IL-7 is an important cytokine for T cell lymphopoiesis. Blockade of the IL-7 signaling pathway has been shown to induce long-term graft survival or graft tolerance in murine transplant models through inhibiting T cell homeostasis and favoring immunoregulation. In this study, we assessed for the first time the effects of a blocking anti-human cluster of differentiation 127 (CD127) mAb administered in combination with low-dose tacrolimus or thymoglobulin in a life-sustaining kidney allograft model in baboons. Contrary to our expectation, the addition of an anti-CD127 mAb to the treatment protocols did not prolong graft survival compared to low-dose tacrolimus alone or thymoglobulin alone. Anti-CD127 mAb administration led to full CD127 receptor occupancy during the follow-up period. However, all treated animals lost their kidney graft between 1 week and 2 weeks after transplantation. Unlike in rodents, in nonhuman primates, anti-CD127 mAb treatment does not decrease the absolute numbers of lymphocyte and lymphocyte subsets and does not effectively inhibit postdepletional T cell proliferation and homeostasis, suggesting that IL-7 is not a limiting factor for T cell homeostasis in primates.

High neutralizing potency of swine glyco-humanized polyclonal antibodies against SARS-CoV-2.

Perfusion of convalescent plasma (CP) has demonstrated a potential to improve the pneumonia induced by SARS-CoV-2, but procurement and standardization of CP are barriers to its wide usage. Many monoclonal antibodies (mAbs) have been developed but appear insufficient to neutralize SARS-CoV-2 unless two or three of them are being combined. Therefore, heterologous polyclonal antibodies of animal origin, that have been used for decades to fight against infectious agents might represent a highly efficient alternative to the use of CP or mAbs in COVID-19 by targeting multiple antigen epitopes. However, conventional heterologous polyclonal antibodies trigger human natural xenogeneic antibody responses particularly directed against animal-type carbohydrate epitopes, mainly the N-glycolyl form of the neuraminic acid (Neu5Gc) and the Gal α1,3-galactose (αGal), ultimately forming immune complexes and potentially leading to serum sickness or allergy. To circumvent these drawbacks, we engineered animals lacking the genes coding for the cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) and α1,3-galactosyl-transferase (GGTA1) enzymes to produce glyco-humanized polyclonal antibodies (GH-pAb) lacking Neu5Gc and α-Gal epitopes. We found that pig IgG Fc domains fail to interact with human Fc receptors and thereby should confer the safety advantage to avoiding macrophage dependent exacerbated inflammatory responses, a drawback possibly associated with antibody responses against SARS-CoV-2 or to avoiding a possible antibody-dependent enhancement (ADE). Therefore, we immunized CMAH/GGTA1 double knockout (DKO) pigs with the SARS-CoV-2 spike receptor-binding domain (RBD) to elicit neutralizing antibodies. Animals rapidly developed a hyperimmune response with anti-SARS-CoV-2 end-titers binding dilutions over one to a million and end-titers neutralizing dilutions of 1:10,000. The IgG fraction purified and formulated following clinical Good Manufacturing Practices, named XAV-19, neutralized Spike/angiotensin converting enzyme-2 (ACE-2) interaction at a concentration < 1µg/mL and inhibited infection of human cells by SARS-CoV-2 in cytopathic assays. These data and the accumulating safety advantages of using glyco-humanized swine antibodies in humans warranted clinical assessment of XAV-19 to fight against COVID-19.

In Vivo Analysis of Human Immune Responses in Immunodeficient Rats.

BACKGROUND: Humanized immune system immunodeficient mice have been extremely useful for the in vivo analyses of immune responses in a variety of models, including organ transplantation and graft versus host disease (GVHD) but they have limitations. Rat models are interesting complementary alternatives presenting advantages over mice, such as their size and their active complement compartment. Immunodeficient rats have been generated but human immune responses have not yet been described. METHODS: We generated immunodeficient Rat Rag-/- Gamma chain-/- human signal regulatory protein alpha-positive (RRGS) rats combining Rag1 and Il2rg deficiency with the expression of human signal regulatory protein alpha, a negative regulator of macrophage phagocytosis allowing repression of rat macrophages by human CD47-positive cells. We then immune humanized RRGS animals with human peripheral blood mononuclear cells (hPBMCs) to set up a human acute GVHD model. Treatment of GVHD was done with a new porcine antihuman lymphocyte serum active through complement-dependent cytotoxicity. We also established a tumor xenograft rejection model in these hPBMCs immune system RRGS animals by subcutaneous implantation of a human tumor cell line. RESULTS: RRGS animals receiving hPBMCs showed robust and reproducible reconstitution, mainly by T and B cells. A dose-dependent acute GVHD process was observed with progressive weight loss, tissue damage, and death censoring. Antihuman lymphocyte serum (L1S1) antibody completely prevented acute GVHD. In the human tumor xenograft model, detectable tumors were rejected upon hPBMCs injection. CONCLUSIONS: hPBMC can be implanted in RRGS animals and elicit acute GVHD or rejection of human tumor cells and these are useful models to test new immunotherapies.

Human Tolerogenic Dendritic Cells Regulate Immune Responses through Lactate Synthesis.

Cell therapy is a promising strategy for treating patients suffering from autoimmune or inflammatory diseases or receiving a transplant. Based on our preclinical studies, we have generated human autologous tolerogenic dendritic cells (ATDCs), which are being tested in a first-in-man clinical trial in kidney transplant recipients. Here, we report that ATDCs represent a unique subset of monocyte-derived cells based on phenotypic, transcriptomic, and metabolic analyses. ATDCs are characterized by their suppression of T cell proliferation and their expansion of Tregs through secreted factors. ATDCs produce high levels of lactate that shape T cell responses toward tolerance. Indeed, T cells take up ATDC-secreted lactate, leading to a decrease of their glycolysis. In vivo, ATDCs promote elevated levels of circulating lactate and delay graft-versus-host disease by reducing T cell proliferative capacity. The suppression of T cell immunity through lactate production by ATDCs is a novel mechanism that distinguishes ATDCs from other cell-based immunotherapies.

SIRPα/CD47 axis controls the maintenance of transplant tolerance sustained by myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature hematopoietic precursors known to suppress immune responses. Interaction of SIRP alpha (SIRPα), expressed by myeloid cells, with the ubiquitous receptor CD47 is an important immune checkpoint of the innate response regulating macrophages and dendritic cells functions. We previously described that MDSC expressing SIRPα accumulated after transplantation and maintained kidney allograft tolerance. However, the role of the SIRPα/CD47 axis on MDSC function remained unknown. Here, we found that blocking SIRPα or CD47 with monoclonal antibodies (mAbs) induced differentiation of MDSC into myeloid cells overexpressing MHC class II, CD86 costimulatory molecule and increased secretion of macrophage-recruiting chemokines (eg, MCP-1). Using a model of long-term kidney allograft tolerance sustained by MDSC, we observed that administration of blocking anti-SIRPα or CD47 mAbs induced graft dysfunction and rejection. Loss of tolerance came along with significant decrease of MDSC and increase in MCP-1 concentration in the periphery. Graft histological and transcriptomic analyses revealed an inflammatory (M1) macrophagic signature at rejection associated with overexpression of MCP-1 mRNA and protein in the graft. These findings indicate that the SIRPα-CD47 axis regulates the immature phenotype and chemokine secretion of MDSC and contributes to the induction and the active maintenance of peripheral acquired immune tolerance.