The impact of IdeS (imlifidase) on allo-specific, xeno-reactive, and protective antibodies in a sensitized rhesus macaque model

BACKGROUND

Highly sensitized patients face many barriers to kidney transplantation, including higher rates of antibody-mediated rejection after HLA-incompatible transplant. IdeS, an endopeptidase that cleaves IgG nonspecifically, has been trialed as desensitization prior to kidney transplant, and successfully cleaves donor-specific antibody (DSA), albeit with rebound.

METHODS

IdeS was generated and tested (2 mg/kg, IV) in two naïve and four allosensitized nonhuman primates (NHP). Peripheral blood samples were collected at regular intervals following IdeS administration. Total IgG, total IgM, and anti-CMV antibodies were quantified with ELISA, and donor-specific antibody (DSA) and anti-pig antibodies were evaluated using flow cytometric crossmatch. B cell populations were assessed using flow cytometry.

RESULTS

IdeS successfully cleaved rhesus IgG in vitro. In allosensitized NHP, robust reduction of total, DSA, anti-pig, and anti-CMV IgG was observed within one day following IdeS administration. Rapid rebound of all IgG antibody populations was observed, with antibody levels returning to baseline around day 14 post-infusion. Total IgM level was not affected by IdeS. Interestingly, a comparable reduction in antibody populations was observed after the second dose of IdeS. However, we have not observed any significant modulation of B cell subpopulations after IdeS.

CONCLUSIONS

This study evaluated efficacy of IdeS in the allosensitized NHP in IgG with various specificities, mirroring antibody kinetics in human patients. The efficacy of IdeS on preexisting anti-pig antibodies may be useful in clinical xenotransplantation. However, given the limitation of IdeS on its durability as a monotherapy, optimization of IdeS with other agents targeting the humoral response is further needed.

Efficacy of pediatric SARS-CoV-2 vaccines against high-dose B.1.617.2 challenge one year after vaccination of infant rhesus macaques

To advance SARS-CoV-2 vaccines in infants younger than 5 years, we tested the efficacy of two SARS-CoV-2 vaccine platforms against challenge with the delta variant one year after immunization of infant rhesus macaques (RM).

Infant RMs (n=8/ group; 2 month-old) were immunized intramuscularly at weeks 0 and 4 with 30 mg stabilized prefusion SARS-CoV-2 S-2P spike (S) protein (Washington strain) encoded by mRNA encapsulated in lipid nanoparticles (mRNA-LNP) or 15 mg S protein mixed with 3M-052 in stable emulsion (Protein). At 1 year, vaccinated and age-matched unvaccinated RM (n=8) were challenged intranasally (106 pfu) and intratracheally (2×106 pfu) with B.1.617.2. Lung pathology was blindly assessed on day 7. Viral RNA copies of the N gene (vRNA) were measured by qPCR in nasal and pharyngeal swabs.

Severe lung pathology was observed in 7 of 8 controls compared to 1 of 8 or 0 of 8 RM in the mRNA-LNP or protein group, respectively. On days 2 and 4, vRNA copies/ml were significantly higher in pharyngeal swabs of control RM (day 2: 4.2p>

Supported by grants from NIH PO1 AI117915

Neonatal vaccination primes persistent HIV Env-specific antibodies that are augmented by a single booster immunization in late infancy

Breastmilk transmission of HIV remains unacceptably high. Vaccine approaches that prime robust virus-specific immune responses in infancy may prevent acquisition during the breastfeeding period. Moreover, vaccine responses that generate robust immunological memory that persists into adolescence could prevent sexual transmission later in life.

The current study investigated the immunological benefit of late boosting following vaccination in infancy. Two groups of neonatal rhesus macaques were immunized with a clade C HIV Env protein adjuvanted with 3M-052 stable emulsion (SE) vaccine (Env Only) alone or together with a modified vaccinia Ankara (MVA) vector expressing HIV Env and SIV Gag (MVA/Env) at 0, 6, and 12 weeks of age. Env-specific B cells were present in blood yet absent from lymph nodes in the Env Only group by week 14. At week 32, 18 weeks following the last immunization, we could still detect Env-specific plasma IgG responses capable of autologous and heterologous HIV Env binding, Env-specific ADCC activity and CD4 blocking in both groups. A final booster immunization at week 32 enhanced avidity and function of Env-specific plasma IgG in both groups. These data confirmed previous work by our group that demonstrated HIV Env protein adjuvanted with the TLR7/8-based 3M-052-SE primed greater immune responses than Span85-Tween 80 Squalene.

Our data from the Env Only vaccine regimen are consistent with the induction of Env-specific antibody responses in human infants. These results support the idea that early life vaccination is an effective means to induce persistent HIV Env-specific IgG responses that can be boosted in infancy and could be exploited to drive protective immunity against HIV acquisition prior to sexual debut.

An oral prime/boost pediatric vaccine strategy for the prevention of mother-to-child transmission of HIV by breast-feeding

In 2014, an estimated 220,000 children became newly HIV-infected, with 50% being transmitted via breast-feeding. The present study assessed whether inclusion of an oral route of immunization would increase pediatric vaccine efficacy in the rhesus macaque model of oral SIV infection.

Two groups of 6 neonatal macaques received 2 DNA-SIV immunizations at weeks 0 and 3, followed by 2 boosts with modified vaccinia Ankara virus (MVA)-SIVgag/pol/env at weeks 6 and 9. Group A was immunized by the intramuscular (IM) route. Infants in Group B received the DNA-prime both per-orally (PO) and IM and MVA-SIV was administered both by the sublingual (SL) and IM route. Mock control animals received saline immunizations PO+IM at weeks 0 and 3 and mock MVA vector SL+IM at weeks 6 and 9. At week 12, all infants were challenged once weekly using a low-dose (102 TCID50) oral SIVmac251 challenge regimen until systemic infection was confirmed by PCR. Statistical significance was determined using nonparametric Mann-Whitney or Kruskal-Wallis tests with p<0.05.

Infants vaccinated by the SL/IM route had a significantly lower per-exposure risk of oral SIV infection (p<0.0001; log-ranked Mantel-Cox test) compared to mock- and IM/IM-vaccinated animals and lower peak viremia (p=0.03) compared to mock controls. Control of viremia was associated with higher fecal IgG responses to SIV V1V2 (p=0.0087) and p55 gag (p=0.0087) at the time of oral challenge initiation. In contrast, plasma SIV-specific antibodies did not influence challenge outcome.

These data indicate that the inclusion of an oral route in a pediatric vaccine to prevent oral SIV infection is superior to an IM only regimen and emphasizes the importance of enhancing mucosal immune responses via local immunization.

Vaccine-induced salivary IgA reduces SIV viremia in neonatal rhesus macaques. (P4501)

Vertical transmission of HIV in breast milk remains a primary route of pediatric infections. While neutralizing antibodies are important for preventing viral entry, the role of mucosal antibodies for virus neutralization is still not well described. Neonates produce less mucosal IgA than adults and are thus more susceptible to oral pathogens. Here we tested whether an oral pediatric SIV vaccine could induce salivary IgA and protect against oral SIV acquisition. Rhesus macaques were immunized orally at birth with a live, attenuated Mycobacterium tuberculosis strain engineered to express SIVgag, pol and env proteins and boosted at 3 and 6 weeks with rMVAgag/pol/env. Starting at week 9, animals were orally challenged using a regimen of low-dose SIVmac251 (5000 TCID50) weekly. Although the vaccine did not prevent infection, vaccinated infants with higher SIV-specific salivary IgA antibodies at the time of challenge had lower peak viremia (p=0.034). A similar inverse correlation was observed between peak viremia and fecal IgA (p=0.0019). Salivary IgA concentrations correlated with fecal IgA (p=0.018) but not with plasma IgA (p=0.911). In fact, both plasma IgA and IgG showed trends towards a positive association with viremia. Thus, mucosal, but not systemic, antibodies efficiently controlled virus replication. Vaccine strategies that promote the development of mucosal IgA antibodies will likely improve the efficacy of pediatric vaccines to prevent oral HIV acquisition.

A novel combination vaccine for HIV-1 and tuberculosis is safe and immunogenic in infant rhesus macaques (53.25)

Despite improved therapies, breast milk transmission of HIV to newborns does not decline. In many resource-poor countries, these infants are also at risk for Mycobacterium tuberculosis infection. We hypothesized that a highly attenuated Mtb with improved safety and similar immunogenicity to the current BCG vaccine, but modified to harbor HIV genes, could protect infants against both HIV and Tb. We have tested 3 different rAMtb-SIV vectors in infant rhesus macaques. Vaccine safety was evaluated by immunizing 1-week old SIV-infected macaques orally (PO) and intradermally (ID) with rAMtb. Next, we tested the immunogenicity of (1) a PO prime/ID boost rAMtb-SIV, (2) a PO rAMtb-SIV prime/IM Ad5-SIV boost, and (3) an ID rAMtb-SIV prime/IM Ad5-SIV boost vaccine regimen. Our studies show that rAMtb-SIV does not cause rAMtb dissemination, even when given to immunocompromised SIV infected infants. Further, our data confirm that the oral route of immunization is effective in infant macaques. Vaccinated animals showed increased dendritic cell responsiveness to in vitro TLR stimulation, supporting our hypothesis that rAMtb is highly immunogenic in infants. While all vaccine regimens elicited cellular and humoral Mtb-specific immune responses, SIV-specific responses were greatly enhanced by the heterologous boost. Thus, rAMtb-HIV should be further developed as a pediatric combination vaccine. We will test vaccine efficacy against multiple oral SIV challenges and against Mtb exposure.

Development of an LC-MS/MS assay to determine plasma pharmacokinetics of the radioprotectant octadecenyl thiophosphate (OTP) in monkeys

Octadecenyl thiophosphate (OTP), a synthetic analogue of the lysophospholipid growth factor lysophosphatidic acid (LPA), significantly reduces mortality following a lethal dose of LD(80/30) radiation exposure in a mouse model of whole-body irradiation. To facilitate dose scaling between species, we developed a novel liquid chromatography/tandem mass spectrometry (LC-MS/MS) for the preclinical pharmacokinetic characterization of OTP in monkeys. Sample extraction was carried out using a butanol based liquid-liquid extraction method. A partially deuterated OTP analogue was used as internal standard (IS). OTP and IS were separated by reversed-phase liquid chromatography on a C-8 column using 10mM ammonium acetate and acetonitrile. A triple quadrupole mass spectrometer operating in the negative electrospray ionization mode with multiple reaction monitoring was used to detect OTP and IS transitions of m/z 363.1-->95.0 and 403.1-->95.0. The method was applied to determine pharmacokinetic parameters in monkeys receiving a single oral OTP dose (3mg/kg). OTP is readily absorbed with a relatively long half-life which supports further preclinical testing of OTP as a radioprotectant in monkeys.

Enhanced in vivo immunogenicity of SIV vaccine candidates with cationic liposome-DNA complexes in a rhesus macaque pilot study

This pilot study tested the immunogenicity of a novel cationic liposome-DNA complex (CLDC) immunomodulatory vaccine adjuvant. Combined with a specific antigen, CLDC enhanced anti-SIV immune responses induced by various SIV vaccine candidates. Rhesus macaques immunized in the presence of CLDC developed stronger SIV-specific T and B cell responses compared to animals immunized without CLDC. These differences persisted and resulted in better memory responses after an in vivo boost of the animals several months later with whole AT-2 inactivated SIVmac239. Thus, CLDC should be explored further as a potential immunomodulatory adjuvant in HIV vaccine design.

Rhesus macaque polyclonal and monoclonal antibodies inhibit simian immunodeficiency virus in the presence of human or autologous rhesus effector cells

Although antibodies can prevent or modulate lentivirus infections in nonhuman primates, the biological functions of antibody responsible for such effects are not known. We sought to determine the role of antibody-dependent cell-mediated virus inhibition (ADCVI), an antibody function that inhibits virus yield from infected cells in the presence of Fc receptor-bearing effector cells, in preventing or controlling SIVmac251 infection in rhesus macaques (Macaca mulatta). Using CEMx174 cells infected with simian immunodeficiency virus mac251 (SIVmac251), both polyclonal and monoclonal anti-SIV antibodies were capable of potent virus inhibition in the presence of human peripheral blood mononuclear cell (PBMC) effector cells. In the absence of effector cells, virus inhibition was generally very poor. PBMCs from healthy rhesus macaques were also capable of mediating virus inhibition either against SIVmac251-infected CEMx174 cells or against infected, autologous rhesus target cells. We identified both CD14(+) cells and, to a lesser extent, CD8(+) cells as the effector cell population in the rhesus PBMCs. Finally, pooled, nonneutralizing SIV-antibody-positive serum, shown in a previous study to prevent infection of neonatal macaques after oral SIVmac251 challenge, had potent virus-inhibitory activity in the presence of effector cells; intact immunoglobulin G, rather than F(ab')(2), was required for such activity. This is the first demonstration of both humoral and cellular ADCVI functions in the macaque-SIV model. ADCVI activity in nonneutralizing serum that prevents SIV infection suggests that ADCVI may be a protective immune function. Finally, our data underscore the potential importance of Fc-Fc receptor interactions in mediating biological activities of antibody.

Immunoprophylaxis to Prevent Mother-to-Child Transmission of HIV-1

Antiretroviral therapy can profoundly reduce the risk of mother-to-child transmission (MTCT) of HIV, but the drugs have a relatively short half-life and should thus be administered throughout breast-feeding to optimally prevent postnatal infection of the infant. The potential toxicities and the development of resistance may limit the long-term efficacy of antiretroviral prophylaxis, and a safe and effective active/passive immunoprophylaxis regimen, begun at birth, and potentially overlapping with interpartum or neonatal chemoprophylaxis, would pose an attractive alternative. This review draws on data presented at the Ghent Workshop on prevention of breast milk transmission and on selected issues from a workshop specifically relating to immunoprophylaxis held in Seattle in October 2002. This purpose of this review is to address the scientific rationale for the development of passive (antibody) and active (vaccine) immunization strategies for prevention of MTCT. Data regarding currently or imminently available passive and active immunoprophylaxis products are reviewed for their potential use in neonatal trials within the coming 1-2 years.

Use of Antiretroviral Drugs to Prevent HIV-1 Transmission Through Breast-feeding: From Animal Studies to Randomized Clinical Trials

The major remaining challenge in the prevention of mother-to-child transmission is the reduction of the risk in settings where breast-feeding is common. This review gives an update on ongoing or planned antiretroviral intervention studies in resource-limited settings that are aimed at reducing the risk of mother-to-infant HIV transmission during lactation. These strategies include antiretroviral therapy given to the mother to reduce viral load in plasma and breast milk as well as antiretroviral regimens providing prophylaxis to uninfected infants during the period of breast-feeding. The rationale for the interventions based on animal models and human studies is described as well as the study designs of clinical trials. Potential risks and benefits of these interventions to mothers and infants are also highlighted. Laboratory studies nested within several of these trials will provide a better understanding of the pathogenesis of postnatal HIV transmission and its potential prevention using antiretroviral drugs.