Engineered IgM and IgG cleaving enzymes for mitigating antibody neutralization and complement activation in AAV gene transfer.

Systemic dosing of adeno-associated viral (AAV) vectors poses potential risk of adverse side effects including complement activation triggered by anti-capsid immunity. Due to the multifactorial nature of toxicities observed in this setting, a wide spectrum of immune modulatory regimens are being investigated in the clinic. Here, we discover an IgM cleaving enzyme (IceM) that degrades human IgM, a key trigger in the anti-AAV immune cascade. We then engineer a fusion enzyme (IceMG) with dual proteolytic activity against human IgM and IgG. IceMG cleaves B cell surface antigen receptors and inactivates phospholipase gamma signaling in vitro. Importantly, IceMG is more effective at inhibiting complement activation compared with an IgG cleaving enzyme alone. Upon IV dosing, IceMG rapidly and reversibly clears circulating IgM and IgG in macaques. Antisera from these animals treated with IceMG shows decreased ability to neutralize AAV and activate complement. Consistently, pre-conditioning with IceMG restores AAV transduction in mice passively immunized with human antisera. Thus, IgM cleaving enzymes show promise in simultaneously addressing multiple aspects of anti-AAV immunity mediated by B cells, circulating antibodies and complement. These studies have implications for improving safety of AAV gene therapies and possibly broader applications including organ transplantation and autoimmune diseases.

Correlation of antigen expression with epigenetic modifications after rAAV delivery of a human factor IX variant in mice and rhesus macaques.

We investigated long-term human coagulation factor IX (huFIX) expression of a novel variant when delivered into mice and rhesus macaques and compared transduction efficiencies using two different adeno-associated virus (AAV) capsids. In hemophilic mice injected with KP1-packaged recombinant AAV (rAAV) expressing the hyperactive FIX variant specific activity plasma levels were 10-fold or 2-fold enhanced when compared with wild-type or Padua huFIX injected mice, respectively. In rhesus macaques AAV-LK03 capsid outperformed AAV-KP1 in terms of antigen expression and liver transduction. Two animals from each group showed sustained low-level huFIX expression at 3 months after administration, while one animal from each group lost huFIX mRNA and protein expression over time, despite comparable vector copies. We investigated whether epigenetic differences in the vector episomes could explain this loss of transcription. Cut&Tag analysis revealed lower levels of activating histone marks in the two animals that lost expression. When comparing rAAV genome associated histone modifications in rhesus macaques with those in mice injected with the same vector, the activating histone marks were starkly decreased in macaque-derived episomes. Differential epigenetic marking of AAV genomes may explain different expression profiles in mice and rhesus macaques, as well as the wide dose response variation observed in primates in both preclinical and human clinical trials.

Expression patterns of CYP26A1, FGF8, CDKN1A, and NPVF in the developing rhesus monkey retina.

The fovea centralis (fovea) is a specialized region of the primate retina that plays crucial roles in high-resolution visual acuity and color perception. The fovea is characterized by a high density of cone photoreceptors and no rods, and unique anatomical properties that contribute to its remarkable visual capabilities. Early histological analyses identified some of the key events that contribute to foveal development, but the mechanisms that direct the specification of this area are not understood. Recently, the expression of the retinoic acid-metabolizing enzyme CYP26A1 has become a hallmark of some of the retinal specializations found in vertebrates, including the primate fovea and the high-acuity area in avian species. In chickens, the retinoic acid pathway regulates the expression of FGF8 to then direct the development of a rod-free area. Similarly, high levels of CYP26A1, CDKN1A, and NPVF expression have been observed in the primate macula using transcriptomic approaches. However, which retinal cells express these genes and their expression dynamics in the developing primate eye remain unknown. Here, we systematically characterize the expression patterns of CYP26A1, FGF8, CDKN1A, and NPVF during the development of the rhesus monkey retina, from early stages of development in the first trimester until the third trimester (near term). Our data suggest that some of the markers previously proposed to be fovea-specific are not enriched in the progenitors of the rhesus monkey fovea. In contrast, CYP26A1 is expressed at high levels in the progenitors of the fovea, while it localizes in a subpopulation of macular Müller glia cells later in development. Together these data provide invaluable insights into the expression dynamics of several molecules in the nonhuman primate retina and highlight the developmental advancement of the foveal region.

Imaging the fetal nonhuman primate brain with SV2A positron emission tomography (PET).

PURPOSE: Exploring synaptic density changes during brain growth is crucial to understanding brain development. Previous studies in nonhuman primates report a rapid increase in synapse number between the late gestational period and the early neonatal period, such that synaptic density approaches adult levels by birth. Prenatal synaptic development may have an enduring impact on postnatal brain development, but precisely how synaptic density changes in utero are unknown because current methods to quantify synaptic density are invasive and require post-mortem brain tissue. METHODS: We used synaptic vesicle glycoprotein 2A (SV2A) positron emission tomography (PET) radioligands [11C]UCB-J and [18F]Syn-VesT-1 to conduct the first assessment of synaptic density in the developing fetal brain in gravid rhesus monkeys. Eight pregnant monkeys were scanned twice during the third trimester at two imaging sites. Fetal post-mortem samples were collected near term in a subset of subjects to quantify SV2A density by Western blot. RESULTS: Image-derived fetal brain SV2A measures increased during the third trimester. SV2A concentrations were greater in subcortical regions than in cortical regions at both gestational ages. Near term, SV2A density was higher in primary motor and visual areas than respective associative regions. Post-mortem quantification of SV2A density was significantly correlated with regional SV2A PET measures. CONCLUSION: While further study is needed to determine the exact relationship of SV2A and synaptic density, the imaging paradigm developed in the current study allows for the effective in vivo study of SV2A development in the fetal brain.

Fetal Rhesus Monkey First Trimester Zika Virus Infection Impacts Cortical Development in the Second and Third Trimesters.

Zika virus is a teratogen similar to other neurotropic viruses, notably cytomegalovirus and rubella. The goal of these studies was to address the direct impact of Zika virus on fetal development by inoculating early gestation fetal rhesus monkeys using an ultrasound-guided approach (intraperitoneal vs. intraventricular). Growth and development were monitored across gestation, maternal samples collected, and fetal tissues obtained in the second trimester or near term. Although normal growth and anatomical development were observed, significant morphologic changes were noted in the cerebral cortex at 3-weeks post-Zika virus inoculation including massive alterations in the distribution, density, number, and morphology of microglial cells in proliferative regions of the fetal cerebral cortex; an altered distribution of Tbr2+ neural precursor cells; increased diameter and volume of blood vessels in the cortical proliferative zones; and a thinner cortical plate. At 3-months postinoculation, alterations in morphology, distribution, and density of microglial cells were also observed with an increase in blood vessel volume; and a thinner cortical plate. Only transient maternal viremia was observed but sustained maternal immune activation was detected. Overall, these studies suggest persistent changes in cortical structure result from early gestation Zika virus exposure with durable effects on microglial cells.

Cortical Interlaminar Astrocytes Are Generated Prenatally, Mature Postnatally, and Express Unique Markers in Human and Nonhuman Primates.

Interlaminar astrocytes (ILAs) are a subset of cortical astrocytes that reside in layer I, express GFAP, have a soma contacting the pia, and contain long interlaminar processes that extend through several cortical layers. We studied the prenatal and postnatal development of ILAs in three species of primates (rhesus macaque, chimpanzee, and human). We found that ILAs are generated prenatally likely from radial glial (RG) cells, that ILAs proliferate locally during gestation, and that ILAs extend interlaminar processes during postnatal stages of development. We showed that the density and morphological complexity of ILAs increase with age, and that ILAs express multiple markers that are expressed by RG cells (Pax6, Sox2, and Nestin), specific to inner and outer RG cells (Cryab and Hopx), and astrocyte markers (S100ß, Aqp4, and GLAST) in prenatal stages and in adult. Finally, we demonstrated that rudimentary ILAs in mouse also express the RG markers Pax6, Sox2, and Nestin, but do not express S100ß, Cryab, or Hopx, and that the density and morphological complexity of ILAs differ between primate species and mouse. Together these findings contribute new information on astrogenesis of this unique class of cells and suggest a lineal relationship between RG cells and ILAs.

Fetal Surgery in the Primate 4.0: A New Technique 30 Years Later.

INTRODUCTION: Open fetal surgery requires a hemostatic hysterotomy that minimizes membrane separation. For over 30 years, the standard of care for hysterotomy in the gravid uterus has been the AutoSuture Premium Poly CS*-57 stapler. OBJECTIVE: In this study, we sought to test the feasibility of hysterotomy in a rhesus monkey model with the Harmonic ACE®+7 Shears. METHODS: A gravid rhesus monkey underwent midgestation hysterotomy at approximately 90 days of gestation (2nd trimester; term = 165 ± 10 days) using the Harmonic ACE®+7 Shears. A two-layer uterine closure was completed and the dam was monitored by ultrasound intermittently throughout the pregnancy. At 58 days after hysterotomy (near term), a final surgery was performed to evaluate the uterus and hysterotomy site. RESULTS: A 3.5-cm hysterotomy was completed in 2 min 7 s. The opening was hemostatic and the membranes were sealed. Immediately after closure and throughout the pregnancy, ultrasound revealed intact membranes without separation and normal amniotic fluid levels. At term, the scar was well healed without signs of thinning or dehiscence. CONCLUSIONS: The Harmonic ACE®+7 Shears produced a hemostatic midgestation hysterotomy with membrane sealing in the rhesus monkey model. Importantly, healing was acceptable.

Microglia: An Intrinsic Component of the Proliferative Zones in the Fetal Rhesus Monkey (Macaca mulatta) Cerebral Cortex.

Microglial cells are increasingly recognized as modulators of brain development. We previously showed that microglia colonize the cortical proliferative zones in the prenatal brain and regulate the number of precursor cells through phagocytosis. To better define cellular interactions between microglia and proliferative cells, we performed lentiviral vector-mediated intraventricular gene transfer to induce enhanced green fluorescent protein expression in fetal cerebrocortical cells. Tissues were collected and counterstained with cell-specific markers to label microglial cells and identify other cortical cell types. We found that microglial cells intimately interact with the radial glial scaffold and make extensive contacts with neural precursor cells throughout the proliferative zones, particularly in the rhesus monkey fetus when compared to rodents. We also identify a subtype of microglia, which we term 'periventricular microglia', that interact closely with mitotic precursor cells in the ventricular zone. Our data suggest that microglia are structural modulators that facilitate remodeling of the proliferative zones as precursor cells migrate away from the ventricle and may facilitate the delamination of precursor cells. Taken together, these results indicate that microglial cells are an integral component of cortical proliferative zones and contribute to the interactive milieu in which cortical precursor cells function.

Highly efficient maternal-fetal Zika virus transmission in pregnant rhesus macaques.

Infection with Zika virus (ZIKV) is associated with human congenital fetal anomalies. To model fetal outcomes in nonhuman primates, we administered Asian-lineage ZIKV subcutaneously to four pregnant rhesus macaques. While non-pregnant animals in a previous study contemporary with the current report clear viremia within 10-12 days, maternal viremia was prolonged in 3 of 4 pregnancies. Fetal head growth velocity in the last month of gestation determined by ultrasound assessment of head circumference was decreased in comparison with biparietal diameter and femur length within each fetus, both within normal range. ZIKV RNA was detected in tissues from all four fetuses at term cesarean section. In all pregnancies, neutrophilic infiltration was present at the maternal-fetal interface (decidua, placenta, fetal membranes), in various fetal tissues, and in fetal retina, choroid, and optic nerve (first trimester infection only). Consistent vertical transmission in this primate model may provide a platform to assess risk factors and test therapeutic interventions for interruption of fetal infection. The results may also suggest that maternal-fetal ZIKV transmission in human pregnancy may be more frequent than currently appreciated.

Safety profile after prolonged C3 inhibition.

The central component of the complement cascade, C3, is involved in various biological functions, including opsonization of foreign bodies, clearance of waste material, activation of immune cells, and triggering of pathways controlling development. Given its broad role in immune responses, particularly in phagocytosis and the clearance of microbes, a deficiency in complement C3 in humans is often associated with multiple bacterial infections. Interestingly, an increased susceptibility to infections appears to occur mainly in the first two years of life and then wanes throughout adulthood. In view of the well-established connection between C3 deficiency and infections, therapeutic inhibition of complement at the level of C3 is often considered with caution or disregarded. We therefore set out to investigate the immune and biochemical profile of non-human primates under prolonged treatment with the C3 inhibitor compstatin (Cp40 analog). Cynomolgus monkeys were dosed subcutaneously with Cp40, resulting in systemic inhibition of C3, for 1 week, 2 weeks, or 3 months. Plasma concentrations of both C3 and Cp40 were measured periodically and complete saturation of plasma C3 was confirmed. No differences in hematological, biochemical, or immunological parameters were identified in the blood or tissues of animals treated with Cp40 when compared to those injected with vehicle alone. Further, skin wounds showed no signs of infection in those treated with Cp40. In fact, Cp40 treatment was associated with a trend toward accelerated wound healing when compared with the control group. In addition, a biodistribution study in a rhesus monkey indicated that the distribution of Cp40 in the body is associated with the presence of C3, concentrating in organs that accumulate blood and produce C3. Overall, our data suggest that systemic C3 inhibition in healthy adult non-human primates is not associated with a weakened immune system or susceptibility to infections.

Neonatal Systemic AAV Induces Tolerance to CNS Gene Therapy in MPS I Dogs and Nonhuman Primates.

The potential host immune response to a nonself protein poses a fundamental challenge for gene therapies targeting recessive diseases. We demonstrate in both dogs and nonhuman primates that liver-directed gene transfer using an adeno-associated virus (AAV) vector in neonates induces a persistent state of immunological tolerance to the transgene product, substantially improving the efficacy of subsequent vector administration targeting the central nervous system (CNS). We applied this approach to a canine model of mucopolysaccharidosis type I (MPS I), a progressive neuropathic lysosomal storage disease caused by deficient activity of the enzyme α-l-iduronidase (IDUA). MPS I dogs treated systemically in the first week of life with a vector expressing canine IDUA did not develop antibodies against the enzyme and exhibited robust expression in the CNS upon intrathecal AAV delivery at 1 month of age, resulting in complete correction of brain storage lesions. Newborn rhesus monkeys treated systemically with AAV vector expressing human IDUA developed tolerance to the transgene, resulting in high cerebrospinal fluid (CSF) IDUA expression and no antibody induction after subsequent CNS gene therapy. These findings suggest that inducing tolerance to the transgene product during a critical period in immunological development can improve the efficacy and safety of gene therapy.

Comparable Genital Tract Infection, Pathology, and Immunity in Rhesus Macaques Inoculated with Wild-Type or Plasmid-Deficient Chlamydia trachomatis Serovar D.

Rhesus macaques were studied to directly address the potential for plasmid-deficient Chlamydia trachomatis to serve as a live attenuated vaccine in the genital tract. Five repeated cervical inoculations of rhesus macaques with wild-type serovar D strain D/UW-3/Cx or a plasmid-deficient derivative of this strain, CTD153, resulted in infections with similar kinetics and induced comparable levels of protective immunity. After all animals received five challenges with D/UW-3/Cx, levels of inflammation observed grossly and histologically were similar between the groups. Animals in both groups developed evidence of oviduct dilatation; however, reduced oviduct dilatation was observed for "controllers," i.e., animals without detectable chlamydial DNA in the fimbriae at weeks 5 and 12. Grouping animals into "ascenders" and "controllers" revealed that elevated early T cell responses were associated with protection, whereas higher antibody responses were associated with ascension. Protected animals shared common major histocompatibility complex (MHC) alleles. Overall, genetic differences of individual animals, rather than the presence or absence of the chlamydial plasmid in the primary infecting strain, appeared to play a role in determining the outcome of infection.

Clonidine inhibits anti-non-Gal IgM xenoantibody elicited in multiple pig-to-primate models.

BACKGROUND: Survival of vascularized xenografts is dependent on pre-emptive inhibition of the xenoantibody response against galactosyltransferase knockout (GTKO) porcine organs. Our analysis in multiple GTKO pig-to-primate models of xenotransplantation has demonstrated that the anti-non-gal-α-1,3-gal (anti-non-Gal) xenoantibody response displays limited structural diversity. This allowed our group to identify an experimental compound which selectively inhibited induced anti-non-Gal IgM xenoantibodies. However, because this compound had an unknown safety profile, we extended this line of research to include screening small molecules with known safety profiles allowing rapid advancement to large animal models. METHODS: The NIH clinical collections of small molecules were screened by ELISA for their ability to inhibit xenoantibody binding to GTKO pig endothelial cells. Serum collected from non-immunosuppressed rhesus monkeys at day 14 post-injection with GTKO pig endothelial cells was utilized as a source of elicited xenoantibody for initial screening. Virtual small molecule screening based on xenoantibody structure was used to assess the likelihood that the identified small molecules bound xenoantibody directly. As a proxy for selectivity, ELISAs against tetanus toxoid and the natural antigens laminin, thyroglobulin, and single-stranded DNA (ssDNA) were utilized to assess the ability of the identified reagents to inhibit additional antibody responses. The identified inhibitory small molecules were further tested for their ability to inhibit xenoantibody elicited in multiple settings, including rhesus monkeys pre-treated with an anti-non-Gal selective anti-idiotypic antibody, non-immunosuppressed rhesus monkeys immunized with wild-type fetal pig isletlike cell clusters, and non-immunosuppressed baboons transplanted with GTKO multiple transgenic pig kidneys. RESULTS: Four clinically relevant small molecules inhibited anti-non-Gal IgM binding to GTKO pig endothelial cells in vitro. Three of these drugs displayed a limited region of structural similarity suggesting they may inhibit xenoantibody by a similar mechanism. One of these, the anti-hypertensive agent clonidine, displayed only minimal inhibition of antibodies elicited by vaccination against tetanus toxoid or pre-existing natural antibodies against laminin, thyroglobulin, or ssDNA. Furthermore, clonidine inhibited elicited anti-non-Gal IgM from all animals that demonstrated a xenoantibody response in each experimental setting. CONCLUSIONS: Clinically relevant small molecule drugs with known safety profiles can inhibit xenoantibody elicited against non-Gal antigens in diverse experimental xenotransplantation settings. These molecules are ready to be tested in large animal models. However, it will first be necessary to optimize the timing and dosing required to inhibit xenoantibodies in vivo.

Rhesus monkey (Macaca mulatta) lipoprotein(a) and apolipoprotein(a): high frequency of small size apolipoprotein(a) isoforms.

BACKGROUND: Levels of lipoprotein(a), Lp(a), a genetically regulated independent cardiovascular risk factor present in humans and Old World monkeys, are impacted by the apolipoprotein(a), apo(a), gene. Allele-specific apo(a) levels, taking both the apo(a) genotypic and phenotypic characteristics into account, are useful markers to determine atherosclerotic cardiovascular risk. METHODS: We determined (i) the genetic variability of apo(a), (ii) Lp(a) levels, and (iii) allele-specific apo(a) levels in rhesus monkeys (n = 95). RESULTS: Lp(a) levels differed substantially between animals (range: 4-247 nmol/l) with a skewed distribution toward lower levels. Lp(a) and allele-specific apo(a) levels were inversely related to the number of apo(a) Kringle 4 (K4) repeats. The median apo(a) size was 23 K4 repeats, and the prevalence of a small size apo(a) (≤22 K4) was 43%. CONCLUSIONS: Distribution of Lp(a) and allele-specific apo(a) levels in rhesus monkeys reflected the corresponding human patterns, but with a high prevalence of smaller apo(a) sizes.

Intra-amniotic IL-1ß induces fetal inflammation in rhesus monkeys and alters the regulatory T cell/IL-17 balance.

Very low birth weight preterm newborns are susceptible to the development of debilitating inflammatory diseases, many of which are associated with chorioamnionitis. To define the effects of chorioamnionitis on the fetal immune system, IL-1ß was administered intra-amniotically at ~80% gestation in rhesus monkeys. IL-1ß caused histological chorioamnionitis, as well as lung inflammation (infiltration of neutrophils or monocytes in the fetal airways). There were large increases in multiple proinflammatory cytokine mRNAs in the lungs at 24 h postadministration, which remained elevated relative to controls at 72 h. Intra-amniotic IL-1ß also induced the sustained expression of the surfactant proteins in the lungs. Importantly, IL-1ß significantly altered the balance between inflammatory and regulatory T cells. Twenty-four hours after IL-1ß injection, the frequency of CD3(+)CD4(+)FOXP3(+) T cells was decreased in lymphoid organs. In contrast, IL-17A-producing cells (CD3(+)CD4(+), CD3(+)CD4(-), and CD3(-)CD4(-) subsets) were increased in lymphoid organs. The frequency of IFN-γ-expressing cells did not change. In this model of a single exposure to an inflammatory trigger, CD3(+)CD4(+)FOXP3(+) cells rebounded quickly, and their frequency was increased at 72 h compared with controls. IL-17 expression was also transient. Interestingly, the T cell profile alteration was confined to the lymphoid organs and not to circulating fetal T cells. Together, these results suggest that the chorioamnionitis-induced IL-1/IL-17 axis is involved in the severe inflammation that can develop in preterm newborns. Boosting regulatory T cells and/or controlling IL-17 may provide a means to ameliorate these abnormalities.

Effects of vector backbone and pseudotype on lentiviral vector-mediated gene transfer: studies in infant ADA-deficient mice and rhesus monkeys.

Systemic delivery of a lentiviral vector carrying a therapeutic gene represents a new treatment for monogenic disease. Previously, we have shown that transfer of the adenosine deaminase (ADA) cDNA in vivo rescues the lethal phenotype and reconstitutes immune function in ADA-deficient mice. In order to translate this approach to ADA-deficient severe combined immune deficiency patients, neonatal ADA-deficient mice and newborn rhesus monkeys were treated with species-matched and mismatched vectors and pseudotypes. We compared gene delivery by the HIV-1-based vector to murine γ-retroviral vectors pseudotyped with vesicular stomatitis virus-glycoprotein or murine retroviral envelopes in ADA-deficient mice. The vesicular stomatitis virus-glycoprotein pseudotyped lentiviral vectors had the highest titer and resulted in the highest vector copy number in multiple tissues, particularly liver and lung. In monkeys, HIV-1 or simian immunodeficiency virus vectors resulted in similar biodistribution in most tissues including bone marrow, spleen, liver, and lung. Simian immunodeficiency virus pseudotyped with the gibbon ape leukemia virus envelope produced 10- to 30-fold lower titers than the vesicular stomatitis virus-glycoprotein pseudotype, but had a similar tissue biodistribution and similar copy number in blood cells. The relative copy numbers achieved in mice and monkeys were similar when adjusted to the administered dose per kg. These results suggest that this approach can be scaled-up to clinical levels for treatment of ADA-deficient severe combined immune deficiency subjects with suboptimal hematopoietic stem cell transplantation options.

AAV-mediated gene transfer in the perinatal period results in expression of FVII at levels that protect against fatal spontaneous hemorrhage.

We explored adeno-associated viral vector (AAV)-mediated gene transfer in the perinatal period in animal models of severe congenital factor VII (FVII) deficiency, a disease associated with early postnatal life-threatening hemorrhage. In young adult mice with plasma FVII < 1% of normal, a single tail vein administration of AAV (1 × 10(13) vector genomes [vg]/kg) resulted in expression of murine FVII at 266% ± 34% of normal for ≥ 67 days, which mediated protection against fatal hemorrhage and significantly improved survival. Codon optimization of human FVII (hFVIIcoop) improved AAV transgene expression by 37-fold compared with the wild-type hFVII cDNA. In adult macaques, a single peripheral vein injection of 2 × 10(11) vg/kg of the hFVIIcoop AAV vector resulted in therapeutic levels of hFVII expression that were equivalent in males (10.7% ± 3.1%) and females (12.3% ± 0.8%). In utero delivery of this vector in the third trimester to fetal monkeys conferred expression of hFVII at birth of 20.4% ± 3.7%, with a gradual decline to > 1% by 7 weeks. Re-administration of an alternative serotype at 12 months postnatal age increased hFVII levels to 165% ± 6.2% of normal, which remained at therapeutic levels for a further 28 weeks without toxicity. Thus, perinatal AAV-mediated gene transfer shows promise for disorders with onset of pathology early after birth.

Anti-non-Gal-specific combination treatment with an anti-idiotypic Ab and an inhibitory small molecule mitigates the xenoantibody response.

BACKGROUND: B-cell depletion significantly extends survival of α-1,3-galactosyltranferase knockout (GTKO) porcine organs in pig-to-primate models. Our previous work demonstrated that the anti-non-Gal xenoantibody response is structurally restricted. Selective inhibition of xenoantigen/xenoantibody interactions could prolong xenograft survival while preserving B-cell-mediated immune surveillance. METHODS: The anti-idiotypic antibody, B4N190, was selected from a synthetic human phage display library after enrichment against a recombinant anti-non-Gal xenoantibody followed by functional testing in vitro. The inhibitory small molecule, JMS022, was selected from the NCI diversity set III using virtual screening based on predicted xenoantibody structure. Three rhesus monkeys were pre-treated with anti-non-Gal-specific single-chain anti-idiotypic antibody, B4N190. A total of five monkeys, including two untreated controls, were then immunized with GTKO porcine endothelial cells to initiate an anti-non-α-1,3-Gal (non-Gal) xenoantibody response. The efficacy of the inhibitory small molecule specific for anti-non-Gal xenoantibody, JMS022, was tested in vitro. RESULTS: After the combination of in vivo anti-id and in vitro small molecule treatments, IgM xenoantibody binding to GTKO cells was reduced to pre-immunization levels in two-thirds of animals; however, some xenoantibodies remained in the third animal. Furthermore, when treated with anti-id alone, all three experimental animals displayed a lower anti-non-Gal IgG xenoantibody response compared with controls. Treatment with anti-idiotypic antibody alone reduced IgM xenoantibody response intensity in only one of three monkeys injected with GTKO pig endothelial cells. In the one experimental animal, which displayed reduced IgM and IgG responses, select B-cell subsets were also reduced by anti-id therapy alone. Furthermore, natural antibody responses, including anti-laminin, anti-ssDNA, and anti-thyroglobulin antibodies were intact despite targeted depletion of anti-non-Gal xenoantibodies in vivo indicating that selective reduction of xenoantibodies can be accomplished without total B-cell depletion. CONCLUSIONS: This preliminary study demonstrates the strength of approaches designed to selectively inhibit anti-non-Gal xenoantibody. Both anti-non-Gal-specific anti-idiotypic antibody and small molecules can be used to selectively limit xenoantibody responses.

Rhesus monkeys and baboons develop clotting factor VIII inhibitors in response to porcine endothelial cells or islets.

BACKGROUND: Xenotransplantation of porcine organs holds promise of solving the human organ donor shortage. The use of α-1,3-galactosyltransferase knockout (GTKO) pig donors mitigates hyperacute rejection, while delayed rejection is currently precipitated by potent immune and hemostatic complications. Previous analysis by our laboratory suggests that clotting factor VIII (FVIII) inhibitors might be elicited by the structurally restricted xenoantibody response which occurs after transplantation of either pig GTKO/hCD55/hCD59/hHT transgenic neonatal islet cell clusters or GTKO endothelial cells. METHODS: A recombinant xenoantibody was generated using sequences from baboons demonstrating an active xenoantibody response at day 28 after GTKO/hCD55/hCD59/hHT transgenic pig neonatal islet cell cluster transplantation. Rhesus monkeys were immunized with GTKO pig endothelial cells to stimulate an anti-non-Gal xenoantibody response. Serum was collected at days 0 and 7 after immunization. A two-stage chromogenic assay was used to measure FVIII cofactor activity and identify antibodies which inhibit FVIII function. Molecular modeling and molecular dynamics simulations were used to predict antibody structure and the residues which contribute to antibody-FVIII interactions. Competition ELISA was used to verify predictions at the domain structural level. RESULTS: Antibodies that inhibit recombinant human FVIII function are elicited after non-human primates are transplanted with either GTKO pig neonatal islet cell clusters or endothelial cells. There is an apparent increase in inhibitor titer by 15 Bethesda units (Bu) after transplant, where an increase greater than 5 Bu can indicate pathology in humans. Furthermore, competition ELISA verifies the computer modeled prediction that the recombinant xenoantibody, H66K12, binds the C1 domain of FVIII. CONCLUSIONS: The development of FVIII inhibitors is a novel illustration of the potential impact the humoral immune response can have on coagulative dysfunction in xenotransplantation. However, the contribution of these antibodies to rejection pathology requires further evaluation because "normal" coagulation parameters after successful xenotransplantation are not fully understood.

AAV5 Delivery of CRISPR/Cas9 Mediates Genome Editing in the Lungs of Young Rhesus Monkeys.

Genome editing has the potential to treat genetic diseases in a variety of tissues, including the lung. We have previously developed and validated a dual adeno-associated virus (AAV) CRISPR platform that supports effective editing in the airways of mice. To validate this delivery vehicle in a large animal model, we have shown that intratracheal instillation of CRISPR/Cas9 in AAV5 can edit a housekeeping gene or a disease-related gene in the lungs of young rhesus monkeys. We observed up to 8% editing of angiotensin-converting enzyme 2 (ACE2) in lung lobes after single-dose administration. Single-nuclear RNA sequencing revealed that AAV5 transduces multiple cell types in the caudal lung lobes, including alveolar cells, macrophages, fibroblasts, endothelial cells, and B cells. These results demonstrate that AAV5 is efficient in the delivery of CRISPR/Cas9 in the lung lobes of young rhesus monkeys.