CD28 blockade controls T cell activation to prevent graft-versus-host disease in primates

Controlling graft-versus-host disease (GVHD) remains a major unmet need in stem cell transplantation, and new, targeted therapies are being actively developed. CD28-CD80/86 costimulation blockade represents a promising strategy, but targeting CD80/CD86 with CTLA4-Ig may be associated with undesired blockade of coinhibitory pathways. In contrast, targeted blockade of CD28 exclusively inhibits T cell costimulation and may more potently prevent GVHD. Here, we investigated FR104, an antagonistic CD28-specific pegylated-Fab', in the nonhuman primate (NHP) GVHD model and completed a multiparameter interrogation comparing it with CTLA4-Ig, with and without sirolimus, including clinical, histopathologic, flow cytometric, and transcriptomic analyses. We document that FR104 monoprophylaxis and combined prophylaxis with FR104/sirolimus led to enhanced control of effector T cell proliferation and activation compared with the use of CTLA4-Ig or CTLA4-Ig/sirolimus. Importantly, FR104/sirolimus did not lead to a beneficial impact on Treg reconstitution or homeostasis, consistent with control of conventional T cell activation and IL-2 production needed to support Tregs. While FR104/sirolimus had a salutary effect on GVHD-free survival, overall survival was not improved, due to death in the absence of GVHD in several FR104/sirolimus recipients in the setting of sepsis and a paralyzed INF-γ response. These results therefore suggest that effectively deploying CD28 in the clinic will require close scrutiny of both the benefits and risks of extensively abrogating conventional T cell activation after transplant.

Fc-Silent Anti-CD154 Domain Antibody Effectively Prevents Nonhuman Primate Renal Allograft Rejection

The advent of costimulation blockade provides the prospect for targeted therapy with improved graft survival in transplant patients. Perhaps the most effective costimulation blockade in experimental models is the use of reagents to block the CD40/CD154 pathway. Unfortunately, successful clinical translation of anti-CD154 therapy has not been achieved. In an attempt to develop an agent that is as effective as previous CD154 blocking antibodies but lacks the risk of thromboembolism, we evaluated the efficacy and safety of a novel anti-human CD154 domain antibody (dAb, BMS-986004). The anti-CD154 dAb effectively blocked CD40-CD154 interactions but lacked crystallizable fragment (Fc) binding activity and resultant platelet activation. In a nonhuman primate kidney transplant model, anti-CD154 dAb was safe and efficacious, significantly prolonging allograft survival without evidence of thromboembolism (Median survival time 103 days). The combination of anti-CD154 dAb and conventional immunosuppression synergized to effectively control allograft rejection (Median survival time 397 days). Furthermore, anti-CD154 dAb treatment increased the frequency of CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells. This study demonstrates that the use of a novel anti-CD154 dAb that lacks Fc binding activity is safe without evidence of thromboembolism and is equally as potent as previous anti-CD154 agents at prolonging renal allograft survival in a nonhuman primate preclinical model.

Interruption of OX40L signaling prevents costimulation blockade-resistant allograft rejection

The potential of costimulation blockade to serve as a novel transplant immunosuppression strategy has been explored for over 20 years, culminating in the recent clinical approval of belatacept for renal transplant patients. Despite improving long-term graft function and survival compared with calcineurin inhibitors, clinical acceptance of belatacept has been hindered by elevated rates of acute rejection. We examined the signaling pathways required to activate costimulation blockade-resistant alloreactive T cells and identified the OX40/OX40L secondary costimulatory pathway as a promising target. We next sought to improve the clinical efficacy of traditional costimulation blockade using belatacept by coupling it with anti-OX40L. Using a murine transplant model, we demonstrate that combined blockade enhances the suppression of alloreactive T cell proliferation and effector functions including both cytokine release and cytotoxic degranulation. We also show that anti-OX40L may be particularly useful in targeting alloreactive memory T cell responses that are relatively unaffected by traditional costimulation blockade regimens. Finally, we translated this therapy to a clinically relevant nonhuman primate renal transplant model, validating the efficacy of this regimen in a potentially novel steroid- and calcineurin inhibitor-free immunosuppression regimen.

Self-Injurious Behavior Secondary to Cytomegalovirus-Induced Neuropathy in an SIV-Infected Rhesus Macaque (Macaca mulatta)

A 3.5-y-old, female rhesus macaque (Macaca mulatta) inoculated with SIVmac239 presented 8 mo later for inappetence and facial bruising. Physical examination revealed a superficial skin abrasion below the left eye, bruising below the left brow, and epistaxis of the left nostril. There were no significant findings on CBC, serum chemistry, urinalysis, or radiographs. Differential diagnoses included infectious etiologies, self-injurious behavior, immune-mediated dermatitis, and neoplasia. Lack of response to antibiotic and analgesic therapy and observations of the macaque made it apparent that the skin lesions were self-inflicted. The excoriations rapidly progressed to extend over the nose, and the left palpebrae became edematous. Euthanasia was elected because the macaque appeared to be experiencing continued discomfort despite analgesic therapy. Histopathologic examination revealed systemic cytomegalovirus (CMV) infection involving the facial nerves, periocular nerves, meninges, and perimesenteric lymph nodes. CMV is a common infection in macaques, with adult seroprevalence close to 100% in most colonies. Infection in immunocompetent animals is usually asymptomatic but can cause significant clinical disease in immunodeficient hosts. CMV is associated with a painful peripheral neuropathy in human AIDS patients, and analgesic treatment is often unsatisfactory. Peripheral neuropathy secondary to CMV should be considered as an underlying cause of self-injurious behavior in SIV-infected macaques. Macaques affected by other diseases and disorders may also be at risk for development of painful peripheral neuropathies.

A pilot trial targeting the ICOS-ICOS-L pathway in nonhuman primate kidney transplantation

Costimulation blockade with the B7-CD28 pathway-specific agent belatacept is now used in clinical kidney transplantation, but its efficacy remains imperfect. Numerous alternate costimulatory pathways have been proposed as targets to synergize with belatacept, one of which being the inducible costimulator (ICOS)-ICOS ligand (ICOS-L) pathway. Combined ICOS-ICOS-L and CD28-B7 blockade has been shown to prevent rejection in mice, but has not been studied in primates. We therefore tested a novel ICOS-Ig human Fc-fusion protein in a nonhuman primate (NHP) kidney transplant model alone and in combination with belatacept. ICOS-Ig did not prolong rejection-free survival as a monotherapy or in combination with belatacept. In ICOS-Ig alone treated animals, most graft-infiltrating CD4(+) and CD8(+) T cells expressed ICOS, and ICOS(+) T cells were present in peripheral blood to a lesser degree. Adding belatacept reduced the proportion of graft-infiltrating ICOS(+) T cells and virtually eliminated their presence in peripheral blood. Graft-infiltrating T cells in belatacept-resistant rejection were primarily CD8(+) CD28(-) , but importantly, very few CD8(+) CD28(-) T cells expressed ICOS. We conclude that ICOS-Ig, alone or combined with belatacept, does not prolong renal allograft survival in NHPs. This may relate to selective loss of ICOS with CD28 loss.

Heart disease is common in humans and chimpanzees, but is caused by different pathological processes

Heart disease is common in both humans and chimpanzees, manifesting typically as sudden cardiac arrest or progressive heart failure. Surprisingly, although chimpanzees are our closest evolutionary relatives, the major cause of heart disease is different in the two species. Histopathology data of affected chimpanzee hearts from two primate centers, and analysis of literature indicate that sudden death in chimpanzees (and in gorillas and orangutans) is commonly associated with diffuse interstitial myocardial fibrosis of unknown cause. In contrast, most human heart disease results from coronary artery atherosclerosis, which occludes myocardial blood supply, causing ischemic damage. The typical myocardial infarction of humans due to coronary artery thrombosis is rare in these apes, despite their human-like coronary-risk-prone blood lipid profiles. Instead, chimpanzee ‘heart attacks’ are likely due to arrythmias triggered by myocardial fibrosis. Why do humans not often suffer from the fibrotic heart disease so common in our closest evolutionary cousins? Conversely, why do chimpanzees not have the kind of heart disease so common in humans? The answers could be of value to medical care, as well as to understanding human evolution. A preliminary attempt is made to explore possibilities at the histological level, with a focus on glycosylation changes.

Spontaneously arising concurrent ileocaecal adenocarcinoma and renal pelvis transitional cell carcinoma in a rhesus macaque (Macaca mulatta)

A 25-year-old, female rhesus macaque (Macaca mulatta) presented with a history of weight loss despite a normal appetite and supportive care. The animal was humanely destroyed due to poor prognosis. Post-mortem examination revealed a focally extensive, firm, white annular constriction at the ileocaecal junction and an incidental finding of a pale white nodule approximately 0.8 cm in diameter in the left renal pelvis. Based on the microscopical findings, ileocaecal adenocarcinoma and renal pelvis transitional cell carcinoma (TCC) were diagnosed. The use of cytokeratin (CK)-7 and -20 and uroplakin III as potential renal TCC markers was evaluated. The neoplastic cells were labelled intensely with antibodies to uroplakin III, but not to CK-7 or -20. Spontaneous intestinal adenocarcinoma has been documented in the rhesus macaque, but concurrent renal pelvis TCC is highly unusual.

Post-transplant lymphoproliferative disorder associated with immunosuppressive therapy for renal transplantation in rhesus macaques (Macaca mulatta)

Human post-transplant lymphoproliferative disorder (PTLD) is an abnormal lymphoid proliferation that arises in 1-12% of transplant recipients as a consequence of prolonged immunosuppression and Epstein-Barr viral infection (EBV). Nonhuman primates, primarily rhesus macaques (Macaca mulatta), have been used extensively in research models of solid organ transplantation, as the nonhuman primate immune system closely resembles that of the human. Lymphocryptovirus of rhesus monkeys has been characterized and shown to be very similar to EBV in humans in regards to its cellular tropism, host immune response, and ability to stimulate B lymphocyte proliferation and lymphomagenesis. Thus, it appears that the NHP may be an appropriate animal model for EBV-associated lymphoma development in humans. The clinical management of post-transplant nonhuman primates that are receiving multiple immunosuppressive agents can be complicated by the risk of PTLD and other opportunistic infections. We report 3 cases of PTLD in rhesus macaques that illustrate this risk potential in the setting of potent immunosuppressive therapies for solid organ transplantation.

Cerebrovascular accident (stroke) in captive, group-housed, female chimpanzees

Over a 5-y period, 3 chimpanzees at our institution experienced cerebrovascular accidents (strokes). In light of the increasing population of aged captive chimpanzees and lack of literature documenting the prevalence and effectiveness of various treatments for stroke in chimpanzees, we performed a retrospective review of the medical records and necropsy reports from our institution. A survey was sent to other facilities housing chimpanzees that participate in the Chimpanzee Species Survival Plan to inquire about their experience with diagnosing and treating stroke. This case report describes the presentation, clinical signs, and diagnosis of stroke in 3 recent cases and in historical cases at our institution. Predisposing factors, diagnosis, and treatment options of cerebral vascular accident in the captive chimpanzee population are discussed also.

A novel monoclonal antibody to CD40 prolongs islet allograft survival

The importance of CD40/CD154 costimulatory pathway blockade in immunosuppression strategies is well-documented. Efforts are currently focused on monoclonal antibodies specific for CD40 because of thromboembolic complications associated with monoclonal antibodies directed towards CD154. Here we present the rational development and characterization of a novel antagonistic monoclonal antibody to CD40. Rhesus macaques were treated with the recombinant anti-CD40 mAb, 2C10, or vehicle before immunization with keyhole limpet hemocyanin (KLH). Treatment with 2C10 successfully inhibited T cell-dependent antibody responses to KLH without significant peripheral B cell depletion. Subsequently, MHC-mismatched macaques underwent intraportal allogeneic islet transplantation and received basiliximab and sirolimus with or without 2C10. Islet graft survival was significantly prolonged in recipients receiving 2C10 (graft survival time 304, 296, 265, 163 days) compared to recipients receiving basiliximab and sirolimus alone (graft survival time 8, 8, 10 days). The survival advantage conferred by treatment with 2C10 provides further evidence for the importance of blockade of the CD40/CD154 pathway in preventing alloimmune responses. 2C10 is a particularly attractive candidate for translation given its favorable clinical profile.

Alternative immunomodulatory strategies for xenotransplantation: CD40/154 pathway-sparing regimens promote xenograft survival

Immunosuppressive therapies that block the CD40/CD154 costimulatory pathway have proven to be uniquely effective in preclinical xenotransplant models. Given the challenges facing clinical translation of CD40/CD154 pathway blockade, we examined the efficacy and tolerability of CD40/CD154 pathway-sparing immunomodulatory strategies in a pig-to-nonhuman primate islet xenotransplant model. Rhesus macaques were rendered diabetic with streptozocin and given an intraportal infusion of ≈ 50 000 islet equivalents/kg wild-type neonatal porcine islets. Base immunosuppression for all recipients included maintenance therapy with belatacept and mycophenolate mofetil plus induction with basiliximab and LFA-1 blockade. Cohort 1 recipients (n = 3) were treated with the base regimen alone; cohort 2 recipients (n = 5) were additionally treated with tacrolimus induction and cohort 3 recipients (n = 5) were treated with alefacept in place of basiliximab, and more intense LFA-1 blockade. Three of five recipients in both cohorts 2 and 3 achieved sustained insulin-independent normoglycemia (median rejection-free survivals 60 and 111 days, respectively), compared to zero of three recipients in cohort 1. These data show that CD40/CD154 pathway-sparing regimens can promote xenoislet survival. Further optimization of these strategies is warranted to aid the clinical translation of islet xenotransplantation.

Evidence for kidney rejection after combined bone marrow and renal transplantation despite ongoing whole-blood chimerism in rhesus macaques

Although there is evidence linking hematopoietic chimerism induction and solid organ transplant tolerance, the mechanistic requirements for chimerism-induced tolerance are not clearly elucidated. To address this, we used an MHC-defined primate model to determine the impact of impermanent, T cell-poor, mixed-chimerism on renal allograft survival. We compared two cohorts: one receiving a bone marrow and renal transplant ("BMT/renal") and one receiving only a renal transplant. Both cohorts received maintenance immunosuppression with CD28/CD40-directed costimulation blockade and sirolimus. As previously demonstrated, this transplant strategy consistently induced compartmentalized donor chimerism, (significant whole-blood chimerism, lacking T cell chimerism). This chimerism was not sufficient to prolong renal allograft acceptance: the BMT/renal mean survival time (MST, 76 days) was not significantly different than the renal transplant alone MST (85 days, p = 0.46), with histopathology documenting T cell mediated rejection. Flow cytometric analysis revealed significant enrichment for CD28-/CD95+ CD4+ and CD8+ Tem cells in the rejected kidney, suggesting a link between CD28-negative Tem and costimulation blockade-resistant rejection. These results suggest that in some settings, transient T cell-poor chimerism is not sufficient to induce tolerance to a concurrently placed renal allograft and that the presence of this chimerism per se is not an independent biomarker to identify tolerance.

CD40 blockade combines with CTLA4Ig and sirolimus to produce mixed chimerism in an MHC-defined rhesus macaque transplant model

In murine models, T-cell costimulation blockade of the CD28:B7 and CD154:CD40 pathways synergistically promotes immune tolerance after transplantation. While CD28 blockade has been successfully translated to the clinic, translation of blockade of the CD154:CD40 pathway has been less successful, in large part due to thromboembolic complications associated with anti-CD154 antibodies. Translation of CD40 blockade has also been slow, in part due to the fact that synergy between CD40 blockade and CD28 blockade had not yet been demonstrated in either primate models or humans. Here we show that a novel, nondepleting CD40 monoclonal antibody, 3A8, can combine with combined CTLA4Ig and sirolimus in a well-established primate bone marrow chimerism-induction model. Prolonged engraftment required the presence of all three agents during maintenance therapy, and resulted in graft acceptance for the duration of immunosuppressive treatment, with rejection resulting upon immunosuppression withdrawal. Flow cytometric analysis revealed that upregulation of CD95 expression on both CD4+ and CD8+ T cells correlated with rejection, suggesting that CD95 may be a robust biomarker of graft loss. These results are the first to demonstrate prolonged chimerism in primates treated with CD28/mTOR blockade and nondepletional CD40 blockade, and support further investigation of combined costimulation blockade targeting the CD28 and CD40 pathways.

Islet xenotransplantation using gal-deficient neonatal donors improves engraftment and function

Significant deficiencies in understanding of xenospecific immunity have impeded the success of preclinical trials in xenoislet transplantation. Although galactose-α1,3-galactose, the gal epitope, has emerged as the principal target of rejection in pig-to-primate models of solid organ transplant, the importance of gal-specific immunity in islet xenotransplant models has yet to be clearly demonstrated. Here, we directly compare the immunogenicity, survival and function of neonatal porcine islets (NPIs) from gal-expressing wild-type (WT) or gal-deficient galactosyl transferase knockout (GTKO) donors. Paired diabetic rhesus macaques were transplanted with either WT (n = 5) or GTKO (n = 5) NPIs. Recipient blood glucose, transaminase and serum xenoantibody levels were used to monitor response to transplant. Four of five GTKO versus one of five WT recipients achieved insulin-independent normoglycemia; transplantation of WT islets resulted in significantly greater transaminitis. The WT NPIs were more susceptible to antibody and complement binding and destruction in vitro. Our results confirm that gal is an important variable in xenoislet transplantation. The GTKO NPI recipients have improved rates of normoglycemia, likely due to decreased susceptibility of xenografts to innate immunity mediated by complement and preformed xenoantibody. Therefore, the use of GTKO donors is an important step toward improved consistency and interpretability of results in future xenoislet studies.

CD40-specific costimulation blockade enhances neonatal porcine islet survival in nonhuman primates

The widespread clinical implementation of alloislet transplantation as therapy for type 1 diabetes has been hindered by the lack of suitable islet donors. Pig-to-human islet xenotransplantation is one strategy with potential to alleviate this shortage. Long-term survival of porcine islets has been achieved using CD154-specific antibodies to interrupt the CD40/CD154 costimulation pathway; however, CD154-specific antibodies seem unlikely candidates for clinical translation. An alternative strategy for CD40/CD154 pathway interruption is use of CD40-specific antibodies. Herein, we evaluate the ability of a chimeric CD40-specific monoclonal antibody (Chi220) to protect islet xenografts. Neonatal porcine islets (~50,000 IEQ/kg) were transplanted intraportally into pancreatectomized diabetic macaques. Immunosuppression consisted of induction therapy with Chi220 and the IL-2 receptor-specific antibody basiliximab, and maintenance therapy with sirolimus and the B7-specific fusion protein belatacept. Chi220 effectively promoted xenoislet engraftment and survival, with five of six treated recipients achieving insulin-independent normoglycemia (median rejection-free survival 59 days; mean 90.8 days, maximum 203 days). No thromboembolic phenomena were observed. CD40 represents a promising alternative to CD154 as a therapeutic target, and the efficacy of CD40-specific antibodies in islet xenotransplantation warrants further investigation.

Biomedical differences between human and nonhuman hominids: potential roles for uniquely human aspects of sialic acid biology

Although humans are genetically very similar to the evolutionarily related nonhuman hominids (chimpanzees, bonobos, gorillas, and orangutans), comparative studies suggest a surprising number of uniquely human differences in the incidence and/or severity of biomedical conditions. Some differences are due to anatomical changes that occurred during human evolution. However, many cannot be explained either by these changes or by known environmental factors. Because chimpanzees were long considered models for human disease, it is important to be aware of these differences, which appear to have been deemphasized relative to similarities. We focus on the pathophysiology and pathobiology of biomedical conditions that appear unique to humans, including several speculative possibilities that require further study. We pay particular attention to the possible contributions of uniquely human changes in the biology of cell-surface sialic acids and the proteins that recognize them. We also discuss the metabolic incorporation of a diet-derived nonhuman sialic acid, which generates a novel xeno-autoantigen reaction, and chronic inflammation known as xenosialitis.

An MHC-defined primate model reveals significant rejection of bone marrow after mixed chimerism induction despite full MHC matching

In murine models, mixed hematopoietic chimerism induction leads to robust immune tolerance. However, translation to primates and to patients has been difficult. In this study, we used a novel MHC-defined rhesus macaque model to examine the impact of MHC matching on the stability of costimulation blockade-/sirolimus-mediated chimerism, and to probe possible mechanisms of bone marrow rejection after nonmyeloablative transplant. Using busulfan-based pretransplant preparation and maintenance immunosuppression with sirolimus, as well as CD28 and CD154 blockade, all recipients demonstrated donor engraftment after transplant. However, the mixed chimerism that resulted was compartmentalized, with recipients demonstrating significantly higher whole blood chimerism compared to T cell chimerism. Thus, the vast majority of T cells presenting posttransplant were recipient-rather than donor-derived. Surprisingly, even in MHC-matched transplants, rejection of donor hematopoiesis predominated after immunosuppression withdrawal. Weaning of immunosuppression was associated with a surge of antigen-experienced T cells, and transplant rejection was associated with the acquisition of donor-directed T cell alloreactivity. These results suggest that a reservoir of alloreactive cells was present despite prior costimulation blockade and sirolimus, and that the post-immunosuppression lymphocytic rebound may have lead to a phenotypic shift in these recipient T cells towards an activated, antigen-experienced phenotype, and ultimately, to transplant rejection.

Relative transmissibility of an R5 clade C simian-human immunodeficiency virus across different mucosae in macaques parallels the relative risks of sexual HIV-1 transmission in humans via different routes

BACKGROUND

Worldwide, approximately 90% of all human immunodeficiency virus (HIV) transmissions occur mucosally; almost all involve R5 strains. Risks of sexual HIV acquisition are highest for rectal, then vaginal, and finally oral exposures.

METHODS

Mucosal lacerations may affect the rank order of susceptibility to HIV but cannot be assessed in humans. We measured relative virus transmissibility across intact mucosae in macaques using a single stock of SHIV-1157ipd3N4, a simian-human immunodeficiency virus encoding a primary R5 HIV clade C env (SHIV-C).

RESULTS

The penetrability of rhesus macaque mucosae differed significantly, with rectal challenge requiring the least virus, followed by vaginal and then oral routes (P = .031, oral vs vaginal; P < .001 rectal vs vaginal). These findings imply that intrinsic mucosal properties are responsible for the differential mucosal permeability. The latter paralleled the rank order reported for humans, with relative risk estimates within the range of epidemiological human studies. To test whether inflammation facilitates virus transmission--as predicted from human studies--we established a macaque model of localized buccal inflammation. Systemic infection occurred across inflamed but not normal buccal mucosa.

CONCLUSION

Our primate data recapitulate virus transmission risks observed in humans, thus establishing R5 SHIV-1157ipd3N4 in macaques as a robust model system to study cofactors involved in human mucosal HIV transmission and its prevention.

Studies on the Salvador I strain of Plasmodium vivax in non-human primates and anopheline mosquitoes

A review is presented on studies conducted in New World monkeys and chimpanzees with the Salvador I strain of Plasmodium vivax. This isolate has been adapted to Aotus and Saimiri (squirrel) monkeys and developed as a model for the testing of antimalarial vaccines. After the injection of 10,000 sporozoites, the median prepatent period in S. boliviensis monkeys was 21.5 days. In 103 sporozoite-induced infections in splenectomized monkeys, the median maximum parasite count ranged from 2,139 to 202,368/microL, with a median maximum parasite count of 48,174/microL. Median maximum parasite counts in Aotus lemurinus griseimembra, A. nancymaae, A. azarae boliviensis, and A. vociferans monkeys were 19,902, 18,390, 21,420, and 18,210/microL, respectively and ranged from 124 to 156,000/microL. Mosquito infections were readily obtained in different species of Anopheles mosquitoes. The S. boliviensis monkey and Salvador I strain seems suitable for the testing of sporozoite and liver stage vaccines but not for blood-stage vaccines against P. vivax unless adapted further in spleen-intact Saimiri boliviensis monkeys.

Expanded nonhuman primate tregs exhibit a unique gene expression signature and potently downregulate alloimmune responses

We have established two complementary strategies for purifying naturally occurring regulatory T cells (Tregs) from rhesus macaques in quantities that would be sufficient for use as an in vivo cellular therapeutic. The first strategy identified Tregs based on their being CD4+/CD25(bright). The second incorporated CD127, and purified Tregs based on their expression of CD4 and CD25 and their low expression of CD127. Using these purification strategies, we were able to purify as many as 1x10(6) Tregs from 120 cc of peripheral blood. Cultures of these cells with anti-CD3, anti-CD28 and IL-2 over 21 days yielded as much as a 450-fold expansion, ultimately producing as many as 4.7x10(8) Tregs. Expanded Treg cultures potently inhibited alloimmune proliferation as measured by a carboxyfluorescein succinimidyl ester- mixed lymphocyte reaction (CFSE-MLR) assay even at a 1:100 ratio with responder T cells. Furthermore, both responder-specific and third-party Tregs downregulated alloproliferation similarly. Both freshly isolated and cultured Tregs had gene expression signatures distinguishable from concurrently isolated bulk CD4+ T-cell populations, as measured by singleplex reverse transcriptase-polymerase chain reaction (RT-PCR) and gene array. Moreover, an overlapping yet distinct gene expression signature seen in freshly isolated compared to expanded Tregs identifies a subset of Treg genes likely to be functionally significant.

SHIV-1157i and passaged progeny viruses encoding R5 HIV-1 clade C env cause AIDS in rhesus monkeys

Background

Infection of nonhuman primates with simian immunodeficiency virus (SIV) or chimeric simian-human immunodeficiency virus (SHIV) strains is widely used to study lentiviral pathogenesis, antiviral immunity and the efficacy of AIDS vaccine candidates. SHIV challenges allow assessment of anti-HIV-1 envelope responses in primates. As such, SHIVs should mimic natural HIV-1 infection in humans and, to address the pandemic, encode HIV-1 Env components representing major viral subtypes worldwide.

Results

We have developed a panel of clade C R5-tropic SHIVs based upon env of a Zambian pediatric isolate of HIV-1 clade C, the world's most prevalent HIV-1 subtype. The parental infectious proviral clone, SHIV-1157i, was rapidly passaged through five rhesus monkeys. After AIDS developed in the first animal at week 123 post-inoculation, infected blood was infused into a sixth monkey. Virus reisolated at this late stage was still exclusively R5 tropic and mucosally transmissible. Here we describe the long-term follow-up of this initial cohort of six monkeys. Two have remained non-progressors, whereas the other four gradually progressed to AIDS within 123–270 weeks post-exposure. Two progressors succumbed to opportunistic infections, including a case of SV40 encephalitis.

Conclusion

These data document the disease progression induced by the first mucosally transmissible, pathogenic R5 non-clade B SHIV and suggest that SHIV-1157i-derived viruses, including the late-stage, highly replication-competent SHIV-1157ipd3N4 previously described (Song et al., 2006), display biological characteristics that mirror those of HIV-1 clade C and support their expanded use for AIDS vaccine studies in nonhuman primates.

Identification of enteroviruses in naturally infected captive primates

In a recent study, we investigated cases of diarrheal disease among monkeys at a U.S. primate center. In that study, enteroviruses were detected in a high proportion of the fecal specimens tested. To determine whether the enterovirus detections represented the circulation of one or more simian enteroviruses within the colony or the transmission of human enteroviruses from animal handlers, we determined in the present study the serotype identity of each virus by reverse transcription-PCR and sequencing of a portion of the VP1 gene, a region whose sequence corresponds to antigenic type. Enteroviruses were identified in 37 of 56 specimens (66%), 30 of 40 rhesus macaques, 5 of 11 pigtail macaques, 2 of 4 sooty mangabeys, and 0 of 1 chimpanzee. No previously known human viruses were detected. Three previously known simian enterovirus serotypes--SV6, SV19, and SV46--were among the viruses identified, but more than half of the identified viruses were previously unknown; these have been assigned as new types: EV92 and EV103.

Preclinical assessment of the receptor-binding domain of Plasmodium vivax Duffy-binding protein as a vaccine candidate in rhesus macaques

The receptor-binding domain of Plasmodium vivax Duffy-binding protein, region II (PvRII), is an attractive candidate for a vaccine against P. vivax malaria. Here, we have studied the safety and immunogenicity of recombinant PvRII in Macaca mulatta (rhesus monkeys). Recombinant PvRII with a C-terminal 6-histidine tag was expressed in E. coli, recovered from inclusion bodies, refolded into its functional conformation, purified to homogeneity and formulated with three adjuvants, namely, Alhydrogel, Montanide ISA 720 and the GSK proprietary Adjuvant System AS02A for use in immunogenicity studies. All the PvRII vaccine formulations tested were safe and highly immunogenic. The overall magnitude of the antibody response was significantly higher for both Montanide ISA 720 and AS02A formulations in comparison with Alhydrogel. Furthermore, there was a significant correlation between antibody recognition titers by ELISA and binding inhibition titers in in vitro binding assays. The PvRII vaccine formulations also induced IFN-gamma recall responses that were identified using ex vivo ELISPOT assays. These results provide support for further clinical development of a vaccine for P. vivax malaria based on recombinant PvRII.

Induction of multi-antigen multi-stage immune responses against Plasmodium falciparum in rhesus monkeys, in the absence of antigen interference, with heterologous DNA prime/poxvirus boost immunization

The present study has evaluated the immunogenicity of single or multiple Plasmodium falciparum (Pf) antigens administered in a DNA prime/poxvirus boost regimen with or without the poloxamer CRL1005 in rhesus monkeys. Animals were primed with PfCSP plasmid DNA or a mixture of PfCSP, PfSSP2/TRAP, PfLSA1, PfAMA1 and PfMSP1-42 (CSLAM) DNA vaccines in PBS or formulated with CRL1005, and subsequently boosted with ALVAC-Pf7, a canarypox virus expressing the CSLAM antigens. Cell-mediated immune responses were evaluated by IFN-γ ELIspot and intracellular cytokine staining, using recombinant proteins and overlapping synthetic peptides. Antigen-specific and parasite-specific antibody responses were evaluated by ELISA and IFAT, respectively. Immune responses to all components of the multi-antigen mixture were demonstrated following immunization with either DNA/PBS or DNA/CRL1005, and no antigen interference was observed in animals receiving CSLAM as compared to PfCSP alone. These data support the down-selection of the CSLAM antigen combination. CRL1005 formulation had no apparent effect on vaccine-induced T cell or antibody responses, either before or after viral boost. In high responder monkeys, CD4+IL-2+ responses were more predominant than CD8+ T cell responses. Furthermore, CD8+ IFN-γ responses were detected only in the presence of detectable CD4+ T cell responses. Overall, this study demonstrates the potential for multivalent Pf vaccines based on rational antigen selection and combination, and suggests that further formulation development to increase the immunogenicity of DNA encoded antigens is warranted.

Engraftment of adult porcine islet xenografts in diabetic nonhuman primates through targeting of costimulation pathways

Recent advances in human allogeneic islet transplantation have established beta-cell replacement therapy as a potentially viable treatment option for individuals afflicted with Type 1 diabetes. Two recent successes, one involving neonatal porcine islet xenografts transplanted into diabetic rhesus macaques treated with a costimulation blockade-based regimen and the other involving diabetic cynomolgus monkeys transplanted with adult porcine islet xenografts treated with an alternative multidrug immunosuppressive regimen have demonstrated the feasibility of porcine islet xenotransplantation in nonhuman primate models. In the current study, we assessed whether transplantation of adult porcine islet xenografts into pancreatectomized macaques, under the cover of a costimulation blockade-based immunosuppressive regimen (CD28 and CD154 blockade), could correct hyperglycemia. Our findings suggest that the adult porcine islets transplanted into rhesus macaques receiving a costimulation blockade-based regimen are not uniformly subject to hyperacute rejection, can engraft (2/5 recipients), and have the potential to provide sustained normoglycemia. These results provide further evidence to suggest that porcine islet xenotransplantation may be an attainable strategy to alleviate the islet supply crisis that is one of the principal obstacles to large-scale application of islet replacement therapy in the treatment of Type 1 diabetes.

Live attenuated Listeria monocytogenes expressing HIV Gag: immunogenicity in rhesus monkeys

Induction of strong cellular immunity will be important for AIDS vaccine candidates. Natural infection with wild-type Listeria monocytogenes (Lm), an orally transmitted organism, is known to generate strong cellular immunity, thus raising the possibility that live attenuated Lm could serve as a vaccine vector. We sought to examine the potential of live attenuated Lm to induce cellular immune responses to HIV Gag. Rhesus macaques were immunized with Lmdd-gag that expresses HIV gag and lacks two genes in the D-alanine (D-ala) synthesis pathway. Without this key component of the bacterial cell wall, vaccine vector replication critically depends on exogenous D-ala. Lmdd-gag was given to animals either solely orally or by oral priming followed by intramuscular (i.m.) boosting; D-ala was co-administered with all vaccinations. Lmdd-gag and D-ala were well tolerated. Oral priming/oral boosting induced Gag-specific cellular immune responses, whereas oral priming/i.m. boosting induced systemic as well as mucosal anti-Gag antibodies. These results suggest that the route of vaccination may bias anti-Gag immune responses either towards T-helper type 1 (Th1) or Th2 responses; overall, our data show that live attenuated, recombinant Lmdd-gag is safe and immunogenic in primates.

Disseminated intravascular coagulation complicated by peripheral gangrene in a rhesus macaque (Macaca mulatta) experimentally infected with Plasmodium coatneyi

We report the first case of disseminated intravascular coagulation (DIC) complicated by peripheral gangrene induced by Plasmodium coatneyi in rhesus monkeys. Ten days after experimental challenge, numerous petechiae were noted over the trunk and extremities, with polychromasia, severe anemia, thrombocytopenia, and moderate parasitemia. These changes were accompanied by elevated serum activity of blood urea nitrogen, creatinine, transaminases, and creatinine phosphokinase. The animal received intravenous fluid support, artemether, and blood transfusion. Three days after treatment, the platelet counts returned to normal, and parasitemia was abated. However, several areas of skin discoloration with gangrenous tissue in the hands and the tail were observed. Coagulation profile showed elevated D-dimers and elevated levels of fibrinogen/fibrin degradation products with low levels of protein S functional activity. DIC with peripheral gangrene is very rare in Plasmodium-infected individuals. Our results indicate that the experimental model of P. coatneyi infection of rhesus monkeys is important for studies of malarial anemia and coagulopathy.

Induction of chimerism in rhesus macaques through stem cell transplant and costimulation blockade-based immunosuppression

A strategy for producing high-level hematopoietic chimerism after non-myeloablative conditioning has been established in the rhesus macaque. This strategy relies on hematopoietic stem cell transplantation after induction with a non-myeloablative dose of busulfan and blockade of the IL2-receptor in the setting of mTOR inhibition with sirolimus and combined CD28/CD154 costimulation blockade. Hematopoietic stem cells derived from bone marrow and leukopheresis products both were found to be successful in inducing high-level chimerism. Mean peripheral blood peak donor chimerism was 81% with a median chimerism duration of 145 days. Additional immune modulation strategies, such as pre-transplant CD8 depletion, donor-specific transfusion, recipient thymectomy or peritransplant deoxyspergualin treatment did not improve the level or durability of chimerism. Recipient immunologic assessment suggested that chimerism occurred amidst donor-specific down-regulation of alloreactive T cells, and the reappearance of vigorous T-mediated alloreactivity accompanied rejection of the transplants. Furthermore, viral reactivation constituted a significant transplant-related toxicity and may have negatively impacted the ability to achieve indefinite survival of transplanted stem cells. Nevertheless, this chimerism-induction regimen induced amongst the longest-lived stem cell chimerism reported to date for non-human primates and thus represents a platform upon which to evaluate emerging tolerance-induction strategies.

Studies on sporozoite-induced and chronic infections with Plasmodium fragile in Macaca mulatta and New World monkeys

Plasmodium fragile continues to be investigated because of its biologic similarities to the human malaria parasite, Plasmodium falciparum. Two strains of P. fragile are available for study; one strain is able to infect mosquitoes, whereas the other strain is transmissible only by blood inoculation. The Sri Lanka strain of P. fragile was transmitted to Macaca mulatta, Macaca fascicularis, Aotus lemurinus griseimembra, Aotus nancymaae, Aotus vociferans, and Saimiri boliviensis monkeys via sporozoites that developed to maturity only in Anopheles dirus mosquitoes. The prepatent periods ranged from 12 to 35 days for macaques and from 15 to 30 days for New World monkeys after intravenous injection of sporozoites. Eight rhesus monkeys were infected with the Nilgiri strain and followed for 482 days. Parasitemia in 6 animals persisted at relatively high density through the period of observation. Erythrocyte, hematocrit, and hemoglobin values reached their lowest levels 3 wk after infection and slowly recovered; however, the values did not approach preinfection levels as long as parasitemia persisted in the monkeys. The mean corpuscular volume and corpuscular hemoglobin concentration reached their peak and lowest values, respectively, at day 38 and then returned to the preinfection level. The mean corpuscular hemoglobin value decreased to its lowest level at day 87 and then returned to preinfection level.

Molecularly cloned SHIV-1157ipd3N4: a highly replication- competent, mucosally transmissible R5 simian-human immunodeficiency virus encoding HIV clade C Env

Human immunodeficiency virus type 1 (HIV-1) clade C causes >50% of all HIV infections worldwide, and an estimated 90% of all transmissions occur mucosally with R5 strains. A pathogenic R5 simian-human immunodeficiency virus (SHIV) encoding HIV clade C env is highly desirable to evaluate candidate AIDS vaccines in nonhuman primates. To this end, we generated SHIV-1157i, a molecular clone from a Zambian infant isolate that carries HIV clade C env. SHIV-1157i was adapted by serial passage in five monkeys, three of which developed peripheral CD4(+) T-cell depletion. After the first inoculated monkey developed AIDS at week 137 postinoculation, transfer of its infected blood to a naïve animal induced memory T-cell depletion and thrombocytopenia within 3 months in the recipient. In parallel, genomic DNA from the blood donor was amplified to generate the late proviral clone SHIV-1157ipd3. To increase the replicative capacity of SHIV-1157ipd3, an extra NF-kappaB binding site was engineered into its 3' long terminal repeat, giving rise to SHIV-1157ipd3N4. This virus was exclusively R5 tropic and replicated more potently in rhesus peripheral blood mononuclear cells than SHIV-1157ipd3 in the presence of tumor necrosis factor alpha. Rhesus macaques of Indian and Chinese origin were next inoculated intrarectally with SHIV-1157ipd3N4; this virus replicated vigorously in both sets of monkeys. We conclude that SHIV-1157ipd3N4 is a highly replication-competent, mucosally transmissible R5 SHIV that represents a valuable tool to test candidate AIDS vaccines targeting HIV-1 clade C Env.

Long-term survival of neonatal porcine islets in nonhuman primates by targeting costimulation pathways

We evaluated the ability of neonatal porcine islets to engraft and restore glucose control in pancreatectomized rhesus macaques. Although porcine islets transplanted into nonimmunosuppressed macaques were rapidly rejected by a process consistent with cellular rejection, recipients treated with a CD28-CD154 costimulation blockade regimen achieved sustained insulin independence (median survival, >140 days) without evidence of porcine endogenous retrovirus dissemination. Thus, neonatal porcine islets represent a promising solution to the crucial supply problem in clinical islet transplantation.

Assessment of transmission-blocking activity of candidate Pvs25 vaccine using gametocytes from chimpanzees

Macaca mulatta monkeys were immunized with the candidate transmission-blocking vaccine against Plasmodium vivax, Pvs25, combined with alum or Montanide ISA 720. Efficacy was measured by combining post-immunization sera with gametocytes obtained from infections induced in chimpanzees using membrane-feeding techniques. The results indicate that immunization of M. mulatta monkeys with Pvs25 and Montanide ISA 720 was more effective than with alum in efficacy and resulted in the maintenance of a lasting transmission-blocking immunity to P. vivax. This was evident two weeks after the second immunization, and more strongly demonstrable 62 and 152 days after the second immunization. This transmission-blocking activity was strongly reinforced by a third immunization given 181 days after the primary immunization, as measured three weeks later by indirect membrane feeding. The use of gametocytes of P. vivax derived from infections induced in chimpanzees can contribute to the selection of appropriate constructs, formulations, and immunization regimens for the development of effective transmission-blocking vaccines.

Rational development of LEA29Y (belatacept), a high-affinity variant of CTLA4-Ig with potent immunosuppressive properties

Current success in organ transplantation is dependent upon the use of calcineurin-inhibitor-based immunosuppressive regimens. Unfortunately, current immunotherapy targets molecules with ubiquitous expression resulting in devastating non-immune side effects. T-cell costimulation has been identified as a new potential immunosuppressive target. The best characterized pathway includes CD28, its homologue CTLA4 and their ligands CD80 and CD86. While an immunoglobulin fusion protein construct of CTLA4 suppressed rejection in rodents, it lacked efficacy in primate transplant models. In an attempt to increase the biologic potency of the parent molecule a novel, modified version of CTLA4-Ig, LEA29Y (belatacept), was constructed. Two amino acid substitutions (L104E and A29Y) gave rise to slower dissociation rates for both CD86 and CD80. The increased avidity resulted in a 10-fold increase in potency in vitro and significant prolongation of renal allograft survival in a pre-clinical primate model. The use of immunoselective biologics may provide effective maintenance immunosuppression while avoiding the collateral toxicities associated with conventional immunsuppressants.

Anti-CD40 therapy extends renal allograft survival in rhesus macaques

BACKGROUND

Organ transplant recipients currently require lifetime immunosuppressive therapy, with its accompanying side effects. Biological agents that block T-cell costimulatory pathways are important components of strategies being developed to induce transplantation tolerance. The aim of this study was to test the effect of a novel chimeric anti-human CD40 monoclonal antibody (Chi 220), either alone or in combination with CTLA4-Ig, on the survival of renal allografts in a nonhuman primate model.

METHODS

Captive-bred adolescent male rhesus monkeys (Macaca mulatta) (4-10 kg) were used as recipients and donors. Four treatment protocols were tested: Chi220 monotherapy, CTLA4-Ig monotherapy, Chi220 combined with CTLA4-Ig, and H106 (anti-CD40L) combined with CTLA4-Ig. Control animals received human albumin. Recipients were followed for survival, renal allograft function as determined by measurement of serum blood urea nitrogen (BUN) and creatinine, chemistries (sodium, potassium, chloride, and bicarbonate), complete blood cell count (CBC) with differential, and the development of donor-specific alloantibody.

RESULTS

Treatment with Chi220 for 14 days prolonged renal allograft survival (MST 38.5 vs. 7 days in untreated controls). Notably, simultaneous blockade of the CD28/B7 pathway did not further augment graft survival but did suppress the development of donor-specific antibodies, an effect not achieved with Chi220 alone, despite peripheral B cell depletion. Finally, treatment with Chi220 suppressed the primary immune response to cytomegalovirus, resulting in severe systemic manifestations.

CONCLUSIONS

Blockade of the CD40 pathway with anti-CD40 mAb is immunosuppressive in a large animal, preclinical renal transplant model. The potential effect of this therapy on viral immune responses will be important to consider for the design of safe clinical trials.

Calcineurin inhibitor-free CD28 blockade-based protocol protects allogeneic islets in nonhuman primates

Recent success using a steroid-free immunosuppressive regimen has renewed enthusiasm for the use of islet transplantation to treat diabetes. Toxicities associated with the continued use of a calcineurin inhibitor may limit the wide-spread application of this therapy. Biological agents that block key T-cell costimulatory signals, in particular the CD28 pathway, have demonstrated extraordinary promise in animal models. LEA29Y (BMS-224818), a mutant CTLA4-Ig molecule with increased binding activity, was evaluated for its potential to replace tacrolimus and protect allogeneic islets in a preclinical primate model. Animals received either the base immunosuppression regimen (rapamycin and anti-IL-2R monoclonal antibody [mAb]) or the base immunosuppression and LEA29Y. Animals receiving the LEA29Y/rapamycin/anti-IL-2R regimen (n = 5) had significantly prolonged islet allograft survival (204, 190, 216, 56, and >220 days). In contrast, those animals receiving the base regimen alone (n = 2) quickly rejected the transplanted islets at 1 week (both at 7 days). The LEA29Y-based regimen prevented the priming of anti-donor T- and B-cell responses, as detected by interferon-gamma enzyme-linked immunospot and allo-antibody production, respectively. The results of this study suggest that LEA29Y is a potent immunosuppressant that can effectively prevent rejection in a steroid-free immunosuppressive protocol and produce marked prolongation of islet allograft survival in a preclinical model.

Adaptation of a strain of Plasmodium vivax from India to New World monkeys, chimpanzees, and anopheline mosquitoes

A strain of Plasmodium vivax from India was adapted to develop in splenectomized Saimiri boliviensis, Aotus lemurinus griseimembra, A vociferans, A. nancymai, A. azarae boliviensis, hybrid Aotus monkeys, and splenectomized chimpanzees. Infections were induced via the inoculation of sporozoites dissected from the salivary glands of Anopheles stephensi and An. dirus mosquitoes to 12 Aotus and 8 Saimiri monkeys; transmission via the bites of infected An. stephensi was made to 1 Aotus monkey and 1 chimpanzee. The intravenous passage of infected erythrocytes was made to 9 Aotus monkeys and 4 chimpanzees. Gametocytes in 13 Aotus monkeys and 4 chimpanzees were infectious to mosquitoes. Infection rates were markedly higher in mosquitoes fed on chimpanzees. PCR studies on 10 monkeys injected with sporozoites revealed the presence of parasites before their detection by microscopic examination. The India VII strain of P. vivax develops in Aotus and Saimiri monkeys and chimpanzees following the injection of parasitized erythrocytes, or sporozoites, or both. The transmission rate via sporozoites to New World monkeys of approximately 50% may be too low for the testing of sporozoite vaccines or drugs directed against the exoerythrocytic stages. However, the strain is highly infectious to commonly available laboratory-maintained anopheline mosquitoes. Mosquito infection is especially high when feedings are made with gametocytes from splenectomized chimpanzees.

Administration of daniplestim and granulocyte colony-stimulating factor for the mobilization of hematopoietic progenitor cells in nonhuman primates

We investigated the effects of administering a high-affinity interleukin-3 receptor agonist (daniplestim) and granulocyte colony-stimulating factor (G-CSF) on the mobilization of primitive hematopoietic progenitor cells into peripheral blood (PB). Groups of five rhesus monkeys were treated with 100 mg/kg of daniplestim for 5 days followed by 10 microg/kg of G-CSF for 5 days (D/G), daniplestim and G-CSF administered concurrently for 10 days (D+G), or G-CSF alone for 10 days. Phenotypic PB analysis indicated that the number of CD34+ cells in the G-CSF group had increased to 28 x 10(6)/L by Day 3 and then declined. In contrast, CD34+ cell counts of up to 68 x 10(6)/L were maintained until Day 10 in both the D/G and D+G groups. On Day 5, the total number of colony-forming cells in the PB had increased 15-fold in the D+G group and eightfold in both the D/G group and the G-CSF groups. By Day 7, the numbers of colony-forming units granulocyte/macrophage were comparable in all three groups, and 45-fold increases in the numbers of burst-forming units-erythroid and 12-fold increases in the numbers of multipotent colony-forming units were seen in both the D+G and the D/G groups. The frequency of circulating primitive progenitor cells in long-term stromal cultures was highest with D+G and lowest with G-CSF alone. These results indicate that the combination of daniplestim and G-CSF produces higher and more sustained levels of circulating stem cells than does G-CSF alone. D+G may offer advantages over D/G because it generates more long- and short-term clonogenic cells.

Plasmodium vivax infections in chimpanzees for sporozoite challenge studies in monkeys

The development and testing of vaccines directed against Plasmodium vivax has relied on Saimiri and Aotus monkeys as the animal test system and on chimpanzees to provide infective gametocytes to produce sporozoites for monkey challenge studies and vaccine development. One sporozoite-induced and 29 blood-induced infections with the Salvador I strain of P. vivax were studied in splenectomized chimpanzees. Eighteen primary infections with P. vivax resulted in maximum parasite counts ranging from 1,519 to 81,810/ microliters (median 29,100/microliters). Twelve infections induced in animals previously infected with the homologous or heterologous strains of P. vivax had maximum parasite counts ranging from 155 to 14,136/microliters (median 1,736/microliters). A total of 202 of 237 lots containing a total of 293,175 Anopheles freeborni, An. stephensi, An. gambiae, An. dirus, An. quadrimaculatus, and An. maculatus mosquitoes were infected by membrane feeding on gametocytes from chimpanzees. Despite lower levels of parasitemia during secondary (reinfection) parasitemia, 66 of 70 lots of mosquitoes (94.3%) were infected. Based on the mean number of oocysts per positive mosquito gut, An. freeborni was more heavily infected than An. stephensi; An. stephensi was more heavily infected than An. gambiae; there was no significant difference between An. stephensi and An. dirus. Sporozoites from An. stephensi, An. gambiae, An. dirus, and An. freeborni infected with the Salvador I strain of P. vivax produced in chimpanzees were used to infect 193 Saimiri and six Aotus monkeys as well as one chimpanzee.

The Nigerian I/CDC strain of Plasmodium ovale in chimpanzees

The chimpanzee is the only animal host currently available that can support the development of the human malaria parasite Plasmodium ovale. Thirty-one infections with the Nigerian I/CDC strain were induced in splenectomized chimpanzees. Maximum parasite counts ranged from 1,240 to 127,224/microliters. Infections were transient and unpredictable. Anopheles stephensi, Anopheles gambiae, Anopheles freeborni, and Anopheles dirus mosquitoes were infected by feeding through parafilm membranes on heparinized blood containing gametocytes; each species supported development to sporozoites in the salivary glands. Mean oocyst counts per infected mosquito ranged from 1 to 85.1; 21.7% of infected lots of mosquitoes averaged > 20 oocysts per positive mosquito gut. One infection was induced via the bites of infected An. gambiae. The prepatent period was 16 days.

Onchocerca volvulus: parasitologic and serologic responses in experimentally infected chimpanzees and mangabey monkeys

Six chimpanzees (Pan troglodytes) and six mangabey monkeys (Cercocebus atys) were inoculated with Onchocerca volvulus third-stage larvae (L3) of West African origin. Two chimpanzees each received 200, 300, or 400 L3, while three mangabeys each received either 50 or 250 L3. All six chimpanzees became microfilaria positive between 11 and 25 months postinoculation (PI), while two of the six mangabeys were skin-snip positive at 24 and 37 months PI, respectively. All chimpanzees developed antibodies to two native antigens of 14 and 22 kDa and to the recombinant antigens OV16, OC3.6, and OC9.3. Marked antibody responses were observed in the mangabey monkeys, and in general, the responses were similar to those observed in the chimpanzees. However, in the mangabeys, these responses did not generally manifest themselves until later in the infection. The results of this study suggest that in chimpanzees, the smallest inoculum used, 200 L3, was sufficient to initiate consistent infections that had parasitologic and immunologic parameters equivalent to animals inoculated with larger numbers of larvae. Similarly, inoculation of mangabey monkeys with small numbers of larvae appeared to be as likely to establish infection and induce immunologic responses as did inoculation of larger numbers of larvae. Microfilaria-positive chimpanzees and mangabey monkeys were examined by three conventional imaging techniques (X ray, ultrasound, and magnetic resonance imaging (MRI)), but no adult worms or nodules could be identified in any animal.(ABSTRACT TRUNCATED AT 250 WORDS)

The China I/CDC strain of Plasmodium malariae in Aotus monkeys and chimpanzees

Five Aotus monkeys and two chimpanzees were infected with Plasmodium malariae isolated from a patient who acquired her infection approximately 50 years ago. All animals were splenectomized. The chimpanzees supported the highest parasite densities of 22,271/microliters and 18,544/microliters. Three Aotus monkeys with a previous history of infection with P. vivax had maximum parasite counts of from 1,818/microliters to 2,909/microliters, whereas two monkeys not previously infected had maximum parasite counts of 6,908/microliters. The establishment of new isolates in these animals aides the development of diagnostic probes and the identification of areas of antigenic variation within the species.

Experimental infection of Anopheles gambiae s.s., Anopheles freeborni and Anopheles stephensi with Plasmodium malariae and Plasmodium brasilianum

Susceptibility to infection of 2 strains of Anopheles gambiae s.s., An. freeborni and An. stephensi, was determined for 2 closely related malaria parasites, Plasmodium malariae and P. brasilianum. Neither strain of An. gambiae supported development of oocyst densities as great as the other 2 anopheline mosquitoes. The ZAN strain of An. gambiae s.s. from Zanzibar was more susceptible to infection with the strain of P. malariae from Uganda than the G-3 strain of An. gambiae s.s. from The Gambia. All species and strains of mosquitoes supported complete development to the presence of sporozoites in the salivary glands.

Experimental Onchocerca volvulus infections in mangabey monkeys (Cercocebus atys) compared to infections in humans and chimpanzees (Pan troglodytes)

Three chimpanzees, three mangabey monkeys (Cercocebus atys), and 14 patas monkeys (Erythrocebus patas) were inoculated with L3 Onchocerca volvulus of Guatemalan origin. One chimpanzee and two mangabey monkeys developed antibody activity to at least three different antigens. Both mangabey monkeys recognized a 20 kDa antigen 3.5-5 months post-inoculation, and the monkeys and the chimpanzee developed antibody activity to 14 and 22 kDa antigens 7.5-13 months post-inoculation. One mangabey monkey and the chimpanzee became microfilaria-positive in skin snips at 16 and 21 months post-inoculation, respectively. Antibody activity to the 20 kDa antigen in the mangabey monkeys is noteworthy because of the prominence of this antigen among putatively immune persons living in onchocerciasis-endemic areas. The two mangabey monkeys responded parasitologically in a manner comparable to immune humans. No microfilariae were detected in one monkey and only scant numbers of microfilariae were observed in the second. The mangabey monkey may be a good animal model for the study of onchocerciasis.

Infection of chimpanzees with the Uganda I/CDC strain of Plasmodium malariae

Nine splenectomized chimpanzees were infected with the Uganda I/CDC strain of Plasmodium malariae. Two had no history of previous malarial infection, whereas 6 had been infected with P. vivax and 1 with P. vivax and P. ovale. The animals with no previous infection had maximum parasitemias of 8,740 and 10,800/mm3. The other animals had maximum parasite counts of 930-75,700/mm3. Anopheles freeborni, An. stephensi, An. dirus, An. maculatus, An. quadrimaculatus, An. culicifacies, An. arabiensis, and An. gambiae were readily infected by feeding through membranes on heparinized blood from these animals.