Camelid Species Research Articles

The record of camelids (Artiodactyla, Camelidae) from the Valsequillo Basin, late Pleistocene of Puebla State, Central Mexico: taxonomy, diet, and geographic distribution

Dental and postcranial fossil material referable to camelids, which has been recovered from Quaternary deposits that outcrop in the Valsequillo Basin, Puebla State, central Mexico, is formally described. A comparative study indicates the presence of two species of camelids, including Hemiauchenia macrocephala and Camelops hesternus. The sample referable to H. macrocephala includes maxillary and mandibular fragments, isolated teeth, and several postcranial remains (astragalus, metapodials, and proximal phalanges), which show the following diagnostic features of the species: molariforms covered by a layer of cementum; a mandible increasing in depth from p4 to m3; p4 triangular in outline; long and slender metapodials; and proximal phalanges with a W-shaped suspensory ligament scar. The sample referable to C. hesternus is represented by maxillary and mandibular fragments, isolated teeth, and metapodials, sharing with the species its large size; P4 quadrate in outline; p4 triangular in outline and simply folded; and a mandible that is significantly deeper from p4 to m3. A microwear analysis was performed in order to characterize the diet of studied samples, indicating a browser and mixed feeding behavior in H. macrocephala and C. hesternus respectively. The differences in size and trophic regimes in these species should explained the resource partitioning between them. In the late Pleistocene these camelids were common in Mexican sites between the 19°-25° N, and the record from the Valsequillo Basin is one of the few sites where both species have been reported.

Prospects for rewilding with camelids

The wild camelids wild Bactrian camel (Camelus ferus), guanaco (Lama guanicoe), and vicuña (Vicugna vicugna) as well as their domestic relatives llama (Lama glama), alpaca (Vicugna pacos), dromedary (Camelus dromedarius) and domestic Bactrian camel (Camelus bactrianus) may be good candidates for rewilding, either as proxy species for extinct camelids or other herbivores, or as reintroductions to their former ranges. Camels were among the first species recommended for Pleistocene rewilding. Camelids have been abundant and widely distributed since the mid-Cenozoic and were among the first species recommended for Pleistocene rewilding. They show a range of adaptations to dry and marginal habitats, and have been found in deserts, grasslands and savannas throughout paleohistory. Camelids have also developed close relationships with pastoralist and farming cultures wherever they occur. We review the evolutionary and paleoecological history of extinct and extant camelids, and then discuss their potential ecological roles within rewilding projects for deserts, grasslands and savannas. The functional ecosystem ecology of camelids has not been well researched, and we highlight functions that camelids are likely to have, but which require further study. We also discuss alternative rewilding-inspired land-use models given the close relationships between humans and some camelid species.

Molecular characterization of rotavirus isolated from alpaca (Vicugna pacos) crias with diarrhea in the Andean Region of Cusco, Peru

Alpacas (Vicugna pacos), a species of South American camelids (SAC), suffer high morbidity and mortality from infectious diseases. Diarrhea is one of the leading causes of alpaca cria mortality in Peru and elsewhere. In order to develop appropriate control and/or treatment, it is necessary to identify infectious pathogens that cause diarrhea in crias. Rotavirus was isolated in cell culture from feces collected from crias with acute diarrhea that tested positive to rotaviral antigen by rapid immunochromatographic methods in an earlier study. The isolates were identified as rotaviruses by RT-PCR run with specific primers for human rotavirus VP7 coding sequences using total RNA extracted from cells displaying cytopathic effects as template. These alpaca isolates were further identified as group A rotaviruses by means of a VP6-specific PCR and were designated as ALRVA-K’ayra/Perú/3368-10 and ALRVA-K’ayra/Perú/3386-10. Molecular G and P typing, placed the former as G3/P11 and the latter as G3/P?. Sequence analysis of two genome segments (coding for VP4 and VP7) from the alpaca isolates revealed partial homologies to swine and human rotaviruses, respectively. These results demonstrate that rotaviruses are associated with a proportion of cases of diarrhea in crias, although prevalence and impact remain to be determined. The isolation of rotaviruses from alpaca crias with diarrhea will contribute positively to further understand the pathogen and its role in the diarrhea complex.

Bluetongue in Europe and the role of wildlife in the epidemiology of disease.

The article reviews a current bluetongue (BT) epidemiological situation in Europe, BT restricted zones and the role of wild ungulates as a reservoir for bluetongue virus (BTV) and its transmission. BT has been eradicated from central and northern Europe, however it is still circulating in some regions of southern and south-eastern Europe. According to the recent information of the Directoriate General for Health and Consumer Affairs (DG SANCO) disease caused by BTV1 was spreading at the beginning of 2014 in Corsica (France). Moreover, four BTV1 cases were noticed in the west Spain (Cáceres province), 59 BTV4 outbreaks in south Spain (Andalusia), 10 in the region of Algarve in Portugal and about 200 outbreaks of BTV4 in Greece (Peloponesse and Evros regions). On 4th July the first outbreak of BTV4 was also confirmed at the south Bulgarian border and by 5th September 2014 disease was noticed in 21 of 28 administrative districts of Bulgaria. In August 2014 the BTV4 disease was reported in south-east of Romania and as for 8th September 184 outbreaks of BT were confirmed in 17 counties of this country. As of 3 September 2014 in Europe there has been fourteen BT-affected zones, in different regions of Italy, Spain, Portugal, Cyprus, Malta, France (Corsica), Greece, Bulgaria and Romania. Most species of wild ruminants and camelids are susceptible to BTV infection, although frequently asymptomatically. Wild sheep, bighorn and mouflon, are susceptible to BTV infection and can develop fatal clinical disease, as do domestic sheep. Experimental or natural infection of antelope, wapiti, musk, ox, bison, yak, white-tailed deer and African buffalo also produced clinical disease, whereas blesbock, mountain gazelle, roe deer, red deer and Eurasian elk did not show clinical sign after natural or experimental infection and infection was recognized by the presence of BTV viral RNA or specific antibodies. The wildlife due to the long-term carrier state may act as a reservoir for BTV and play an important role in its transmission.

Bayesian inference on the effect of density dependence and weather on a guanaco population from Chile.

Understanding the mechanisms that drive population dynamics is fundamental for management of wild populations. The guanaco (Lama guanicoe) is one of two wild camelid species in South America. We evaluated the effects of density dependence and weather variables on population regulation based on a time series of 36 years of population sampling of guanacos in Tierra del Fuego, Chile. The population density varied between 2.7 and 30.7 guanaco/km2, with an apparent monotonic growth during the first 25 years; however, in the last 10 years the population has shown large fluctuations, suggesting that it might have reached its carrying capacity. We used a Bayesian state-space framework and model selection to determine the effect of density and environmental variables on guanaco population dynamics. Our results show that the population is under density dependent regulation and that it is currently fluctuating around an average carrying capacity of 45,000 guanacos. We also found a significant positive effect of previous winter temperature while sheep density has a strong negative effect on the guanaco population growth. We conclude that there are significant density dependent processes and that climate as well as competition with domestic species have important effects determining the population size of guanacos, with important implications for management and conservation.

Serum and urine analyte comparison between llamas and alpacas fed three forages.

Serum and urine analytes were measured in 4 healthy adult llama and alpaca geldings housed in metabolism crates and fed three diets consisting of alfalfa (AH), barley (BH) or grass (GH) hay and water ad libitum. This comparative study was conducted to determine if differences exist in serum metabolites and urinary indices in llamas and alpacas consuming the same forages of differing protein and carbohydrate quality. Daily feed intake was determined and concurrent serum and urine samples were obtained at 4-hr intervals on d13 and d14 for analysis of electrolytes, urea N, and creatinine. AH was consumed more than BH or GH by both species, but llamas consumed more forage on both a body weight (BW) and metabolic BW (MBW, kg .75 ) basis. Serum electrolytes were similarly affected by diet between species, indicating that renal homeostatic mechanisms were functional and analogous in llamas and alpacas. Serum and urine urea N were affected by forage (P<0.05). Urine volume was highest for both camelid species when consuming AH (P<0.05). Mean urine electrolyte excretion only differed by diet. Dissimilarities between these species was evidenced by differences in renal excretion of urea N and differences in urine volume on a MBW (kg .75 ) basis.

Density but not climate affects the population growth rate of guanacos ( Lama guanicoe) (Artiodactyla, Camelidae).

We analyzed the effects of population density and climatic variables on the rate of population growth in the guanaco ( Lama guanicoe), a wild camelid species in South America. We used a time series of 36 years (1977-2012) of population sampling in Tierra del Fuego, Chile. Individuals were grouped in three age-classes: newborns, juveniles, and adults; for each year a female population transition matrix was constructed, and the population growth rate (λ) was estimated for each year as the matrix highest positive eigenvalue. We applied a regression analysis with finite population growth rate (λ) as dependent variable, and total guanaco population, sheep population, annual mean precipitation, and winter mean temperature as independent variables, with and without time lags. The effect of guanaco population size was statistically significant, but the effects of the sheep population and the climatic variables on guanaco population growth rate were not statistically significant.

Density but not climate affects the population growth rate of guanacos (Lama guanicoe) (Artiodactyla, Camelidae)

We analyzed the effects of population density and climatic variables on the rate of population growth in the guanaco ( Lama guanicoe ), a wild camelid species in South America. We used a time series of 36 years (1977-2012) of population sampling in Tierra del Fuego, Chile. Individuals were grouped in three age-classes: newborns, juveniles, and adults; for each year a female population transition matrix was constructed, and the population growth rate (λ) was estimated for each year as the matrix highest positive eigenvalue. We applied a regression analysis with finite population growth rate (λ) as dependent variable, and total guanaco population, sheep population, annual mean precipitation, and winter mean temperature as independent variables, with and without time lags. The effect of guanaco population size was statistically significant, but the effects of the sheep population and the climatic variables on guanaco population growth rate were not statistically significant.

Density but not climate affects the population growth rate of guanacos ( Lama guanicoe) (Artiodactyla, Camelidae)

We analyzed the effects of population density and climatic variables on the rate of population growth in the guanaco ( Lama guanicoe), a wild camelid species in South America. We used a time series of 36 years (1977-2012) of population sampling in Tierra del Fuego, Chile. Individuals were grouped in three age-classes: newborns, juveniles, and adults; for each year a female population transition matrix was constructed, and the population growth rate (λ) was estimated for each year as the matrix highest positive eigenvalue. We applied a regression analysis with finite population growth rate (λ) as dependent variable, and total guanaco population, sheep population, annual mean precipitation, and winter mean temperature as independent variables, with and without time lags. The effect of guanaco population size was statistically significant, but the effects of the sheep population and the climatic variables on guanaco population growth rate were not statistically significant.

Methane emission by camelids.

Methane emissions from ruminant livestock have been intensively studied in order to reduce contribution to the greenhouse effect. Ruminants were found to produce more enteric methane than other mammalian herbivores. As camelids share some features of their digestive anatomy and physiology with ruminants, it has been proposed that they produce similar amounts of methane per unit of body mass. This is of special relevance for countrywide greenhouse gas budgets of countries that harbor large populations of camelids like Australia. However, hardly any quantitative methane emission measurements have been performed in camelids. In order to fill this gap, we carried out respiration chamber measurements with three camelid species (Vicugna pacos, Lama glama, Camelus bactrianus; n = 16 in total), all kept on a diet consisting of food produced from alfalfa only. The camelids produced less methane expressed on the basis of body mass (0.32±0.11 L kg−1 d−1) when compared to literature data on domestic ruminants fed on roughage diets (0.58±0.16 L kg−1 d−1). However, there was no significant difference between the two suborders when methane emission was expressed on the basis of digestible neutral detergent fiber intake (92.7±33.9 L kg−1 in camelids vs. 86.2±12.1 L kg−1 in ruminants). This implies that the pathways of methanogenesis forming part of the microbial digestion of fiber in the foregut are similar between the groups, and that the lower methane emission of camelids can be explained by their generally lower relative food intake. Our results suggest that the methane emission of Australia's feral camels corresponds only to 1 to 2% of the methane amount produced by the countries' domestic ruminants and that calculations of greenhouse gas budgets of countries with large camelid populations based on equations developed for ruminants are generally overestimating the actual levels.

A review of experimental infections with bluetongue virus in the mammalian host

Experimental infection studies with bluetongue virus (BTV) in the mammalian host have a history that stretches back to the late 18th century. Studies in a wide range of ruminant and camelid species as well as mice have been instrumental in understanding BTV transmission, bluetongue (BT) pathogenicity/pathogenesis, viral virulence, the induced immune response, as well as reproductive failures associated with BTV infection. These studies have in many cases been complemented by in vitro studies with BTV in different cell types in tissue culture. Together these studies have formed the basis for the understanding of BTV-host interaction and have contributed to the design of successful control strategies, including the development of effective vaccines. This review describes some of the fundamental and contemporary infection studies that have been conducted with BTV in the mammalian host and provides an overview of the principal animal welfare issues that should be considered when designing experimental infection studies with BTV in in vivo infection models. Examples are provided from the authors’ own laboratory where the three Rs (replacement, reduction and refinement) have been implemented in the design of experimental infection studies with BTV in mice and goats. The use of the ARRIVE guidelines for the reporting of data from animal infection studies is emphasized.

Analysis of heavy and light chain sequences of conventional camelid antibodies from Camelus dromedarius and Camelus bactrianus species

Camel antibodies have been widely investigated, but work has focused upon the unique heavy chain antibodies found across camelid species. These are homodimers, devoid of light chains and the first constant heavy chain domain. Camelid species also display conventional hetero-tetrameric antibodies with identical pairs of heavy and light chains; in Camelus dromedarius these constitute 25% of circulating antibodies. Few investigations have been made on this subset of antibodies and complete conventional camel IgG sequences have not been reported.Here we study the sequence diversity of functional variable and constant regions observed in 57 conventional heavy, 18 kappa and 35 lambda light chains of C. dromedarius and Camelus bactrianus. We detail sequences of the full kappa and lambda light chain, variable and CH1 region for IgG1a and IgG1b and the CH2 and CH3 region for IgG1a. The majority (60%) of IgG1 variable region sequences aligned with the human IgHV3 family (clan III) and had leader sequences beginning with MELG whereas the remaining sequences aligned with the IgHV4 (clan II) and had leader sequences beginning with MRLL. Distinct differences in CDR length were observed between the two; where CDR1 was typically 5 and 7 residues and CDR2 at 17 and 16 residues, respectively. CDR3 length of IgHV4 (range 11 to 20) was closer to that typical of VHH antibodies than that of IgHV3 (range 3 to 18 residues). Designed oligonucleotide primers have enabled identification of paired heavy and light chains of conventional camel antibodies from individual B cell clones.

Characteristics of residency training associated with first‐time pass rate on the American College of Veterinary Ophthalmologists certifying examination

The aim of this study was to examine the association of various aspects of veterinary ophthalmology residency training with the first-time pass rate (FTPR) of the American College of Veterinary Ophthalmologists (ACVO) examination, as well as the individual written, image recognition, animal examination, and surgical sections of the examination. Program type, resident evaluations, cumulative surgery and case logs, and scores from ACVO examinations from 2007 to 2010 were evaluated. Data were available for 71 candidates. The overall FTPR was 35% (n = 25). For the different sections of the examination, FTPRs were as follows: written (68%), image recognition (76%), intraocular surgery (80%), extraocular surgery (65%), and animal examination (75%). The overall FTPR among candidates from academic residency (AR) programs was 43% (20 of 47), while the FTPR of residents in private practice (PPR) programs was 21% (5 of 24; P = 0.07). The AR candidates were more likely to pass the written portion than PPR residents (P = 0.02), and AR candidates had significantly more time off clinics (median 25%) vs PPR residents (median 18%; P = 0.007). The AR residents also had a higher reported percentage of direct supervision than PPR residents (95% vs 76%, respectively). Although PPR residents did significantly more surgeries and examined significantly more dogs and cats, those from ARs examined significantly more equine, bovine, avian, camelid, and reptile species. Overall, AR residents had a higher FTPR and were more likely to pass the written portion of the examination. Total case and surgery numbers were not associated with FTPR.

Density but not climate affects the population growth rate of guanacos ( Lama guanicoe) (Artiodactyla, Camelidae).

We analyzed the effects of population density and climatic variables on the rate of population growth in the guanaco ( Lama guanicoe), a wild camelid species in South America. We used a time series of 36 years (1977-2012) of population sampling in Tierra del Fuego, Chile. Individuals were grouped in three age-classes: newborns, juveniles, and adults; for each year a population transition matrix was constructed, and the population growth rate (λ) was estimated for each year as the matrix highest positive eigenvalue. We applied a stepwise regression analysis with population growth rate (λ) as dependent variable, and total guanaco population (in natural logs), annual mean precipitation, and winter mean temperature as independent variables, with and without time lags. The effect of population size was statistically significant, but the effect of the climatic variables on guanaco population growth rate was not significant.

Amblyomma parvitarsum (Acari: Ixodidae): localities, hosts and host-parasite ecology

Only a few aspects of the biology of Amblyomma parvitarsum Neumann are known. Adults of this hard tick species are parasites of South American camelids in the Andean plateau of Argentina, Bolivia, Peru and Chile and also in the Argentine Patagonia, but they have been also rarely found on other artyodactils and two species of birds. The larva has been collected from reptiles in northern Chile, whereas the hosts for the nymph remain unknown. On nine localities included within Altitude Tropical and Perarid Mediterranean ecoregions in northern Chile, we analyzed 237 reptiles, 285 birds, 624 rodents and 52 camelids for infestation with A. parvitarsum to calculate seasonal prevalence of this tick. We also reviewed the literature of this tick and three entomological collections for obtaining and summarizing all the information to date about this tick. None of the analyzed birds and rodents were parasitized with A. parvitarsum; however, seven over a total of ten reptile species that we caught were infested with the larva. In the camelid species Lama glama and Vicugna pacos we collected adult specimens of this tick. Larval prevalence was higher during fall (75 %) in Liolaemus pleopholis in the Altitude Tropical ecoregion. We also collected adult specimens of A. parvitarsum from camelid manure heaps during summer in Salar de Surire and Llullaillaco localities. Additionally, we also reviewed the literature of this tick and examined specimens in three entomological collections for obtaining and summarizing all the information to date about this tick. By this study, nine localities and seven new hosts are added for A. parvitarsum and we confirm reptiles as specific hosts of this tick larva.

Exploring Human Subsistence Strategies and Environmental Change through Stable Isotopes in the Dry Puna of Argentina

ABSTRACTThis article explores the feeding and territorial behaviour of the wild camelids – guanacos and vicuñas – consumed by the inhabitants of the Dry Puna during the Early and Mid‐Holocene, as a way to deal with the strategies for resource exploitation employed by these human groups. We present 38 stable isotope values (δ13C and δ15N) generated from bone collagen extracted from the faunal remains obtained from the Hornillos 2 archaeological site (Susques, Jujuy Province, Argentina). These bone assemblages were recovered from nine layers that comprise human occupations corresponding to both periods (from 9710 to 6130 years bp). These data will be discussed considering ecological and ethological information about wild camelids, especially regarding territorial behaviour and dietary selectiveness of vicuñas and guanacos that currently inhabit the Puna. Finally, the trends and patterns identified in these isotopic evidences will be analysed in the light of the environmental and cultural changes that took place during the mentioned chronological span.Our results show no significant differences between camelid species, implying that δ13C and δ15N values of bone collagen constitute a poor taxonomical indicator, dismissing the possibility to identify the early incidence of human intervention in animal diet as an initial step to deal with the problem of domestication. In chronological terms, the δ15N results from Early and Mid‐Holocene show certain differences that can be linked to the preponderance of arid conditions during the latter. This underscores the usefulness of this line of evidence when evaluating environmental changes. On the other hand, the δ13C values show no substantial differences, meaning that carbon isotopic composition of bone collagen in mixed C3–C4 systems is not a reliable paleoenvironmental proxy. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Proteomic characterization and cross species comparison of mammalian seminal plasma

Seminal plasma contains a large protein component which has been implicated in the function, transit and survival of spermatozoa within the female reproductive tract. However, the identity of the majority of these proteins remains unknown and a direct comparison between the major domestic mammalian species has yet to be made. As such, the present study characterized and compared the seminal plasma proteomes of cattle, horse, sheep, pig, goat, camel and alpaca. GeLC-MS/MS and shotgun proteomic analysis by 2D-LC-MS/MS identified a total of 302 proteins in the seminal plasma of the chosen mammalian species. Nucleobindin 1 and RSVP14, a member of the BSP (binder of sperm protein) family, were identified in all species. Beta nerve growth factor (bNGF), previously identified as an ovulation inducing factor in alpacas and llamas, was identified in this study in alpaca and camel (induced ovulators), cattle, sheep and horse (spontaneous ovulators) seminal plasma. These findings indicate that while the mammalian species studied have common ancestry as ungulates, their seminal plasma is divergent in protein composition, which may explain variation in reproductive capacity and function. The identification of major specific proteins within seminal plasma facilitates future investigation of the role of each protein in mammalian reproduction. This proteomic study is the first study to compare the protein composition of seminal plasma from seven mammalian species including two camelid species. Beta nerve growth factor, previously described as the ovulation inducing factor in camelids is shown to be the major protein in alpaca and camel seminal plasma and also present in small amounts in bull, ram, and horse seminal plasma.

Expression of Orexin A and its Receptor 1 in the Epididymis of the South American Camelid Alpaca (Vicugna pacos)

Orexins A (ox A) and B are two peptides originally discovered in neurons of rat hypothalamus, and later found in different cellular types of the gastrointestinal and genital tracts. They arise from the proteolytic cleavage of a common precursor molecule, prepro-orexin, and bind to two receptors, namely receptor 1 (ox1r) and receptor 2 for orexins, that show different binding affinity. The central role of the two peptides has been extensively studied, whereas their activity in the periphery is still poorly known. Here, we investigated the presence of ox A and ox1r in the epididymis of a South American camelid species, the alpaca, by immunohistochemistry, and we also assessed the expression of prepro-orexin and ox1r in tissue extracts by Western blotting analysis. Ox A- and ox1r-immunoreactivity was found in the cytoplasm of principal cells of the caput epididymis. A prevalent supranuclear localization of granular-shaped positive material was observed. No positivity was present in the other cytotypes of epididymis. The expression of two peptides with molecular weight corresponding to those of prepro-orexin and ox1r, respectively, was detected in the tissue extracts from the organ.

Discovery and molecular characterization of a group A rotavirus strain detected in an Argentinean vicuña (Vicugna vicugna)

The wild vicuña (Vicugna vicugna) is one of the four species of native South American camelids (SACs) in addition to the wild guanaco, and their domesticated counterparts, alpaca and llama, respectively. Serological data have indicated the presence of group A rotaviruses (RVA) specific antibodies in all 4 members of the SAC, and so far, RVA has been detected from alpacas, llamas and guanacos. A total of 59 fecal samples from healthy wild newborn and juvenile vicuñas, raised in captivity in Jujuy, Argentina were collected and analyzed by ELISA to detect RVA antigen. Two samples (3%) were found to contain G8 RVA strains and one strain (RVA/Vicuña-wt/ARG/C75/2010/G8P[14]) was selected for further genome analyses, revealing the G8-P[14]-I2-R2-C2-M2-Ax-N2-T6-E3-Hx genotype constellation. Unfortunately, no sequence data could be obtained for NSP1 and NSP5. Except for the E3 NSP4 genotype, this partial genotype constellation is reminiscent to bovine RVA strains and bovine-like RVA strains isolated from sheep, guanaco, antelope and humans. This relationship was confirmed phylogenetically, providing further evidence of the widespread presence of this genotype constellation in animals belonging to the artiodactyls. In particular, a close phylogenetic relationship was found between C75 and guanaco RVA strain RVA/Guanaco-wt/ARG/Chubut/1999/G8P[14] for at least 5 gene segments, suggesting a partial conservation of the genotype constellation of RVA strains infecting different species of SACs, even though nowadays their natural habitats are not overlapping. The further monitoring of the sanitary health of wild newborn and juvenile vicuñas is essential to improve the management practices applied in their sustainable exploitation.

Abstract 3853: TAS266, a novel tetrameric nanobody agonist targeting death receptor 5 (DR5), elicits superior antitumor efficacy than conventional DR5-targeted approaches

Abstract Preferential induction of apoptosis in cancer cells has been the objective of therapeutic strategies targeting apoptotic pathways. To this end, multiple therapeutic agonists of Death Receptors 4 and 5 (DR4, DR5), have been developed and are under clinical evaluation. Although these agonists, including antibodies and soluble ligand TRAIL, demonstrate significant anti-tumor activity in preclinical models, the clinical efficacy in human cancer patients has been notably disappointing. One possible explanation for the discrepant pre-clinical and clinical results is that DR5 may play a more prominent role in in vitro model systems as opposed to cancers in humans. Alternatively, these results might indicate that the current classes of therapeutic molecules are not sufficiently potent to elicit significant response in patients. In particular, naturally dimeric antibody agonists require secondary cross-linking via Fcα receptors expressed on immune cells present in the tumor microenvironment to achieve optimal clustering of DR5 into a ternary active state. Because immune cell content in the tumor can be heterogeneous, reliance on this secondary mechanism for activity may limit the potency of these antibodies. To overcome this limitation, a novel nanobody approach was taken to eliminate the need for cross-linking and improve receptor activation with the goal of generating a significantly more potent DR5 agonist. Nanobodies are a class of therapeutic proteins based on single, high affinity heavy chain domain (VHH) antibodies that naturally occur in camelid species, and these VHH domains can be linked to form multivalent structures (di-, tri-, tetra-, etc). This approach led to the development of a tetrameric DR5 targeted agonist, TAS266, with significantly greater avidity for DR5 binding. TAS266 activates downstream caspases with more rapid kinetics and is up to 1000-fold more potent in cell death assays when compared to a cross-linked DR5 antibody or TRAIL. In vivo, TAS266 elicits single dose tumor regressions in multiple tumor xenograft models and sustained tumor regressions after treatment cessation. TAS266 showed superior anti-tumor activity compared to a DR5 agonist antibody and TRAIL, including the ability to induce tumor regression in a patient-derived primary pancreatic tumor model that is insensitive to the agonist antibody. Thus, TAS266 has the potential for superior clinical activity in settings insensitive to the conventional therapeutic approaches to DR5. First-in-man trials are expected to begin in 2012. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3853. doi:1538-7445.AM2012-3853